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Sample records for adsorbed polymer chains

  1. Stabilization of nanorods in polymer melts by end-adsorbed chains

    NASA Astrophysics Data System (ADS)

    Frischknecht, Amalie L.

    2007-03-01

    Adsorbed or grafted polymers are often used to provide steric stabilization of colloidal particles. When the particle size approaches the nanoscale, the curvature of the particles becomes relevant, and rules of thumb based on the behavior of polymers attached to flat surfaces may no longer apply. To investigate this effect for the case of cylindrical symmetry, I use a classical density functional theory applied to a coarse-grained model to study the polymer-mediated interactions between two nanorods. The rods are immersed in a polymer melt consisting of two kinds of chains: 1) a small fraction of chains of length N with ends that are attracted to the rods so that they form a polymer brush on the rods; and 2) a matrix of chains of length P which have no interactions with the rods. Calculations of the density profiles and potential of mean force reveal the effects of curvature compared to similar calculations for chains adsorbed to flat planar surfaces.

  2. The Effect of Acid-Base Interactions on Conformation of Adsorbed Polymer Chains

    NASA Astrophysics Data System (ADS)

    Dhopatkar, Nishad; Zhu, He; Dhinojwala, Ali

    Adsorption of polymer chains from solutions is of fundamental interest in polymer science. This absorption process is governed by the complex interplay between the solvent-polymer, polymer-substrate, and solvent-substrate interaction energies. In early 1970's, Fowkes and his coworkers have introduced the concept of acid base interactions in explaining why PMMA (basic) adsorption was extremely low on acidic substrates from acidic solvents. The acidic solvent molecules compete with the surface for binding with the basic polymer sites and this reduces the adsorption of PMMA. Here, by using interface-selective sum frequency generation spectroscopy (SFG) and attenuated-total-reflectance (ATR)-FTIR spectroscopy we directly measure whether the solvent or polymer molecules interact with the substrate in acidic, basic, and neutral solvents. Surprisingly, we find that the surface acidic site (hydroxyl) groups are still covered with PMMA chains in acidic solvent. The PMMA chains in acidic solvent adsorb with much higher fraction of chains as trains in comparison to loops and tails. Such differences in the static and dynamic conformations have consequences in understanding the exchange kinetics, colloidal stabilization, chromatographic separations, adhesion and friction, and stabilization of nanocomposites.

  3. Untangleing the effects of chain rigidity on the structure and dynamics of strongly adsorbed polymer melts

    SciTech Connect

    Carrillo, Jan-Michael Y.; Cheng, Shiwang; Kumar, Rajeev; Goswami, Monojoy; Sokolov, Alexei P; Sumpter, Bobby G.

    2015-06-11

    Here, we present a detailed analysis of coarse-grained molecular dynamics simulations of semiflexible polymer melts in contact with a strongly adsorbing substrate. We have characterized the segments in the interfacial layer by counting the number of trains, loops, tails and unadsorbed segments. For more rigid chains, a tail and an adsorbed segment (a train) dominate while loops are more prevalent in more flexible chains. The tails exhibit a non-uniformly stretched conformation akin to the polydispersed pseudobrush envisioned by Guiselin. To probe the dynamics of the segments we computed the layer z-resolved intermediate coherent collective dynamics structure factor, S(q, t, z), mean-square displacement of segments, and the 2nd Legendre polynomial of the time-autocorrelation of unit bond vectors, 2[ni(t,z)•ni(0,z)]>. Our results show that segmental dynamics is slower for stiffer chains and there is a strong correlation between the structure and dynamics in the interfacial layer. There is no glassy layer, and the slowing down in dynamics of stiffer chains in the adsorbed region can be attributed to the densification and the more persistent layering of segments.

  4. Untangleing the effects of chain rigidity on the structure and dynamics of strongly adsorbed polymer melts

    DOE PAGESBeta

    Carrillo, Jan-Michael Y.; Cheng, Shiwang; Kumar, Rajeev; Goswami, Monojoy; Sokolov, Alexei P; Sumpter, Bobby G.

    2015-06-11

    Here, we present a detailed analysis of coarse-grained molecular dynamics simulations of semiflexible polymer melts in contact with a strongly adsorbing substrate. We have characterized the segments in the interfacial layer by counting the number of trains, loops, tails and unadsorbed segments. For more rigid chains, a tail and an adsorbed segment (a train) dominate while loops are more prevalent in more flexible chains. The tails exhibit a non-uniformly stretched conformation akin to the polydispersed pseudobrush envisioned by Guiselin. To probe the dynamics of the segments we computed the layer z-resolved intermediate coherent collective dynamics structure factor, S(q, t, z),more » mean-square displacement of segments, and the 2nd Legendre polynomial of the time-autocorrelation of unit bond vectors, 2[ni(t,z)•ni(0,z)]>. Our results show that segmental dynamics is slower for stiffer chains and there is a strong correlation between the structure and dynamics in the interfacial layer. There is no glassy layer, and the slowing down in dynamics of stiffer chains in the adsorbed region can be attributed to the densification and the more persistent layering of segments.« less

  5. Equilibrium flattening process of irreversibly adsorbed polymer chains on a solid

    NASA Astrophysics Data System (ADS)

    Sen, Mani; Jiang, Naisheng; Endoh, Maya; Koga, Tadanori; Kawaguchi, Daisuke; Tanaka, Keiji

    We here report the equilibrium process of adsorbed polymer chains on a solid by sum frequency generation (SFG) spectroscopy. Polystyrene (PS,Mw = 290 kDa) thin films prepared onto quartz prisms (a weakly attractive system) were used as a model system. Spin-cast PS 50 nm films on quartz surface (QS) were annealed at 150 °C >Tg for up to 100 h and subsequently rinsed with chloroform to derive the ``flattened chains'' that lie flat onto the substrate surface. The SFG results for the ``matured'' flattened chains after annealing for 96 h revealed the strong interfacial orientation of the backbone chains and weak orientation of PS phenyl rings at the QS which is in contrast to a PS spin-cast film annealed at 150 °C for 1 h: the phenyl rings were strongly directed toward the QS, while the backbone chains were weakly orientated at the QS. We postulate that the increase in the number of solid/segment contacts of the backbone chains is the driving force for this equilibrium flattening process. We will also discuss the generality of this flattening process by using solvent-cast PS thin films where the chains are randomly oriented near the QS. Acknowledgement: NSF Grant No. CMMI-1332499.

  6. Phase behaviour of a dispersion of charge-stabilised colloidal spheres with added non-adsorbing interacting polymer chains.

    PubMed

    Gögelein, C; Tuinier, R

    2008-10-01

    We present a theory for the phase behaviour of mixtures of charge-stabilised colloidal spheres plus interacting polymer chains in good and theta -solvents within the framework of free-volume theory. We use simple but accurate combination rules for the depletion thickness around a colloidal particle and for the osmotic pressure up to the semi-dilute concentration regime. Hence, we obtain expressions for the free energy for mixtures of charged colloidal particles and non-adsorbing interacting polymers. From that, we calculate the phase behaviour, and discuss its topology in dependence on the competition between the charge-induced repulsion and the polymer-induced attraction. The homogeneous mixture of colloids and polymers becomes more stabilised against demixing when increasing the electrostatic repulsion. This charge-induced stabilisation is strongest for small polymer-to-colloid size ratios and is more pronounced for charged colloids mixed with polymers in a good solvent than for polymers in a theta -solvent. For the weakly charged regime we find that the phase diagram becomes salt-concentration-independent in the protein limit for charged colloids plus polymers in a theta -solvent. The liquid window, i.e., the concentration regimes where a colloidal liquid exists, is narrowed down upon increasing the charge-induced repulsion. Also this effect is more pronounced when charged colloids are mixed with polymer chains in a good solvent. In summary, we demonstrate that the solvent quality significantly influences the phase behaviour of mixtures of charged colloids plus non-adsorbing polymers if the range of the screened electrostatic repulsion becomes of the order of the range of the depletion-induced attraction. PMID:18791755

  7. Statistical mechanics of polymer chains grafted to adsorbing boundaries of fractal lattices embedded in three-dimensional space

    NASA Astrophysics Data System (ADS)

    Živić, I.; Elezović-Hadžić, S.; Milošević, S.

    2014-11-01

    We study the adsorption problem of linear polymers, immersed in a good solvent, when the container of the polymer-solvent system is taken to be a member of the Sierpinski gasket (SG) family of fractals, embedded in the three-dimensional Euclidean space. Members of the SG family are enumerated by an integer b (2≤b<∞), and it is assumed that one side of each SG fractal is impenetrable adsorbing boundary. We calculate the surface critical exponents γ11,γ1, and γs which, within the self-avoiding walk model (SAW) of polymer chain, are associated with the numbers of all possible SAWs with both, one, and no ends grafted to the adsorbing surface (adsorbing boundary), respectively. By applying the exact renormalization group method, for 2≤b≤4, we have obtained specific values for these exponents, for various types of polymer conformations. To extend the obtained sequences of exact values for surface critical exponents, we have applied the Monte Carlo renormalization group method for fractals with 2≤b≤40. The obtained results show that all studied exponents are monotonically increasing functions of the parameter b, for all possible polymer states. We discuss mutual relations between the studied critical exponents, and compare their values with those found for other types of lattices, in order to attain a unified picture of the attacked problem.

  8. The persistence length of adsorbed dendronized polymers.

    PubMed

    Grebikova, Lucie; Kozhuharov, Svilen; Maroni, Plinio; Mikhaylov, Andrey; Dietler, Giovanni; Schlüter, A Dieter; Ullner, Magnus; Borkovec, Michal

    2016-07-21

    The persistence length of cationic dendronized polymers adsorbed onto oppositely charged substrates was studied by atomic force microscopy (AFM) and quantitative image analysis. One can find that a decrease in the ionic strength leads to an increase of the persistence length, but the nature of the substrate and of the generation of the side dendrons influence the persistence length substantially. The strongest effects as the ionic strength is being changed are observed for the fourth generation polymer adsorbed on mica, which is a hydrophilic and highly charged substrate. However, the observed dependence on the ionic strength is much weaker than the one predicted by the Odijk, Skolnik, and Fixman (OSF) theory for semi-flexible chains. Low-generation polymers show a variation with the ionic strength that resembles the one observed for simple and flexible polyelectrolytes in solution. For high-generation polymers, this dependence is weaker. Similar dependencies are found for silica and gold substrates. The observed behavior is probably caused by different extents of screening of the charged groups, which is modified by the polymer generation, and to a lesser extent, the nature of the substrate. For highly ordered pyrolytic graphite (HOPG), which is a hydrophobic and weakly charged substrate, the electrostatic contribution to the persistence length is much smaller. In the latter case, we suspect that specific interactions between the polymer and the substrate also play an important role. PMID:27353115

  9. The persistence length of adsorbed dendronized polymers

    NASA Astrophysics Data System (ADS)

    Grebikova, Lucie; Kozhuharov, Svilen; Maroni, Plinio; Mikhaylov, Andrey; Dietler, Giovanni; Schlüter, A. Dieter; Ullner, Magnus; Borkovec, Michal

    2016-07-01

    The persistence length of cationic dendronized polymers adsorbed onto oppositely charged substrates was studied by atomic force microscopy (AFM) and quantitative image analysis. One can find that a decrease in the ionic strength leads to an increase of the persistence length, but the nature of the substrate and of the generation of the side dendrons influence the persistence length substantially. The strongest effects as the ionic strength is being changed are observed for the fourth generation polymer adsorbed on mica, which is a hydrophilic and highly charged substrate. However, the observed dependence on the ionic strength is much weaker than the one predicted by the Odijk, Skolnik, and Fixman (OSF) theory for semi-flexible chains. Low-generation polymers show a variation with the ionic strength that resembles the one observed for simple and flexible polyelectrolytes in solution. For high-generation polymers, this dependence is weaker. Similar dependencies are found for silica and gold substrates. The observed behavior is probably caused by different extents of screening of the charged groups, which is modified by the polymer generation, and to a lesser extent, the nature of the substrate. For highly ordered pyrolytic graphite (HOPG), which is a hydrophobic and weakly charged substrate, the electrostatic contribution to the persistence length is much smaller. In the latter case, we suspect that specific interactions between the polymer and the substrate also play an important role.The persistence length of cationic dendronized polymers adsorbed onto oppositely charged substrates was studied by atomic force microscopy (AFM) and quantitative image analysis. One can find that a decrease in the ionic strength leads to an increase of the persistence length, but the nature of the substrate and of the generation of the side dendrons influence the persistence length substantially. The strongest effects as the ionic strength is being changed are observed for the fourth

  10. Examining Adsorbed Polymer Conformations with Fluorescence Imaging

    NASA Astrophysics Data System (ADS)

    Parkes, Maria; Chennaoui, Mourad; Wong, Janet; Tribology Group, Dept. of Mechanical Engineering Team

    2011-03-01

    The conformation of adsorbed polymers can have significant impact on their properties such as dynamics and elasticity as well as their ability to take part in reactions with other molecules. Experimental research to determine adsorbed polymer conformation has relied mainly on atomic force microscopy (AFM) studies. During an AFM scan, the contact between the scanning probe and the polymer could affect the polymer conformation, particularly where parts of the polymer might have formed projected loops and tails. In this work, conformations of model polymers are examined with total internal reflection fluorescence microscopy (TIRFM). The advantage of TIRFM over AFM is that TIRFM is a non contact technique. Lambda DNA labelled along its length with fluorescent probes was adsorbed in a projected 2D -- 3D state. With TIRFM, the relationship between intensity and depth was used as a basis to determine how the conformation of the adsorbed polymers evolved with time using our custom algorithm.

  11. Entropic elasticity of end adsorbed polymer chains: The spectrin network of red blood cells as C*-gel

    NASA Astrophysics Data System (ADS)

    Everaers, Ralf; Graham, Ian S.; Zuckermann, Martin J.; Sackmann, Erich

    1996-03-01

    We use Monte Carlo methods to investigate the end-to-end distance distribution and entropic elasticity of self-avoiding walks in a three-dimensional half-space with both ends adsorbed on the limiting surface. The obtained distributions are well described by the Redner-des Cloizeaux (RdC) ansatz q(x)=Cxθ exp(-(Kx)t), x being the rescaled length. Using the recent solution of the junction affine model for networks of RdC springs we apply the results to the cytoskeleton of the red blood cell (RBC), a two-dimensional network of spectrin molecules which is attached to the inner surface of the erythrocyte membrane. The shear moduli predicted for a noninteracting surface are in close agreement with simulation results by Boal for a bead-spring model of the spectrin network. Moreover, we calculate stress-strain relations for finite deformations. In particular for a network which is fully adsorbed on the bilayer we find a strongly nonlinear elastic response. Our results suggest that the elastic properties of RBCs cannot be obtained within the usual Gaussian models and depend sensitively on the degree of adsorption of the spectrin network.

  12. Monte Carlo lattice models for adsorbed polymer conformation

    NASA Technical Reports Server (NTRS)

    Good, B. S.

    1985-01-01

    The adhesion between a polymer film and a metal surface is of great technological interest. However, the prediction of adhesion and wear properties of polymer coated metals is quite difficult because a fundamental understanding of the polymer surface interaction does not yet exist. A computer model for the conformation of a polymer molecule adsorbed on a surface is discussed. The chain conformation is assumed to be described by a partially directed random walk on a three dimensional simple cubic lattice. An attractive surface potential is incorporated into the model through the use of a random walk step probability distribution that is anisotropic in the direction normal to the attractive surface. The effects of variations in potential characteristics are qualitatively included by varying both the degree of anisotropy of the step distribution and the range of the anisotropy. Polymer conformation is characterized by the average end to end distance, average radius of gyration, and average number of chain segments adsorbed on the surface.

  13. Density functional theory study of epoxy polymer chains adsorbing onto single-walled carbon nanotubes: electronic and mechanical properties.

    PubMed

    Ahangari, Morteza Ghorbanzadeh; Fereidoon, Abdolhosein; Ganji, Masoud Darvish

    2013-08-01

    We performed first principles calculations based on density functional theory (DFT) to investigate the effect of epoxy monomer content on the electronic and mechanical properties of single-walled carbon nanotubes (SWCNTs). Our calculation results reveal that interfacial interaction increases with increasing numbers of epoxy monomers on the surface of SWCNTs. Furthermore, density of states (DOS) results showed no orbital hybridization between the epoxy monomers and nanotubes. Mulliken charge analysis shows that the epoxy polymer carries a positive charge that is directly proportional to the number of monomers. The Young's modulus of the nanotubes was also studied as a function of monomer content. It was found that, with increasing number of monomers on the nanotubes, the Young's modulus first decreases and then approaches a constant value. The results of a SWCNT pullout simulation suggest that the interfacial shear stress of the epoxy/SWCNT complex is approximately 68 MPa. These results agreed well with experimental results, thus proving that the simulation methods used in this study are viable. PMID:23609226

  14. Conformational properties of an adsorbed charged polymer.

    PubMed

    Cheng, Chi-Ho; Lai, Pik-Yin

    2005-06-01

    The behavior of a strongly charged polymer adsorbed on an oppositely charged surface of a low-dielectric constant is formulated by the functional integral method. By separating the translational, conformational, and fluctuational degrees of freedom, the scaling behaviors for both the height of the polymer and the thickness of the diffusion layer are determined. Unlike the results predicted by scaling theory, we identified the continuous crossover from the weak compression to the compression regime. All the analytical results are found to be consistent with Monte Carlo simulations. Finally, an alternative (operational) definition of a charged polymer adsorption is proposed. PMID:16089715

  15. Adsorption of polymer chains at penetrable interfaces

    SciTech Connect

    Gerasimchuk, I. V.; Sommer, J.-U.; Gerasimchuk, V. S.

    2011-03-15

    We investigate the problem of adsorption (localization) of polymer chains in the system of two penetrable interfaces within the mean-field approximation. The saturation of the polymer system in the limit case of zero bulk concentration is studied. We find the exact solution of this mean-field polymer adsorption problem that opens the possibility to treat various localization problems for polymer chains in such environments using appropriate boundary conditions. The exact solution is controlled by a single scaling variable that describes the coupling between the interfaces due to the polymer chains. We obtain a nonmonotonic behavior of the amount of adsorbed polymers as a function of the distance between the interfaces. This leads to a high-energy and a low-energy phase for the double layer with respect to the amount of polymers localized. At the saturation point, we find the total energy of the system and determine the force acting between the interfaces to be strictly attractive and to monotonically decay to zero when the interface distance increases.

  16. Structure of Non-Equilibrium Adsorbed Polymer Layers

    NASA Astrophysics Data System (ADS)

    O'Shaughnessy, Ben; Vavylonis, Dimitrios

    2004-03-01

    Equilibrium polymer adsorption has been widely studied theoretically. Many experiments however implicate strong non-equilibrium effects for monomer sticking energies somewhat larger than kT, the most common case. The structure and slow dynamics in these layers is not understood. We analyze theoretically non-equilibrium layers from dilute solutions in the limit of irreversible monomer adsorption. We find the density profile ˜ z-4/3 and loop distribution ˜ s-11/5 of the resulting layer are no different to equilibrium. However, single chain statistics are radically different: the layer consists of a flat inner portion of fully collapsed chains plus an outer part whose chains make only fN surface contacts where N is chain length. The contact fractions f follow a broad distribution, P(f) ˜ f-4/5, consistent with experiment [H. M. Schneider et al, Langmuir 12, 994 (1996)], and the lateral size R of adsorbed chains is of order the bulk coil size, R ˜ N^3/5. For equilibrium layers, by contrast, P has a unique peak at a value of f of order unity, while R ˜ N^1/2 is significantly less. The relaxation of a non-equilibrium layer towards equilibrium thus entails chain shrinkage and tighter binding. We speculate that the observed decrease of bulk-layer chain exchange rates with increasing aging reflects these internal layer dynamics.

  17. Interlocking order parameter fluctuations in structural transitions between adsorbed polymer phases.

    PubMed

    Martins, Paulo H L; Bachmann, Michael

    2016-01-21

    By means of contact-density chain-growth simulations of a simple coarse-grained lattice model for a polymer grafted at a solid homogeneous substrate, we investigate the complementary behavior of the numbers of surface-monomer and monomer-monomer contacts under various solvent and thermal conditions. This pair of contact numbers represents an appropriate set of order parameters that enables the distinct discrimination of significantly different compact phases of polymer adsorption. Depending on the transition scenario, these order parameters can interlock in perfect cooperation. The analysis helps understand the transitions from compact filmlike adsorbed polymer conformations into layered morphologies and dissolved adsorbed structures, respectively, in more detail. PMID:26690091

  18. Dynamics of Confined Flexible and Unentangled Polymer Melts in Highly Adsorbing Cylindrical Pores

    SciTech Connect

    Carrillo, Jan-Michael Y; Sumpter, Bobby G

    2014-01-01

    Inspired by the recent neutron spin echo experiments (NSE) designed to address the dynamic phenomena in polymer melts that are induced by interactions with a confining surface, we performed coarse-grained molecular dynamics simulations to replicate the experimental results in order to provide new molecular insight for the observations. The results show excellent agreement in the values obtained for the normalized coherent single chain dynamic structure factor, S(Q;Dt)/S(Q;0) , between experiments and simulations. The simulations indicate that using different chain molecular weights that are used to achieve scattering contrast results in the uneven distribution of scatterers in the radial direction because lower molecular weight chains prefer to adsorb in the confining surface. In the bulk configuration, both simulations and experiments confirm that the polymer chains follow Rouse dynamics. However, under confinement, the Rouse modes are suppressed. The mean-squared radius of gyration, R2g, and the average relative shape anisotropy k2 of the conformation of the polymer chains indicate a pancake-like conformation near the surface and a bulk-like conformation near the center of the confining cylinder. Direct visualization of the polymers in the simulation confirm the pancake-like conformation of the adsorbed chains and the presence of trains, loops and tails in the region between the adsorbed chains and the chains not in contact with the surface. Despite the presence of these different conformations, the average form factor of the confined chains still follows the Debye function which describes linear ideal chains, which is in agreement with small angle neutron scattering (SANS) experiments. The experimentally inaccessible mean squared displacement of the confined monomers, calculated as a function of radial distance from the pore surface, was obtained in the simulations. The simulation shows a gradual increase of the MSD from the adsorbed, but mobile layer, to that

  19. Effects of the Adsorbed Polymer Nanolayers on the Dewetting of Polystyrene Thin Films

    NASA Astrophysics Data System (ADS)

    Cheung, Justin; Wang, Jiaxun; Jiang, Naisheng; Endoh, Maya; Koga, Tadanori

    2015-03-01

    It was previously reported that irreversibly adsorbed polymer nanolayers can be produced on solid substrates by thermal annealing. This study sought to determine the impact of the adsorbed nanolayers on film stability of ultrathin polystyrene (PS) films. A series of bilayers composed of the bottom PS adsorbed nanolayers and PS overlayers with different molecular weights were prepared as model systems. The surface structures of the bilayer films annealed above the bulk glass transition temperature were analyzed by using optical and atomic force microscopes. We will discuss the unique roles of the adsorbed polymer chains in the stability of the liquid thin films. T. K. acknowledges the partial financial support from NSF Grant No. CMMI-1332499.

  20. Phase transition and winding properties of a flexible polymer adsorbed to a rigid perioidic copolymer.

    PubMed

    Liu, Lei; Schubert, David; Chu, Min; Heermann, Dieter W

    2015-03-01

    Motivated by the noncovalent binding of polypeptides to DNA, the adsorption of a flexible polymer to a rigid periodic copolymer is studied in two dimensions and three dimensions. The fraction of adsorbed monomers, the specific heat, and the Binder cumulant are analyzed and compared with analytical results for an ideal chain. As the interaction strength ε increases, a second-order phase transition occurs from a nonadsorbed state to an adsorbed state, in two dimensions, and a higher-order transition occurs in three dimensions. The transition point is estimated as ε0∼2.2 for d=2 and ε0∼2.1 for d=3, where ε is given in units of kBT. The dependence of the number of adsorbed monomers Nads on the chain length L of the flexible polymer shows a power law scaling relation Nads∼Lϕ, with ϕ∼0.46,0.42 for d=2,3, respectively. We also find an optimal ε∼2.8 for the winding of the flexible polymer around the rigid one in three dimensions. Compared to the adsorbed monomers, the successive nonadsorbed monomers contribute more to the winding. When the interaction is strong, ε>3.5, the winding value or the number of winding turns of the flexible polymer becomes linearly dependent on the chain length. PMID:25871135

  1. Microscopic Chain Motion in Polymer Nanocomposites with Dynamically Asymmetric Interphases

    NASA Astrophysics Data System (ADS)

    Senses, Erkan; Faraone, Antonio; Akcora, Pinar

    2016-07-01

    Dynamics of the interphase region between matrix and bound polymers on nanoparticles is important to understand the macroscopic rheological properties of nanocomposites. Here, we present neutron scattering investigations on nanocomposites with dynamically asymmetric interphases formed by a high-glass transition temperature polymer, poly(methyl methacrylate), adsorbed on nanoparticles and a low-glass transition temperature miscible matrix, poly(ethylene oxide). By taking advantage of selective isotope labeling of the chains, we studied the role of interfacial polymer on segmental and collective dynamics of the matrix chains from subnanoseconds to 100 nanoseconds. Our results show that the Rouse relaxation remains unchanged in a weakly attractive composite system while the dynamics significantly slows down in a strongly attractive composite. More importantly, the chains disentangle with a remarkable increase of the reptation tube size when the bound polymer is vitreous. The glassy and rubbery states of the bound polymer as temperature changes underpin the macroscopic stiffening of nanocomposites.

  2. Microscopic Chain Motion in Polymer Nanocomposites with Dynamically Asymmetric Interphases.

    PubMed

    Senses, Erkan; Faraone, Antonio; Akcora, Pinar

    2016-01-01

    Dynamics of the interphase region between matrix and bound polymers on nanoparticles is important to understand the macroscopic rheological properties of nanocomposites. Here, we present neutron scattering investigations on nanocomposites with dynamically asymmetric interphases formed by a high-glass transition temperature polymer, poly(methyl methacrylate), adsorbed on nanoparticles and a low-glass transition temperature miscible matrix, poly(ethylene oxide). By taking advantage of selective isotope labeling of the chains, we studied the role of interfacial polymer on segmental and collective dynamics of the matrix chains from subnanoseconds to 100 nanoseconds. Our results show that the Rouse relaxation remains unchanged in a weakly attractive composite system while the dynamics significantly slows down in a strongly attractive composite. More importantly, the chains disentangle with a remarkable increase of the reptation tube size when the bound polymer is vitreous. The glassy and rubbery states of the bound polymer as temperature changes underpin the macroscopic stiffening of nanocomposites. PMID:27457056

  3. Microscopic Chain Motion in Polymer Nanocomposites with Dynamically Asymmetric Interphases

    PubMed Central

    Senses, Erkan; Faraone, Antonio; Akcora, Pinar

    2016-01-01

    Dynamics of the interphase region between matrix and bound polymers on nanoparticles is important to understand the macroscopic rheological properties of nanocomposites. Here, we present neutron scattering investigations on nanocomposites with dynamically asymmetric interphases formed by a high-glass transition temperature polymer, poly(methyl methacrylate), adsorbed on nanoparticles and a low-glass transition temperature miscible matrix, poly(ethylene oxide). By taking advantage of selective isotope labeling of the chains, we studied the role of interfacial polymer on segmental and collective dynamics of the matrix chains from subnanoseconds to 100 nanoseconds. Our results show that the Rouse relaxation remains unchanged in a weakly attractive composite system while the dynamics significantly slows down in a strongly attractive composite. More importantly, the chains disentangle with a remarkable increase of the reptation tube size when the bound polymer is vitreous. The glassy and rubbery states of the bound polymer as temperature changes underpin the macroscopic stiffening of nanocomposites. PMID:27457056

  4. Nanoscience of single polymer chains revealed by nanofishing.

    PubMed

    Nakajima, Ken; Nishi, Toshio

    2006-01-01

    The invention of atomic force microscopy (AFM) enabled us to study the statistical properties of single polymer chains by a method called "nanofishing," which stretches a single polymer chain adsorbed on a substrate with its one end by picking it at the other end. A force-extension curve obtained for a single polystyrene chain in a Theta solvent (cyclohexane) shows good agreement with a worm-like chain model and, therefore, gives microscopic information about entropic elasticity. Furthermore, the nanofishing technique can be used for dynamic viscoelastic measurement of single polymer chains. An AFM cantilever is mechanically oscillated at its resonant frequency during the stretching process. This technique enables the estimation of quantitative and simultaneous elongation-dependent changes of stiffness and viscosity of a single chain with the use of a phenomenological model. In this study, the effect of solvent on viscosity in low extension regions reveals that the viscosity is attributed to monomer-solvent friction. Thus, static and dynamic nanofishing techniques are shown to give powerful experimental proofs for several basic questions in polymer physics. The techniques are expected to reveal hidden properties of polymer chains or polymer solutions by any types of macroscopic measurements in the future. PMID:17099889

  5. Analysis of structure and orientation of adsorbed polymers in solution subject to a dynamic shear stress

    SciTech Connect

    Smith, G.; Baker, S.; Toprakcioglu, C.

    1996-09-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Polymer-based separation techniques rely on the ability of a binding portion of the polymer to interact with a specific molecule in a solution flowing past the polymer. The location of the binding site within or out of the entangled polymer chains is thus crucial to the effectiveness of these methods. For this reason, the details of flow induced deformation of the polymer chains is important in such applications as exclusion chromatography, waste water treatment, ultrafiltration, enhanced oil recovery and microbial adhesion. Few techniques exist to examine the structure and orientation of polymeric materials, and even fewer to examine systems in a dynamic fluid flow. The goal of this project was to understand the molecular structure and orientation of adsorbed polymers with and without active binding ligands as a function of solvent shear rate, solvent power, polymer molecular weight, surface polymer coverage and heterogeneity of the surface polymer chains by neutron reflectometry in a newly designed shear cell. Geometrical effects on binding of molecules in the flow was also studied subject to the same parameters.

  6. Glass formation behavior of an isolated polymer chain

    NASA Astrophysics Data System (ADS)

    Merling, Weston; Mileski, Jack; Simmons, David

    2015-03-01

    A single polymer chain in isolation logically represents the extreme limit of nanoconfinement with respect to segmental dynamics and glass formation. Work in thin polymer films suggests that one should expect a large Tg suppression in such systems. However, recent dielectric relaxation measurements of isolated chains of P2VP on a silica substrate found bulk-like Tg in this system, apparently raising questions about the nature of observed nanoconfinement effects on the glass transition. Here we describe simulations of glass formation in an isolated polymer chain, both free-floating and deposited on a substrate. Results indicate that free-floating isolated polymer chains exhibit a depression in the dynamic glass transition temperature equivalent to more than 100K in polystyrene units. However, when a chain is deposited on a substrate with sufficiently favorable surface interactions, bulk-like dynamics can be recovered due to competition between the free-surface and adsorbed interface. When this compensation effect is taken account, these results indicate that the observation of bulk-like dynamics in isolated P2VP chains on a silica substrate is consistent with observations of large Tg suppressions in polymer films supported by less attractive substrates. This material is based upon work supported by the National Science Foundation under Grant No. DMR1310433.

  7. Theory of colloid depletion stabilization by unattached and adsorbed polymers.

    PubMed

    Semenov, A N; Shvets, A A

    2015-12-01

    The polymer-induced forces between colloidal particles in a semidilute or concentrated polymer solution are considered theoretically. This study is focussed on the case of partially adsorbing colloidal surfaces involving some attractive centers able to trap polymer segments. In the presence of free polymers the particles are covered by self-assembled fluffy layers whose structure is elucidated. It is shown that the free-polymer-induced interaction between the particles is repulsive at distances exceeding the polymer correlation length, and that this depletion repulsion can be strongly enhanced due to the presence of fluffy layers. This enhanced depletion stabilization mechanism (which works in tandem with a more short-range steric repulsion of fluffy layers) can serve on its own to stabilize colloidal dispersions. More generally, we identify three main polymer-induced interaction mechanisms: depletion repulsion, depletion attraction, and steric repulsion. Their competition is analyzed both numerically and analytically based on an asymptotically rigorous mean-field theory. It is shown that colloid stabilization can be achieved by simply increasing the molecular weight of polymer additives, or by changing their concentration. PMID:26400677

  8. Removal of acutely hazardous pharmaceuticals from water using multi-template imprinted polymer adsorbent.

    PubMed

    Venkatesh, Avinash; Chopra, Nikita; Krupadam, Reddithota J

    2014-05-01

    Molecularly imprinted polymer adsorbent has been prepared to remove a group of recalcitrant and acutely hazardous (p-type) chemicals from water and wastewaters. The polymer adsorbent exhibited twofold higher adsorption capacity than the commercially used polystyrene divinylbenzene resin (XAD) and powdered activated carbon adsorbents. Higher adsorption capacity of the polymer adsorbent was explained on the basis of high specific surface area formed during molecular imprinting process. Freundlich isotherms drawn showed that the adsorption of p-type chemicals onto polymer adsorbent was kinetically faster than the other reference adsorbents. Matrix effect on adsorption of p-type chemicals was minimal, and also polymer adsorbent was amenable to regeneration by washing with water/methanol (3:1, v/v) solution. The polymer adsorbent was unaltered in its adsorption capacity up to 10 cycles of adsorption and desorption, which will be more desirable in cost reduction of treatment compared with single-time-use activated carbon. PMID:24499987

  9. Surface Diffusion of Single Polymer Chain Using Molecular Dynamics SIMULATION*

    NASA Astrophysics Data System (ADS)

    Desai, Tapan; Keblinski, Pawel; Kumar, Sanat; Granick, Steve

    2004-05-01

    Results of recent experiments on polymer chains adsorbed from dilute solution at solid-liquid interface show the power scaling law dependence of the chain diffusivity, D, as a function of the degree of polymerization, N, D ˜ N^3/2. By contrast, DNA molecules bound to fluid cationic lipid bilayers follows Rouse dynamics with D ˜ N^1. We used molecular dynamics simulations to gain an understanding of these dissimilar scaling behaviors. Our model systems contain chains comprised of N monomers connected by anharmonic springs described by the finite extendible nonlinear elastic, FENE potential, embedded into a solvent of N=1 monomers. Two types of simulations we performed: (i) the chain is confined to two dimensions, (ii) the three dimensional chain in the solvent is confined between two solids plates. With randomly placed impenetrable obstacles on the surface, the diffusion of 2D chains exhibits, D ˜ N^3/2 behavior, when the chain radius of gyration, Rg, is larger than half the distance between obstacles, and D ˜ N^1 for shorter chains. In the presence of an athermal solvent, the scaling exponent is 0.75 due to hydrodynamic forces, for the two-dimensional system. We will also discuss the nature of dynamic adsorption transition and effects of hydrodynamics forces on chain diffusion for the three-dimensional simulations.

  10. Polymer Chain Reinforcement across Narrow Interfaces: Entanglements Versus Chain Friction

    NASA Astrophysics Data System (ADS)

    Benkoski, Jason J.; Fredrickson, Glenn H.; Kramer, Edward J.

    2002-03-01

    It is widely believed that entangled chains that bridge a glassy polymer/polymer interface solely determine its fracture energy (G_c). However, experiments show that while Gc increases with interfacial width (w), Gc vs. w/d_t, where dt is the tube diameter of the melt, is not universal. For some polymer pairs Gc increases dramatically even when w << d_t, while for others Gc does not increase until w >= d_t. We demonstrate that the friction stress for polymer loop pull-out from the interface is given by f_monoρ_merw/2 where f_mono is the static friction coefficient per mer and ρ_mer is the mer number density. Unlike interfaces with short block copolymers, where the friction stress for block pull-out is limited by a maximum areal density of block copolymer, the polymer/polymer friction stress grows linearly with w. For interfaces as narrow as 3 nm, it can be large enough to induce crazing. A model that includes both loop pull-out and chain entanglement shows that modest changes in f_mono can account for the fact that Gc versus w/dt is non-universal. A high areal density of bridging, entangled chains is therefore sufficient, but not necessary, to reinforce polymer interfaces.

  11. Equilibrium chain conformations of bound polymers at the polymer melt/solid interface

    NASA Astrophysics Data System (ADS)

    Sen, Mani; Jiang, Naisheng; Sendogdular, Levent; Endoh, Maya; Koga, Tadanori

    2014-03-01

    We report the equilibrium conformations of bound polymer chains formed on planar solids. In this study, bound polystyrene (PS) layers onto silicon (Si) substrates were used as a model system. Three 50 nm-thick PS thin films were prepared by using different film processes (i.e., spin coating, dip coating, and floating) following prolonged thermal annealing and subsequent solvent leaching. The structures of the bound layers on Si were then characterized by using x-ray reflectivity and atomic force microscopy. We found that the adsorption kinetics for the dip coating film is much longer than that for the spun cast film or the floating film. It was also found that all the bound PS layers are composed of two different nanoarchitectures: flattened chains that constitute the inner higher density region of the bound layers and loosely adsorbed polymer chains that form the outer bulk-like density region. We acknowledge the financial support from NSF Grant No. CMMI-084626.

  12. Effect of chain stiffness on polymer properties

    NASA Astrophysics Data System (ADS)

    Luettmer-Strathmann, Jutta

    2008-03-01

    Static and dynamic properties of polymers are affected by the stiffness of the chains. In this work, we investigate structural and thermodynamic properties of a lattice model for semiflexible polymer chains. The model is an extension of Shaffer's bond- fluctuation model and includes attractive interactions between monomers and an adjustable bending penalty that determines the Kuhn segment length. For isolated chains, a competition between monomer-monomer interactions and bending penalties determines the chain conformations at low temperatures. For dense melts, packing effects play an important role in the structure and thermodynamics of the polymeric liquid. In order to investigate static properties as a function of temperature and chain stiffness, we perform Wang-Landau type simulations and construct densities of states over the two-dimensional state space of monomer-monomer and bending contributions to the internal energy.

  13. Chain extension of a confined polymer in steady shear flow

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Pinaki; Cherayil, Binny J.

    2012-11-01

    The growing importance of microfluidic and nanofluidic devices to the study of biological processes has highlighted the need to better understand how confinement affects the behavior of polymers in flow. In this paper we explore one aspect of this question by calculating the steady-state extension of a long polymer chain in a narrow capillary tube in the presence of simple shear. The calculation is carried out within the framework of the Rouse-Zimm approach to chain dynamics, using a variant of a nonlinear elastic model to enforce finite extensibility of the chain, and assuming that the only effect of the confining surface is to modify the pre-averaged hydrodynamic interaction. The results, along with results from the corresponding calculations of finitely extensible versions of both the Rouse and Rouse-Zimm models, are compared with data from experiments on the flow-induced stretching of λ-phage DNA near a non-adsorbing glass surface [L. Fang, H. Hu, and R. G. Larson, J. Rheol. 49, 127 (2005), 10.1122/1.1822930]. The comparison suggests that close to a surface hydrodynamic screening is significant, and causes the chains to become effectively free-draining.

  14. Polymer nanocomposites: permeability, chain dynamics, mechanical properties

    NASA Astrophysics Data System (ADS)

    Sahu, Laxmi

    2005-03-01

    Polymer nanocomposites based on dispersion of surfactant treated expandable smectite clays such as montmorillonite layered silicates (MLS) have shown promise as organic-inorganic hybrids with the potential to improve barrier properties. Separately, flexible displays based on plastic substrates have reduced lifetimes tied to the low barrier properties. While there has been a general attribution of improved barrier properties to the tortuous path, this does not consider the influence the introduction of a secondary filler has on the morphology of the host polymer. Here we examine the influence of MLS nanoplatelets on the barrier properties and chain dynamics of polymers. We investigate the potential for host polymer modification by comparing two crystallizable polymers nylon and PET and resulting well dispersed nanocomposites. We study mechanical, cyclic fatigue and permeability of films. Permeability of the biaxially stretched film and when the film undergoes fatigue of 50 and 10000 cycles are also measured. Chain dynamics were modeled based on the Burger model fit to creep-recovery data. A systematic approach to predict the permeability considering amorphous, crystalline and MLS content and comparison with experimental values were done. We also conducted water absorption measurements to highlight the water absorption differences in the two polymers. Dimensional stability of PET was studied by measuring coefficient of thermal expansion of thin film on Si substrate by ellipsometry method.

  15. The Packing of Granular Polymer Chains

    SciTech Connect

    Zou, Ling-Nan; Cheng, Xiang; Rivers, Mark L.; Jaeger, Heinrich M.; Nagel, Sidney R.; UC

    2009-12-01

    Rigid particles pack into structures, such as sand dunes on the beach, whose overall stability is determined by the average number of contacts between particles. However, when packing spatially extended objects with flexible shapes, additional concepts must be invoked to understand the stability of the resulting structure. Here, we examine the disordered packing of chains constructed out of flexibly connected hard spheres. Using x-ray tomography, we find that long chains pack into a low-density structure whose mechanical rigidity is mainly provided by the backbone. On compaction, randomly oriented, semi-rigid loops form along the chain, and the packing of chains can be understood as the jamming of these elements. Finally, we uncover close similarities between the packing of chains and the glass transition in polymers.

  16. Plasma protein adsorbed biomedical polymers: activation of human monocytes and induction of interleukin 1.

    PubMed

    Bonfield, T L; Colton, E; Anderson, J M

    1989-06-01

    These studies involved the evaluation of human monocyte/macrophage activation by biomedical polymers coated with human blood proteins. The biomedical polymers were polyethylene, polydimethylsiloxane, woven Dacron fabric, expanded polytetrafluoroethylene, Biomer, and tissue culture treated polystyrene as the control. They were adsorbed with human blood proteins: albumin, fibrinogen, fibronectin, hemoglobin, and gamma globulin. The protein adsorbed polymers were evaluated for their potential to activate the monocyte/macrophage cellular population in vitro as assessed by the induction of the monocyte/macrophage inflammatory mediator, Interleukin 1 (IL1). Suppression of IL1 was observed when protein adsorbed polymers were compared to the appropriate protein adsorbed control. Protein adsorbed polymers, when compared to polymers without protein adsorption, stimulated IL1 production. The data presented in this manuscript show the level of induction and secretion of IL1 was dependent on the biomedical polymer and the protein adsorbed, as well as the requirement of lipopolysaccharide. These results show differential interactions occur between the proteins, monocytes/macrophages, and biomedical polymers which alter activation and induction of IL1. PMID:2786877

  17. Single-Chain Semiconducting Polymer Dots

    PubMed Central

    2015-01-01

    This work describes the preparation and validation of single-chain semiconducting polymer dots (sPdots), which were generated using a method based on surface immobilization, washing, and cleavage. The sPdots have an ultrasmall size of ∼3.0 nm as determined by atomic force microscopy, a size that is consistent with the anticipated diameter calculated from the molecular weight of the single-chain semiconducting polymer. sPdots should find use in biology and medicine as a new class of fluorescent probes. The FRET assay this work presents is a simple and rapid test to ensure methods developed for preparing sPdot indeed produced single-chain Pdots as designed. PMID:25521606

  18. Macromolecular recognition: Recognition of polymer side chains by cyclodextrin

    NASA Astrophysics Data System (ADS)

    Hashidzume, Akihito; Harada, Akira

    2015-12-01

    The interaction of cyclodextrins (CD) with water soluble polymers possessing guest residues has been investigated as model systems in biological molecular recognition. The selectivity of interaction of CD with polymer-carrying guest residues is controlled by polymer chains, i.e., the steric effect of polymer main chain, the conformational effect of polymer main chain, and multi-site interaction. Macroscopic assemblies have been also realized based on molecular recognition using polyacrylamide-based gels possessing CD and guest residues.

  19. Binding energies and electronic structures of adsorbed titanium chains on carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Yang, Chih-Kai; Zhao, Jijun; Lu, Jianping

    2002-03-01

    Our calculations based on first principles have shown that titanium is much favored energetically over gold and aluminum to form a continuous chain on a variety of single-wall carbon nanotubes (SWNT). Results from two zigzag nanotubes, (10,0) and (14,0), and two armchairs, (6,6) and (8,8), indicate that binding energy for a Ti-adsorbed SWNT is generally six to seven eV per unit cell larger than a Au or Al-adsorbed SWNT. Furthermore, the adsorbed Ti chain generates additional states in the band gaps of the two semi-conducting zigzag nanotubes, transforming them into metals.

  20. Static and dynamic properties of tethered chains at adsorbing surfaces: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Descas, Radu; Sommer, Jens-Uwe; Blumen, Alexander

    2004-05-01

    We present extensive Monte Carlo simulations of tethered chains of length N on adsorbing surfaces, considering the dilute case in good solvents, and analyze our results using scaling arguments. We focus on the mean number M of chain contacts with the adsorbing wall, on the chain's extension (the radius of gyration) perpendicular and parallel to the adsorbing surface, on the probability distribution of the free end and on the density profile for all monomers. At the critical adsorption strength ɛc one has Mc˜Nφ, and we find (using the above results) as best candidate φ to equal 0.59. However, slight changes in the estimation of ɛc lead to large deviations in the resulting φ; this might be a possible reason for the difference in the φ values reported in the literature. We also investigate the dynamical scaling behavior at ɛc, by focusing on the end-to-end correlation function and on the correlation function of monomers adsorbed at the wall. We find that at ɛc the dynamic scaling exponent a (which describes the relaxation time of the chain as a function of N) is the same as that of free chains. Furthermore, we find that for tethered chains the modes perpendicular to the surface relax quicker than those parallel to it, which may be seen as a splitting in the relaxation spectrum.

  1. Glassy dynamics in condensed isolated polymer chains.

    PubMed

    Tress, Martin; Mapesa, Emmanuel U; Kossack, Wilhelm; Kipnusu, Wycliffe K; Reiche, Manfred; Kremer, Friedrich

    2013-09-20

    In the course of miniaturization down to the nanometer scale, much remains unknown concerning how and to what extent the properties of materials are changed. To learn more about the dynamics of condensed isolated polymer chains, we used broadband dielectric spectroscopy and a capacitor with nanostructured electrodes separated by 35 nanometers. We measured the dynamic glass transition of poly(2-vinylpyridine) and found it to be bulk-like; only segments closer than 0.5 nanometer to the substrate were weakly slowed. Our approach paves the way for numerous experiments on the dynamics of isolated molecules. PMID:24052303

  2. Surfactant induced aggregation behavior of Merocyanine-540 adsorbed on polymer coated positively charged gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Das, K.; Uppal, A.; Saini, R. K.

    2016-01-01

    Surfactant induced aggregation behavior of Merocyanine 540 adsorbed on polymer (PDD) coated gold nanoparticles (AuNP) is reported. The absorption band of the dye shifts to higher energy in the presence of free polymer and polymer coated AuNP implying aggregation. Addition of a negatively charged surfactant (SDS) induces multiple bands in the extinction spectrum of the dye adsorbed on nanoparticle surface. The highest (460 nm) and lowest (564 nm) energy bands of the dye become prominent at 10 and >50 μM SDS concentrations respectively (dye: 10 μM; AuNP: 100-200 pM). Based on earlier results the high energy band is likely to originate from dye aggregates and the low energy band is likely to originate from dye monomers. This is attributed to the interplay between polymer-surfactant and polymer-dye interactions at the AuNP surface. The extinction spectra of dye adsorbed at AuNP surface remain unaffected in the presence of a positively charged (CTAB) or a neutral surfactant (Tx-100), at low surfactant concentrations. However at higher surfactant concentrations (>60 μM) dye aggregation takes place which is attributed to dye-surfactant interactions. The fluorescence intensity of the dye quenched significantly but its lifetime increased in the presence of polymer coated AuNP. This is attributed to aggregation and reduction in the photoisomerization rate of the dye adsorbed on AuNP surface.

  3. Detailed simulation of the role of functionalized polymer chains on the structural, dynamic and mechanical properties of polymer nanocomposites.

    PubMed

    Liu, Jun; Shen, Jianxiang; Gao, Yangyang; Zhou, Huanhuan; Wu, Youping; Zhang, Liqun

    2014-11-28

    To systematically study the effect of functionalized chain groups on polymer nanocomposites, we perform our simulation work in the following two ways. In the case of dilute loading of nanoparticles (NPs) with different geometries (spherical, sheet-like, rod-like NPs), we adopt coarse-grained molecular dynamics simulation to study the structural, dynamic and mechanical properties of polymer nanocomposites influenced by the terminal groups of linear polymer chains. We observe that the terminal groups have more probability to be adsorbed onto the surface of NPs with decreasing temperature, chain molecular weight and increasing chain stiffness. For all NPs with different geometries, more terminal groups segregate into the surface of NPs with increase in the interaction energy εf-n between the terminal groups and the NPs. We also notice that the attractive interaction between the terminal groups and the sheet-like NPs induces the appearance of a gradient of translational dynamics of polymer chains, and the relaxation at the chain length scale is evidently different for various adsorbed layers, whereas the segmental relaxation only becomes slightly slower nearby the sheet-like NPs. For both pure and filled systems with spherical NPs, it is found that the stress-strain curves and bond orientations are significantly enhanced with increase in the interaction strength between the terminal groups as well as terminal groups and NPs. In the case of concentrated loading of NPs, we construct the atomistic models of C60, CNT and graphene to accurately account for the "many body effect." We explore the influence of the functionalization position along the chain backbone on the dispersion kinetics, realizing that the end-functionalization is more effective. The end-groups effect on the chain configuration, chain packing and graphene equilibrium dispersibility is examined. The translational and rotational (segmental and terminal relaxation) dynamics influenced by the interactions

  4. Towards Understanding KOH Conditioning of Amidoxime-based Polymer Adsorbents for Sequestering Uranium from Seawater

    SciTech Connect

    Pan, Horng-Bin; Kuo, Li-Jung; Wood, Jordana R.; Strivens, Jonathan E.; Gill, Gary A.; Janke, C.; Wai, Chien M.

    2015-11-16

    Conditioning of polymer fiber adsorbents grafted with amidoxime and carboxylic acid groups is necessary to make the materials hydrophilic for sequestering uranium from seawater. Spectroscopic techniques were employed to study the effectiveness of the traditional KOH conditioning method (2.5% KOH at 80 oC) on recently developed high-surface-area amidoxime-based polymer fiber adsorbents developed at Oak Ridge National Laboratory. FTIR spectra reveal that the KOH conditioning process removes the proton from the carboxylic acids and also converts the amidoxime groups to carboxylate groups in the adsorbent. With prolonged KOH treatment (>1 hr) at 80 oC, physical damage to the adsorbent material occurs which can lead to a significant reduction in the adsorbent’s uranium adsorption capability in real seawater during extended exposure times (>21 days). The physical damage to the adsorbent can be minimized by lowering KOH conditioning temperature. For the high-surface-area amidoxime-based adsorbents, 20 min of conditioning in 2.5% KOH at 80 oC or 1 hr of conditioning in 2.5% KOH at 60 oC appears sufficient to achieve de-protonation of the carboxylic acid with minimal harmful effects to the adsorbent material. The use of NaOH instead of KOH can also reduce the cost of the base treatment process required for conditioning the amidoxime-based sorbents with minimal loss of adsorption capacity (≤ 7%).

  5. Polymer composite adsorbents using particles of molecularly imprinted polymers or aluminium oxide nanoparticles for treatment of arsenic contaminated waters.

    PubMed

    Önnby, L; Pakade, V; Mattiasson, B; Kirsebom, H

    2012-09-01

    Removal of As(V) by adsorption from water solutions was studied using three different synthetic adsorbents. The adsorbents, (a) aluminium nanoparticles (Alu-NPs, <50 nm) incorporated in amine rich cryogels (Alu-cryo), (b) molecular imprinted polymers (<38 μm) in polyacrylamide cryogels (MIP-cryo) and (c) thiol functionalised cryogels (SH-cryo) were evaluated regarding material characteristics and arsenic removal in batch test and continuous mode. Results revealed that a composite design with particles incorporated in cryogels was a successful means for applying small particles (nano- and micro- scale) in water solutions with maintained adsorption capacity and kinetics. Low capacity was obtained from SH-cryo and this adsorbent was hence excluded from the study. The adsorption capacities for the composites were 20.3 ± 0.8 mg/g adsorbent (Alu-cryo) and 7.9 ± 0.7 mg/g adsorbent (MIP-cryo) respectively. From SEM images it was seen that particles were homogeneously distributed in Alu-cryo and heterogeneously distributed in MIP-cryo. The particle incorporation increased the mechanical stability and the polymer backbones of pure polyacrylamide (MIP-cryo) were of better stability than the amine containing polymer backbone (Alu-cryo). Both composites worked well in the studied pH range of pH 2-8. Adsorption tested in real wastewater spiked with arsenic showed that co-ions (nitrate, sulphate and phosphate) affected arsenic removal for Alu-cryo more than for MIP-cryo. Both composites still adsorbed well in the presence of counter-ions (copper and zinc) present at low concentrations (μg/l). The unchanged and selective adsorption in realistic water observed for MIP-cryo was concluded to be due to a successful imprinting, here controlled using a non-imprinted polymer (NIP). A development of MIP-cryo is needed, considering its low adsorption capacity. PMID:22687522

  6. Analytic liquid-state theory of the interactions between colloids mediated by reversibly adsorbed polymers.

    PubMed

    Chervanyov, A I

    2014-12-28

    We develop an analytic liquid-state theory of the effective interactions induced by reversibly adsorbing polymers, acting between colloids immersed in a polymer melt. This theory is based on the polymer reference interaction site model that has no restrictions with respect to the density of the polymer system and colloid-to-polymer size ratio. By making use of the developed theory, we calculate the potential of the polymer mediated interactions as a function of the colloid radius, strength and range of the adsorption potential, and the polymer density. In addition, we investigate the behavior of the second virial coefficient as a function of the polymer density in both the colloid and nano-particle limits. We found out that the presence of the adsorption interactions significantly changes the polymer mediated forces relative to the case of the pure entropic depletion interactions, showing most pronounced difference in the case of large polymer densities and small colloid-to-polymer size ratios. The significance of the above differences is determined by the relation between the range of the adsorption potential and polymer correlation length. PMID:25554175

  7. Touching polymer chains by organic field-effect transistors

    PubMed Central

    Shao, Wei; Dong, Huanli; Wang, Zhigang; Hu, Wenping

    2014-01-01

    Organic field-effect transistors (OFETs) are used to directly “touch” the movement and dynamics of polymer chains, and then determine Tg. As a molecular-level probe, the conducting channel of OFETs exhibits several unique advantages: 1) it directly detects the motion and dynamics of polymer chain at Tg; 2) it allows the measurement of size effects in ultrathin polymer films (even down to 6 nm), which bridges the gap in understanding effects between surface and interface. This facile and reliable determination of Tg of polymer films and the understanding of polymer chain dynamics guide a new prospect for OFETs besides their applications in organic electronics and casting new light on the fundamental understanding of the nature of polymer chain dynamics. PMID:25227159

  8. Preferential positioning of a nanoparticle bound to a polymer: Exact enumeration of a self-avoiding walk chain model

    NASA Astrophysics Data System (ADS)

    Khoo, Andy; Iwaki, Takafumi; Shew, Chwen-Yang; Yoshikawa, Kenichi

    2009-09-01

    A lattice chain model is extended to investigate the preferential position of a sticky sphere bound to a polymer chain, motivated by wrapping one nanosize core-histone with DNA to form a nucleosome structure. It was shown that the single bound histone is populated in DNA chain ends from the experiment by T. Sakaue et al. [Phys. Rev. Lett. 87, 078105 (2001)]. Here, the possible mechanisms are examined to elucidate such behavior. For neutral chains or ionic chains in high salt concentrations, spheres bound on the middle of chain may trigger conformational constraints to reduce conformational entropy. For ionic chains, the bound sphere can be driven to chain ends if its effective charge and the charge of chain monomers are of like charge. The two-dimensional chain is further studied to mimic the chromosome strongly adsorbed onto surfaces, of which behavior is similar to the three-dimensional case with minor difference due to surface confinement.

  9. Mechanisms of chain adsorption on porous substrates and critical conditions of polymer chromatography.

    PubMed

    Cimino, Richard T; Rasmussen, Christopher J; Brun, Yefim; Neimark, Alexander V

    2016-11-01

    Polymer adsorption is a ubiquitous phenomenon with numerous technological and healthcare applications. The mechanisms of polymer adsorption on surfaces and in pores are complex owing to a competition between various entropic and enthalpic factors. Due to adsorption of monomers to the surface, the chain gains in enthalpy yet loses in entropy because of confining effects. This competition leads to the existence of critical conditions of adsorption when enthalpy gain and entropy loss are in balance. The critical conditions are controlled by the confining geometry and effective adsorption energy, which depends on the solvent composition and temperature. This phenomenon has important implications in polymer chromatography, since the retention at the critical point of adsorption (CPA) is chain length independent. However, the mechanisms of polymer adsorption in pores are poorly understood and there is an ongoing discussion in the theoretical literature about the very existence of CPA for polymer adsorption on porous substrates. In this work, we examine the mechanisms of chain adsorption on a model porous substrate using Monte Carlo (MC) simulations. We distinguish three adsorption mechanisms depending on the chain location: on external surface, completely confined in pores, and also partially confined in pores in so-called "flower" conformations. The free energies of different conformations of adsorbed chains are calculated by the incremental gauge cell MC method that allows one to determine the partition coefficient as a function of the adsorption potential, pore size, and chain length. We confirm the existence of the CPA for chain length independent separation on porous substrates, which is explained by the dominant contributions of the chain adsorption at the external surface, in particular in flower conformations. Moreover, we show that the critical conditions for porous and nonporous substrates are identical and depend only on the surface chemistry. The theoretical

  10. Spin currents and filtering behavior in zigzag graphene nanoribbons with adsorbed molybdenum chains

    NASA Astrophysics Data System (ADS)

    García-Fuente, A.; Gallego, L. J.; Vega, A.

    2015-04-01

    By means of density-functional-theoretic calculations, we investigated the structural, electronic and transport properties of hydrogen-passivated zigzag graphene nanoribbons (ZGNRs) on which a one-atom-thick Mo chain was adsorbed (with or without one or two missing atoms), or in which the passivating hydrogen atoms were replaced by Mo atoms. Mo-passivated ZGNRs proved to be nonmagnetic. ZGNRs with an adsorbed defect-free Mo chain were most stable with the Mo atoms forming dimers above edge bay sites, which suppressed the magnetic moments of the C atoms in that half of the ribbon; around the Fermi level of these systems, each spin component had a transmission channel via the Mo spz band and one had an additional channel created by polarization of the ZGNR π* band, leading to a net spin current. The absence of an Mo dimer from an Mo chain adsorbed at the ZGNR edge made the system a perfect spin filter at low voltage bias by suppressing the Mo spz band channels. Thus this last kind of hybrid system is a potential spin valve.

  11. Mass Distributions of Linear Chain Polymers

    PubMed Central

    Hubler, Shane L.; Craciun, Gheorghe

    2012-01-01

    Biochemistry has many examples of linear chain polymers, i.e., molecules formed from a sequence of units from a finite set of possibilities; examples include proteins, RNA, single-stranded DNA, and paired DNA. In the field of mass spectrometry, it is useful to consider the idea of weighted alphabets, with a word inheriting weight from its letters. We describe the distribution of the mass of these words in terms of a simple recurrence relation, the general solution to that relation, and a canonical form that explicitly describes both the exponential form of this distribution and its periodic features, thus explaining a wave pattern that has been observed in protein mass databases. Further, we show that a pure exponential term dominates the distribution and that there is exactly one such purely exponential term. Finally, we illustrate the use of this theorem by describing a formula for the integer mass distribution of peptides and we compare our theoretical results with mass distributions of human and yeast peptides. PMID:23024448

  12. Variational collision integrator for polymer chains

    NASA Astrophysics Data System (ADS)

    Leyendecker, Sigrid; Hartmann, Carsten; Koch, Michael

    2012-05-01

    The numerical simulation of many-particle systems (e.g. in molecular dynamics) often involves constraints of various forms. We present a symplectic integrator for mechanical systems with holonomic (bilateral) and unilateral contact constraints, the latter being in the form of a non-penetration condition. The scheme is based on a discrete variant of Hamilton's principle in which both the discrete trajectory and the unknown collision time are varied (cf. [R. Fetecau, J. Marsden, M. Ortiz, M. West, Nonsmooth Lagrangian mechanics and variational collision integrators, SIAM J. Appl. Dyn. Syst. 2 (2003) 381-416]). As a consequence, the collision event enters the discrete equations of motion as an unknown that has to be computed on-the-fly whenever a collision is imminent. The additional bilateral constraints are efficiently dealt with employing a discrete null space reduction (including a projection and a local reparametrisation step) which considerably reduces the number of unknowns and improves the condition number during each time-step as compared to a standard treatment with Lagrange multipliers. We illustrate the numerical scheme with a simple example from polymer dynamics, a linear chain of beads, and test it against other standard numerical schemes for collision problems.

  13. Nonaffine chain and primitive path deformation in crosslinked polymers

    NASA Astrophysics Data System (ADS)

    Davidson, J. D.; Goulbourne, N. C.

    2016-08-01

    Chains in a polymer network deform nonaffinely at small length scales due to the ability for extensive microscopic rearrangement. Classically, the conformations of an individual chain can be described solely by an end-to-end length. This picture neglects interchain interactions and therefore does not represent the behavior of a real polymer network. The primitive path concept provides the additional detail to represent interchain entanglements, and techniques have recently been developed to identify the network of primitive paths in a polymer simulation. We use coarse-grained molecular dynamics (MD) to track both chain end-to-end and primitive path deformation in crosslinked polymer networks. The range of simulated materials includes short chain unentangled networks to long, entangled chain networks. Both chain end-to-end and primitive path length are found to be linear functions of the applied deformation, and a simple relationship describes the behavior of a network in response to large stretch uniaxial, pure shear, and equi-biaxial deformations. As expected, end-to-end chain length deformation is nonaffine for short chain networks, and becomes closer to affine for networks of long, entangled chains. However, primitive path deformation is found to always be nonaffine, even for long, entangled chains. We demonstrate how the microscopic constraints of crosslinks and entanglements affect nonaffine chain deformation as well as the simulated elastic behavior of the different networks.

  14. Adsorption of phenolic compounds from aqueous solutions using carbon nanoporous adsorbent coated with polymer

    NASA Astrophysics Data System (ADS)

    Anbia, Mansoor; Ghaffari, Arezoo

    2009-09-01

    Phenolic compounds are a widespread class of water pollutants that are known to cause serious human health problems; and the demand for effective adsorbents for the removal of toxic compounds is increasing. In this work adsorption of phenol, resorcinol and p-cresol on mesoporous carbon material (CMK-1) and modified with polyaniline polymer (CMK-1/PANI) has been investigated in attempt to explore the possibility of using nanoporous carbon as an efficient adsorbent for pollutants. It was found that CMK-1/PANI exhibits significant adsorption for phenolic derivatives. Batch adsorption studies were carried out to study the effect of various parameters like adsorbent dose, pH, initial concentration and contact time. From the sorption studies it was observed that the uptake of resorcinol was higher than other phenolic derivatives. Freundlich and Langmuir adsorption isotherms were used to model the equilibrium adsorption data for phenolic compounds.

  15. Imparting Nonfouling Properties to Chemically Distinct Surfaces with a Single Adsorbing Polymer: A Multimodal Binding Approach.

    PubMed

    Serrano, Ângela; Zürcher, Stefan; Tosatti, Samuele; Spencer, Nicholas D

    2016-04-01

    Surface-active polymers that display nonfouling properties and carry binding groups that can adsorb onto different substrates are highly desirable. We present a postmodification protocol of an active-ester-containing polymer that allows the creation of such a versatile platform. Poly(pentafluorophenyl acrylate) has been postmodified with a fixed grafting ratio of a nonfouling function (mPEG) and various combinations of functional groups, such as amine, silane and catechol, which can provide strong affinity to two model substrates: SiO2 and TiO2 . Adsorption, stability and resistance to nonspecific protein adsorption of the polymer films were studied. A polymer was obtained that maintained its surface functionality under a variety of harsh conditions. EG surface-density calculations show that this strategy generates a denser packing when both negatively and positively charged groups are present within the backbone, and readily allows the fabrication of a broad combinatorial matrix. PMID:26858017

  16. Polymer chain simulations in microchannels with Dissipative Particle Dynamics

    NASA Astrophysics Data System (ADS)

    Symeonidis, Vasileios; Karniadakis, George; Caswell, Bruce

    2006-03-01

    In this work we employ Dissipative Particle Dynamics (dpd) for simulations of dilute polymer solutions using bead-spring representations. We present comparison of two time-marching schemes: the popular velocity-Verlet and Lowe's scheme. Schmidt number effects are investigated for a series of cases, including λ-dna molecules under shear (using the Marko-Siggia wormlike chain spring law) and Poiseuille flow in microchannels. Effects on the polymer depletion layer, power-law profiles and apparent viscosities are presented as a function of the number of beads per polymer chain.

  17. Adsorption of charged and neutral polymer chains on silica surfaces: The role of electrostatics, volume exclusion, and hydrogen bonding

    NASA Astrophysics Data System (ADS)

    Spruijt, Evan; Biesheuvel, P. M.; de Vos, Wiebe M.

    2015-01-01

    We develop an off-lattice (continuum) model to describe the adsorption of neutral polymer chains and polyelectrolytes to surfaces. Our continuum description allows taking excluded volume interactions between polymer chains and ions directly into account. To implement those interactions, we use a modified hard-sphere equation of state, adapted for mixtures of connected beads. Our model is applicable to neutral, charged, and ionizable surfaces and polymer chains alike and accounts for polarizability effects of the adsorbed layer and chemical interactions between polymer chains and the surface. We compare our model predictions to data of a classical system for polymer adsorption: neutral poly(N -vinylpyrrolidone) (PVP) on silica surfaces. The model shows that PVP adsorption on silica is driven by surface hydrogen bonding with an effective maximum binding energy of about 1.3 kBT per PVP segment at low p H . As the p H increases, the Si-OH groups become increasingly dissociated, leading to a lower capacity for H bonding and simultaneous counterion accumulation and volume exclusion close to the surface. Together these effects result in a characteristic adsorption isotherm, with the adsorbed amount dropping sharply at a critical p H . Using this model for adsorption data on silica surfaces cleaned by either a piranha solution or an O2 plasma, we find that the former have a significantly higher density of silanol groups.

  18. Stretching of Single Polymer Chains Using the Atomic Force Microscope

    NASA Astrophysics Data System (ADS)

    Ortiz, C.; van der Vegte, E. W.; van Swieten, E.; Robillard, G. T.; Hadziioannou, G.

    1998-03-01

    A variety of macroscopic phenomenon involve "nanoscale" polymer deformation including rubber elasticity, shear yielding, strain hardening, stress relaxation, fracture, and flow. With the advent of new and improved experimental techniques, such as the atomic force microscope (AFM), the probing of physical properties of polymers has reached finer and finer scales. The development of mixed self-assembling monolayer techniques and the chemical functionalization of AFM probe tips has allowed for mechanical experiments on single polymer chains of molecular dimensions. In our experiments, mixed monolayers are prepared in which end-functionalized, flexible polymer chains of thiol-terminated poly(methacrylic acid) are covalently bonded, isolated, and randomly distributed on gold substrates. The coils are then imaged, tethered to a gold-coated AFM tip, and stretched between the tip and the substrate in a conventional force / distance experiment. An increase in the attractive force due to entropic, elastic resistance to stretching, as well as fracture of the polymer chain is observed. The effect of chain stiffness, topological constraints, strain rate, mechanical hysteresis, and stress relaxation were investigated. Force modulation techniques were also employed in order to image the viscoelastic character of the polymer chains. Parallel work includes similar studies of biological systems such as wheat gluten proteins and polypeptides.

  19. Theoretical study of line and boundary tension in adsorbed colloid-polymer mixtures.

    PubMed

    Koning, Jesper; Vandecan, Yves; Indekeu, Joseph

    2014-07-28

    An extended theoretical study of interface potentials in adsorbed colloid-polymer mixtures is performed. To describe the colloid-polymer mixture near a hard wall, a simple Cahn-Nakanishi-Fisher free-energy functional is used. The bulk phase behaviour and the substrate-adsorbate interaction are modelled by the free-volume theory for ideal polymers with polymer-to-colloid size ratios q = 0.6 and q = 1. The interface potentials are constructed with help from a Fisher-Jin crossing constraint. By manipulating the crossing density, a complete interface potential can be obtained from natural, single-crossing, profiles. The line tension in the partial wetting regime and the boundary tension along prewetting are computed from the interface potentials. The line tensions are of either sign, and descending with increasing contact angle. The line tension takes a positive value of 10(-14)-10(-12) N near a first-order wetting transition, passes through zero and decreases to minus 10(-14)-10(-12) N away from the first-order transition. The calculations of the boundary tension along prewetting yield values increasing from zero at the prewetting critical point up to the value of the line tension at first-order wetting. PMID:25084953

  20. Theoretical study of line and boundary tension in adsorbed colloid-polymer mixtures

    NASA Astrophysics Data System (ADS)

    Koning, Jesper; Vandecan, Yves; Indekeu, Joseph

    2014-07-01

    An extended theoretical study of interface potentials in adsorbed colloid-polymer mixtures is performed. To describe the colloid-polymer mixture near a hard wall, a simple Cahn-Nakanishi-Fisher free-energy functional is used. The bulk phase behaviour and the substrate-adsorbate interaction are modelled by the free-volume theory for ideal polymers with polymer-to-colloid size ratios q = 0.6 and q = 1. The interface potentials are constructed with help from a Fisher-Jin crossing constraint. By manipulating the crossing density, a complete interface potential can be obtained from natural, single-crossing, profiles. The line tension in the partial wetting regime and the boundary tension along prewetting are computed from the interface potentials. The line tensions are of either sign, and descending with increasing contact angle. The line tension takes a positive value of 10-14-10-12 N near a first-order wetting transition, passes through zero and decreases to minus 10-14-10-12 N away from the first-order transition. The calculations of the boundary tension along prewetting yield values increasing from zero at the prewetting critical point up to the value of the line tension at first-order wetting.

  1. Generalized conservation law for main-chain polymer nematics

    NASA Astrophysics Data System (ADS)

    Svenšek, Daniel; Podgornik, Rudolf

    2016-05-01

    We explore the implications of the conservation law(s) and the corresponding so-called continuity equation(s), resulting from the coupling between the positional and the orientational order in main-chain polymer nematics, by showing that the vectorial and tensorial forms of these equations are in general not equivalent and cannot be reduced to one another, but neither are they disjoint alternatives. We analyze the relation between them and elucidate the fundamental role that the chain backfolding plays in the determination of their relative strength and importance. Finally, we show that the correct penalty potential in the effective free energy, implementing these conservation laws, should actually connect both the tensorial and the vectorial constraints. We show that the consequences of the polymer chains' connectivity for their consistent mesoscopic description are thus not only highly nontrivial but that its proper implementation is absolutely crucial for a consistent coarse-grained description of the main-chain polymer nematics.

  2. Supramolecular polymers: Chain growth in control

    NASA Astrophysics Data System (ADS)

    Deng, Renren; Liu, Xiaogang

    2015-06-01

    Supramolecular polymerizations typically proceed through stepwise intermolecular mechanisms, concomitant with many side reactions to yield aggregates of unpredictable size, shape and mass. Now, a chain-growth strategy is shown to allow assembly of molecules into supramolecular chain structures endowed with precisely controlled characteristics.

  3. Main chain type benzoxaine polymers for high performance applications

    NASA Astrophysics Data System (ADS)

    Chernykh, Andrey

    A new polymer with benzoxazine group in the main chain has been synthesized through the Mannich condensation of a difunctional phenol, formaldehyde and a diamine. Obtained polymer has weight average molecular weight of approximately 10,000 Da and a moderately broad polydispersity index. The new polymer is used to manufacturer self-supporting film of thermosetting resins. Aiming to obtain higher molecular weight, click chemistry approach has been applied to synthesize linear benzoxazine polymers. Three types of polymers have been prepared from dipropargyl- and novel diazide-functionalized benzoxazine monomers, showing a tremendous flexibility for applying click reaction to obtain various polymer architectures. The weight average molecular weight is estimated to be in the range from 50,000 to 100,000 Da which is significantly higher than the benzoxazine polymers which have been chain extended via Mannich reaction. Further developing approach of polycondensation of the monomers containing ozaxine rings, the oxidative coupling approach has been utilized in order to couple benzoxazines with terminal acetylene groups. A model benzoxazine compound containing diacetylene linkage exhibits unexpectedly low exothermic peak with the onset around 140°C, which is significantly lower than the temperature of conventional benzoxazine polymerization. The initial model studies have been made in order to understand this phenomenon and preliminary explanation is given. Extending this pathway to the difunctional propargyl- and ethynyl-functionalized benzoxazine monomers, a series of novel benzoxazine polymers containing diacetylene groups in the main chain have been synthesized. The weight average molecular weight of the polymers is achieved to be up to 50,000 Da. The effect of diacetylene moiety on the benzoxazine crosslinking behavior is even more pronounced for the obtained linear polymers showing exothermic peak with the onset at around 125°C and its maximum at 185°C. Upon

  4. Ozonolysis of surface adsorbed methoxyphenols: kinetics of aromatic ring cleavage vs. alkene side-chain oxidation

    NASA Astrophysics Data System (ADS)

    O'Neill, E. M.; Kawam, A. Z.; Van Ry, D. A.; Hinrichs, R. Z.

    2013-07-01

    Lignin pyrolysis products, which include a variety of substituted methoxyphenols, constitute a major component of organics released by biomass combustion and may play a central role in the formation of atmospheric brown carbon. Understanding the atmospheric fate of these compounds upon exposure to trace gases is therefore critical to predicting the chemical and physical properties of biomass burning aerosol. We used diffuse reflectance infrared spectroscopy to monitor the heterogeneous ozonolysis of 4-propylguaiacol, eugenol, and isoeugenol adsorbed on NaCl and α-Al2O3 substrates. Adsorption of gaseous methoxyphenols onto these substrates produced near monolayer surface concentrations of 3 × 1018 molecules m-2. The subsequent dark heterogeneous ozonolysis of adsorbed 4-propylguaiacol cleaved the aromatic ring between the methoxy and phenol groups with the product conclusively identified by GC-MS and 1H-NMR. Kinetic analysis of eugenol and isoeugenol dark ozonolysis also suggested the formation of ring-cleaved products, although ozonolysis of the unsaturated substituent groups forming carboxylic acids and aldehydes was an order of magnitude faster. Average uptake coefficients for NaCl-adsorbed methoxyphenols were γ = 2.3 (±0.8) × 10-7 and 2 (±1) × 10-6 for ozonolysis of the aromatic ring and the unsaturated side chain, respectively, and reactions on α-Al2O3 were approximately two times slower. UV-visible radiation (λ>300 nm) enhanced eugenol ozonolysis of the aromatic ring by a factor of 4(±1) but had no effect on ozonolysis of the alkene side-chain.

  5. Anionic synthesis of in-chain and chain-end functionalized polymers

    NASA Astrophysics Data System (ADS)

    Roy Chowdhury, Sumana

    The objective of this work was to anionically synthesize well-defined polymers having functional groups either at the chain-end or along the polymer chain. General functionalization methods (GFM) were used for synthesizing both kinds of polymers. Chain-end functionalized polymers were synthesized by terminating the anionically synthesized, living polymer chains using chlorodimethylsilane. Hydrosilation reactions were then done between the silyl-hydride groups at the chain-ends and the double bonds of commercially available substituted alkenes. This produced a range of well-defined polymers having the desired functional groups at the chain-ends. In-chain functionalized polymers were synthesized by anionically polymerizing a silylhydride functionalized styrene monomer: (4-vinylphenyl)dimethysilane. Polymerizations were done at room temperature in hydrocarbon solvents to produce well-defined polymers. Functional groups were then introduced into the polymer chains by use of hydrosilation reactions done post-polymerization. The functionalized polymers produced were characterized using SEC, 1H and 13C NMR, FTIR, MALDI TOF mass spectrometry and DSC. The monomer reactivity ratios in the copolymerization of styrene with (4-vinylphenyl)dimethylsilane were also measured. A series of copolymerizaions was done with different molar ratios of styrene(S) and (4-vinylphenyl)dimethylsilane(Si). Three different methods were used to determine the values of the monomer reactivity ratios: Fineman-Ross, Kelen-Tudos and Error-In-Variable (EVM) methods. The average values of the two monomer reactivity ratios obtained were: r Si = 0.16 and rS = 1.74. From these values it was observed that in the copolymerization of styrene with (4-vinylphenyl)dimethylsilane, the second monomer was preferentially incorporated into the copolymer chain. Also, rSirS = 0.27, which shows that the copolymer has a tendency to have an alternating structure. Amino acid-functionalized polymers (biohybrids) were

  6. DPPG Liposomes Adsorbed on Polymer Cushions: Effect of Roughness on Amount, Surface Composition and Topography.

    PubMed

    Duarte, Andreia A; Botelho do Rego, Ana M; Salerno, Marco; Ribeiro, Paulo A; El Bari, Nezha; Bouchikhi, Benachir; Raposo, Maria

    2015-07-01

    The adsorption of intact liposomes onto solid supports is a fundamental issue when preparing systems with encapsulated biological molecules. In this work, the adsorption kinetic of 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (sodium salt) liposomes onto cushions prepared from commom polyelectrolytes by the layer-by-layer technique was investigated with the main objective of finding the surface conditions leading to the adsorption of intact liposomes. For this purpose, different cushion surface roughnesses were obtained by changing the number of cushion bilayers. The adsorbed amount per unit area was measured through quartz crystal microbalance, surface morphology was characterized by atomic force microscopy, and the surface composition was assessed by X-ray photoelectron spectroscopy. The results show that (1) the amount of adsorbed lipids depends on the number of cushion bilayers, (2) the cushions are uniformly covered by the adsorbed lipids, and (3) the surface morphology of polymer cushions tunes liposome rupture and its adsorption kinetics. The fraction of ruptured liposomes, calculated from the measured amount of adsorbed lipids, is a function of surface roughness together with other surface morphology parameters, namely the dominating in-plane spatial feature size, the fractal dimension, and other textural features as well as amplitude and hybrid parameters. PMID:26076391

  7. Single chain stochastic polymer modeling at high strain rates.

    SciTech Connect

    Harstad, E. N.; Harlow, Francis Harvey,; Schreyer, H. L.

    2001-01-01

    Our goal is to develop constitutive relations for the behavior of a solid polymer during high-strain-rate deformations. In contrast to the classic thermodynamic techniques for deriving stress-strain response in static (equilibrium) circumstances, we employ a statistical-mechanics approach, in which we evolve a probability distribution function (PDF) for the velocity fluctuations of the repeating units of the chain. We use a Langevin description for the dynamics of a single repeating unit and a Lioville equation to describe the variations of the PDF. Moments of the PDF give the conservation equations for a single polymer chain embedded in other similar chains. To extract single-chain analytical constitutive relations these equations have been solved for representative loading paths. By this process we discover that a measure of nonuniform chain link displacement serves this purpose very well. We then derive an evolution equation for the descriptor function, with the result being a history-dependent constitutive relation.

  8. Highly Ordered Single Conjugated Polymer Chain Rod Morphologies

    SciTech Connect

    Adachi, Takuji; Brazard, Johanna; Chokshi, Paresh; Ganesan, Venkat; Bolinger, Joshua; Barbara, Paul F.

    2010-10-15

    We have reexamined the fluorescence polarization anisotropy of single polymer chains of the prototypical conjugated polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) isolated in a poly(methyl methacrylate) (PMMA) matrix employing improved synthetic samples that contain a much smaller number of tetrahedral chemical defects per chain. The new measurements reveal a much larger fraction of highly anisotropic MEH-PPV chains, with >70% of the chains exhibiting polarization anisotropy values falling in the range of 0.6-0.9. High anisotropy is strong evidence for a rod-shaped conformation. A comparison of the experimental results with coarse grain, beads on a chain simulations reveals that simulations with the usual bead-bead pairwise additive potentials cannot reproduce the observed large fraction of high polarization values. Apparently, this type of potential lacks some yet to be identified molecular feature that is necessary to accurately simulate the experimental results.

  9. Particle-directed assembly of semiflexible polymer chains.

    PubMed

    McGovern, Michael; Dorfman, Kevin D; Morse, David C

    2016-07-20

    We use Langevin dynamics simulations to study aggregation of semiflexible polymers driven by attractions between polymers and spherical particles. We consider a simple model with purely repulsive polymer/polymer and particle/particle interactions but attractive polymer/particle interactions. We find a rich "phase diagram" that contains several different types of globular and rod-like aggregates with either liquid-like or crystalline structure for the particle positions. Systems that exhibit rod-like aggregates with crystalline internal order exhibit a discontinuous rod-globule transition, while systems with liquid-like internal order exhibit a smooth crossover between isotropic and elongated aggregates with increasing chain stiffness. Polymers in elongated liquid-like aggregates often adopt helical configurations that wind around the axis of the aggregate. PMID:27378073

  10. Characteristics of main chain decomposable STAR polymer for EUV resist

    NASA Astrophysics Data System (ADS)

    Iwashita, Jun; Hirayama, Taku; Takagi, Isamu; Matsuzawa, Kensuke; Suzuki, Kenta; Yoshizawa, Sachiko; Konno, Kenri; Yahagi, Masahito; Sato, Kazufumi; Tagawa, Seiichi; Enomoto, Kazuyuki; Oshima, Akihiro

    2011-04-01

    The concept of nonlinear acid diffusion coefficient would be emphasized to achieve better latent image quality, resulting in better lithographic performance. Focusing on realizing the concept, we previously reported about a main chain decomposable star shaped polymer (STAR polymer).STAR polymer consists of a core unit and several arm units which connect to the core unit with easily acid cleavable bonding. (Fig.1) The main chain decomposition system is ideal to achieve promoted acid diffusion at exposed area because it accompanies great molecular weight reduction at exposed area. The significance of the STAR system had been confirmed for partially protected poly(p-hydroxystyrene) (PHS) considering arm length and core structure. Employing p-hydroxy-α-methylstylene (PHOMS) for arm structure, novel STAR polymer with appropriate glass transition temperature (Tg) could be realized. (Fig.2) Poly PHOMS is known to undergo acid-catalyzed decomposition from the polymer end. Lithographic performance comparison between the STAR polymer and the linear polymer as a control using a Micro Exposure Tool (MET) would be exhibited. Thermal property change with exposure and dissolution charactersitic will be also discussed. Moreover main chain decomposition mechanism was investigated with flood EB irradiation.

  11. Polymer chain organization in tensile-stretched poly(ethylene oxide)-based polymer electrolytes.

    PubMed

    Burba, Christopher M; Woods, Lauren; Millar, Sarah Y; Pallie, Jonathan

    2011-12-15

    Polymer chain orientation in tensile-stretched poly(ethylene oxide)-lithium trifluoromethanesulfonate polymer electrolytes are investigated with polarized infrared spectroscopy as a function of the degree of strain and salt composition (ether oxygen atom to lithium ion ratios of 20:1, 15:1, and 10:1). The 1359 and 1352 cm(-1) bands are used to probe the crystalline PEO and P(EO)(3)LiCF(3)SO(3) domains, respectively, allowing a direct comparison of chain orientation for the two phases. Two-dimensional correlation FT-IR spectroscopy indicates that the two crystalline domains align at the same rate as the polymer electrolytes are stretched. Quantitative measurements of polymer chain orientation obtained through dichroic infrared spectroscopy show that chain orientation predominantly occurs between strain values of 150% and 250%, regardless of salt composition investigated. There are few changes in chain orientation for either phase when the films are further elongated to a strain of 300%; however, the PEO domains are slightly more oriented at the high strain values. The spectroscopic data are consistent with stretching-induced melt-recrystallization of the unoriented crystalline domains in the solution-cast polymer films. Stretching the films pulls polymer chains from the crystalline domains, which subsequently recrystallize with the polymer helices parallel to the stretch direction. If lithium ion conduction in crystalline polymer electrolytes is viewed as consisting of two major components (facile intra-chain lithium ion conduction and slow helix-to-helix inter-grain hopping), then alignment of the polymer helices will affect the ion conduction pathways for these materials by reducing the number of inter-grain hops required to migrate through the polymer electrolyte. PMID:22184475

  12. Does a polymer chain probe solvent dynamics?

    NASA Astrophysics Data System (ADS)

    Peterson, Steve; Echeverria, Isabel; Schrag, John

    2001-03-01

    We have examined the dynamics of polyisoprene (both in bulk and in solution) using viscoelastic and oscillatory flow birefringence measurements. Surprisingly, the breadth of the relaxation time spectrum for the polymer appears to narrow significantly when going from bulk to solution conditions. This suggests an apparent flexibility difference in the polymer that may actually reflect dynamic spatial heterogeneity in the solvent (a glass former). Our results suggest a connection with experimental evidence of dynamic heterogeneities in glass forming liquids (Ediger, M.D., Annu. Rev. Phys. Chem., 2000, 51:99-128) and results of molecular dynamics simulations (Donati, C., et al., PRL, 80, 11, 1998).

  13. Kinetic Assembly of Near-IR Active Gold Nanoclusters using Weakly Adsorbing Polymers to Control Size

    PubMed Central

    Tam, Jasmine M.; Murthy, Avinash K.; Ingram, Davis R.; Nguyen, Robin; Sokolov, Konstantin V.; Johnston, Keith P.

    2013-01-01

    Clusters of metal nanoparticles with an overall size less than 100 nm and high metal loadings for strong optical functionality, are of interest in various fields including microelectronics, sensors, optoelectronics and biomedical imaging and therapeutics. Herein we assemble ~5 nm gold particles into clusters with controlled size, as small as 30 nm and up to 100 nm, which contain only small amounts of polymeric stabilizers. The assembly is kinetically controlled with weakly adsorbing polymers, PLA(2K)-b-PEG(10K)-b-PLA(2K) or PEG (MW = 3350), by manipulating electrostatic, van der Waals (VDW), steric, and depletion forces. The cluster size and optical properties are tuned as a function of particle volume fractions and polymer/gold ratios to modulate the interparticle interactions. The close spacing between the constituent gold nanoparticles and high gold loadings (80–85% w/w gold) produce a strong absorbance cross section of ~9×10−15 m2 in the NIR at 700 nm. This morphology results from VDW and depletion attractive interactions that exclude the weakly adsorbed polymeric stabilizer from the cluster interior. The generality of this kinetic assembly platform is demonstrated for gold nanoparticles with a range of surface charges from highly negative to neutral, with the two different polymers. PMID:20361735

  14. Identification of polymer surface adsorbed proteins implicated in pluripotent human embryonic stem cell expansion.

    PubMed

    Hammad, Moamen; Rao, Wei; Smith, James G W; Anderson, Daniel G; Langer, Robert; Young, Lorraine E; Barrett, David A; Davies, Martyn C; Denning, Chris; Alexander, Morgan R

    2016-08-16

    Improved biomaterials are required for application in regenerative medicine, biosensing, and as medical devices. The response of cells to the chemistry of polymers cultured in media is generally regarded as being dominated by proteins adsorbed to the surface. Here we use mass spectrometry to identify proteins adsorbed from a complex mouse embryonic fibroblast (MEF) conditioned medium found to support pluripotent human embryonic stem cell (hESC) expansion on a plasma etched tissue culture polystyrene surface. A total of 71 proteins were identified, of which 14 uniquely correlated with the surface on which pluripotent stem cell expansion was achieved. We have developed a microarray combinatorial protein spotting approach to test the potential of these 14 proteins to support expansion of a hESC cell line (HUES-7) and a human induced pluripotent stem cell line (ReBl-PAT) on a novel polymer (N-(4-Hydroxyphenyl) methacrylamide). These proteins were spotted to form a primary array yielding several protein mixture 'hits' that enhanced cell attachment to the polymer. A second array was generated to test the function of a refined set of protein mixtures. We found that a combination of heat shock protein 90 and heat shock protein-1 encourage elevated adherence of pluripotent stem cells at a level comparable to fibronectin pre-treatment. PMID:27466628

  15. Contact line of adsorbed colloid-polymer droplets in theory and experiment.

    PubMed

    Koning, Jesper; Hennequin, Yves; Bonn, Daniel; Indekeu, Joseph O

    2016-05-01

    The contact line between the colloid-rich bulk liquid and an adsorbed thin film in colloid-polymer mixtures (CPM) is studied by means of an interface displacement model. The interface displacement profiles are compared to laser scanning confocal microscopy (LSCM) images. The mixtures consist of poly(methylmetacrylate) (PMMA) colloids and polystyrene (PS) polymers with polymer-to-colloid size ratio q = 1.18. Based on the experimental parameters, the theoretical model predicts a contact angle for colloid-rich liquid droplets adsorbed on glass of θ∞ = 59°, assuming a contact line with infinite radius, R = ∞. When a contact-line curvature correction and a correction for the protein-limit character of the CPM are taken into account, a modest shift is obtained. The refined theory predicts θ≈ 56°. The contact angle determined visually from the LSCM images is θ≈ 30°. The model predicts a three-phase contact-line tension of τ = -1.2 × 10(-12) N (uncorrected) and τ = -2.3 × 10(-13) N (with protein-limit correction), which is physically sound both in sign and magnitude. The line tension influences the contact angle to a small extent due to the contact line curvature. The predicted width of the transition zone between the thin film and the droplet is about 2 μm. The effect of gravity is noticeable as a deformation near the middle of the droplet. PMID:27029605

  16. Static properties of polymer chains in porous media

    NASA Astrophysics Data System (ADS)

    Honeycutt, J. D.; Thirumalai, D.

    1989-04-01

    The static properties of a polymer molecule in a porous medium are investigated. The porous medium is simulated using a site percolation model in which the various sites are occupied (or unoccupied) randomly. A freely jointed chain is allowed to move in continuous space between the obstacles. Effects of excluded volume interactions between the links have also been studied. Using a generalized Flory theory, we have shown that, when the strength of disorder is large enough, the mean square end-to-end distance scales as N2ν, where N is the number of links in the chain, and ν takes on a value different from that for a free chain. Under these conditions, the polymer assumes a compact, globule-like conformation. For sufficiently large N, the Flory theory gives ν=1/(d+2) for freely jointed chains and ν=1/d for chains with excluded volume. Various correlation functions such as the distribution of the end-to-end distance and density profile of monomers with respect to the center of mass of the chain have been computed using Monte Carlo simulations. These results are interpreted using scaling concepts and an approximate variational theory based on replica methods. The limitations of the replica variational theory are assessed by an application to the directed polymer in a quenched random environment. We have also studied the shape fluctuations that the polymer molecule undergoes in the random environment. It is argued that these shape fluctuations are relevant to the transport mechanism of polymers in random media. The results obtained for the porous media are contrasted with those found for polymers in media where the obstacles are arranged in a regular manner.

  17. New polymer systems: Chain extension by dianhydrides

    NASA Technical Reports Server (NTRS)

    Rhein, R. A.; Ingham, J. D.

    1972-01-01

    The results are presented for a systematic investigation on the use of anhydrides to prepare stable elastomeric materials for space use, under mild reaction conditions. The three anhydrides investigated were found to provide effective chain extension of hydroxy-terminated poly(alkylene oxides) and poly(butadienes). These were tetrahydrofuran tetracarboxylic dianhydride, pyromellitic dianhydride, and benzophenone tetracarboxylic diahydride. The most effective catalyst investigated was ferric acetylacetonate, which resulted in chain extension at 333 K (60 C). One feature of these anhydride reactants is that they are difunctional as anhydrides, but tetrafunctional if conditions are selected that lead to reaction of all carboxyl groups. Therefore, chain extension can be effected and then followed by crosslinking via the residual carboxyl groups.

  18. Grafted polymers inside cylindrical tubes: Chain stretching vs layer thickness

    NASA Astrophysics Data System (ADS)

    Suo, Tongchuan; Whitmore, Mark D.

    2013-04-01

    We present a study of the detailed structure of grafted polymer chains and the layers they form inside cylindrical tubes, using the finitely extensible nonlinear elastic chain model and numerical self-consistent field theory. For very large tube radius, the chain stretching and layer thicknesses are the same as for polymers grafted to a planar surface. For decreasing radius, our calculations indicate that the layer almost always gets thinner, although there can be situations where it is very slightly thicker. However, we find that this thinning is not necessarily due to changes to the polymers: in fact, the root-mean-squared layer thickness would decrease even if the polymers themselves are completely unchanged. Furthermore, we find that the polymer stretching can increase at the same time that the layer thickness decreases. These apparent paradoxes are resolved by analyzing and distinguishing between the volume fraction profiles and monomer number distributions in these systems, including how they change and why. We also find that, in a given system, parts of each polymer move towards the curved surface and parts away from it, and that these differences are key to understanding the behavior.

  19. Effect of nanoconfinement on liquid-crystal polymer chains

    NASA Astrophysics Data System (ADS)

    Micheletti, Davide; Muccioli, Luca; Berardi, Roberto; Ricci, Matteo; Zannoni, Claudio

    2005-12-01

    We apply a Monte Carlo polymerization model for Gay-Berne [J. Chem. Phys. 74, 3316 (1981)] monomers that we have recently introduced [J. Chem. Phys. 121, 9123 (2004)] to investigate with computer simulations the effects of nanoconfinement and anchoring type on the structure of the main-chain liquid-crystal polymers formed in thin films, in the presence of several types of surface alignment: parallel to the interface (random and uniform) or perpendicular to it (homeotropic). We perform first a study of the confined monomers and then we examine the features of the polymer chains obtained from an isotropic or nematic sample. We find a significant effect of the anchoring conditions on the characteristics of the chains and particularly striking differences between planar and homeotropic boundaries. Furthermore, our results indicate that the choice of different anchorings could be used to tune the linearity and degree of polymerization of the chains.

  20. Effect of nanoconfinement on liquid-crystal polymer chains.

    PubMed

    Micheletti, Davide; Muccioli, Luca; Berardi, Roberto; Ricci, Matteo; Zannoni, Claudio

    2005-12-01

    We apply a Monte Carlo polymerization model for Gay-Berne [J. Chem. Phys. 74, 3316 (1981)] monomers that we have recently introduced [J. Chem. Phys. 121, 9123 (2004)] to investigate with computer simulations the effects of nanoconfinement and anchoring type on the structure of the main-chain liquid-crystal polymers formed in thin films, in the presence of several types of surface alignment: parallel to the interface (random and uniform) or perpendicular to it (homeotropic). We perform first a study of the confined monomers and then we examine the features of the polymer chains obtained from an isotropic or nematic sample. We find a significant effect of the anchoring conditions on the characteristics of the chains and particularly striking differences between planar and homeotropic boundaries. Furthermore, our results indicate that the choice of different anchorings could be used to tune the linearity and degree of polymerization of the chains. PMID:16375493

  1. Long-time dynamics of chains in polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Green, Peter

    2009-03-01

    In polymer nanocomposites (PNCs), the presence of the nanoparticles has a marked effect on the dynamics and the Tg. In one limit, the chains become strongly attached to the particles, and two glass transitions, and bimodal dynamics, may be observed. In the other, where the chain/particle interactions are weak, the chain friction factor, z(T) can undergo significant changes, manifested in the translational diffusion and viscosity. In the polymethyl methacrylate (PMMA)/C60 system, the dynamics slow down, accompanied by an increase in the glass transition. At the same time, the temperature dependence of the relaxations remains the same as pure PMMA. In polystyrene (PS)/Au-thiol capped PS ligands, the dynamics and the glass transition could be induced to increase or decrease, through manipulation of molecular parameters in the system. In this presentation, we propose a mechanism to describe translational diffusion and Tg in PNC systems in which the polymer chain/nanoparticle interactions are weak.

  2. Molecular Dynamics Simulation of Electrophoresis of a Telehelic Polymer Chain

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Aniket

    2002-08-01

    We report the conformational and the dynamical properties of an end-labeled polymer chain embedded in a porous medium made of randomly distributed immobile spherical obstacles using a stochastic Molecular Dynamic(MD) simulation method for several obstacle densities and for various bias strenghts applied only to one end of the chain. First, various properties of the chain are studied when the external bias is set to zero. We then extend the stochastic MD simulation to study the electrophresis of a polymer chain driven by (i) a steady and (ii) a time dependent electric field. These studies are relevant for various time dependent gel electrophoresis methods widely used to separate DNA molecules. The qualitative features are compared with experiments, analytic theories, and recent Monte Carlo Simulation results.

  3. Membrane consisting of polyquaternary amine ion exchange polymer network interpenetrating the chains of thermoplastic matrix polymer

    NASA Technical Reports Server (NTRS)

    Rembaum, A.; Wallace, C. J. (Inventor)

    1978-01-01

    An ion exchange membrane was formed from a solution containing dissolved matrix polymer and a set of monomers which are capable of reacting to form a polyquaternary ion exchange material; for example vinyl pyride and a dihalo hydrocarbon. After casting solution and evaporation of the volatile component's, a relatively strong ion exchange membrane was obtained which is capable of removing anions, such as nitrate or chromate from water. The ion exchange polymer forms an interpenetrating network with the chains of the matrix polymer.

  4. New polymer systems: Chain extension by dianhydrides

    NASA Technical Reports Server (NTRS)

    Rhein, R. A.; Ingham, J. D.

    1974-01-01

    Three anhydrides provide effective chain extension of hydroxy-terminated polyalkylene oxides and polybutadienes. Novel feature of these anhydride reactants is that they are difunctional as anhydrides, but they are tetrafunctional if conditions are selected that lead to total esterification or reaction of all carboxyl groups.

  5. Statistical Behavior of Polymer Chains in Curved Space

    NASA Astrophysics Data System (ADS)

    Li, Jianfeng; Shi, An-Chang; Zhang, Hongdong; Qiu, Feng; Yang, Yuliang

    2014-03-01

    Recently, we have derived the modified diffusion equation of the propagator (the end-segment distribution function) in general curved space for both Gaussian and wormlike chains. Mathematically, a Gaussian-curvature term appears as an extra external field in the diffusion equation of Gaussian chains while there is an additional normal-curvature term for the case of wormlike chains. The basic statistical behavior of polymer chains in curved space can be also extracted by examining these newly derived diffusion equations revealing that Gaussian chains are aware of the intrinsic curvature of the space but are blind to the external curvature while wormlike chains can feel both. We thank the financial support from NSFC (No. 21104010).

  6. Nanostructured Membranes from Triblock Polymer Precursors as High Capacity Copper Adsorbents.

    PubMed

    Weidman, Jacob L; Mulvenna, Ryan A; Boudouris, Bryan W; Phillip, William A

    2015-10-13

    Membrane adsorbers are a proposed alternative to packed beds for chromatographic separations. To date, membrane adsorbers have suffered from low binding capacities and/or complex processing methodologies. In this work, a polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (PI-PS-PDMA) triblock polymer is cast into an asymmetric membrane that possesses a high density of nanopores (d ∼ 38 nm) at the upper surface of the membrane. Exposing the membrane to a 6 M aqueous hydrochloric acid solution converts the PDMA brushes that line the pore walls to poly(acrylic acid) (PAA) brushes, which are capable of binding metal ions (e.g., copper ions). Using mass transport tests and static binding experiments, the saturation capacity of the PI-PS-PAA membrane was determined to be 4.1 ± 0.3 mmol Cu(2+) g(-1). This experimental value is consistent with the theoretical binding capacity of the membranes, which is based on the initial PDMA content of the triblock polymer precursor and assumes a 1:1 stoichiometry for the binding interaction. The uniformly sized nanoscale pores provide a short diffusion length to the binding sites, resulting in a sharp breakthrough curve. Furthermore, the membrane is selective for copper ions over nickel ions, which permeate through the membrane over 10 times more rapidly than copper during the loading stage. This selectivity is present despite the fact that the sizes of these two ions are nearly identical and speaks to the chemical selectivity of the triblock polymer-based membrane. Furthermore, addition of a pH 1 solution releases the bound copper rapidly, allowing the membrane to be regenerated and reused with a negligible loss in binding capacity. Because of the high binding capacities, facile processing method implemented, and ability to tailor further the polymer brushes lining the pore walls using straightforward coupling reactions, these membrane adsorbers based on block polymer precursors have potential as a separation media that can

  7. Hyperbranched polymer stars with Gaussian chain statistics revisited.

    PubMed

    Polińska, P; Gillig, C; Wittmer, J P; Baschnagel, J

    2014-02-01

    Conformational properties of regular dendrimers and more general hyperbranched polymer stars with Gaussian statistics for the spacer chains between branching points are revisited numerically. We investigate the scaling for asymptotically long chains especially for fractal dimensions df = 3 (marginally compact) and df = 2.5 (diffusion limited aggregation). Power-law stars obtained by imposing the number of additional arms per generation are compared to truly self-similar stars. We discuss effects of weak excluded-volume interactions and sketch the regime where the Gaussian approximation should hold in dense solutions and melts for sufficiently large spacer chains. PMID:24574057

  8. Folding of Polymer Chains in Early Stage of Crystallization

    NASA Astrophysics Data System (ADS)

    Yuan, Shichen; Miyoshi, Toshikazu

    Understanding the structural formation of long polymer chains in the early stage of crystallization is one of the long-standing problems in polymer science. Using solid state NMR, we investigated chain trajectory of isotactic polypropylene in the mesomorphic nano-domains formed via rapid and deep quenching. Comparison of experimental and simulated 13C-13C Double Quantum (DQ) buildup curves demonstrated that instead of random re-entry models and solidification models, individual chains in the mesomorphic form iPP adopt adjacent reentry sequences with an average folding number of = 3-4 (assuming an adjacent re-entry fraction of of 100%) during mesomorphic formation process via nucleation and growth in the early stage. This work was financially supported by the National Science Foundation (Grant DMR-1105829 and 1408855) and startup funds from the UA.

  9. Mechanism of dialkyl phthalates removal from aqueous solution using γ-cyclodextrin and starch based polyurethane polymer adsorbents.

    PubMed

    Okoli, Chukwunonso Peter; Adewuyi, Gregory Olufemi; Zhang, Qian; Diagboya, Paul N; Guo, Qingjun

    2014-12-19

    Phthalate esters have been known as potent endocrine disruptors and carcinogens; and their removal from water have been of considerable concern recently. In the present study, γ-cyclodextrin polyurethane polymer (GPP), γ-cyclodextrin/starch polyurethane copolymer (GSP), and starch polyurethane polymer (SPP) have been synthesized and characterized. Their adsorption efficiencies for the removal of dimethyl phthalate (DMP) and diethyl phthalate (DEP) from aqueous solutions were investigated. The characterization results showed the success of the synthesis. The isotherms were L-type, and both the Langmuir and Freundlich adsorption isotherm gave good fittings to the adsorption data. Adsorption mechanisms suggested that these adsorbents spontaneously adsorb phthalate molecules driven mainly by enthalpy change, and the adsorption process was attributed to multiple adsorbent-adsorbate interactions such as hydrogen bonding, π-π stacking, and pore filling. The results showed that starch and γ-cyclodextrin polyurethane polymer adsorbents have excellent potential as adsorbent materials for the removal of phthalates from the contaminated water. PMID:25263912

  10. Dynamics of a polymer chain confined in a membrane.

    PubMed

    Ramachandran, S; Komura, S; Seki, K; Gompper, G

    2011-05-01

    We present a Brownian dynamics theory with full hydrodynamics (Stokesian dynamics) for a Gaussian polymer chain embedded in a liquid membrane which is surrounded by bulk solvent and walls. The mobility tensors are derived in Fourier space for the two geometries, namely, a free membrane embedded in a bulk fluid, and a membrane sandwiched by the two walls. Within the preaveraging approximation, a new expression for the diffusion coefficient of the polymer is obtained for the free-membrane geometry. We also carry out a Rouse normal mode analysis to obtain the relaxation time and the dynamical structure factor. For large polymer size, both quantities show Zimm-like behavior in the free-membrane case, whereas they are Rouse-like for the sandwiched membrane geometry. We use the scaling argument to discuss the effect of excluded-volume interactions on the polymer relaxation time. PMID:21562968

  11. Particle-Directed Assembly of Semiflexible Polymer Chains

    NASA Astrophysics Data System (ADS)

    McGovern, Michael; Dorfman, Kevin; Morse, David

    We use molecular dynamics simulations to investigate several models of semiflexible polymers that exhibit an attractive interaction with spherical particles. The organization of semiflexible polymer chains through attractive interactions with spherical particles occurs in several important processes in nature, such as the winding of DNA around histones and counter-ion condensation of charged polymers. The process is also of technological interest in the packaging of DNA for delivery to cells. In this presentation, we will present data on both the phase behavior and the kinetics of self-assembly as a function of the stiffness of the polymers, the attractive potential between the monomers and the particles, and the relative size of the monomers and particles. Our simulations suggest a transition between globular and rod-like aggregates that changes from a gradual to a sudden transition depending on particle size, and that rod formation is a slow, nucleation dependent process.

  12. Anomalous chain diffusion in polymer nanocomposites for varying polymer-filler interaction strengths

    NASA Astrophysics Data System (ADS)

    Goswami, Monojoy; Sumpter, Bobby G.

    2010-04-01

    Anomalous diffusion of polymer chains in a polymer nanocomposite melt is investigated for different polymer-nanoparticle interaction strengths using stochastic molecular dynamics simulations. For spherical nanoparticles dispersed in a polymer matrix the results indicate that the chain motion exhibits three distinct regions of diffusion, the Rouse-like motion, an intermediate subdiffusive regime followed by a normal Fickian diffusion. The motion of the chain end monomers shows a scaling that can be attributed to the formation of strong “networklike” structures, which have been seen in a variety of polymer nanocomposite systems. Irrespective of the polymer-particle interaction strengths, these three regimes seem to be present with small deviations. Further investigation on dynamic structure factor shows that the deviations simply exist due to the presence of strong enthalpic interactions between the monomers with the nanoparticles, albeit preserving the anomaly in the chain diffusion. The time-temperature superposition principle is also tested for this system and shows a striking resemblance with systems near glass transition and biological systems with molecular crowding. The universality class of the problem can be enormously important in understanding materials with strong affinity to form either a glass, a gel or networklike structures.

  13. Self-Assembly of Emulsion Droplets into Polymer Chains

    NASA Astrophysics Data System (ADS)

    Bargteil, Dylan; McMullen, Angus; Brujic, Jasna

    We experimentally investigate `beads-on-a-string' models of polymers using the spontaneous assembly of emulsion droplets into linear chains. Droplets functionalized with surface-mobile DNA allow for programmable 'monomers' through which we can influence the three-dimensional structure of the assembled 'polymer'. Such model polymers can be used to study conformational changes of polypeptides and the principles governing protein folding. In our system, we find that droplets bind via complementary DNA strands that are recruited into adhesion patches. Recruitment is driven by the DNA hybridization energy, and is limited by the energy cost of surface deformation and the entropy loss of the mobile linkers, yielding adhesion patches of a characteristic size with a given number of linkers. By tuning the initial surface coverage of linkers, we control valency between the droplets to create linear or branched polymer chains. We additionally control the flexibility of the model polymers by varying the salt concentration and study their dynamics between extended and collapsed states. This system opens the possibility of programming stable three-dimensional structures, such as those found within folded proteins.

  14. Rouse mode analysis of chain relaxation in polymer nanocomposites

    DOE PAGESBeta

    Kalathi, Jagannathan T.; Kumar, Sanat K.; Rubinstein, Michael; Grest, Gary S.

    2015-04-20

    Large-scale molecular dynamics simulations are used to study the internal relaxations of chains in nanoparticle (NP)/polymer composites. We examine the Rouse modes of the chains, a quantity that is closest in spirit to the self-intermediate scattering function, typically determined in an (incoherent) inelastic neutron scattering experiment. Our simulations show that for weakly interacting mixtures of NPs and polymers, the effective monomeric relaxation rates are faster than in a neat melt when the NPs are smaller than the entanglement mesh size. In this case, the NPs serve to reduce both the monomeric friction and the entanglements in the polymer melt, asmore » in the case of a polymer–solvent system. However, for NPs larger than half the entanglement mesh size, the effective monomer relaxation is essentially unaffected for low NP concentrations. Even in this case, we observe a strong reduction in chain entanglements for larger NP loadings. Furthermore, the role of NPs is to always reduce the number of entanglements, with this effect only becoming pronounced for small NPs or for high concentrations of large NPs. Our studies of the relaxation of single chains resonate with recent neutron spin echo (NSE) experiments, which deduce a similar entanglement dilution effect.« less

  15. Rouse mode analysis of chain relaxation in polymer nanocomposites

    SciTech Connect

    Kalathi, Jagannathan T.; Kumar, Sanat K.; Rubinstein, Michael; Grest, Gary S.

    2015-04-20

    Large-scale molecular dynamics simulations are used to study the internal relaxations of chains in nanoparticle (NP)/polymer composites. We examine the Rouse modes of the chains, a quantity that is closest in spirit to the self-intermediate scattering function, typically determined in an (incoherent) inelastic neutron scattering experiment. Our simulations show that for weakly interacting mixtures of NPs and polymers, the effective monomeric relaxation rates are faster than in a neat melt when the NPs are smaller than the entanglement mesh size. In this case, the NPs serve to reduce both the monomeric friction and the entanglements in the polymer melt, as in the case of a polymer–solvent system. However, for NPs larger than half the entanglement mesh size, the effective monomer relaxation is essentially unaffected for low NP concentrations. Even in this case, we observe a strong reduction in chain entanglements for larger NP loadings. Furthermore, the role of NPs is to always reduce the number of entanglements, with this effect only becoming pronounced for small NPs or for high concentrations of large NPs. Our studies of the relaxation of single chains resonate with recent neutron spin echo (NSE) experiments, which deduce a similar entanglement dilution effect.

  16. Phase Transitions of Single Semistiff Polymer Chains

    NASA Astrophysics Data System (ADS)

    Bastolla, Ugo; Grassberger, Peter

    1997-12-01

    We study numerically a lattice model of semiflexible homopolymers with nearest neighbor (nn) attraction and energetic preference for straight joints between bonded monomers. For this we use a new Monte Carlo algorithm, the “prunedenriched Rosenbluth Method” (PERM). It is very efficient both for relatively open configurations at high temperatures and for compact and frozen-in low- T states. This allows us to study in detail the phase diagram as a function of nn attraction ɛ and stiffness x. It shows a θ-collapse line with a transition from open coils (small ɛ) to molten compact globules (large ɛ) and a freezing transition toward a state with orientational global order (large stiffness x). Qualitatively this is similar to a recently studied mean-field theory [S. Doniach, T. Garel, and H. Orland (1996), J. Chem. Phys. 105(4), 1601], but there are important differences in details. In contrast to the mean-field theory and to naive expectations, the θ-temperature increases with stiffness x. The freezing temperature increases even faster, and reaches the θ-line at a finite value of x. For even stiffer chains, the freezing transition takes place directly, without the formation of an intermediate globular state. Although being in conflict with mean-field theory, the latter had been conjectured already by Doniach et al. on the basis of heuristic arguments and of low-statistics Monte Carlo simulations. Finally, we discuss the relevance of the present model as a very crude model for protein folding.

  17. Conformational switching of modified guest chains in polymer brushes

    NASA Astrophysics Data System (ADS)

    Romeis, D.; Sommer, J.-U.

    2013-07-01

    Using a numerical quasi off-lattice self-consistent field method which describes heterogeneous chains of spherical monomers we study the case of a densely grafted polymer brush with a fraction of free chain ends being replaced by a modified end-group differing in size and solvent selectivity. We can confirm the observation from molecular dynamics simulations that upon changing the solvent conditions, a switching in location of end-groups which are bigger than monomers from a state "exposed" to the solvent (on the top of the brush) to a "hidden" state (inside the brush) takes place. Our numerical method allows a detailed study of the switching effect as a function of the relevant parameters, such as grafting density, chain length, size of end-groups and their volume fraction. We find that the switching effect is enhanced for long chains, low fractions of modified chains, and big end-groups. We consider the case of low fraction of modified chains in more detail using a test chain method. Here, we explore the optimal grafting density as a function of the size of the end-groups, where the switching is most sensitive. These values can be in the experimental range for end-groups which are at least 3-4 times bigger than the monomers. The end-groups can be realized by attaching nano-particles to the last monomer of a brush-chain.

  18. Polymer side-chains as arms for molecular recognition

    NASA Astrophysics Data System (ADS)

    South, Clinton Ray

    This thesis describes research based on synthetic protocols, methodologies, and applications of polymers containing side-chain molecular recognition elements. The motivation for the thesis lies in the belief among many in the field that a strict covalent paradigm for polymer chemistry is reaching its limit. The use of molecular recognition, in lieu of covalent chemistry, potentially presents a path through the current limits of polymer science. The work described in the following chapters of this thesis is, at least in part, a testament to this proposal. The first two chapters present a basic introduction and survey of the fundamental noncovalent interactions that are ubiquitous in the research of supramolecular polymers and molecular recognition. A hierarchy of noncovalent interactions, molecular recognition, and self-assembly is outlined and discussed. Chapter 2 lays the foundation for the remaining chapters of this thesis by presenting several examples of prior work related specifically to the use of molecular recognition on the side-chains of polymers. The next two chapters present research focused on advancing the functionalization of polymers through molecular recognition. The goal of this research is primarily to develop a general polymer backbone that both site-specifically and strongly associates noncovalently with small molecular substrates. These chapters demonstrate that both architecturally controlled block copolymers and random terpolymers can accept a full load of different substrates without interference among distinct molecular recognition elements along the polymer backbone. Chapters 5 and 6 present a unique application of polymers containing molecular recognition elements, templated synthesis. Chapter 5 first discusses lessons learned from small molecule based templated synthesis in which a template and a substrate are held together by metal coordination and a subsequent bond forming reaction occurs. Ultimately, the results of this chapter

  19. Large deviations of Rouse polymer chain: First passage problem

    NASA Astrophysics Data System (ADS)

    Cao, Jing; Zhu, Jian; Wang, Zuowei; Likhtman, Alexei E.

    2015-11-01

    The purpose of this paper is to investigate several analytical methods of solving first passage (FP) problem for the Rouse model, a simplest model of a polymer chain. We show that this problem has to be treated as a multi-dimensional Kramers' problem, which presents rich and unexpected behavior. We first perform direct and forward-flux sampling (FFS) simulations and measure the mean first-passage time τ(z) for the free end to reach a certain distance z away from the origin. The results show that the mean FP time is getting faster if the Rouse chain is represented by more beads. Two scaling regimes of τ(z) are observed, with transition between them varying as a function of chain length. We use these simulation results to test two theoretical approaches. One is a well known asymptotic theory valid in the limit of zero temperature. We show that this limit corresponds to fully extended chain when each chain segment is stretched, which is not particularly realistic. A new theory based on the well known Freidlin-Wentzell theory is proposed, where dynamics is projected onto the minimal action path. The new theory predicts both scaling regimes correctly, but fails to get the correct numerical prefactor in the first regime. Combining our theory with the FFS simulations leads us to a simple analytical expression valid for all extensions and chain lengths. One of the applications of polymer FP problem occurs in the context of branched polymer rheology. In this paper, we consider the arm-retraction mechanism in the tube model, which maps exactly on the model we have solved. The results are compared to the Milner-McLeish theory without constraint release, which is found to overestimate FP time by a factor of 10 or more.

  20. Large deviations of Rouse polymer chain: First passage problem.

    PubMed

    Cao, Jing; Zhu, Jian; Wang, Zuowei; Likhtman, Alexei E

    2015-11-28

    The purpose of this paper is to investigate several analytical methods of solving first passage (FP) problem for the Rouse model, a simplest model of a polymer chain. We show that this problem has to be treated as a multi-dimensional Kramers' problem, which presents rich and unexpected behavior. We first perform direct and forward-flux sampling (FFS) simulations and measure the mean first-passage time τ(z) for the free end to reach a certain distance z away from the origin. The results show that the mean FP time is getting faster if the Rouse chain is represented by more beads. Two scaling regimes of τ(z) are observed, with transition between them varying as a function of chain length. We use these simulation results to test two theoretical approaches. One is a well known asymptotic theory valid in the limit of zero temperature. We show that this limit corresponds to fully extended chain when each chain segment is stretched, which is not particularly realistic. A new theory based on the well known Freidlin-Wentzell theory is proposed, where dynamics is projected onto the minimal action path. The new theory predicts both scaling regimes correctly, but fails to get the correct numerical prefactor in the first regime. Combining our theory with the FFS simulations leads us to a simple analytical expression valid for all extensions and chain lengths. One of the applications of polymer FP problem occurs in the context of branched polymer rheology. In this paper, we consider the arm-retraction mechanism in the tube model, which maps exactly on the model we have solved. The results are compared to the Milner-McLeish theory without constraint release, which is found to overestimate FP time by a factor of 10 or more. PMID:26627948

  1. Adsorption-driven translocation of polymer chain into nanopores

    NASA Astrophysics Data System (ADS)

    Yang, Shuang; Neimark, Alexander V.

    2012-06-01

    The polymer translocation into nanopores is generally facilitated by external driving forces, such as electric or hydrodynamic fields, to compensate for entropic restrictions imposed by the confinement. We investigate the dynamics of translocation driven by polymer adsorption to the confining walls that is relevant to chromatographic separation of macromolecules. By using the self-consistent field theory, we study the passage of a chain trough a small opening from cis to trans compartments of spherical shape with adsorption potential applied in the trans compartment. The chain transfer is modeled as the Fokker-Plank diffusion along the free energy landscape of the translocation pass represented as a sum of the free energies of cis and trans parts of the chain tethered to the pore opening. We investigate how the chain length, the size of trans compartment, the magnitude of adsorption potential, and the extent of excluded volume interactions affect the translocation time and its distribution. Interplay of these factors brings about a variety of different translocation regimes. We show that excluded volume interactions within a certain range of adsorption potentials can cause a local minimum on the free energy landscape, which is absent for ideal chains. The adsorption potential always leads to the decrease of the free energy barrier, increasing the probability of successful translocation. However, the translocation time depends non-monotonically of the magnitude of adsorption potential. Our calculations predict the existence of the critical magnitude of adsorption potential, which separates favorable and unfavorable regimes of translocation.

  2. Adsorption-driven translocation of polymer chain into nanopores.

    PubMed

    Yang, Shuang; Neimark, Alexander V

    2012-06-01

    The polymer translocation into nanopores is generally facilitated by external driving forces, such as electric or hydrodynamic fields, to compensate for entropic restrictions imposed by the confinement. We investigate the dynamics of translocation driven by polymer adsorption to the confining walls that is relevant to chromatographic separation of macromolecules. By using the self-consistent field theory, we study the passage of a chain trough a small opening from cis to trans compartments of spherical shape with adsorption potential applied in the trans compartment. The chain transfer is modeled as the Fokker-Plank diffusion along the free energy landscape of the translocation pass represented as a sum of the free energies of cis and trans parts of the chain tethered to the pore opening. We investigate how the chain length, the size of trans compartment, the magnitude of adsorption potential, and the extent of excluded volume interactions affect the translocation time and its distribution. Interplay of these factors brings about a variety of different translocation regimes. We show that excluded volume interactions within a certain range of adsorption potentials can cause a local minimum on the free energy landscape, which is absent for ideal chains. The adsorption potential always leads to the decrease of the free energy barrier, increasing the probability of successful translocation. However, the translocation time depends non-monotonically of the magnitude of adsorption potential. Our calculations predict the existence of the critical magnitude of adsorption potential, which separates favorable and unfavorable regimes of translocation. PMID:22697566

  3. Molecular Insights into the pH-Dependent Adsorption and Removal of Ionizable Antibiotic Oxytetracycline by Adsorbent Cyclodextrin Polymers

    PubMed Central

    Zhang, Yu; Cai, Xiyun; Xiong, Weina; Jiang, Hao; Zhao, Haitong; Yang, Xianhai; Li, Chao; Fu, Zhiqiang; Chen, Jingwen

    2014-01-01

    Effects of pH on adsorption and removal efficiency of ionizable organic compounds (IOCs) by environmental adsorbents are an area of debate, because of its dual mediation towards adsorbents and adsorbate. Here, we probe the pH-dependent adsorption of ionizable antibiotic oxytetracycline (comprising OTCH2+, OTCH±, OTC−, and OTC2−) onto cyclodextrin polymers (CDPs) with the nature of molecular recognition and pH inertness. OTCH± commonly has high adsorption affinity, OTC− exhibits moderate affinity, and the other two species have negligible affinity. These species are evidenced to selectively interact with structural units (e.g., CD cavity, pore channel, and network) of the polymers and thus immobilized onto the adsorbents to different extents. The differences in adsorption affinity and mechanisms of the species account for the pH-dependent adsorption of OTC. The mathematical equations are derived from the multiple linear regression (MLR) analysis of quantitatively relating adsorption affinity of OTC at varying pH to adsorbent properties. A combination of the MLR analysis for OTC and molecular recognition of adsorption of the species illustrates the nature of the pH-dependent adsorption of OTC. Based on this finding, γ-HP-CDP is chosen to adsorb and remove OTC at pH 5.0 and 7.0, showing high removal efficiency and strong resistance to the interference of coexisting components. PMID:24465975

  4. Communication: Polarizable polymer chain under external electric field in a dilute polymer solution

    NASA Astrophysics Data System (ADS)

    Budkov, Yu. A.; Kolesnikov, A. L.; Kiselev, M. G.

    2015-11-01

    We study the conformational behavior of polarizable polymer chain under an external homogeneous electric field within the Flory type self-consistent field theory. We consider the influence of electric field on the polymer coil as well as on the polymer globule. We show that when the polymer chain conformation is a coil, application of external electric field leads to its additional swelling. However, when the polymer conformation is a globule, a sufficiently strong field can induce a globule-coil transition. We show that such "field-induced" globule-coil transition at the sufficiently small monomer polarizabilities goes quite smoothly. On the contrary, when the monomer polarizability exceeds a certain threshold value, the globule-coil transition occurs as a dramatic expansion in the regime of first-order phase transition. The developed theoretical model can be applied to predicting polymer globule density change under external electric field in order to provide more efficient processes of polymer functionalization, such as sorption, dyeing, and chemical modification

  5. Communication: Polarizable polymer chain under external electric field in a dilute polymer solution

    SciTech Connect

    Budkov, Yu. A.; Kolesnikov, A. L.; Kiselev, M. G.

    2015-11-28

    We study the conformational behavior of polarizable polymer chain under an external homogeneous electric field within the Flory type self-consistent field theory. We consider the influence of electric field on the polymer coil as well as on the polymer globule. We show that when the polymer chain conformation is a coil, application of external electric field leads to its additional swelling. However, when the polymer conformation is a globule, a sufficiently strong field can induce a globule-coil transition. We show that such “field-induced” globule-coil transition at the sufficiently small monomer polarizabilities goes quite smoothly. On the contrary, when the monomer polarizability exceeds a certain threshold value, the globule-coil transition occurs as a dramatic expansion in the regime of first-order phase transition. The developed theoretical model can be applied to predicting polymer globule density change under external electric field in order to provide more efficient processes of polymer functionalization, such as sorption, dyeing, and chemical modification.

  6. Communication: Polarizable polymer chain under external electric field in a dilute polymer solution.

    PubMed

    Budkov, Yu A; Kolesnikov, A L; Kiselev, M G

    2015-11-28

    We study the conformational behavior of polarizable polymer chain under an external homogeneous electric field within the Flory type self-consistent field theory. We consider the influence of electric field on the polymer coil as well as on the polymer globule. We show that when the polymer chain conformation is a coil, application of external electric field leads to its additional swelling. However, when the polymer conformation is a globule, a sufficiently strong field can induce a globule-coil transition. We show that such "field-induced" globule-coil transition at the sufficiently small monomer polarizabilities goes quite smoothly. On the contrary, when the monomer polarizability exceeds a certain threshold value, the globule-coil transition occurs as a dramatic expansion in the regime of first-order phase transition. The developed theoretical model can be applied to predicting polymer globule density change under external electric field in order to provide more efficient processes of polymer functionalization, such as sorption, dyeing, and chemical modification. PMID:26627943

  7. Effects of Alkylthio and Alkoxy Side Chains in Polymer Donor Materials for Organic Solar Cells.

    PubMed

    Cui, Chaohua; Wong, Wai-Yeung

    2016-02-01

    Side chains play a considerable role not only in improving the solubility of polymers for solution-processed device fabrication, but also in affecting the molecular packing, electron affinity and thus the device performance. In particular, electron-donating side chains show unique properties when employed to tune the electronic character of conjugated polymers in many cases. Therefore, rational electron-donating side chain engineering can improve the photovoltaic properties of the resulting polymer donors to some extent. Here, a survey of some representative examples which use electron-donating alkylthio and alkoxy side chains in conjugated organic polymers for polymer solar cell applications will be presented. It is envisioned that an analysis of the effect of such electron-donating side chains in polymer donors would contribute to a better understanding of this kind of side chain behavior in solution-processed conjugated organic polymers for polymer solar cells. PMID:26754772

  8. Analytical theory of finite-size effects in mechanical desorption of a polymer chain.

    PubMed

    Skvortsov, A M; Klushin, L I; Fleer, G J; Leermakers, F A M

    2010-02-14

    We discuss a unique system that allows exact analytical investigation of first- and second-order transitions with finite-size effects: mechanical desorption of an ideal lattice polymer chain grafted with one end to a solid substrate with a pulling force applied to the other end. We exploit the analogy with a continuum model and use accurate mapping between the parameters in continuum and lattice descriptions, which leads to a fully analytical partition function as a function of chain length, temperature (or adsorption strength), and pulling force. The adsorption-desorption phase diagram, which gives the critical force as a function of temperature, is nonmonotonic and gives rise to re-entrance. We analyze the chain length dependence of several chain properties (bound fraction, chain extension, and heat capacity) for different cross sections of the phase diagram. Close to the transition a single parameter (the product of the chain length N and the deviation from the transition point) describes all thermodynamic properties. We discuss finite-size effects at the second-order transition (adsorption without force) and at the first-order transition (mechanical desorption). The first-order transition has some unusual features: The heat capacity in the transition region increases anomalously with temperature as a power law, metastable states are completely absent, and instead of a bimodal distribution there is a flat region that becomes more pronounced with increasing chain length. The reason for this anomaly is the absence of an excess surface energy for the boundary between adsorbed and stretched coexisting phases (this boundary is one segment only): The two states strongly fluctuate in the transition point. The relation between mechanical desorption and mechanical unzipping of DNA is discussed. PMID:20151736

  9. Folding of polymer chains with short-range binormal interactions

    NASA Astrophysics Data System (ADS)

    Craig, A.; Terentjev, E. M.

    2006-05-01

    We study the structure of chains which have anisotropic short-range contact interactions that depend on the alignment of the binormal vectors of chain segments. This represents a crude model of hydrogen bonding or 'stacking' interactions out of the plane of curvature. The polymers are treated as ribbon-like semi-flexible chains, where the plane of the ribbon is determined by the local binormal. We show that with dipole-dipole interactions between the binormals of contacting chain segments, mean-field theory predicts a first-order transition to a binormally aligned state. We describe the onset of this transition as a function of the temperature-dependent parameters that govern the chain stiffness and the strength of the binormal interaction, as well as the binormal alignment's coupling to chain collapse. We also examine a metastable state governing the folding kinetics. Finally, we discuss the possible mesoscopic structure of the aligned phase, and application of our model to secondary structure motifs like β-sheets and α-helices, as well as composite structures like β-(amyloid) fibrils.

  10. Localization of chain dynamics in entangled polymer melts

    NASA Astrophysics Data System (ADS)

    Guenza, M. G.

    2014-05-01

    The dynamics of polymer melts in both the unentangled and entangled regimes is described by a Langevin equation for the correlated motion of a group of chains, interacting through both intra- and inter-molecular potentials. Entanglements are represented by an intermolecular monomer-monomer confining potential that has no effect on short chains, while interpolymer interactions, responsible for correlated motion and subdiffusive center-of-mass dynamics, are represented by an intermolecular center-of-mass potential derived from the Ornstein-Zernike equation. This potential ensures that the liquid of phantom chains reproduces the compressibility and free energy of the real samples. For polyethylene melts the calculated dynamic structure factor is found to be in quantitative agreement with neutron spin echo experiments of polyethylene melts with chain lengths that span both the unentangled and the entangled regimes. The theory shows a progressive localization of the cooperative chain dynamics at the crossover from the unentangled to the entangled regime, in the spirit of the reptation model.

  11. Finite cohesion due to chain entanglement in polymer melts.

    PubMed

    Cheng, Shiwang; Lu, Yuyuan; Liu, Gengxin; Wang, Shi-Qing

    2016-04-14

    Three different types of experiments, quiescent stress relaxation, delayed rate-switching during stress relaxation, and elastic recovery after step strain, are carried out in this work to elucidate the existence of a finite cohesion barrier against free chain retraction in entangled polymers. Our experiments show that there is little hastened stress relaxation from step-wise shear up to γ = 0.7 and step-wise extension up to the stretching ratio λ = 1.5 at any time before or after the Rouse time. In contrast, a noticeable stress drop stemming from the built-in barrier-free chain retraction is predicted using the GLaMM model. In other words, the experiment reveals a threshold magnitude of step-wise deformation below which the stress relaxation follows identical dynamics whereas the GLaMM or Doi-Edwards model indicates a monotonic acceleration of the stress relaxation dynamics as a function of the magnitude of the step-wise deformation. Furthermore, a sudden application of startup extension during different stages of stress relaxation after a step-wise extension, i.e. the delayed rate-switching experiment, shows that the geometric condensation of entanglement strands in the cross-sectional area survives beyond the reptation time τd that is over 100 times the Rouse time τR. Our results point to the existence of a cohesion barrier that can prevent free chain retraction upon moderate deformation in well-entangled polymer melts. PMID:26931322

  12. Pyrocarbons prepared by carbonisation of polymers adsorbed or synthesised on a surface of silica and mixed oxides

    NASA Astrophysics Data System (ADS)

    Gun'ko, V. M.; Skubiszewska-Zi ęba, J.; Leboda, R.; Voronin, E. F.; Zarko, V. I.; Levitskaya, S. I.; Brei, V. V.; Guzenko, N. V.; Kazakova, O. A.; Seledets, O.; Janusz, W.; Chibowski, S.

    2004-04-01

    Initial oxides fumed silica, alumina/silica and titania/silica and silica gel and hybrid adsorbents with pyrocarbon formed on these oxide substrates by carbonisation of immobilised (adsorbed or synthesised) polymers such as starch, methyl cellulose, polyvinylpyrrolidone, polystyrene, and polybutylvinyl ether were studied by adsorption, AFM, TEM, and FTIR methods. Polymer/oxide materials were investigated by nitrogen and Pb(II) adsorption, FTIR, and potentiometric titration methods. Analysis of nitrogen adsorption-desorption isotherms by different methods, FTIR spectra, AFM and TEM images of the initial and hybrid adsorbents reveals that the morphology of the substrates significantly changes on carbonisation of oxygen-containing polymers because of hydrothermal treatment of them by water eliminated as a product of pyrolysis. Contribution of own microporosity of pyrocarbon deposits formed on carbonisation of immobilised polymers is greater (dependent on reaction conditions) than that on pyrolysis of low-molecular compounds at the same oxide substrates. Pyrocarbon particles formed on silica gel are larger than those formed on fumed oxides and larger than those formed on silica gel on pyrolysis of low-molecular compounds.

  13. Effects of polymer side chains on the self-assembling of conjugated polymer in thin film

    NASA Astrophysics Data System (ADS)

    Jiang, Yunfei; Wang, Yiqing; Bunz, Uvw H. F.; Perahia, Dvora

    2006-03-01

    Conjugated polymers are inherently semi-conducting and optically active materials, with immense potential applications in organic electro-optical devices. The chemical structure of the polymer including the rigidity of the backbone and the nature of substituents affect their association as well as their electro-optical response. The following work reports the effects of different side chains on the structure and fluorescence of highly conjugated polymer, poly(para phenyleneethynylene) (PPE). When substituted by long polylactide side chains they self-assemble into wires with fingerprint-like arrangement, casting from chloroform solutions on oxidized silicon wafer. With increasing content of poor solvent, the dimension of the structures increased and then crystallized area appeared, as showed in AFM studies. The introducing of the long flexible polymer side chains has significantly reduced the stacking between rigid backbones. This in tern results in a frequency shift in their fluoresces response, indication changes in the electronic levels. Direct measurements of the electronic levels using ATM are currently in progress.

  14. Polymer Chain Dynamics in a Random Environment: Heterogeneous Mobilities

    SciTech Connect

    Niedzwiedz, K.; Wischnewski, A.; Monkenbusch, M.; Richter, D.; Strauch, M.; Straube, E.; Genix, A.-C.; Arbe, A.

    2007-04-20

    We present a neutron scattering investigation on a miscible blend of two polymers with greatly different glass-transition temperatures T{sub g}. Under such conditions, the nearly frozen high-T{sub g} component imposes a random environment on the mobile chain. The results demand the consideration of a distribution of heterogeneous mobilities in the material and demonstrate that the larger scale dynamics of the fast component is not determined by the average local environment alone. This distribution of mobilities can be mapped quantitatively on the spectrum of local relaxation rates measured at high momentum transfers.

  15. Star/linear polymer topology transformation facilitated by mechanical linking of polymer chains.

    PubMed

    Aoki, Daisuke; Uchida, Satoshi; Takata, Toshikazu

    2015-06-01

    Topology transformation of a star polymer to a linear polymer is demonstrated for the first time. A three-armed star polymer possessing a mechanical linking of two polymer chains was synthesized by the living ring-opening polymerization of δ-valerolactone initiated by a pseudo[2]rotaxane having three hydroxy groups as the initiator sites on the wheel component and at both axle termini. The polymerization was followed by the propagation end-capping reaction with a bulky isocyanate not only to prevent the wheel component deslippage but also to introduce the urethane moiety at the axle terminal. The resulting rotaxane-linked star polymer with a fixed rotaxane linkage based on the ammonium/crown ether interaction was subjected to N-acetylation of the ammonium moiety, which liberated the components from the interaction to move the wheel component to the urethane terminal as the interaction site, eventually affording the linear polymer. The physical property change caused by the present topology transformation was confirmed by the hydrodynamic volume and viscosity. PMID:25892579

  16. Thrombocyte adhesion and release of extracellular microvesicles correlate with surface morphology of adsorbent polymers for lipid apheresis.

    PubMed

    Weiss, René; Spittler, Andreas; Schmitz, Gerd; Fischer, Michael B; Weber, Viktoria

    2014-07-14

    Whole blood lipid apheresis is clinically applied to reduce low density lipoprotein cholesterol in patients with homozygous familial hypercholesterolemia. Here, we studied the correlation between physicochemical parameters, in particular, surface roughness and blood compatibility, of two polyacrylate-based and a dextran sulfate-based polymer for lipid apheresis. The adsorbent surface roughness was assessed by atomic force microscopy. Freshly isolated human thrombocytes were circulated over adsorbent columns downscaled equivalent to clinical use to study thrombocyte adhesion and microvesicle generation. Quantification of thrombocytes and microvesicles in the flow-through of the columns revealed that both thrombocyte adhesion and microvesicle generation increased with increasing adsorbent surface roughness. Activation of thrombocytes with thrombin receptor-activating peptide-6 favored their adhesion to the adsorbents, as demonstrated by preferential depletion of CD62(+) and PAC-1(+) thrombocytes. Taken together, enhanced polymer surface roughness fostered cell adhesion and microvesicle release, underscoring the role of extracellular microvesicles as markers of cellular activation and of blood compatibility. PMID:24844344

  17. Novel negatively charged hybrids. 3. Removal of Pb2+ from aqueous solution using zwitterionic hybrid polymers as adsorbent.

    PubMed

    Liu, Junsheng; Ma, Yue; Zhang, Yaping; Shao, Guoquan

    2010-01-15

    Using zwitterionic hybrid polymers as adsorbent, the adsorption kinetics and isotherm, thermodynamic parameters of Delta G, Delta H and DeltaS for the removal of Pb(2+) from aqueous solution were investigated. It is indicated that the adsorption of Pb(2+) ions on these zwitterionic hybrid polymers followed the Lagergren second-order kinetic model and Freundlich isotherm model, demonstrating that the adsorption process might be Langmuir monolayer adsorption. The negative values of Delta G and the positive values of Delta H evidence that Pb(2+) adsorption on these zwitterionic hybrid polymers is spontaneous and endothermic process in nature. Moreover, the zwitterionic hybrid polymers produced reveal relatively higher desorption efficiency in 2 mol dm(-3) aqueous HNO(3) solution, indicating that they can be recycled in industrial processes. These findings suggest that these zwitterionic hybrid polymers are the promising adsorbents for Pb(2+) removal and can be potentially applied in the separation and recovery of Pb(2+) ions from the waste chemicals and contaminated water of lead-acid rechargeable battery. PMID:19744785

  18. Poly(ethylene oxide) Mushrooms Adsorbed at Silica-Ionic Liquid Interfaces Reduce Friction.

    PubMed

    Sweeney, James; Webber, Grant B; Atkin, Rob

    2016-03-01

    The adsorbed layer conformation and lubricity of 35, 100, and 300 kDa PEO adsorbed to ionic liquid (IL)-silica interfaces from 0.01 wt % solutions have been investigated using colloid probe atomic force microscopy. The ILs used were propylammonium nitrate (PAN) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), which are protic and aprotic ILs, respectively. Normal force curves reveal steric interactions consistent with adsorbed polymer layers which are best fit using the mushroom model. Friction measurements show that the adsorbed polymer layer markedly reduces friction compared to surfaces sliding in the pure ILs and that lubricity increases with polymer length. When polymer is adsorbed to the sliding surfaces, friction is controlled by the creation and disruption of intermolecular interactions between entangled chains and the dragging of polymer chains through the interpenetration region. These experiments show that added polymer can reduce friction while maintaining the useful properties of ILs as lubricants. PMID:26844589

  19. Elution of uranium and transition metals from amidoxime-based polymer adsorbents for sequestering uranium from seawater

    DOE PAGESBeta

    Pan, Horng-Bin; Kuo, Li-Jung; Miyamoto, Naomi; Wood, Jordana; Strivens, Jonathan E.; Gill, Gary; Janke, Christopher James; Wai, Chien

    2015-11-30

    High-surface-area amidoxime and carboxylic acid grafted polymer adsorbents developed at Oak Ridge National Laboratory were tested for sequestering uranium in a flowing seawater flume system at the PNNL-Marine Sciences Laboratory. FTIR spectra indicate that a KOH conditioning process is necessary to remove the proton from the carboxylic acid and make the sorbent effective for sequestering uranium from seawater. The alkaline conditioning process also converts the amidoxime groups to carboxylate groups in the adsorbent. Both Na2CO3 H2O2 and hydrochloric acid elution methods can remove ~95% of the uranium sequestered by the adsorbent after 42 days of exposure in real seawater. Themore » Na2CO3 H2O2 elution method is more selective for uranium than conventional acid elution. Iron and vanadium are the two major transition metals competing with uranium for adsorption to the amidoxime-based adsorbents in real seawater. Tiron (4,5-Dihydroxy-1,3-benzenedisulfonic acid disodium salt, 1 M) can remove iron from the adsorbent very effectively at pH around 7. The coordination between vanadium (V) and amidoxime is also discussed based on our 51V NMR data.« less

  20. Elution of uranium and transition metals from amidoxime-based polymer adsorbents for sequestering uranium from seawater

    SciTech Connect

    Pan, Horng-Bin; Kuo, Li-Jung; Miyamoto, Naomi; Wood, Jordana; Strivens, Jonathan E.; Gill, Gary; Janke, Christopher James; Wai, Chien

    2015-11-30

    High-surface-area amidoxime and carboxylic acid grafted polymer adsorbents developed at Oak Ridge National Laboratory were tested for sequestering uranium in a flowing seawater flume system at the PNNL-Marine Sciences Laboratory. FTIR spectra indicate that a KOH conditioning process is necessary to remove the proton from the carboxylic acid and make the sorbent effective for sequestering uranium from seawater. The alkaline conditioning process also converts the amidoxime groups to carboxylate groups in the adsorbent. Both Na2CO3 H2O2 and hydrochloric acid elution methods can remove ~95% of the uranium sequestered by the adsorbent after 42 days of exposure in real seawater. The Na2CO3 H2O2 elution method is more selective for uranium than conventional acid elution. Iron and vanadium are the two major transition metals competing with uranium for adsorption to the amidoxime-based adsorbents in real seawater. Tiron (4,5-Dihydroxy-1,3-benzenedisulfonic acid disodium salt, 1 M) can remove iron from the adsorbent very effectively at pH around 7. The coordination between vanadium (V) and amidoxime is also discussed based on our 51V NMR data.

  1. New 4,5-dichlorophthalhydrazidate-bridged chained coordination polymers

    NASA Astrophysics Data System (ADS)

    Jin, Juan; Wu, Di; Jia, Ming-Jun; Peng, Yu; Yu, Jie-Hui; Wang, Yu-Chang; Xu, Ji-Qing

    2011-03-01

    The hydrothermal self-assemblies of Pb 2+/Cd 2+ salt, 4,5-dichlorophthalic acid (dcpha), N 2H 4·H 2O together with 1,10-phenanthroline·H 2O (phen) or 2,2'-bipyridine (bpy) generated two new monoacylhydrazidate-bridged 1-D chained coordination polymers [Pb 2(DCPTH) 4(phen) 2] 1 and [Cd 3(DCPTH) 2(dcph) 2(bpy) 2] 2 (DCPTH=4,5-dichlorophthalhydrazidate, dcph=4,5-dichlorophthalate). The monoacylhydrazidate ligand DCPTH originated from the hydrothermal in situ acylation reaction between dcpha and N 2H 4·H 2O. In compound 1, two types of coordination modes for DCPTH are found, which link alternately the Pb(II) centers into a 1-D chain structure of compound 1 with ancillary phen molecules. In compound 2, DCPTH and dcph as the mixed bridges extend the Cd(II) centers into a 1-D chain structure of compound 2 with auxiliary bpy molecules. DCPTH in compound 2 shows a different coordination mode from those observed in compound 1.

  2. Diketopyrrolopyrrole-based Conjugated Polymers Bearing Branched Oligo(Ethylene Glycol) Side Chains for Photovoltaic Devices.

    PubMed

    Chen, Xingxing; Zhang, Zijian; Ding, Zicheng; Liu, Jun; Wang, Lixiang

    2016-08-22

    Conjugated polymers are essential for solution-processable organic opto-electronic devices. In contrast to the great efforts on developing new conjugated polymer backbones, research on developing side chains is rare. Herein, we report branched oligo(ethylene glycol) (OEG) as side chains of conjugated polymers. Compared with typical alkyl side chains, branched OEG side chains endowed the resulting conjugated polymers with a smaller π-π stacking distance, higher hole mobility, smaller optical band gap, higher dielectric constant, and larger surface energy. Moreover, the conjugated polymers with branched OEG side chains exhibited outstanding photovoltaic performance in polymer solar cells. A power conversion efficiency of 5.37 % with near-infrared photoresponse was demonstrated and the device performance could be insensitive to the active layer thickness. PMID:27258171

  3. Theoretical study of the three-phase contact line and its tension in adsorbed colloid-polymer mixtures.

    PubMed

    Vandecan, Yves; Indekeu, Joseph O

    2008-03-14

    We perform a theoretical study of the three-phase contact line and the line tension in an adsorbed colloid-polymer mixture near a first-order wetting transition, employing an interface displacement model. We use a simple free-energy functional to describe a colloid-polymer mixture near a hard wall. The bulk phase behavior and the substrate-adsorbate interaction are modeled by the free-volume theory for ideal polymers. The large size of the colloidal particles and the suppression of the van der Waals interaction by optical matching of colloid and solvent justify the planar hard wall model for the substrate. Following the Fisher-Jin scheme, we derive from the free-energy functional an interface potential V(l) for these mixtures. For a particle diameter of 10-100 nm, the calculations indicate a line tension tau approximately 10(-12)-10(-13) N at room temperature. In view of the ultralow interfacial tension in colloid-polymer mixtures, gamma approximately 10(-7) Nm, this leads to a rather large characteristic length scale taugamma in the micrometer range for the three-phase contact zone width. In contrast with molecular fluids, this zone could be studied directly with optical techniques such as confocal scanning laser microscopy. PMID:18345923

  4. Fluorescence Correlation Spectroscopy to Study Diffusion of Polymer Chains within Layered Hydrogen-Bonded Polymer Films

    NASA Astrophysics Data System (ADS)

    Pristinski, Denis; Kharlampieva, Evguenia; Sukhishvili, Svetlana

    2002-03-01

    Fluorescence Correlation Spectroscopy (FCS) has been used to probe molecular motions within polymer multilayers formed by hydrogen-bonding sequential self-assembly. Polyethylene glycol (PEG) molecules were end-labeled with the fluorescent tags, and self-assembled with polymethacrylic acid (PMAA) using layer-by-layer deposition. We have found that molecules included in the top adsorbed layer have significant mobility at the millisecond time scale, probably due to translational diffusion. However, their dynamics deviate from classical Brownian motion with a single diffusion time. Possible reasons for the deviation are discussed. We found that motions were significantly slowed with increasing depth within the PEG/PMAA multilayer. This phenomena occured in a narrow pH range around 4.0 in which intermolecular interactions were relatively weak.

  5. Force extension response of single self-associating polymer chains

    NASA Astrophysics Data System (ADS)

    Sing, Charles; Alexander-Katz, Alfredo

    2012-02-01

    The structure and dynamics of polymeric molecules plays a crucial role in a number of synthetic and biological processes. Great progress has been made in using force spectroscopy methods, such as optical tweezers and atomic force microscopy, to probe these properties of single molecules in novel ways. While there has been significant advances at using analytical theory to model the behavior of, for example, single domain unfolding or multi-domain unfolding of identical domains, we consider for the first time the force-extension behavior of self-associating homopolymers. We use a Brownian dynamics simulation with a Bell-like association model that represents, in a coarse-grained fashion, biological polymers such as von Willebrand Factor that use domain-domain interactions to modulate a larger quaternary structure. We also present a theoretical description of pulling that utilizes a master equation description of the relevant coordinate of the polymer network's ``shortest chain.'' We can accurately reproduce the force-extension features, notably the appearance of a dissipative plateau upon the increase of the association time scale, and provide a clear conceptual description of the appearance of this feature. Qualitative comparison to von Willebrand pulling in experiment is shown.

  6. Enzyme stabilization by linear chain polymers in ultrafiltration membrane reactors

    SciTech Connect

    Greco, G.; Gianfreda, L.

    1981-10-01

    The experimental results discussed in this article concern pi-nitrophenylphosphate hydrolysis by acid phosphatase in an ultrafiltration membrane reactor. The basic conclusions drawn are : 1) Linking the enzyme to a soluble support does not give rise to an increase in its stability while the chemical manipulations involved result in marked reductions in enzymic activity. 2) Enzyme entrapment within a proteic gel produces a considerable increase in its thermal stability as compared to the diluted native enzyme; this presumably stems from drastic reductions in enzyme mobility. 3) Correspondingly, considerable reductions occur in enzyme activity that depend on substrate mass transfer resistances within the gel layer. 4) Small amounts of linear chain water-soluble synthetic polymers (polyacrylamides) give rise to high macromolecular concentration levels in the reactor region where the enzyme is dynamically immobilized and produce the same enzyme stabilization as gel entrapment. 5) Only minor substrate mass transfer limitations take place in this region and hence enzyme activity is virtually unaffected. 6) Both effects (stabilization and slight activity reduction) seem not to depend strongly on the characteristics of the soluble polymer (molecular weight and ionic character). (Refs. 16).

  7. Elution of Uranium and Transition Metals from Amidoxime-Based Polymer Adsorbents for Sequestering Uranium from Seawater

    SciTech Connect

    Pan, Horng-Bin; Kuo, Li-Jung; Wai, Chien M.; Miyamoto, Naomi; Joshi, Ruma; Wood, Jordana R.; Strivens, Jonathan E.; Janke, Christopher J.; Oyola, Yatsandra; Das, Sadananda; Mayes, Richard T.; Gill, Gary A.

    2015-11-30

    High-surface-area amidoxime and carboxylic acid grafted polymer adsorbents developed at Oak Ridge National Laboratory were tested for sequestering uranium in a flowing seawater flume system at the PNNL-Marine Sciences Laboratory. FTIR spectra indicate that a KOH conditioning process is necessary to remove the proton from the carboxylic acid and make the sorbent effective for sequestering uranium from seawater. The alkaline conditioning process also converts the amidoxime groups to carboxylate groups in the adsorbent. Both Na2CO3-H2O2 and hydrochloric acid elution methods can remove ~95% of the uranium sequestered by the adsorbent after 42 days of exposure in real seawater. The Na2CO3-H2O2 elution method is more selective for uranium than conventional acid elution. Iron and vanadium are the two major transition metals competing with uranium for adsorption to the amidoxime-based adsorbents in real seawater.

  8. Adsorption of enzymes to stimuli-responsive polymer brushes: Influence of brush conformation on adsorbed amount and biocatalytic activity.

    PubMed

    Koenig, Meike; Bittrich, Eva; König, Ulla; Rajeev, Bhadra Lakshmi; Müller, Martin; Eichhorn, Klaus-Jochen; Thomas, Sabu; Stamm, Manfred; Uhlmann, Petra

    2016-10-01

    Polyelectrolyte brushes can be utilized to immobilize enzymes on macroscopic surfaces. This report investigates the influence of the pH value of the surrounding medium on the amount and the activity of enzymes adsorbed to poly(2-vinylpyridine) and poly(acrylic acid) brushes, as well as the creation of thermoresponsive biocatalytically active coatings via the adsorption of enzymes onto a mixed brush consisting of a polyelectrolyte and temperature-sensitive poly(N-isopropylacryl amide). Spectroscopic ellipsometry and attenuated total reflection-Fourier transform infrared spectroscopy are used to monitor the adsorption process. Additionally, infrared spectra are evaluated in terms of the secondary structure of the enzymes. Glucose oxidase is used as a model enzyme, where the enzymatic activity is measured after different adsorption conditions. Poly(acrylic acid) brushes generally adsorb larger amounts of enzyme, while less glucose oxidase is found on poly(2-vinylpyridine), which however exhibits higher specific activity. This difference in activity could be attributed to a difference in secondary structure of the adsorbed enzyme. For glucose oxidase adsorbed to mixed brushes, switching of enzymatic activity between an active state at 20°C and a less active state at 40°C as compared to the free enzyme in solution is observed. However, this switching is strongly depending on pH in mixed brushes of poly(acrylic acid) and poly(N-isopropylacryl amide) due to interactions between the polymers. PMID:27447452

  9. Stretching of a polymer chain anchored to a surface: the massive field theory approach

    NASA Astrophysics Data System (ADS)

    Usatenko, Zoryana

    2014-09-01

    Taking into account the well-known correspondence between the field theoretical φ4 O(n)-vector model in the limit n → 0 and the behaviour of long-flexible polymer chains, the investigation of stretching of an ideal and a real polymer chain with excluded volume interactions in a good solvent anchored to repulsive and inert surfaces is performed. The calculations of the average stretching force which arises when the free end of a polymer chain moves away from a repulsive or inert surface are performed up to one-loop order of the massive field theory approach in fixed space dimensions d = 3. The analysis of the obtained results indicates that the average stretching force for a real polymer chain anchored to a repulsive surface demonstrates different behaviour for the cases \\tilde{z}\\ll1 and \\tilde{z}\\gg1 , where \\tilde{z}=z^\\prime/Rz . Besides, the results obtained in the framework of the massive field theory approach are in good agreement with previous theoretical results for an ideal polymer chain and results of a density functional theory approach for the region of small applied forces when deformation of a polymer chain in the direction of the applied force is not bigger than the linear extension of a polymer chain in this direction. The better agreement between these two methods is observed in the case where the number of monomers increases and the polymer chain becomes longer.

  10. Optical properties of extended-chain polymers under stress

    NASA Astrophysics Data System (ADS)

    Ramirez, Rafael G.; Eby, R. K.

    1995-09-01

    Birefringence and x-ray diffraction experiments have been carried out on Kevlar 49(superscript R) fibers under tensile stress to monitor structure changes under the stress field. The origin of the observed birefringence is discussed in some detail. Results from theoretical calculations using semi-empirical molecular orbital techniques are presented and contrasted to the experimental observations. The calculations involved the estimation of chain polarizability and were performed under simulated stress conditions using the AM1 Hamiltonian in MOPAC. Polarizability is then used to calculate the birefringence as a function of tensile stress, by using existing internal field theory. This theoretical approach is applied to predict the optical properties of highly oriented extended-chain polyethylene, as well as those for poly(p' phenylene therephtalamide); the latter being the base polymer in Kevlar fibers. Results reveal reasonable birefringence predictions when compared to available experimental results in the literature. Also, it is found that the contribution from orienting crystallites under the stress field, to the measured birefringence in Kevlar fibers, is only a small fraction of the total. However, the calculations predict a significant contribution from deformation (extension) at the molecular level.

  11. Ozonolysis of surface-adsorbed methoxyphenols: kinetics of aromatic ring cleavage vs. alkene side-chain oxidation

    NASA Astrophysics Data System (ADS)

    O'Neill, E. M.; Kawam, A. Z.; Van Ry, D. A.; Hinrichs, R. Z.

    2014-01-01

    Lignin pyrolysis products, which include a variety of substituted methoxyphenols, constitute a major component of organics released by biomass combustion, and may play a central role in the formation of atmospheric brown carbon. Understanding the atmospheric fate of these compounds upon exposure to trace gases is therefore critical to predicting the chemical and physical properties of biomass burning aerosol. We used diffuse reflectance infrared spectroscopy to monitor the heterogeneous ozonolysis of 4-propylguaiacol, eugenol, and isoeugenol adsorbed on NaCl and α-Al2O3 substrates. Adsorption of gaseous methoxyphenols onto these substrates produced near-monolayer surface concentrations of 3 × 1018 molecules m-2. The subsequent dark heterogeneous ozonolysis of adsorbed 4-propylguaiacol cleaved the aromatic ring between the methoxy and phenol groups with the product conclusively identified by GC-MS and 1H-NMR. Kinetic analysis of eugenol and isoeugenol dark ozonolysis also suggested the formation of ring-cleaved products, although ozonolysis of the unsaturated substituent groups forming carboxylic acids and aldehydes was an order of magnitude faster. Average uptake coefficients for NaCl-adsorbed methoxyphenols were γ = 2.3 (± 0.8) × 10-7 and 2 (± 1) × 10-6 for ozonolysis of the aromatic ring and the unsaturated side chain, respectively, and reactions on α-Al2O3 were approximately two times slower. UV-visible radiation (λ > 300 nm) enhanced eugenol ozonolysis of the aromatic ring by a factor of 4(± 1) but had no effect on ozonolysis of the alkene side chain.

  12. Molecular description of the collapse of hydrophobic polymer chains in water

    NASA Astrophysics Data System (ADS)

    Livadaru, Lucian; Kovalenko, Andriy

    2004-09-01

    We propose a self-consistent molecular theory of conformational properties of flexible polymers in solution. It is applied to the collapse of a hydrophobic polymer chain in water, and can be readily generalized to any polymer-solvent system (e.g., copolymers with high complexity). We stress the potential of this method for a variety of problems, such as protein folding.

  13. Distribution of Chains in Polymer Brushes Produced by a “Grafting From” Mechanism

    DOE PAGESBeta

    Martinez, Andre P.; Carrillo, Jan-Michael Y.; Dobrynin, Andrey V.; Adamson, Douglas H.

    2016-01-11

    The molecular weight and polydispersity of the chains in a polymer brush are critical parameters determining the brush properties. However, the characterization of polymer brushes is hindered by the vanishingly small mass of polymer present in brush layers. In this study, in order to obtain sufficient quantities of polymer for analysis, polymer brushes were grown from high surface area fibrous nylon membranes by ATRP. We synthesized the brushes with varying surface initiator densities, polymerization times, and amounts of sacrificial initiator, then cleaved from the substrate, and analyzed by GPC and NMR. Characterization showed that the surface-grown polymer chains were moremore » polydisperse and had lower average molecular weight compared to solution-grown polymers synthesized concurrently. Furthermore, the molecular weight distribution of the polymer brushes was observed to be bimodal, with a low molecular weight population of chains representing a significant mass fraction of the polymer chains at high surface initiator densities. Moreover, the origin of this low MW polymer fraction is proposed to be the termination of growing chains by recombination during the early stages of polymerization, a mechanism confirmed by molecular dynamics simulations of brush polymerization.« less

  14. Identification of vitronectin as a major plasma protein adsorbed on polymer surfaces of different copolymer composition.

    PubMed

    Bale, M D; Wohlfahrt, L A; Mosher, D F; Tomasini, B; Sutton, R C

    1989-12-01

    The arrays of proteins adsorbed from plasma onto a series of polystyrene copolymeric latexes were analyzed by enzyme-linked immunosorbent assay (ELISA) of washed beads and immunoblotting of proteins desorbed from the beads and separated by polyacrylamide gel electrophoresis (PAGE). Beads were prepared by continuous emulsion polymerization in the absence of surfactant. Coomassie brilliant blue staining of gel electropherograms of desorbed proteins indicated that the presence of small amounts of comonomers (1 to 10 mole %) significantly influenced the composition of the adsorbed protein layer. Immunoblotting revealed that fibrinogen, fibronectin, and vitronectin were adsorbed by all surfaces investigated. C3 and Clq adsorption varied significantly with copolymer composition. The ELISAs revealed that although the concentrations of vitronectin and fibronectin in plasma are similar, the extent of vitronectin adsorption from 70% to 85% plasma was greater by two orders of magnitude than fibronectin adsorption. Vitronectin adsorbed on carboxylic acid-containing copolymers reacted more strongly with a conformationally sensitive antivitronectin monoclonal antibody (MoAb) than vitronectin adsorbed to polystyrene and was more susceptible to cleavage by plasma proteases(s). The results show that vitronectin is a major protein adsorbed from concentrated plasma and that small changes in the chemical composition of a copolymer profoundly affects the extent and nature of protein adsorption from complex mixtures such as plasma. PMID:2479428

  15. Foam-based adsorbents having high adsorption capacities for recovering dissolved metals and methods thereof

    DOEpatents

    Janke, Christopher J.; Dai, Sheng; Oyola, Yatsandra

    2015-06-02

    Foam-based adsorbents and a related method of manufacture are provided. The foam-based adsorbents include polymer foam with grafted side chains and an increased surface area per unit weight to increase the adsorption of dissolved metals, for example uranium, from aqueous solutions. A method for forming the foam-based adsorbents includes irradiating polymer foam, grafting with polymerizable reactive monomers, reacting with hydroxylamine, and conditioning with an alkaline solution. Foam-based adsorbents formed according to the present method demonstrated a significantly improved uranium adsorption capacity per unit weight over existing adsorbents.

  16. Powder-based adsorbents having high adsorption capacities for recovering dissolved metals and methods thereof

    DOEpatents

    Janke, Christopher J.; Dai, Sheng; Oyola, Yatsandra

    2016-05-03

    A powder-based adsorbent and a related method of manufacture are provided. The powder-based adsorbent includes polymer powder with grafted side chains and an increased surface area per unit weight to increase the adsorption of dissolved metals, for example uranium, from aqueous solutions. A method for forming the powder-based adsorbent includes irradiating polymer powder, grafting with polymerizable reactive monomers, reacting with hydroxylamine, and conditioning with an alkaline solution. Powder-based adsorbents formed according to the present method demonstrated a significantly improved uranium adsorption capacity per unit weight over existing adsorbents.

  17. Effect of chain architecture on the size, shape, and intrinsic viscosity of chains in polymer solutions: A molecular simulation study

    NASA Astrophysics Data System (ADS)

    Khabaz, Fardin; Khare, Rajesh

    2014-12-01

    Effect of chain architecture on the chain size, shape, and intrinsic viscosity was investigated by performing molecular dynamics simulations of polymer solutions in a good solvent. Four types of chains - linear, comb shaped, H-shaped, and star - were studied for this purpose using a model in which the solvent particles were considered explicitly. Results indicated that the chain length (N) dependence of the mean squared radius of gyration of the chains followed a power-law behavior < {R_g^2 } rangle ^{1/2} ˜ N^\\upsilon with scaling exponents of υ = 0.605, 0.642, 0.602, and 0.608, for the linear, comb shaped, H-shaped, and star shaped chains, respectively. The simulation results for the geometrical shrinking factor were higher than the prior theoretical predictions for comb shaped chains. Analysis of chain shape demonstrated that the star chains were significantly smaller and more spherical than the others, while the comb and H-shaped polymer chains showed a more cylindrical shape. It is shown that the intrinsic viscosity of the chains can be calculated by plotting the specific viscosity determined from simulations against the solution concentration. The intrinsic viscosity exhibited linear behavior with the reciprocal of the overlap concentration for all chain architectures studied. The molecular weight dependence of the intrinsic viscosity followed the Mark-Houwink relation, [η] = KMa, for all chain architectures. When comparing the calculated values of exponent a with the literature experimental values, agreement was found only for the H and star chains, and a disagreement for the linear and comb chains. The viscosity shrinking factor of the branched chains was compared with the available experimental data and the theoretical predictions and a general agreement was found.

  18. Chain Length and Grafting Density Dependent Enhancement in the Hydrolysis of Ester-Linked Polymer Brushes.

    PubMed

    Melzak, Kathryn A; Yu, Kai; Bo, Deng; Kizhakkedathu, Jayachandran N; Toca-Herrera, José L

    2015-06-16

    Poly(N,N-dimethylacrylamide) (PDMA) brushes with different grafting density and chain length were grown from an ester group-containing initiator using surface-initiated polymerization. Hydrolysis of the PDMA chains from the surface was monitored by measuring thickness of the polymer layer by ellipsometry and extension length by atomic force microscopy. It was found that the initial rate of cleavage of one end-tethered PDMA chains was dependent on the grafting density and chain length; the hydrolysis rate was faster for high grafting density brushes and brushes with higher molecular weights. Additionally, the rate of cleavage of polymer chains during a given experiment changed by up to 1 order of magnitude as the reaction progressed, with a distinct transition to a lower rate as the grafting density decreased. Also, polymer chains undergo selective cleavage, with longer chains in a polydisperse brush being preferentially cleaved at one stage of the hydrolysis reaction. We suggest that the enhanced initial hydrolysis rates seen at high grafting densities and high chain lengths are due to mechanical activation of the ester bond connecting the polymer chains to the surface in association with high lateral pressure within the brush. These results have implications for the preparation of polymers brushes, their stability under harsh conditions, and the analysis of polymer brushes from partial hydrolysates. PMID:26010390

  19. Particle Restabilization in Silica/PEG/Ethanol Suspensions: How Strongly do Polymers Need To Adsorb To Stabilize Against Aggregation?

    SciTech Connect

    Kim, So Youn; Zukoski, Charles F.

    2014-09-24

    We study the effects of increasing the concentration of a low molecular weight polyethylene glycol on the stability of 44 nm diameter silica nanoparticles suspended in ethanol. Polymer concentration, c{sub p}, is increased from zero to that characterizing the polymer melt. Particle stability is accessed through measurement of the particle second-virial coefficient, B{sub -2}, performed by light scattering and ultrasmall angle X-ray scattering (USAXS). The results show that at low polymer concentration, c{sub p} < 3 wt %, B{sub -2} values are positive, indicating repulsive interactions between particles. B{sub -2} decreases at intermediate concentrations (3 wt % < c{sub p} < 50 wt %), and particles aggregates are formed. At high concentrations (50 wt % < c{sub p}) B{sub -2} increases and stabilizes at a value expected for hard spheres with a diameter near 44 nm, indicating the particles are thermodynamically stable. At intermediate polymer concentrations, rates of aggregation are determined by measuring time-dependent changes in the suspension turbidity, revealing that aggregation is slowed by the necessity of the particles diffusing over a repulsive barrier in the pair potential. The magnitude of the barrier passes through a minimum at c{sub p} {approx} 12 wt % where it has a value of {approx}12kT. These results are understood in terms of a reduction of electrostatic repulsion and van der Waals attractions with increasing c{sub p}. Depletion attractions are found to play a minor role in particle stability. A model is presented suggesting displacement of weakly adsorbed polymer leads to slow aggregation at intermediate concentration, and we conclude that a general model of depletion restabilization may involve increased strength of polymer adsorption with increasing polymer concentration.

  20. Segregation of chain ends to the surface of a polymer melt: Effect of surface profile versus chain discreteness.

    PubMed

    Mahmoudi, P; Matsen, M W

    2016-08-01

    Silberberg has argued that the surface of a polymer melt behaves like a reflecting boundary on the random-walk statistics of the polymers. Although this is approximately true, independent studies have shown that violations occur due to the finite width of the surface profile and to the discreteness of the polymer molecule, resulting in an excess of chain ends at the surface and a reduction in surface tension inversely proportional to the chain length, N . Using self-consistent field theory (SCFT), we compare the magnitude of these two effects by examining a melt of discrete polymers modeled as N monomers connected by Hookean springs of average length, a , next to a polymer surface of width [Formula: see text]. The effects of the surface width and the chain discreteness are found to be comparable for realistic profiles of [Formula: see text] ∼ a. A semi-analytical approximation is developed to help explain the behavior. The relative excess of ends at the surface is dependent on the details of the model, but in general it decreases for shorter polymers. The excess is balanced by a long-range depletion that has a universal shape independent of the molecular details. Furthermore, the approximation predicts that the reduction in surface energy equals one unit of kBT for every extra chain end at the surface. PMID:27498981

  1. Shear Flow Induced Transition from Liquid-Crystalline to Polymer Behavior in Side-Chain Liquid Crystal Polymers

    NASA Astrophysics Data System (ADS)

    Noirez, L.; Lapp, A.

    1997-01-01

    We determine the structure and conformation of side-chain liquid-crystalline polymers subjected to shear flow in the vicinity of the smectic phase by neutron scattering on the velocity gradient plane. Below the nematic-smectic transition we observe a typical liquid-crystal behavior; the smectic layers slide, leading to a main-chain elongation parallel to the velocity direction. In contrast, a shear applied above the transition induces a tilted main-chain conformation which is typical for polymer behavior.

  2. Polymer chain alignment and transistor properties of nanochannel-templated poly(3-hexylthiophene) nanowires

    NASA Astrophysics Data System (ADS)

    Oh, Seungjun; Hayakawa, Ryoma; Pan, Chengjun; Sugiyasu, Kazunori; Wakayama, Yutaka

    2016-08-01

    Nanowires of semiconducting poly(3-hexylthiophene) (P3HT) were produced by a nanochannel-template technique. Polymer chain alignment in P3HT nanowires was investigated as a function of nanochannel widths (W) and polymer chain lengths (L). We found that the ratio between chain length and channel width (L/W) was a key parameter as regards promoting polymer chain alignment. Clear dichroism was observed in polarized ultraviolet-visible (UV-Vis) absorption spectra only at a ratio of approximately L/W = 2, indicating that the L/W ratio must be optimized to achieve uniaxial chain alignment in the nanochannel direction. We speculate that an appropriate L/W ratio is effective in confining the geometries and conformations of polymer chains. This discussion was supported by theoretical simulations based on molecular dynamics. That is, the geometry of the polymer chains, including the distance and tilting angles of the chains in relation to the nanochannel surface, was dominant in determining the longitudinal alignment along the nanochannels. Thus prepared highly aligned polymer nanowire is advantageous for electrical carrier transport and has great potential for improving the device performance of field-effect transistors. In fact, a one-order improvement in carrier mobility was observed in a P3HT nanowire transistor.

  3. Monte Carlo simulations for a fluctuating sphere labeled on a flexible polymer chain in good solvents

    NASA Astrophysics Data System (ADS)

    Chen, Yong; Shew, Chwen-Yang

    2001-11-01

    Monte Carlo simulations are conducted to investigate a model composed of a fluctuating sphere labeled on one chain end of an isolated flexible chain polymer in good solvents. The labeled sphere is to model the instantaneous size of a bound flexible chain segment or a vibrating chromophore on a polymer chain. We assume the vibration of the sphere is governed by a harmoniclike potential, and the sphere size stays positive. We first address the issue regarding the confinement effect induced by a flexible chain. To rationalize the simulation results, we carry out a detailed analysis for a simple case containing a dimer grafted onto a fluctuating sphere. Using the sphere with a large size fluctuation, we find that the fluctuating sphere can be confined within the coiled polymer chain, and even trapped inside the grooves between neighboring monomers. The results imply the confinement effects may influence the properties of chromophores labeled on polymers or drugs bound to biopolymers. Moreover, in a separate study, we show the fluctuating sphere model can be used to fit a bound flexible chain segment, and provides a means to parameterize a polymer chain to a dumbbell, with possible applications in the dynamics of dilute polymer solutions.

  4. High-productivity membrane adsorbers: Polymer surface-modification studies for ion-exchange and affinity bioseparations

    NASA Astrophysics Data System (ADS)

    Chenette, Heather C. S.

    This dissertation centers on the surface-modification of macroporous membranes to make them selective adsorbers for different proteins, and the analysis of the performance of these membranes relative to existing technology. The common approach used in these studies, which is using membrane technology for chromatographic applications and using atom transfer radical polymerization (ATRP) as a surface modification technique, will be introduced and supported by a brief review in Chapter 1. The specific approaches to address the unique challenges and motivations of each study system are given in the introduction sections of the respective dissertation chapters. Chapter 2 describes my work to develop cation-exchange membranes. I discuss the polymer growth kinetics and characterization of the membrane surface. I also present an analysis of productivity, which measures the mass of protein that can bind to the stationary phase per volume of stationary phase adsorbing material per time. Surprisingly and despite its importance, this performance measure was not described in previous literature. Because of the significantly shorter residence time necessary for binding to occur, the productivity of these cation-exchange membrane adsorbers (300 mg/mL/min) is nearly two orders of magnitude higher than the productivity of a commercial resin product (4 mg/mL/min). My work studying membrane adsorbers for affinity separations was built on the productivity potential of this approach, as articulated in the conclusion of Chapter 2. Chapter 3 focuses on the chemical formulation work to incorporate glycoligands into the backbone of polymer tentacles grown from the surface of the same membrane stationary phase. Emphasis is given to characterizing and testing the working formulation for ligand incorporation, and details about how I arrived at this formulation are given in Appendix B. The plant protein, or lectin, Concanavalin A (conA) was used as the target protein. The carbohydrate affinity

  5. A flexible polymer chain in a critical solvent: Coil or globule?

    NASA Astrophysics Data System (ADS)

    Budkov, Yu. A.; Kolesnikov, A. L.; Georgi, N.; Kiselev, M. G.

    2015-02-01

    We study the behavior of a flexible polymer chain in the presence of a low-molecular weight solvent in the vicinity of a liquid-gas critical point within the framework of a self-consistent field theory. The total free energy of the dilute polymer solution is expressed as a function of the radius of gyration of the polymer and the average solvent number density within the gyration volume at the level of the mean-field approximation. Varying the strength of attraction between polymer and solvent we show that two qualitatively different regimes occur at the liquid-gas critical point. In case of weak polymer-solvent interactions the polymer chain is in a globular state. On the contrary, in case of strong polymer-solvent interactions the polymer chain attains an expanded conformation. We discuss the influence of the critical solvent density fluctuations on the polymer conformation. The reported effect could be used to excert control on the polymer conformation by changing the thermodynamic state of the solvent. It could also be helpful to estimate the solvent density within the gyration volume of the polymer for drug delivery and molecular imprinting applications.

  6. Conjugated polymers containing diketopyrrolopyrrole units in the main chain

    PubMed Central

    Rabindranath, A Raman; Zhang, Kai; Zhu, Yu

    2010-01-01

    Summary Research activities in the field of diketopyrrolopyrrole (DPP)-based polymers are reviewed. Synthetic pathways to monomers and polymers, and the characteristic properties of the polymers are described. Potential applications in the field of organic electronic materials such as light emitting diodes, organic solar cells and organic field effect transistors are discussed. PMID:20978619

  7. Novel adhesive properties of poly(ethylene-oxide) adsorbed nanolayers

    NASA Astrophysics Data System (ADS)

    Zeng, Wenduo

    Solid-polymer interfaces play crucial roles in the multidisciplinary field of nanotechnology and are the confluence of physics, chemistry, biology, and engineering. There is now growing evidence that polymer chains irreversibly adsorb even onto weakly attractive solid surfaces, forming a nanometer-thick adsorbed polymer layer ("adsorbed polymer nanolayers"). It has also been reported that the adsorbed layers greatly impact on local structures and properties of supported polymer thin films. In this thesis, I aim to clarify adhesive and tribological properties of adsorbed poly(ethylene-oxide) (PEO) nanolayers onto silicon (Si) substrates, which remain unsolved so far. The adsorbed nanolayers were prepared by the established protocol: one has to equilibrate the melt or dense solution against a solid surface; the unadsorbed chains can be then removed by a good solvent, while the adsorbed chains are assumed to maintain the same conformation due to the irreversible freezing through many physical solid-segment contacts. I firstly characterized the formation process and the surface/film structures of the adsorbed nanolayers by using X-ray reflectivity, grazing incidence X-ray diffraction, and atomic force microscopy. Secondly, to compare the surface energy of the adsorbed layers with the bulk, static contact angle measurements with two liquids (water and glycerol) were carried out using a optical contact angle meter equipped with a video camera. Thirdly, I designed and constructed a custom-built adhesion-testing device to quantify the adhesive property. The experimental results provide new insight into the microscopic structure - macroscopic property relationship at the solid-polymer interface.

  8. Effects of nanostructure geometry on polymer chain alignment and device performance in nanoimprinted polymer solar cell

    NASA Astrophysics Data System (ADS)

    Yang, Yi; Mielczarek, Kamil; Zakhidov, Anvar; Hu, Walter

    2013-03-01

    Among the various organic photovoltaic devices, the conjugated polymer/fullerene approach has drawn the most research interest. The performance of these types of solar cells is greatly determined by the nanoscale morphology of the two components (donor/acceptor) and the molecular orientation/crystallinity in the photoactive layer. This article demonstrates our recent studies on the nanostructure geometry effects on the nanoimprint induced poly(3 hexylthiophene-2,5-diyl) (P3HT) chain alignment and photovoltaic performance. Out-of-plane and in-plane grazing incident X-ray diffractions are employed to characterize the chain orientations in P3HT nanogratings with different widths and heights. It is found that nanoimprint procedure changes the initial edge-on alignment in non-imprinted P3HT thin film to a vertical orientation which favors the hole transport, with an organization height H≥ 170 nm and width in the range of 60 nm<= W< 210 nm. Samples with better aligned molecules lead to a larger crystallite sizes as well. Imprinted P3HT/[6,6]-penyl-C61-butyric-acid-methyl-ester (PCBM) solar cells show an increase in power conversion efficiency (PCE) with the decrease of nanostructure width, and with the increase of height and junction area. Devices with the highest PCE are made by the fully aligned and highest P3HT nanostructures (width w= 60 nm, height h= 170 nm), allowing for the most efficient charge separation, transport and light absorption. We believe this work will contribute to the optimal geometry design of nanoimprinted polymer solar cells.

  9. Record high hole mobility in polymer semiconductors via side-chain engineering.

    PubMed

    Kang, Il; Yun, Hui-Jun; Chung, Dae Sung; Kwon, Soon-Ki; Kim, Yun-Hi

    2013-10-01

    Charge carrier mobility is still the most challenging issue that should be overcome to realize everyday organic electronics in the near future. In this Communication, we show that introducing smart side-chain engineering to polymer semiconductors can facilitate intermolecular electronic communication. Two new polymers, P-29-DPPDBTE and P-29-DPPDTSE, which consist of a highly conductive diketopyrrolopyrrole backbone and an extended branching-position-adjusted side chain, showed unprecedented record high hole mobility of 12 cm(2)/(V·s). From photophysical and structural studies, we found that moving the branching position of the side chain away from the backbone of these polymers resulted in increased intermolecular interactions with extremely short π-π stacking distances, without compromising solubility of the polymers. As a result, high hole mobility could be achieved even in devices fabricated using the polymers at room temperature. PMID:24053786

  10. Solid-phase microextraction of phthalate esters in water sample using different activated carbon-polymer monoliths as adsorbents.

    PubMed

    Lirio, Stephen; Fu, Chung-Wei; Lin, Jhih-Yun; Hsu, Meng-Ju; Huang, Hsi-Ya

    2016-07-13

    In this study, the application of different activated carbon-polymer (AC-polymer) monoliths as adsorbents for the solid-phase microextraction (SPME) of phthalate esters (PAEs) in water sample were investigated. The activated carbon (AC) was embedded in organic polymers, poly(butyl methacrylate-co-ethylene dimethacrylate) (poly(BMA-EDMA)) or poly(styrene-co-divinylbenzene) (poly(STY-DVB)), via a 5-min microwave-assisted or a 15-min water bath heating polymerization. Preliminary investigation on the performance of the native poly(BMA-EDMA) and poly(STY-DVB) demonstrated remarkable adsorption efficiencies for PAEs. However, due to the strong hydrophobic, π-π, and hydrogen bonding interactions between the analytes and polymers, low extraction recoveries were achieved. In contrast, the presence of AC in native polymers not only enhanced the adsorption efficiencies but also assisted the PAE desorption, especially for AC-poly(STY-DVB) with extraction recovery ranged of 76.2-99.3%. Under the optimized conditions, the extraction recoveries for intra-, inter-day and column-to-column were in the range of 76.5-100.8% (<3.7% RSDs), 77.2-97.6% (<5.6% RSDs) and 75.5-99.7% (<6.2% RSDs), respectively. The developed AC-poly(STY-DVB) monolithic column showed good mechanical stability, which can be reused for more than 30 extraction times without any significant loss in the extraction recoveries of PAEs. The AC-poly(STY-DVB) monolithic column was successfully applied in SPME of PAEs in water sample with extraction recovery ranged of 78.8%-104.6% (<5.5% RSDs). PMID:27237837

  11. Effect of alkane chain length and counterion on the freezing transition of cationic surfactant adsorbed film at alkane mixture - water interfaces.

    PubMed

    Tokiwa, Yuhei; Sakamoto, Hiroyasu; Takiue, Takanori; Aratono, Makoto; Matsubara, Hiroki

    2015-05-21

    Penetration of alkane molecules into the adsorbed film gives rise to a surface freezing transition of cationic surfactant at the alkane-water interface. To examine the effect of the alkane chain length and counterion on the surface freezing, we employed interfacial tensiometry and ellipsometry to study the interface of cetyltrimethylammonium bromide and cetyltrimethylammonium chloride aqueous solutions against dodecane, tetradecane, hexadecane, and their mixtures. Applying theoretical equations to the experimental results obtained, we found that the alkane molecules that have the same chain length as the surfactant adsorb preferentially into the surface freezing film. Furthermore, we demonstrated that the freezing transition temperature of cationic surfactant adsorbed film was independent of the kind of counterion. PMID:25932500

  12. Forced desorption of semiflexible polymers, adsorbed and driven by molecular motors.

    PubMed

    Chaudhuri, Abhishek; Chaudhuri, Debasish

    2016-02-21

    We formulate and characterize a model to describe the dynamics of semiflexible polymers in the presence of activity due to motor proteins attached irreversibly to a substrate, and a transverse pulling force acting on one end of the filament. The stochastic binding-unbinding of the motor proteins and their ability to move along the polymer generate active forces. As the pulling force reaches a threshold value, the polymer eventually desorbs from the substrate. Performing underdamped Langevin dynamics simulation of the polymer, and with stochastic motor activity, we obtain desorption phase diagrams. The correlation time for fluctuations in the desorbed fraction increases as one approaches complete desorption, captured quantitatively by a power law spectral density. We present theoretical analysis of the phase diagram using mean field approximations in the weakly bending limit of the polymer and performing linear stability analysis. This predicts an increase in the desorption force with the polymer bending rigidity, active velocity and processivity of the motor proteins to capture the main features of the simulation results. PMID:26750537

  13. Adsorbed serum albumin is permissive to macrophage attachment to perfluorocarbon polymer surfaces in culture

    PubMed Central

    Godek, M.L.; Michel, R.; Chamberlain, L. M.; Castner, D. G.; Grainger, D.W.

    2013-01-01

    Monocyte/macrophage adhesion to biomaterials, correlated with foreign body response, occurs through protein-mediated surface interactions. Albumin-selective perfluorocarbon (FC) biomaterials are generally poorly cell-conducive due to insufficient receptor-mediated surface interactions, but macrophages bind to albumin-coated substrates and also preferentially to highly hydrophobic fluorinated surfaces. Bone marrow macrophages (BMMO) and IC-21, RAW 264.7 and J774A.1 monocyte/macrophage cells were cultured on FC surfaces. Protein deposition onto two distinct FC surfaces from complex and single-component solutions was tracked using fluorescence and time-of-flight secondary ion mass spectrometry (ToF-SIMS) methods. Cell adhesion and growth on protein pre-treated substrates were compared by light microscopy. Flow cytometry and integrin-directed antibody receptor blocking assessed integrins critical for monocyte/macrophage adhesion in vitro. Albumin predominantly adsorbs onto both FC surfaces from 10% serum. In cultures pre-adsorbed with albumin or serum-dilutions, BMMO responded similar to IC-21 at early time points. Compared to Teflon® AF, plasma-polymerized FC was less permissive to extended cell proliferation. The β2 integrins play major roles in macrophage adhesion to FC surfaces: antibody blocking significantly disrupted cell adhesion. Albumin-mediated cell adhesion mechanisms to FC surfaces could not be clarified. Primary BMMO and secondary IC-21 macrophages behave similarly on FC surfaces, regardless of pre-adsorbed protein biasing, with respect to adhesion, cell morphology, motility and proliferation. PMID:18306309

  14. Excluded-volume interaction induced stiffness of comb polymer with densely grafted side-chains

    NASA Astrophysics Data System (ADS)

    Qiu, Feng

    2014-03-01

    Excluded-volume interaction has been widely recognized to cause expansion of polymer chain at large length scale. However, its effect on chain conformations at small length scale has been studied to less extent. Here we consider a comb polymer with its backbone densely grafted by side-chains as a model system. The method analogue to solving the electrostatic persistence length problem for either rigid or flexible polyelectrolytes is employed. For comb polymers with rigid backbone near the rod limit, the excluded-volume interaction induced persistence length scales linearly with the volume of the side-chain. While for flexible backbone, the persistence length depends on the side-chain volume more weakly. Field theoretic method that is relevant to address this problem is also explored and discussed. Work supported by NSFC.

  15. Conformation of a flexible polymer in explicit solvent: Accurate solvation potentials for Lennard-Jones chains.

    PubMed

    Taylor, Mark P; Ye, Yuting; Adhikari, Shishir R

    2015-11-28

    The conformation of a polymer chain in solution is coupled to the local structure of the surrounding solvent and can undergo large changes in response to variations in solvent density and temperature. The many-body effects of solvent on the structure of an n-mer polymer chain can be formally mapped to an exact n-body solvation potential. Here, we use a pair decomposition of this n-body potential to construct a set of two-body potentials for a Lennard-Jones (LJ) polymer chain in explicit LJ solvent. The solvation potentials are built from numerically exact results for 5-mer chains in solvent combined with an approximate asymptotic expression for the solvation potential between sites that are distant along the chain backbone. These potentials map the many-body chain-in-solvent problem to a few-body single-chain problem and can be used to study a chain of arbitrary length, thereby dramatically reducing the computational complexity of the polymer chain-in-solvent problem. We have constructed solvation potentials at a large number of state points across the LJ solvent phase diagram including the vapor, liquid, and super-critical regions. We use these solvation potentials in single-chain Monte Carlo (MC) simulations with n ≤ 800 to determine the size, intramolecular structure, and scaling behavior of chains in solvent. To assess our results, we have carried out full chain-in-solvent MC simulations (with n ≤ 100) and find that our solvation potential approach is quantitatively accurate for a wide range of solvent conditions for these chain lengths. PMID:26627969

  16. Ammonium-Functionalized Hollow Polymer Particles As a pH-Responsive Adsorbent for Selective Removal of Acid Dye.

    PubMed

    Qin, Yan; Wang, Li; Zhao, Changwen; Chen, Dong; Ma, Yuhong; Yang, Wantai

    2016-07-01

    In this work, a novel type of ammonium-functionalized hollow polymer particles (HPP-NH3(+)) with a high density of ammonium groups in the shell has been specially designed and synthesized. Benefiting from both the high surface area and from the high density of positively charged ammonium groups, the as-prepared HPP-NH3(+) can serve as a selective adsorbent for the removal of negatively charged acid dye (e.g., methyl blue a-MB). The equilibrium adsorption data of a-MB on the HPP-NH3(+) were evaluated using Freundlich and Langmuir isotherm models, and Langmuir isotherm exhibited a better fit with a maximum adsorption capacity of 406 mg/g. Most importantly, because of the presence of dual functional groups (ammonium and carboxyl groups), the HPP-NH3(+) showed a significant pH-dependent equilibrium adsorption capacity, which increased dramatically from 59 mg/g to 449 mg/g as the solution pH decreased from 9 to 2. This uniqueness makes the dye-adsorbed HPP-NH3(+) can be facilely regenerated under mild condition (in weak alkaline solution, pH 10) to recover both a-MB and the HPP-NH3(+), whereas the recovery of conventional adsorbents is commonly performed under particularly severe conditions. The regenerated HPP-NH3(+) can be reused for dye removal and the dye removal efficiency remained above 98% even after five adsorption-desorption cycles. Because of its high adsorption capacity, pH-sensitivity, easy regeneration, and good reusability, the HPP-NH3(+) has great potential for the application in the field of water treatment, controlled drug release, and pH-responsive delivery. PMID:27302068

  17. Prediction of Solution Properties of Flexible-Chain Polymers: A Computer Simulation Undergraduate Experiment

    ERIC Educational Resources Information Center

    de la Torre, Jose Garcia; Cifre, Jose G. Hernandez; Martinez, M. Carmen Lopez

    2008-01-01

    This paper describes a computational exercise at undergraduate level that demonstrates the employment of Monte Carlo simulation to study the conformational statistics of flexible polymer chains, and to predict solution properties. Three simple chain models, including excluded volume interactions, have been implemented in a public-domain computer…

  18. Translocation of a Polymer Chain across a Nanopore: A Brownian Dynamics Simulation Study

    NASA Technical Reports Server (NTRS)

    Tian, Pu; Smith, Grant D.

    2003-01-01

    We carried out Brownian dynamics simulation studies of the translocation of single polymer chains across a nanosized pore under the driving of an applied field (chemical potential gradient). The translocation process can be either dominated by the entropic barrier resulted from restricted motion of flexible polymer chains or by applied forces (or chemical gradient across the wall), we focused on the latter case in our studies. Calculation of radius of gyrations at the two opposite sides of the wall shows that the polymer chains are not in equilibrium during the translocation process. Despite this fact, our results show that the one-dimensional diffusion and the nucleation model provide an excellent description of the dependence of average translocation time on the chemical potential gradients, the polymer chain length and the solvent viscosity. In good agreement with experimental results and theoretical predictions, the translocation time distribution of our simple model shows strong non-Gaussian characteristics. It is observed that even for this simple tubelike pore geometry, more than one peak of translocation time distribution can be generated for proper pore diameter and applied field strengths. Both repulsive Weeks-Chandler-Anderson and attractive Lennard-Jones polymer-nanopore interaction were studied, attraction facilitates the translocation process by shortening the total translocation time and dramatically improve the capturing of polymer chain. The width of the translocation time distribution was found to decrease with increasing temperature, increasing field strength, and decreasing pore diameter.

  19. Lattice model of linear telechelic polymer melts. II. Influence of chain stiffness on basic thermodynamic properties

    SciTech Connect

    Xu, Wen-Sheng; Freed, Karl F.

    2015-07-14

    The lattice cluster theory (LCT) for semiflexible linear telechelic melts, developed in Paper I, is applied to examine the influence of chain stiffness on the average degree of self-assembly and the basic thermodynamic properties of linear telechelic polymer melts. Our calculations imply that chain stiffness promotes self-assembly of linear telechelic polymer melts that assemble on cooling when either polymer volume fraction ϕ or temperature T is high, but opposes self-assembly when both ϕ and T are sufficiently low. This allows us to identify a boundary line in the ϕ-T plane that separates two regions of qualitatively different influence of chain stiffness on self-assembly. The enthalpy and entropy of self-assembly are usually treated as adjustable parameters in classical Flory-Huggins type theories for the equilibrium self-assembly of polymers, but they are demonstrated here to strongly depend on chain stiffness. Moreover, illustrative calculations for the dependence of the entropy density of linear telechelic polymer melts on chain stiffness demonstrate the importance of including semiflexibility within the LCT when exploring the nature of glass formation in models of linear telechelic polymer melts.

  20. Novel biaxial nematic phases of side-chain liquid crystalline polymers

    NASA Astrophysics Data System (ADS)

    Matsuyama, Akihiko

    2012-12-01

    We present a mean field theory to describe biaxial nematic phases of side-chain liquid crystalline polymers, in which rigid side-chains (mesogens) and rigid-backbone chains favor mutually perpendicular orientations. Taking into account both excluded volume and attractive interactions between rigid rods, novel biaxial nematic phases are theoretically predicted. We calculate uniaxial and biaxial orientational order parameters as a function of temperature and the length of backbone chains. We find a first-order biaxial-biaxial phase transition and a first (or second)-order uniaxial-biaxial one, depending on the length of mesogens and backbone chains.

  1. Enhanced physical stabilization of fenofibrate nanosuspensions via wet co-milling with a superdisintegrant and an adsorbing polymer.

    PubMed

    Azad, Mohammad; Afolabi, Afolawemi; Bhakay, Anagha; Leonardi, Jonathan; Davé, Rajesh; Bilgili, Ecevit

    2015-08-01

    Drug nanoparticles in suspensions can form aggregates leading to physical instability, which is traditionally mitigated using soluble polymers and surfactants. The aim of this paper was to explore common superdisintegrants, i.e., sodium starch glycolate (SSG), croscarmellose sodium (CCS), and crospovidone (CP), as novel class of dispersants for enhanced stabilization of fenofibrate (FNB), a model BCS Class II drug, suspensions. FNB was wet-milled with superdisintegrants along with hydroxypropyl methylcellulose (HPMC), a soluble adsorbing polymer, in a stirred media mill. For comparison, FNB was also milled in the presence of HPMC and/or SDS (sodium dodecyl sulfate) without superdisintegrants. Laser diffraction, scanning electron microscopy, viscometry, differential scanning calorimetry, and powder X-ray diffraction were used to characterize the suspensions. The results show that 2% HPMC along with 1% SSG or 1% CCS mitigated the aggregation of FNB nanoparticles significantly similar to the use of either 5% HPMC or 1% HPMC-0.075% SDS, whereas CP was not effective due to its low swelling capacity. CCS/SSG enhanced steric-kinetic stabilization of the FNB suspensions owing to their high swelling capacity, viscosity enhancement, and physical barrier action. Overall, this study provides a mechanistic basis for a novel method of formulating surfactant-free drug nanosuspensions with co-milled superdisintegrants. PMID:26079832

  2. Gyration tensor based analysis of the shapes of polymer chains in an attractive spherical cage.

    PubMed

    Arkın, Handan; Janke, Wolfhard

    2013-02-01

    In a recent computational study, we found highly structured conformations for the polymer-attractive sphere model system. Those conformations are of highly ordered spherical shape or form two-dimensional planar, compact to extended, random coil structures. The observed conformations range from desorbed to partially or even completely adsorbed. In order to present their shape characteristics, here we calculate the gyration tensor and related shape descriptors. PMID:23406146

  3. Determination of ractopamine in pork using a magnetic molecularly imprinted polymer as adsorbent followed by HPLC.

    PubMed

    Tang, Yiwei; Gao, Jingwen; Liu, Xiuying; Lan, Jianxing; Gao, Xue; Ma, Yong; Li, Min; Li, Jianrong

    2016-06-15

    A new magnetic molecularly imprinted polymers (MMIPs) for separation and concentration of ractopamine (RAC) were prepared using surface molecular imprinting technique with methacryloyl chloride as functional monomer and RAC as template. The MMIPs were characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometer. The results of re-binding experiments indicated that the MMIPs had fast adsorption kinetics and could reach binding equilibrium within 20 min, and the adsorption capacity of the MMIPs was 2.87-fold higher than that of the corresponding non-imprinted polymer. The selectivity of the MMIPs was evaluated according to its recognition to RAC and its analogues. The synthesized MMIPs were successfully applied to extraction, followed by high performance liquid chromatography to determine RAC in real food samples. Spiked recoveries ranged from 73.60% to 94.5%, with relative standard deviations of <11.17%. PMID:26868550

  4. Computational polymer physics: Hard-sphere chain in solvent systems

    NASA Astrophysics Data System (ADS)

    Gautam, Avinash; Gavazzi, Daniel; Taylor, Mark

    2009-10-01

    In this work we present results for chain conformation in two simple chain-in-solvent systems constructed from hard-sphere monomers of diameter D. The first system consists of a flexible chain of fused hard spheres (i.e., bond length L=D) in a monomeric hard-sphere solvent. The second system consists of a flexible tangent hard-sphere chain (L=D) in a dimeric hard-sphere solvent with L=D. These systems are studied using Monte Carlo simulations which employ both single-site crankshaft and multi-site pivot moves to sample the configuration space of the chain. We report chain structure, in terms of site-site probability functions, as a function of solvent density. In all cases, increasing solvent density leads to an overall compression of the chain. At high solvent density the chain conformation is closely coupled to the local solvent structure and we speculate that incommensurate structures may lead to interesting conformational transitions.

  5. Phase transfer of citrate stabilized gold nanoparticles using nonspecifically adsorbed polymers.

    PubMed

    Alkilany, Alaaldin M; Caravana, Aidan C; Hamaly, Majd A; Lerner, Kevin T; Thompson, Lucas B

    2016-01-01

    Many synthetic approaches for gold nanoparticles rely on an aqueous media, resulting in water-soluble nanoparticles, which limits the ability to incorporate gold nanoparticles into other organic solvents or hydrophobic polymeric composites. Surface functionalization and phase transfer approaches using alkylthiols or alkylamines, which strongly bind the gold surface, are common routes to overcome this limitation, however they are typically challenging methods. In this paper we report an approach to transport citrate capped gold nanoparticles into a variety of solvents, including ones that are hydrophobic and not miscible with water without the need for phase transfer agents. We suspend gold nanoparticles in a water-miscible polar organic solvent that also is a solvent for a hydrophobic polymer. After drying, polymer-stabilized gold nanoparticles were found to be dispersible in various hydrophobic solvents with maintained colloidal stability. This work investigates two hydrophobic polymers, namely (polymethylmethacrylate and polyvinylacetate), which share common chemical motifs but have significantly different physiochemical properties. Interestingly, a significant difference in their ability to stabilize the transferred gold nanoparticles is observed and discussed. PMID:26397907

  6. Stretching Response of Knotted and Unknotted Polymer Chains

    NASA Astrophysics Data System (ADS)

    Caraglio, Michele; Micheletti, Cristian; Orlandini, Enzo

    2015-10-01

    Recent theoretical and experimental advances have clarified the major effects of knotting on the properties of stretched chains. Yet, how knotted chains respond to weak mechanical stretching and how this behavior differs from the unknotted case are still open questions and we address them here by profiling the complete stretching response of chains of hundreds of monomers and different topology. We find that the ratio of the knotted and unknotted chain extensions varies nonmonotonically with the applied force. This surprising feature is shown to be a signature of the crossover between the well-known high-force stretching regime and the previously uncharacterized low-force one. The observed differences of knotted and unknotted chain response increases with knot complexity and are sufficiently marked that they could be harnessed in single-molecule contexts to infer the presence and complexity of physical knots in micron-long biomolecules.

  7. Topological coarse graining of polymer chains using wavelet-accelerated Monte Carlo. II. Self-avoiding chains.

    PubMed

    Ismail, Ahmed E; Stephanopoulos, George; Rutledge, Gregory C

    2005-06-15

    In the preceding paper [A. E. Ismail, G. C. Rutledge, and G. Stephanopoulos J. Chem. Phys. (in press)] we introduced wavelet-accelerated Monte Carlo (WAMC), a coarse-graining methodology based on the wavelet transform, as a method for sampling polymer chains. In the present paper, we extend our analysis to consider excluded-volume effects by studying self-avoiding chains. We provide evidence that the coarse-grained potentials developed using the WAMC method obey phenomenological scaling laws, and use simple physical arguments for freely jointed chains to motivate these laws. We show that coarse-grained self-avoiding random walks can reproduce results obtained from simulations of the original, more-detailed chains to a high degree of accuracy, in orders of magnitude less time. PMID:16008482

  8. Chain conformation near the substrate interface in nanoparticle stabilized polymer thin films

    NASA Astrophysics Data System (ADS)

    Barkley, Deborah; Sen, Mani; Jiang, Naisheng; Endoh, Maya; Koga, Tadanori; Yuan, Guangcui; Satija, Sushil; Zhang, Yugang; Gang, Oleg; Karim, Alamgir

    When nanoparticles (NPs) are added to polymer thin films, they often migrate to the film-substrate interface and form a ``diffused immobile interfacial layer'', which serves to screen the polymer-substrate interaction and suppress dewetting. The fundamental, but unsolved question is how the conformations of the polymer chains in the layer are affected by the NPs and how that impacts the enhancement of film stability. To address the question, we used dodecane thiol-functionalized gold NPs (2.4 nm diameter) and polystyrene (PS, Mw =30kDa). We found that the critical concentration of the Au NPs to induce complete dewetting suppression of 20 nm-thick PS/Au thin films on cleaned Si substrates is 5 wt% (wt of particle/wt of polymer). To investigate the interfacial structures at the polymer-solid interface, we rinsed the annealed PS/Au thin films with toluene and characterized the residual interfacial layers by using various x-ray and neutron scattering techniques. The results indicate that the conformation of the polymer chains closer to the substrate becomes less flattened with the addition of gold NPs, allowing chains at the substrate to entangle more effectively with free chains comprising the bulk film. The detailed mechanism will be discussed. T.K. acknowledges funding from NSF Grant (CMMI-1332499).

  9. Parallelized event chain algorithm for dense hard sphere and polymer systems

    SciTech Connect

    Kampmann, Tobias A. Boltz, Horst-Holger; Kierfeld, Jan

    2015-01-15

    We combine parallelization and cluster Monte Carlo for hard sphere systems and present a parallelized event chain algorithm for the hard disk system in two dimensions. For parallelization we use a spatial partitioning approach into simulation cells. We find that it is crucial for correctness to ensure detailed balance on the level of Monte Carlo sweeps by drawing the starting sphere of event chains within each simulation cell with replacement. We analyze the performance gains for the parallelized event chain and find a criterion for an optimal degree of parallelization. Because of the cluster nature of event chain moves massive parallelization will not be optimal. Finally, we discuss first applications of the event chain algorithm to dense polymer systems, i.e., bundle-forming solutions of attractive semiflexible polymers.

  10. Brownian Dynamics Simulations of Flow Induced Conformation of Single Polymer Chains

    NASA Astrophysics Data System (ADS)

    Oztekin, Alparslan; Webb, Edward; Zhang, Frank; Cheng, Xuanhong

    2012-11-01

    Coarse-grained molecular dynamics simulation of single polymer chains is conducted to examine flow induced conformational changes of single polymer chains in shear and extensional flows. Dynamic properties of polymeric molecules are described using bead-spring models; these models put coarse grain groups of atoms into single particles, connected to adjacent particles via spring like interactions. A common representation of the bonded interaction, or spring, is given by the Finitely Extensible Non-linear Elastic model. The constants used in the model are determined form single-molecule force spectroscopic experiments. Simulations and experiments will help to achieve a clear picture of how von Willebrand Factor, a blood clotting protein, model system for flow-induced activation, achieves flow sensing at the single protein/polymer level. The model includes bead-bead interactions, hydrodynamic interaction, the volume of the beads and spring-spring interaction for finitely extensible dumbbell and other spring models. The effects of walls on the dynamics of polymer chains are also presented. The results are presented for various chain lengths and flow conditions. Hydrodynamic interaction and the presence of wall have strong influences on the dynamics of the polymer chain.

  11. Scattering function of semiflexible polymer chains under good solvent conditions.

    PubMed

    Hsu, Hsiao-Ping; Paul, Wolfgang; Binder, Kurt

    2012-11-01

    Using the pruned-enriched Rosenbluth Monte Carlo algorithm, the scattering functions of semiflexible macromolecules in dilute solution under good solvent conditions are estimated both in d = 2 and d = 3 dimensions, considering also the effect of stretching forces. Using self-avoiding walks of up to N = 25,600 steps on the square and simple cubic lattices, variable chain stiffness is modeled by introducing an energy penalty ε(b) for chain bending; varying q(b) = exp (-ε(b)∕k(B)T) from q(b) = 1 (completely flexible chains) to q(b) = 0.005, the persistence length can be varied over two orders of magnitude. For unstretched semiflexible chains, we test the applicability of the Kratky-Porod worm-like chain model to describe the scattering function and discuss methods for extracting persistence length estimates from scattering. While in d = 2 the direct crossover from rod-like chains to self-avoiding walks invalidates the Kratky-Porod description, it holds in d = 3 for stiff chains if the number of Kuhn segments n(K) does not exceed a limiting value n(K)(*) (which depends on the persistence length). For stretched chains, the Pincus blob size enters as a further characteristic length scale. The anisotropy of the scattering is well described by the modified Debye function, if the actual observed chain extension (end-to-end distance in the direction of the force) as well as the corresponding longitudinal and transverse linear dimensions - (2), are used. PMID:23145745

  12. Selective Ni-P electroless plating on photopatterned cationic adsorption films influenced by alkyl chain lengths of polyelectrolyte adsorbates and additive surfactants.

    PubMed

    Nakagawa, Masaru; Nawa, Nozomi; Iyoda, Tomokazu

    2004-10-26

    We demonstrated that the photopatterned single-layer adsorption film of poly(1-dodecyl-4-pyridinium bromide) on a silica surface was available for a template of nickel-phosphorus (Ni-P) electroless plating through sensitization with a SnCl(2) aqueous solution and activation with a PdCl(2) aqueous solution. Four kinds of poly(1-alkyl-4-vinylpyridinium halide)s bearing methyl, propyl, hexyl, and dodecyl groups were prepared. The cationic polymers were adsorbed by a negatively charged silica surface from their solutions, to form single-layer adsorption films exhibiting desorption-resistance toward deionized water and ethanol. The organic adsorption films could be decomposed completely by exposure to 172 nm deep-UV light. The formation and decomposition of the single-layer films were confirmed by deep-UV absorption spectral measurement and zeta-potential measurement. Ni-P electroless plating was carried out on the photopatterned adsorption films, using three types of SnO(x) colloidal materials without and with cationic or anionic surfactant as catalyst precursors in the sensitization step. In the case of the negatively charged SnO(x) colloids surrounded by anionic surfactant, Ni-deposition took place preferentially on the cationic adsorption films remaining in unexposed regions. The Ni-deposition was accelerated significantly on the cationic adsorption film bearing dodecyl groups. It was obvious by ICP-AES analyses that the hydrophobic long-chain dodecyl groups in the adsorption film could promote the adsorption of the negative SnO(x) colloids on the film surface, followed by much nucleus formation of zerovalent Pd catalysts useful for the electroless plating. The result of our experiment clearly showed that, in addition to electrostatic interaction, van der Waals interaction generating between the hydrophobic long-chain hydrocarbons of the adsorption film and the surfactant improved significantly the adsorption stability of the SnO(x) colloids, resulting in highly

  13. Tribochemical synthesis of nano-lubricant films from adsorbed molecules at sliding solid interface: Tribo-polymers from α-pinene, pinane, and n-decane

    NASA Astrophysics Data System (ADS)

    He, Xin; Barthel, Anthony J.; Kim, Seong H.

    2016-06-01

    The mechanochemical reactions of adsorbed molecules at sliding interfaces were studied for α-pinene (C10H16), pinane (C10H18), and n-decane (C10H22) on a stainless steel substrate surface. During vapor phase lubrication, molecules adsorbed at the sliding interface could be activated by mechanical shear. Under the equilibrium adsorption condition of these molecules, the friction coefficient of sliding steel surfaces was about 0.2 and a polymeric film was tribochemically produced. The synthesis yield of α-pinene tribo-polymers was about twice as much as pinane tribo-polymers. In contrast to these strained bicyclic hydrocarbons, n-decane showed much weaker activity for tribo-polymerization at the same mechanical shear condition. These results suggested that the mechanical shear at tribological interfaces could induce the opening of the strained ring structure of α-pinene and pinane, which leads to polymerization of adsorbed molecules at the sliding track. On a stainless steel surface, such polymerization reactions of adsorbed molecules do not occur under typical surface reaction conditions. The mechanical properties and boundary lubrication efficiency of the produced tribo-polymer films are discussed.

  14. Chain-length dependence of the dissociation dynamics of oriented molecular adsorbates: n-alkyl bromides on GaAs(110)

    SciTech Connect

    Khan, K.A.; Camillone, N. III; Osgood, R.M. Jr.

    1999-07-01

    Brominated hydrocarbons adsorbed on semiconductor surfaces serve as ideal model systems for investigating the photoinduced chemistry of oriented molecules in the condensed phase. Under UV irradiation these adsorbates dissociate via attachment of photoexcited substrate electrons giving rise to energetic alkyl and surface-bound bromine fragments. In this report the authors describe the effect on the fragmentation dynamics due to systematic variation of the complexity (alkyl chain length) of the adsorbate. Increasing the length of the alkyl chain leads to distinct changes in the alkyl fragment angular distributions. For methyl bromide, the angular distribution is dominated by a focused beam of directly ejected hyperthermal methyl radicals at 44{degree} (in the [0{bar 1}] direction) from the surface normal. While a similar direct beam is observed for ethyl and propyl bromide, inelastic scattering of these fragments is found to result in increased importance of a slower diffuse cos{sup n} {theta} desorption. In addition, significant retention of alkyl fragments is detected by postirradiation thermal desorption measurements for these longer-chain homologues. Increasing the number of degrees of freedom of the adsorbate is also observed to dramatically alter the energetics of the ejection of the photofragments from the surface. As the number of carbons in the fragment is increased from one to three, the average energy of the directly ejected radicals decreases from 1.48 to 1.1 to 0.69 eV (UV incident at {lambda} = 193 nm). Variations in the energy and angular distributions are discussed in terms of initial adsorbate orientation, energy partitioning into rovibrational modes, and influence of radical-surface interactions.

  15. Adsorbed serum albumin is permissive to macrophage attachment to perfluorocarbon polymer surfaces in culture.

    PubMed

    Godek, M L; Michel, R; Chamberlain, L M; Castner, D G; Grainger, D W

    2009-02-01

    Monocyte/macrophage adhesion to biomaterials, correlated with foreign body response, occurs through protein-mediated surface interactions. Albumin-selective perfluorocarbon (FC) biomaterials are generally poorly cell-conducive because of insufficient receptor-mediated surface interactions, but macrophages bind to albumin-coated substrates and also preferentially to highly hydrophobic fluorinated surfaces. Bone marrow macrophages (BMMO) and IC-21, RAW 264.7, and J774A.1 monocyte/macrophage cells were cultured on FC surfaces. Protein deposition onto two distinct FC surfaces from complex and single-component solutions was tracked using fluorescence and time-of-flight secondary ion mass spectrometry (ToF-SIMS) methods. Cell adhesion and growth on protein pretreated substrates were compared by light microscopy. Flow cytometry and integrin-directed antibody receptor blocking were used to assess integrins critical for monocyte/macrophage adhesion in vitro. Albumin predominantly adsorbs onto both FC surfaces from 10% serum. In cultures preadsorbed with albumin or serum-dilutions, BMMO responded similar to IC-21 at early time points. Compared with Teflon AF, plasma-polymerized FC was less permissive to extended cell proliferation. The beta(2) integrins play major roles in macrophage adhesion to FC surfaces: antibody blocking significantly disrupted cell adhesion. Albumin-mediated cell adhesion mechanisms to FC surfaces could not be clarified. Primary BMMO and secondary IC-21 macrophages behave similarly on FC surfaces, regardless of preadsorbed protein biasing, with respect to adhesion, cell morphology, motility, and proliferation. PMID:18306309

  16. Simple model for chain packing and crystallization of soft colloidal polymers

    NASA Astrophysics Data System (ADS)

    Hoy, Robert S.; Karayiannis, Nikos Ch.

    2013-07-01

    We study a simple bead-spring polymer model exhibiting competing crystallization and glass transitions. Constant-pressure molecular dynamics simulations are employed to study phase behavior and morphological order. For adequately slow quench rates, chain systems exhibit a first-order phase transition (crystallization) below a critical temperature T=Tcryst. We observe the formation of close-packed crystallites of FCC and/or HCP order, separated by domain walls, twin defects, and amorphous regions. Such crystal structures closely resemble the corresponding ordered morphologies of athermal polymer packings: fully flexible chains retain random-walk-like configurations in the crystalline state and do not form lamellae, while semiflexible chains do form lamellae. The model presented here is well suited to the modeling of granular and colloidal polymers, in particular for elucidating the factors that dictate the formation of specific ordered morphologies.

  17. High-order sampling schemes for path integrals and Gaussian chain simulations of polymers

    SciTech Connect

    Müser, Martin H.; Müller, Marcus

    2015-05-07

    In this work, we demonstrate that path-integral schemes, derived in the context of many-body quantum systems, benefit the simulation of Gaussian chains representing polymers. Specifically, we show how to decrease discretization corrections with little extra computation from the usual O(1/P{sup 2}) to O(1/P{sup 4}), where P is the number of beads representing the chains. As a consequence, high-order integrators necessitate much smaller P than those commonly used. Particular emphasis is placed on the questions of how to maintain this rate of convergence for open polymers and for polymers confined by a hard wall as well as how to ensure efficient sampling. The advantages of the high-order sampling schemes are illustrated by studying the surface tension of a polymer melt and the interface tension in a binary homopolymers blend.

  18. Primitive-path statistics of entangled polymers: mapping multi-chain simulations onto single-chain mean-field models

    NASA Astrophysics Data System (ADS)

    Steenbakkers, Rudi J. A.; Tzoumanekas, Christos; Li, Ying; Liu, Wing Kam; Kröger, Martin; Schieber, Jay D.

    2014-01-01

    We present a method to map the full equilibrium distribution of the primitive-path (PP) length, obtained from multi-chain simulations of polymer melts, onto a single-chain mean-field ‘target’ model. Most previous works used the Doi-Edwards tube model as a target. However, the average number of monomers per PP segment, obtained from multi-chain PP networks, has consistently shown a discrepancy of a factor of two with respect to tube-model estimates. Part of the problem is that the tube model neglects fluctuations in the lengths of PP segments, the number of entanglements per chain and the distribution of monomers among PP segments, while all these fluctuations are observed in multi-chain simulations. Here we use a recently proposed slip-link model, which includes fluctuations in all these variables as well as in the spatial positions of the entanglements. This turns out to be essential to obtain qualitative and quantitative agreement with the equilibrium PP-length distribution obtained from multi-chain simulations. By fitting this distribution, we are able to determine two of the three parameters of the model, which govern its equilibrium properties. This mapping is executed for four different linear polymers and for different molecular weights. The two parameters are found to depend on chemistry, but not on molecular weight. The model predicts a constant plateau modulus minus a correction inversely proportional to molecular weight. The value for well-entangled chains, with the parameters determined ab initio, lies in the range of experimental data for the materials investigated.

  19. Chemically Realistic Tetrahedral Lattice Models for Polymer Chains: Application to Polyethylene Oxide.

    PubMed

    Dietschreit, Johannes C B; Diestler, Dennis J; Knapp, Ernst W

    2016-05-10

    To speed up the generation of an ensemble of poly(ethylene oxide) (PEO) polymer chains in solution, a tetrahedral lattice model possessing the appropriate bond angles is used. The distance between noncovalently bonded atoms is maintained at realistic values by generating chains with an enhanced degree of self-avoidance by a very efficient Monte Carlo (MC) algorithm. Potential energy parameters characterizing this lattice model are adjusted so as to mimic realistic PEO polymer chains in water simulated by molecular dynamics (MD), which serves as a benchmark. The MD data show that PEO chains have a fractal dimension of about two, in contrast to self-avoiding walk lattice models, which exhibit the fractal dimension of 1.7. The potential energy accounts for a mild hydrophobic effect (HYEF) of PEO and for a proper setting of the distribution between trans and gauche conformers. The potential energy parameters are determined by matching the Flory radius, the radius of gyration, and the fraction of trans torsion angles in the chain. A gratifying result is the excellent agreement of the pair distribution function and the angular correlation for the lattice model with the benchmark distribution. The lattice model allows for the precise computation of the torsional entropy of the chain. The generation of polymer conformations of the adjusted lattice model is at least 2 orders of magnitude more efficient than MD simulations of the PEO chain in explicit water. This method of generating chain conformations on a tetrahedral lattice can also be applied to other types of polymers with appropriate adjustment of the potential energy function. The efficient MC algorithm for generating chain conformations on a tetrahedral lattice is available for download at https://github.com/Roulattice/Roulattice . PMID:27045228

  20. Interplay between chain stiffness and excluded volume of semiflexible polymers confined in nanochannels

    NASA Astrophysics Data System (ADS)

    Muralidhar, Abhiram; Tree, Douglas R.; Wang, Yanwei; Dorfman, Kevin D.

    2014-02-01

    The properties of channel-confined semiflexible polymers are determined by a complicated interplay of chain stiffness and excluded volume effects. Using Pruned-Enriched Rosenbluth Method (PERM) simulations, we study the equilibrium properties of channel-confined polymers by systematically controlling chain stiffness and excluded volume. Our calculations of chain extension and confinement free energy for freely jointed chains with and without excluded volume show excellent agreement with theoretical predictions. For ideal wormlike chains, the extension is seen to crossover from Odijk behavior in strong confinement to zero-stretching, bulk-like behavior in weak confinement. In contrast, for self-avoiding wormlike chains, we always observe that the linear scaling of the extension with the contour length is valid in the long-chain limit irrespective of the regime of confinement, owing to the coexistence of stiffness and excluded volume effects. We further propose that the long-chain limit for the extension corresponds to chain lengths wherein the projection of the end-to-end distance along the axis of the channel is nearly equal to the mean span parallel to the axis. For DNA in nanochannels, this limit was identified using PERM simulations out to molecular weights of more than 1 megabase pairs; the molecular weight of λ-DNA is found to exhibit nearly asymptotic fractional extension for channels sizes used commonly in experiments.

  1. Linear DNA-linked colloidal chains: a model to visualize polymer dynamics

    NASA Astrophysics Data System (ADS)

    Biswal, Sibani; Byrom, Julie; Du, Daniel

    2012-02-01

    We present the development of synthetic materials consisting of chains of DNA-linked paramagnetic colloids that have rigidity and length specificity. These chains have demonstrated capability for folding and self-assembly. This is classic bead-spring-bead model can be a model system to visualize polymer dynamics. Here, I will describe the formation mechanism and stability of these DNA-linked magnetic particle chains. I will also describe a model that describes the total energy landscape that describes the inter-particle interactions and provides a workable theory toward the optimization of experimental parameters in synthesizing more stable and reliable colloidal assemblies. In addition to stability, we will also present the use of a colloidal worm-like chain (WLC) model system to describe chain dynamics. We measure bending rigidity by monitoring the thermal fluctuations of the chains. We show that the persistence length of the chains can be tuned from 1 to 50 mm (L/LP = 0.002 - 0.1), by changing the length of the DNA used to link adjacent particles from 75 to 15 bases. We also will show that the bending relaxation dynamics of these chains, which match well with theoretical predictions, further supporting the validity of using these colloidal chains as models for semiflexible polymer systems in both equilibrium and dynamic studies.

  2. Disorder, pre-stress and non-affinity in polymer 8-chain models

    NASA Astrophysics Data System (ADS)

    Cioroianu, Adrian R.; Spiesz, Ewa M.; Storm, Cornelis

    2016-04-01

    To assess the role of single-chain elasticity, non-affine strain fields and pre-stressed reference states we present and discuss the results of numerical and analytical analyses of a modified 8-chain Arruda-Boyce model for cross-linked polymer networks. This class of models has proved highly successful in modeling the finite-strain response of flexible rubbers. We extend it to include the effects of spatial disorder and the associated non-affinity, and use it to assess the validity of replacing the constituent chain's nonlinear elastic response with equivalent linear, Hookean springs. Surprisingly, we find that even in the regime of linear response, the full polymer model gives very different results from its linearized counterpart, even though none of the chains are stretched beyond their linear regime. We demonstrate that this effect is due to the fact that the polymer models are under considerable pre-stress in their ground state. We show that pre-stress strongly suppresses non-affinity in these unit cell models, resulting in a marked stiffening of the bulk response. Polymer networks with some degree of flexibility are thus intrinsically prestressed, and one effect of such prestresses is to reduce non-affine deformations. Combined, these findings may help explain why fully affine mechanical models, in many cases, predict the bulk mechanical response of disordered polymer networks so well.

  3. Naphthalene Tetracarboxydiimide-Based n-Type Polymers with Removable Solubility via Thermally Cleavable Side Chains.

    PubMed

    Hillebrandt, Sabina; Adermann, Torben; Alt, Milan; Schinke, Janusz; Glaser, Tobias; Mankel, Eric; Hernandez-Sosa, Gerardo; Jaegermann, Wolfram; Lemmer, Uli; Pucci, Annemarie; Kowalsky, Wolfgang; Müllen, Klaus; Lovrincic, Robert; Hamburger, Manuel

    2016-02-01

    Multilayer solution-processed devices in organic electronics show the tendency of intermixing of subsequently deposited layers. Here, we synthesize naphthalene tetracarboxydiimide (NDI)-based n-type semiconducting polymers with thermally cleavable side chains which upon removal render the polymer insoluble. Infrared and photoelectron spectroscopy were performed to investigate the pyrolysis process. Characterization of organic field-effect transistors provides insight into charge transport. After the pyrolysis homogeneous films could be produced which are insoluble in the primary solvent. By varying curing temperature and time we show that these process parameters govern the amount of side chains in the film and influence the device performance. PMID:26829619

  4. Equilibrium and shear-induced conformations of a side-chain liquid crystal polymer

    NASA Astrophysics Data System (ADS)

    Castelletto, V.; Noirez, L.; Vigoureux, P.

    2000-11-01

    These studies delineate the conformations adopted by a side-chain liquid-crystalline polymer subjected to a steady-state shear flow as well as the corresponding me so pha se director orientations. Two distinct director orientations are identified in the nematic phase, giving evidence of a shear-induced transition from a flow-aligning to a non flow-aligning behavior. This transition coincides, at rest, with a subtle change from prolate to oblate polymer main-chain conformation. In the smectic phase, the layers form multilayer cylinders oriented along the velocity axis.

  5. Anionic surfactant with hydrophobic and hydrophilic chains for nanoparticle dispersion and shape memory polymer nanocomposites.

    PubMed

    Iijima, Motoyuki; Kobayakawa, Murino; Yamazaki, Miwa; Ohta, Yasuhiro; Kamiya, Hidehiro

    2009-11-18

    An anionic surfactant comprising a hydrophilic poly(ethylene glycol) (PEG) chain, hydrophobic alkyl chain, and polymerizable vinyl group was synthesized as a capping agent of nanoparticles. TiO(2) nanoparticles modified by this surfactant were completely dispersible in various organic solvents with a wide range of polarities, such as nitriles, alcohols, ketones, and acetates. Furthermore, these particles were found to be dispersible in various polymers with different properties, such as thermosetting epoxy resins and radical polymerized poly(methylmethacrylate) (PMMA). A polymer composite of surface-modified TiO(2) nanoparticles in epoxy resins prepared by using the developed surfactant also possessed temperature-induced shape memory properties. PMID:19852463

  6. Pore translocation of polymer chains with physical knots

    NASA Astrophysics Data System (ADS)

    Suma, Antonio; Rosa, Angelo; Micheletti, Cristian

    The driven traslocation of knotted chains through narrow pores has important implications for single-molecule manipulation contexts. Its complex phenomenology is, however, still largely unexplored, both as a function of knot complexity and the magnitude of the driving, translocating force. We accordingly report on a systematic theoretical and computational investigation of both aspects. In particular we consider the case of flexible chains accommodating a large repertoire of knots that are driven through pores too narrow to allow for their passage. We show that the observed rich translocation phenomenology can be rationalised in a transparent mechanical framework that can further be used for predictive purposes.

  7. Single polymer chains in poor solvent: Using the bond fluctuation method with explicit solvent

    NASA Astrophysics Data System (ADS)

    Jentzsch, Christoph; Werner, Marco; Sommer, Jens-Uwe

    2013-03-01

    We use the bond fluctuation model with explicit solvent to study single polymer chains under poor solvent conditions. Static and dynamic properties of the bond fluctuation model with explicit solvent are compared with the implicit solvent model, and the Θ-temperatures are determined for both solvent models. We show that even in the very poor solvent regime, dynamics is not frozen for the explicit solvent model. We investigate some aspects of the structure of a single collapsed globule and show that rather large chain lengths are necessary to reach the scaling regime of a dense sphere. The force-extension curve of a single polymer chain under poor solvent conditions in the fixed end-to-end distance ensemble is analyzed. We find that the transition of the tadpole conformation to the stretched chain conformation is rather smooth because of fluctuation effects, which is in agreement with recent experimental results.

  8. Single polymer chains in poor solvent: using the bond fluctuation method with explicit solvent.

    PubMed

    Jentzsch, Christoph; Werner, Marco; Sommer, Jens-Uwe

    2013-03-01

    We use the bond fluctuation model with explicit solvent to study single polymer chains under poor solvent conditions. Static and dynamic properties of the bond fluctuation model with explicit solvent are compared with the implicit solvent model, and the Θ-temperatures are determined for both solvent models. We show that even in the very poor solvent regime, dynamics is not frozen for the explicit solvent model. We investigate some aspects of the structure of a single collapsed globule and show that rather large chain lengths are necessary to reach the scaling regime of a dense sphere. The force-extension curve of a single polymer chain under poor solvent conditions in the fixed end-to-end distance ensemble is analyzed. We find that the transition of the tadpole conformation to the stretched chain conformation is rather smooth because of fluctuation effects, which is in agreement with recent experimental results. PMID:23485321

  9. Recent advances in metathesis-derived polymers containing transition metals in the side chain.

    PubMed

    Dragutan, Ileana; Dragutan, Valerian; Simionescu, Bogdan C; Demonceau, Albert; Fischer, Helmut

    2015-01-01

    This account critically surveys the field of side-chain transition metal-containing polymers as prepared by controlled living ring-opening metathesis polymerization (ROMP) of the respective metal-incorporating monomers. Ferrocene- and other metallocene-modified polymers, macromolecules including metal-carbonyl complexes, polymers tethering early or late transition metal complexes, etc. are herein discussed. Recent advances in the design and syntheses reported mainly during the last three years are highlighted, with special emphasis on new trends for superior applications of these hybrid materials. PMID:26877797

  10. Recent advances in metathesis-derived polymers containing transition metals in the side chain

    PubMed Central

    Demonceau, Albert; Fischer, Helmut

    2015-01-01

    Summary This account critically surveys the field of side-chain transition metal-containing polymers as prepared by controlled living ring-opening metathesis polymerization (ROMP) of the respective metal-incorporating monomers. Ferrocene- and other metallocene-modified polymers, macromolecules including metal-carbonyl complexes, polymers tethering early or late transition metal complexes, etc. are herein discussed. Recent advances in the design and syntheses reported mainly during the last three years are highlighted, with special emphasis on new trends for superior applications of these hybrid materials. PMID:26877797

  11. The Frozen State in the Liquid Phase of Side-Chain Liquid-Crystal Polymers

    NASA Astrophysics Data System (ADS)

    Mendil, H.; Noirez, L.; Baroni, P.; Grillo, I.

    2006-02-01

    Quenched isotropic melts of side-chain liquid-crystal polymers reveal surprisingly an anisotropic polymer conformation. This small-angle neutron-scattering (SANS) result is consistent with the identification of a macroscopic, solidlike response in the isotropic phase. Both experiments (rheology and SANS) indicate that the polymer system appears frozen on millimeter length scales and at the time scales of the observation. This result implies that the flow behavior is not the terminal behavior and that cross-links or entanglements are not a necessary condition to provide elasticity in melts.

  12. Gene analysis of multiple oral bacteria by the polymerase chain reaction coupled with capillary polymer electrophoresis.

    PubMed

    Liu, Chenchen; Yamaguchi, Yoshinori; Sekine, Shinichi; Ni, Yi; Li, Zhenqing; Zhu, Xifang; Dou, Xiaoming

    2016-03-01

    Capillary polymer electrophoresis is identified as a promising technology for the analysis of DNA from bacteria, virus and cell samples. In this paper, we propose an innovative capillary polymer electrophoresis protocol for the quantification of polymerase chain reaction products. The internal standard method was modified and applied to capillary polymer electrophoresis. The precision of our modified internal standard protocol was evaluated by measuring the relative standard deviation of intermediate capillary polymer electrophoresis experiments. Results showed that the relative standard deviation was reduced from 12.4-15.1 to 0.6-2.3%. Linear regression tests were also implemented to validate our protocol. The modified internal standard method showed good linearity and robust properties. Finally, the ease of our method was illustrated by analyzing a real clinical oral sample using a one-run capillary polymer electrophoresis experiment. PMID:26648455

  13. Distortion of chain conformation and reduced entanglement in polymer-graphene oxide nanocomposites

    NASA Astrophysics Data System (ADS)

    Weir, Michael; Boothroyd, Stephen; Johnson, David; Thompson, Richard; Coleman, Karl; Clarke, Nigel

    Graphene and related two-dimensional materials are excellent candidates as filler materials in polymer nanocomposites due to their extraordinary physical properties and high aspect ratio. To explore the mechanism by which the filler affects the bulk properties of these unique systems, and to build understanding from the macromolecular level upwards, we use a combination of small-angle neutron scattering (SANS) and oscillatory rheology. Where a good dispersion is achieved in poly(methyl methacrylate)-graphene oxide (PMMA-GO) nanocomposites, we observe a reduction in the polymer radius of gyration with increasing GO concentration that is consistent with the predicted behavior of polymer melt chains at a solid interface. We use concepts from thin-film polymer physics to formulate a scaling relation for the reduction in entanglements caused by the GO interfaces. Using these scaling arguments, we utilize SANS results to directly estimate the changes to the elastic plateau modulus of the network of entangled polymer chains, and find a correlation with the measured bulk rheology. We present a direct link between interfacial confinement effects and the bulk polymer nanocomposite properties, whilst demonstrating a model system for measuring thin film polymer physics in the bulk.

  14. Reversible melting of extended-chain and folded-chain polymer crystals

    NASA Astrophysics Data System (ADS)

    Androsch, Rene; Wunderlich, Bernhard; Radusch, Hans-Joachim

    2005-03-01

    The reversibility of crystallization and melting of crystals of polytetrafluoroethylene (PTFE) and polyethylene (PE) of extended-chain and folded-chain morphology has been investigated by temperature-modulated differential scanning calorimetry (TMDSC). The total and average specific reversibility of folded-chain crystals is considerably larger than in the case of extended-chain crystals. This experimental observation can be attributed to a different number of points of possible decoupling between crystallized and amorphous sequences along individual, partially crystallized molecules within the globally semi-crystalline superstructure in extended-chain and folded-chain crystals. Due to incomplete melting of the macromolecules, the morphology of the folded-chain crystal allows molecular segments to reversibly melt and crystallize as a function of temperature. The extended-chain conformation, in turn, inhibits reversible melting due to the required molecular nucleation after complete melting of a single molecule. The experimental findings support both, the concepts of lateral-surface activity and molecular nucleation presented earlier.

  15. C,N-bipyrazole receptor grafted onto a porous silica surface as a novel adsorbent based polymer hybrid.

    PubMed

    Radi, Smaail; Attayibat, Ahmed; El-Massaoudi, Mohamed; Bacquet, Maryse; Jodeh, Shehdeh; Warad, Ismail; Al-Showiman, Salim S; Mabkhot, Yahia N

    2015-10-01

    A simple heterogeneous synthesis of pure adsorbent based polymer hybrid made by condensing a functionalized C,N-bipyrazole with a 3-glycidoxypropyl-trimethoxysilane silylant agent, previously anchored on a silica surface was developed. The formed material (SG2P) was characterized through elemental analysis, FT-IR spectroscopy, (13)C NMR of solid state, scanning electron microscope (SEM), and was studied and evaluated by determination of the surface area using the BET equation, the adsorption and desorption capability using the isotherm of nitrogen and B.J.H. pore sizes. The new material exhibits good thermal stability determined by thermogravimetry curves and good chemical stability was examined in various acidic and buffer solutions (pH 1-7). The binding and adsorption abilities of SG2P were investigated for Hg(2+), Cd(2+), Pb(2+), Zn(2+), K(+), Na(+) and Li(+) cations and compared to the results of classical liquid-liquid extraction with the unbound C,N-bipyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the SG2P exhibits a high selectivity toward Hg(2+) ion with no complexation being observed towards zinc and alkali metals. The extracted and the complexing cation percentages were determined by atomic absorption measurements. PMID:26078121

  16. High basicity adsorbents from solid residue of cellulose and synthetic polymer co-pyrolysis for phenol removal: Kinetics and mechanism

    NASA Astrophysics Data System (ADS)

    Lorenc-Grabowska, Ewa; Rutkowski, Piotr

    2014-10-01

    The activated carbons (ACs) produced from solid residue of cellulose and synthetic polymer co-pyrolysis (CACs) and commercial activated carbon from coconut shell (GC) were used for phenol removal. The adsorption kinetics and mechanism were investigated. All studied activated carbons are predominantly microporous and are characterized by basic surface characteristics. Surface area SBET varies between 1235 and 1499 m2/g, whereas the pHPZC changes from 7.70 to 10.63. The bath adsorption of phenol (P) was carried out at ambient temperature. The equilibrium time and equilibrium sorption capacity were determined. It was found that the boundary layer effect is bigger in AC with high basic characteristics of the surface. The rate controlling step is the intraparticle diffusion in CACs only, whereas in ACs with higher amount of acidic functionalities the adsorbate-surface interaction influences the rate of kinetic as well. The equilibrium isotherms are L2 type for commercial AC and L4 for CACs. The CACs are characterized by very high adsorption capacity that vary between 312 and 417 mg/g. The main mechanism of phenol adsorption is micropore filling within pores smaller than 1.4 nm. In the absence of solvent effect further adsorption of phenol on CACs takes place. The enhanced adsorption is due to dispersive/repulsive interaction induced by oxygen functionalities.

  17. Capillary electrophoresis-mass spectrometry of basic proteins using a new physically adsorbed polymer coating. Some applications in food analysis.

    PubMed

    Simó, Carolina; Elvira, Carlos; González, Nieves; San Román, J; Barbas, Coral; Cifuentes, Alejandro

    2004-07-01

    A new physically adsorbed capillary coating for capillary electrophoresis-mass spectrometry (CE-MS) of basic proteins is presented, which is easily obtained by flushing the capillary with a polymer aqueous solution for two min. This coating significantly reduces the electrostatic adsorption of a group of basic proteins (i.e., cytochrome c, lysozyme, and ribonuclease A) onto the capillary wall allowing their analysis by CE-MS. The coating protocol is compatible with electrospray inonization (ESI)-MS via the reproducible separation of the standard basic proteins (%RSD values (n = 5) < 1% for analysis time reproducibility and < 5% for peak heights, measured from the total ion electropherograms (TIEs) within the same day). The LODs determined using cytochrome c with total ion current and extracted ion current defection were 24.5 and 2.9 fmol, respectively. Using this new coating lysozymes from chicken and turkey egg white could be easily distinguished by CE-MS, demonstrating the usefulness of this method to differentiate animal species. Even after sterilization at 120 degrees C for 30 min, lysozyme could be detected, as well as in wines at concentrations much lower than the limit marked by the EC Commission Regulation. Adulteration of minced meat with 5% of egg-white could also be analysed by our CE-MS protocol. PMID:15237406

  18. Correlation functions of main-chain polymer nematics constrained by tensorial and vectorial conservation laws.

    PubMed

    Svenšek, Daniel; Podgornik, Rudolf

    2015-09-21

    We present and analyze correlation functions of a main-chain polymer nematic in a continuum worm-like chain description for two types of constraints formalized by the tensorial and vectorial conservation laws, both originating in the microscopic chain integrity, i.e., the connectivity of the polymer chains. In particular, our aim is to identify the features of the correlation functions that are most susceptible to the differences between the two constraints. Besides the density and director autocorrelations in both the tensorial and vectorial cases, we calculate also the density-director correlation functions, the latter being a direct signature of the presence of a specific constraint. Its amplitude is connected to the strength of the constraint and is zero if none of the constraints are present, i.e., for a standard non-polymeric nematic. Generally, the correlation functions with the constraints differ substantially from the correlation functions in the non-polymeric case, if the constraints are strong which in practice requires long chains. Moreover, for the tensorial conservation law to be well distinguishable from the vectorial one, the chain persistence length should be much smaller than the total length of the chain, so that hairpins (chain backfolding) are numerous and the polar order is small. PMID:26395733

  19. On the thermodynamic and kinetic investigations of a [c2]daisy chain polymer

    SciTech Connect

    Hmadeh, Mohamad; Fang, Lei; Trabolsi, Ali; Elhabiri, Mourad; Albrecht-Gary, Anne-Marie; Stoddart, J. Fraser

    2010-01-01

    We report a variety of [c2]daisy chain molecules which undergo quantitative, efficient, and fully reversible molecular movements upon the addition of base/acid in organic solvents. Such externally triggered molecular movements can induce the contraction and extension of the [c2]daisy chain molecule as a whole. A linear polymer of such a bistable [c2]daisy chain exerts similar types of movements and can be looked upon as a candidate for the development of artificial muscles. The spectrophotometric investigations of both the monomeric and polymeric bistable [c2]daisy chains, as well as the corresponding model compounds, were performed in MeCN at room temperature, in order to obtain the thermodynamic parameters for these mechanically interlocked molecules. Based on their spectrophotometric and thermodynamic characteristics, kinetic analysis of the acid/base-induced contraction and extension of the [c2]daisy chain monomer and polymer were conducted by employing a stopped-flow technique. These kinetic data suggest that the rates of contraction and extension for these [c2]daisy chain molecules are determined by the thermodynamic stabilities of the corresponding kinetic intermediates. Faster switching rates for both the contraction and extension processes of the polymeric [c2]daisy chain were observed when compared to those of its monomeric counterpart. These kinetic and thermodynamic investigations on [c2]daisy chain-based muscle-like compounds provide important information for those seeking an understanding of the mechanisms of actuation in mechanically interlocked macromolecules.

  20. Correlation functions of main-chain polymer nematics constrained by tensorial and vectorial conservation laws

    NASA Astrophysics Data System (ADS)

    Svenšek, Daniel; Podgornik, Rudolf

    2015-09-01

    We present and analyze correlation functions of a main-chain polymer nematic in a continuum worm-like chain description for two types of constraints formalized by the tensorial and vectorial conservation laws, both originating in the microscopic chain integrity, i.e., the connectivity of the polymer chains. In particular, our aim is to identify the features of the correlation functions that are most susceptible to the differences between the two constraints. Besides the density and director autocorrelations in both the tensorial and vectorial cases, we calculate also the density-director correlation functions, the latter being a direct signature of the presence of a specific constraint. Its amplitude is connected to the strength of the constraint and is zero if none of the constraints are present, i.e., for a standard non-polymeric nematic. Generally, the correlation functions with the constraints differ substantially from the correlation functions in the non-polymeric case, if the constraints are strong which in practice requires long chains. Moreover, for the tensorial conservation law to be well distinguishable from the vectorial one, the chain persistence length should be much smaller than the total length of the chain, so that hairpins (chain backfolding) are numerous and the polar order is small.

  1. Synthesis, Development, and Testing of High-Surface-Area Polymer-Based Adsorbents for the Selective Recovery of Uranium from Seawater

    DOE PAGESBeta

    Oyola, Yatsandra; Janke, Christopher J.; Dai, Sheng

    2016-02-29

    The ocean contains uranium with an approximate concentration of 3.34 ppb, which can serve as an incredible supply source to sustain nuclear energy in the United States. Unfortunately, technology currently available to recover uranium from seawater is not efficient enough and mining uranium on land is still more economical. For this study, we have developed polymer-based adsorbents with high uranium adsorption capacities by grafting amidoxime onto high-surface-area polyethylene (PE) fibers. Various process conditions have been screened, in combination with developing a rapid testing protocol (<24 h), to optimize the process. These adsorbents are synthesized through radiation-induced grafting of acrylonitrile (AN)more » and methacrylic acid (MAA) onto PE fibers, followed by the conversion of nitriles to amidoximes and basic conditioning. In addition, the uranium adsorption capacity, measured in units of gU/kgads, is greatly increased by reducing the diameter of the PE fiber or changing its morphology. An increase in the surface area of the PE polymer fiber allows for more grafting sites that are positioned in more-accessible locations, thereby increasing access to grafted molecules that would normally be located in the interior of a fiber with a larger diameter. Polymer fibers with hollow morphologies are able to adsorb beyond 1 order of magnitude more uranium from simulated seawater than current commercially available adsorbents. Finally, several high-surface-area fibers were tested in natural seawater and were able to extract 5–7 times more uranium than any adsorbent reported to date.« less

  2. Chain entanglements and fracture energy in interfaces between immiscible polymers

    NASA Astrophysics Data System (ADS)

    Silvestri, Leonardo; Brown, Hugh R.; Carrà, Stefano; Carrà, Sergio

    2003-10-01

    It is a very well-known experimental fact that the toughness of interfaces obtained by joining pairs of immiscible glassy polymers is strongly correlated to the interfacial width. Several models have been proposed in the literature to estimate the fracture energy of these interfaces, but the agreement displayed with the experimental data cannot be considered satisfactory. In this paper a new model is proposed for polymers with molecular weight higher than the critical value for the onset of entanglements. The model is based on a precise and realistic calculation of the areal density of entangled strands across the interface, that is the crucial parameter determining the toughness of the glassy joints. In this paper a new fracture regime is also introduced, called "partial crazing," corresponding to a situation where, due to the fact that some of the load-bearing strands are broken during plastic deformation, the craze can start, but not fully develop. Model predictions are then compared with a series of literature fracture energy experimental data, showing excellent agreement.

  3. Novel Fluorinated Polymers Containing Short Perfluorobutyl Side Chains and Their Super Wetting Performance on Diverse Substrates.

    PubMed

    Jiang, Jingxian; Zhang, Guangfa; Wang, Qiongyan; Zhang, Qinghua; Zhan, Xiaoli; Chen, Fengqiu

    2016-04-27

    Because the emission of perfluorooctanoic acid (PFOA) was completely prohibited in 2015, the widely used poly- and perfluoroalkyl substances with long perfluoroalkyl groups must be substituted by environmentally friendly alternatives. In this study, one kind of potential alternative (i.e., fluorinated polymers with short perfluorobutyl side chains) has been synthesized from the prepared monomers {i.e., (perfluorobutyl)ethyl acrylate (C4A), (perfluorobutyl)ethyl methacrylate (C4MA), 2-[[[[2-(perfluorobutyl)]sulfonyl]methyl]amino]ethyl acrylate (C4SA), and methacrylate (C4SMA)}, and the microstructure, super wetting performance, and applications of the synthesized fluorinated polymers were systematically investigated. The thermal and crystallization behaviors of the fluoropolymer films were characterized by differential scanning calorimetry and wide-angle X-ray diffraction analysis, respectively. Dynamic water-repellent models were constructed. The stable low surface energy and dynamic water- and oil-repellent properties of these synthesized fluorinated polymers with short perfluorobutyl side chains were attributed to the synergetic effect of amorphous fluorinated side chains in perfluoroalkyl acrylate and crystalline hydrocarbon pendant groups in stearyl acrylate. Outstanding water- and oil-repellent properties of fabrics and any other substrates could be achieved by a facile dip-coating treatment using a fluorinated copolymer dispersion. As a result, we believe that our prepared fluorinated copolymers are potential candidates to replace the fluoroalkylated polymers with long perfluorinated chains in nonstick and self-cleaning applications in our daily life. PMID:27052113

  4. Novel effects of chain flexibility, external force, and background stochasticity on polymer translocation

    NASA Astrophysics Data System (ADS)

    Sung, Wokyung

    2011-03-01

    The polymer translocation through membranes and the polymer crossing over activation barriers in general, are ubiquitous in cell biology and biotechnological applications. Because they are interconnected flexible systems, polymers in translocation incur entropic barriers but can thermally surmount them with unusual sensitivity to background biases. In the presence of non-equilibrium noises characteristic of living environments, the translocation can speed up much when resonant activation occurs. As a related issue, I will also discuss the problem of polymer surmounting a potential barrier, where the chain flexibility enhances the crossing. Furthermore, when the chain flexibility leads to conformational changes, the crossing rate can be even more dramatically increased. This conformational flexibility and variability enhance the stochastic resonance, where the chain crossing dynamics at an optimal temperature and chain length is maximally coherent and resonant to a minute periodic force. Utilizing the self-organizing behaviors mentioned above, we may learn about bio-molecular machinery of living as well as clever means of manipulating it. Korea Research Foundation.

  5. Z-Group ketone chain transfer agents for RAFT polymer nanoparticle modification via hydrazone conjugation

    PubMed Central

    Bandyopadhyay, Saibal; Xia, Xin; Maiseiyeu, Andrei; Mihai, Georgeta; Rajagopalan, Sanjay

    2012-01-01

    A ketal-containing trithiocarbonyl compound has been synthesized and characterized as a chain transfer agent (CTA) in Reversible Addition Fragmentation Transfer (RAFT) polymerization. The ketal functionality does not interfere with RAFT polymerization of acrylate monomers, which proceeds as previously reported to yield macro-CTA polymers and block co-polymers. Post-polymerization ketal cleavage revealed ketone functionality at the polar terminus of an amphiphilic block co-polymer. Hydrazone-formation was facile in both organic solution as well as in aqueous buffer where polymer nanoparticle assemblies were formed, indicating a conjugation/end-functionalization yield of 40–50%. Conjugation was verified with fluorescein, biotin and Gd-DOTA derivatives, and though the trithiocarbonate linkage is hydrolytically labile, we observed stable conjugation for several days at pH 7.4. and 37°C. As expected, streptavidin binding to biotinylated polymer micelles was observed, and size-change based relaxivity increases were observed when Gd-DOTA hydrazide was conjugated to polymer micelles. Cell-uptake of fluorescently labeled polymer micelles was also readily tracked by FACS and fluorescence microscopy. These polymer derivatives demonstrate a range of potential theranostic/biotechnological applications for this conveniently accessible keto-CTA, which include ligand-based nanoparticle targeting and fluorescent/MR nanoparticle contrast agents. PMID:23148126

  6. Main chain acid-degradable polymers for the delivery of bioactive materials

    DOEpatents

    Frechet, Jean M. J.; Standley, Stephany M.; Jain, Rachna; Lee, Cameron C.

    2012-03-20

    Novel main chain acid degradable polymer backbones and drug delivery systems comprised of materials capable of delivering bioactive materials to cells for use as vaccines or other therapeutic agents are described. The polymers are synthesized using monomers that contain acid-degradable linkages cleavable under mild acidic conditions. The main chain of the resulting polymers readily degrade into many small molecules at low pH, but remain relatively stable and intact at physiological pH. The new materials have the common characteristic of being able to degrade by acid hydrolysis under conditions commonly found within the endosomal or lysosomal compartments of cells thereby releasing their payload within the cell. The materials can also be used for the delivery of therapeutics to the acidic regions of tumors and other sites of inflammation.

  7. The effect of chain rigidity on the interfacial layer thickness and dynamics of polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Cheng, Shiwang; Carrillo, Jan-Michael Y.; Carroll, Bobby; Sumpter, Bobby G.; Sokolov, Alexei P.

    There are growing experimental evidences showing the existence of an interfacial layer that has a finite thickness with slowing down dynamics in polymer nanocomposites (PNCs). Moreover, it is believed that the interfacial layer plays a significant role on various macroscopic properties of PNCs. A thicker interfacial layer is found to have more pronounced effect on the macroscopic properties such as the mechanical enhancement. However, it is not clear what molecular parameter controls the interfacial layer thickness. Inspired by our recent computer simulations that showed the chain rigidity correlated well with the interfacial layer thickness, we performed systematic experimental studies on different polymer nanocomposites by varying the chain stiffness. Combining small-angle X-ray scattering, broadband dielectric spectroscopy and temperature modulated differential scanning calorimetry, we find a good correlation between the polymer Kuhn length and the thickness of the interfacial layer, confirming the earlier computer simulations results. Our findings provide a direct guidance for the design of new PNCs with desired properties.

  8. First steps toward the construction of a hyperphase diagram that covers different classes of short polymer chains

    NASA Astrophysics Data System (ADS)

    Sabeur, Sid

    2014-06-01

    We present the results of a multicanonical Monte Carlo study of flexible and wormlike polymer chains, where we investigate how the polymer structures observed during the simulations, mainly coil, liquid, and crystalline structures, can help to construct a hyperphase diagram that covers different polymer classes according to their thermodynamic behavior.

  9. A Microscopic Model for Diffusion of a Polymer Chain in the Entangled Regime

    NASA Astrophysics Data System (ADS)

    Canpolat, Murat; Erzan, Ayþe; Pekcan, Önder

    1997-01-01

    In the entangled regime the reptation concept [1,2] is the most successful in describing the dynamical behavior of a single chain. Using scaling concepts some quantities such as translational diffussion coefficient for the polymer center of mass Dtr, and renewal time {t} [3] have been calculated in the reptation model. This model is used for representing the low-frequency motions of a polymer molecule in a fluid of entangled chains, neglecting rapid relaxation processes that are attributed to local conformal transitions of backbone. Helfand and collabrators have studied the kinetics of conformational transitions in chain molecules, and they find that single-bond rotations followed by the compensating rearrangement of neigboring units are predominantly responsible for local motions [4]. Such models have also been considered by Erman and co-workers [5]. The purpose of this study to understand reptation at a microscopic level. We consedir rapid relaxation processes, that are singlet- or double -bond rotations; motion along the contour of the chain is due to displacments caused by rearangements of the neighboring units. We recover the usual scaling behavior of the diffusion coefficients and relaxation times with the chain mass. Moreover, the effective activation energy that is found from the local jump model for translational motion of the chain center of mass compares favorably with experiment and is independent of the molecular weight for large enough chains [6]. We are also able to account for the apparent temperature of this "activation energy".

  10. Impact of systematic chain architecture changes on the glass transition and modulus of thin polymer films

    NASA Astrophysics Data System (ADS)

    Vogt, Bryan; Torres, Jessica; Stafford, Christopher; Register, Richard; Uhrig, David

    2012-02-01

    We will discuss two systems that significantly impact the thin film behavior with minor changes in chemistry and chain architecture. First, two polymers based on 5-(2-phenylethylnorbornene) are examined. Depending on the polymerization route chosen, the resulting polymer backbone is comprised of either bicyclic (norbornyl) units, which leads to a relatively rigid polymer with a high bulk Tg, or monocyclic (cyclopentyl) units, which leads to a more flexible structure with a lower bulk Tg. The modulus and Tg of the rigid bicyclic polymer is thickness independent down to <10 nm, whereas the modulus of the more flexible monocyclic polymer decreases with decreasing thickness. By hydrogenation of the pendant phenyl ring to the cyclohexyl counterpart, we illustrate that minor changes in the relative flexibility of the side chain do not impact the observed thin film behavior. Second, a series of polystyrene with controlled branching including linear, comb, 6-arm star and centipede. Based upon the molecular mass of the arms, the comb polymer has a significantly larger persistence length and interestingly exhibits only a modest decrease in Tg (9 K) at 5 nm, while the moduli is thickness independent.

  11. Entangled polymer chain melts: orientation and deformation dependent tube confinement and interchain entanglement elasticity

    SciTech Connect

    Sussman, Daniel; Schweizer, Kenneth

    2013-01-01

    The phenomenological reptation-tube model is based on a single chain perspective and was originally proposed to explain the remarkable viscoelastic properties of dense entangled polymer liquids. However, simulations over the last two decades have revealed a fundamental tension in the model: it assumes that bonded, single-chain backbone stresses are the sole polymer contribution to the slowly relaxing component of stress storage and elasticity, but mounting evidence suggests that at the local level of forces it is interchain contributions that dominate, as in simple liquids. Here we show that based on a chain model constructed at the level of self-consistently determined primitive paths, an explicit force-level treatment of the correlated intermolecular contributions to stress that arise from chain uncrossability can essentially quantitatively predict the entanglement plateau modulus associated with the soft rubbery response of polymer liquids. Analogies to transient localization and elasticity in glass-forming liquids are identified. Predictions for the effect of macroscopic deformation and anisotropic orientational order on the tube diameter are also made. Based on the interchain stress perspective the theory reproduces some aspects of the rheological response to shear and extensional deformations associated with the single chain tube model.

  12. Intrinsic electrical conductivity of nanostructured metal-organic polymer chains

    PubMed Central

    Hermosa, Cristina; Vicente Álvarez, Jose; Azani, Mohammad-Reza; Gómez-García, Carlos J.; Fritz, Michelle; Soler, Jose M.; Gómez-Herrero, Julio; Gómez-Navarro, Cristina; Zamora, Félix

    2013-01-01

    One-dimensional conductive polymers are attractive materials because of their potential in flexible and transparent electronics. Despite years of research, on the macro- and nano-scale, structural disorder represents the major hurdle in achieving high conductivities. Here we report measurements of highly ordered metal-organic nanoribbons, whose intrinsic (defect-free) conductivity is found to be 104 S m−1, three orders of magnitude higher than that of our macroscopic crystals. This magnitude is preserved for distances as large as 300 nm. Above this length, the presence of structural defects (~ 0.5%) gives rise to an inter-fibre-mediated charge transport similar to that of macroscopic crystals. We provide the first direct experimental evidence of the gapless electronic structure predicted for these compounds. Our results postulate metal-organic molecular wires as good metallic interconnectors in nanodevices. PMID:23591876

  13. Brownian dynamics simulations of a flexible polymer chain which includes continuous resistance and multibody hydrodynamic interactions

    NASA Astrophysics Data System (ADS)

    Butler, Jason E.; Shaqfeh, Eric S. G.

    2005-01-01

    Using methods adapted from the simulation of suspension dynamics, we have developed a Brownian dynamics algorithm with multibody hydrodynamic interactions for simulating the dynamics of polymer molecules. The polymer molecule is modeled as a chain composed of a series of inextensible, rigid rods with constraints at each joint to ensure continuity of the chain. The linear and rotational velocities of each segment of the polymer chain are described by the slender-body theory of Batchelor [J. Fluid Mech. 44, 419 (1970)]. To include hydrodynamic interactions between the segments of the chain, the line distribution of forces on each segment is approximated by making a Legendre polynomial expansion of the disturbance velocity on the segment, where the first two terms of the expansion are retained in the calculation. Thus, the resulting linear force distribution is specified by a center of mass force, couple, and stresslet on each segment. This method for calculating the hydrodynamic interactions has been successfully used to simulate the dynamics of noncolloidal suspensions of rigid fibers [O. G. Harlen, R. R. Sundararajakumar, and D. L. Koch, J. Fluid Mech. 388, 355 (1999); J. E. Butler and E. S. G. Shaqfeh, J. Fluid Mech. 468, 204 (2002)]. The longest relaxation time and center of mass diffusivity are among the quantities calculated with the simulation technique. Comparisons are made for different levels of approximation of the hydrodynamic interactions, including multibody interactions, two-body interactions, and the "freely draining" case with no interactions. For the short polymer chains studied in this paper, the results indicate a difference in the apparent scaling of diffusivity with polymer length for the multibody versus two-body level of approximation for the hydrodynamic interactions.

  14. Compliant random fields in gels formed from side-chain liquid crystalline polymers

    NASA Astrophysics Data System (ADS)

    Goldbart, Paul; Ye, Fangfu; Lu, Bing; Xing, Xiangjun

    2013-03-01

    Localized polymer-chain backbones in gels formed from side-chain liquid crystalline polymers serve to create random fields that induce local orientational order of the nematogenic pendants of the side chains. These random fields differ, however, from conventional ones, in that they are compliant, and thus themselves undergo thermal fluctuations. We develop a free energy that describes local nematic ordering in presence of such compliant random fields. In particular, we show that, as a result of this compliance, the free energy has a qualitatively new structure, unattainable via truly static random fields. We discuss the physical implications this free energy, focusing on the consequences of the compliant nature of the random fields.

  15. Sensing Polymer Chain Dynamics through Ring Topology: A Neutron Spin Echo Study.

    PubMed

    Gooßen, Sebastian; Krutyeva, Margarita; Sharp, Melissa; Feoktystov, Artem; Allgaier, Jürgen; Pyckhout-Hintzen, Wim; Wischnewski, Andreas; Richter, Dieter

    2015-10-01

    Using neutron spin echo spectroscopy, we show that the segmental dynamics of polymer rings immersed in linear chains is completely controlled by the host. This transforms rings into ideal probes for studying the entanglement dynamics of the embedding matrix. As a consequence of the unique ring topology, in long chain matrices the entanglement spacing is directly revealed, unaffected by local reptation of the host molecules beyond this distance. In shorter entangled matrices, where in the time frame of the experiment secondary effects such as contour length fluctuations or constraint release could play a role, the ring motion reveals that the contour length fluctuation is weaker than assumed in state-of-the-art rheology and that the constraint release is negligible. We expect that rings, as topological probes, will also grant direct access to molecular aspects of polymer motion which have been inaccessible until now within chains adhering to more complex architectures. PMID:26551826

  16. Thermochromism of a poly(phenylene vinylene): untangling the roles of polymer aggregate and chain conformation.

    PubMed

    Wang, Chun-Chih; Gao, Yuan; Shreve, Andrew P; Zhong, Chang; Wang, Leeyih; Mudalige, Kumara; Wang, Hsing-Lin; Cotlet, Mircea

    2009-12-17

    We report reversible thermochromism of a conjugated polymer, poly{2,5-bis[3-(N,N-diethylamino)-1-oxapropyl]-1,4-phenylenevinylene} (DAO-PPV), in diluted solutions of toluene and 1,2-dichlorobenzene. By means of temperature- and solvent-dependent steady-state spectroscopy, picosecond time-resolved photoluminescence spectroscopy, and dynamic light scattering, we provide new insights into the role of polymer aggregates in defining the thermochromic behavior of PPVs. We find DAO-PPV to exhibit a low temperature state with vibronically structured red visible absorption and emission spectra. Structurally, this low temperature state is a densely packed and disordered polymer aggregate, which contains a fraction of well-ordered, packed polymer chains. These ordered regions serve as low energy trap sites for the more disordered regions in the aggregate, thus regulating the final emission of the aggregate and imposing a vibronically resolved emission spectrum, which is usually associated with emission from one or a few chromophores. The high temperature state of DAO-PPV is a loose aggregate, with structureless absorption and emission spectra in the green visible range. Structurally, the loose aggregate is a well-solvated aggregate retaining the physical dimension of the dense aggregate but for which interchain interactions are diminished with the increase of temperature. As a result, the spectroscopic behavior of the loose aggregate is very similar if not identical to that of the single polymer chain. Increased solubility untangles polymer aggregates into single, dispersed, polymer chains, as we demonstrate here for DAO-PPV in 1,2-dichlorobenzene and at high temperature. PMID:19928846

  17. Dependence of the viscosity on the chain end dynamics in polymer melts

    NASA Astrophysics Data System (ADS)

    Paeßens, Matthias

    2003-06-01

    We compare the Rubinstein-Duke model for reptation to a model where the boundary dynamics are modified by calculating the viscosity of polymer melts. The question is investigated whether the viscosity is determined by details of the dynamics of the polymer ends or by the stretching of the polymer. Toward this end, the dependence of the viscosity on the particle density of the lattice gas models which can be identified by the stretching is determined. We show that the influence of the stretching of the polymer on the absolute value of the viscosity in the scaling limit of very long chains is much bigger than the influence of the boundary dynamics, whereas the corrections of the scaling of the viscosity depends significantly on the details of the boundary dynamics.

  18. Searching for low percolation thresholds within amphiphilic polymer membranes: The effect of side chain branching

    NASA Astrophysics Data System (ADS)

    Dorenbos, G.

    2015-06-01

    Percolation thresholds for solvent diffusion within hydrated model polymeric membranes are derived from dissipative particle dynamics in combination with Monte Carlo (MC) tracer diffusion calculations. The polymer backbones are composed of hydrophobic A beads to which at regular intervals Y-shaped side chains are attached. Each side chain is composed of eight A beads and contains two identical branches that are each terminated with a pendant hydrophilic C bead. Four types of side chains are considered for which the two branches (each represented as [C], [AC], [AAC], or [AAAC]) are splitting off from the 8th, 6th, 4th, or 2nd A bead, respectively. Water diffusion through the phase separated water containing pore networks is deduced from MC tracer diffusion calculations. The percolation threshold for the architectures containing the [C] and [AC] branches is at a water volume fraction of ˜0.07 and 0.08, respectively. These are much lower than those derived earlier for linear architectures of various side chain length and side chain distributions. Control of side chain architecture is thus a very interesting design parameter to decrease the percolation threshold for solvent and proton transports within flexible amphiphilic polymer membranes.

  19. Critical Behavior of Two Interacting Linear Polymer Chains in a Good Solvent

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjay; Singh, Yashwant

    1997-12-01

    A model of two interacting (chemically different) linear polymer chains is solved exactly using the real-space renormalization group transformation on a family of Sierpinski gasket type fractals and on a truncated 4-simplex lattice. The members of the family of the Sierpinski gasket-type fractals are characterized by an integer scale factor b which runs from 2 to ∞. The Hausdorff dimension d F of these fractals tends to 2 from below as b → ∞. We calculate the contact exponent y for the transition from the State of segregation to a State in which the two chains are entangled for b = 2-5. Using arguments based on the finite-size scaling theory, we show that for b→∞, y = 2 - v(b) d F, where v is the end-toend distance exponent of a chain. For a truncated 4-simplex lattice it is shown that the system of two chains either remains in a State in which these chains are intermingled in such a way that they cannot be told apart, in the sense that the chemical difference between the polymer chains completely drop out of the thermodynamics of the system, or in a State in which they are either zipped or entangled. We show the region of existence of these different phases separated by tricritical lines. The value of the contact exponent y is calculated at the tricritical points.

  20. Searching for low percolation thresholds within amphiphilic polymer membranes: The effect of side chain branching

    SciTech Connect

    Dorenbos, G.

    2015-06-14

    Percolation thresholds for solvent diffusion within hydrated model polymeric membranes are derived from dissipative particle dynamics in combination with Monte Carlo (MC) tracer diffusion calculations. The polymer backbones are composed of hydrophobic A beads to which at regular intervals Y-shaped side chains are attached. Each side chain is composed of eight A beads and contains two identical branches that are each terminated with a pendant hydrophilic C bead. Four types of side chains are considered for which the two branches (each represented as [C], [AC], [AAC], or [AAAC]) are splitting off from the 8th, 6th, 4th, or 2nd A bead, respectively. Water diffusion through the phase separated water containing pore networks is deduced from MC tracer diffusion calculations. The percolation threshold for the architectures containing the [C] and [AC] branches is at a water volume fraction of ∼0.07 and 0.08, respectively. These are much lower than those derived earlier for linear architectures of various side chain length and side chain distributions. Control of side chain architecture is thus a very interesting design parameter to decrease the percolation threshold for solvent and proton transports within flexible amphiphilic polymer membranes.

  1. Entropy-Driven Conformational Control of α,ω-Difunctional Bidentate-Dithiol Azo-Based Adsorbates Enables the Fabrication of Thermally Stable Surface-Grafted Polymer Films.

    PubMed

    Lee, Han Ju; Jamison, Andrew C; Lee, T Randall

    2016-06-22

    Thermally stable radical initiator monolayers were prepared from uniquely designed α,ω-difunctional adsorbates with bidentate headgroups for the growth of nanoscale polymer films on metal surfaces. The length of the spacer separating the bidentate headgroups was varied to afford 4,4'-(diazene-1,2-diyl)bis(N-(16-(3,5-bis(mercaptomethyl)phenoxy)hexadecyl)-4-cyanopentanamide) (B16), 4,4'-(diazene-1,2-diyl)bis(N-(16-(3,5-bis(mercapto-methyl)phenoxy)decyl)-4-cyanopentanamide) (B10), and 4,4'-(diazene-1,2-diyl)bis(N-(4-(3,5-bis(mercaptomethyl)phenoxy)butyl)-4-cyanopentanamide) (B4). The structural features of the self-assembled monolayers (SAMs) derived from B16, B10, and B4 were characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry, and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and compared to those derived from an analogous α,ω-difunctional adsorbate with monodentate headgroups, 4,4'-(diazene-1,2-diyl)bis(4-cyano-N-(16-mercaptohexadecyl)pentanamide (M). These studies demonstrate that the conformation (i.e., hairpin vs standing up) of the bidentate initiator adsorbates on gold surfaces was easily controlled by adjusting the concentration of the adsorbates in solution. The results of solution-phase thermal desorption tests revealed that the radical initiator monolayers generated from B16, B10, and B4 exhibit an enhanced thermal stability when compared to those generated from M. Furthermore, a study of the growth of polymer films was performed to evaluate the utility of these new bidentate adsorbate SAMs as film-development platforms for new functional materials and devices. Specifically, surface-grafted polystyrene films were successfully generated from SAMs derived from B16. In contrast, attempts to grow polystyrene films from SAMs derived from M under a variety of analogous conditions were unsuccessful. PMID:27219525

  2. Terahertz time domain and far-infrared spectroscopies of side-chain electro-optic polymers

    NASA Astrophysics Data System (ADS)

    Yamada, Toshiki; Kaji, Takahiro; Aoki, Isao; Yamada, Chiyumi; Mizuno, Maya; Saito, Shingo; Tominari, Yukihiro; Tanaka, Shukichi; Otomo, Akira

    2016-03-01

    We investigated the dielectric properties of side-chain electro-optic polymers in a broad THz frequency region (90 GHz to 7 THz). For this investigation, we used terahertz time domain spectroscopy and the absorption coefficient in a broader frequency region of up to 20 THz that was obtained by far-infrared spectroscopy. The polymers studied were a new methacrylate polymer with a high-hyperpolarizability chromophore as the sidechain, a side-chain copolymer Disperse Red 1 polymethylmethacrylate, and pure polymethylmethacrylate. The dielectric properties in the low THz frequency region (∼0.1 THz) provide us with important information about the intrinsic refractive index for ultrahigh-speed electro-optic modulation (∼100 GHz), as well as versatile information such as the absorption coefficient and dielectric loss. The THz and far-infrared spectroscopic data in the wide frequency region provide us with the fundamental data for applications of side-chain electro-optic polymers within THz generation and detection.

  3. Communication: Role of short chain branching in polymer structure and dynamics

    NASA Astrophysics Data System (ADS)

    Kim, Jun Mo; Baig, Chunggi

    2016-02-01

    A comprehensive understanding of chain-branching effects, essential for establishing general knowledge of the structure-property-phenomenon relationship in polymer science, has not yet been found, due to a critical lack of knowledge on the role of short-chain branches, the effects of which have mostly been neglected in favor of the standard entropic-based concepts of long polymers. Here, we show a significant effect of short-chain branching on the structural and dynamical properties of polymeric materials, and reveal the molecular origins behind the fundamental role of short branches, via atomistic nonequilibrium molecular dynamics and mesoscopic Brownian dynamics by systematically varying the strength of the mobility of short branches. We demonstrate that the fast random Brownian kinetics inherent to short branches plays a key role in governing the overall structure and dynamics of polymers, leading to a compact molecular structure and, under external fields, to a lesser degree of structural deformation of polymer, to a reduced shear-thinning behavior, and to a smaller elastic stress, compared with their linear analogues. Their fast dynamical nature being unaffected by practical flow fields owing to their very short characteristic time scale, short branches would substantially influence (i.e., facilitate) the overall relaxation behavior of polymeric materials under various flowing conditions.

  4. Communication: Role of short chain branching in polymer structure and dynamics.

    PubMed

    Kim, Jun Mo; Baig, Chunggi

    2016-02-28

    A comprehensive understanding of chain-branching effects, essential for establishing general knowledge of the structure-property-phenomenon relationship in polymer science, has not yet been found, due to a critical lack of knowledge on the role of short-chain branches, the effects of which have mostly been neglected in favor of the standard entropic-based concepts of long polymers. Here, we show a significant effect of short-chain branching on the structural and dynamical properties of polymeric materials, and reveal the molecular origins behind the fundamental role of short branches, via atomistic nonequilibrium molecular dynamics and mesoscopic Brownian dynamics by systematically varying the strength of the mobility of short branches. We demonstrate that the fast random Brownian kinetics inherent to short branches plays a key role in governing the overall structure and dynamics of polymers, leading to a compact molecular structure and, under external fields, to a lesser degree of structural deformation of polymer, to a reduced shear-thinning behavior, and to a smaller elastic stress, compared with their linear analogues. Their fast dynamical nature being unaffected by practical flow fields owing to their very short characteristic time scale, short branches would substantially influence (i.e., facilitate) the overall relaxation behavior of polymeric materials under various flowing conditions. PMID:26931673

  5. Ordering of anisotropic polarizable polymer chains on the full many-body level.

    PubMed

    Dean, David S; Podgornik, Rudolf

    2012-04-21

    We study the effect of dielectric anisotropy of polymers on their equilibrium ordering within mean-field theory, but with a formalism that takes into account the full n-body nature of van der Waals (vdW) forces. Dielectric anisotropy within polymers is to be expected as the electronic properties of the polymer will typically be different along the polymer than across its cross section. It is therefore physically intuitive that larger charge fluctuations can be induced along the chain than perpendicular to it. We show that this dielectric anisotropy leads to n-body interactions which can induce an isotropic-nematic transition. The two body and three body components of the full vdW interaction are extracted and it is shown how the two body term behaves like the phenomenological self-aligning-pairwise nematic interaction. At the three body interaction level we see that the nematic phase that is energetically favorable is discotic, however, on the full n-body interaction level we find that the normal axial nematic phase is always the stable ordered phase. The n-body nature of our approach also shows that the key parameter driving the nematic-isotropic transition is the bare persistence length of the polymer chain. PMID:22519348

  6. Inorganic polymers: morphogenic inorganic biopolymers for rapid prototyping chain.

    PubMed

    Müller, Werner E G; Schröder, Heinz C; Shen, Zhijian; Feng, Qingling; Wang, Xiaohong

    2013-01-01

    In recent years, considerable progress has been achieved towards the development of customized scaffold materials, in particular for bone tissue engineering and repair, by the introduction of rapid prototyping or solid freeform fabrication techniques. These new fabrication techniques allow to overcome many problems associated with conventional bone implants, such as inadequate external morphology and internal architecture, porosity and interconnectivity, and low reproducibility. However, the applicability of these new techniques is still hampered by the fact that high processing temperature or a postsintering is often required to increase the mechanical stability of the generated scaffold, as well as a post-processing, i.e., surface modification/functionalization to enhance the biocompatibility of the scaffold or to bind some bioactive component. A solution might be provided by the introduction of novel inorganic biopolymers, biosilica and polyphosphate, which resist harsh conditions applied in the RP chain and are morphogenetically active and do not need supplementation by growth factors/cytokines to stimulate the growth and the differentiation of bone-forming cells. PMID:24420716

  7. Lattice model of linear telechelic polymer melts. I. Inclusion of chain semiflexibility in the lattice cluster theory

    NASA Astrophysics Data System (ADS)

    Xu, Wen-Sheng; Freed, Karl F.

    2015-07-01

    The lattice cluster theory (LCT) for the thermodynamics of polymer systems has recently been reformulated to treat strongly interacting self-assembling polymers composed of fully flexible linear telechelic chains [J. Dudowicz and K. F. Freed, J. Chem. Phys. 136, 064902 (2012)]. Here, we further extend the LCT for linear telechelic polymer melts to include a description of chain semiflexibility, which is treated by introducing a bending energy penalty whenever a pair of consecutive bonds from a single chain lies along orthogonal directions. An analytical expression for the Helmholtz free energy is derived for the model of semiflexible linear telechelic polymer melts. The extension provides a theoretical tool for investigating the influence of chain stiffness on the thermodynamics of self-assembling telechelic polymers, and for further exploring the influence of self-assembly on glass formation in such systems.

  8. Lattice model of linear telechelic polymer melts. I. Inclusion of chain semiflexibility in the lattice cluster theory.

    PubMed

    Xu, Wen-Sheng; Freed, Karl F

    2015-07-14

    The lattice cluster theory (LCT) for the thermodynamics of polymer systems has recently been reformulated to treat strongly interacting self-assembling polymers composed of fully flexible linear telechelic chains [J. Dudowicz and K. F. Freed, J. Chem. Phys. 136, 064902 (2012)]. Here, we further extend the LCT for linear telechelic polymer melts to include a description of chain semiflexibility, which is treated by introducing a bending energy penalty whenever a pair of consecutive bonds from a single chain lies along orthogonal directions. An analytical expression for the Helmholtz free energy is derived for the model of semiflexible linear telechelic polymer melts. The extension provides a theoretical tool for investigating the influence of chain stiffness on the thermodynamics of self-assembling telechelic polymers, and for further exploring the influence of self-assembly on glass formation in such systems. PMID:26178121

  9. Lattice model of linear telechelic polymer melts. I. Inclusion of chain semiflexibility in the lattice cluster theory

    SciTech Connect

    Xu, Wen-Sheng; Freed, Karl F.

    2015-07-14

    The lattice cluster theory (LCT) for the thermodynamics of polymer systems has recently been reformulated to treat strongly interacting self-assembling polymers composed of fully flexible linear telechelic chains [J. Dudowicz and K. F. Freed, J. Chem. Phys. 136, 064902 (2012)]. Here, we further extend the LCT for linear telechelic polymer melts to include a description of chain semiflexibility, which is treated by introducing a bending energy penalty whenever a pair of consecutive bonds from a single chain lies along orthogonal directions. An analytical expression for the Helmholtz free energy is derived for the model of semiflexible linear telechelic polymer melts. The extension provides a theoretical tool for investigating the influence of chain stiffness on the thermodynamics of self-assembling telechelic polymers, and for further exploring the influence of self-assembly on glass formation in such systems.

  10. Oligomer-to-polymer transition in short ethylene glycol chains connected to mobile hydrophobic anchors.

    PubMed

    Tanaka, Motomu; Rehfeldt, Florian; Schneider, Matthias F; Gege, Christian; Schmidt, Richard R; Funari, Sérgio S

    2005-01-01

    We studied the structure of short ethylene glycol (EG) chains with N repeating units (EGN, N = 3, 6, 9, 12, and 15) connected to hydrophobic dihexadecyl chains by means of a combination of differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS/WAXS). These synthetic amphiphiles dispersed in water form planar lamellar stacks and hexagonal cylinders confining the EG chains to restricted geometries. Owing to the self-assembly of the anchoring points, the lateral density of EG chains in planar lamella can be quantitatively controlled. Furthermore, the chain-melting phase transition of the anchors enables us to "switch" the intermolecular distance reversibly. SAXS/WAXS results suggest that the shorter EG chains (N = 3, 6, and 9) assume a helical conformation in stacks of planar lamella. When the EG chains are further elongated (N = 12 and 15), the lamellar periodicities cannot be explained by a linear extrapolation of shorter oligomers, but can be interpreted well as polymer brushes following the scaling theorem. Such rich phase behaviors of EGN molecules can be used as a simple model of oligo/poly-saccharide chains on cell surfaces, which act not only as flexible repellers between neighboring cells but also as stable spacers for functional ligands. PMID:15688653

  11. Unlocking Chain Exchange in Highly Amphiphilic Block Polymer Micellar Systems: Influence of Agitation

    PubMed Central

    2015-01-01

    Chain exchange between block polymer micelles in highly selective solvents, such as water, is well-known to be arrested under quiescent conditions, yet this work demonstrates that simple agitation methods can induce rapid chain exchange in these solvents. Aqueous solutions containing either pure poly(butadiene-b-ethylene oxide) or pure poly(butadiene-b-ethylene oxide-d4) micelles were combined and then subjected to agitation by vortex mixing, concentric cylinder Couette flow, or nitrogen gas sparging. Subsequently, the extent of chain exchange between micelles was quantified using small angle neutron scattering. Rapid vortex mixing induced chain exchange within minutes, as evidenced by a monotonic decrease in scattered intensity, whereas Couette flow and sparging did not lead to measurable chain exchange over the examined time scale of hours. The linear kinetics with respect to agitation time suggested a surface-limited exchange process at the air–water interface. These findings demonstrate the strong influence of processing conditions on block polymer solution assemblies. PMID:25642383

  12. Effect of chain stiffness on structural and thermodynamic properties of polymer melts

    NASA Astrophysics Data System (ADS)

    Luettmer-Strathmann, Jutta

    2008-03-01

    Static and dynamic properties of polymers are affected by the stiffness of the chains. In this work, we investigate structural and thermodynamic properties of a lattice model for semiflexible polymer chains. The model is an extension of Shaffer's bond- fluctuation model [1] and includes attractive interactions between monomers and an adjustable bending penalty that determines the Kuhn segment length. For isolated chains, a competition between monomer-monomer interactions and bending penalties determines the chain conformations at low temperatures. For dense melts, packing effects play an important role in the structure and thermodynamics of the polymeric liquid. In order to investigate static properties as a function of temperature and chain stiffness, we perform Wang-Landau type simulations and construct densities of states over the two- dimensional state space of monomer-monomer and bending contributions to the internal energy. In addition, we present first results from an algorithm for equation-of-state effects in lattice models. [1] J. S. Shaffer, J. Chem. Phys. 101, 4205 (1994).

  13. Consistent model reduction of polymer chains in solution in dissipative particle dynamics: Model description

    NASA Astrophysics Data System (ADS)

    Moreno, Nicolas; Nunes, Suzana P.; Calo, Victor M.

    2015-11-01

    We introduce a framework for model reduction of polymer chain models for dissipative particle dynamics (DPD) simulations, where the properties governing the phase equilibria such as the characteristic size of the chain, compressibility, density, and temperature are preserved. The proposed methodology reduces the number of degrees of freedom required in traditional DPD representations to model equilibrium properties of systems with complex molecules (e.g., linear polymers). Based on geometrical considerations we explicitly account for the correlation between beads in fine-grained DPD models and consistently represent the effect of these correlations in a reduced model, in a practical and simple fashion via power laws and the consistent scaling of the simulation parameters. In order to satisfy the geometrical constraints in the reduced model we introduce bond-angle potentials that account for the changes in the chain free energy after the model reduction. Following this coarse-graining process we represent high molecular weight DPD chains (i.e.,  ≥ 200 beads per chain) with a significant reduction in the number of particles required (i.e.,  ≥ 20 times the original system). We show that our methodology has potential applications modeling systems of high molecular weight molecules at large scales, such as diblock copolymer and DNA.

  14. Effect of chain stiffness on interfacial slip in nanoscale polymer films

    NASA Astrophysics Data System (ADS)

    Priezjev, Nikolai

    2013-11-01

    The results obtained from molecular dynamics simulations of the friction at an interface between polymer melts and weakly attractive crystalline surfaces are reported. We consider a coarse-grained bead-spring model of linear chains with adjustable intrinsic stiffness. The structure and relaxation dynamics of polymer chains near interfaces are quantified by the radius of gyration and decay of the time autocorrelation function of the first normal mode. We found that the friction coefficient at small slip velocities exhibits a distinct maximum which appears due to shear-induced alignment of semiflexible chain segments in contact with solid walls. At large slip velocities, the friction coefficient is independent of the chain stiffness. The data for the friction coefficient and shear viscosity are used to elucidate main trends in the nonlinear shear rate dependence of the slip length. The influence of chain stiffness on the relationship between the friction coefficient and the structure factor in the first fluid layer is discussed. Financial support from the National Science Foundation (CBET-1033662) is gratefully acknowledged.

  15. Effect of cation type, alkyl chain length, adsorbate size on adsorption kinetics and isotherms of bromide ionic liquids from aqueous solutions onto microporous fabric and granulated activated carbons.

    PubMed

    Hassan, Safia; Duclaux, Laurent; Lévêque, Jean-Marc; Reinert, Laurence; Farooq, Amjad; Yasin, Tariq

    2014-11-01

    The adsorption from aqueous solution of imidazolium, pyrrolidinium and pyridinium based bromide ionic liquids (ILs) having different alkyl chain lengths was investigated on two types of microporous activated carbons: a fabric and a granulated one, well characterized in terms of surface chemistry by "Boehm" titrations and pH of point of zero charge measurements and of porosity by N2 adsorption at 77 K and CO2 adsorption at 273 K. The influence of cation type, alkyl chain length and adsorbate size on the adsorption properties was analyzed by studying kinetics and isotherms of eight different ILs using conductivity measurements. Equilibrium studies were carried out at different temperatures in the range [25-55 °C]. The incorporation of ILs on the AC porosity was studied by N2 adsorption-desorption measurements at 77 K. The experimental adsorption isotherms data showed a good correlation with the Langmuir model. Thermodynamic studies indicated that the adsorption of ILs onto activated carbons was an exothermic process, and that the removal efficiency increased with increase in alkyl chain length, due to the increase in hydrophobicity of long chain ILs cations determined with the evolution of the calculated octanol-water constant (Kow). The negative values of free energies indicated that adsorption of ILs with long chain lengths having hydrophobic cations was more spontaneous at the investigated temperatures. PMID:24929502

  16. Interaction of Nano-Sized Materials With Polymer Chains in Polymer-Nanocomposite Thin Films-An AFM Perspective

    SciTech Connect

    Verma, Gaurav; Kaushik, Anupama; Ghosh, Anup K.

    2011-12-12

    Nanocomposite thin films were prepared with polyurethane as a matrix and organically modified clay as a filler. The interfacial interaction between the exfoliated clay nanoplatelets and the polymeric chains has been investigated by using Atomic Force Microscopy (AFM). The nanoclay platelets show a preferential association with the hard domains of polyurethane matrix on the surface of the thin films. The pendant hydroxyl group on the nanoplatelets attract the isocyanate of the polyisocyanate and a urethane group is formed. This leads to the 'clouding' and 'entwining' of the nanoplatelets by the hard segmental chains. This is the first visual evidence of nanomaterial filler and polymer matrix interaction and it could open up a spectrum of novel property achievements in nanocomposite thin films. Also the understanding of this interaction can lead to more controlled architecture of nanocomposites.

  17. Interplay between polymer chain conformation and nanoparticle assembly in model industrial silica/rubber nanocomposites.

    PubMed

    Bouty, Adrien; Petitjean, Laurent; Chatard, Julien; Matmour, Rachid; Degrandcourt, Christophe; Schweins, Ralf; Meneau, Florian; Kwasńiewski, Paweł; Boué, François; Couty, Marc; Jestin, Jacques

    2016-04-12

    The question of the influence of nanoparticles (NPs) on chain dimensions in polymer nanocomposites (PNCs) has been treated mainly through the fundamental way using theoretical or simulation tools and experiments on well-defined model PNCs. Here we present the first experimental study on the influence of NPs on the polymer chain conformation for PNCs designed to be as close as possible to industrial systems employed in the tire industry. PNCs are silica nanoparticles dispersed in a styrene-butadiene-rubber (SBR) matrix whose NP dispersion can be managed by NP loading with interfacial coatings or coupling additives usually employed in the manufacturing mixing process. We associated specific chain (d) labeling, and the so-called zero average contrast (ZAC) method, with SANS, in situ SANS and SAXS/TEM experiments to extract the polymer chain scattering signal at rest for non-cross linked and under stretching for cross-linked PNCs. NP loading, individual clusters or connected networks, as well as the influence of the type, the quantity of interfacial agent and the influence of the elongation rate have been evaluated on the chain conformation and on its related deformation. We clearly distinguish the situations where the silica is perfectly matched from those with unperfected matching by direct comparison of SANS and SAXS structure factors. Whatever the silica matching situation, the additive type and quantity and the filler content, there is no significant change in the polymer dimension for NP loading up to 15% v/v within a range of 5%. One can see an extra scattering contribution at low Q, as often encountered, enhanced for non-perfect silica matching but also visible for perfect filler matching. This contribution can be qualitatively attributed to specific h or d chain adsorption on the NP surface inside the NP cluster that modifies the average scattering neutron contrast of the silica cluster. Under elongation, NPs act as additional cross-linking junctions

  18. Chain conformations dictate multiscale charge transport phenomena in disordered semiconducting polymers.

    PubMed

    Noriega, Rodrigo; Salleo, Alberto; Spakowitz, Andrew J

    2013-10-01

    Existing models for the electronic properties of conjugated polymers do not capture the spatial arrangement of the disordered macromolecular chains over which charge transport occurs. Here, we present an analytical and computational description in which the morphology of individual polymer chains is dictated by well-known statistical models and the electronic coupling between units is determined using Marcus theory. The multiscale transport of charges in these materials (high mobility at short length scales, low mobility at long length scales) is naturally described with our framework. Additionally, the dependence of mobility with electric field and temperature is explained in terms of conformational variability and spatial correlation. Our model offers a predictive approach to connecting processing conditions with transport behavior. PMID:24062459

  19. Drift of a polymer chain in a porous medium —A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Avramova, K.; Milchev, A.

    2002-01-01

    We investigate the drift of an end-labeled telehelic polymer chain in a frozen disordered medium under the action of a constant force applied to the one end of the macromolecule by means of an off-lattice bead spring Monte Carlo model. The length of the polymers N is varied in the range 8chains can be interpreted as described by a scaling theory based on Pincus blobs. The variation of drag velocity with C in this interval of field intensities is qualitatively described by the law of Mackie-Meares. The threshold field intensity B_ab{c} itself is found to decrease linearly with C.

  20. Volume holographic recording in nanoparticle-polymer composites doped with multifunctional chain transfer agents

    NASA Astrophysics Data System (ADS)

    Guo, Jinxin; Fujii, Ryuta; Tomita, Yasuo

    2015-10-01

    We report on an experimental investigation of the properties of volume holographic recording in photopolymerizable nanoparticle-polymer composites (NPCs) doped with chain transferring multifunctional di- and tri-thiols as chain transfer agents. It is shown that the incorporation of the multifunctional thiols into NPCs more strongly influences on volume holographic recording than that doped with mono-thiol since more chemical reactions involve in the polymer network formation. It is found that, as similar to the case of mono-thiol doping, there exist optimum concentrations of di- and tri-thiols for maximizing the saturated refractive index modulation. It is also seen that recording sensitivity monotonically decreases with an increase in multifunctional thiol concentration due to the partial inhibition of the photopolymerization event by excessive thiols.

  1. Conformation and elasticity of a charged polymer chain bridging two nanoparticles

    SciTech Connect

    Nowicki, W. Nowicka, G.

    2013-12-07

    A complex composed of a charged flexible polymer chain irreversibly attached with its ends to surfaces of two nanoparticles was investigated using the Metropolis Monte Carlo method on a simple cubic lattice. The simulations were performed in the presence of explicit ions. The bridging chain and the nanoparticles bearing the same and the opposite sign charges were considered. Changes in the free energy of the complex upon its stretching or compression, together with the magnitude of the elastic force, were examined. The relative roles of energetic and entropic effects in determining the properties of the complex were identified. Also, the adsorption of charged monomers on the opposite-sign charged nanoparticles and its influence on the examined quantities was studied. Moreover, a simple semi-analytical approach to the thermodynamics of the polymer bridge was derived.

  2. Single-chain folding of polymers for catalytic systems in water.

    PubMed

    Terashima, Takaya; Mes, Tristan; De Greef, Tom F A; Gillissen, Martijn A J; Besenius, Pol; Palmans, Anja R A; Meijer, E W

    2011-04-01

    Enzymes are a source of inspiration for chemists attempting to create versatile synthetic catalysts. In order to arrive at a polymeric chain carrying catalytic units separated spatially, it is a prerequisite to fold these polymers in water into well-defined compartmentalized architectures thus creating a catalytic core. Herein, we report the synthesis, physical properties, and catalytic activity of a water-soluble segmented terpolymer in which a helical structure in the apolar core is created around a ruthenium-based catalyst. The supramolecular chirality of this catalytic system is the result of the self-assembly of benzene-1,3,5-tricarboxamide side chains, while the catalyst arises from the sequential ruthenium-catalyzed living radical polymerization of the different monomers followed by ligand exchange. The polymers exhibit a two-state folding process and show transfer hydrogenation in water. PMID:21405022

  3. Impact of molecular orientation on thermal conduction in linear-chain polymer films

    SciTech Connect

    Kurabayashi, K.; Goodson, K.E.

    1999-07-01

    Polymer films are serving as passive regions in fast logic circuits and as active regions in organic optoelectronic devices, such as light-emitting diodes. Recent data illustrated the strong anisotropy in the thermal conductivity of polyimide films of thickness near one micrometer, with the in-plane value larger by a factor of approximately five. This manuscript extends previous theoretical work on heat conduction in stretched bulk polymers to model the conductivity anisotropy in linear-chain polymer films. Predictions are based on the standard deviation of the angle of molecular orientation with respect to the film in-plane direction, which can be investigated using birefringence data, and the expected conductivity anisotropy in a material with perfectly-aligned strands. The modeling and previous data indicate that the anisotropy factor could increase to a value larger than 10 for polyimide films much thinner than 1 micrometer.

  4. Inducing Planar Orientation in Side‐Chain Liquid‐Crystalline Polymer Systems via Interfacial Control

    PubMed Central

    2016-01-01

    Abstract For efficient photoresponses of liquid‐crystal (LC) azobenzene (Az) polymer systems, planar LC orientation of the Az mesogenic group is required because the light irradiation process usually occurs with normal incidence to the film surface. However, LC molecules with a rodlike shape tend to orient perpendicularly to the film surface according to the excluded volume effect theory. This review introduces new approaches for inducing planar orientation in side‐chain LC Az polymer films via interface and surface molecular designs. The planar orientation offers efficient in‐plane photoalignment and photoswitching to hierarchical LC architectures from molecular LC mesogens and LC phases to mesoscopic microphase‐separated structures. These approaches are expected to provide new concepts and possibilities in new LC polymer devices. PMID:26775770

  5. Inducing Planar Orientation in Side-Chain Liquid-Crystalline Polymer Systems via Interfacial Control.

    PubMed

    Nagano, Shusaku

    2016-02-01

    For efficient photoresponses of liquid-crystal (LC) azobenzene (Az) polymer systems, planar LC orientation of the Az mesogenic group is required because the light irradiation process usually occurs with normal incidence to the film surface. However, LC molecules with a rodlike shape tend to orient perpendicularly to the film surface according to the excluded volume effect theory. This review introduces new approaches for inducing planar orientation in side-chain LC Az polymer films via interface and surface molecular designs. The planar orientation offers efficient in-plane photoalignment and photoswitching to hierarchical LC architectures from molecular LC mesogens and LC phases to mesoscopic microphase-separated structures. These approaches are expected to provide new concepts and possibilities in new LC polymer devices. PMID:26775770

  6. Biodegradation of medium chain hydrocarbons by Acinetobacter venetianus 2AW immobilized to hair-based adsorbent mats.

    PubMed

    Luckarift, Heather R; Sizemore, Susan R; Farrington, Karen E; Fulmer, Preston A; Biffinger, Justin C; Nadeau, Lloyd J; Johnson, Glenn R

    2011-01-01

    The natural attenuation of hydrocarbons can be hindered by their rapid dispersion in the environment and limited contact with bacteria capable of oxidizing hydrocarbons. A functionalized composite material is described herein, that combines in situ immobilized alkane-degrading bacteria with an adsorbent material that collects hydrocarbon substrates, and facilitates biodegradation by the immobilized bacterial population. Acinetobacter venetianus 2AW was isolated for its ability to utilize hydrophobic n-alkanes (C10-C18) as the sole carbon and energy source. Growth of strain 2AW also resulted in the production of a biosurfactant that aided in the dispersion of complex mixtures of hydrophobic compounds. Effective immobilization of strain 2AW to the surface of Ottimat™ adsorbent hair mats via vapor phase deposition of silica provided a stable and reproducible biocatalyst population that facilitates in situ biodegradation of n-alkanes. Silica-immobilized strain 2AW demonstrated ca. 85% removal of 1% (v/v) tetradecane and hexadecane within 24 h, under continuous flow conditions. The methodology for immobilizing whole bacterial cells at the surface of an adsorbent, for in situ degradation of hydrocarbons, has practical application in the bioremediation of oil in water emulsions. Published 2011 American Institute of Chemical Engineers Biotechnol Prog., 2011. PMID:21948333

  7. Path Integral Approach to a Single Polymer Chain with Random Media

    NASA Astrophysics Data System (ADS)

    Kunsombat, Ch.; Sa-Yakanit, V.

    In this paper we consider the problem of a polymer chain in random media with finite correlation. We show that the mean square end-to-end distance of a polymer chain can be obtained using the Feynman path integral developed by Feynman for treating the polaron problem and successfuly applied to the theory of heavily doped semiconductor. We show that for short-range correlation or the white Gaussian model we derive the results obtained by Edwards and Muthukumar using the replica method and for long-range correlation we obtain the result of Yohannes Shiferaw and Yadin Y. Goldschimidt. The main idea of this paper is to generalize the model proposed by Edwards and Muthukumar for short-range correlation to finite correlation. Instead of using a replica method, we employ the Feynman path integral by modeling the polymer Hamiltonian as a model of non-local quadratic trial Hamiltonian. This non-local trial Hamiltonian is essential as it will reflect the translation invariant of the original Hamiltonian. The calculation is proceeded by considering the differences between the polymer propagator and the trial propagator as the first cumulant approximation. The variational principle is used to find the optimal values of the variational parameters and the mean square end-to-end distance is obtained. Several asymptotic limits are considered and a comparison between this approaches and replica approach will be discussed.

  8. Determination of imidazole derivatives by micellar electrokinetic chromatography combined with solid-phase microextraction using activated carbon-polymer monolith as adsorbent.

    PubMed

    Shih, Yung-Han; Lirio, Stephen; Li, Chih-Keng; Liu, Wan-Ling; Huang, Hsi-Ya

    2016-01-01

    In this study, an effective method for the separation of imidazole derivatives 2-methylimidazole (2-MEI), 4- methylimidazole (4-MEI) and 2-acetyl-4-tetrahydroxybutylimidazole (THI) in caramel colors using cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-sweeping-MEKC) was developed. The limits of detection (LOD) and quantitation (LOQ) for the CSEI-sweeping-MEKC method were in the range of 4.3-80μgL(-1) and 14-270μgL(-1), respectively. Meanwhile, a rapid fabrication activated carbon-polymer (AC-polymer) monolithic column as adsorbent for solid-phase microextraction (SPME) of imidazole colors was developed. Under the optimized SPME condition, the extraction recoveries for intra-day, inter-day and column-to-column were in the range of 84.5-95.1% (<6.3% RSDs), 85.6-96.1% (<4.9% RSDs), and 81.3-96.1% (<7.1% RSDs), respectively. The LODs and LOQs of AC-polymer monolithic column combined with CSEI-sweeping-MEKC method were in the range of 33.4-60.4μgL(-1) and 111.7-201.2μgL(-1), respectively. The use of AC-polymer as SPME adsorbent demonstrated the reduction of matrix effect in food samples such as soft drink and alcoholic beverage thereby benefiting successful determination of trace-level caramel colors residues using CSEI-sweeping-MEKC method. The developed AC-polymer monolithic column can be reused for more than 30 times without any significant loss in the extraction recovery for imidazole derivatives. PMID:26363948

  9. Preparation of amino acid-based polymer functionalized magnetic nanoparticles as adsorbents for analysis of plant growth regulators in bean sprouts.

    PubMed

    Ji, Shilei; Qi, Li; Li, Nan; Wang, Minglin

    2016-09-01

    A novel magnetic solid phase extraction (MSPE) adsorbent has been developed for enriching two plant growth regulators, including 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chlorophenoxyacetic acid (4-CPA), in bean sprouts. For preparing the MSPE adsorbent, poly(N-methacryloyl-L-phenylalanine methyl ester (P(MA-L-Phe-OMe)), amino acid-based polymer, was modified onto the magnetic nanoparticles via "grafting to" method by free radical polymerization. The resultant P(MA-L-Phe-OMe)-functionalized magnetic nanoparticles (Fe3O4@P(MA-L-Phe-OMe)) were characterized by Fourier transform infrared (FT-IR) spectroscopy and elemental analysis. The adsorption amount of Fe3O4@P(MA-L-Phe-OMe) nanoparticles to 2,4-D and 4-CPA were 39.82mgg(-1) and 29.02mgg(-1), respectively. Moreover, the prepared MSPE adsorbents showed good selectivity towards 2,4-D and 4-CPA due to the hydrophobic interactions and electrostatic forces between the target analytes and Fe3O4@P(MA-L-Phe-OMe). The results demonstrated that the proposed MSPE adsorbents have high affinity to the targets 2,4-D and 4-CPA. Under the optimized conditions, the proposed materials were successfully applied to enrich 2,4-D and 4-CPA in bean sprouts samples. The recovery values of the bean sprouts solution spiked the targets were from 90.9% to 96.4% with the relative standard deviations of 2.3-3.9%. Our work proved that the novel Fe3O4@P(MA-L-Phe-OMe) nanoparticles were the good adsorbents of magnetic solid phase extraction (MSPE) and have good potential for the analysis of trace compound in real samples. PMID:27343600

  10. Folding mechanism of a polymer chain with short-range attractions

    NASA Astrophysics Data System (ADS)

    Leitold, Christian; Dellago, Christoph

    2014-10-01

    We investigate the crystallization of a single, flexible homopolymer chain using transition path sampling. The chain consists of N identical spherical monomers evolved according to Langevin dynamics. While neighboring monomers are coupled via harmonic springs, the non-neighboring monomers interact via a hard core and a short-ranged attractive potential. For a sufficiently small interaction range λ, the system undergoes a first-order freezing transition from an expanded, disordered phase to a compact crystalline state. Using a new shooting move tailored to polymers combined with a committor analysis, we study the transition state ensemble of an N = 128 chain and search for possible reaction coordinates based on likelihood maximization. We find that typical transition states consist of a crystalline nucleus with one or more chain fragments attached to it. Furthermore, we show that the number of particles in the crystalline core is not well suited as a reaction coordinate. We then present an improved reaction coordinate, which includes information from the potential energy and the overall crystallinity of the polymer.

  11. Coarse-grained description of polymer blends as chains of interacting soft particles

    NASA Astrophysics Data System (ADS)

    Walton, Kevin; Guenza, Marina

    We present an analytic pair potential in a coarse grain description of a polymer blend where each chain is represented as a chain of soft-colloidal particles. This coarse grain model is based on integral theory that can represent the chains at variable levels.The particles have soft repulsion at separation less than the size of each coarse grain unit and a long repulsive tail with small attractive portion. While the short range pieces of the potential dominates the liquid structure, the long range tail dominate the thermodynamics of the system. So an accurate potential in both the short and long range distances is need to keep give correct structure and thermodynamical properties in the coarse grain description.

  12. Topological Constraints on Chain-Folding Structure of Semicrystalline Polymer as Studied by 13C-13C Double Quantum NMR

    NASA Astrophysics Data System (ADS)

    Hong, Youlee; Miyoshi, Toshikazu

    Chain-folding process is a prominent feature of long polymer chains during crystallization. Over the last half century, much effort has been paid to reveal the chain trajectory. Even though various chain-folding models as well as theories of crystallization at molecule levels have been proposed, they could be not reconciled due to the limited experimental evidences. Recent development of double quantum NMR with selective isotope labeling identified the chain-trajectory of 13C labeled isotactic poly(1-butene). The systematic experiments covered a wide range of parameters, i.e. kinetics, concentration, and molecular weight (Mw) . It was demonstrated that i) adjacent re-entry site was invariant as a function of crystallization temperature (Tc) , concentration, andMw, ii) long-range order of adjacent re-entry sequence is independence of kinetics at a given concentration while it decreased with increasing the polymer concentration at a given Tc due to the increased interruption between the chains, and iii) high Mw chains led to the multilayer folded structures in single crystals, but the melt state induced the identical short adjacent sequences of long and short polymer over a wide range of Tc due to the entanglements. The behaviors indicated that the topological restriction plays significant roles in the chain-folding process rather than the kinetics. The proposed framework to control the chain-folding structure presents a new perspective into the chain organization by either the intra- or inter-chain interaction. National Science Foundation Grants DMR-1105829 and 1408855.

  13. Multi-functionalized side-chain supramolecular polymers: A methodology towards tunable functional materials

    NASA Astrophysics Data System (ADS)

    Nair, Kamlesh Prabhakaran

    Even as we see a significant growth in the field of supramolecular polymers in the last ten years, multi-functionalized systems have been scarcely studied. Noncovalent multi-functionalization provides unique advantages such as rapid materials optimization via reversible functionalization as well as for the tuning of materials properties by exploiting the differences in the nature of these reversible interactions. This thesis involves the design principles, synthesis & methodology of supramolecular side-chain multi-functionalized polymers. The combination of a functionally tolerant & controlled polymerization technique such as ROMP with multiple noncovalent interactions such as hydrogen bonding, metal coordination and ionic interactions has been successfully used to synthesize these polymers. Furthermore, the orthogonality between the above interactions in block/random copolymers has been studied in detail. It has been found that the studied interactions were orthogonal to each other. To validate the viability of this methodology using multiple orthogonal interactions towards materials design noncovalent crosslinking of polymers has been used as a potential application. Three classes of networks have been studied: complementary multiple hydrogen bonded networks, metal crosslinked networks, & multi-functionalized hydrogen bonded and metal coordinated networks. The first room temperature decrosslinking by exclusive complementary hydrogen bonded interactions has been successfully achieved. Furthermore network properties have been successfully tuned by varying the network micro-structure which in turn was tuned by the hydrogen bonding motifs used for inter-chain crosslinking. By combining two different noncovalent interactions used for inter-chain crosslinking, it was possible to make multi-functionalized materials whose properties could be controlled by varying the crosslinking strategy. Hence by employing multi-functionalization methodology, important materials

  14. Monte Carlo simulations to study the effect of chain stiffness on static and dynamic properties of polymer melts

    NASA Astrophysics Data System (ADS)

    Khanal, Kiran; Luettmer-Strathmann, Jutta

    2009-04-01

    Static and dynamic properties of polymers are affected by the stiffness of the chains. In this work, we investigate structural and thermodynamic properties of a lattice model for semiflexible polymer chains. The model is an extension of Shaffer's bond- fluctuation model and includes attractive interactions between monomers and an adjustable bending penalty that determines the Kuhn segment length. This allows us to model melts of flexible and semiflexible chains. For this work, we performed Monte Carlo simulations for polymer melts with a range of bending parameters and densities. Results for chain dimensions show that the Kuhn segment length increases monotonously with the bending penalty and has a linear dependence for a range of bending parameters. Results for self diffusion constants show that the translational mobility is strongly reduced by increasing chain stiffness. We also investigate equation-of-state properties of the melts.

  15. The chain sucker: translocation dynamics of a polymer chain into a long narrow channel driven by longitudinal flow.

    PubMed

    Luo, Kaifu; Metzler, Ralf

    2011-04-01

    Using analytical techniques and Langevin dynamics simulations, we investigate the dynamics of polymer translocation into a narrow channel of width R embedded in two dimensions, driven by a force proportional to the number of monomers in the channel. Such a setup mimics typical experimental situations in nano/microfluidics. During the translocation process if the monomers in the channel can sufficiently quickly assume steady state motion, we observe the scaling τ ∼ N∕F of the translocation time τ with the driving force F per bead and the number N of monomers per chain. With smaller channel width R, steady state motion cannot be achieved, effecting a nonuniversal dependence of τ on N and F. From the simulations we also deduce the waiting time distributions under various conditions for the single segment passage through the channel entrance. For different chain lengths but the same driving force, the curves of the waiting time as a function of the translocation coordinate s feature a maximum located at identical s(max), while with increasing the driving force or the channel width the value of s(max) decreases. PMID:21476775

  16. Memory effect in the chain-collapse process in a dilute polymer solution

    NASA Astrophysics Data System (ADS)

    Maki, Yasuyuki; Sasaki, Naoki; Nakata, Mitsuo

    2004-12-01

    The effect of temperature perturbation on a single-chain-collapse process was studied for poly(methyl methacrylate) with the molecular weight Mw=1.05×107 in the mixed solvent of tert-butyl alcohol+water (2.5 vol %). In the chain-collapse process after a quench from the θ temperature to a temperature T1, the temperature was changed from T1 to T2 at the time t1 after the quench and returned to T1 at the time t1+t2. In the three stages at T1, T2, and T1, measurements of the mean-square radius of gyration of polymer chains were carried out by static light scattering and the chain-collapse process was represented by the expansion factor as a function of time. An effect of chain aggregation on the measurements was negligibly small because of the very slow phase separation. For the negative temperature perturbation (T1>T2), the chain-collapse processes observed in the first and third stages were connected smoothly and agreed with the collapse process due to a single-stage quench to T1. A memory of the chain collapse in the first stage at T1 was found to persist into the third stage at the same temperature T1 without being affected by the temperature perturbation of T2 during t2. The memory effect was observed irrespective of the time period of t2. The positive temperature perturbation (T1chain-collapse process.

  17. Optical Nanofluidic Piston: Assay for Dynamic Force-Compression of Single Confined Polymer Chains

    NASA Astrophysics Data System (ADS)

    Khorshid, Ahmed; Zimny, Philip; Macos, Patrick; Massarelli, Geremia; Tétreault-La Roche, David; Reisner, Walter

    2014-03-01

    While single-molecule approaches now have a long-history in polymer physics, past methodology has a key limitation : it is not currently possible to apply well-defined forces to a precise number of chains in a well-defined volume. To this end,we have developed a nanofluidic assay for the study of DNA compression in vitro, the optical nanofluidic piston. The optical nanofluidic piston is a nanofluidic analog of a macroscopic piston-cylinder apparatus based on a nanosphere (``the piston'') optically trapped inside a 200-400nm nanochannel with embedded barrier (the ``cylinder''). The nanofluidic piston enables quantification of force required to compress single or multiple chains within a defined volume. We present combined fluorescence and force-measurements for the compression of T4 DNA under a variety of compression rates. Surprisingly, we find that compression occurs on a force-scale roughly 100x higher than that predicted by equilibrium theories, suggesting that the DNA is present in highly entangled states during the compression. Moreover, we observe that compression at high rates induces a ``shock-wave'' of high-polymer concentration near the bead, suggesting that our setup can quantitatively access novel non-equilibrium polymer phenomena.

  18. Chain Dynamics in Solid Polymers and Polymerizing Systems as Revealed by Broadband Dielectric Spectroscopy

    NASA Astrophysics Data System (ADS)

    Williams, Graham

    2008-08-01

    A number of techniques are used to study the chain-dynamics of solid polymers, including those of dielectric relaxation [1-4], dynamic mechanical thermal analysis (DMTA) [1, 5], multinuclear NMR relaxations [6], quasi-elastic dynamic light scattering [7] and neutron scattering [8] (QELS & QENS) and transient fluorescence depolarization (TFD) [9]. Each technique has its own particular probe of the dynamics in a material. e.g. dielectric relaxation gives information on the angular motions of molecular chain-dipoles (for dipole relaxation) and the translational motions of ions (for f-dependent electrical conduction); NMR relaxations relate to the angular motions of chemical bonds; QELS relates to fluctuations in local refractive index; QENS to the time-dependent van Hove correlation function (suitably-defined) for proton-containing groups; TFD to the angular motions of fluorescent groups in a chain. Due to its relevance to practical applications of materials, DMTA is pre-eminent among the many physical techniques applied to solid polymers, but interpretations of behaviour in terms of molecular properties remain difficult since the direct link between an applied macroscopic stress and the molecular response of polymer chains in a bulk material remains an unsolved problem. Of the above techniques, Broadband Dielectric Spectroscopy (BDS) offers several advantages. (a) Materials may be studied in the frequency range 10-6 to 1010 Hz, over wide ranges of temperature and applied pressure, using commercially-available instrumentation. (b) Since the electrical capacitance of a film is inversely proportional its thickness, free-standing and supported films may be studied down to nm-thicknesses, giving e.g. information on the behaviour of the dynamic Tg as sample thickness approaches molecular dimensions. (c) Theoretical interpretations of dielectric relaxation and a.c. conduction are well-established in terms of Fourier transforms of molecular time correlation functions (TCFs

  19. Crystallization of Polymer Chains Chemically Attached on a Surface: Lamellar Orientation from Flat-on to Edge-on.

    PubMed

    Chen, Yihuang; Gan, Tiansheng; Ma, Chunfeng; Wang, Linge; Zhang, Guangzhao

    2016-05-26

    Crystallization of polymer chains confined on a surface greatly influences surface properties. We have grafted comb-like copolymer, consisting of poly(2-hydroxyethyl methacrylate) (PHEMA) backbone and semicrystalline poly(ε-caprolactone) (PCL) side chains, on silicon surface and investigated the crystallization of such confined PCL chains upon solvent evaporation by using atomic force microscopy (AFM), grazing incidence wide-angle X-ray scattering (GI-WAXS), and polarized optical microscope (POM). Our studies reveal that the PCL chains align and form "flat-on" lamellae at a low PCL chain density. As the chain density increases, the comb-like polymer (PHEMA-g-PCL) chains undergo pancake-to-mushroom-to-brush transition, and the lamellae turn from "flat-on" to "edge-on" in orientation. Further increasing PCL chain density leads the "edge-on" lamellae to change from a quasi-two-dimensional (quasi-2D) to quasi-three-dimensional (quasi-3D). Because of the confinements of polymer chains, we can observe the evolution of spherulites at different stages during the mushroom-to-brush transition of PHEMA-g-PCL chains. The confinements also result in knobbly substructures in the edge-on lamellae. PMID:27149242

  20. Efficient estimation of contact probabilities from inter-bead distance distributions in simulated polymer chains

    NASA Astrophysics Data System (ADS)

    Meluzzi, Dario; Arya, Gaurav

    2015-02-01

    The estimation of contact probabilities (CP) from conformations of simulated bead-chain polymer models is a key step in methods that aim to elucidate the spatial organization of chromatin from analysis of experimentally determined contacts between different genomic loci. Although CPs can be estimated simply by counting contacts between beads in a sample of simulated chain conformations, reliable estimation of small CPs through this approach requires a large number of conformations, which can be computationally expensive to obtain. Here we describe an alternative computational method for estimating relatively small CPs without requiring large samples of chain conformations. In particular, we estimate the CPs from functional approximations to the cumulative distribution function (cdf) of the inter-bead distance for each pair of beads. These cdf approximations are obtained by fitting the extended generalized lambda distribution (EGLD) to inter-bead distances determined from a sample of chain conformations, which are in turn generated by Monte Carlo simulations. We find that CPs estimated from fitted EGLD cdfs are significantly more accurate than CPs estimated using contact counts from samples of limited size, and are more precise with all sample sizes, permitting as much as a tenfold reduction in conformation sample size for chains of 200 beads and samples smaller than 105 conformations. This method of CP estimation thus has potential to accelerate computational efforts to elucidate the spatial organization of chromatin.

  1. Efficient estimation of contact probabilities from inter-bead distance distributions in simulated polymer chains.

    PubMed

    Meluzzi, Dario; Arya, Gaurav

    2015-02-18

    The estimation of contact probabilities (CP) from conformations of simulated bead-chain polymer models is a key step in methods that aim to elucidate the spatial organization of chromatin from analysis of experimentally determined contacts between different genomic loci. Although CPs can be estimated simply by counting contacts between beads in a sample of simulated chain conformations, reliable estimation of small CPs through this approach requires a large number of conformations, which can be computationally expensive to obtain. Here we describe an alternative computational method for estimating relatively small CPs without requiring large samples of chain conformations. In particular, we estimate the CPs from functional approximations to the cumulative distribution function (cdf) of the inter-bead distance for each pair of beads. These cdf approximations are obtained by fitting the extended generalized lambda distribution (EGLD) to inter-bead distances determined from a sample of chain conformations, which are in turn generated by Monte Carlo simulations. We find that CPs estimated from fitted EGLD cdfs are significantly more accurate than CPs estimated using contact counts from samples of limited size, and are more precise with all sample sizes, permitting as much as a tenfold reduction in conformation sample size for chains of 200 beads and samples smaller than 10(5) conformations. This method of CP estimation thus has potential to accelerate computational efforts to elucidate the spatial organization of chromatin. PMID:25563926

  2. Side Chain Engineering of Naphthalenediimide-Based N-type Polymer for High-Performance All-Polymer Solar Cell near 6% Efficiency

    NASA Astrophysics Data System (ADS)

    Lee, Changyeon; Kang, Hyunbum; Lee, Wonho; Kim, Taesu; Kim, Ki-Hyun; Woo, Han Young; Wang, Cheng; Kim, Bumjoon; Pusan National University (PNU) Collaboration; Lawrence Berkeley National Laboratory Collaboration

    2015-03-01

    Despite the attractive features of all-polymer solar cells (all-PSCs), i.e., enhanced absorption coefficients, the tunability of their energetic and chemical properties and their thermal and mechanical stabilities, they still face the great challenge of having significantly low power conversion efficiency (PCE) values of only 3-5%. The prominent origins of the poor efficiency of all-PSCs are the undesirable features of the bulk-heterojunction (BHJ) blend morphology including the phase-separated large-scale domain size, reduced ordering of the polymer chains. Tuning side alkyl chains of conjugated polymers is an effective route for manipulating the blend morphology in BHJ type solar cells. However, the role of side chains in all-PSCs is poorly understood. Herein, we report high-performing all-PSCs with 5.96% efficiency by developing a series of naphthalenediimide (NDI)-based polymer acceptors with different alkyl side chains. We demonstrated that the use of the PNDIT with hexyldecyl side chains produced highly-ordered polymer stackings with strong face-on geometry and at the same time, forming the optimal BHJ morphology with finely separated phase domains, all of which contributed together to induce well-balanced μe/ μh ratio and generate efficient all-PSCs with PCEs near 6%.

  3. Interface relaxation in electrophoretic deposition of polymer chains: effects of segmental dynamics, molecular weight, and field.

    PubMed

    Bentrem, Frank W; Xie, Jun; Pandey, R B

    2002-04-01

    Using different segmental dynamics and relaxation, characteristics of the interface growth is examined in an electrophoretic deposition of polymer chains on a three (2+1)-dimensional discrete lattice with a Monte Carlo simulation. Incorporation of faster modes such as crankshaft and reptation movements along with the relatively slow kink-jump dynamics seems crucial in relaxing the interface width. As the continuously released polymer chains are driven (via segmental movements) and deposited, the interface width W grows with the number of time steps t, W proportional, variant t(beta), (beta approximately 0.4-0.8), which is followed by its saturation to a steady-state value W(s). Stopping the release of additional chains after saturation while continuing the segmental movements relaxes the saturated width to an equilibrium value (W(s)-->W(r)). Scaling of the relaxed interface width W(r) with the driving field E, W(r) proportional, variant E(-1/2) remains similar to that of the steady-state W(s) width. In contrast to monotonic increase of the steady-state width W(s), the relaxed interface width W(r) is found to decay (possibly as a stretched exponential) with the molecular weight. PMID:12005836

  4. Uranium Recovery from Seawater: Development of Fiber Adsorbents Prepared via Atom-Transfer Radical Polymerization

    SciTech Connect

    Saito, Tomonori; Brown, Suree; Chatterjee, Sabornie; Kim, Jungseung; Tsouris, Costas; Mayes, Richard T; Kuo, Li-Jung; Gill, Gary; Oyola, Yatsandra; Janke, Christopher James; Dai, Sheng

    2014-01-01

    A novel adsorbent preparation method using atom-transfer radical polymerization (ATRP) combined with radiation-induced graft polymerization (RIGP) was developed to synthesize an adsorbent for uranium recovery from seawater. The ATRP method allowed a much higher degree of grafting on the adsorbent fibers (595 2818%) than that allowed by RIGP alone. The adsorbents were prepared with varied composition of amidoxime groups and hydrophilic acrylate groups. The successful preparation revealed that both ligand density and hydrophilicity were critical for optimal performance of the adsorbents. Adsorbents synthesized in this study showed a relatively high performance (141 179 mg/g at 49 62 % adsorption) in laboratory screening tests using a uranium concentration of ~6 ppm. This performance is much higher than that of known commercial adsorbents. However, actual seawater experiment showed impeded performance compared to the recently reported high-surface-area-fiber adsorbents, due to slow adsorption kinetics. The impeded performance motivated an investigation of the effect of hydrophilic block addition on the graft chain terminus. The addition of hydrophilic block on the graft chain terminus nearly doubled the uranium adsorption capacity in seawater, from 1.56 mg/g to 3.02 mg/g. The investigation revealed the importance of polymer chain conformation, in addition to ligand and hydrophilic group ratio, for advanced adsorbent synthesis for uranium recovery from seawater.

  5. Stretching semiflexible polymer chains: evidence for the importance of excluded volume effects from Monte Carlo simulation.

    PubMed

    Hsu, Hsiao-Ping; Binder, Kurt

    2012-01-14

    Semiflexible macromolecules in dilute solution under very good solvent conditions are modeled by self-avoiding walks on the simple cubic lattice (d = 3 dimensions) and square lattice (d = 2 dimensions), varying chain stiffness by an energy penalty ε(b) for chain bending. In the absence of excluded volume interactions, the persistence length l(p) of the polymers would then simply be l(p) = l(b)(2d - 2)(-1)q(b) (-1) with q(b) = exp(-ε(b)/k(B)T), the bond length l(b) being the lattice spacing, and k(B)T is the thermal energy. Using Monte Carlo simulations applying the pruned-enriched Rosenbluth method (PERM), both q(b) and the chain length N are varied over a wide range (0.005 ≤ q(b) ≤ 1, N ≤ 50,000), and also a stretching force f is applied to one chain end (fixing the other end at the origin). In the absence of this force, in d = 2 a single crossover from rod-like behavior (for contour lengths less than l(p)) to swollen coils occurs, invalidating the Kratky-Porod model, while in d = 3 a double crossover occurs, from rods to Gaussian coils (as implied by the Kratky-Porod model) and then to coils that are swollen due to the excluded volume interaction. If the stretching force is applied, excluded volume interactions matter for the force versus extension relation irrespective of chain stiffness in d = 2, while theories based on the Kratky-Porod model are found to work in d = 3 for stiff chains in an intermediate regime of chain extensions. While for q(b) ≪ 1 in this model a persistence length can be estimated from the initial decay of bond-orientational correlations, it is argued that this is not possible for more complex wormlike chains (e.g., bottle-brush polymers). Consequences for the proper interpretation of experiments are briefly discussed. PMID:22260610

  6. Polymer chain in a good solvent between attracting walls. A scaling approach

    NASA Astrophysics Data System (ADS)

    Allegra, Giuseppe; Colombo, Emanuele

    1996-09-01

    measurements of the force exerted by polymer chains on confining surfaces, obtained by Klein and co-workers, appear to be consistent with these theoretical results.

  7. Concentration fluctuations in miscible polymer blends: Influence of temperature and chain rigidity

    SciTech Connect

    Dudowicz, Jacek; Freed, Karl F.; Douglas, Jack F.

    2014-05-21

    In contrast to binary mixtures of small molecule fluids, homogeneous polymer blends exhibit relatively large concentration fluctuations that can strongly affect the transport properties of these complex fluids over wide ranges of temperatures and compositions. The spatial scale and intensity of these compositional fluctuations are studied by applying Kirkwood-Buff theory to model blends of linear semiflexible polymer chains with upper critical solution temperatures. The requisite quantities for determining the Kirkwood-Buff integrals are generated from the lattice cluster theory for the thermodynamics of the blend and from the generalization of the random phase approximation to compressible polymer mixtures. We explore how the scale and intensity of composition fluctuations in binary blends vary with the reduced temperature τ ≡ (T − T{sub c})/T (where T{sub c} is the critical temperature) and with the asymmetry in the rigidities of the components. Knowledge of these variations is crucial for understanding the dynamics of materials fabricated from polymer blends, and evidence supporting these expectations is briefly discussed.

  8. Vitrification of thin polymer films: from linear chain to soft-colloid like behavior

    NASA Astrophysics Data System (ADS)

    Glynos, Emmanouil; Frieberg, Bradley; Sakellariou, Georgios; Chremos, Alexandros; Green, Peter

    2015-03-01

    The glass transition temperature Tg of sufficiently thin, supported, polymer films is dependent on the film thickness. Based on the nature of the polymer substrate interactions Tg may increase, ΔTg >0, or decrease, ΔTg <0, in relation to the bulk. We show that for star-shaped macromolecules the value of ΔTg depends on the functionality f of the molecule, for polymer films supported by the same substrate. Specifically in the case of polystyrene (PS) macromolecules, with arms of molecular weight Marm<10 kg./mol., supported by silicon oxide substrates, ΔTg <0, when f<4. For much higher functionalities, f >= 32, where the polymer exhibits soft-colloid like behavior ΔTg ~ 0. For values of 40. The transition from the linear-chain to the soft-colloid behavior is gradual and occurs with increasing f and/or decreasing Marm. With the help of molecular dynamics simulations we rationalize this behavior in terms of competing entropic effects, associated with changes in f and Marm, which drives the ability of these molecules to efficiently pack at interfaces.

  9. Single molecule spectroscopy of conjugated polymer chains in an electric field-aligned liquid crystal.

    PubMed

    Chang, Wei-Shun; Link, Stephan; Yethiraj, Arun; Barbara, Paul F

    2008-01-17

    Using single molecule polarization spectroscopy, we investigated the alignment of a polymer solute with respect to the liquid crystal (LC) director in an LC device while applying an external electric field. The polymer solute is poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (or MEH-PPV), and the LC solvent is 5CB. The electric field induces a change in the LC director orientation from a planar alignment (no electric field) to a perpendicular (homeotropic) alignment with an applied field of 5.5 x 103 V/cm. We find that the polymer chains align with the LC director in both planar and homeotropic alignment when measured in the bulk of the LC solution away from the device interface. Single molecule polarization distributions measured as a function of distance from the LC device interface reveal a continuous change of the MEH-PPV alignment from planar to homeotropic. The observed polarization distributions are modeled using a conventional elastic model that predicts the depth profile of the LC director orientation for the applied electric field. The excellent agreement between experiment and simulations shows that the alignment of MEH-PPV follows the LC director throughout the LC sample. Furthermore, our results suggest that conjugated polymers such as MEH-PPV can be used as sensitive local probes to explore complex (and unknown) structures in anisotropic media. PMID:17975912

  10. High-performance polymer semiconducting heterostructure devices by nitrene-mediated photocrosslinking of alkyl side chains.

    PubMed

    Png, Rui-Qi; Chia, Perq-Jon; Tang, Jie-Cong; Liu, Bo; Sivaramakrishnan, Sankaran; Zhou, Mi; Khong, Siong-Hee; Chan, Hardy S O; Burroughes, Jeremy H; Chua, Lay-Lay; Friend, Richard H; Ho, Peter K H

    2010-02-01

    Heterostructures are central to the efficient manipulation of charge carriers, excitons and photons for high-performance semiconductor devices. Although these can be formed by stepwise evaporation of molecular semiconductors, they are a considerable challenge for polymers owing to re-dissolution of the underlying layers. Here we demonstrate a simple and versatile photocrosslinking methodology based on sterically hindered bis(fluorophenyl azide)s. The photocrosslinking efficiency is high and dominated by alkyl side-chain insertion reactions, which do not degrade semiconductor properties. We demonstrate two new back-infiltrated and contiguous interpenetrating donor-acceptor heterostructures for photovoltaic applications that inherently overcome internal recombination losses by ensuring path continuity to give high carrier-collection efficiency. This provides the appropriate morphology for high-efficiency polymer-based photovoltaics. We also demonstrate photopatternable polymer-based field-effect transistors and light-emitting diodes, and highly efficient separate-confinement-heterostructure light-emitting diodes. These results open the way to the general development of high-performance polymer semiconductor heterostructures that have not previously been thought possible. PMID:19966791

  11. Multiplicative luminescence enhancement induced by chain relaxation in ultrathin films of a conjugated polymer (MEH-PPV)

    NASA Astrophysics Data System (ADS)

    Yang, Chih-Wei; Jou, Juo-Huei; Chang-Mou Yang, Arnold

    2006-03-01

    A surprising multiplication of light-emitting efficiency was observed in dewetting process of the conjugated luminescent polymer of poly (2-methoxy- 5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV). The luminescent efficiency increased with the dewetting process and became about six-fold when the polymer film ruptured into tiny droplets. This enhancement appeared to be related to the carrier transport mechanisms and the motions of polymer chains. The effects of inter-molecular energy transport and molecular deformation of polymer chains were studied by examining the emission behavior in liquid and solid solutions. It was found that the molecular movements during stretching in the glassy state were quite different from that in the dewetting process. The latter was dominated by disengagement of inter-molecular entanglements while the former was strongly influenced by trapping mechanisms of chain entanglements due to rapid local molecular strains. This work is supported by National Science Council of Taiwan.

  12. Understanding entangled polymers: What we can learn from athermal chain packings

    NASA Astrophysics Data System (ADS)

    Karayiannis, Nikos

    2012-02-01

    The study of random and ordered packings (from atoms and colloidal particles to sand grains) has been the focus of extensive research. This is not surprising since an understanding of the mechanisms that control morphology and packing is the key to the design and synthesis of novel ``smart'' materials and functionalities. In particular, the study of packings of chain molecules presents challenges but also insights which are absent in monatomic systems and further allows for a direction comparison with them. In this contribution we give an overview of our work on very dense and nearly jammed packings of athermal polymers. We show that chain molecules can be as efficiently and as densely packed as monatomic analogs up to the same maximally random jammed state. We also show that an exact correspondence can be established between the statistical-mechanical ensembles of packings of monatomic, and chain systems, which yields insights on the universality of jamming. By studying the effect of concentration on polymer size and on the underlying network of topological hindrances we precisely identify the distinct universal scaling regimes and the corresponding exponents. An unsuspected connection, valid from dilute up to very dense assemblies, is established between knots (of intermolecular origin) and entanglements (intermolecular constraints). We finally show that, against expectations, entropy-driven crystallization can occur in dense systems of athermal polymers once a critical volume fraction is reached. Such phase transition is driven by the increase in translational entropy: ordered sites exhibit enhanced mobility as their local free volume becomes more spherical and symmetric. Incipient nuclei develop well defined, stack-faulted layered crystal morphologies with a single stacking direction. The ordering transition and the resulting complex morphologies are analyzed, highlighting similarities and differences with respect to monatomic crystallization.

  13. Two unprecedented 1D coordination polymer chains based on tetranuclear copper(II) building blocks

    SciTech Connect

    Li Gaijuan; Xing Yan Song Shuyan; Xu Ning; Liu Xianchun; Su Zhongmin

    2008-09-15

    The reaction of copper(II) sulfate with pyridine in DMF or methanol yield two unprecedented Cu(II) coordination polymers {l_brace}[Cu{sub 4}({mu}{sub 4}-O)(py){sub 4}(SO{sub 4}){sub 4}][{mu}-Cu(py)(DMF){sub 2}]{r_brace}{sub n}(1) and {l_brace}[Cu{sub 4}({mu}{sub 4}-O)(py){sub 4}(SO{sub 4}){sub 4}][{mu}-Cu(py){sub 4}]{r_brace}{sub n}(2), respectively. Single-crystal X-ray diffraction indicated that compound 1 crystallizes in the monoclinic system, space group p2(1)/n, a=14.542(5) A, b=16.359(5) A, c=18.951(5) A, {beta}=92.047(5){sup o}, V=4505(2) A{sup 3}, Z=4 while 2 is monoclinic C2/c, a=23.078(5) A, b=10.214(5) A, c=23.142(5) A, {beta}=115.471(5){sup o}, V=4925(3) A{sup 3}, Z=4. Both of the two compounds consist of tetrahedral tetranuclear [Cu{sub 4}({mu}{sub 4}-O)(py){sub 4}(SO{sub 4}){sub 4}] clusters that are bridged by pentacoordinated Cu atom for 1 or hexacoordinated Cu atoms for 2 through the sulfate oxygen to form the infinite one-dimensional polymer chains. - Graphical abstract: Two unprecedented Cu(II) coordination polymers have been prepared by using solvothermal method; they consist of tetrahedral tetranuclear clusters that are bridged by unique Cu(II) atom through the sulfate oxygen to form the infinite one-dimensional polymer chains (a) for complex 1 and (b) for complex 2.

  14. Dehydrocoupling and Silazane Cleavage Routes to Organic-Inorganic Hybrid Polymers with NBN Units in the Main Chain.

    PubMed

    Lorenz, Thomas; Lik, Artur; Plamper, Felix A; Helten, Holger

    2016-06-13

    Despite the great potential of both π-conjugated organoboron polymers and BN-doped polycyclic aromatic hydrocarbons in organic optoelectronics, our knowledge of conjugated polymers with B-N bonds in their main chain is currently scarce. Herein, the first examples of a new class of organic-inorganic hybrid polymers are presented, which consist of alternating NBN and para-phenylene units. Polycondensation with B-N bond formation provides facile access to soluble materials under mild conditions. The photophysical data for the polymer and molecular model systems of different chain lengths reveal a low extent of π-conjugation across the NBN units, which is supported by DFT calculations. The applicability of the new polymers as macromolecular polyligands is demonstrated by a cross-linking reaction with Zr(IV) . PMID:27151314

  15. Effect of bidispersity in grafted chain length on grafted chain conformations and potential of mean force between polymer grafted nanoparticles in a homopolymer matrix.

    PubMed

    Nair, Nitish; Wentzel, Nathaniel; Jayaraman, Arthi

    2011-05-21

    In efforts to produce polymeric materials with tailored physical properties, significant interest has grown around the ability to control the spatial organization of nanoparticles in polymer nanocomposites. One way to achieve controlled particle arrangement is by grafting the nanoparticle surface with polymers that are compatible with the matrix, thus manipulating the interfacial interactions between the nanoparticles and the polymer matrix. Previous work has shown that the molecular weight of the grafted polymer, both at high grafting density and low grafting density, plays a key role in dictating the effective inter-particle interactions in a polymer matrix. At high grafting density nanoparticles disperse (aggregate) if the graft molecular weight is higher (lower) than the matrix molecular weight. At low grafting density the longer grafts can better shield the nanoparticle surface from direct particle-particle contacts than the shorter grafts and lead to the dispersion of the grafted particles in the matrix. Despite the importance of graft molecular weight, and evidence of non-trivial effects of polydispersity of chains grafted on flat surfaces, most theoretical work on polymer grafted nanoparticles has only focused on monodisperse grafted chains. In this paper, we focus on how bidispersity in grafted chain lengths affects the grafted chain conformations and inter-particle interactions in an implicit solvent and in a dense homopolymer polymer matrix. We first present the effects of bidispersity on grafted chain conformations in a single polymer grafted particle using purely Monte Carlo (MC) simulations. This is followed by calculations of the potential of mean force (PMF) between two grafted particles in a polymer matrix using a self-consistent Polymer Reference Interaction Site Model theory-Monte Carlo simulation approach. Monte Carlo simulations of a single polymer grafted particle in an implicit solvent show that in the bidisperse polymer grafted particles

  16. A molecular dynamics study on universal properties of polymer chains in different solvent qualities. Part I. A review of linear chain properties.

    PubMed

    Steinhauser, Martin Oliver

    2005-03-01

    This paper investigates the conformational and scaling properties of long linear polymer chains. These investigations are done with the aid of Monte Carlo (MC) and molecular dynamics (MD) simulations. Chain lengths that comprise several orders of magnitude to reduce errors of finite size scaling, including the effect of solvent quality, ranging from the athermal limit over the theta-transition to the collapsed state of chains are investigated. Also the effect of polydispersity on linear chains is included which is an important issue in the real fabrication of polymers. A detailed account of the hybrid MD and MC simulation model and the exploited numerical methods is given. Many results of chain properties in the extrapolated limit of infinite chain lengths are documented and universal properties of the chains within their universality class are given. An example of the difference between scaling exponents observed in actual solvents and those observed in the extremes of "good solvents" and "theta-solvents" in simulations is provided by comparing simulation results with experimental data on low density polyethylene. This paper is concluded with an outlook on the extension of this study to branched chain systems of many different branching types. PMID:15836175

  17. Cyclic side-chain phenylazo naphthalene polymers: enhanced fluorescence emission and surface relief grating formation.

    PubMed

    Zhang, Hao; Zhou, Nianchen; Zhu, Xing; Chen, Xinrong; Zhang, Zhengbiao; Zhang, Wei; Zhu, Jian; Hu, Zhijun; Zhu, Xiulin

    2012-11-14

    Well-defined cyclic-polymers (cyclic-PAzoMMAs), bearing side-chain phenylazo naphthalene chromophore, were successfully synthesized by the combination of atom transfer radical polymerization (ATRP) and copper(I)-catalyzed azide/alkyne cycloaddition "click" reaction, as verified by GPC, (1) H NMR, FTIR, and MALDI-TOF mass spectrometry. The cyclic-PAzoMMA showed higher glass transition temperatures than the linear-PAzoMMA with the same molecular weight. Interestingly, the cyclic-PAzoMMA exhibited deeper modulation depth (M.D.) induced by SRG, larger value of the photoinduced birefringence, increased fluorescence emission, and longer fluorescence lifetime in comparison with its linear counterpart. PMID:22965741

  18. Adsorption of a single polymer chain on a surface: effects of the potential range.

    PubMed

    Klushin, Leonid I; Polotsky, Alexey A; Hsu, Hsiao-Ping; Markelov, Denis A; Binder, Kurt; Skvortsov, Alexander M

    2013-02-01

    We investigate the effects of the range of adsorption potential on the equilibrium behavior of a single polymer chain end-attached to a solid surface. The exact analytical theory for ideal lattice chains interacting with a planar surface via a box potential of depth U and width W is presented and compared to continuum model results and to Monte Carlo (MC) simulations using the pruned-enriched Rosenbluth method for self-avoiding chains on a simple cubic lattice. We show that the critical value U(c) corresponding to the adsorption transition scales as W(-1/ν), where the exponent ν=1/2 for ideal chains and ν≈3/5 for self-avoiding walks. Lattice corrections for finite W are incorporated in the analytical prediction of the ideal chain theory U(c)≈(π(2)/24)(W+1/2)(-2) and in the best-fit equation for the MC simulation data U(c)=0.585(W+1/2)(-5/3). Tail, loop, and train distributions at the critical point are evaluated by MC simulations for 1≤W≤10 and compared to analytical results for ideal chains and with scaling theory predictions. The behavior of a self-avoiding chain is remarkably close to that of an ideal chain in several aspects. We demonstrate that the bound fraction θ and the related properties of finite ideal and self-avoiding chains can be presented in a universal reduced form: θ(N,U,W)=θ(NU(c),U/U(c)). By utilizing precise estimations of the critical points we investigate the chain length dependence of the ratio of the normal and lateral components of the gyration radius. Contrary to common expectations this ratio attains a limiting universal value /=0.320±0.003 only at N~5000. Finite-N corrections for this ratio turn out to be of the opposite sign for W=1 and for W≥2. We also study the N dependence of the apparent crossover exponent φ(eff)(N). Strong corrections to scaling of order N(-0.5) are observed, and the extrapolated value φ=0.483±0.003 is found for all values of W. The strong correction

  19. Revealing the supramolecular nature of side-chain terpyridine-functionalized polymer networks.

    PubMed

    Brassinne, Jérémy; Jochum, Florian D; Fustin, Charles-André; Gohy, Jean-François

    2015-01-01

    Nowadays, finely controlling the mechanical properties of polymeric materials is possible by incorporating supramolecular motifs into their architecture. In this context, the synthesis of a side-chain terpyridine-functionalized poly(2-(dimethylamino)ethyl methacrylate) is reported via reversible addition-fragmentation chain transfer polymerization. By addition of transition metal ions, concentrated aqueous solutions of this polymer turn into metallo-supramolecular hydrogels whose dynamic mechanical properties are investigated by rotational rheometry. Hence, the possibility for the material to relax mechanical constrains via dissociation of transient cross-links is brought into light. In addition, the complex phenomena occurring under large oscillatory shear are interpreted in the context of transient networks. PMID:25569082

  20. Revealing the Supramolecular Nature of Side-Chain Terpyridine-Functionalized Polymer Networks

    PubMed Central

    Brassinne, Jérémy; Jochum, Florian D.; Fustin, Charles-André; Gohy, Jean-François

    2015-01-01

    Nowadays, finely controlling the mechanical properties of polymeric materials is possible by incorporating supramolecular motifs into their architecture. In this context, the synthesis of a side-chain terpyridine-functionalized poly(2-(dimethylamino)ethyl methacrylate) is reported via reversible addition-fragmentation chain transfer polymerization. By addition of transition metal ions, concentrated aqueous solutions of this polymer turn into metallo-supramolecular hydrogels whose dynamic mechanical properties are investigated by rotational rheometry. Hence, the possibility for the material to relax mechanical constrains via dissociation of transient cross-links is brought into light. In addition, the complex phenomena occurring under large oscillatory shear are interpreted in the context of transient networks. PMID:25569082

  1. Chain Gang-The Chemistry of Polymers (edited by Mickey Sarquis)

    NASA Astrophysics Data System (ADS)

    Collard, David M.

    1999-01-01

    Science in Our World, Vol. 5. Mickey Sarquis, series editor. Terrific Science Press: Middletown, OH, 1995. xiv + 149 pp. ISBN 1-883822-13-0. Spiral-bound, $13.95. Our familiarity with plastics makes polymers ideal examples of chemicals for discussion in K-12 science classes. Most importantly, polymers can be used as examples of chemicals that are safe to handle and of obvious use to society. The structures of polymers are easily represented by a number of models. These simple models go a long way in explaining the familiar physical properties of plastics. However, the introduction of polymers in the classroom relies on the availability of teaching material, experiments, and demonstrations that illustrate concepts in the current science curriculum. Chain Gang-The Chemistry of Polymers, one of the Science in Our World series published by the Center for Chemical Education at Miami University-Middletown (Ohio), will serve as a great resource for teachers interested in providing their students with a series of activities that can be related to their everyday experiences with these ubiquitous chemicals. After a brief introduction to some basic concepts, the book presents a series of 23 experiments. The collection of experiments presented here spans illustrations of chemistry, physical properties, analysis, and processing. Each experiment is recommended as either a hands-on activity or demonstration for various grade levels. A guide for the teacher suggests how the experiment can be used to illustrate topics in the science curriculum. The materials required for each activity are listed in detail, with quantities and sources (all materials are available from Flinn Scientific or hardware stores). There are detailed instructions for preparation of each experiment and how to introduce the experiment to students, and step-by-step instructions for activity. Very importantly, safety and disposal issues are clearly presented. Suggestions for cross-curriculum integration are also

  2. Phthalocyaninato complexes with peripheral alkylthio chains: disk-like adsorbate species for the vertical anchoring of ligands on gold surfaces

    PubMed Central

    Siemeling, Ulrich; Schirrmacher, Christian; Glebe, Ulrich; Bruhn, Clemens; Baio, Joe E.; Árnadóttir, Líney; Castner, David G.; Weidner, Tobias

    2011-01-01

    Thin metalorganic films were prepared on gold by self-assembly of thioether-functionalised phthalocyaninato complexes from solution. The phthalocyaninato ligands used contain eight peripheral, β-positioned, alkylthio substituents SR (1a: R = n-C8H17, 1b: R = n-C12H25), which serve as headgroups for surface binding and promote lateral assembly, while the disk-like phthalocyaninato core offers the scope for the attachment of axial ligands to the adsorbed molecules. This process was mimicked by coordination of pyridine (Py) to [Zn(1a)] and [Zn(1b)], respectively. The crystal structures of the products [Zn(1a)(Py)] and [Zn(1b)(Py)] were determined. The crystal structures of 4,5-bis(octylthio)phthalodinitrile and 4,5-bis(dodecylthio)phthalodinitrile were also determined. The films fabricated from [Mn(1a)Cl] and [Mn(1b)Cl] on gold were characterised by XPS, ToF-SIMS and NEXAFS spectroscopy, which revealed the presence of well-defined and homogeneous self-assembled monolayers (SAMs), whose constituents are bound to the substrate by thioether–gold linkages. The orientation of the macrocycles is predominantly parallel to the surface. Strong electronic interaction of the manganese(III) centre with the substrate leads to Cl loss upon adsorption and its reduction to MnII. PMID:21857743

  3. Thermal breakage and self-healing of a polymer chain under tensile stress

    NASA Astrophysics Data System (ADS)

    Ghosh, A.; Dimitrov, D. I.; Rostiashvili, V. G.; Milchev, A.; Vilgis, T. A.

    2010-05-01

    We consider the thermal breakage of a tethered polymer chain of discrete segments coupled by Morse potentials under constant tensile stress. The chain dynamics at the onset of fracture is studied analytically by Kramers-Langer multidimensional theory and by extensive molecular dynamics simulations in one dimension (1D) and three dimension (3D) space. Comparison with simulation data in one and three dimensions demonstrates that the Kramers-Langer theory provides good qualitative description of the process of bond scission as caused by a collective unstable mode. We derive distributions of the probability for scission over the successive bonds along the chain which reveal the influence of chain ends on rupture in good agreement with theory. The breakage time distribution of an individual bond is found to follow an exponential law as predicted by theory. Special attention is focused on the recombination (self-healing) of broken bonds. Theoretically derived expressions for the recombination time and distance distributions comply with MD observations and indicate that the energy barrier position crossing is not a good criterion for true rupture. It is shown that the fraction of self-healing bonds increases with rising temperature and friction.

  4. Slow knot formation by suppressed self-reptation in a collapsed polymer chain

    NASA Astrophysics Data System (ADS)

    Nakata, Mitsuo; Nakamura, Yoshiki; Sasaki, Naoki; Maki, Yasuyuki

    2012-02-01

    Chain-expansion processes from knotted globules have been measured for poly(methyl methacrylate) (PMMA) in the mixed solvent tert-butyl alcohol (TBA) + water (2.5 vol %) by static light scattering. The solution was quenched from the Θ temperature of 41.5 ∘C to 37.0 ∘C, aged there for a time period tp, and then returned rapidly to the Θ temperature. The chain-expansion process was determined as a time evolution of the expansion factor α2 after the temperature increase. The measurement was carried out by changing the aging time tp from 240 to 7200 min, and the molecular weight from Mw = 4.0 × 106 to 1.5 × 107, by taking advantage of the extremely slow chain aggregation in the solution. The chain-expansion process obtained for Mw = 1.22 × 107 became slow with increasing tp, which revealed the knot formation in single globules. The characteristic time of the chain expansion from globules aged for tp = 7200 min was found to depend on the molecular weight as Mw2.7. This exponent, which is close to 3, demonstrated a disentanglement process due to self-reptation. The present data were compared with the previous data of the chain expansion from compact globules aged at 25.0 ∘C. The comparison made at Mw = 1.22 × 107 and at the same values of tp revealed that the chain expansion from the globules aged at 25.0 ∘C was much faster than that from the globules at 37.0 ∘C, indicating a lower knot density in the more compact globules. It was conjectured that the knot formation due to self-reptation would be suppressed in a compact globule because an entire conformational change required by knot formation would become difficult to occur in the confined space of high segment concentration, particularly for a long polymer chain. The chain collapse of PMMA in the mixed solvent has been observed to occur extremely slowly at the later stage. This slow process was explained by the suppressed self-reptation.

  5. Slow knot formation by suppressed self-reptation in a collapsed polymer chain.

    PubMed

    Nakata, Mitsuo; Nakamura, Yoshiki; Sasaki, Naoki; Maki, Yasuyuki

    2012-02-01

    Chain-expansion processes from knotted globules have been measured for poly(methyl methacrylate) (PMMA) in the mixed solvent tert-butyl alcohol (TBA) + water (2.5 vol %) by static light scattering. The solution was quenched from the Θ temperature of 41.5 °C to 37.0 °C, aged there for a time period t(p,) and then returned rapidly to the Θ temperature. The chain-expansion process was determined as a time evolution of the expansion factor α(2) after the temperature increase. The measurement was carried out by changing the aging time t(p) from 240 to 7200 min, and the molecular weight from M(w) = 4.0 × 10(6) to 1.5 × 10(7), by taking advantage of the extremely slow chain aggregation in the solution. The chain-expansion process obtained for M(w) = 1.22 × 10(7) became slow with increasing t(p), which revealed the knot formation in single globules. The characteristic time of the chain expansion from globules aged for t(p) = 7200 min was found to depend on the molecular weight as M(w)(2.7). This exponent, which is close to 3, demonstrated a disentanglement process due to self-reptation. The present data were compared with the previous data of the chain expansion from compact globules aged at 25.0 °C. The comparison made at M(w) = 1.22 × 10(7) and at the same values of t(p) revealed that the chain expansion from the globules aged at 25.0 °C was much faster than that from the globules at 37.0  °C, indicating a lower knot density in the more compact globules. It was conjectured that the knot formation due to self-reptation would be suppressed in a compact globule because an entire conformational change required by knot formation would become difficult to occur in the confined space of high segment concentration, particularly for a long polymer chain. The chain collapse of PMMA in the mixed solvent has been observed to occur extremely slowly at the later stage. This slow process was explained by the suppressed self-reptation. PMID:22463231

  6. Adsorbing a PVDF polymer via noncovalent interactions to effectively tune the electronic and magnetic properties of zigzag SiC nanoribbons.

    PubMed

    Li, Hui; Chen, Wei; Sun, Yuanhui; Huang, Xuri; Yu, Guangtao

    2015-10-01

    On the basis of first-principle computations, we first propose a simple and effective strategy through surface-adsorbing a poly(vinylidene fluoride) (PVDF) polymer via noncovalent interactions to tune the electronic and magnetic behaviors of zigzag SiC nanoribbons (zSiCNRs). It is revealed that depositing the strong electron-withdrawing PVDF polymer with a permanent dipole moment can induce the evident change of the electrostatic potential in the substrate zSiCNRs, like applying an electric field. As a result, this kind of noncovalent surface-modification by a polymer can break the magnetic degeneracy of zSiCNRs independent of the adsorption type and position, and sole ferromagnetic metallicity and even antiferromagnetic half-metallicity can be achieved. Moreover, all PVDF-modified zSiCNR systems can exhibit considerable adsorption energies in the range of -0.436 to -1.315 eV, indicating that these joint systems possess high structural stabilities. These intriguing findings will be advantageous for promoting excellent SiC-based nanomaterials in the applications of spintronics and multifunctional nanodevices in the near future. PMID:26312553

  7. Theory of microphase separation on side-chain liquid-crystalline polymers with flexible spacers.

    PubMed

    Hernández-Jiménez, M; Westfahl, H

    2007-05-01

    We model a melt of monodisperse side-chain liquid-crystalline polymers as a melt of comb copolymers in which the side groups are rod-coil diblock copolymers. We consider both excluded-volume and Maier-Saupe interactions. The first acts among any pair of segments while the latter acts only between rods. Using a free-energy functional calculated from this microscopic model, we study the spinodal stability of the isotropic phase against density and orientational fluctuations. The phase diagram obtained in this way predicts nematic and smectic instabilities as well as the existence of microphases or phases with modulated wave vector but without nematic ordering. Such microphases are the result of the competition between the incompatibility among the blocks and the connectivity constraints imposed by the spacer and the backbone. Also the effects of the polymerization degree and structural conformation of the monomeric units on the phase behavior of the side-chain liquid-crystalline polymers are studied. PMID:17541501

  8. Ionic polymer cluster energetics: Computational analysis of pendant chain stiffness and charge imbalance

    NASA Astrophysics Data System (ADS)

    Weiland, Lisa Mauck; Leo, Donald J.

    2005-06-01

    In recent years there has been considerable study of the potential mechanisms underlying the electromechanical response of ionic-polymer-metal composites. The most recent models have been based on the response of the ion-containing clusters that are formed when the material is synthesized. Most of these efforts have employed assumptions of uniform ion distribution within spherical cluster shapes. This work investigates the impact of dispensing with these assumptions in order to better understand the parameters that impact cluster shape, size, and ion transport potential. A computational micromechanics model applying Monte Carlo methodology is employed to predict the equilibrium state of a single cluster of a solvated ionomeric polymer. For a constant solvated state, the model tracks the position of individual ions within a given cluster in response to ion-ion interaction, mechanical stiffness of the pendant chain, cluster surface energy, and external electric-field loading. Results suggest that cluster surface effects play a significant role in the equilibrium cluster state, including ion distribution; pendant chain stiffness also plays a role in ion distribution but to a lesser extent. Moreover, ion pairing is rarely complete even in cation-rich clusters; this in turn supports the supposition of the formation of anode and cathode boundary layers.

  9. Preparation of nanoparticles bearing high density carbohydrate chains using carbohydrate-carrying polymers as emulsifier.

    PubMed

    Maruyama, A; Ishihara, T; Adachi, N; Akaike, T

    1994-10-01

    A novel method of preparing nanoparticles bearing high density carbohydrate chains on their surface is described. Carbohydrate-bearing nanoparticles of poly(lactic acid) or polystyrene were prepared by the solvent evaporation method using a carbohydrate-carrying polystyrene derivative which served as both an emulsifier and a surface coating. The diameter of the obtained nanoparticles ranged from 80 to 300 nm depending on the concentration of the polystyrene derivative. As the concentration of the polystyrene derivatives increased the nanoparticle diameter decreased, indicating that the polystyrene derivatives worked as an emulsifier. The obtained particles were specifically aggregated by carbohydrate-specific lectin, showing that the polystyrene derivative was retained on the particle surfaces and expressed carbohydrate residues. The density of carbohydrates on the particle surfaces was determined to be 3-5 molecules per square nanometre. The particles prepared by the present method were stably dispersed and hardly aggregated in aqueous media during storage and centrifugal treatment compared with the post-coated particles that were prepared by adsorbing polystyrene particles with the polystyrene derivative. In vitro study with isolated rat hepatocytes revealed that surface carbohydrate chains were recognized by hepatocytes. PMID:7888573

  10. Graft copolymer composed of cationic backbone and bottle brush-like side chains as a physically adsorbed coating for protein separation by capillary electrophoresis.

    PubMed

    Zhou, Dan; Xiang, Lina; Zeng, Rongju; Cao, Fuhu; Zhu, Xiaoxi; Wang, Yanmei

    2011-12-01

    To stabilize electroosmotic flow (EOF) and suppress protein adsorption onto the silica capillary inner wall, a cationic hydroxyethylcellulose-graft-poly (poly(ethylene glycol) methyl ether methacrylate) (cat-HEC-g-PPEGMA) graft copolymer composed of cationic backbone and bottle brush-like side chains was synthesized for the first time and used as a novel physically adsorbed coating for protein separation by capillary electrophoresis. Reversed (anodal) and very stable EOF was obtained in cat-HEC-g-PPEGMA-coated capillary at pH 2.2-7.8. The effects of degree of cationization, PEGMA grafting ratio, PEGMA molecular mass, and buffer pH on the separation of basic proteins were investigated. A systematic comparative study of protein separation in bare and HEC-coated capillaries and in cat-HEC-g-PPEGMA-coated capillary was also performed. The basic proteins can be well separated in cat-HEC-g-PPEGMA-coated capillary over the pH range of 2.8-6.8 with good repeatability and high separation efficiency, because the coating combines good protein-resistant property of bottle brush-like PPEGMA side chains with excellent coating ability of cat-HEC backbone. Besides its success in separation of basic proteins, the cat-HEC-g-PPEGMA coating was also superior in the fast separation of other protein samples, such as protein mixture, egg white, and saliva, which indicates that it is a promising coating for further proteomics analysis. PMID:22038787

  11. End-Functionalized Polymers and Junction-Functionalized Diblock Copolymers Via RAFT Chain Extension with Maleimido Monomers

    PubMed Central

    Henry, Scott M.; Convertine, Anthony J.; Benoit, Danielle S. W.; Hoffman, Allan S.; Stayton, Patrick S.

    2010-01-01

    A new strategy is described for functionalizing the ω-terminal end of polymers synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization that provides spatially controlled bioconjugation sites. Traditional methods for preparing ω-functional polymers require the reduction of the RAFT chain-transfer agent to yield secondary or tertiary thiols of low reactivity or the synthesis of novel chain-transfer agents that contain reactive groups. As an additional strategy, N-substituted maleimido monomers have been used in a modified block polymerization to add a single maleimido unit onto the RAFT polymer with nearly quantitative efficiency. Unique reactive groups contained in the N-substituent are thereby added to the ω-terminal end of the polymer and are subsequently available for conjugation reactions. This technique has been demonstrated using N-(2-aminoethyl)maleimide trifluoroacetate to introduce a single primary amine to the ω-terminus of poly(dimethy-laminoethyl methacrylate) and poly(N-isopropyl acrylamide) and to a specialized block copolymer for siRNA delivery. Evidence for retention of functional RAFT endgroups is provided by synthesis results where chain-extended polyDMAEMA (Mn = 10 600 g/mol, Mw/Mn = 1.14) was used as a macro chain transfer agent for the polymerization of styrene, yielding a diblock polymer of low polydispersity (Mn = 20 300 g/mol, Mw/Mn = 1.11). It is thus also possible to construct diblock copolymers with a bioconjugation site precisely located at the junction between the two blocks. The chain-extended polymers are functionalized with an amine-reactive fluorescent dye or folic acid at conjugation efficiencies of 86 and 94%, respectively. The versatile chain-extension technique described here offers unique opportunities for the synthesis of well-defined polymeric conjugates to molecules of biological and targeting interest. PMID:19480416

  12. On the Anomalous Diffusion of a Polymer Chain in an Unentangled Melt

    NASA Astrophysics Data System (ADS)

    Baschnagel, Jorg

    2014-03-01

    The dynamics of polymer chains in unentangled melts is commonly described by the Rouse model. However, various experimental and simulation studies show that certain dynamical phenomena in unentangled melts cannot be explained by the Rouse theory. One of the puzzling observations is the anomalous diffusion of the center-of-mass (CM) of a polymer chain for times t polymer consisting of N monomers. We explore two attempts to explain this observation: (i) an approach based on the effective interactions between the CMs in the melt and (ii) an approach based on the hydrodynamic flow and viscoelasticity of the melt. For approach (i) we find a partial success: The theory accounts for the anomalous motion by yielding a negative power-law tail for the CM velocity autocorrelation function (CM VAF), Ccm(t) ~ -N-1t - 5 / 4 . This prediction is in good agreement with molecular-dynamics (MD) simulations utilizing Langevin dynamics with a strong damping constant. On the other hand, for simulations with momentum conserving dynamics (i.e., the experimentally relevant situation) the prediction of approach (i) is qualitatively incorrect. In the latter case, the CM VAF rather scales as Ccm(t) ~ -N - 1 / 2t - 3 / 2 . This behavior can be rationalized by approach (ii). The predictions of approach (ii) are found to be good quantitative agreement with the MD simulations. In collaboration with: J. Farago, H. Meyer, A. N. Semenov, J. P. Wittmer, A. Johner (Institut Charles Sadron).

  13. Detachment of semiflexible polymer chains from a substrate: A molecular dynamics investigation

    SciTech Connect

    Paturej, J.; Erbas, A.; Milchev, A.; Rostiashvili, V. G.

    2014-12-07

    Using Molecular Dynamics simulations, we study the force-induced detachment of a coarse-grained model polymer chain from an adhesive substrate. One of the chain ends is thereby pulled at constant speed off the attractive substrate and the resulting saw-tooth profile of the measured mean force 〈f〉 vs height D of the end-segment over the plane is analyzed for a broad variety of parameters. It is shown that the observed characteristic oscillations in the 〈f〉-D profile depend on the bending and not on the torsional stiffness of the detached chains. Allowing for the presence of hydrodynamic interactions (HI) in a setup with explicit solvent and dissipative particle dynamics-thermostat, rather than the case of Langevin thermostat, one finds that HI have little effect on the 〈f〉-D profile. Also the change of substrate affinity with respect to the solvent from solvophilic to solvophobic is found to play negligible role in the desorption process. In contrast, a changing ratio ε{sub s}{sup B}/ε{sub s}{sup A} of the binding energies of A- and B-segments in the detachment of an AB-copolymer from adhesive surface strongly changes the 〈f〉-D profile whereby the B-spikes vanish when ε{sub s}{sup B}/ε{sub s}{sup A}<0.15. Eventually, performing an atomistic simulation of (bio)-polymers, we demonstrate that the simulation results, derived from our coarse-grained model, comply favorably with those from the all-atom simulation.

  14. Detachment of semiflexible polymer chains from a substrate: A molecular dynamics investigation

    NASA Astrophysics Data System (ADS)

    Paturej, J.; Erbas, A.; Milchev, A.; Rostiashvili, V. G.

    2014-12-01

    Using Molecular Dynamics simulations, we study the force-induced detachment of a coarse-grained model polymer chain from an adhesive substrate. One of the chain ends is thereby pulled at constant speed off the attractive substrate and the resulting saw-tooth profile of the measured mean force ⟨f⟩ vs height D of the end-segment over the plane is analyzed for a broad variety of parameters. It is shown that the observed characteristic oscillations in the ⟨f⟩-D profile depend on the bending and not on the torsional stiffness of the detached chains. Allowing for the presence of hydrodynamic interactions (HI) in a setup with explicit solvent and dissipative particle dynamics-thermostat, rather than the case of Langevin thermostat, one finds that HI have little effect on the ⟨f⟩-D profile. Also the change of substrate affinity with respect to the solvent from solvophilic to solvophobic is found to play negligible role in the desorption process. In contrast, a changing ratio ɛ _s^B / ɛ _s^A of the binding energies of A- and B-segments in the detachment of an AB-copolymer from adhesive surface strongly changes the ⟨f⟩-D profile whereby the B-spikes vanish when ɛ _s^B / ɛ _s^A < 0.15. Eventually, performing an atomistic simulation of (bio)-polymers, we demonstrate that the simulation results, derived from our coarse-grained model, comply favorably with those from the all-atom simulation.

  15. Specific features of the force and thermal elastic deformations of chain molecules and their energetics in polymer crystals

    NASA Astrophysics Data System (ADS)

    Slutsker, A. I.; Vettegren, V. I.; Kulik, V. B.; Gilyarov, V. L.; Polikarpov, Yu. I.; Karov, D. D.

    2016-04-01

    In polymer crystals (in particular, polyethylene), changes in the axial and contour lengths of skeletal interatomic bonds in chain molecules under mechanical loading (stretching) and heat treatment (heating) were measured using X-ray diffractometry and Raman spectrometry. The performed analysis of the measured force and temperature dependences gave theoretical descriptions of the deformation of a polymer crystal (the confirmation of the data available in the literature for mechanical loading and an original development for heating). The components of the potential energy of a deformed polymer crystal were determined both for stretching of skeletal bonds and for bending of chain molecules. It was found that there is a significant difference in the ratios of these components for a deformed polymer crystal under mechanical loading and during heating.

  16. Polymer gels with associating side chains and their interaction with surfactants

    NASA Astrophysics Data System (ADS)

    Gordievskaya, Yulia D.; Rumyantsev, Artem M.; Kramarenko, Elena Yu.

    2016-05-01

    Conformational behaviour of hydrophobically modified (HM) polymer gels in solutions of nonionic surfactants is studied theoretically. A HM gel contains hydrophobic side chains (stickers) grafted to its subchains. Hydrophobic stickers are capable to aggregate into joint micelles with surfactant molecules. Micelles containing more than one sticker serve as additional physical cross-links of the network, and their formation causes gel shrinking. In the proposed theoretical model, the interior of the gel/surfactant complex is treated as an array of densely packed spherical polymer brushes consisting of gel subchains tethered to the surface of the spherical sticker/surfactant micelles. Effect of stickers length and grafting density, surfactant concentration and hydrophobicity on gel swelling as well as on hydrophobic association inside it is analyzed. It is shown that increasing surfactant concentration can result in a gel collapse, which is caused by surfactant-induced hydrophobic aggregation of stickers, and a successive gel reswelling. The latter should be attributed to a growing fraction of surfactants in joint aggregates and, hence, increasing number of micelles containing only one sticker and not participating in gel physical cross-linking. In polyelectrolyte (PE) gels hydrophobic aggregation is opposed by osmotic pressure of mobile counterions, so that at some critical ionization degree hydrophobic association is completely suppressed. Hydrophobic modification of polymers is shown to open new ways for controlling gel responsiveness. In particular, it is discussed that incorporation of photosensitive groups into gel subchains and/or surfactant tail could give a possibility to vary the gel volume by light. Since hydrophobic aggregation regularities in gels and solutions are common, we hope our findings will be useful for design of polymer based self-healing materials as well.

  17. Polymer gels with associating side chains and their interaction with surfactants.

    PubMed

    Gordievskaya, Yulia D; Rumyantsev, Artem M; Kramarenko, Elena Yu

    2016-05-14

    Conformational behaviour of hydrophobically modified (HM) polymer gels in solutions of nonionic surfactants is studied theoretically. A HM gel contains hydrophobic side chains (stickers) grafted to its subchains. Hydrophobic stickers are capable to aggregate into joint micelles with surfactant molecules. Micelles containing more than one sticker serve as additional physical cross-links of the network, and their formation causes gel shrinking. In the proposed theoretical model, the interior of the gel/surfactant complex is treated as an array of densely packed spherical polymer brushes consisting of gel subchains tethered to the surface of the spherical sticker/surfactant micelles. Effect of stickers length and grafting density, surfactant concentration and hydrophobicity on gel swelling as well as on hydrophobic association inside it is analyzed. It is shown that increasing surfactant concentration can result in a gel collapse, which is caused by surfactant-induced hydrophobic aggregation of stickers, and a successive gel reswelling. The latter should be attributed to a growing fraction of surfactants in joint aggregates and, hence, increasing number of micelles containing only one sticker and not participating in gel physical cross-linking. In polyelectrolyte (PE) gels hydrophobic aggregation is opposed by osmotic pressure of mobile counterions, so that at some critical ionization degree hydrophobic association is completely suppressed. Hydrophobic modification of polymers is shown to open new ways for controlling gel responsiveness. In particular, it is discussed that incorporation of photosensitive groups into gel subchains and/or surfactant tail could give a possibility to vary the gel volume by light. Since hydrophobic aggregation regularities in gels and solutions are common, we hope our findings will be useful for design of polymer based self-healing materials as well. PMID:27179504

  18. Evaluation of the end-to-end distance of chains solubilized in a polymer Langmuir monolayer by atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Kumaki, Jiro

    Polymer chain packing in two-dimensional (2D) condense state is still not well understood. Direct observation of the chain packing in a monolayer should be the best way to understand this, however, it is still difficult even using atomic force microscopy (AFM) except for extraordinarily thick polymers. In this study, we successfully evaluate the end-to-end distance of the chains in a Langmuir-Blodgett monolayer composed of a conventional polymer by AFM. We successfully solubilized a small amount of a polystyrene-b-poly(methyl methacrylate)-b-polystyrene (PS-b-PMMA-b-PS) triblock copolymer in a PMMA Langmuir monolayer with the PS blocks being condensed as single-PS-block particles which could be used as a probe of the position of the chain ends. The evaluated end-to-end distance was 2.5 times longer than that of the 2D ideal chain, indicating the chains in the 2D monolayer are not strongly segregated but interpenetrates into other chains.

  19. Electrorheological Behavior of Main Chain Liquid Crystal Polymers in Thermotropic Nematic Solvents

    NASA Astrophysics Data System (ADS)

    Chiang, Yen-Ching; Jamieson, Alex. M.

    1998-03-01

    The increment in Miesowicz viscosity, δ η c on dissolving a main-chain liquid crystal polymer (LCP) in a nematic solvent was measured by cone-and-plate rheometry in the presence of a saturation electric field, applied perpendicular to the flow direction. In addition, the corresponding increment in the Leslie viscosity coefficient, δ α 2 was obtained from the dependence of the apparent viscosity response on the applied field strength, by curve-fitting to the torque balance equation using the 2D Ericksen-Leslie-Parodi theory. For the main-chain LCP TPB10, which has mesogenic groups separated by decamethylene spacers, both δ η c and δ α 2 exhibit, within experimental uncertainty, a linear dependence on the molecular weight. Using a hydrodynamic model of Brochard, this observation suggests that the chain behaves as a free-draining random coil, biased along the director. The temperature dependence of the relative viscosity increments, δ η c / η c ^o and δ α 2 / α 2 ^o, where η c ^o and α 2 ^o are the relevant solvent viscosities, exhibits Arrhenius behavior with an activation energy comparable to that for formation of hairpin turns in the spacer groups.

  20. Primitive models of chemical association. IV. Polymer Percus{endash}Yevick ideal-chain approximation for heteronuclear hard-sphere chain fluids

    SciTech Connect

    Kalyuzhnyi, Y.V. |; Lin, C.; Stell, G.

    1998-04-01

    We continue here our series of studies in which integral-equation theory is developed and used for the monomer-monomer correlation functions in a fluid of multicomponent freely jointed hard-sphere polymers. In this study our approach is based on Wertheim{close_quote}s polymer Percus{endash}Yevick (PPY) theory supplemented by the ideal-chain approximation; it can be regarded as a simplified version of Wertheim{close_quote}s four-density PPY approximation for associating fluids considered in the complete-association limit. The numerical procedure of this simplified theory is much easier than that of the original Wertheim{close_quote}s four-density PPY approximation, but the degree of accuracy is reduced. The theory can also be regarded as an extension of the PPY theory for the homonuclear polymer system proposed by Chang and Sandler [J. Chem. Phys. {bold 102}, 437 (1995)]. Their work is based upon a description of a system of hard-sphere monomers that associate into a polydisperse system of chains of prescribed mean length. Our theory instead directly describes a multicomponent system of associating monomers that form monodisperse chains of prescribed length upon complete association. An analytical solution of the PPY ideal-chain approximation for the general case of a multicomponent mixture of heteronuclear hard-sphere linear chain molecules is given. Its use is illustrated by numerical results for two models of copolymer fluids, a symmetrical diblock copolymer system, and an alternating copolymer system. The comparison with Monte Carlo simulations is given to gauge the accuracy of the theory. We find for the molecules we study here that predictions of our theory for heteronuclear chain systems have the same degree of accuracy as Chang and Sandler{close_quote}s theory for homonuclear chain systems. {copyright} {ital 1998 American Institute of Physics.}

  1. Organization of polymer chains onto long, single-wall carbon nano-tubes: effect of tube diameter and cooling method.

    PubMed

    Kumar, Sunil; Pattanayek, Sudip K; Pereira, Gerald G

    2014-01-14

    We use molecular dynamics simulations to investigate the arrangement of polymer chains when absorbed onto a long, single-wall carbon nano-tube (SWCNT). We study the conformation and organization of the polymer chains on the SWCNT and their dependence on the tube's diameter and the rate of cooling. We use two types of cooling processes: direct quenching and gradual cooling. The radial density distribution function and bond orientational order parameter are used to characterize the polymer chain structure near the surface. In the direct cooling process, the beads of the polymer chain organize in lamella-like patterns on the surface of the SWCNT with the long axis of the lamella parallel to the axis of the SWCNT. In a stepwise, gradual cooling process, the polymer beads form a helical pattern on the surface of a relatively thick SWCNT, but form a lamella-like pattern on the surface of a very thin SWCNT. We develop a theoretical (free energy) model to explain this difference in pattern structures for the gradual cooling process and also provide a qualitative explanation for the pattern that forms from the direct cooling process. PMID:24437908

  2. Interaction of polymer with discotic clay particles.

    SciTech Connect

    Auvray, L.; Lal, J.

    1999-08-04

    Normally synthetic well defined monodisperse discotic laponite clays are known to form a gel phase at mass concentrations as low as a few percent in distilled water. Hydrosoluble polymer polyethylene oxide was added to this intriguing clay system, it was observed that it either prevents gelation or slows it down extremely depending on the polymer weight, concentration or the laponite concentration. Small Angle Neutron scattering (SANS) was used to study these systems because only by isotopic labeling can the structure of the adsorbed polymer layers be determined. The contrast variation technique is specifically used to determine separately the different partial structure factors of the clay and polymer. In this way the signal of the adsorbed chains is separated from the signal of the free chains in the dilute regime. Attempts have also been made to characterize the structure in the concentrated regime of laponite with polymer.

  3. Effect of alkyl chain length on the conformation and order of simple ionic surfactants adsorbed at the D{sub 2}O/CCl{sub 4} interface as studied by sum-frequency vibrational spectroscopy

    SciTech Connect

    Conboy, J.C.; Messmer, M.C.; Richmond, G.L.

    1998-11-10

    The conformational order of three alkanesulfonates, sodium hexanesulfonate (HS), sodium undecanesulfonate (UDS), and sodium dodecanesulfonate (DDS), adsorbed at the D{sub 2}O/CCl{sub 4} interface are examined in detail by sum-frequency vibrational spectroscopy. An increase in surfactant concentration at the interface results in the reduction of gauche defects in the hydrocarbon chains as determined from the intensity ratio of the methyl to methylene symmetric stretch vibrational modes. The degree of disorder in the alkyl chains varies greatly with alkyl chain length. The alkyl chain of HS displays the fewest gauche defects while DDS and UDS display more disorder in their hydrocarbon chains at similar surface concentrations. This observation is interpreted as a reduction in the possible number of gauche conformations for the shorter alkyl chain.

  4. The glass transition of polymers with different side-chain stiffness confined in free-standing thin films

    NASA Astrophysics Data System (ADS)

    Xie, Shi-Jie; Qian, Hu-Jun; Lu, Zhong-Yuan

    2015-02-01

    The effect of confinement on the glass transition temperature Tg of polymeric glass formers with different side chain stiffness is investigated by coarse-grained molecular dynamics simulations. We find that polymer with stiffer side groups exhibits much more pronounced Tg variation in confinement compared to that with relatively flexible side groups, in good agreement with experiments. Our string analysis demonstrates that the polymer species dependence of dynamics can be described by an Adam-Gibbs like relation between the size of cooperatively rearranging regions and relaxation time. However, the primary effect of changing side-group stiffness is to alter the activation barrier for rearrangement, rather than string size. We clarify that free-surface perturbation is the primary factor in determining the magnitude of Tg variation for polymers in confinement: It is more significant for polymers having higher Tg and results in much more pronounced reduction of surface Tg and then the overall Tg of the polymers.

  5. Orientation Difference of Chemically Immobilized and Physically Adsorbed Biological Molecules on Polymers Detected at the Solid/Liquid Interfaces in Situ

    PubMed Central

    Ye, Shuji; Nguyen, Khoi Tan; Boughton, Andrew P.; Mello, Charlene M.; Chen, Zhan

    2009-01-01

    A surface sensitive second order nonlinear optical technique, sum frequency generation (SFG) vibrational spectroscopy, was applied to study peptide orientation on polymer surfaces, supplemented by a linear vibrational spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Using the antimicrobial peptide Cecropin P1 as a model system, we have quantitatively demonstrated that chemically immobilized peptides on polymers adopt a more ordered orientation than less tightly bound physically adsorbed peptides. These differences were also observed in different chemical environments, e.g., air versus water. Although numerous studies have reported a direct correlation between the choice of immobilization method and the performance of an attached biological molecule, the lack of direct biomolecular structure and orientation data has made it difficult to elucidate the relationship between structure, orientation and function at a surface. In this work, we directly studied the effect of chemical immobilization method on biomolecular orientation/ordering, an important step for future studies of biomolecular activity. The methods for orientation analysis described within are also of relevance to understanding biosensors, biocompatibility, marine-antifouling, membrane protein functions, and antimicrobial peptide activities. PMID:19961170

  6. On the Interfacial Properties of Polymers/Functionalized Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Ansari, R.; Rouhi, S.; Ajori, S.

    2016-06-01

    Molecular dynamics (MD) simulations is used to study the adsorption of polyethylene (PE) and poly(ethylene oxide) (PEO) on the functionalized single-walled carbon nanotubes (SWCNTs). The effects of functionalization factor weight percent on the interaction energies of polymer chains with nanotubes are studied. Besides, the influences of different functionalization factors on the SWCNT/polymer interactions are investigated. It is shown that for both types of polymer chains, the largest interaction energies associates with the random O functionalized nanotubes. Besides, increasing temperature results in increasing the nanotube/polymer interaction energy. Considering the final shapes of adsorbed polymer chains on the SWCNTs, it is observed that the adsorbed conformations of PE chains are more contracted than those of PEO chains.

  7. On the Interfacial Properties of Polymers/Functionalized Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Ansari, R.; Rouhi, S.; Ajori, S.

    2016-03-01

    Molecular dynamics (MD) simulations is used to study the adsorption of polyethylene (PE) and poly(ethylene oxide) (PEO) on the functionalized single-walled carbon nanotubes (SWCNTs). The effects of functionalization factor weight percent on the interaction energies of polymer chains with nanotubes are studied. Besides, the influences of different functionalization factors on the SWCNT/polymer interactions are investigated. It is shown that for both types of polymer chains, the largest interaction energies associates with the random O functionalized nanotubes. Besides, increasing temperature results in increasing the nanotube/polymer interaction energy. Considering the final shapes of adsorbed polymer chains on the SWCNTs, it is observed that the adsorbed conformations of PE chains are more contracted than those of PEO chains.

  8. Shape-Selectivity with Liquid Crystal and Side-Chain Liquid Crystalline Polymer SAW Sensor Interfaces

    SciTech Connect

    FRYE-MASON,GREGORY CHARLES; OBORNY,MICHAEL C.; PUGH,COLEEN; RICCO,ANTONIO; THOMAS,ROSS C.; ZELLERS,EDWARD T.; ZHANG,GUO-ZHENG

    1999-09-23

    A liquid crystal (LC) and a side-chain liquid crystalline polymer (SCLCP) were tested as surface acoustic wave (SAW) vapor sensor coatings for discriminating between pairs of isomeric organic vapors. Both exhibit room temperature smectic mesophases. Temperature, electric-field, and pretreatment with self-assembled monolayers comprising either a methyl-terminated or carboxylic acid-terminated alkane thiol anchored to a gold layer in the delay path of the sensor were explored as means of affecting the alignment and selectivity of the LC and SCLCP films. Results for the LC were mixed, while those for the SCLCP showed a consistent preference for the more rod-like isomer of each isomer pair examined.

  9. Magnetic hydrophilic methacrylate-based polymer microspheres designed for polymerase chain reactions applications.

    PubMed

    Spanová, Alena; Horák, Daniel; Soudková, Eva; Rittich, Bohuslav

    2004-02-01

    Magnetic hydrophilic non-porous P(HEMA-co-EDMA), P(HEMA-co-GMA) and PGMA microspheres were prepared by dispersion (co)polymerization of 2-hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate (EDMA) or glycidyl methacrylate (GMA) in the presence of several kinds of magnetite. It was found that some components used in the preparation of magnetic carriers interfered with polymerase chain reaction (PCR). Influence of non-magnetic and magnetic microspheres, including magnetite nanoparticles and various components used in their synthesis, on the PCR course was thus investigated. DNA isolated from bacterial cells of Bifidobacterium longum was used in PCR evaluation of non-interfering magnetic microspheres. The method enabled verification of the incorporation of magnetite nanoparticles in the particular methacrylate-based polymer microspheres and evaluation of suitability of their application in PCR. Preferably, electrostatically stabilized colloidal magnetite (ferrofluid) should be used in the design of new magnetic methacrylate-based microspheres by dispersion polymerization. PMID:14698232

  10. Exploring the low temperature thermodynamics of lattice proteins and polymers with chain lengths > 1000

    NASA Astrophysics Data System (ADS)

    Wuest, Thomas

    2012-02-01

    Coarse-grained (lattice-) models have a long tradition in aiding to decipher the physical or biological complexity of polymers and proteins. Despite their simplicity however, numerical simulations of such models are often computationally very demanding and the quest for efficient algorithms is as old as the models themselves. I present a computational method based on Wang-Landau sampling in combination with suitable trial move sets which is particularly effective to study models such as the hydrophobic-polar (HP) lattice model of protein folding or its counterpart in polymer physics, the interactive self-avoiding walk (ISAW) at low temperatures. The approach provides a versatile and powerful mean for both the ground state search and the determination of the entire energy density of states (DOS) yielding reliable estimates of thermodynamic quantities for chain lengths > 4000 (ISAW) even in the very dense collapsed phase. The appearance of multiple low temperature pseudo-transitions for ISAWs will be elucidated. Further methodological improvements will be discussed.

  11. Large-scale simulations of a polymer melt/brush interface: Adhesion enhancement due to surface-tethered chains

    NASA Astrophysics Data System (ADS)

    Sides, Scott; Grest, Gary; Stevens, Mark

    2000-03-01

    Many important adhesives consist of polymeric materials, that are used to bind together flat, hard surfaces. Experiments like the JKR pull test are able to measure the work needed to separate a polymer melt in contact with a flat substrate. Ignoring macroscopic dissipation mechanisms due to viscoelastic effects within the polymer melt, the work of adhesion is related to van der Waals forces between the substrate and melt. Recent experiments have shown that polymer chains tethered to the substrate enhance adhesion due to entanglements with the polymer melt. (L. Léger, E. Raphaël and H. Hervet, in Advances In Polymer Science), edited by S. Granick (Springer, Berlin, 1999), v. 138, p. 185. This increase in the work of adhesion (W_A) is a non-monotonic function of both the length (N) and surface density (σ) of the tethered chains. Using molecular dynamics (MD) simulations we study the dependence of WA on N, σ and the pulling rate. In our simulations, we also observe the various microscopic dissipation mechanisms such as pull-out and scission of the end-tethered chains, which is difficult to observe directly in an experiment. These large simulations are made possible by using a massively-parallel MD code run on Sandia's teraflop machine.

  12. Hydrothermal synthesis and structural characterization of two novel lanthanide supramolecular coordination polymers with nano-chains

    NASA Astrophysics Data System (ADS)

    Wan, Yong-Hong; Jin, Lin-Pei; Wang, Ke-Zhi

    2003-04-01

    Two novel lanthanide supramolecular coordination polymers, {[Nd 2(phth) 3(phen)(H 2O)]·H 2O} n ( 1, phth=phthalate, phen=1,10-phenanthroline) and {[Ho 2(phth) 3(phen)(H 2O) 2]·3H 2O} n ( 2), have been synthesized by hydrothermal method and characterized by X-ray diffraction. The results show that complex 1 crystallizes in triclinic space group P 1¯ with a=7.605(2) Å, b=12.972(4) Å, c=18.773(6) Å, α=109.778(5)°, β=91.657(5)°, γ=103.951(5)° and Z=2. Complex 1 has a one-dimentional nano-chain structure and the existence of hydrogen bonds and π- π interactions results in 2D network structure. Complex 2 crystallizes in triclinic space group P 1¯ with a=11.695(2) Å, b=13.488(3) Å, c=13.761(3) Å, α=87.09(3)°, β=67.40(3)°, γ=67.41(3)° and Z=2. Complex 2 features a zigzag double-chain and the hydrogen bonds lead to the formation of a three-dimensional network. Both Complex 1 and 2 have two metal environments.

  13. Theoretical modeling of the effect of polymer chain immobilization rates on holographic recording in photopolymers.

    PubMed

    Mackey, Dana; O'Reilly, Paul; Naydenova, Izabela

    2016-05-01

    This paper introduces an improved mathematical model for holographic grating formation in an acrylamide-based photopolymer, which consists of partial differential equations derived from physical laws. The model is based on the two-way diffusion theory of [Appl. Opt.43, 2900 (2004)10.1364/AO.43.002900APOPAI1559-128X], which assumes short polymer chains are free to diffuse, and generalizes a similar model presented in [J. Opt. Soc. Am. B27, 197 (2010)10.1364/JOSAB.27.000197JOBPDE0740-3224] by introducing an immobilization rate governed by chain growth and cross-linking. Numerical simulations were carried out in order to investigate the behavior of the photopolymer system for short and long exposures, with particular emphasis on the effect of recording parameters (such as illumination frequency and intensity), as well as material permeability, on refractive index modulation, refractive index profile, and grating distortion. The model reproduces many well-known experimental observations, such as the decrease of refractive index modulation at high spatial frequencies and appearance of higher harmonics in the refractive index profile when the diffusion rate is much slower than the polymerization rate. These properties are supported by a theoretical investigation which uses perturbation techniques to approximate the solution over various time scales. PMID:27140889

  14. The effect of chain stiffness on moisture diffusion in polymer hydrogel by applying obstruction-scaling model

    NASA Astrophysics Data System (ADS)

    Yang, Yoona; Chun, Myung-Suk

    2013-11-01

    In order to understand the moisture diffusion, we combine the obstruction-scaling model with the moisture clustering in confined spaces of the polymer hydrogel, with relevance to the performance of the super desiccant polymer. Special attention is focused on elucidating the effect of chain stiffness by considering the conformation of polymer chain on the basis of polymer physics. Relevant parameters for calculations are determined from literature information as well as the best fits for reported data performed with the copolymer. Our results exhibit the moisture diffusion decreases with increasing chain stiffness represented by the persistence length. Note that the larger persistence length provides smaller radius of openings in void spaces, resulting in the stronger hindrance effect on the moisture diffusion. Higher temperature makes the water molecules to be easier to form clusters, which provides the decrease in diffusivity. The increase of moisture diffusion at low humidity is attributed to the swelling of the chain, whereas its decrease at high humidity results from the water clustering.

  15. Fiber-based adsorbents having high adsorption capacities for recovering dissolved metals and methods thereof

    DOEpatents

    Janke, Christopher J; Dai, Sheng; Oyola, Yatsandra

    2014-05-13

    A fiber-based adsorbent and a related method of manufacture are provided. The fiber-based adsorbent includes polymer fibers with grafted side chains and an increased surface area per unit weight over known fibers to increase the adsorption of dissolved metals, for example uranium, from aqueous solutions. The polymer fibers include a circular morphology in some embodiments, having a mean diameter of less than 15 microns, optionally less than about 1 micron. In other embodiments, the polymer fibers include a non-circular morphology, optionally defining multiple gear-shaped, winged-shaped or lobe-shaped projections along the length of the polymer fibers. A method for forming the fiber-based adsorbents includes irradiating high surface area polymer fibers, grafting with polymerizable reactive monomers, reacting the grafted fibers with hydroxylamine, and conditioning with an alkaline solution. High surface area fiber-based adsorbents formed according to the present method demonstrated a significantly improved uranium adsorption capacity per unit weight over existing adsorbents.

  16. Monte Carlo simulations of a polymer chain conformation. The effectiveness of local moves algorithms and estimation of entropy.

    PubMed

    Mańka, Agnieszka; Nowicki, Waldemar; Nowicka, Grażyna

    2013-09-01

    A linear chain on a simple cubic lattice was simulated by the Metropolis Monte Carlo method using a combination of local and non-local chain modifications. Kink-jump, crankshaft, reptation and end-segment moves were used for local changes of the chain conformation, while for non-local chain rearrangements the "cut-and-paste" algorithm was employed. The statistics of local micromodifications was examined. An approximate method for estimating the conformational entropy of a polymer chain, based on the efficiency of the kink-jump motion respecting chain continuity and excluded volume constraints, was proposed. The method was tested by calculating the conformational entropy of the undisturbed chain, the chain under tension and in different solvent conditions (athermal, theta and poor) and also of the chain confined in a slit. The results of these test calculations are qualitatively consistent with expectations. Moreover, the obtained values of the conformational entropy of self avoiding chain with ends fixed over different separations, agree very well with the available literature data. PMID:23765038

  17. Triazine‐Based Sequence‐Defined Polymers with Side‐Chain Diversity and Backbone–Backbone Interaction Motifs

    PubMed Central

    Mo, Kai‐For; Daily, Michael D.

    2016-01-01

    Abstract Sequence control in polymers, well‐known in nature, encodes structure and functionality. Here we introduce a new architecture, based on the nucleophilic aromatic substitution chemistry of cyanuric chloride, that creates a new class of sequence‐defined polymers dubbed TZPs. Proof of concept is demonstrated with two synthesized hexamers, having neutral and ionizable side chains. Molecular dynamics simulations show backbone–backbone interactions, including H‐bonding motifs and pi–pi interactions. This architecture is arguably biomimetic while differing from sequence‐defined polymers having peptide bonds. The synthetic methodology supports the structural diversity of side chains known in peptides, as well as backbone–backbone hydrogen‐bonding motifs, and will thus enable new macromolecules and materials with useful functions. PMID:26865312

  18. Control of the anchoring behavior of polymer-dispersed liquid crystals: effect of branching in the side chains of polyacrylates.

    PubMed

    Zhou, Jian; Collard, David M; Park, Jung O; Srinivasarao, Mohan

    2002-08-28

    A temperature-driven anchoring transition in a polymer/nematic fluid composite that is far from the bulk nematic-isotropic transition temperature is reported. A series of poly(methylheptyl acrylates) were studied to probe the subtle effects of the side chain structure of the polymer on control of the anchoring. A polymer-dispersed liquid crystal film made from TL205 and 1-methylheptyl acrylate shows only planar anchoring over the temperature range studied, while the films made from TL205 and each of the other methylheptyl acrylates or n-heptyl acrylate show the homeotropic-to-planar anchoring transition at temperatures between 70 and 78 degrees C. An interfacial model is proposed in which the different conformation of the side chains is suggested as the cause for the dramatic difference in the observed anchoring behavior. PMID:12188649

  19. Importance of Chain Connectivity in the Formation of Non-covalent Interactions between Polymers and Single-Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Linton, Dias; Miller, Brad C.; Li, Huimin; Feigerle, Charles; Sumpter, Bobby G.; Dadmun, Mark D.

    2009-03-01

    Our work is focused on understanding and utilizing non-covalent electron donor-acceptor (EDA) interactions between polymers and SWNT to optimize interfacial adhesion and homogeneity of nanocomposites without modifying the SWNT native surface. Nanocomposites with polymer bound electron donating 2-(dimethylamino)ethyl methacrylate or electron accepting acrylonitrile and cyanostyrene moieties leads to improved SWNT dispersion if the interacting functional group is a minor component of a copolymer matrix. Correlation of experimental (Raman mapping, Raman D* band peak shifts, and optical microscopy) and computational results indicates that chain connectivity is critical in controlling the accessibility of the functional groups to form EDA interactions. Thus, controlling the amount of e^- donating or withdrawing moieties throughout the polymer chain will direct the extent of EDA interaction, which enables tuning the SWNT dispersion.

  20. Calculation of the Radius of Gyration for a Linear Flexible Polymer Chain with Excluded Volume Interaction.

    NASA Astrophysics Data System (ADS)

    Shanes, Fredrick Charles

    1990-01-01

    We have calculated the radius of gyration for a three dimensional linear flexible polymer chain with excluded volume interaction. The resulting < S^2> is written as a perturbation series in the dimensionless excluded volume parameter z, and the series is written to O(z ^4) as = (Ll/6)(1 + 1.276190476z - 2.081948603z^2 + 6.564897382z^3 - 26.70629003z^4 + ...) where z = (3/2pil) ^{3/2}omegaL^ {1/2} with l the effective segment length, L the contour length, and omegal^2 the effective binary cluster integral for a pair of segments. The perturbation theory used to calculate has recently been applied to the mean square end-to-end distance for a linear flexible polymer chain by Muthukumar and Nickel. The theory essentially uses the continuum limit of the two -parameter model, Laplace transforms, and a diagrammatic expansion in conjunction with field theory methods. The perturbation theory was found to be much simpler to implement than the usual cluster expansion method, and thus we were able to extend the series from the previously known O(z^2) to O(z^4 ). The perturbation series for < S^2> and are divergent, and are only valid for small z values. However, the most interesting information about these properties occurs for large z values. The large z limit of the and series were extracted by using the direct renormalization method, and estimates for the critical exponents and scaling amplitudes were obtained. A quantity that is of theoretical interest is the large z limit of the ratio 6/< R^2>, since it is believed to be a universal constant (i.e., independent of the model). We calculated the ratio by applying four different renormalization schemes to the perturbation series for and , and we obtained a final estimate of 6 / = 0.9631 +/- 0.0003. We also analysed the Monte Carlo self-avoiding walk data for the ratio and found the large chain limit of 6 / = 0.9602 +/- 0.0002. The

  1. Effect of chain stiffness on the competition between crystallization and glass-formation in model unentangled polymers

    NASA Astrophysics Data System (ADS)

    Nguyen, Hong T.; Smith, Tyler B.; Hoy, Robert S.; Karayiannis, Nikos Ch.

    2015-10-01

    We map out the solid-state morphologies formed by model soft-pearl-necklace polymers as a function of chain stiffness, spanning the range from fully flexible to rodlike chains. The ratio of Kuhn length to bead diameter (lK/r0) increases monotonically with increasing bending stiffness kb and yields a one-parameter model that relates chain shape to bulk morphology. In the flexible limit, monomers occupy the sites of close-packed crystallites while chains retain random-walk-like order. In the rodlike limit, nematic chain ordering typical of lamellar precursors coexists with close-packing. At intermediate values of bending stiffness, the competition between random-walk-like and nematic chain ordering produces glass-formation; the range of kb over which this occurs increases with the thermal cooling rate | T ˙ | implemented in our molecular dynamics simulations. Finally, values of kb between the glass-forming and rodlike ranges produce complex ordered phases such as close-packed spirals. Our results should provide a useful initial step in a coarse-grained modeling approach to systematically determining the effect of chain stiffness on the crystallization-vs-glass-formation competition in both synthetic and colloidal polymers.

  2. The synthesis and imaging study of a series of novel photoactive polymers with diazoketo groups in their side chains

    NASA Astrophysics Data System (ADS)

    Liu, Lu; Zou, Yingquan; Yang, Yuchun; Huang, Yong; Liu, Qisheng; Niu, Huinan

    2009-12-01

    A kind of photoactive polymer with diazoketo groups in its side chains has been reported in SPIE and other related papers, and this photoactive polymer can be used in deep UV non-CARs (non-chemically amplified resists) system. Based on the work above, a series of novel photoactive monomers with substituents like phenyl, p-methylphenyl, p-methoxyphenyl, p-dimethylaminophenyl on the end of the molecule are designed and synthesized. By changing their substituents, the maximum-absorption wavelength of the photoactive monomers has been moved to 356nm, and it still has comparatively large absorption at 365nm (I-line). A series of photoactive polymers were obtained by polymerizing the monomer with methyl methacrylate and 2-hydroxyethyl methacrylate together. Upon irradiaton in the waveleng of 365nm, the diazoketo groups which are in the side chains of the photoactive polymers undergo the wolff rearrangment and afford ketens that react with water to provide base-soluble photoproducts. Applying this kind of photoactive polymers to non-CARs, a positive image can be obtained. This kind of photoactive polymers have great value in I-line non-CARs, TFT-LCD and IC discrete devices processing. And its anti-dry etching ability is enhanced by the introduction of the benzene ring.

  3. Static and dynamic properties of the interface between a polymer brush and a melt of identical chains.

    PubMed

    Pastorino, C; Binder, K; Kreer, T; Müller, M

    2006-02-14

    Molecular-dynamics simulations of a short-chain polymer melt between two brush-covered surfaces under shear have been performed. The end-grafted polymers which constitute the brush have the same chemical properties as the free chains in the melt and provide a soft deformable substrate. Polymer chains are described by a coarse-grained bead-spring model, which includes excluded volume and backbone connectivity of the chains. The grafting density of the brush layer offers a way of controlling the behavior of the surface without altering the molecular interactions. We perform equilibrium and nonequilibrium molecular-dynamics simulations at constant temperature and volume using the dissipative particle dynamics thermostat. The equilibrium density profiles and the behavior under shear are studied as well as the interdigitation of the melt into the brush, the orientation on different length scales (bond vectors, radius of gyration, and end-to-end vector) of free and grafted chains, and velocity profiles. The obtained boundary conditions and slip length show a rich behavior as a function of grafting density and shear velocity. PMID:16483239

  4. Site blocking effects on adsorbed polyacrylamide conformation

    NASA Astrophysics Data System (ADS)

    Brotherson, Brett A.

    The use of polymers as flocculating additives is a common practice in many manufacturing environments. However, exactly how these polymers interact with surfaces is relatively unknown. One specific topic which is thought to be very important to flocculation is an adsorbed polymer's conformation. Substantial amounts of previous work, mainly using simulations, have been performed to elucidate the theory surrounding adsorbed polymer conformations. Yet, there is little experimental work which directly verifies current theory. In order to optimize the use of polymer flocculants in industrial applications, a better understanding of an adsorbed polymer's conformation on a surface beyond theoretical simulations is necessary. This work looks specifically at site blocking, which has a broad impact on flocculation, adsorption, and surface modification, and investigated its effects on the resulting adsorbed polymer conformation. Experimental methods which would allow direct determination of adsorbed polymer conformational details and be comparable with previous experimental results were first determined or developed. Characterization of an adsorbed polymer's conformation was then evaluated using dynamic light scattering, a currently accepted experimental technique to examine this. This commonly used technique was performed to allow the comparison of this works results with past literature. Next, a new technique using atomic force microscopy was developed, building on previous experimental techniques, to allow the direct determination of an adsorbed polymer's loop lengths. This method also was able to quantify changes in the length of adsorbed polymer tails. Finally, mesoscopic simulation was attempted using dissipative particle dynamics. In order to determine more information about an adsorbed polymer's conformation, three different environmental factors were analyzed: an adsorbed polymer on a surface in water, an adsorbed polymer on a surface in aqueous solutions of varying

  5. Intricacies of Polymer Dewetting: Nanoscaled Architectures for the Tailored Control of Polystyrene Thin Film Stability

    NASA Astrophysics Data System (ADS)

    Cheung, Justin; Sen, Mani; Chen, Zhizhao; Jiang, Naisheng; Endoh, Maya; Koga, Tadanori; Satija, Sushil

    Recently, structural properties of polymer thin films have garnered attention for their relevance in the fields of organic photovoltaics and biosensors. The dewetting of polymer films poses an obstacle in the face of widespread implementation. For this study, we show that adsorbed polymer chains on a substrate surface play crucial roles in film stability. Polystyrene (PS) thin films (20 nm in thickness) with different molecular weights (Mw) on silicon (Si) substrates were used as a model. The PS films were annealed at high temperatures for several days, and Mw dependence on film stability was evidenced. At the same time, the annealed PS films were leached with a good solvent and the residue films (i.e., irreversibly adsorbed layers) were characterized by x-ray reflectivity (XR). We reveal strong correlation between film stability and two different interfacial structures of the adsorbed polymer chains: their opposing wettability against chemically identical free polymer chains results in a wetting-dewetting transition at the adsorbed polymer-free polymer interface. This is a unique aspect of polymer thin film stability and may be generalizable to other polymer systems regardless of the magnitude of solid-polymer attractive interactions. We acknowledge the financial support of NSF Grant (CMMI-1332499).

  6. Dissipative particle dynamics study of translational diffusion of rigid-chain rodlike polymer in nematic phase

    NASA Astrophysics Data System (ADS)

    Zhao, Tongyang; Wang, Xiaogong

    2013-09-01

    In this study, dissipative particle dynamics (DPD) method was employed to investigate the translational diffusion of rodlike polymer in its nematic phase. The polymer chain was modeled by a rigid rod composed of consecutive DPD particles and solvent was represented by independent DPD particles. To fully understand the translational motion of the rods in the anisotropic phase, four diffusion coefficients, D_{||}u, D_ bot u, D_{||}n, D_ bot n were obtained from the DPD simulation. By definition, D_{||}n and D_ bot n denote the diffusion coefficients parallel and perpendicular to the nematic director, while D_{||}u and D_ bot u denote the diffusion coefficients parallel and perpendicular to the long axis of a rigid rod u. In the simulation, the velocity auto-correlation functions were used to calculate the corresponding diffusion coefficients from the simulated velocity of the rods. Simulation results show that the variation of orientational order caused by concentration and temperature changes has substantial influences on D_{||}u and D_ bot u. In the nematic phase, the changes of concentration and temperature will result in a change of local environment of rods, which directly influence D_{||}u and D_ bot u. Both D_{||}n and D_ bot n can be represented as averages of D_{||}u and D_ bot u, and the weighted factors are functions of the orientational order parameter S2. The effect of concentration and temperature on D_{||}n and D_ bot n demonstrated by the DPD simulation can be rationally interpreted by considering their influences on D_{||}u, D_ bot u and the order parameter S2.

  7. Liquid crystalline polymers in good nematic solvents: Free chains, mushrooms, and brushes

    SciTech Connect

    Williams, D.R.M. . Lab. de Physique de la Matiere Condensee); Halperin, A. . Dept. of Materials)

    1993-08-02

    The swelling of main chain liquid crystalline polymers (LCPs) in good nematic solvents is theoretically studied, focusing on brushes of terminally anchored, grafted LCPs. The analysis is concerned with long LCPs, of length L, with n[sub 0] >> 1 hairpin defects. The extension behavior of the major axis, R[parallel], of these ellipsoidal objects gives rise to an Ising elasticity with a free energy penalty of F[sub el](R[parallel])/kT [approx] n[sub 0] [minus] n[sub 0](1 [minus] R[parallel][sup 2]/L[sup 2])[sup 1/2]. The theory of the extension behavior enables the formulation of a Flory type theory of swelling of isolated LCPs yielding R[parallel] [approx] exp(2U[sub h]/5kT)N[sup 3/5] and R [perpendicular] [approx] exp([minus]U[sub h]/10kT)N[sup 3/5], with N the degree of polymerization and U[sub h] the hairpin energy. It also allows the generalization of the Alexander model for polymer brushes to the case of grafted LCPs. The behavior of LCP brushes depends on the alignment imposed by the grafting surface and the liquid crystalline solvent. A tilting phase transition is predicted as the grafting density is increased for a surface imposing homogeneous, parallel anchoring. A related transition is expected upon compression of a brush subject to homeotropic, perpendicular alignment. The effect of magnetic or electric fields on these phase transitions is also studied. The critical magnetic/electric field for the Frederiks transition can be lowered to arbitrarily small values by using surfaces coated by brushes of appropriate density.

  8. Impact of glucose polymer chain length on heat and physical stability of milk protein-carbohydrate nutritional beverages.

    PubMed

    Chen, Biye; O'Mahony, James A

    2016-11-15

    This study investigated the impact of glucose polymer chain length on heat and physical stability of milk protein isolate (MPI)-carbohydrate nutritional beverages containing 8.5% w/w total protein and 5% w/w carbohydrate. The maltodextrin and corn syrup solids glucose polymers used had dextrose equivalent (DE) values of 17 or 38, respectively. Increasing DE value of the glucose polymers resulted in a greater increase in brown colour development, ionic calcium, protein particle size, apparent viscosity and pseudoplastic rheological behaviour, and greater reduction in pH, hydration and heat stability on sterilisation at 120°C. Incorporation of glucose polymers with MPI retarded sedimentation of protein during accelerated physical stability testing, with maltodextrin DE17 causing a greater reduction in sedimentation velocity and compressibility of sediment formed than corn syrup solids DE38. The results demonstrate that chain length of the glucose polymer used strongly impacts heat and physical stability of MPI-carbohydrate nutritional beverages. PMID:27283657

  9. Synthesis and Photophysical Properties of Soluble Low-Bandgap Thienothiophene Polymers with Various Alkyl Side-Chain Lengths

    SciTech Connect

    Bae, W. J.; Scilla, C.; Duzhko, V. V.; Jo, Jang; Coughlin, E. B.

    2011-05-27

    We report the facile synthesis and characterization of a class of thienothiophene polymers with various lengths of alkyl side chains. A series of 2-alkylthieno[3,4-b]thiophene monomers (Ttx) have been synthesized in a two-step protocol in an overall yield of 28–37%. Poly(2-alkylthieno[3,4-b]thiophenes) (PTtx, alkyl: pentyl, hexyl, heptyl, octyl, and tridecyl) were synthesized by oxidative polymerization with FeCl₃ or via Grignard metathesis (GRIM) polymerization methods. The polymers are readily soluble in common organic solvents. The polymers synthesized by GRIM polymerization method (PTtx-G) have narrower molecular weight distribution (Ð) with lower molecular weight (Mn) than those synthesized by oxidative polymerization (PTtx-O). The band structures of the polymers with various lengths of alkyl side chains were investigated by UV–vis spectroscopy, cyclic voltammetry, and ultraviolet photoelectron spectroscopy. These low-bandgap polymers are good candidates for organic transistors, organic light-emitting diodes, and organic photovoltaic cells.

  10. Structure and Electronic Properties of Polymer Chains and Graphene Nanoribbon Formed by Molecular Self-Assembly on Au(111)

    NASA Astrophysics Data System (ADS)

    Ma, Chuanxu; Fuentes-Cabrera, Miguel A.; Sumpter, Bobby G.; Hong, Kunlun; Li, An-Ping; Xiao, Zhongcan; Lu, Wenchang; Bernholc, J.

    Graphene nanoribbons (GNRs) with bandgaps are promising building blocks for ultra-fast electronics. Bottom-up synthesis of GNRs from aromatic hydrocarbon molecules has been proven to be an effective way to control GNR's width with atomically precise edge structures. Using scanning tunneling microscopy (STM), we study the formation of both linear polymer chains and narrow GNRs in the bottom-up self-assembly process with the DBBA molecules as the precursor on Au(111). The linear polymer chains are formed after the deposition of DBBA and 200 °C annealing for 30 min. The polymers can be converted to 7-AGNRs (seven-carbon wide armchair GNRs) after 400 °C annealing. Interestingly, second-layer polymer is seen to survive on the GNRs during the annealing process. This result indicates that the Au(111) substrate plays an important role in the dehydrogenation process and the formation of GNRs, which is confirmed by our DFT calculations. Electronically, the polymers show a bandgap of 3.4 eV, much larger than that of GNRs. After annealing at 500 °C for 30 min, wider GNRs can form: 14-AGNR, 21-AGNR. The 7-AGNR shows a typical edge state at -1.1 eV, while for 14-AGNR it is at -1.35 eV. Moreover, junctions of GNRs with different widths can be formed with pronounced boundary states.

  11. Solution‐crystallization and related phenomena in 9,9‐dialkyl‐fluorene polymers. II. Influence of side‐chain structure

    PubMed Central

    Perevedentsev, Aleksandr; Stavrinou, Paul N.; Smith, Paul

    2015-01-01

    ABSTRACT Solution‐crystallization is studied for two polyfluorene polymers possessing different side‐chain structures. Thermal analysis and temperature‐dependent optical spectroscopy are used to clarify the nature of the crystallization process, while X‐ray diffraction and scanning electron microscopy reveal important differences in the resulting microstructures. It is shown that the planar‐zigzag chain conformation termed the β‐phase, which is observed for certain linear‐side‐chain polyfluorenes, is necessary for the formation of so‐called polymer‐solvent compounds for these polymers. Introduction of alternating fluorene repeat units with branched side‐chains prevents formation of the β‐phase conformation and results in non‐solvated, i.e. melt‐crystallization‐type, polymer crystals. Unlike non‐solvated polymer crystals, for which the chain conformation is stabilized by its incorporation into a crystalline lattice, the β‐phase conformation is stabilized by complexation with solvent molecules and, therefore, its formation does not require specific inter‐chain interactions. The presented results clarify the fundamental differences between the β‐phase and other conformational/crystalline forms of polyfluorenes. © 2015 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1492–1506

  12. An Adsorbate Discriminatory Gate Effect in a Flexible Porous Coordination Polymer for Selective Adsorption of CO2 over C2H2.

    PubMed

    Foo, Maw Lin; Matsuda, Ryotaro; Hijikata, Yuh; Krishna, Rajamani; Sato, Hiroshi; Horike, Satoshi; Hori, Akihiro; Duan, Jingui; Sato, Yohei; Kubota, Yoshiki; Takata, Masaki; Kitagawa, Susumu

    2016-03-01

    The adsorptive separation of C2H2 and CO2 via porous materials is nontrivial due to the close similarities of their boiling points and kinetic diameters. In this work, we describe a new flexible porous coordination polymer (PCP) [Mn(bdc)(dpe)] (H2bdc = 1,4-benzenedicarboxylic acid, dpe = 1,2-di(4-pyridyl)ethylene) having zero-dimensional pores, which shows an adsorbate discriminatory gate effect. The compound shows gate opening type abrupt adsorption for C2H2 but not for CO2, leading to an appreciable selective adsorption of CO2 over C2H2 at near ambient temperature (273 K). The origin of this unique selectivity, as unveiled by in situ adsorption-X-ray diffraction experiments and density functional theory calculations, is due to vastly different orientations between the phenylene ring of bdc and each gas in the nanopores. The structural change by photochemical transformation of this PCP via [2 + 2] photodimerization leads to the removal of inverse CO2/C2H2 selectivity, verifying the mechanism of the guest discriminatory gate effect. PMID:26876504

  13. Influence of side-chain regiochemistry on the transistor performance of high-mobility, all-donor polymers.

    PubMed

    Fei, Zhuping; Pattanasattayavong, Pichaya; Han, Yang; Schroeder, Bob C; Yan, Feng; Kline, R Joseph; Anthopoulos, Thomas D; Heeney, Martin

    2014-10-29

    Three novel polythiophene isomers are reported whereby the only difference in structure relates to the regiochemistry of the solubilizing side chains on the backbone. This is demonstrated to have a significant impact on the optoelectronic properties of the polymers and their propensity to aggregate in solution. These differences are rationalized on the basis of differences in backbone torsion. The polymer with the largest effective conjugation length is demonstrated to exhibit the highest field-effect mobility, with peak values up to 4.6 cm(2) V(-1) s(-1). PMID:25302474

  14. Exploring the correlation between molecular conformation and optoelectronic properties of conjugated polymers : side-chain versus main-chain electron acceptors

    NASA Astrophysics Data System (ADS)

    Huang, Yu-Chen; Huang, Ching-I.

    2013-03-01

    Polythiophene derivatives have been shown among the most promising materials for solar cell application because of their high charge mobility and light absorption. In the mostly studied, a recombination process often occurs, which is mainly due to the fact that the mobility of hole is much lower than that of electron. Hence, research about conjugated polymers containing donor-accepter pairs (such as PT-TPD) becomes quite popular because these materials have narrow band-gaps. Interestingly, these experimental studies have indicated a much more complex correlation between the optoelectronic properties and molecular conformation for polymers with acceptor units on either main or side chain. However, the effects associated with the molecular packing on the resultant chain conformation behavior and thereafter the optoelectronic properties have not been systematically discussed. In order to clarify the effects of the molecular conformation as well as the optoelectronic properties, we employ molecular dynamics and quantum mechanical methods to examine PBTTPD molecules with acceptor unit (TPD) on either main or side chain Computation resources from the National Center for High-Performance Computing of Taiwan and Computer and Information Networking Center of National Taiwan University.

  15. A hierarchical model for surface effects on chain conformation and rheology of polymer solutions. II. Application to a neutral surface

    NASA Astrophysics Data System (ADS)

    Mavrantzas, Vlasis G.; Beris, Antony N.

    1999-01-01

    In this part, the general formulation described in Part I is applied to the modeling of the behavior of a dilute polymer solution near a purely repulsive, planar solid surface, i.e., near a noninteracting wall. The static equilibrium problem is considered first. The model equations here reduce to a minimization problem for the Helmholtz free energy of the system, which results into the well known equilibrium condition that the chemical potentials of all chain conformations in the interfacial area should be equal to each other. The numerical results show that the loss of polymer conformational entropy in the interfacial region gives rise to a strong polymer depletion which extends up to a distance about three times the equilibrium root-mean-square polymer end-to-end distance. Next, the problem of a polymer solution flowing past the wall is investigated. Here, the full model equations need to be considered; these are solved numerically with a spectral collocation technique. The numerical results show that the flow field enhances polymer depletion phenomena near the wall relative to those observed under equilibrium (static) conditions: By increasing the shear stress, the polymer concentration in the interfacial area decreases, in full agreement with available experimental data. Moreover, the flow field is found to affect significantly the chain conformations near the wall: The applied shear stress is seen to extend the chains along a primary direction, ξ, and to depress them in the transverse direction, η. The depletion of the interfacial region in polymer molecules is further seen to lead to the formation of a boundary layer close to the wall, where the macroscopic fluid velocity increases rapidly from its zero value exactly at the wall to its asymptotic bulk profile, resulting into an apparent macroscopic slip at the wall. The theoretically calculated slip coefficient is found to be of the same order of magnitude with the experimentally measured one, as reported

  16. Impact of charge carrier injection on single-chain photophysics of conjugated polymers

    NASA Astrophysics Data System (ADS)

    Hofmann, Felix J.; Vogelsang, Jan; Lupton, John M.

    2016-06-01

    Charges in conjugated polymer materials have a strong impact on the photophysics and their interaction with the primary excited state species has to be taken into account in understanding device properties. Here, we employ single-molecule spectroscopy to unravel the influence of charges on several photoluminescence (PL) observables. The charges are injected either stochastically by a photochemical process or deterministically in a hole-injection sandwich device configuration. We find that upon charge injection, besides a blue-shift of the PL emission and a shortening of the PL lifetime due to quenching and blocking of the lowest-energy chromophores, the non-classical photon arrival time distribution of the multichromophoric chain is modified towards a more classical distribution. Surprisingly, the fidelity of photon antibunching deteriorates upon charging, whereas one would actually expect the opposite: the number of chromophores to be reduced. A qualitative model is presented to explain the observed PL changes. The results are of interest to developing a microscopic understanding of the intrinsic charge-exciton quenching interaction in devices.

  17. Adsorbent phosphates

    NASA Technical Reports Server (NTRS)

    Watanabe, S.

    1983-01-01

    An adsorbent which uses as its primary ingredient phosphoric acid salts of zirconium or titanium is presented. Production methods are discussed and several examples are detailed. Measurements of separating characteristics of some gases using the salts are given.

  18. Crystal structures and thermodynamics/kinetics of Zn(II) coordination polymers with helical chains

    NASA Astrophysics Data System (ADS)

    He, Tian; Yue, Ke-Fen; Zhao, Yi-xing; Chen, San-Ping; Zhou, Chun-sheng; Yan, Ni

    2016-07-01

    Solvothermal reactions of Zn(II) acetates and four V-shaped carboxylates ligands in the presence of 1,4-Bis(2-methyl-imidazol-1-yl)butane afforded four interesting Zn(II) coordination polymers with helical chains, namely, {[Zn(bib)(atibdc)]·2H2O}n (1), {[Zn(bib)(atbip)]·H2O}n (2), [Zn(bib)(2,2‧-tda)]}n (3) and {[Zn(bib)(5-tbipa)]·EtOH}n (4), (H2atibdc=5-amino-2,4,6-triiodoisophthalic acid, H2atbip=5-amino-2,4,6-tribromoisophthalic acid, 2,2‧-H2tad=2,2‧-thiodiacetic acid, 5-H2tbipa=5-tert-butyl-isophthalic acid). 1 reveals a 3D chiral framework with three kinds of helical chains along a, b and c axis. 2 shows a 2D step-type chiral framework with right-handed helical chains. 3 displays a wavelike 2D layer network possessing alternate left- and right-handed helical chains. 4 presents a four-connected 3D framework with zigzag and meso-helical chains. The different spacers and substituent group of carboxylic acid ligands may lead to the diverse network structures of 1-4. The fluorescent properties of complexes 1-4 were studied. In addition, the thermal decompositions properties of 1-4 were investigated by simultaneous TG/DTG-DSC technique. The apparent activation energy E and the pre-exponential factor (A) of skeleton collapse for the complexes 1-4 are calculated by the integral Kissinger's method and Ozawa-Doyle's method. The activation energy E (E1=209.658 kJ·mol-1, E2=250.037 kJ mol-1, E3=225.300 kJ mol-1, E4=186.529 kJ·mol-1) demonstrates that the reaction rate of the melting decomposition is slow. The thermodynamic parameters (ΔH‡, ΔG‡ and ΔS‡) at the peak temperatures of the DTG curves were also calculated. ΔG‡>0 indicates that the skeleton collapse is not spontaneous. ΔHd>0 suggests that the skeleton collapse is endothermic, corresponding to the intense endothermic peak of the DSC curve. The structural stability could be illustrated from the point of thermodynamics and kinetics. Their thermal decompositions properties of 1-4 were

  19. Core-shell molecularly imprinted polymer nanoparticles with assistant recognition polymer chains for effective recognition and enrichment of natural low-abundance protein.

    PubMed

    Liu, Dejing; Yang, Qian; Jin, Susu; Song, Yingying; Gao, Junfei; Wang, Ying; Mi, Huaifeng

    2014-02-01

    Core-shell molecular imprinting of nanomaterials overcomes difficulties with template transfer and achieves higher binding capacities for macromolecular imprinting, which are more important to the imprinting of natural low-abundance proteins from cell extracts. In the present study, a novel strategy of preparing core-shell nanostructured molecularly imprinted polymers (MIPs) was developed that combined the core-shell approach with assistant recognition polymer chains (ARPCs). Vinyl-modified silica nanoparticles were used as support and ARPCs were used as additional functional monomers. Immunoglobulin heavy chain binding protein (BiP) from the endoplasmic reticulum (ER) was chosen as the model protein. The cloned template protein BiP was selectively assembled with ARPCs from their library, which contained numerous limited-length polymer chains with randomly distributed recognition and immobilization sites. The resulting complex was copolymerized onto the surface of vinyl-modified silica nanoparticles under low concentrations of the monomers. After template removal, core-shell-structured nanoparticles with a thin imprinted polymer layer were produced. The particles demonstrated considerably high adsorption capacity, fast adsorption kinetics and selective binding affinities toward the template BiP. Furthermore, the synthesized MIP nanoparticles successfully isolated cloned protein BiP from protein mixtures and highly enriched BiP from an ER extract containing thousands of kinds of proteins. The enrichment reached 115-fold and the binding capacity was 5.4 μg g(-1), which were higher than those achieved by using traditional MIP microspheres. The advantageous properties of MIP nanoparticles hold promise for further practical applications in biology, such as protein analysis and purification. PMID:24140608

  20. Dielectric properties of liquid-crystal azomethine polymer with a side alkyl-substituted chain, doped with fullerene C60

    NASA Astrophysics Data System (ADS)

    Kovalev, D. S.; Kostromin, S. V.; Musteaţa, V.; Cozan, V.; Bronnikov, S. V.

    2016-04-01

    We studied the actual and imaginary components of the dielectric constant of liquid-crystal azomethine polymer with a side chain, doped with 0.5 wt % of fullerene C60, over a wide range of temperatures and frequencies; measurements were made by means of dielectric spectroscopy. By analyzing the frequency dependence of the dielectric constant, we detected the relaxation processes (α, β1, and β2) in the nanocomposite, corresponding to certain modes of molecular motion and described them by the Arrhenius equations (β1- and β2-processes) and the Vogel-Fulcher-Tamman equation (α-process). An antiplasticization effect is discovered after doping the polymer with fullerene C60, which manifests itself in increasing the glass transition temperature of the nanocomposite compared to this parameter typical of pure polymer.

  1. Mechanochromism and Mechanical-Force-Triggered Cross-Linking from a Single Reactive Moiety Incorporated into Polymer Chains.

    PubMed

    Zhang, Huan; Gao, Fei; Cao, Xiaodong; Li, Yanqun; Xu, Yuanze; Weng, Wengui; Boulatov, Roman

    2016-02-01

    Incorporation of small reactive moieties, the reactivity of which depends on externally imposed load (so-called mechanophores) into polymer chains offers access to a broad range of stress-responsive materials. Here, we report that polymers incorporating spirothiopyran (STP) manifest both green mechanochromism and load-induced addition reactions in solution and solid. Stretching a macromolecule containing colorless STP converts it into green thiomerocyanine (TMC), the mechanically activated thiolate moiety of which undergoes rapid thiol-ene click reactions with certain reactive C=C bonds to form a graft or a cross-link. The unique dual mechanochemical response of STP makes it of potentially great utility both for the design of new stress-responsive materials and for fundamental studies in polymer physics, for example, the dynamics of physical and mechanochemical remodeling of loaded materials. PMID:26805709

  2. Amide side chain amphiphilic polymers disrupt surface established bacterial bio-films and protect mice from chronic Acinetobacter baumannii infection.

    PubMed

    Uppu, Divakara S S M; Samaddar, Sandip; Ghosh, Chandradhish; Paramanandham, Krishnamoorthy; Shome, Bibek R; Haldar, Jayanta

    2016-01-01

    Bacterial biofilms represent the root-cause of chronic or persistent infections in humans. Gram-negative bacterial infections due to nosocomial and opportunistic pathogens such as Acinetobacter baumannii are more difficult to treat because of their inherent and rapidly acquiring resistance to antibiotics. Due to biofilm formation, A. baumannii has been noted for its apparent ability to survive on artificial surfaces for an extended period of time, therefore allowing it to persist in the hospital environment. Here we report, maleic anhydride based novel cationic polymers appended with amide side chains that disrupt surface established multi-drug resistant A. baumannii biofilms. More importantly, these polymers significantly (p < 0.0001) decrease the bacterial burden in mice with chronic A. baumannii burn wound infection. The polymers also show potent antibacterial efficacy against methicillin resistant Staphylococcus aureus (MRSA), vancomycin resistant Enterococci (VRE) and multi-drug resistant clinical isolates of A. baumannii with minimal toxicity to mammalian cells. We observe that optimal hydrophobicity dependent on the side chain chemical structure of these polymers dictate the selective toxicity to bacteria. Polymers interact with the bacterial cell membranes by causing membrane depolarization, permeabilization and energy depletion. Bacteria develop rapid resistance to erythromycin and colistin whereas no detectable development of resistance occurs against these polymers even after several passages. These results suggest the potential use of these polymeric biomaterials in disinfecting biomedical device surfaces after the infection has become established and also for the topical treatment of chronic bacterial infections. PMID:26454051

  3. Biomedical applications of polymers derived by reversible addition - fragmentation chain-transfer (RAFT).

    PubMed

    Fairbanks, Benjamin D; Gunatillake, Pathiraja A; Meagher, Laurence

    2015-08-30

    RAFT- mediated polymerization, providing control over polymer length and architecture as well as facilitating post polymerization modification of end groups, has been applied to virtually every facet of biomedical materials research. RAFT polymers have seen particularly extensive use in drug delivery research. Facile generation of functional and telechelic polymers permits straightforward conjugation to many therapeutic compounds while synthesis of amphiphilic block copolymers via RAFT allows for the generation of self-assembled structures capable of carrying therapeutic payloads. With the large and growing body of literature employing RAFT polymers as drug delivery aids and vehicles, concern over the potential toxicity of RAFT derived polymers has been raised. While literature exploring this complication is relatively limited, the emerging consensus may be summed up in three parts: toxicity of polymers generated with dithiobenzoate RAFT agents is observed at high concentrations but not with polymers generated with trithiocarbonate RAFT agents; even for polymers generated with dithiobenzoate RAFT agents, most reported applications call for concentrations well below the toxicity threshold; and RAFT end-groups may be easily removed via any of a variety of techniques that leave the polymer with no intrinsic toxicity attributable to the mechanism of polymerization. The low toxicity of RAFT-derived polymers and the ability to remove end groups via straightforward and scalable processes make RAFT technology a valuable tool for practically any application in which a polymer of defined molecular weight and architecture is desired. PMID:26050529

  4. Block copolymer adsorbed layers on solids

    NASA Astrophysics Data System (ADS)

    Sen, Mani; Jiang, Naisheng; Gowd, Bhoje; Endoh, Maya; Koga, Tadanori

    Block copolymer thin films offer a simple and effective route to fabricate highly ordered periodic microdomain structures. The fundamental, yet unsolved question is whether these highly oriented microdomain structures persist even near an impenetrable solid wall. We here report the adsorbed structures of polystyrene-block-poly (4-vinylpyridine) (PS-block-P4VP, Mw = 41,000, PS (weight fraction =0.81) formed on planar silicon substrates. Perpendicularly aligned cylindrical microdomains were created by solvent vapor annealing (Gowd et al., Soft Matter, 2014, 10, 7753), and the adsorbed layer was derived by solvent leaching with chloroform, a good solvent for the polymers and thereafter characterized by using atomic force microscopy, scanning electron microscopy, grazing incidence small angle x-ray scattering, and x-ray reflectivity. The results showed that both PS and P4VP chains lie flat on the substrate, forming a microphase-separated structure (MSS) without long-range order. Moreover, a spin-coated PS-block-P4VP thin film annealed under vacuum at 190 °C showed similar MSS on the substrate, indicating the generality of the interfacial polymer structure. Details will be discussed in the presentation. NSF Grant No. CMMI-1332499.

  5. Interphase and particle dispersion correlations in polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Senses, Erkan

    Particle dispersion in polymer matrices is a major parameter governing the mechanical performance of polymer nanocomposites. Controlling particle dispersion and understanding aging of composites under large shear and temperature variations determine the processing conditions and lifetime of composites which are very important for diverse applications in biomedicine, highly reinforced materials and more importantly for the polymer composites with adaptive mechanical responses. This thesis investigates the role of interphase layers between particles and polymer matrices in two bulk systems where particle dispersion is altered upon deformation in repulsive composites, and good-dispersion of particles is retained after multiple oscillatory shearing and aging cycles in attractive composites. We demonstrate that chain desorption and re-adsorption processes in attractive composites under shear can effectively enhance the bulk microscopic mechanical properties, and long chains of adsorbed layers lead to a denser entangled interphase layer. We further designed experiments where particles are physically adsorbed with bimodal lengths of homopolymer chains to underpin the entanglement effect in interphases. Bimodal adsorbed chains are shown to improve the interfacial strength and used to modulate the elastic properties of composites without changing the particle loading, dispersion state or polymer conformation. Finally, the role of dynamic asymmetry (different mobilities in polymer blends) and chemical heterogeneity in the interphase layer are explored in systems of poly(methyl methacrylate) adsorbed silica nanoparticles dispersed in poly(ethylene oxide) matrix. Such nanocomposites are shown to exhibit unique thermal-stiffening behavior at temperatures above glass transitions of both polymers. These interesting findings suggest that the mobility of the surface-bound polymer is essential for reinforcement in polymer nanocomposites, contrary to existing glassy layer theories

  6. Gel-like elasticity in glass-forming side-chain liquid-crystal polymers

    NASA Astrophysics Data System (ADS)

    Pozo, O.; Collin, D.; Finkelmann, H.; Rogez, D.; Martinoty, P.

    2009-09-01

    We study the complex shear modulus G of two side-chain liquid-crystal polymers (SCLCPs), a methoxy-phenylbenzoate substituted polyacrylate (thereafter called PAOCH3 ), and a cyanobiphenyl substituted polyacrylate supplied by Merck (thereafter called LCP105) using a piezoelectric rheometer. Two methods of filling the cell are used: (a) a capillary method, which can be used only at high temperature because of the low value of the viscosity, and (b) the classical one, thereafter called compression method, which consists in placing the sample between the two slides of the cell and to bring them closer. By filling the cell at high temperature either with the compression or the capillary method, we show that the response of both compounds is liquidlike ( G'˜f2 and G″˜f , where f is the frequency) for temperatures higher than a certain temperature T0 and gel-like (G'˜const,G″˜f) below T0 . This change in behavior from the conventional flow response to a gel-like response, when approaching the glass transition, is observed for nonsliding conditions and for very weak-imposed shear strains. It can be explained by a percolation-type mechanism of preglassy elastic clusters, which correspond to long-range and long-lived density fluctuations that are frozen at the time scale of the experiment. The sample response is therefore the sum of two contributions: one is due to the flow response of the polymer melt and the other to the elastic response of the network formed by the preglassy elastic clusters. By filling the cell below T0 with the compression method, both compounds exhibit a gel-type behavior by gently bringing closer the slides of the cell and an anomalous low-frequency behavior characterized by G'=const and G″=const by increasing the pressure used to bring closer the slides of the cell. A compression-assisted aggregation of the preglassy elastic clusters can explain both the increase in the low-frequency elastic plateau when the sample thickness is decreased

  7. New paradigm for stabilization of liquid polymer films on solids

    NASA Astrophysics Data System (ADS)

    Koga, Tad; Jiang, Naisheng; Wang, Jiaxun; di, Xiaoyu; Cheung, Justin; Endoh, Maya

    2015-03-01

    We report that wetting/dewetting behavior of liquid polymer films on solids can be controlled by nanoscale architectures of polymer chains irreversibly adsorbed on the impenetrable surfaces. Monodisperse polystyrene (PS) ultrathin films (20 nm in thickness) with different molecular weights on silicon (Si) substrates with a natural amorphous Si dioxide layer were used as models. The PS thin films were annealed at high temperatures at T>Tg (Tg is the bulk glass transition temperature) for several days, and the surface structures were studied by using optical and atomic force microscopes. At the same time, the annealed PS films were further leached with a good solvent and the residue films (i.e., irreversibly adsorbed layers) were characterized by x-ray reflectivity. The experimental data reveals a strong correlation between the conformations of the adsorbed polymer chains and the stability of the liquid films on top. T. K. acknowledges the partial financial support from NSF Grant No. CMMI-1332499.

  8. A hybrid model for molecular-dynamics simulations of semiflexible main-chain liquid-crystalline polymer melts

    NASA Astrophysics Data System (ADS)

    Yung, K. L.; He, Lan; Xu, Yan; Shen, Y. W.

    2005-12-01

    This Note proposes a new hybrid model that combines the Gay-Berne/Lennard-Jones (GB/LJ) and bead-spring models to simulate semiflexible main-chain liquid-crystalline polymers (LCPs) for improving simulation efficiency without compromising accuracy. In the new model, one bead and two nonlinear springs are used to describe the flexible spacers between two adjacent rigid units described by ellipsoidal particles. The model is found to be able to describe, with accuracy, detailed structural properties of semiflexible main-chain LCPs, such as the odd-even effects of their thermodynamic properties, where the bead-spring model cannot depict. In our experiments, the speed of simulation for the hybrid model was shown to be up to ten times faster than that for the GB/LJ model when the number of molecular chains exceeded 150.

  9. Main-chain Chiral Smectic Polymers Showing a Large Electroclinic Effect in the SmA* Phase

    SciTech Connect

    Walba,D.; Yang, H.; Shoemaker, R.; Keller, P.; Shao, r.; Coleman, D.; Jones, C.; Nakata, M.; Clark, N.

    2006-01-01

    The synthesis and characterization of a main-chain smectic liquid-crystalline polymer system designed for development into electromechanical actuators is described. The chemical structure is chosen to provide a large electroclinic effect in the SmA* phase, with large concomitant layer shrinkage (a rare combination). The polymers are prepared by acyclic diene metathesis polymerization (ADMET) of liquid-crystalline ,-dienes. Oligomers with a degree of polymerization of {approx}10-30 are obtained using Grubbs first-generation catalyst, while oligomers with a degree of polymerization of {approx}200 are obtained using Grubbs second-generation catalyst. All polymer samples show the following phase sequence: I - SmA* - SmC* - Glass. X-ray analysis of polymer powder samples demonstrates the desired layer shrinkage at the SmA* - SmC* transition. The polymers form well-aligned fibers by pulling from the isotropic melt, and X-ray analysis of fibers in the SmA* phase shows that in the bulk of the fiber the layers are oriented perpendicular to the fiber axis, while at the surfaces there appears to be a thin sheath where the layers are parallel to the fiber/air interface. The desired layer shrinkage with tilt at the SmA* - SmC* transition in these fibers is seen as well, and in the SmC* phase the fibers exhibit an interesting conical chevron layer structure. Electro-optic investigation of aligned thin films of the polymer, prepared from quenched fiber glasses using a novel technique, exhibit a large electroclinic effect, with substantial degradation of alignment quality upon field-induced tilt. This degradation in alignment quality, coupled with the layer shrinkage at the SmA* - SmC* transition demonstrated by X-ray scattering, strongly suggests the desired layer shrinkage with electroclinic tilt is in fact occurring in the polymer films.

  10. Highly grafted polystyrene/polyvinylpyridine polymer gold nanoparticles in a good solvent: effects of chain length and composition.

    PubMed

    Posel, Zbyšek; Posocco, Paola; Lísal, Martin; Fermeglia, Maurizio; Pricl, Sabrina

    2016-04-21

    In this work, the structural features of spherical gold nanoparticles (NPs) decorated with highly grafted poly(styrene) (PS), poly(vinylpyridine) (PVP) and PS-PVP diblock copolymer brushes immersed in a good solvent are investigated by means of Dissipative Particle Dynamics (DPD) simulations as a function of grafted chain length and of homopolymer and copolymer chain composition. For NPs grafted either by PS or PVP homopolymer brushes (selected as a proof of concept), good agreement between the Daoud-Cotton theory, experimental evidence, and our DPD simulations is observed in the scaling behavior of single chain properties, especially for longer grafted chains, and in brush thickness prediction. On the other hand, for grafted chain lengths comparable to NP dimensions parabolic-like profiles of the end-monomer distributions are obtained. Furthermore, a region of high concentration of polymer segments is observed in the monomer density distribution for long homopolymers. In the case of copolymer-decorated NPs, the repulsion between PS and PVP blocks is found to substantially influence the radius of gyration and the shape of the end-monomer distribution of the relevant polymer shell. Moreover, for diblock chains, the un-swollen region is observed to be thinner (and, correspondingly, the swollen layer thicker) than that of a NP modified with a homopolymer of the same length. Finally, the lateral segregation of PS and PVP blocks is evidenced by our calculations and a detailed analysis of the corona behavior is reported, thus revealing the key parameters in controlling the surface properties and the response of diblock copolymer modified nanoparticles. PMID:26980360

  11. Effect of cationic side-chains on intracellular delivery and cytotoxicity of pH sensitive polymer-doxorubicin nanocarriers

    NASA Astrophysics Data System (ADS)

    Fang, Chen; Kievit, Forrest M.; Cho, Yong-Chan; Mok, Hyejung; Press, Oliver W.; Zhang, Miqin

    2012-10-01

    Fine-tuning the design of polymer-doxorubicin conjugates permits optimization of an efficient nanocarrier to greatly increase intracellular uptake and cytotoxicity. Here, we report synthesis of a family of self-assembled polymer-doxorubicin nanoparticles and an evaluation of the effects of various types of side-chains on intracellular uptake and cytotoxicity of the nanocarriers for lymphoma cells. Monomers with three different cationic side-chains (CA) and pKa's, i.e., a guanidinium group (Ag), an imidazole group (Im), and a tertiary amine group (Dm), were comparatively investigated. The cationic monomer, poly(ethylene glycol) (PEG), and doxorubicin (Dox) were reacted with 1,4-(butanediol) diacrylate (BUDA) to prepare a poly(β-amino ester) (PBAE) polymer via Michael addition. All three polymer-Dox conjugates spontaneously formed nanoparticles (NP) through hydrophobic interactions between doxorubicin in aqueous solution, resulting in NP-Im/Dox, NP-Ag/Dox, and NP-Dm/Dox, with hydrodynamic sizes below 80 nm. Doxorubicin was linked to all 3 types of NPs with a hydrazone bond to assure selective release of doxorubicin only at acidic pH, as it occurs in the tumor microenvironment. Both NP-Im/Dox and NP-Ag/Dox exhibited much higher intracellular uptake by Ramos cells (Burkitt's lymphoma) than NP-Dm/Dox, suggesting that the type of side chain in the NPs determines the extent of intracellular uptake. As a result, NP-Im/Dox and NP-Ag/Dox showed cytotoxicity that was comparable to free Dox in vitro. Our findings suggest that the nature of surface cationic group on nanocarriers may profoundly influence their intracellular trafficking and resulting therapeutic efficacy. Thus, it is a crucial factor to be considered in the design of novel carriers for intracellular drug delivery.

  12. Dynamics of a self-avoiding polymer chain in slit, tube, and cube confinements.

    PubMed

    Cui, Ting; Ding, Jiandong; Chen, Jeff Z Y

    2008-12-01

    Monte Carlo simulations are presented for the observation of the dynamics of a self-avoiding polymer in three types of confinement: slit, tube, and cube. We pay special attention to the parameter regime where the characteristic confinement dimension is smaller than the radius of gyration of the unconfined polymer. On the basis of the bond-fluctuation model, we measured the rotation time of the end-to-end vector of the polymer, the diffusion time for the center of the polymer to move a distance comparable to the root mean square end-to-end distance, and the looping time for the ends of the polymer to approach each other from an open position. As functions of the confinement width and polymer length, these three time scales are discussed in light of scaling theories. PMID:19256859

  13. Dynamics of a self-avoiding polymer chain in slit, tube, and cube confinements

    NASA Astrophysics Data System (ADS)

    Cui, Ting; Ding, Jiandong; Chen, Jeff Z. Y.

    2008-12-01

    Monte Carlo simulations are presented for the observation of the dynamics of a self-avoiding polymer in three types of confinement: slit, tube, and cube. We pay special attention to the parameter regime where the characteristic confinement dimension is smaller than the radius of gyration of the unconfined polymer. On the basis of the bond-fluctuation model, we measured the rotation time of the end-to-end vector of the polymer, the diffusion time for the center of the polymer to move a distance comparable to the root mean square end-to-end distance, and the looping time for the ends of the polymer to approach each other from an open position. As functions of the confinement width and polymer length, these three time scales are discussed in light of scaling theories.

  14. Strain hardening in startup shear of long-chain branched polymer solutions.

    PubMed

    Liu, Gengxin; Cheng, Shiwang; Lee, Hyojoon; Ma, Hongwei; Xu, Hongde; Chang, Taihyun; Quirk, Roderic P; Wang, Shi-Qing

    2013-08-01

    We show for the first time that entangled polymeric liquids containing long-chain branching can exhibit strain hardening upon startup shear. As the significant long-chain branching impedes chain disentanglement, Gaussian coils between entanglements can deform to reach the finite extensibility limit where the intrachain retraction force exceeds the value expected from the usual conformational entropy loss evaluated based on Gaussian chain statistics. The phenomenon is expected to lead to further theoretical understanding. PMID:23971617

  15. Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization in Undergraduate Polymer Science Lab

    ERIC Educational Resources Information Center

    Nguyen, T. L. U.; Bennet, Francesca; Stenzel, Martina H.; Barner-Kowollik, Christopher

    2008-01-01

    This 8-hour experiment (spread over two 4-hour sessions) is designed to equip students with essential skills in polymer synthesis, particularly in synthesizing polymers of well-defined molecular weight. The experiment involves the synthesis and characterization of poly(vinyl neodecanoate) via living free radical polymerization, specifically the…

  16. Surface segregation of fluorinated moieties on random copolymer films controlled by random-coil conformation of polymer chains in solution.

    PubMed

    Xue, Dongwu; Wang, Xinping; Ni, Huagang; Zhang, Wei; Xue, Gi

    2009-02-17

    The relationship between solution properties, film-forming methods, and the solid surface structures of random copolymers composed of butyl methacrylate and dodecafluorheptyl methylacrylate (DFHMA) was investigated by contact angle measurements, X-ray photoelectron spectroscopy, sum frequency generation vibrational spectroscopy, and surface tension measurements. The results, based on thermodynamic considerations, demonstrated that the random copolymer chain conformation at the solution/air interface greatly affected the surface structure of the resulting film, thereby determining the surface segregation of fluorinated moieties on films obtained by various film-forming techniques. When the fluorinated monomer content of the copolymer solution was low, entropic forces dominated the interfacial structure, with the perfluoroalkyl groups unable to migrate to the solution/air interface and thus becoming buried in a random-coil chain conformation. When employing this copolymer solution for film preparation by spin-coating, the copolymer chains in solution were likely extended due to centrifugal forces, thereby weakening the entropy effect of the polymer chains. Consequently, this resulted in the segregation of the fluorinated moieties on the film surface. For the films prepared by casting, the perfluoroalkyl groups were, similar to those in solution, incapable of segregating at the film surface and were thus buried in the random-coil chains. When the copolymers contained a high content of DFHMA, the migration of perfluoroalkyl groups at the solution/air interface was controlled by enthalpic forces, and the perfluoroalkyl groups segregated at the surface of the film regardless of the film-forming technique. The aim of the present work was to obtain an enhanced understanding of the formation mechanism of the chemical structure on the surface of the polymer film, while demonstrating that film-forming methods may be used in practice to promote the segregation of fluorinated

  17. A Comprehensive study of the Effects of Chain Morphology on the Transport Properties of Amorphous Polymer Films.

    PubMed

    Mendels, Dan; Tessler, Nir

    2016-01-01

    Organic semiconductors constitute one of the main components underlying present-day paradigm shifting optoelectronic applications. Among them, polymer based semiconductors are deemed particularly favorable due to their natural compatibility with low-cost device fabrication techniques. In light of recent advances in the syntheses of these classes of materials, yielding systems exhibiting charge mobilities comparable with those found in organic crystals, a comprehensive study of their charge transport properties is presented. Among a plethora of effects arising from these systems morphological and non morphological attributes, it is shown that a favorable presence of several of these attributes, including that of rapid on-chain carrier propagation and the presence of elongated conjugation segments, can lead to an enhancement of the system's mobility by more than 5 orders of magnitude with respect to 'standard' amorphous organic semiconductors. New insight for the formulation of new engineering strategies for next generation polymer based semiconductors is thus gathered. PMID:27405103

  18. Thermodynamics of polymer nematics described with a worm-like chain model: particle-based simulations and SCF theory calculations

    NASA Astrophysics Data System (ADS)

    Greco, Cristina; Yiang, Ying; Kremer, Kurt; Chen, Jeff; Daoulas, Kostas

    Polymer liquid crystals, apart from traditional applications as high strength materials, are important for new technologies, e.g. Organic Electronics. Their studies often invoke mesoscale models, parameterized to reproduce thermodynamic properties of the real material. Such top-down strategies require advanced simulation techniques, predicting accurately the thermodynamics of mesoscale models as a function of characteristic features and parameters. Here a recently developed model describing nematic polymers as worm-like chains interacting with soft directional potentials is considered. We present a special thermodynamic integration scheme delivering free energies in particle-based Monte Carlo simulations of this model, avoiding thermodynamic singularities. Conformational and structural properties, as well as Helmholtz free energies are reported as a function of interaction strength. They are compared with state-of-art SCF calculations invoking a continuum analog of the same model, demonstrating the role of liquid-packing and fluctuations.

  19. A Comprehensive study of the Effects of Chain Morphology on the Transport Properties of Amorphous Polymer Films

    NASA Astrophysics Data System (ADS)

    Mendels, Dan; Tessler, Nir

    2016-07-01

    Organic semiconductors constitute one of the main components underlying present-day paradigm shifting optoelectronic applications. Among them, polymer based semiconductors are deemed particularly favorable due to their natural compatibility with low-cost device fabrication techniques. In light of recent advances in the syntheses of these classes of materials, yielding systems exhibiting charge mobilities comparable with those found in organic crystals, a comprehensive study of their charge transport properties is presented. Among a plethora of effects arising from these systems morphological and non morphological attributes, it is shown that a favorable presence of several of these attributes, including that of rapid on-chain carrier propagation and the presence of elongated conjugation segments, can lead to an enhancement of the system’s mobility by more than 5 orders of magnitude with respect to ‘standard’ amorphous organic semiconductors. New insight for the formulation of new engineering strategies for next generation polymer based semiconductors is thus gathered.

  20. Fabrication of chain-like Mn 2O 3 nanostructures via thermal decomposition of manganese phthalate coordination polymers

    NASA Astrophysics Data System (ADS)

    Salavati-Niasari, Masoud; Mohandes, Fatemeh; Davar, Fatemeh; Saberyan, Kamal

    2009-12-01

    A novel manganese coordination polymer [Mn(Pht)(H 2O)] n as a precursor was obtained by chemical precipitation involving an aqueous solution of anhydrous manganese acetate and phthalate anion as a potential O-banded ligand. Fourier transform infrared (FT-IR) results proved that phthalate anions coordinate to metal cations as a chelating bidentate ligand, making polymeric structure. The Mn 2O 3 nanostructures have been prepared via thermal decomposition of as-prepared manganese phthalate polymers as precursor in the presence of oleic acid (OA) and triphenylphosphine (TPP) as a stabilizer and capping. Different approaches such as FT-IR, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied to characterize the products. TEM images and XRD analysis indicated that the as-synthesized chain-like Mn 2O 3 has a crystal phase of cubic syngony with a mean size of ˜40 nm.

  1. Migration insertion polymerization (MIP) of cyclopentadienyldicarbonyldiphenylphosphinopropyliron (FpP): a new concept for main chain metal-containing polymers (MCPs).

    PubMed

    Wang, Xiaosong; Cao, Kai; Liu, Yibo; Tsang, Brian; Liew, Sean

    2013-03-01

    We report a conceptually new polymerization technique termed migration insertion polymerization (MIP) for main chain metal-containing polymer (MCP) synthesis. Cyclopentadienyldicarbonyldiphenylphosphinopropyliron (FpP) is synthesized and polymerized via MIP, resulting in air stable poly(cyclopentadienylcarbonyldiphenylphosphinobutanoyliron) (PFpP) displaying narrow molecular weight distribution. The backbone of PFpP contains asymmetric iron units connected by both phosphine coordination and Fe-acyl bonds, which is representative of a new type of polymer. Furthermore, PFpP is tested to be soluble in a wide range of organic solvents and shown to possess reactive Fp end groups. PFpP amphiphiles have therefore been prepared via an end group migration insertion reaction in the presence of oligoethylene phosphine. PMID:23425192

  2. A Comprehensive study of the Effects of Chain Morphology on the Transport Properties of Amorphous Polymer Films

    PubMed Central

    Mendels, Dan; Tessler, Nir

    2016-01-01

    Organic semiconductors constitute one of the main components underlying present-day paradigm shifting optoelectronic applications. Among them, polymer based semiconductors are deemed particularly favorable due to their natural compatibility with low-cost device fabrication techniques. In light of recent advances in the syntheses of these classes of materials, yielding systems exhibiting charge mobilities comparable with those found in organic crystals, a comprehensive study of their charge transport properties is presented. Among a plethora of effects arising from these systems morphological and non morphological attributes, it is shown that a favorable presence of several of these attributes, including that of rapid on-chain carrier propagation and the presence of elongated conjugation segments, can lead to an enhancement of the system’s mobility by more than 5 orders of magnitude with respect to ‘standard’ amorphous organic semiconductors. New insight for the formulation of new engineering strategies for next generation polymer based semiconductors is thus gathered. PMID:27405103

  3. Mechanically durable and highly conductive elastomeric composites from long single-walled carbon nanotubes mimicking the chain structure of polymers.

    PubMed

    Ata, Seisuke; Kobashi, Kazufumi; Yumura, Motoo; Hata, Kenji

    2012-06-13

    By using long single-walled carbon nanotubes (SWNTs) as a filler possessing the highest aspect ratio and small diameter, we mimicked the chain structure of polymers in the matrix and realized a highly conductive elastomeric composite (30 S/cm) with an excellent mechanical durability (4500 strain cycles until failure), far superior to any other reported conductive elastomers. This exceptional mechanical durability was explained by the ability of long and traversing SWNTs to deform in concert with the elastomer with minimum stress concentration at their interfaces. The conductivity was sufficient to operate many active electronics components, and thus this material would be useful for practical stretchable electronic devices. PMID:22546049

  4. Evidence for Distinct Polymer Chain Orientations in KC{sub 60} and RbC{sub 60 }

    SciTech Connect

    Launois, P.; Moret, R.; Hone, J.; Zettl, A. |

    1998-11-01

    The KC{sub 60} and RbC{sub 60} polymer phases exhibit contrasting electronic properties while powder diffraction studies have revealed no definite structural difference. We have performed single crystal x-ray diffraction and diffuse scattering studies of these compounds. It is found that KC{sub 60} and RbC{sub 60} possess different chain orientations about their axes, which are described by distinct space groups Pmnn and I2/m , respectively. Such a structural difference will be of great importance to a complete understanding of the physical properties. {copyright} {ital 1998} {ital The American Physical Society}

  5. Molecular engineering of side-chain liquid crystalline polymers by living cationic polymerization using Webster`s initiating system

    SciTech Connect

    Percec, V.

    1993-12-31

    Webster`s cationic initiating system (HO{sub 3}SCF{sub 3}/SMe{sub 2}) (Macromolecules, 23, 1918 (1990)) was shown by us (for a review see Adv. Mater., 4, 548 (1992)) to polymerize, via a living mechanism, mesogenic vinyl ethers which contain a large variety of functional groups. This is mostly because SMe{sub 2} is a softer nucleophile than any of the functional groups available in these monomers. The molecular engineering of side-chain liquid crystalline polymers with conventional and complex architectures via this polymerization technique will be discussed.

  6. New syndioregic main-chain, nonlinear optical polymers, and their ellipsometric characterization

    NASA Astrophysics Data System (ADS)

    Lindsay, Geoffrey A.; Nee, Soe-Mie F.; Hoover, James M.; Stenger-Smith, John D.; Henry, Ronald A.; Kubin, R. F.; Seltzer, Michael D.

    1991-12-01

    New nonlinear optical polymers (NLOP) having potential utility in waveguides for the modulation and switching of optical signals are reported. A new class of chromophoric polymers which assume a folded, polar conformation of the backbone have been prepared. The polymers have a syndioregic arrangement of chromophores within the backbone (i.e., a head-to-head, tail-to-tail configuration). Polymers were synthesized by the polymerization of difunctional, precoupled pairs of chromophores and difunctional, bridging groups. Glassy, noncentrosymmetric films were prepared by electric field poling and by Langmuir-Blodgett (LB) deposition. Characterization of multilayer LB films by null ellipsometry to determine the anisotropic refractive parameters was performed at different angles of incidence and at a wavelength of 1.0 (mu).

  7. Photoinduced changes of surface order in coumarin side-chain polymer films used for liquid crystal photoalignment

    SciTech Connect

    Bergmann, G.; Jackson, P.O.; Hogg, J.H.C.; Stirner, T.; O'Neill, M.; Duffy, W.L.; Kelly, S.M.; Clark, G.F.

    2005-08-08

    Specular x-ray reflectivity probes morphological changes in a crosslinkable coumarin photoalignment polymer film resulting from ultraviolet irradiation. An ordered surface layer with density oscillations compatible with planar side-chain alignment is obtained before irradiation. The ordering is enhanced in the early stages of crosslinking. This is attributed to the photoinduced increase of mobility of the side-chains resulting from the creation of free volume by the crosslinking process. The expansion of the thin film confirms that free volume is created. The surface ordering decreases with prolonged ultraviolet irradiation because of increased material viscosity resulting from a high crosslinked density. The implications of surface ordering on liquid crystal photoalignment are discussed.

  8. Reflectivity studies on adsorbed block copolymers under shear

    SciTech Connect

    Smith, G.S.; Wages, S.; Baker, S.M.; Toprakcioglu, C.; Hadziioannou, G.

    1994-12-01

    The authors report neutron reflectivity data on (poly)styrene-(poly)ethylene oxide (PS-PEO) diblock copolymers adsorbed onto quartz from the selective solvent cyclohexane (a non-solvent for PEO and a poor solvent for PS). The PEO ``anchor block`` adsorbs strongly to form a thin layer on the quartz substrate, while the deuterated PS chains dangle into the solvent. They find that under static conditions the density profile of the PS block in a poor solvent can be well described by a Schultz function which is indicative of a polymer ``mushroom.`` Furthermore, they have studied the same system under shear at shear rates from 0--400s{sup {minus}1}. They find that there is a dramatic increase in the thickness of the PS layer under shear in cyclohexane and that the relaxation time from the shear-on profile back to the static profile is on the order of several days.

  9. The effects of long-chain polymers on tip vortex flow and cavitation inception

    NASA Astrophysics Data System (ADS)

    Zhang, Quan; Hsiao, Chao-Tsung; Chahine, Georges L.

    2011-11-01

    Experiments have shown that propeller/hydrofoil tip vortex cavitation can be suppressed by properly injecting dilute polymer solutions at the tip. However, the mechanisms for this phenomenon are not well understood yet. To understand better the underlying flow physics the tip vortex flow generated by a rotating propeller in water and a dilute polymer solution (FENE-P model) was numerically simulated. It is found that the vortex flow structure is changed by the non-Newtonian features of polymers. Phenomenally the vortical rotation in a polymer solution is slower and the vortex center pressure is higher than in water. The non-Newtonian stress is much stronger than the Newtonian stresses in water. To further understand the non-Newtonian stresses contribution, the FENE-P model is also applied to a simplified quasi-cylindrical vortex. It is found analytically that in addition to the three normal stresses that are expected to be quadratic in the shear rate, one of the shear components is also quadratic. We also studied polymer effects on the dynamics of a bubble nucleus in the tip vortex. The bubble was found to grow to an elongated large cavity in water while it collapses in the polymer solution for the same cavitation number. This work was supported by the Office of Naval Research, Contract N00014-04-C-0110, monitored by Dr. Ki-Han Kim.

  10. Co-assembly of Zn(SPh){sub 2} and organic linkers into helical and zig-zag polymer chains

    SciTech Connect

    Liu Yi; Yu Lingmin; Loo, Say Chye Joachim; Blair, Richard G.; Zhang Qichun

    2012-07-15

    Two novel one-dimensional coordination polymers, single helicate [Zn(SPh){sub 2}(TPyTA)(EG)]{sub n} (EG=ethylene glycol) (1) and zig-zag structure [Zn(SPh){sub 2}(BPyVB)]{sub n} (2), were synthesized under solvothermal conditions at 150 Degree-Sign C or room temperature by the co-assembly of Zn(SPh){sub 2} and organic linkers such as 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPyTA) and 1,3-bis(trans-4-pyridylvinyl)benzene (BPyVB). X-ray crystallography study reveals that both polymers 1 and 2 crystallize in space group P2{sub 1}/c of the monoclinic system. The solid-state UV-vis absorption spectra show that 1 and 2 have maxium absorption onsets at 400 nm and 420 nm, respectively. TGA analysis indicates that 1 and 2 are stable up to 110 Degree-Sign C and 210 Degree-Sign C. - Graphical abstract: Two novel one-dimensional coordination polymers, single helicate [Zn(SPh){sub 2}(TPyTA)(EG)]{sub n} (1) and zig-zag structure [Zn(SPh){sub 2}(BPyVB)]{sub n} (2), were synthesized. Solid-state UV-vis absorptions show that 1 and 2 have maxium absorption onsets at 400 nm and 420 nm, respectively. TGA analysis indicates that 1 and 2 are stable up to 110 Degree-Sign C and 210 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Two novel one-dimensional coordination polymers have been synthesized. Black-Right-Pointing-Pointer TPyTA results in helical structures in 1 while BPyVB leads to zig-zag chains in 2. Black-Right-Pointing-Pointer Solid-state UV-vis absorption spectra and TGA analysis of the title polymers were studied.

  11. Polymers encapsulated in short single wall carbon nanotubes: pseudo-1D morphologies and induced chirality.

    PubMed

    Kumar, Sunil; Pattanayek, Sudip K; Pereira, Gerald G

    2015-03-21

    Molecular dynamics simulations are performed to investigate the stable morphologies of semi-flexible polymer chains within a single wall carbon nanotube (CNT). We characterize these morphologies with a variety of measures. Due to the different curvature inside the CNT to outside, there are increased numbers of polymer-CNT bead contacts for polymers which reside inside the CNT. A sufficiently long polymer chain first adsorbs on the exterior of the nanotube and subsequently moves inside the cavity of the nanotube. At equilibrium, the polymer configuration consists of a central stem surrounded by helically wrapped layers. Sections of the polymer outside the CNT have helical conformations (for CNTs of small radius) or circular arrangements (for CNTs of larger radius). Polymers encapsulated within the CNT have an increased chirality due to packing of the beads and this chirality is further enhanced for moderately stiff chains. PMID:25796260

  12. Long-Chain Aliphatic Polymers To Bridge the Gap between Semicrystalline Polyolefins and Traditional Polycondensates.

    PubMed

    Stempfle, Florian; Ortmann, Patrick; Mecking, Stefan

    2016-04-13

    Other than their established short-chain congeners, polycondensates based on long-chain difunctional monomers are often dominated by the long methylene sequences of the repeat units in their solid-state structures and properties. This places them between traditional polycondensates and polyethylenes. The availability of long-chain monomers as a key prerequisite has benefited much from advances in the catalytic conversion of plant oils, via biotechnological and purely chemical approaches, likewise. This has promoted studies of, among others, applications-relevant properties. A comprehensive account is given of long-chain monomer syntheses and the preparation and physical properties, morphologies, mechanical behavior, and degradability of long-chain polyester, polyamides, polyurethanes, polyureas, polyacetals, and polycarbonates. PMID:27023340

  13. Note: Percolation in two-dimensional flexible chains systems

    NASA Astrophysics Data System (ADS)

    Pawłowska, Monika; Żerko, Szymon; Sikorski, Andrzej

    2012-01-01

    The structure of a two-dimensional film formed by adsorbed polymer chains was studied by means of Monte Carlo simulations. The polymer chains were represented by linear sequences of lattice beads and positions of these beads were restricted to vertices of a two-dimensional square lattice. Two different Monte Carlo methods were employed to determine the properties of the model system. The first was the random sequential adsorption (RSA) and the second one was based on Monte Carlo simulations with a Verdier-Stockmayer sampling algorithm. The methodology concerning the determination of the percolation thresholds for an infinite chain system was discussed. The influence of the chain length on both thresholds was presented and discussed. It was shown that the RSA method gave considerably lower thresholds for longer chains. This behavior can be explained by a different pool of chain conformations used in the calculations in both methods under consideration.

  14. Influence of Belousov-Zhabotinsky substrate concentrations on autonomous oscillation of polymer chains with Fe(bpy)3 catalyst.

    PubMed

    Hara, Yusuke; Mayama, Hiroyuki; Fujimoto, Kenji

    2014-06-19

    We studied the effect of initial substrate concentrations in the Belousov-Zhabotinsky (BZ) reaction on the optical transmittance self-oscillation behavior of a polymer chain consisting of N-isopropylacrylamide (NIPAAm) and a Fe catalyst ([Fe(bpy)3]). The driving force of this transmittance self-oscillation was the solubility difference between the reduced and oxidized states of the [Fe(bpy)3] moiety in the polymer chain. The amplitude of the soluble-insoluble self-oscillation of poly(NIPAAm-co-[Fe(bpy)3]) was significantly smaller than that of poly(NIPAAm-co-[Ru(bpy)3]). Theoretical simulation results attributed this behavior to the small difference in the solvent qualities, C*, of the reduced and oxidized states. Furthermore, we clarified that poly(NIPAAm-co-[Fe(bpy)3]) required a narrower concentration range of HNO3 to exhibit self-oscillation than poly(NIPAAm-co-[Ru(bpy)3]), since transmittance self-oscillation occurred only for [HNO3] = 0.3 M. The period of self-oscillation of poly(NIPAAm-co-[Fe(bpy)3]) in solution was controlled mainly by NaBrO3 concentration and was hardly influenced by the initial concentration of malonic acid. PMID:24853126

  15. A statistical theory of coil-to-globule-to-coil transition of a polymer chain in a mixture of good solvents

    NASA Astrophysics Data System (ADS)

    Budkov, Yu. A.; Kolesnikov, A. L.; Kalikin, N. N.; Kiselev, M. G.

    2016-05-01

    We present an off-lattice statistical model of a single polymer chain in mixed-solvent media. Taking into account the polymer conformational entropy, renormalization of solvent composition near the polymer backbone, the universal intermolecular excluded-volume and van der Waals interactions within the self-consistent field theory, the reentrant coil-to-globule-to-coil transition (co-nonsolvency) has been described in this paper. For convenience we split the system volume in two parts: the volume occupied by the polymer chain and the volume of bulk solution. Considering the equilibrium between two sub-volumes, the polymer solvation free energy as a function of radius of gyration and co-solvent mole fraction within internal polymer volume has been obtained. Minimizing the free energy of solvation with respect to its arguments, we show two qulitatively different regimes of co-nonsolvency. Namely, at sufficiently high temperature the reentrant coil-to-globule-to-coil transition proceeds smoothly. On the contrary, when the temperature drops below a certain threshold value a coil-globule transition occurs in the regime of first-order phase transition, i.e., discontinuous changes of the radius of gyration and the local co-solvent mole fraction near the polymer backbone. We show that, when the collapse of the polymer chain takes place, the entropy and enthalpy contributions to the solvation free energy of the globule strongly grow. From the first principles of statistical thermodynamics we confirm earlier speculations based on the MD simulations results that the co-nonsolvency is the essentially enthalpic-entropic effect and is caused by enthalpy-entropy compensation. We show that the temperature dependences of the solution heat capacity change due to the solvation of the polymer chain are in qualitative agreement with the differential scanning calorimetry data for PNIPAM in aqueous methanol.

  16. Exploiting Supramolecular Interactions for the Intramolecular Folding of Side-Chain Functionalized Polymers and Assembly of Anisotropic Colloids

    NASA Astrophysics Data System (ADS)

    Romulus, Joy

    The overarching goal presented in this thesis is the self-assembly of synthetic systems into higher ordered structures utilizing supramolecular chemistry. Noncovalent interactions including charge-transfer and hydrogen bonding as well as DNA hybridization are exploited to induce the assembly of polymers and colloids into well-defined architectures. This strategy provides a tunable handle on materials bulk properties that can be adjusted by simply changing variables such as temperature and solvent. A brief overview of design principles for the supramolecular assembly of side-chain functionalized polymers is presented. The polymerization technique selected was living ring-opening metathesis polymerization (ROMP), thus affording control over molecular weight and molecular weight distributions. ROMP also allowed for the incorporation of functional groups that were used to assemble the polymers into ordered structures. Charge-transfer motifs were exploited and shown to drive the assembly of random and alternating copolymers via intramolecular side-chain interactions. Incorporation of complementary hydrogen bonding motifs was shown to guide the single-chain folding of a multifunctional triblock copolymer into sheet-like structures. Precision over the size, shape, and monomer sequence were identified as key elements for efficient self-assembly. The self-assembly of colloids using DNA hybridization was also investigated. Previously, the majority of colloid-based research relied upon the self-assembly of spherical isotropic particles into closed-packed arrangements. In contrast, anisotropic particles may allow for the realization of open structures. By expanding upon a method to permanently cross-link DNA strands incubated on a colloidal surface, a new strategy to engineer patchy particles is described. These functional DNA-coated patches are demonstrated to direct particle assembly. The self-assembly of polymer and colloidal systems utilizing noncovalent interactions

  17. Effect of side-chain carbonyl groups on the interface of vinyl polymers with water.

    PubMed

    Oda, Yukari; Horinouchi, Ayanobu; Kawaguchi, Daisuke; Matsuno, Hisao; Kanaoka, Shokyoku; Aoshima, Sadahito; Tanaka, Keiji

    2014-02-11

    The nature of the polymer-water interface in the poly(methyl 2-propenyl ether) (PMPE)-water model system is investigated by sum-frequency generation spectroscopy, which at the moment gives the best depth resolution among available techniques. PMPE, synthesized via living cationic polymerization, is structurally similar to poly(methyl methacrylate) (PMMA) except for lacking a carbonyl group. We here probe the polymer local conformation as well as the aggregation states of water at the interface. Comparing the results of our measurements to the PMMA-water system, the effect of a carbonyl group on the water structure at the interface is discussed. This knowledge should be crucial to the design and construction of highly functionalized polymer interfaces for bioapplications. PMID:24467626

  18. Translocation of a Polymer Chain Through a Nanopore Starting From a Confining Nanotube: The Limit of high Peclet Numbers

    NASA Astrophysics Data System (ADS)

    Slater, Gary W.; Sean, David; de Haan, Hendrick

    2015-03-01

    We use Langevin Dynamics simulations to study a scenario where a confining nanotube is used as a way to limit the range of conformations available to a polymer chain prior to driven translocation. We find that the tube not only reduces the variance in translocation times (a useful result for practical applications), but also that the elongated polymer conformations yield longer translocation times (also a useful result) that can be dominated by the post-propagation process when the diameter of the nanotube is smaller than a universal critical value. We adapt the tension propagation theory for this geometry and find agreement with the simulations using a single friction parameter to model the roles of both the nanopore and the crowding. To gain insight into the physical mechanisms behind this effective friction, we systematically remove i) crowding on the trans-side and/or ii) monomer collisions with the membrane containing the nanopore. We find that higher Peclet numbers increase the impact of crowding on the trans side but diminish the impact of the friction between the nanopore and the polymer.

  19. Crystal-to-crystal transformation from a chain compound to a layered coordination polymer.

    PubMed

    Shi, Jinbiao; Zhang, Yan; Zhang, Bin; Zhu, Daoben

    2016-01-01

    A crystal-to-crystal transformation was observed from a green chain compound CuBr2(1,4-dioxane)2(H2O)2 (1) to a brown layered compound (CuBr2)3(1,4-dioxane)2 (2). The hydrogen bond connecting chains in were replaced by a μ-Br bridge in and the antiferromagnetic interaction between the metal atoms in became stronger than in 1. PMID:26600206

  20. Influence of alkyl chain length on charge transport in symmetrically substituted poly(2,5-dialkoxy- p -phenylenevinylene) polymers

    NASA Astrophysics Data System (ADS)

    Tuladhar, Sachetan M.; Sims, Marc; Kirkpatrick, James; Maher, Robert C.; Chatten, Amanda J.; Bradley, Donal D. C.; Nelson, Jenny; Etchegoin, Pablo G.; Nielsen, Christian B.; Massiot, Philippe; George, Wayne N.; Steinke, Joachim H. G.

    2009-01-01

    We report on the hole transport characteristics, as measured by time of flight, of a family of symmetrically substituted dialkoxy poly( p -phenylenevinylene) polymers with different side-chain length. As side-chain length is decreased, the magnitude of the hole mobility μh increases while the field dependence of μh becomes more positive and the temperature dependence of μh becomes stronger. For the shortest side-chain derivative studied, μh exceeds 10-4cm2V-1s-1 at electric fields greater than 105Vcm-1 . The trend in magnitude of μh with side-chain length is consistent with the expected increase in electronic wave-function overlap as interchain separation decreases, while the trends in electric-field and temperature dependences of μh are consistent with increasing site energy disorder. We show that the electrostatic contribution to the site energy difference for pairs of oligomers follows the observed trend as a function of interchain separation, although the pairwise contribution is too small to explain the data quantitatively. Nonresonant Raman spectroscopy is used to characterize the microstructure of our films. We construct spatial maps of the Raman ratio I1280/I1581 and confirm an expected decrease in average film density with side-chain extension. The structural heterogeneity in the maps is analyzed but no clear correlation is observed with transport properties, suggesting that the structural variations relevant for charge transport occur on a length scale finer than the resolution of ˜1μm .

  1. Novel polymer electrolytes based on cationic polyurethane with different alkyl chain length

    NASA Astrophysics Data System (ADS)

    Liu, Libin; Wu, Xiwen; Li, Tianduo

    2014-03-01

    A series of comb-like cationic polyurethanes (PUs) were synthesized by quaternizing different bromoalkane (C2H5Br, C8H17Br, and C14H29Br) with polyurethane. Solid polymer electrolytes were prepared by complexes cationic PUs with different content of LiClO4. All the solid polymer electrolytes had sufficient thermal stability as confirmed by TGA and exhibited a single-phase behavior evidenced by DSC results. For these electrolytes, FT-IR spectra indicated the formation of polymer-ion complexes. The ac impedance spectra show that the conductivity of the electrolytes follow the Arrhenius behavior, and ionic conductivity is associated with both the charge migration of ions between coordination sites and transmission between aggregates, as confirmed by FT-IR and SEM. Alkyl quaternary ammonium salts in the polymer backbone are recognized as inherent plasticizers, which make the electrolytes exhibit liquid-like behavior. The plasticizing effect of PU-C8 and PU-C14 electrolytes are more effective than that of PU-C2 electrolyte. Maximum ionic conductivity at room temperature for PU-C8 electrolytes containing 50 wt% LiClO4 reached 1.1 × 10-4 S cm-1. This work provides a new research clue that alkyl quaternary ammonium salts could be used as inherent plasticizers and hence make the system behave like a liquid with high ionic conductivity, while preserving the dimensional stability of the solids.

  2. Peculiarities in gel permeation chromatography of flexible-chain polymers on macroporous swelling sorbents.

    PubMed

    Belenkii, B G; Vilenchik, L Z; Nesterov, V V; Kolegov, V J; Frenkel, S Y

    1975-06-18

    In gel permeation chromatography on macroporous swelling sorbents, deviations from the Benoit principle of universal calibration were observed. It is suggested that these are caused by different degrees of thermodynamic compatibility of the eluted polymers with the sorbent matrix. PMID:1150817

  3. A new 68Ge/68Ga generator system using an organic polymer containing N-methylglucamine groups as adsorbent for 68Ge.

    PubMed

    Nakayama, M; Haratake, M; Ono, M; Koiso, T; Harada, K; Nakayama, H; Yahara, S; Ohmomo, Y; Arano, Y

    2003-01-01

    A macroporous styrene-divinylbenzene copolymer containing N-methylglucamine groups was selected for a new 68Ge/68Ga generator system. This resin packed into a column effectively adsorbed the parent nuclide 68Ge. The daughter 68Ga was eluted from the resin with a solution of a low-affinity gallium chelating ligand such as citric or phosphoric acid. The 68Ge leakage was less than 0.0004% of the 68Ge adsorbed on the resin. By simple mixing of transferrin and desferoxamine conjugated HSA and IgG with the eluate from the column, 68Ga-labeling was completed in high yield. PMID:12485657

  4. Thermally triggered reversible transformation between parallel staggered stacking and plywood-like stacking of 1D coordination polymer chains.

    PubMed

    Sun, Jian-Ke; Jin, Xu-Hui; Chen, Chao; Zhang, Jie

    2010-08-01

    An unusual example showing reversible interconversion of chain-like isomers under controlled experimental settings is reported, which illustrates the key role of assembly conditions for the target packing architecture with related properties. The reaction of Mn(II) ions with an organic ligand 2-hydroxypyrimidine-4,6-dicarboxylic acid (H(3)hpdc) at room temperature gives a coordination polymer {[Mn(3)(hpdc)(2)(H(2)O)(6)] x 2 H(2)O}(n) containing parallel staggered stacking, whereas the reaction under hydrothermal conditions at 150 degrees C affords a compound {[Mn(3)(hpdc)(2)(H(2)O)(6)] x H(2)O}(n) possessing plywood-like stacking. Interestingly, two compounds contain similar one-dimensional chain components with different orientations that can be controlled by thermodynamic factors. Thermally triggered reversible interconversion of the two compounds was verified by X-ray powder, IR, and element analysis. The spin-canted antiferromagnetic behaviors are observed in as-synthesized samples, and the influence of chain orientations on magnetic properties has been detected. PMID:20608747

  5. Elastic coefficient of a single polymer chain by using Brownian dynamics analysis

    NASA Astrophysics Data System (ADS)

    Horinaka, J.; Maniwa, T.; Oharada, K.; Takigawa, T.

    2007-08-01

    The elastic coefficient of a single polystyrene chain has been experimentally evaluated by using Brownian dynamics analysis. The Brownian motion of the chain is probed using a particle trapped by optical tweezers with a negligibly small spring constant. The displacement of the particle due to Brownian motion is measured by an interferometer assembled using the same laser beam as the optical tweezers. Two methods are employed for Brownian dynamics analysis: (1) the analysis of the time course of the displacement of the particle and (2) the fitting of the power spectrum of Brownian motion with a Lorentzian. The elastic constant of a polystyrene chain in dichloromethane at 21 °C is estimated to be 6.4×10-6 and 1.1×10-5 N/m when methods (1) and (2) are employed, respectively. The elastic constant obtained by approximating the polystyrene chain to a freely jointed chain is in agreement with the experimentally evaluated elastic constant.

  6. Surface Dynamics of Free PS Chains on Chemically Identical Polymer Brushes: An XPCS Study

    NASA Astrophysics Data System (ADS)

    Ugur, Gokce; Akgun, Bulent; Jiang, Zhang; Narayanan, Suresh; Brittain, William J.; Foster, Mark D.

    2009-03-01

    We found no relaxation of fluctuations of the brush surfaces within the range of time (0.2 -1100 s) and length scale (0.6-3 um) studied by X-ray photon correlation spectroscopy(XPCS). This is true for PS brushes of thicknesses of 9 - 101 nm and grafting density of 0.12-0.6 chains/nm^2 at temperatures up to 130C above bulk Tg. Results on the dynamics of a layer of untethered 2.2k PS chains on top of a PS brush surface show that placing the PS chains atop the brush dramatically slows down the surface relaxations of the film surface. As the ratio of the thickness of the layer of untethered chains to the thickness of the highly dense brush drops below ˜0.5, the surface relaxations become too slow to be observed readily with XPCS. Reducing grafting density of the underlying brush markedly slows the surface dynamics. The surface dynamics of the layer of ``free'' PS chains are coupled with those of the underlying brush.

  7. Neutron reflectivity as a tool to study the interdigitation of grafted polymer chains and its dynamics

    NASA Astrophysics Data System (ADS)

    Leger, Liliane; Restagno, Frédéric; Cousin, Fabrice; Boue, François; Chenneviere, Alexis

    Three series of experiments aimed at characterizing the interdigitation between a brush and a melt, and based on neutron reflectivity, are presented and discussed. The density profile of brush chains has been analysed for series of annealing times, on h-PS brushes in contact with d-PS melts, as a function of molecular weights and grafting densities. We show that the relaxation dynamics of the brush chains can be modelled taking into account the long relaxation time of end tethered chains along with the reptation of the melt chains which accelerates the arm retraction process. Using a non-grafted layer with a thickness smaller than the equilibrium size of the brush when immersed into a thick melt allows one to apply chosen degrees of confinement to the brush. We show that the interdigitation dynamics is affected by such confinements, in a way reminiscent of the change of the glass transition temperature in nanometric PS films. Finally, when the upper d-PS layer is sheared above Tg, flow with large slip at the wall has been observed and interpreted in terms of stretching and expulsion of the grafted chains from the melt. We show how neutron reflectivity directly evidence this expulsion.

  8. Use of side-chain for rational design of n-type diketopyrrolopyrrole-based conjugated polymers: what did we find out?

    PubMed

    Kanimozhi, Catherine; Yaacobi-Gross, Nir; Burnett, Edmund K; Briseno, Alejandro L; Anthopoulos, Thomas D; Salzner, Ulrike; Patil, Satish

    2014-08-28

    The primary role of substituted side chains in organic semiconductors is to increase their solubility in common organic solvents. In the recent past, many literature reports have suggested that the side chains play a critical role in molecular packing and strongly impact the charge transport properties of conjugated polymers. In this work, we have investigated the influence of side-chains on the charge transport behavior of a novel class of diketopyrrolopyrrole (DPP) based alternating copolymers. To investigate the role of side-chains, we prepared four diketopyrrolopyrrole-diketopyrrolopyrrole (DPP-DPP) conjugated polymers with varied side-chains and carried out a systematic study of thin film microstructure and charge transport properties in polymer thin-film transistors (PTFTs). Combining results obtained from grazing incidence X-ray diffraction (GIXD) and charge transport properties in PTFTs, we conclude side-chains have a strong influence on molecular packing, thin film microstructure, and the charge carrier mobility of DPP-DPP copolymers. However, the influence of side-chains on optical properties was moderate. The preferential "edge-on" packing and dominant n-channel behavior with exceptionally high field-effect electron mobility values of >1 cm(2) V(-1) s(-1) were observed by incorporating hydrophilic (triethylene glycol) and hydrophobic side-chains of alternate DPP units. In contrast, moderate electron and hole mobilities were observed by incorporation of branched hydrophobic side-chains. This work clearly demonstrates that the subtle balance between hydrophobicity and hydrophilicity induced by side-chains is a powerful strategy to alter the molecular packing and improve the ambipolar charge transport properties in DPP-DPP based conjugated polymers. Theoretical analysis supports the conclusion that the side-chains influence polymer properties through morphology changes, as there is no effect on the electronic properties in the gas phase. The exceptional

  9. Structure and rheology of star polymers in confined geometries: a mesoscopic simulation study.

    PubMed

    Zheng, Feiwo; Goujon, Florent; Mendonça, Ana C F; Malfreyt, Patrice; Tildesley, Dominic J

    2015-11-28

    Mesoscopic simulations of star polymer melts adsorbed onto solid surfaces are performed using the dissipative particle dynamics (DPD) method. A set of parameters is developed to study the low functionality star polymers under shear. The use of a new bond-angle potential between the arms of the star creates more rigid chains and discriminates between different functionalities at equilibrium, but still allows the polymers to deform appropriately under shear. The rheology of the polymer melts is studied by calculating the kinetic friction and viscosity and there is good agreement with experimental properties of these systems. The study is completed with predictive simulations of star polymer solutions in an athermal solvent. PMID:26435466

  10. Effect of Long-chain Branching on Surface Dynamics of Polymer Films

    NASA Astrophysics Data System (ADS)

    Foster, Mark D.; Wang, Shih-Fan; Lee, Jae Sik; Yang, Sewoo; Jiang, Zhang; Narayanan, Suresh; Wu, David

    2009-03-01

    Thermally stimulated fluctuations of the surface of films of branched polystyrene chains have been studied using x-ray photon correlation spectroscopy (XPCS), a recently-developed technique that has already been applied to study the surfaces of melts of linear polystyrene chains. Surface relaxations of films of branched chains are faster than are those of films of linear analogs. However, the Tg's of the branched molecules are also lower. The variation in surface relaxation time as a function of scattering vector can be described well by a continuum hydrodynamic theory of thermally stimulated capillary waves with a nonslip boundary condition. However, the film viscosities inferred from fits of the theory to the data differ markedly from viscosities from bulk measurements. Acknowledgements: NSF support (CBET 0730692)

  11. Untying a nanoscale knotted polymer structure to linear chains for efficient gene delivery in vitro and to the brain

    NASA Astrophysics Data System (ADS)

    Newland, B.; Aied, A.; Pinoncely, A. V.; Zheng, Y.; Zhao, T.; Zhang, H.; Niemeier, R.; Dowd, E.; Pandit, A.; Wang, W.

    2014-06-01

    The purpose of this study was to develop a platform transfection technology, for applications in the brain, which could transfect astrocytes without requiring cell specific functionalization and without the common cause of toxicity through high charge density. Here we show that a simple and scalable preparation technique can be used to produce a ``knot'' structured cationic polymer, where single growing chains can crosslink together via disulphide intramolecular crosslinks (internal cyclizations). This well-defined knot structure can thus ``untie'' under reducing conditions, showing a more favorable transfection profile for astrocytes compared to 25 kDa-PEI (48-fold), SuperFect® (39-fold) and Lipofectamine®2000 (18-fold) whilst maintaining neural cell viability at over 80% after four days of culture. The high transfection/lack of toxicity of this knot structured polymer in vitro, combined with its ability to mediate luciferase transgene expression in the adult rat brain, demonstrates its use as a platform transfection technology which should be investigated further for neurodegenerative disease therapies.The purpose of this study was to develop a platform transfection technology, for applications in the brain, which could transfect astrocytes without requiring cell specific functionalization and without the common cause of toxicity through high charge density. Here we show that a simple and scalable preparation technique can be used to produce a ``knot'' structured cationic polymer, where single growing chains can crosslink together via disulphide intramolecular crosslinks (internal cyclizations). This well-defined knot structure can thus ``untie'' under reducing conditions, showing a more favorable transfection profile for astrocytes compared to 25 kDa-PEI (48-fold), SuperFect® (39-fold) and Lipofectamine®2000 (18-fold) whilst maintaining neural cell viability at over 80% after four days of culture. The high transfection/lack of toxicity of this knot

  12. Two Zn coordination polymers with meso-helical chains based on mononuclear or dinuclear cluster units

    NASA Astrophysics Data System (ADS)

    Qin, Ling; Qiao, Wen-Cheng; Zuo, Wei-Juan; Zeng, Si-Ying; Mei, Cao; Liu, Chang-Jiang

    2016-07-01

    Two zinc coordination polymers {[Zn2(TPPBDA)(oba)2]·DMF·1.5H2O}n (1), {[Zn(TPPBDA)1/2(tpdc)]·DMF}n (2) have been synthesized by zinc metal salt, nanosized tetradentate pyridine ligand with flexible or rigid V-shaped carboxylate co-ligands. These complexes were characterized by elemental analyses and X-ray single-crystal diffraction analyses. Compound 1 is a 2-fold interpenetrated 3D framework with [Zn2(CO2)4] clusters. Compound 2 can be defined as a five folded interpenetrating bbf topology with mononuclear Zn2+. These mononuclear or dinuclear cluster units are linked by mix-ligands, resulting in various degrees of interpenetration. In addition, the photoluminescent properties for TPPBDA ligand under different state and coordination polymers have been investigated in detail.

  13. Side-Chain Supramolecular Polymers Employing Conformer Independent Triple Hydrogen Bonding Arrays

    PubMed Central

    2013-01-01

    Derivatives of thymine have been extensively used to promote supramolecular materials assembly. Such derivatives can be synthetically challenging to access and may be susceptible to degradation. The current article uses a conformer-independent acceptor–donor–acceptor array (ureidopyrimidine) which forms moderate affinity interactions with diamidopyridine derivatives to effect supramolecular blend formation between polystyrene and poly(methyl methacrylate) polymers obtained by RAFT which have been functionalized with the hydrogen bonding motifs. PMID:24478529

  14. Chain Confinement in Electrospun Nanocomposites: using Thermal Analysis to Investigate Polymer-Filler Interactions

    SciTech Connect

    Q Ma; B Mao; P Cebe

    2011-12-31

    We investigate the interaction of the polymer matrix and filler in electrospun nanofibers using advanced thermal analysis methods. In particular, we study the ability of silicon dioxide nanoparticles to affect the phase structure of poly(ethylene terephthalate), PET. SiO{sub 2} nanoparticles (either unmodified or modified with silane) ranging from 0 to 2.0 wt% in PET were electrospun from hexafluoro-2-propanol solutions. The morphologies of both the electrospun (ES) nanofibers and the SiO{sub 2} powders were observed by scanning and transmission electron microscopy, while the amorphous or crystalline nature of the fibers was determined by real-time wide-angle X-ray scattering. The fractions of the crystal, mobile amorphous, and rigid amorphous phases of the non-woven, nanofibrous composite mats were quantified by using heat capacity measurements. The amount of the immobilized polymer layer, the rigid amorphous fraction, was obtained from the specific reversing heat capacity for both as-spun amorphous fibers and isothermally crystallized fibers. Existence of the rigid amorphous phase in the absence of crystallinity was verified in nanocomposite fibers, and two origins for confinement of the rigid amorphous fraction are proposed. Thermal analysis of electrospun fibers, including quasi-isothermal methods, provides new insights to quantitatively characterize the polymer matrix phase structure and thermal transitions, such as devitrification of the rigid amorphous fraction.

  15. Introduction to Polymer Chemistry.

    ERIC Educational Resources Information Center

    Harris, Frank W.

    1981-01-01

    Reviews the physical and chemical properties of polymers and the two major methods of polymer synthesis: addition (chain, chain-growth, or chain-reaction), and condensation (step-growth or step-reaction) polymerization. (JN)

  16. Étude thermodynamique du polymère super absorbant X10 vis à vis de l'eau vapeur

    NASA Astrophysics Data System (ADS)

    Bakass, M.; Bellat, J. P.; Mokhlisse, A.; Bertrand, G.

    2004-12-01

    The organic polymers super absorbents present values of specific surface lower than 2m2/g. The isobars of adsorption of water vapor on studied polymer are of type III at ambient temperature with the hysterisis phenomena. For temperatures lower than ambient, the isobars become deformed because of an effect of chains. This type of polymer is characterized by a multi-layer adsorption which occurs before the full-course one is complete. During reactions of adsorption, the polymer undergoes rearrangement polymeric network which results from a co-operative diffusion of the water molecules and from a spacing of chain followed by an expansion of the polymeric network. Three types of water molecules adsorbed on polymer were identified: strongly dependent water, adsorbed water and the water only trapped between the macromolecular chains.

  17. Peptide immobilized monolith containing tentacle-type functionalized polymer chains for high-capacity binding of immunoglobulin G.

    PubMed

    Du, Kaifeng

    2014-12-29

    A peptide immobilized tentacle-type monolith is developed here for high-performance IgG purification. In this work, the glucose-anchored GMA molecules serve as monomers to be grafted into the tentacle-type chains on highly porous monolith by a series of chemical reactions. While maintaining high column permeability, the tentacle grafting endows the monolith with lots of reactive handles to anchor more peptides. With that, the grafted monolith shows high peptide density of about 155μmolmL(-1), up to approximately 4.7 times higher over the ungrafted one (33μmolmL(-1)). As a result, the static adsorbing capacity and dynamic adsorption capacity at 50% breakthrough point reach 101.8 and 83.3mgmL(-1) for IgG adsorption, respectively. Regeneration, recycle and reuse of grafted monolith are highly successful for 25 runs without obvious capacity loss. By taking these advantages of high capacity and excellent structure stability, the affinity grafted monolith is evaluated by using cleared human blood supernatant. And the result shows the peptide immobilized tentacle type monolith displays excellent specificity and high effectiveness for IgG purification. PMID:25476688

  18. Scaling of the rupture dynamics of polymer chains pulled at one end at a constant rate.

    PubMed

    Fugmann, S; Sokolov, I M

    2009-02-01

    We consider the rupture dynamics of a homopolymer chain pulled at one end at a constant loading rate r . Compared to single bond breaking, the existence of the chain introduces two aspects into rupture dynamics: The non-Markovian aspect in the barrier crossing and the slow down of the force propagation to the breakable bond. The relative impact of both these processes is investigated, and the second one was found to be the most important at moderate loading rates. The most probable rupture force is found to decrease with the number of bonds as f{max} proportional, variant-[ln(const N/r)]2/3 and finally to approach a saturation value independent on N . All of our analytical findings are confirmed by extensive numerical simulations. PMID:19391768

  19. Distinct polymer chain orientations in KC{sub 60} and RbC{sub 60}

    SciTech Connect

    Launois, P.; Moret, R.; Erwin, S. C.; Hone, J.; Zettl, A.

    1999-09-30

    Polymerized alkali fullerides KC{sub 60} and RbC{sub 60} display different electronic properties. Single crystal X-ray diffraction and diffuse scattering studies show that the C{sub 60} chains possess different relative orientations about their axes. We will discuss this result in relation with electronic band structure calculations. The influence of pressure will also be discussed. (c) 1999 American Institute of Physics.

  20. The effect of side-chain length on the solid-state structure and optoelectronic properties of fluorene-alt-benzothiadiazole based conjugated polymers--a DFT study.

    PubMed

    Eslamibidgoli, Mohammad J; Lagowski, Jolanta B

    2012-11-01

    Using the dispersion corrected density functional theory (DFT-D/B97D) approach, we have performed bulk solid-state calculations to investigate the influence of side-chain length on the molecular packing and optoelectronic properties of poly (9,9-di-n-alkylfluorene-alt-benzothiadiazole) or FnBT's where n is the number of CH(2) units in the alkyl side-chains. Our results indicate that the FnBT's with longer side-chains in their most stable configurations, due to the significant intermolecular interactions between the side-chains, form lamellar crystal structures. On the other hand, for the FnBT's with shorter side-chains, two nearly degenerate stable crystal structures with nearly hexagonal symmetries have been found. These different packing structures can be attributed to the microphase separations between the flexible side-chains and the rigid backbones whose existence has been discussed in previous investigations for other hairy rod polymers. As a result of the efficient interchain interactions for the lamellar structures, the dihedral angle between the F and BT units is reduced by about 30°, providing a more planar configuration for the backbone. In turn, a more planar backbone leads to a decrease, about 0.2 and 0.3 eV, of the band gaps of the lamellar structures relative to the gap values for the gas and the nearly hexagonal phases, respectively. Time-dependent DFT (TD-DFT) was used to study the excited states of the monomers of FnBT's with various lengths of side-chains. TD-DFT study suggests that the absorption spectrum of the polymers with longer side-chains is red-shifted relative to the polymers with shorter side-chains and the gas phase. PMID:23050864

  1. Polymers.

    ERIC Educational Resources Information Center

    Tucker, David C.

    1986-01-01

    Presents an open-ended experiment which has students exploring polymer chemistry and reverse osmosis. This activity involves construction of a polymer membrane, use of it in a simple osmosis experiment, and application of its principles in solving a science-technology-society problem. (ML)

  2. Crystal nucleation mechanism in melts of short polymer chains under quiescent conditions and under shear flow

    NASA Astrophysics Data System (ADS)

    Anwar, Muhammad; Berryman, Joshua T.; Schilling, Tanja

    2014-09-01

    We present a molecular dynamics simulation study of crystal nucleation from undercooled melts of n-alkanes, and we identify the molecular mechanism of homogeneous crystal nucleation under quiescent conditions and under shear flow. We compare results for n-eicosane (C20) and n-pentacontahectane (C150), i.e., one system below the entanglement length and one above, at 20%-30% undercooling. Under quiescent conditions, we observe that entanglement does not have an effect on the nucleation mechanism. For both chain lengths, the chains first align and then straighten locally, then the local density increases and finally positional ordering sets in. At low shear rates the nucleation mechanism is the same as under quiescent conditions, while at high shear rates the chains align and straighten at the same time. We report on the effects of shear rate and temperature on the nucleation rates and estimate the critical shear rates, beyond which the nucleation rates increase with the shear rate. In agreement with previous experimental observation and theoretical work, we find that the critical shear rate corresponds to a Weissenberg number of order 1. Finally, we show that the viscosity of the system is not affected by the crystalline nuclei.

  3. Treatment of disordered and ordered systems of polymer chains by lattice methods

    PubMed Central

    Flory, Paul J.

    1982-01-01

    Classical lattice theories of systems of long-chain molecules provide estimates of the number Z of random configurations to the exclusion of ordered ones. The decrease of Z thus estimated to values [unk]1 with decrease in chain flexibility at high densities is genuine, but it does not take account of eligible ordered configurations; the latter are not a subset of the configurations whose numbers are estimated by classical lattice methods. Failure to recognize this fact and the fundamental distinction between disordered and ordered states has engendered misinterpretations and has cast doubt on the validity of lattice-statistical methods. In a system at equilibrium, the decline of Z (disordered) with decrease in chain flexibility must be arrested by a first order transition to an ordered state. The inference that approach of Z (disordered) to values <1 presages a thermodynamic transition of second order is tenable only if the array of ordered configurations, not comprehended by theories in which the mean field of unoccupied lattice sites is random, can be ignored. PMID:16593214

  4. Electrophoretic mobilities of counterions and a polymer in cylindrical pores

    PubMed Central

    Singh, Sunil P.; Muthukumar, M.

    2014-01-01

    We have simulated the transport properties of a uniformly charged flexible polymer chain and its counterions confined inside cylindrical nanopores under an external electric field. The hydrodynamic interaction is treated by describing the solvent molecules explicitly with the multiparticle collision dynamics method. The chain consisting of charged monomers and the counterions interact electrostatically with themselves and with the external electric field. We find rich behavior of the counterions around the polymer under confinement in the presence of the external electric field. The mobility of the counterions is heterogeneous depending on their location relative to the polymer. The adsorption isotherm of the counterions on the polymer depends nonlinearly on the electric field. As a result, the effective charge of the polymer exhibits a sigmoidal dependence on the electric field. This in turn leads to a nascent nonlinearity in the chain stretching and electrophoretic mobility of the polymer in terms of their dependence on the electric field. The product of the electric field and the effective polymer charge is found to be the key variable to unify our simulation data for various polymer lengths. Chain extension and the electrophoretic mobility show sigmoidal dependence on the electric field, with crossovers from the linear response regime to the nonlinear regime and then to the saturation regime. The mobility of adsorbed counterions is nonmonotonic with the electric field. For weaker and moderate fields, the adsorbed counterions move with the polymer and at higher fields they move opposite to the polymer's direction. We find that the effective charge and the mobility of the polymer decrease with a decrease in the pore radius. PMID:25240366

  5. Computation of the Mean First-Encounter Time Between the Ends of a Polymer Chain

    NASA Astrophysics Data System (ADS)

    Amitai, A.; Kupka, I.; Holcman, D.

    2012-09-01

    Using a novel theoretical approach, we study the mean first-encounter time (MFET) between the two ends of a polymer. Previous approaches used various simplifications that reduced the complexity of the problem, leading, however, to incompatible results. We construct here for the first time a general theory that allows us to compute the MFET. The method is based on estimating the mean time for a Brownian particle to reach a narrow domain in the polymer configuration space. In dimension two and three, we find that the MFET depends mainly on the first eigenvalue of the associated Fokker-Planck operator and provide precise estimates that are confirmed by Brownian simulations. Interestingly, although many time scales are involved in the encounter process, its distribution can be well approximated by a single exponential, which has several consequences for modeling chromosome dynamics in the nucleus. Another application of our result is computing the mean time for a DNA molecule to form a closed loop (when its two ends meet for the first time).

  6. Stealth filaments: polymer chain length and conformation affect the in vivo fate of PEGylated potato virus X

    PubMed Central

    Lee, Karin L.; Shukla, Sourabh; Wu, Mengzhi; Ayat, Nadia R.; El Sanadi, Caroline E.; Wen, Amy M.; Edelbrock, John F.; Pokorski, Jonathan K.; Commandeur, Ulrich; Dubyak, George R.

    2015-01-01

    Nanoparticles hold great promise for delivering medical cargos to cancerous tissues to enhance contrast and sensitivity of imaging agents or to increase specificity and efficacy of therapeutics. A growing body of data suggests that nanoparticle shape, in combination with surface chemistry, affects their in vivo fates, with elongated filaments showing enhanced tumor targeting and tissue penetration, while promoting immune evasion. The synthesis of high aspect ratio filamentous materials at the nanoscale remains challenging using synthetic routes; therefore we turned toward nature’s materials, developing and studying the filamentous structures formed by the plant virus potato virus X (PVX). We recently demonstrated that PVX shows enhanced tumor homing in various preclinical models. Like other nanoparticle systems, the proteinaceous platform is cleared from circulation and tissues by the mononuclear phagocyte system (MPS). To increase bioavailability we set out to develop PEGylated stealth filaments and evaluate the effects of PEG chain length and conformation on pharmacokinetics, biodistribution, as well as potential immune and inflammatory responses. We demonstrate that PEGylation effectively reduces immune recognition while increasing pharmacokinetic profiles. Stealth filaments show biodistribution consistent with MPS clearance mechanisms; the protein:polymer hybrids are cleared from the body indicating biodegradability and biocompatibility. Tissue compatibility is indicated with no apparent inflammatory signaling in vivo. Tailoring PEG chain length and conformation (brush vs. mushroom) allows tuning of the pharmacokinetics, yielding long-circulating stealth filaments for applications in nanomedicine. PMID:25769228

  7. Stealth filaments: Polymer chain length and conformation affect the in vivo fate of PEGylated potato virus X.

    PubMed

    Lee, Karin L; Shukla, Sourabh; Wu, Mengzhi; Ayat, Nadia R; El Sanadi, Caroline E; Wen, Amy M; Edelbrock, John F; Pokorski, Jonathan K; Commandeur, Ulrich; Dubyak, George R; Steinmetz, Nicole F

    2015-06-01

    Nanoparticles hold great promise for delivering medical cargos to cancerous tissues to enhance contrast and sensitivity of imaging agents or to increase specificity and efficacy of therapeutics. A growing body of data suggests that nanoparticle shape, in combination with surface chemistry, affects their in vivo fates, with elongated filaments showing enhanced tumor targeting and tissue penetration, while promoting immune evasion. The synthesis of high aspect ratio filamentous materials at the nanoscale remains challenging using synthetic routes; therefore we turned toward nature's materials, developing and studying the filamentous structures formed by the plant virus potato virus X (PVX). We recently demonstrated that PVX shows enhanced tumor homing in various preclinical models. Like other nanoparticle systems, the proteinaceous platform is cleared from circulation and tissues by the mononuclear phagocyte system (MPS). To increase bioavailability we set out to develop PEGylated stealth filaments and evaluate the effects of PEG chain length and conformation on pharmacokinetics, biodistribution, as well as potential immune and inflammatory responses. We demonstrate that PEGylation effectively reduces immune recognition while increasing pharmacokinetic profiles. Stealth filaments show reduced interaction with cells of the MPS; the protein:polymer hybrids are cleared from the body tissues within hours to days indicating biodegradability and biocompatibility. Tissue compatibility is indicated with no apparent inflammatory signaling in vivo. Tailoring PEG chain length and conformation (brush vs. mushroom) allows tuning of the pharmacokinetics, yielding long-circulating stealth filaments for applications in nanomedicine. PMID:25769228

  8. Kinetic regimes of polyelectrolyte exchange between the adsorbed state and free solution

    NASA Astrophysics Data System (ADS)

    Sukhishvili, Svetlana A.; Granick, Steve

    1998-10-01

    We studied the exchange between the adsorbed state and free solution when polyelectrolyte chains, adsorbed to a solid surface of opposite charge, were displaced by chains of higher charge density. Metastable states of surface composition were extremely long-lived (>2-3 days). The system was a family of poly(1,4 vinyl)pyridines (PVP) with different fractions of charged segments (14%, 48%, and 98% quaternized and the same degree of polymerization); samples were exposed sequentially from aqueous D2O solution to a single silicon oxide substrate at pH where the surface carried a large negative charge (pH=9.2 or 10.5). Measurements were based on Fourier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR). As a first conclusion, we found charge of adsorbed polymer to be conserved during extended exchange times, suggesting that charge at the surface (not mass adsorbed) regulated the dynamics of adsorption and desorption. Except at the highest ionic strength charge of polymer at the surface during the displacement process considerably exceeded that for the initially-adsorbed layer, suggesting an intermediate state in which newly-adsorbed chains were more extended from the surface and not yet equilibrated in their conformations. Second, we concluded that desorption was the rate-limiting step in adsorption-desorption, since the desorption rate responded more to changes of ionic strength than did the adsorption rate onto previously-adsorbed polymer. Ionic strength appeared to modulate the intensity of sticking to the surface. Third, we found that the initial stages of desorption obeyed a simple functional form, exponential in the square root of elapsed time. This is conclusively slower than a first-order kinetic process and suggests that desorption in this polyelectrolyte system was diffusion-controlled during the initial stages. It is the same functional form observed for flexible polymers in nonpolar solvents. Fourth, we concluded that at relatively low

  9. Non-Monotonic Concentration Effects in the Phase Behavior and Nematic Orders: Mixtures of Side-Chain Liquid Crystalline Polymers and Low-Molecular-Weight Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Zhuang, Bilin; Wang, Zhen-Gang

    2012-02-01

    Mixtures of side-chain liquid crystal polymers (SCLCPs) and low-molecular-weight liquid crystals (LMWLCs) are novel materials with applications such as optical data storage, non-linear optics, solid polymer electrolytes, chromatography and display materials. Recent experiments showed that the nematic-isotropic transition temperature and the nematic orders of each component vary non-monotonically with concentration. Existing theories, which combine the Flory-Huggins theory for isotropic mixing and the Maier-Saupe theory for nematic order, cannot explain such non-monotonicity. Here, we extend the existing theories by, first, incorporating the local steric constraints between the side-chain and the polymer backbone on the SCLCPs, and second, accounting for the crowding effects at high SCLCP concentrations. The new extended theory is able to resolve the discrepancies between the predictions of existing theories and the experimental observations.

  10. Phase equilibria and self-organizing behavior of side-chain liquid crystalline polymer mixtures

    NASA Astrophysics Data System (ADS)

    Chiu, Hao-Wen

    1998-12-01

    Phenomenological models for elucidating phase diagrams of binary smectic-A mixtures, polymer/smectic-A mixtures, induced smectic in nematic mixtures, and nematic/smectic mixtures have been proposed on the basis of the combination of the Flory-Huggins (FH) free energy of isotropic mixing and Maier-Saupe-McMillan (MSM) free energy for nematic/smectic ordering. The nematic and smectic order parameters have been coupled through the normalized partition and the orientation distribution functions. Flory-Huggins interaction parameter (chi) for isotropic mixing and the coupling term involving the nematic interaction parameter (nu) and the McMillan smectic interaction parameter (alpha) for phase transitions of liquid crystals have been incorporated in the calculation. The predictive capability of the combined FH/MSM theory has been demonstrated by testing with reported phase diagrams. Dynamics of phase separation and morphology development in mixtures of a nematic liquid crystal and a polymer due to thermal quenching have been investigated theoretically in comparison with experimental results. In the proposed model, the combined free energy densities of Flory-Huggins theory for isotropic mixing and Maier-Saupe (MS) theory for nematic ordering have been incorporated into the time-dependent Ginzburg-Landau equation (TDGL, type C). The temporal evolution of the structure factor and the emergence of phase separated liquid crystal (LC) domains have been simulated on the basis of an explicit central difference method based on a square lattice with a periodic boundary condition. Of particular interest is the observed plateau (or inflection) region in the growth dynamic curve, which may be attributed to the breakdown of the interconnected domains caused by the nematic ordering. The emergence of LC domains during polymerization induced phase separation in a polymer dispersed liquid crystal (PDLC) has been solved numerically by incorporating the reaction kinetics into the TDGL

  11. Investigation of the effects of short chain processing additives on polymers

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; Stclair, T. L.; Pratt, J. R.

    1986-01-01

    The effects of low level concentrations of several short chain processing additives on the properties of the 4,4'-bis(3,4-dicarboxyphenoxy) diphenylsulfide dianhydride (BDSDA)/4,4'-diaminodiphenyl ether (ODA)/1,3'-diaminobenzene (m-phenylene diamine) (MPA) (422) copolyimide were investigated. It was noted that 5 percent MPD/phthalic anhydride (PA) is more effective than 5 percent ODA/PA and BDSDA/aniline (AN) in strengthening the host material. However, the introduction of 10 percent BDSDA/AN produces disproportionately high effects on free volume and free electron density in the host copolyimide.

  12. Phase diagram of a semiflexible polymer chain in a θ solvent: Application to protein folding

    NASA Astrophysics Data System (ADS)

    Doniach, S.; Garel, T.; Orland, H.

    1996-07-01

    We consider a lattice model of a semiflexible homopolymer chain in a bad solvent. Beside the temperature T, this model is described by (i) a curvature energy ɛh, representing the stiffness of the chain; (ii) a nearest-neighbor attractive energy ɛv, representing the solvent; and (iii) the monomer density ρ=N/Ω, where N and Ω denote, respectively, the number of monomers and the number of lattice sites. This model is a simplified view of the protein folding problem, which encompasses the geometrical competition between secondary structures (the curvature term modelling helix formation) and the global compactness (modeled here by the attractive energy), but contains no side chain information. By allowing the monomer density ρ to depart from unity one has made a first (albeit naive) step to include the role of the water. In previous analytical studies, we considered only the (fully compact) case ρ=1, and found a first order freezing transition towards a crystalline ground state (also called the native state in the protein literature). In this paper, we extend this calculation to the description of both compact and noncompact phases. The analysis is done first at a mean-field level. We then find that the transition from the high temperature swollen coil state to the crystalline ground state is a two-step process for which (i) there is first a θ collapse transition towards a compact ``liquid'' globule, and (ii) at low temperature, this ``liquid'' globule undergoes a discontinuous freezing transition. The mean-field value of the θ collapse temperature is found to be independent of the curvature energy ɛh. This mean-field analysis is improved by a variational bound, which confirms the independence of the θ collapse temperature with respect to ɛh. This result is confirmed by a Monte Carlo simulation, although with a much lower value of the θ temperature. This lowering of the collapse transition allows the possibility (for large ɛh) of a direct first order

  13. Synthesis of metronidazole-imprinted molecularly imprinted polymers by distillation precipitation polymerization and their use as a solid-phase adsorbent and chromatographic filler.

    PubMed

    Liu, Jiang; Zhang, Lu; Li Han Song, Le; Liu, Yuan; Tang, Hui; Li, Yingchun

    2015-04-01

    Metronidazole-imprinted polymers with superior recognition properties were prepared by a novel strategy called distillation-precipitation polymerization. The as-obtained polymers were characterized by Fourier-transform infrared spectroscopy, laser particle size determination and scanning electron microscopy, and their binding performances were evaluated in detail by static, kinetic and dynamic rebinding tests, and Scatchard analysis. The results showed that when the fraction of the monomers was 5 vol% in the whole reaction system, the prepared polymers afforded good morphology, monodispersity, and high adsorption capacity and excellent selectivity to the target molecule, metronidazole. The optimal binding performance is 12.41 mg/g for metronidazole just before leakage occurred and 38.51 mg/g at saturation in dynamic rebinding tests. Metronidazole-imprinted polymers were further applied as packing agents in solid-phase extraction and as chromatographic filler, both of which served for the detection of metronidazole in fish tissue. The results illustrated the recoveries of spiked samples ranged from 82.97 to 87.83% by using molecularly imprinted solid-phase extraction combined with a C18 commercial column and 93.7 to 101.2% by directly using the polymer-packed chromatographic column. The relative standard deviation of both methods was less than 6%. PMID:25594306

  14. Filled elastomers: polymer chain and filler characterization by a SANS-SAXS approach

    NASA Astrophysics Data System (ADS)

    Botti, A.; Pyckhout-Hintzen, W.; Richter, D.; Straube, E.

    2002-02-01

    One of the important features of filled elastomers in general is the so-called strain amplification, or the enhancement of the local deformation of the rubbery matrix in comparison to the macroscopic deformation of the sample. This is due to the presence of the filler, taken as an indeformable substance, that changes the properties of the system, both macroscopically like the stiffnesss or the Young modulus, and microscopically like the local overstrain of chains. We used commercially interesting fillers, all of them based on silica particles showing different surface properties, while the rubbery matrix was a blend of protonated and deuterated polyisoprene (PI). We varied the filler volume fraction and the applied strain. First, we studied separately the two components of the composite, characterizing by X-ray and neutrons the filler, to use this information later in the extraction of the single chain scattering from SANS measurements. For a description of the microscopic deformation we rely on the previous finding on the unfilled network obtained using the tube model by Heinrich and Straube, modified and rewritten for SANS experiments on this kind of system.

  15. Influence of polymer architecture and polymer-wall interaction on the adsorption of polymers into a slit-pore.

    PubMed

    Chen, Zhong; Escobedo, Fernando A

    2004-02-01

    The effects of molecular topology and polymer-surface interaction on the properties of isolated polymer chains trapped in a slit were investigated using off-lattice Monte Carlo simulations. Various methods were implemented to allow efficient simulation of molecular structure, confinement force, and free energy for a chain interacting with such "sticky" surfaces. The simulations were performed in the canonical ensemble, and the free energy was sampled via virtual slit-separation moves. Six different chain architectures were studied: linear, star-branched, dendritic, cyclic, two-node (i.e., containing two tetrafunctional intramolecular crosslinks), and six-node molecules. The first three topologies entail increasing degrees of branching, and the last three topologies entail increasing degrees of intramolecular bonding. The confinement force, monomer density profile, and conformational properties for all these systems were compared (for identical molecular weight N) and analyzed as a function of adsorption strength. The compensation point where the wall attraction counterbalances the polymer-slit exclusion effects was the focus of our study. It was found that the attractive energy at the compensation point, epsilon(c), is a weak increasing function of the chain length for excluded-volume chains. The value of epsilon(c) differs significantly for different topologies, and smaller values are associated with better-adsorbing molecules. Due to their globular shape and numerous chain ends, branched molecules (e.g., stars and dendrimers) experience a relatively small entropic penalty for adsorption at low adsorption force and moderate confinement. However, as the adsorption force increases, the more flexible linear chains reach the compensation point at a weaker attractive energy because of the ease with which monomers can be packed near the walls. In moderate to weak confinement, molecules with intramolecular cross-links, such as cyclic, two-node, and six-node molecules

  16. Influence of polymer architecture and polymer-wall interaction on the adsorption of polymers into a slit-pore

    NASA Astrophysics Data System (ADS)

    Chen, Zhong; Escobedo, Fernando A.

    2004-02-01

    The effects of molecular topology and polymer-surface interaction on the properties of isolated polymer chains trapped in a slit were investigated using off-lattice Monte Carlo simulations. Various methods were implemented to allow efficient simulation of molecular structure, confinement force, and free energy for a chain interacting with such “sticky” surfaces. The simulations were performed in the canonical ensemble, and the free energy was sampled via virtual slit-separation moves. Six different chain architectures were studied: linear, star-branched, dendritic, cyclic, two-node (i.e., containing two tetrafunctional intramolecular crosslinks), and six-node molecules. The first three topologies entail increasing degrees of branching, and the last three topologies entail increasing degrees of intramolecular bonding. The confinement force, monomer density profile, and conformational properties for all these systems were compared (for identical molecular weight N) and analyzed as a function of adsorption strength. The compensation point where the wall attraction counterbalances the polymer-slit exclusion effects was the focus of our study. It was found that the attractive energy at the compensation point, ɛc, is a weak increasing function of the chain length for excluded-volume chains. The value of ɛc differs significantly for different topologies, and smaller values are associated with better-adsorbing molecules. Due to their globular shape and numerous chain ends, branched molecules (e.g., stars and dendrimers) experience a relatively small entropic penalty for adsorption at low adsorption force and moderate confinement. However, as the adsorption force increases, the more flexible linear chains reach the compensation point at a weaker attractive energy because of the ease with which monomers can be packed near the walls. In moderate to weak confinement, molecules with intramolecular cross-links, such as cyclic, two-node, and six-node molecules, always

  17. Polymer-Induced Depletion Interaction and Its Effect on Colloidal Sedimentation in Colloid-Polymer Mixtures

    NASA Technical Reports Server (NTRS)

    Tong, Penger

    1996-01-01

    In this paper we focus on the polymer-induced depletion attraction and its effect on colloidal sedimentation in colloid-polymer mixtures. We first report a small angle neutron scattering (SANS) study of the depletion effect in a mixture of hard-sphere-like colloid and non-adsorbing polymer. Then we present results of our recent sedimentation measurements in the same colloid-polymer mixture. A key parameter in controlling the sedimentation of heavy colloidal particles is the interparticle potential U(tau), which is the work required to bring two colloidal particles from infinity to a distance tau under a give solvent condition. This potential is known to affect the average settling velocity of the particles and experimentally one needs to have a way to continuously vary U(tau) in order to test the theory. The interaction potential U(tau) can be altered by adding polymer molecules into the colloidal suspension. In a mixture of colloid and non-adsorbing polymer, the potential U(tau) can develop an attractive well because of the depletion effect, in that the polymer chains are expelled from the region between two colloidal particles when their surface separation becomes smaller than the size of the polymer chains. The exclusion of polymer molecules from the space between the colloidal particles leads to an unbalanced osmotic pressure difference pushing the colloidal particles together, which results in an effective attraction between the two colloidal particles. The polymer-induced depletion attraction controls the phase stability of many colloid-polymer mixtures, which are directly of interest to industry.

  18. The Role of Morphology and Electronic Chain Aggregation on the Optical Gain Properties of Semiconducting Conjugated Polymers

    NASA Astrophysics Data System (ADS)

    Lampert, Zachary Evan

    Conjugated polymers (CPs) are a novel class of materials that exhibit the optical and electrical properties of semiconductors while still retaining the durability and processability of plastics. CPs are also intrinsically 4-level systems with high luminescence quantum efficiencies making them particularly attractive as organic gain media for solid-state laser applications. However, before CPs can emerge as a commercially available laser technology, a more comprehensive understanding of the morphological dependence of the photophysics is required. In this thesis, the morphology and chain conformation dependence of amplified spontaneous emission (ASE) and optical gain in thin films of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) was investigated. By changing the chemical nature of the solvent from which films were cast, as well as the temperature at which films were annealed, CP films with different morphologies, and hence different degrees of interchain interactions were achieved. Contrary to the common perception that polymer morphology plays a decisive role in determining the ASE behavior of thin CP films, we found that chromophore aggregation and degree of conformational order have minimal impact on optical gain. In fact, experimental results indicated that an extremely large fraction of interchain aggregate species and/or exciton dissociating defects are required to significantly alter the optical properties and suppress stimulated emission. These results are pertinent to the fabrication and optimization of an electrically pumped laser device, as improvements in charge carrier mobility through controlled increases in chain aggregation may provide a viable means of optimizing injection efficiency without significantly degrading optical gain. To offset charge-induced absorption losses under electrical pumping, and to enable the use of more compact and economical sources under optical pumping, conjugated polymers exhibiting low lasing

  19. Magnetic molecularly imprinted polymers synthesized by surface-initiated reversible addition-fragmentation chain transfer polymerization for the enrichment and determination of synthetic estrogens in aqueous solution.

    PubMed

    Chen, Fangfang; Zhang, Jingjing; Wang, Minjun; Kong, Jie

    2015-08-01

    Magnetic molecularly imprinted polymers have attracted significant interest because of their multifunctionality of selective recognition of target molecules and rapid magnetic response. In this contribution, magnetic molecularly imprinted polymers were synthesized via surface-initiated reversible addition addition-fragmentation chain transfer polymerization using diethylstilbestrol as the template for the enrichment of synthetic estrogens. The uniform imprinted surface layer and the magnetic property of the magnetic molecularly imprinted polymers favored a fast binding kinetics and rapid analysis of target molecules. The static and selective binding experiments demonstrated a desirable adsorption capacity and good selectivity of the magnetic molecularly imprinted polymers in comparison to magnetic non-molecularly imprinted polymers. Accordingly, a corresponding analytical method was developed in which magnetic molecularly imprinted polymers were employed as magnetic solid-phase extraction materials for the concentration and determination of four synthetic estrogens (diethylstilbestrol, hexestrol, dienestrol, and bisphenol A) in fish pond water. The recoveries of these synthetic estrogens in spiked fish pond water samples ranged from 61.2 to 99.1% with a relative standard deviation of lower than 6.3%. This study provides a versatile approach to prepare well-defined magnetic molecularly imprinted polymers sorbents for the analysis of synthetic estrogens in water solution. PMID:25989155

  20. The importance of chain connectivity in the formation of non-covalent interactions between polymers and single-walled carbon nanotubes and its impact on dispersion

    SciTech Connect

    Linton, Dias; Driva, Paraskevi; Ivanov, Ilia N; Geohegan, David B; Feigerle, Charles S; Dadmun, Mark D

    2010-05-01

    In this study we investigate the formation of non-covalent electron donor acceptor (EDA) interactions between polymers and single-walled carbon nanotubes (SWNTs) with the goal of optimizing interfacial adhesion and homogeneity of nanocomposites without modifying the SWNT native surface. Nanocomposites of SWNTs and three sets of polymer matrices with varying composition of electron donating 2-(dimethylamino)ethyl methacrylate (DMAEMA) or electron accepting acrylonitrile (AN) and cyanostyrene (CNSt) were prepared, quantitatively characterized by optical microscopy and Raman spectroscopy (Raman mapping, Raman D* peak shifts) and qualitatively compared through thick film composite visualization. The experimental data show that copolymers with 30 mol% DMAEMA, 45 mol% AN, 23 mol% CNSt and polyacrylonitrile homopolymer have the highest extent of intermolecular interaction, which translates to an optimum SWNT spatial dispersion among the series. These results are found to correlate very well with the intermolecular interaction energies obtained from quantum density functional theory calculations. Both experimental and computational results also illustrate that chain connectivity is critical in controlling the accessibility of the functional groups to form intermolecular interactions. This means that an adequate distance between interacting functional groups on a polymer chain is needed in order to allow efficient intermolecular contact. Thus, controlling the amount of electron donating or withdrawing moieties throughout the polymer chain will direct the extent of EDA interaction, which enables tuning the SWNT dispersion.

  1. The importance of chain connectivity in the formation of non-covalent interactions between polymers and single-walled carbon nanotubes and its impact on dispersion

    SciTech Connect

    Sumpter, Bobby G; Dadmun, Mark D; Driva, Paraskevi; Ivanov, Ilia N; Geohegan, David B; Linton, Dias; Feigerle, Charles S

    2010-01-01

    In this study we investigate the formation of non-covalent electron donor acceptor (EDA) interactions between polymers and single-walled carbon nanotubes (SWNTs) with the goal of optimizing interfacial adhesion and homogeneity of nanocomposites without modifying the SWNT native surface. Nanocomposites of SWNTs and three sets of polymer matrices with varying composition of electron donating 2-(dimethylamino)ethyl methacrylate (DMAEMA) or electron accepting acrylonitrile (AN) and cyanostyrene (CNSt) were prepared, quantitatively characterized by optical microscopy and Raman spectroscopy (Raman mapping, Raman D* peak shifts) and qualitatively compared through thick film composite visualization. The experimental data show that copolymers with 30 mol% DMAEMA, 45 mol% AN, 23 mol% CNSt and polyacrylonitrile homopolymer have the highest extent of intermolecular interaction, which translates to an optimum SWNT spatial dispersion among the series. These results are found to correlate very well with the intermolecular interaction energies obtained from quantum density functional theory calculations. Both experimental and computational results also illustrate that chain connectivity is critical in controlling the accessibility of the functional groups to form intermolecular interactions. This means that an adequate distance between interacting functional groups on a polymer chain is needed in order to allow efficient intermolecular contact. Thus, controlling the amount of electron donating or withdrawing moieties throughout the polymer chain will direct the extent of EDA interaction, which enables tuning the SWNT dispersion.

  2. The Rouse-Mooney model for coherent quasielastic neutron scatterings of single chains well entangled in polymer melts

    NASA Astrophysics Data System (ADS)

    Lin, Y.-H.; Huang, C.-F.

    2008-06-01

    The dynamic structure factor (DSF) for single (labeled) chains well entangled in polymer melts has been developed based on the Rouse-Mooney picture; the DSF functions derived from the Langevin equations of the model in both discrete and continuous forms are given. It is shown that for all practical purposes, it is sufficient to use the continuous form to analyze experimental results in the ``safe'' q region (q being the magnitude of the scattering wave vector q) where the Rouse-segment-based theories are applicable. The DSF form reduces to the same limiting form as that of the free Rouse chain as q2a2 or q2R2-->∞ (a and R being the entanglement distance and the root mean square end-to-end distance, respectively), confirming what has been expected physically. The natural reduction to the limiting form allows the full range of DSF curves to be displayed in terms of the reduced Rouse variable q2(Zdt)0.5 in a unified way. The displayed full range represents a framework or ``map,'' with respect to which effects occurring in different regions of the DSF may be located and studied in a consistent manner. One effect is the significant or noticeable deviations of the theoretical DSF curves from the limiting curve in the region ~4>q2(Zdt)0.5>~0.1 (a time region where t<τ1e) to the faster side as qa is in the range 1-5. This is supported by the comparison of the experimental results of an entangled poly(vinylethylene) sample with the theoretical curves. The DSF functional forms predict plateaus with heights depending on the value of q-q-split plateaus-as can be experimentally observed in the time region greater than the relaxation time τ1e of the lowest Rouse-Mooney mode, when qa falls between ~1 and ~7. High sensitivity of the distribution of the q-split plateaus to a enables its value to be extracted from matching the calculated with the experimental results. The thus obtained a value for a well-entangled poly(ethylene-co-butene) polymer is in close agreement with the

  3. Effects of molecular structure on microscopic heat transport in chain polymer liquids

    SciTech Connect

    Matsubara, Hiroki Kikugawa, Gota; Ohara, Taku; Bessho, Takeshi; Yamashita, Seiji

    2015-04-28

    In this paper, we discuss the molecular mechanism of the heat conduction in a liquid, based on nonequilibrium molecular dynamics simulations of a systematic series of linear- and branched alkane liquids, as a continuation of our previous study on linear alkane [T. Ohara et al., J. Chem. Phys. 135, 034507 (2011)]. The thermal conductivities for these alkanes in a saturated liquid state at the same reduced temperature (0.7T{sub c}) obtained from the simulations are compared in relation to the structural difference of the liquids. In order to connect the thermal energy transport characteristics with molecular structures, we introduce the new concept of the interatomic path of heat transfer (atomistic heat path, AHP), which is defined for each type of inter- and intramolecular interaction. It is found that the efficiency of intermolecular AHP is sensitive to the structure of the first neighbor shell, whereas that of intramolecular AHP is similar for different alkane species. The dependence of thermal conductivity on different lengths of the main and side chain can be understood from the natures of these inter- and intramolecular AHPs.

  4. Effects of molecular structure on microscopic heat transport in chain polymer liquids.

    PubMed

    Matsubara, Hiroki; Kikugawa, Gota; Bessho, Takeshi; Yamashita, Seiji; Ohara, Taku

    2015-04-28

    In this paper, we discuss the molecular mechanism of the heat conduction in a liquid, based on nonequilibrium molecular dynamics simulations of a systematic series of linear- and branched alkane liquids, as a continuation of our previous study on linear alkane [T. Ohara et al., J. Chem. Phys. 135, 034507 (2011)]. The thermal conductivities for these alkanes in a saturated liquid state at the same reduced temperature (0.7Tc) obtained from the simulations are compared in relation to the structural difference of the liquids. In order to connect the thermal energy transport characteristics with molecular structures, we introduce the new concept of the interatomic path of heat transfer (atomistic heat path, AHP), which is defined for each type of inter- and intramolecular interaction. It is found that the efficiency of intermolecular AHP is sensitive to the structure of the first neighbor shell, whereas that of intramolecular AHP is similar for different alkane species. The dependence of thermal conductivity on different lengths of the main and side chain can be understood from the natures of these inter- and intramolecular AHPs. PMID:25933776

  5. Wetting and spreading of long-chain ZDOL polymer nanodroplet on graphene-coated amorphous carbon

    NASA Astrophysics Data System (ADS)

    Sorkin, V.; Zhang, Y. W.

    2014-12-01

    Wetting transparency/translucency/opacity of graphene recently has attracted great interest. The underlying mechanisms and physics for simple liquid droplets containing small molecules on graphene coated crystalline substrates have been studied extensively. However, the behavior of more complicated polymeric droplets on graphene coated amorphous substrates has not been explored. In this work, we perform molecular dynamics simulations to examine the wetting of long-chain ZDOL polymeric droplet on graphene coated amorphous hydrogenated diamond-like carbon or DLCH. We find that at room temperature, the droplet adopts a nearly spherical cap shape with no protruding foot on bare DLCH, and a complex multi-layered structure is formed at the droplet-substrate interface. With addition of graphene layers, externally, the height of the droplet decreases and the protruding foot at the droplet edge appears and grows in size; while internally, the complex multi-layered structure near the droplet-substrate interface remains, but the density distribution for the formed layers becomes increasingly non-uniform. A steady state of the droplet is attained when the number of graphene layers reaches three. These changes can be explained by the interactions between the droplet and substrate across the number of graphene layers. Therefore, it is concluded that the graphene monolayer and bilayer are translucent, while trilayer and above are opaque from the wetting point of view.

  6. Amino Acid-Based Stabilization of Oxide Nanocrystals in Polar Media: From Insight in Ligand Exchange to Solution ¹H NMR Probing of Short-Chained Adsorbates.

    PubMed

    De Roo, Jonathan; Coucke, Sofie; Rijckaert, Hannes; De Keukeleere, Katrien; Sinnaeve, Davy; Hens, Zeger; Martins, José C; Van Driessche, Isabel

    2016-03-01

    Ligand exchange is a crucial step between nanocrystal synthesis and nanocrystal application. Although colloidal stability and ligand exchange in nonpolar media are readily established, the exchange of native, hydrophobic ligands with polar ligands is less systematic. In this paper, we present a versatile ligand exchange strategy for the phase transfer of carboxylic acid capped HfO2 and ZrO2 nanocrystals to various polar solvents, based on small amino acids as the incoming ligand. To gain insight in the fundamental mechanism of the exchange, we study this system with a combination of FTIR, zeta potential measurements, and solution (1)H NMR techniques. The detection of surface-associated, small ligands with solution NMR proves challenging in this respect. Tightly bound amino acids are undetectable, but their existence can be proven through displacement with other ligands in titration experiments. Alternatively, we find that methyl moieties belonging to bound species can circumvent these limitations because of their more favorable relaxation properties as a result of internal mobility. As such, our results are not limited to amino acids but to any short-chained ligand and will therefore facilitate the rigorous investigation and understanding of various ligand exchange processes. PMID:26854070

  7. Large and Reversible Plasmon Tuning using Ultrathin Responsive Polymer film

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srikanth; Nergiz, Saide

    2011-03-01

    We demonstrate reversible linear and branched aggregation of gold nanoparticles adsorbed on an ultrathin responsive polymer ((poly(4-vinyl pyridine), P4VP) film. P4VP is a weak cationic polymer, which exhibits a reversible coil to globule transition with change in external pH. Atomic force microscopy revealed that in the coiled state (below the isoelectric point of the polymer) of the polymer chains, gold nanoparticles adsorbed on the polymer layer existed as primarily individual nanoparticles. On the other hand, lowering the pH caused the polymer chains to transition from coil to globule state, resulting in aggregation of the nanoparticles into linear and branched chains. Reversible aggregation of the nanoparticles results in a dramatic change in the optical properties of the metal nanostructures. Apart from the large redistribution of the intensity between the individual (530 nm) and coupled (650 nm) plasmon bands, the coupled plasmon band exhibits a shift of nearly 60 nm with change in external pH. The pH triggered aggregation of the nanoparticles and the dramatic change in the optical properties associated with the same can form an excellent platform for colorimetric sensing. The work reported here is supported by the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine.

  8. Extending framework based on the linear coordination polymers: Alternative chains containing lanthanum ion and acrylic acid ligand

    SciTech Connect

    Li Hui . E-mail: lihui@bit.edu.cn; Guo Ming; Tian Hong; He Feiyue; Lee, G.-H.; Peng, S.-M.

    2006-11-15

    One-dimensional alternative chains of two lanthanum complexes: [La(L{sup 1}){sub 3}(CH{sub 3}OH)(H{sub 2}O){sub 2}].5H{sub 2}O (L{sup 1}=anion of {alpha}-cyano-4-hydroxycinnamic acid ) 1 and [La(L{sup 2}){sub 3}(H{sub 2}O){sub 2}].3H{sub 2}O (L{sup 2}=anion of trans-3-(4-methyl-benzoyl)-acrylic acid) 2 were synthesized and structurally characterized by single-crystal X-ray diffraction, element analysis, IR and thermogravimetric analysis. The crystal structure data are as follows for 1: C{sub 31}H{sub 36}LaN{sub 3}O{sub 17}, triclinic, P-1, a=9.8279(4)A, b=11.8278(5)A, c=17.8730(7)A, {alpha}=72.7960(10){sup o}, {beta}=83.3820(10){sup o}, {gamma}=67.1650(10)-bar , Z=2, R{sub 1}=0.0377, wR{sub 2}=0.0746; for 2: C{sub 33}H{sub 37}LaO{sub 14}, triclinic, P-1, a=8.7174(5)A, b=9.9377(5)A, c=21.153(2)A, {alpha}=81.145(2){sup o}, {beta}=87.591(2){sup o}, {gamma}=67.345(5){sup o}, Z=2, R{sub 1}=0.0869, wR{sub 2}=0.220. 1 is a rare example of the alternative chain constructed by syn-syn and anti-syn coordination mode of carboxylato ligand arranged along the chain alternatively. La(III) ions in 2 are linked by two {eta}{sup 3}-O bridges and four bridges (two {eta}{sup 2}-O and two {eta}{sup 3}-O) alternatively. Both of the linear coordination polymers grow into two- and three-dimensional networks by packing through extending hydrogen-bond network directed by ligands.

  9. In situ x-ray scattering study of a main-chain thermotropic liquid crystalline polymer under oscillatory shear flow

    NASA Astrophysics Data System (ADS)

    Vaish, Nitin; Burghardt, Wesley R.; Zhou, Weijun; Kornfield, Julia A.

    2000-03-01

    Liquid crystalline polymers (LCPs) have been the subject of extensive studies because of potential commercial applications and scientific challenges. The excellent mechanical properties of LCPs arise from highly anisotropic molecular structure, which develops as a complex interplay between molecular dynamics and the applied flow field. We study the behavior of model thermotropic main-chain LCP (DHMS-7,9) under oscillatory shear flow using in situ X-ray scattering techniques. Experiments were done in nematic (140^o C) and x-phase (110^o C) to study the effects of frequency (0.5 - 50 rps) and strain amplitude (50 200In nematic phase, strong alignment in the flow direction (‘parallel’) was observed. The steady state was reached quickly either at high strain amplitudes or high frequencies. In x-phase, molecules aligned in flow direction at high strain levels or oscillation frequency, while alignment in vorticity (‘perpendicular’) direction was observed at low strain amplitude or frequency. In addition, we present the flipping of orientation from parallel to perpendicular alignment as a result of step change in temperature from 140^o C to 110^o C and oscillatory motion from a pre-aligned parallel state in x-phase.

  10. Low half-wave voltage Y-branch electro-optic polymer modulator based on side-chain polyurethane-imide

    NASA Astrophysics Data System (ADS)

    Tang, Jie; Wang, Long-De; Li, Ruo-Zhou; Zhang, Qiang; Zhang, Tong

    2016-06-01

    A Y-branch electro-optic (EO) polymer modulator has been designed and fabricated. High performance side-chain polyurethane-imide (PUI) with a high EO coefficient of larger than 50 pm/V and a moderate glass-transition temperature (Tg) of 206∘C is used as EO polymer core layer of the modulator. The fabricated phase modulator exhibits a low half-wave voltage of 1.94 V at 1550 nm in single arm modulation with 1 cm EO interaction length and 2 cm total length. The results show that the modulator fabricated by side-chain PUI EO materials possesses potential applications in low driving voltage and low cost optical systems.

  11. Liquid film/polymer interfaces

    SciTech Connect

    Allara, David L.

    2003-06-12

    The objectives were: (1) Through experimental studies, advance the fundamental understanding of the principles that govern adsorption and wetting phenomena at polymer and organic surfaces. (2) Establish a firm scientific basis for improving the design of coatings for metal fin cooling surfaces used to control the wetting of water condensate for optimum energy efficiency. Several important findings were: (1) water adsorbed at hydrophobic surfaces has a liquid-like structure, in contrast to the generally held view of an ordered structure; (2) Correlations of large amounts of contact angle wetting data of grafted alkyl chain compounds showed a distinct link between the contact angle and the conformational ordering of the chains; (3) water adsorption at long chain alkysiloxane films showed a strong pH dependence on the film stability, which can be attributed to interfacial chemical effects on the siloxane network.

  12. Unraveling the Nanostructure and Chain Conformation of Peptide-polymer Conjugates in Solution using Small-angle X-ray Scattering

    NASA Astrophysics Data System (ADS)

    Lund, Reidar; Xu, Ting; Dong, He

    For therapeutics, polymer functionalization, often by poly(ethylene glycol), PEG (``PEGylation''), is an effective method to improve the solubility, increase the life time and protect the proteins from the immune system[1]. However it is essential that the proteins maintain their structural integrity in solution- thus the role of the polymer and their interactions with proteins needs to be understood. In this work we show how small-angle X-ray scattering (SAXS) can be used as a powerful technique to characterize the structural components of peptide-polymer conjugates in solution [2, 3]. We specifically show that by applying detailed modelling very detailed structural features can be revealed, including the PEG chain conformation. In the presentation we will provide an overview of the methodology, specifically addressing peptides that form either alpha-helical bundles [2, 3] or beta-sheet structures [4, 5] and relate their structure in solution to their crystal structure.

  13. Exact solution of the thermodynamics and size parameters of a polymer confined to a lattice of finite size: Large chain limit

    NASA Astrophysics Data System (ADS)

    Snyder, Chad R.; Guttman, Charles M.; Di Marzio, Edmund A.

    2014-01-01

    We extend the exact solutions of the Di Marzio-Rubin matrix method for the thermodynamic properties, including chain density, of a linear polymer molecule confined to walk on a lattice of finite size. Our extensions enable (a) the use of higher dimensions (explicit 2D and 3D lattices), (b) lattice boundaries of arbitrary shape, and (c) the flexibility to allow each monomer to have its own energy of attraction for each lattice site. In the case of the large chain limit, we demonstrate how periodic boundary conditions can also be employed to reduce computation time. Advantages to this method include easy definition of chemical and physical structure (or surface roughness) of the lattice and site-specific monomer-specific energetics, and straightforward relatively fast computations. We show the usefulness and ease of implementation of this extension by examining the effect of energy variation along the lattice walls of an infinite rectangular cylinder with the idea of studying the changes in properties caused by chemical inhomogeneities on the surface of the box. Herein, we look particularly at the polymer density profile as a function of temperature in the confined region for very long polymers. One particularly striking result is the shift in the critical condition for adsorption due to surface energy inhomogeneities and the length scale of the inhomogeneities; an observation that could have important implications for polymer chromatography. Our method should have applications to both copolymers and biopolymers of arbitrary molar mass.

  14. Molecular Dynamics Simulation of Ion Solvation in Polymer Melts: Effects of Dielectric Inhomogeneity and Chain Connectivity on Solvation Energy of Ions

    NASA Astrophysics Data System (ADS)

    Liu, Lijun; Nakamura, Issei

    We study the ion solvation in block copolymer melts and polymer blends using molecular dynamics simulations. In our simulations, polymers are formed through the connection of beads that provide the dielectric response. Thus, we highlight the effect of the dielectric contrast between different species on the solvation energy of ions. We demonstrate the local enrichment of higher-dielectric components near ions, which corresponds well with the result of mean-field theories. Moreover, the chain connectivity significantly affects the reorientation of molecular dipoles in response to the electrostatic field from ions. Thus, we illustrate the marked difference in the solvation energy between the block copolymer and polymer blend. Importantly, the solvation energy substantially depends on the chain length of the polymers, in stark contrast to the Born solvation energy. We also show that our simulation results exhibit striking similarity to the result of the recent self-consistent mean field theories. However, for strongly correlated dipoles and ions, our simulations provide qualitatively opposite behaviors to these results, suggesting further development of the theoretical frameworks. This work was supported by the National Natural Science Foundation of China (21474112 and 21404103). We are grateful to the Computing Center of Jilin Province for essential support.

  15. Exact solution of the thermodynamics and size parameters of a polymer confined to a lattice of finite size: Large chain limit

    SciTech Connect

    Snyder, Chad R. Guttman, Charles M.; Di Marzio, Edmund A.

    2014-01-21

    We extend the exact solutions of the Di Marzio-Rubin matrix method for the thermodynamic properties, including chain density, of a linear polymer molecule confined to walk on a lattice of finite size. Our extensions enable (a) the use of higher dimensions (explicit 2D and 3D lattices), (b) lattice boundaries of arbitrary shape, and (c) the flexibility to allow each monomer to have its own energy of attraction for each lattice site. In the case of the large chain limit, we demonstrate how periodic boundary conditions can also be employed to reduce computation time. Advantages to this method include easy definition of chemical and physical structure (or surface roughness) of the lattice and site-specific monomer-specific energetics, and straightforward relatively fast computations. We show the usefulness and ease of implementation of this extension by examining the effect of energy variation along the lattice walls of an infinite rectangular cylinder with the idea of studying the changes in properties caused by chemical inhomogeneities on the surface of the box. Herein, we look particularly at the polymer density profile as a function of temperature in the confined region for very long polymers. One particularly striking result is the shift in the critical condition for adsorption due to surface energy inhomogeneities and the length scale of the inhomogeneities; an observation that could have important implications for polymer chromatography. Our method should have applications to both copolymers and biopolymers of arbitrary molar mass.

  16. Polymer desorption under pulling: A dichotomic phase transition

    NASA Astrophysics Data System (ADS)

    Bhattacharya, S.; Rostiashvili, V. G.; Milchev, A.; Vilgis, T. A.

    2009-03-01

    The structural properties and phase behavior of a self-avoiding polymer chain on an adhesive substrate, subject to pulling at the chain end, are described by means of a grand canonical ensemble approach. We derive analytical expressions for the probability distributions of the basic structural units of an adsorbed polymer, such as loops, trains, and tails, in terms of the adhesive potential γ and applied pulling force f . In contrast to conventional, f=0 , polymer adsorption, the chain detachment transition under pulling turns out to be of first (rather than second) order, albeit it is dichotomic, i.e., no coexistence of different phase states exists. Also, the hitherto controversial value of the critical adsorption exponent ϕ is found to depend essentially on the degree of interaction between different loops so that 0.34⩽ϕ⩽0.59 . The theoretical predictions are verified by means of extensive Monte Carlo simulations.

  17. Polymer desorption under pulling a 1st - order phase transition without phase coexistence

    NASA Astrophysics Data System (ADS)

    Milchev, A.; Rostiashvili, V. G.; Bhattacharya, S.; Vilgis, T. A.

    2010-02-01

    We show that when a self-avoiding polymer chain is pulled off a sticky surface by force applied to the end segment, it undergoes a first-order thermodynamic phase transition albeit without phase coexistence. This unusual feature is demonstrated analytically by means of a Grand Canonical Ensemble (GCE) description of adsorbed macromolecules as well as by Monte Carlo simulations of an off-lattice bead-spring model of a polymer chain. Theoretical treatment and computer experiment can be carried out both in the constant force statistical ensembl whereby at fixed pulling force f one measures the mean height < h > of the chain end above the adsorbing plane, and in the constant-height ensemble where for a given height h one monitors the resulting force < f > applied at the last segment. We find that the force-assisted desorption undergoes a first-order dichotomic phase transition whereby phase coexistence between adsorbed and desorbed states does not exist. In the f-ensemble the order parameter (the fraction of chain contacts with the surface) is characterized by huge fluctuations when the pulling force attains a critical value fD. In the h-ensemble, in contrast, fluctuations are always finite at the critical height hD. The derived analytical expressions for the probability distributions of the basic structural units of an adsorbed polymer, such as loops, trains and tails, in terms of the adhesive potential and f, or h, provide a full description of the polymer structure and behavior upon force-assisted detachment. In addition, one finds that the hitherto controversial value of the universal critical adsorption exponent ϕ depends essentially on the extent of interaction between the loops adsorbed chain so that ϕ may vary within the limits 0.34 ≤ ϕ ≤ 0.59.

  18. Colloidal stability dependence on polymer adsorption through disjoining pressure isotherms.

    PubMed

    Goicochea, A Gama; Nahmad-Achar, E; Pérez, E

    2009-04-01

    The disjoining pressure of polymers confined by colloidal walls was computed using dissipative particle dynamics simulations at constant chemical potential, volume, and temperature. The polymers are able to adsorb on the surfaces according to two models. In the so-called surface-modifying polymers, all monomers composing the chains have the same affinity for the substrate, whereas for the end-grafted polymer only the monomer at one of the ends of the polymer molecule adsorbs on the colloidal surface, resembling the behavior of dispersing agents. We find that these adsorption models yield markedly different disjoining pressure isotherms, which in turn predict different stability conditions for the colloidal dispersion. Our results show that for end-grafted polymers, a larger degree of polymerization at the same monomer concentration leads to better stability than for the surface-modifying ones. But also the unbound monomers of the surface-modifying type dominate over both kinds of polymers at large surface distances. The origin of these differences when the chemical nature of monomers is the same, and molecular weight and polymer concentration are used to characterize colloidal stability, is found to be mainly entropic. PMID:19228014

  19. Monte Carlo study of the percolation in two-dimensional polymer systems.

    PubMed

    Pawłowska, Monika; Sikorski, Andrzej

    2013-10-01

    The structure of a two-dimensional film formed by adsorbed polymer chains was studied by means of Monte Carlo simulations. The polymer chains were represented by linear sequences of lattice beads and positions of these beads were restricted to vertices of a two-dimensional square lattice. Two different Monte Carlo methods were employed to determine the properties of the model system. The first was the random sequential adsorption (RSA) and the second one was based on Monte Carlo simulations with a Verdier-Stockmayer sampling algorithm. The methodology concerning the determination of the percolation thresholds for an infinite chain system was discussed. The influence of the chain length on both thresholds was presented and discussed. It was shown that the RSA method gave considerably lower thresholds for longer chains. This behavior can be explained by a different pool of chain conformations used in the calculations in both methods under consideration. PMID:23765040

  20. Dispersion of carbon nanotubes in organic solvent by commercial polymers with ethylene chains: Experimental and theoretical studies

    NASA Astrophysics Data System (ADS)

    Shigeta, Masahiro; Kamiya, Katsumasa; Uejima, Mitsugu; Okada, Susumu

    2015-03-01

    We demonstrate the possible candidate dispersion agents that can uniformly disperse carbon nanotubes (CNTs) into organic solvent, from among commercially available polymers. We find that CNTs were well dispersed into dimethylacetamide with the use of polystyrene, poly(vinyl chloride), and poly(vinyl pyrrolidone) as dispersion agents. Theoretical calculations revealed that the dispersibility of these polymers arises from the moderate strength and preferential directionality of the interactions between the CNTs and the polymers.

  1. Structure, scattering patterns and phase behavior of polymer nanocomposites with nonspherical fillers

    SciTech Connect

    Hall, Lisa M; Schweizer, Kenneth S

    2010-01-01

    Polymer nanocomposites made with carbon nanotubes, clay platelets, laponite disks and other novel nonspherical fillers have been the focus of many recent experiments. However, the effects of nanoparticle shape on statistical structure, polymer-mediated effective interactions, scattering patterns, and phase diagrams are not well understood. We extend and apply the polymer reference interaction site model liquid state theory to study the equilibrium properties of pseudo one-, two- and threedimensional particles (rod, disk, cube) of modest steric anisotropy and fixed space-filling volume in a dense adsorbing homopolymer melt up to relatively high volume fractions. The second virial coefficient, nanoparticle potential-of-mean force, osmotic compressibilities, and isotropic spinodal demixing boundaries have been determined. The entropic depletion attraction between nanoparticles is dominant for weakly adsorbing polymer, while strongly adsorbing chains induce a bridging attraction. Intermediate interfacial cohesion results in the formation of a steric stabilizing adsorbed polymer layer around each nanoparticle, which can partially damp inter-filler collective order on various length scales and increase order on an averaged length scale. The details of depletion, stabilization, or bridging behavior are shape-dependent and often, but not always, trends are monotonic with increasing filler dimensionality. Distinctive nanoparticle shape-dependent low angle features are predicted for the collective polymer structure factor associated with competing macrophase fluctuations and microphase-like ordering. The influence of nonzero mixture compressibility on the scattering profiles is established.

  2. Influence of Irreversible Adsorption on the Glass Transition Temperature of Polymer Thin Films as Measured by Fluorescence

    NASA Astrophysics Data System (ADS)

    Burroughs, Mary; Priestley, Rodney

    2014-03-01

    Polymers confined to the nanometer length scale have been shown to exhibit deviations in the glass transition temperature (Tg) from the bulk. With the increasing use of confined polymers in nanotechnology, understanding and predicting this behavior is extremely relevant to industries ranging from pharmaceuticals to organic electronics. Recent work (Napolitano, Wübbenhorst, Nature Communications, 2, 260 (2011)) has connected deviations in Tg under confinement with irreversible physical adsorption of polymer chains at substrate interfaces. Here we investigate the influence of irreversibly adsorbed layers on the Tg of polystyrene (PS) thin films supported on silica via fluorescence. We examine the Tg of the brushes as a function of annealing time and irreversibly adsorbed layer thickness. By incorporating fluorescently labeled polymer layers into multilayered films of unlabeled polymer, we will examine the influence of brushes on adjacent layers dynamics. Finally, we will compare the results on PS with those of poly(methyl methacrylate).

  3. Facile Isolation of Adsorbent-Free Long and Highly-Pure Chirality-Selected Semiconducting Single-Walled Carbon Nanotubes Using A Hydrogen-bonding Supramolecular Polymer

    PubMed Central

    Toshimitsu, Fumiyuki; Nakashima, Naotoshi

    2015-01-01

    The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only the chiral- or chemically-purity while sacrificing the sem-SWNT intrinsic structural identities by applying strong ultra-sonication and/or chemical modifications. Toward the ultimate purification of the sem-SWNTs, here we report a mild-conditioned extraction of the sem-SWNTs using removable supramolecular hydrogen-bonding polymers (HBPs) that are composed of dicarboxylic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selective extraction. Replacing conventional strong sonication techniques by a simple shaking using HPBs was found to provide long sem-SWNTs (>2.0 μm) with a very high D/G ratio, which was determined by atomic force microscopy observations. The HBPs were readily removed from the nanotube surfaces by an outer stimulus, such as a change in the solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to propose possible structures for the HBP-wrapped sem-SWNTs, furthermore, the mechanism of the chiral selectivity for the sorted sem-SWNTs is well explained by the relationship between the molecular surface area and mass of the HBP/SWNT composites. PMID:26658356

  4. Facile Isolation of Adsorbent-Free Long and Highly-Pure Chirality-Selected Semiconducting Single-Walled Carbon Nanotubes Using A Hydrogen-bonding Supramolecular Polymer

    NASA Astrophysics Data System (ADS)

    Toshimitsu, Fumiyuki; Nakashima, Naotoshi

    2015-12-01

    The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only the chiral- or chemically-purity while sacrificing the sem-SWNT intrinsic structural identities by applying strong ultra-sonication and/or chemical modifications. Toward the ultimate purification of the sem-SWNTs, here we report a mild-conditioned extraction of the sem-SWNTs using removable supramolecular hydrogen-bonding polymers (HBPs) that are composed of dicarboxylic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selective extraction. Replacing conventional strong sonication techniques by a simple shaking using HPBs was found to provide long sem-SWNTs (>2.0 μm) with a very high D/G ratio, which was determined by atomic force microscopy observations. The HBPs were readily removed from the nanotube surfaces by an outer stimulus, such as a change in the solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to propose possible structures for the HBP-wrapped sem-SWNTs, furthermore, the mechanism of the chiral selectivity for the sorted sem-SWNTs is well explained by the relationship between the molecular surface area and mass of the HBP/SWNT composites.

  5. Facile Isolation of Adsorbent-Free Long and Highly-Pure Chirality-Selected Semiconducting Single-Walled Carbon Nanotubes Using A Hydrogen-bonding Supramolecular Polymer.

    PubMed

    Toshimitsu, Fumiyuki; Nakashima, Naotoshi

    2015-01-01

    The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only the chiral- or chemically-purity while sacrificing the sem-SWNT intrinsic structural identities by applying strong ultra-sonication and/or chemical modifications. Toward the ultimate purification of the sem-SWNTs, here we report a mild-conditioned extraction of the sem-SWNTs using removable supramolecular hydrogen-bonding polymers (HBPs) that are composed of dicarboxylic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selective extraction. Replacing conventional strong sonication techniques by a simple shaking using HPBs was found to provide long sem-SWNTs (>2.0 μm) with a very high D/G ratio, which was determined by atomic force microscopy observations. The HBPs were readily removed from the nanotube surfaces by an outer stimulus, such as a change in the solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to propose possible structures for the HBP-wrapped sem-SWNTs, furthermore, the mechanism of the chiral selectivity for the sorted sem-SWNTs is well explained by the relationship between the molecular surface area and mass of the HBP/SWNT composites. PMID:26658356

  6. Determination of ibuprofen, naproxen and diclofenac in aqueous samples using a multi-template molecularly imprinted polymer as selective adsorbent for solid-phase extraction.

    PubMed

    Madikizela, Lawrence Mzukisi; Chimuka, Luke

    2016-09-01

    This study describes the application of multi-template molecularly imprinted polymer (MIP) as selective sorbent in the solid-phase extraction (SPE) of naproxen, ibuprofen and diclofenac from wastewater and river water. MIP was synthesized at 70°C by employing naproxen, ibuprofen and diclofenac as multi-templates, ethylene glycol dimethacrylate, 2-vinyl pyridine and toluene as cross-linker, functional monomer and porogen, respectively. Wastewater and river water samples (pH 2.5) were percolated through SPE cartridge packed with 50mg of the MIP. The cartridge was washed with 2mL of methanol-water 10:90% (v:v) prior to elution with 2mL of acetic acid-acetonitrile 20:80% (v:v). Quantification of eluted compounds was performed with high performance liquid chromatography equipped with photo diode array detection. The detection limits were 0.15, 1.00 and 0.63μgL(-1) for naproxen, ibuprofen and diclofenac, respectively. Recoveries for naproxen, ibuprofen and diclofenac in deionized water spiked at 5 and 50μgL(-1) were greater than 80%. Ibuprofen was the most frequently detected compound with maximum concentrations of 221, 67.9 and 11.4μgL(-1) in wastewater influent, effluent and river water, respectively. PMID:27268945

  7. Coordination polymer adsorbent for matrix solid-phase dispersion extraction of pesticides during analysis of dehydrated Hyptis pectinata medicinal plant by GC/MS.

    PubMed

    Aquino, Adriano; Wanderley, Kaline A; Paiva-Santos, Carlos de Oliveira; de Sá, Gilberto F; Alexandre, Marcelo da R; Júnior, Severino A; Navickiene, Sandro

    2010-12-15

    The coordination polymer [Zn(BDC)(H(2)O)(2)](n) was tested for extraction of pyrimethanil, ametryn, dichlofluanid, tetraconazole, flumetralin, kresoxim-methyl and tebuconazole from the medicinal plant Hyptis pectinata, with analysis using gas chromatography-mass spectrometry in selected ion monitoring mode (GC/MS, SIM). Experiments carried out at different fortification levels (0.1, 0.5 and 1.0 μg g(-1)) resulted in recoveries in the range 73-97%, and RSD values were between 5 and 12% for the [Zn(BDC)(H(2)O)(2)](n) sorbent. Detection and quantification limits ranged from 0.02 to 0.07 μg g(-1) and from 0.05 to 0.1 μg g(-1), respectively, for the different pesticides studied. The method developed was linear over the range tested (0.04-14.0 μg g(-1)), with correlation coefficients ranging from 0.9987 to 0.9998. Comparison between [Zn(BDC)(H(2)O)(2)](n) and the commercial phase C(18)-bonded silica showed good performance of the [Zn(BDC)(H(2)O)(2)](n) polymeric sorbent for the pesticides tested. PMID:21111184

  8. The Dependence of Strength in Plastics upon Polymer Chain Length and Chain Orientation: An Experiment Emphasizing the Statistical Handling and Evaluation of Data.

    ERIC Educational Resources Information Center

    Spencer, R. Donald

    1984-01-01

    Describes an experiment (using plastic bags) designed to give students practical understanding on using statistics to evaluate data and how statistical treatment of experimental results can enhance their value in solving scientific problems. Students also gain insight into the orientation and structure of polymers by examining the plastic bags.…

  9. Epitaxial crystal growth and solid-state polymerization of piperonyl muconate on the {001} surface of KCl crystal for controlling polymer chain alignment.

    PubMed

    Onodera, Katsuya; Tanioku, Chiaki; Matsumoto, Akikazu

    2012-04-01

    We investigated the crystal growth of piperonyl (E,E)-muconate [bis(3,4-methylenedioxybenzyl) (E,E)-muconate, MDO] on inorganic crystalline substrates during vapor deposition for the control of polymer chain alignment by the subsequent solid-state photopolymerization of the MDO monomer thin films deposited on the substrate. We controlled the arrangement of the MDO molecules and the polymer chains produced on the substrate, depending on the lattice parameters of the substrate surfaces used. The epitaxial crystal growth of MDO on the {001} plane of a KCl single crystal was observed under the condition that the crystal lattice lengths of MDO agreed well with the specific space distance of the substrate; i.e., the KCl cubic crystal resulted in a d(110) value of 4.45 Å, which was very close to the value of the monomer stacking distance in the MDO crystal (d(s) = 4.43 Å). On the other hand, slightly large and too small d(110) values for KBr and NaCl, respectively, resulted in the less controlled and no epitaxial crystal growth of MDO. The irradiation of polarized UV light on the MDO thin-film crystal produced highly regulated polymer alignment in a specific direction on the KCl substrate. PMID:22476888

  10. Escape transition of a polymer chain from a nanotube: how to avoid spurious results by use of the force-biased pruned-enriched Rosenbluth algorithm.

    PubMed

    Hsu, Hsiao-Ping; Binder, Kurt; Klushin, Leonid I; Skvortsov, Alexander M

    2008-10-01

    A polymer chain containing N monomers confined in a finite cylindrical tube of diameter D grafted at a distance L from the open end of the tube may undergo a rather abrupt transition, where part of the chain escapes from the tube to form a "crownlike" coil outside of the tube. When this problem is studied by Monte Carlo simulation of self-avoiding walks on the simple cubic lattice applying a cylindrical confinement and using the standard pruned-enriched Rosenbluth method (PERM), one obtains spurious results, however, with increasing chain length the transition gets weaker and weaker, due to insufficient sampling of the "escaped" states, as a detailed analysis shows. In order to solve this problem, a new variant of a biased sequential sampling algorithm with resampling is proposed, force-biased PERM: the difficulty of sampling both phases in the region of the first order transition with the correct weights is treated by applying a force at the free end pulling it out of the tube. Different strengths of this force need to be used and reweighting techniques are applied. Using rather long chains (up to N=18000 ) and wide tubes (up to D=29 lattice spacings), the free energy of the chain, its end-to-end distance, the number of "imprisoned" monomers can be estimated, as well as the order parameter and its distribution. It is suggested that this algorithm should be useful for other problems involving state changes of polymers, where the different states belong to rather disjunct "valleys" in the phase space of the system. PMID:18999448

  11. Porous silica particles grafted with an amphiphilic side-chain polymer as a stationary phase in reversed-phase high-performance liquid chromatography.

    PubMed

    Shahruzzaman, Md; Takafuji, Makoto; Ihara, Hirotaka

    2015-07-01

    The amphiphilic polymer-grafted silica was newly prepared as a stationary phase in high-performance liquid chromatography. Poly(4-vinylpyridine) with a trimethoxysilyl group at one end was grafted onto porous silica particles and the pyridyl side chains were quaternized with 1-bromooctadecane. The obtained poly(octadecylpyridinium)-grafted silica was characterized by elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy and Brunauer-Emmett-Teller analysis. The degree of quaternization of the pyridyl groups on the obtained stationary phase was estimated to be 70%. The selective retention behaviors of polycyclic aromatic hydrocarbons including some positional isomers were investigated using poly(octadecylpyridinium)-grafted silica as an amphiphilic polymer stationary phase in high-performance liquid chromatography and results were compared with commercially available polymeric octadecylated silica and phenyl-bonded silica columns. The results indicate that the selectivity toward polycyclic aromatic hydrocarbons exhibited by the amphiphilic polymer stationary phase is higher than the corresponding selectivity exhibited by a conventional phenyl-bonded silica column. However, compared with the polymeric octadecylated silica phase, the new stationary phase presents similar retention behavior for polycyclic aromatic hydrocarbons but different retention behavior particularly for positional isomers of disubstituted benzenes as the aggregation structure of amphiphilic polymers on the surface of silica substrate has been altered during mobile phase variation. PMID:25944152

  12. Transient and stationary flow behaviour of side chain liquid-crystalline polymers: Evidence of a shear-induced isotropic-to-nematic phase transition

    NASA Astrophysics Data System (ADS)

    Pujolle-Robic, C.; Olmsted, P. D.; Noirez, L.

    2002-08-01

    This letter describes the non-linear rheology of the isotropic phase of a thermotropic side chain liquid-crystal polymer (SCLCP), from which we infer a flow-induced iso- tropic-to-nematic (IN) phase transition above a critical shear stress and construct non-equilib- rium phase diagrams. In contrast to the well-studied wormlike-micellar solutions and predictions for simple liquid-crystalline systems, the critical stress does not vanish as the equilibrium transition temperature is approached from the above. We postulate that this is due to: i) the coupling between mesogens and the polymer backbone, whose equilibrium oblate nematic backbone conformation contrasts with the prolate non-equilibrium conformation; and ii) the peculiar topological constraints in SCLCP melts, which have been previously postulated as leading to long-lived clusters.

  13. Organometallic Polymers.

    ERIC Educational Resources Information Center

    Carraher, Charles E., Jr.

    1981-01-01

    Reactions utilized to incorporate a metal-containing moiety into a polymer chain (addition, condensation, and coordination) are considered, emphasizing that these reactions also apply to smaller molecules. (JN)

  14. Interactions between charged surfaces mediated by stiff, multivalent zwitterionic polymers.

    PubMed

    Bohinc, Klemen; Reščič, Jurij; Lue, Leo

    2016-05-11

    The interaction between like-charged objects in electrolyte solutions can be heavily altered by the presence of multivalent ions which possess a spatially distributed charge. In this work, we examine the influence of stiff, multivalent zwitterionic polymers on the interaction between charged surfaces using a splitting field theory previously shown to be accurate for the weak to the intermediate to the strong electrostatic coupling regimes. The theory is compared to Monte Carlo simulations and good agreement is found between both approaches. For surface separations shorter than the polymer length, the polymers are mainly oriented parallel to the surfaces, and the surface-surface interaction is repulsive. When the surface separation is comparable to the length of polymers, the polymers have two main orientations. The first corresponds to the polymers adsorbed onto the surface with their centers located near to or in contact with the surface; the second corresponds to polymers which are perpendicular to the charged surfaces, bridging both surfaces and leading to an attractive force between them. Increasing the surface charge density leads to more pronounced attraction via bridging. At surface separations greater than the polymer length, the polymers in the center of the system are still mainly perpendicular to the surfaces, due to "chaining" between zwitterions that enable them to bridge the surfaces at larger separations. This leads to an attractive interaction between the surfaces with a range significantly longer than the length of the polymers. PMID:27087406

  15. The structure of PMDA-PDA polyimide monolayers adsorbed on gold surfaces

    NASA Astrophysics Data System (ADS)

    Keil, M.; Paggel, J. J.; Schedel-Niedrig, Th.; Yokoyama, S.; Sotobayashi, H.; Bradshaw, A. M.

    1995-11-01

    Monolayers of the rod-like PMDA-PDA polyimide adsorbed on flame-annealed polycrystalline gold films have been studied with scanning tunnelling microscopy (STM) and X-ray absorption spectroscopy. The polyimide layer was deposited using the Langmuir-Blodgett preparation technique of Imai and Kakimoto. STM measurements in air showed that the polyimide chains were aligned along the <211> directions of the {111}-oriented single crystal regions of the surface. Although {111}-oriented areas were barely identifiable in the corresponding UHV experiments, aligned polymer chains were also observed over large areas of the surface. X-ray absorption measurements on the latter samples at the nitrogen K-edge showed a preferential orientation of the aromatic ring planes.

  16. Dynamics of various polymer-graphene interfacial systems through atomistic molecular dynamics simulations.

    PubMed

    Rissanou, Anastassia N; Harmandaris, Vagelis

    2014-04-28

    The current work refers to a simulation study on hybrid polymer-graphene interfacial systems. We explore the effect of graphene on the mobility of polymers, by studying three well known and widely used polymers, polyethylene (PE), polystyrene (PS) and poly(methyl-methacrylate) (PMMA). Qualitative and quantitative differences in the dynamical properties of the polymer chains in particular at the polymer-graphene interface are detected. Results concerning both the segmental and the terminal dynamics render PE much faster than the other two polymers; PS follows, while PMMA is the slowest one. Clear spatial dynamic heterogeneity has been observed for all model systems, with different dynamical behavior of the adsorbed polymer segments. The segmental relaxation time of the polymer (τseg) as a function of the distance from graphene shows an abrupt decrease beyond the first adsorption layer for PE, as a result of its well-ordered layered structure close to graphene, though a more gradual decay is observed for PS and PMMA. The distribution of the relaxation times of adsorbed segments was also found to be broader than those of the bulk ones for all three polymer-graphene systems. PMID:24667937

  17. Nonlinear optical studies of liquid crystals and polymers

    NASA Astrophysics Data System (ADS)

    Hong, Seok-Cheol

    Polymers are indispensable in our life. A life is a continuous event maintained by many complex processes in which biological polymers participate. It also gets help from a variety of natural and synthetic polymers with useful functions. Such functions depend on the chemical and conformational structures of polymers and often largely on the surface structures and properties of polymers. We used second order nonlinear optical techniques (sum frequency vibrational spectroscopy (SFVS) and second harmonic generation (SHG)) to obtain structural information on polymers. We also studied liquid crystal molecules deposited on polymer surfaces. The first part of the thesis is aimed at understanding liquid crystal (LC) alignment on rubbed polymer surfaces by determining the molecular orientations of LC adsorbates and surface polymer chains. The alignment of LCs by rubbed polymers is not only of fundamental interest but also of practical importance because it is a technique enabling production of commercial liquid crystal displays. We observed that rubbing induces alignment of surface polymer chains along the rubbing direction, and there is a strong correlation between the molecular orientations of LC adsorbates and the surface chains of rubbed polymers such as polyvinyl alcohol (PVA) and polyimide (6FDA-6CBO). The latter revealed a relatively large but negative pretilt angle, which is highly unusual. On a rubbed polystyrene (PS) surface, we found that the phenyl side groups of PS are oriented perpendicularly to the rubbing direction at the surface, rendering an LC alignment also perpendicular to the rubbing direction. The second part of the thesis is our discovery of rubbing-induced polar ordering on nylon 11 surfaces. Nylon 11 is known to be ferroelectric. We found that mechanical rubbing can induce strong ferroelectric polarization on an initially amorphous film of nylon 11. The surface chains of rubbed nylon 11 are aligned along the rubbing direction while the induced

  18. Adsorption properties of the nanozirconia/anionic polyacrylamide system-Effects of surfactant presence, solution pH and polymer carboxyl groups content

    NASA Astrophysics Data System (ADS)

    Wiśniewska, Małgorzata; Chibowski, Stanisław; Urban, Teresa

    2016-05-01

    The adsorption mechanism of anionic polyacrylamide (PAM) on the nanozirconia surface was examined. The effects of solution pH, carboxyl groups content in macromolecules and anionic surfactant (sodium dodecyl sulfate-SDS) addition were determined. The more probable structure of polymer adsorption layer was characterized based on the data obtained from spectrophotometry, viscosimetry and potentiometric titration methods. The adsorbed amount of polymer, size of macromolecules in the solution and surface charge density of ZrO2 particles in the absence and presence of PAM were assessed, respectively. Analysis of these results indicated that the increase of solution pH and content of carboxyl groups in the polymeric chains lead to more expanded conformations of adsorbing macromolecules. As a result, the adsorption of anionic polyacrylamide decreased. The SDS presence caused the significant increase of PAM adsorbed amount at pH 3, whereas at pH 6 and 9 the surfactant addition resulted in reduction of polymer adsorption level.

  19. Dissipative properties and chain evolution of highly strained nanocomposite hydrogel

    NASA Astrophysics Data System (ADS)

    Tang, Jingda; Xu, Gao; Sun, Youyi; Pei, Yongmao; Fang, Daining

    2014-12-01

    The dissipative property is crucial to the toughness and recovery of hydrogels. In our investigation, systematic uniaxial tension tests were conducted to evaluate the dissipative properties of poly (N-isopropylacrylamide) nanocomposite hydrogels. Two dissipative mechanisms are presented for both small and large stretches. Before yielding, most dissipation results from the orientation of clay platelets along the tensile direction; after yielding, polymer chains peel off from clay platelets to induce hysteresis. For the first time, a quadratic power law between the hysteresis work and the maximum stretch is obtained. The hysteresis work is irrelevant to the detailed loading history. When the hydrogel is unloaded to a critical displacement, polymer chains can re-adsorb to the surfaces of clay platelets. The quantity of re-ruptured physical bonds is proportional to the product of re-adsorption ratio and that of initially ruptured bonds. These results may be useful for the toughening design of hydrogels.

  20. Decades-Scale Degradation of Commercial, Side-Chain, Fluorotelomer-Based Polymers in Soils and Water

    EPA Science Inventory

    Fluorotelomer-based polymers (FTPs) are a primary product of the jluorotelomer industry, yet the role of commercial FTPs in degrading to form perjluorocarboxylic acids (P FCAs), including perjluorooctanoic acid, and P FCA precursors, remains ill-defined. Here we report on a 376-d...

  1. Significant Improvement of Semiconducting Performance of the Diketopyrrolopyrrole-Quaterthiophene Conjugated Polymer through Side-Chain Engineering via Hydrogen-Bonding.

    PubMed

    Yao, Jingjing; Yu, Chenmin; Liu, Zitong; Luo, Hewei; Yang, Yang; Zhang, Guanxin; Zhang, Deqing

    2016-01-13

    Three diketopyrrolopyrrole (DPP)-quaterthiophene conjugated polymers, pDPP4T-1, pDPP4T-2, and pDPP4T-3, in which the molar ratios of the urea-containing alkyl chains vs branching alkyl chains are 1:30, 1:20, and 1:10, respectively, were prepared and investigated. In comparison with pDPP4T without urea groups in the alkyl side chains and pDPP4T-A, pDPP4T-B, and pDPP4T-C containing both linear and branched alkyl chains, thin films of pDPP4T-1, pDPP4T-2, and pDPP4T-3 exhibit higher hole mobilities; thin-film mobility increases in the order pDPP4T-1 < pDPP4T-2 < pDPP4T-3, and hole mobility of a thin film of pDPP4T-3 can reach 13.1 cm(2) V(-1) s(-1) after thermal annealing at just 100 °C. The incorporation of urea groups in the alkyl side chains also has an interesting effect on the photovoltaic performances of DPP-quaterthiophene conjugated polymers after blending with PC71BM. Blended thin films of pDPP4T-1:PC71BM, pDPP4T-2:PC71BM, and pDPP4T-3:PC71BM exhibit higher power conversion efficiencies (PCEs) than pDPP4T:PC71BM, pDPP4T-A:PC71BM, pDPP4T-B:PC71BM, and pDPP4T-C:PC71BM. The PCE of pDPP4T-1:PC71BM reaches 6.8%. Thin films of pDPP4T-1, pDPP4T-2, and pDPP4T-3 and corresponding thin films with PC71BM were characterized with AFM, GIXRD, and STEM. The results reveal that the lamellar packing order of the alkyl chains is obviously enhanced for thin films of pDPP4T-1, pDPP4T-2, and pDPP4T-3; after thermal annealing, slight inter-chain π-π stacking emerges for pDPP4T-2 and pDPP4T-3. Blends of pDPP4T-1, pDPP4T-2, and pDPP4T-3 with PC71BM show a more pronounced micro-phase separation. These observations suggest that the presence of urea groups may further facilitate the assemblies of these conjugated polymers into nanofibers and ordered aggregation of PC71BM. PMID:26669732

  2. Molecular dynamics study of the solution of semiflexible telechelic polymer chains with strongly associating end-groups

    NASA Astrophysics Data System (ADS)

    Khalatur, Pavel G.; Khokhlov, Alexei R.; Kovalenko, Julia N.; Mologin, Dmitrii A.

    1999-03-01

    We present the results of molecular dynamics simulations of micelle organization as well as the formation of micellar aggregates in the solutions of semiflexible telechelic chains with strongly attracting end-groups ("sticker sites"). Using the cluster size distribution function, we study associative equilibrium in the system of flexible and semiflexible chains. It is found that this process corresponds to the so-called "open association" model for micelle formation. The critical temperature of micelle formation Tc is calculated as a function of chain rigidity and system density ρ. We find that the value of Tc increases monotonically with the increase of Kuhn segment length A. Such a behavior takes place in wide range of densities, but only if the value of ρ is somewhat smaller than some threshold value. At high density, we observe the opposite tendency; the temperature Tc decreases monotonically as the value of A is increased. The type of equilibrium microstructures, emerging as a result of micellization in the strong segregation regime, depends essentially on the chain rigidity. In the case of flexible telechelic chains, relatively small flowerlike micellar aggregates are observed. For the system of semiflexible chains, we find rather distinctly appearance of microbundles with pronounced liquid-crystalline-like order. In this case, the spatial organization of the system is characterized by a cellular architecture which looks like "ceramics." Thus, significant morphological changes can be induced by varying of chain rigidity. At fixed system density and Tchain rigidity is increased. In other words, the gradual stretching out of the chains shifts the association equilibrium to formation of larger clusters. We have performed a comparative analysis of our

  3. Coil-bridge transition in a single polymer chain as an unconventional phase transition: Theory and simulation

    NASA Astrophysics Data System (ADS)

    Klushin, Leonid I.; Skvortsov, Alexander M.; Polotsky, Alexey A.; Hsu, Hsiao-Ping; Binder, Kurt

    2014-05-01

    The coil-bridge transition in a self-avoiding lattice chain with one end fixed at height H above the attractive planar surface is investigated by theory and Monte Carlo simulation. We focus on the details of the first-order phase transition between the coil state at large height H ⩾ Htr and a bridge state at H ⩽ Htr, where Htr corresponds to the coil-bridge transition point. The equilibrium properties of the chain were calculated using the Monte Carlo pruned-enriched Rosenbluth method in the moderate adsorption regime at (H/Na)tr ⩽ 0.27 where N is the number of monomer units of linear size a. An analytical theory of the coil-bridge transition for lattice chains with excluded volume interactions is presented in this regime. The theory provides an excellent quantitative description of numerical results at all heights, 10 ⩽ H/a ⩽ 320 and all chain lengths 40 < N < 2560 without free fitting parameters. A simple theory taking into account the effect of finite extensibility of the lattice chain in the strong adsorption regime at (H/Na)tr ⩾ 0.5 is presented. We discuss some unconventional properties of the coil-bridge transition: the absence of phase coexistence, two micro-phases involved in the bridge state, and abnormal behavior in the microcanonical ensemble.

  4. Coil-bridge transition in a single polymer chain as an unconventional phase transition: theory and simulation.

    PubMed

    Klushin, Leonid I; Skvortsov, Alexander M; Polotsky, Alexey A; Hsu, Hsiao-Ping; Binder, Kurt

    2014-05-28

    The coil-bridge transition in a self-avoiding lattice chain with one end fixed at height H above the attractive planar surface is investigated by theory and Monte Carlo simulation. We focus on the details of the first-order phase transition between the coil state at large height H ⩾ Htr and a bridge state at H ⩽ Htr, where Htr corresponds to the coil-bridge transition point. The equilibrium properties of the chain were calculated using the Monte Carlo pruned-enriched Rosenbluth method in the moderate adsorption regime at (H/Na)tr ⩽ 0.27 where N is the number of monomer units of linear size a. An analytical theory of the coil-bridge transition for lattice chains with excluded volume interactions is presented in this regime. The theory provides an excellent quantitative description of numerical results at all heights, 10 ⩽ H/a ⩽ 320 and all chain lengths 40 < N < 2560 without free fitting parameters. A simple theory taking into account the effect of finite extensibility of the lattice chain in the strong adsorption regime at (H/Na)tr ⩾ 0.5 is presented. We discuss some unconventional properties of the coil-bridge transition: the absence of phase coexistence, two micro-phases involved in the bridge state, and abnormal behavior in the microcanonical ensemble. PMID:24880326

  5. Size selective hydrophobic adsorbent for organic molecules

    NASA Technical Reports Server (NTRS)

    Sharma, Pramod K. (Inventor); Hickey, Gregory S. (Inventor)

    1997-01-01

    The present invention relates to an adsorbent formed by the pyrolysis of a hydrophobic silica with a pore size greater than 5 .ANG., such as SILICALITE.TM., with a molecular sieving polymer precursor such as polyfurfuryl alcohol, polyacrylonitrile, polyvinylidene chloride, phenol-formaldehyde resin, polyvinylidene difluoride and mixtures thereof. Polyfurfuryl alcohol is the most preferred. The adsorbent produced by the pyrolysis has a silicon to carbon mole ratio of between about 10:1 and 1:3, and preferably about 2:1 to 1:2, most preferably 1:1. The pyrolysis is performed as a ramped temperature program between about 100.degree. and 800.degree. C., and preferably between about 100.degree. and 600.degree. C. The present invention also relates to a method for selectively adsorbing organic molecules having a molecular size (mean molecular diameter) of between about 3 and 6 .ANG. comprising contacting a vapor containing the small organic molecules to be adsorbed with the adsorbent composition of the present invention.

  6. Molecular Adsorber Coating

    NASA Technical Reports Server (NTRS)

    Straka, Sharon; Peters, Wanda; Hasegawa, Mark; Hedgeland, Randy; Petro, John; Novo-Gradac, Kevin; Wong, Alfred; Triolo, Jack; Miller, Cory

    2011-01-01

    A document discusses a zeolite-based sprayable molecular adsorber coating that has been developed to alleviate the size and weight issues of current ceramic puck-based technology, while providing a configuration that more projects can use to protect against degradation from outgassed materials within a spacecraft, particularly contamination-sensitive instruments. This coating system demonstrates five times the adsorption capacity of previously developed adsorber coating slurries. The molecular adsorber formulation was developed and refined, and a procedure for spray application was developed. Samples were spray-coated and tested for capacity, thermal optical/radiative properties, coating adhesion, and thermal cycling. Work performed during this study indicates that the molecular adsorber formulation can be applied to aluminum, stainless steel, or other metal substrates that can accept silicate-based coatings. The coating can also function as a thermal- control coating. This adsorber will dramatically reduce the mass and volume restrictions, and is less expensive than the currently used molecular adsorber puck design.

  7. Synthesis and Non-Resonant Nonlinear Optical Properties of Push-Pull Side-Chain Azobenzene Polymers

    NASA Astrophysics Data System (ADS)

    Fedus, K.; Smokal, V.; Krupka, O.; Boudebs, G.

    In this work, we report preliminary results obtained for methacrylic polymers incorporating azobenzene side-group as nonlinear optical (NLO) active molecule. The trans-cis isomerization properties are discussed. The third-order non-resonant nonlinear refractive index (n2) and nonlinear absorption coefficient (β) are measured using the Z-scan technique at 1064 nm in the picosecond regime. The influence of different electron-acceptor groups in azobenzene moieties on the nonlinear properties is investigated.

  8. The effects of polymer side-chain structure on roughness formation of ArF photoresist in plasma etching processes

    NASA Astrophysics Data System (ADS)

    Uesugi, Takuji; Okada, Takeru; Wada, Akira; Kato, Keisuke; Yasuda, Atsushi; Maeda, Shinichi; Samukawa, Seiji

    2012-02-01

    Low etching resistance and roughness formation of ArF photoresist during plasma etching are serious problems. We have previously found that decisive factors affecting the plasma resistance and roughness formation in an ArF photoresist are determined by ultraviolet/vacuum ultraviolet radiation and roughness formation is dominated by chemical reactions. In this paper, on the basis of our previous findings on the interaction between radiation species from plasma and ArF photoresist polymers, we investigated the polymer structural dependence for the degradation mechanism of ArF photoresist in the plasma etching processes. The etching resistance of ArF photoresist was improved by controlling the elemental ratio of oxygen atoms and ring structures in photoresist polymer. Furthermore, lactone C=O bond is found to be a key factor for roughness formation during the etching process. We have revealed the importance of the molecular structure of ArF photoresist for improving the surface roughness and etching resistance during the plasma etching process.

  9. Slip and interfacial structure of polymer melts and solutions in contact with end-tethered polymers

    NASA Astrophysics Data System (ADS)

    Gutfreund, Philipp; Korolkovas, Airidas; Liesche, Georg; Dennison, Andrew; Theis-Bröhl, Katharina; Wolff, Max; Akgun, Bulent; Barrat, Jean-Louis

    2014-03-01

    We present a neutron reflectometry (NR) study on polystyrene (PS) sheared in contact with functionalized solid surfaces. These methods provide a non-invasive tool to elucidate the structure of the buried interface with sub-nm resolution. We combine the scattering experiments with in situ surface sensitive rheology to gather information about the microscopic origin of interfacial slip. We have performed in situ shear-NR on PS melts and solutions in contact with chemically grafted PS chains. Entangled polymers can exhibit macroscopic slippage and its origin is supposed to arise from stretching of surface adsorbed chains and subsequent disentanglement from the free flowing chains. The combination of surface sensitive rheometry in a plate-plate torsional shear set-up and NR is potentially a unique technique to address this question by using labeled polymer chains chemically attached to the surface or in the free liquid. We present first results on in situ shear NR on PS melts in contact with high density PS brushes as well as entangled PS solutions flowing over grafted PS chains of the same length of lower density. In both cases we observe a structural change of the grafted PS at a certain shear rate that may be linked tostretching and/or disentanglement of the interfacial chains.

  10. Hydrothermal synthesis, crystal structure and properties of a novel chain coordination polymer constructed by tetrafunctional phosphonate anions and cobalt ions

    SciTech Connect

    Guan, Lei; Wang, Ying

    2015-08-15

    A novel cobalt phosphonate, [Co(HL)(H{sub 2}O){sub 3}]{sub n} (1) (L=N(CH{sub 2}PO{sub 3}H){sub 3}{sup 3−}) has been synthesized by hydrothermal reaction at 150 °C and structurally characterized by X-ray diffraction, infrared spectroscopy, elemental and thermogravimetric analysis. Complex 1 features a 1D chain structure with double-channel built from CoO{sub 6} octahedra bridged together by the phosphonate groups. Each cobalt ion is octahedrally coordinated by three phosphonate oxygen atoms and three water molecules. The coordinated water molecules can form the hydrogen bonds with the phosphonate oxygen atoms to link the 1D chains, building a 2D layered structure, further resulting in a 3D network. The luminescence spectrum indicates an emission maximum at 435 nm. The magnetic susceptibility curve exhibits a dominant antiferromagnetic behavior with a weakly ferromagnetic component at low temperatures. - Graphical abstract: The connectivity between cobalt ions and the ligands results in a chain structure with a 1D double-channel structure, which is constructed by A-type subrings and B-type subrings. - Highlights: • The tetrafunctional phosphonate ligand was used as the ligand. • A novel chain structure can be formed by A-type rings and B-type rings. • Two types of rings can form a 1D double-channel structure, along the c-axis.

  11. Quantitative evaluation of interaction force between functional groups in protein and polymer brush surfaces.

    PubMed

    Sakata, Sho; Inoue, Yuuki; Ishihara, Kazuhiko

    2014-03-18

    To understand interactions between polymer surfaces and different functional groups in proteins, interaction forces were quantitatively evaluated by force-versus-distance curve measurements using atomic force microscopy with a functional-group-functionalized cantilever. Various polymer brush surfaces were systematically prepared by surface-initiated atom transfer radical polymerization as well-defined model surfaces to understand protein adsorption behavior. The polymer brush layers consisted of phosphorylcholine groups (zwitterionic/hydrophilic), trimethylammonium groups (cationic/hydrophilic), sulfonate groups (anionic/hydrophilic), hydroxyl groups (nonionic/hydrophilic), and n-butyl groups (nonionic/hydrophobic) in their side chains. The interaction forces between these polymer brush surfaces and different functional groups (carboxyl groups, amino groups, and methyl groups, which are typical functional groups existing in proteins) were quantitatively evaluated by force-versus-distance curve measurements using atomic force microscopy with a functional-group-functionalized cantilever. Furthermore, the amount of adsorbed protein on the polymer brush surfaces was quantified by surface plasmon resonance using albumin with a negative net charge and lysozyme with a positive net charge under physiological conditions. The amount of proteins adsorbed on the polymer brush surfaces corresponded to the interaction forces generated between the functional groups on the cantilever and the polymer brush surfaces. The weakest interaction force and least amount of protein adsorbed were observed in the case of the polymer brush surface with phosphorylcholine groups in the side chain. On the other hand, positive and negative surfaces generated strong forces against the oppositely charged functional groups. In addition, they showed significant adsorption with albumin and lysozyme, respectively. These results indicated that the interaction force at the functional group level might be

  12. Playing with Polymers.

    ERIC Educational Resources Information Center

    Chemecology, 1997

    1997-01-01

    Presents an activity that enables students to gain a better understanding of the importance of polymers. Students perform an experiment in which polymer chains of polyvinyl acetate form crosslinks. Includes background information and discussion questions. (DDR)

  13. A temperature control method for shortening thermal cycling time to achieve rapid polymerase chain reaction (PCR) in a disposable polymer microfluidic device

    NASA Astrophysics Data System (ADS)

    Bu, Minqiang; Perch-Nielsen, Ivan R.; Sørensen, Karen S.; Skov, Julia; Sun, Yi; Duong Bang, Dang; Pedersen, Michael E.; Hansen, Mikkel F.; Wolff, Anders

    2013-07-01

    We present a temperature control method capable of effectively shortening the thermal cycling time of polymerase chain reaction (PCR) in a disposable polymer microfluidic device with an external heater and a temperature sensor. The method employs optimized temperature overshooting and undershooting steps to achieve a rapid ramping between the temperature steps for DNA denaturation, annealing and extension. The temperature dynamics within the microfluidic PCR chamber was characterized and the overshooting and undershooting parameters were optimized using the temperature-dependent fluorescence signal from Rhodamine B. The method was validated with the PCR amplification of mecA gene (162 bp) from methicillin-resistant Staphylococcus aureus bacterium (MRSA), where the time for 30 cycles was reduced from 50 min (without over- and undershooting) to 20 min.

  14. Influence of the polymer backbone structure on the properties of aromatic ionomers with pendant sulfobenzoyl side chains for use as proton-exchange membranes.

    PubMed

    Jutemar, Elin Persson; Jannasch, Patric

    2010-12-01

    Six different ionomers having various aromatic polymer backbones with pendant 2-sulfobenzoyl side chains were prepared by nucleophilic aromatic substitution reactions of lithium 2,6-difluoro-2'-sulfobenzophenone with 4,4-biphenol, 2,7-dihydroxynaphthalene, 4,4-isopropylidenediphenol, 4,4-dihydroxydiphenyl ether, 4,4'-thiodiphenol, and 4,4'-thiobisbenzenethiol, respectively, to produce four poly(arylene ether)s, one poly(arylene ether sulfide), and one poly(arylene sulfide). Mechanically tough proton-exchange membranes with ion-exchange capacities in the narrow range from 1.9 to 2.3 mequiv/g were cast from the high-molecular-weight ionomers, and subsequently investigated with respect to their structure-property relationships. Glass transitions were only detected for ionomers in the sodium salt form, and increasing glass-transition temperatures (Tg) were found to give higher thermal decomposition temperatures. Analysis by small-angle X-ray scattering indicated that the ionic clustering was promoted for ionomers with flexible polymer backbones and low Tg values. The proton conductivity of the membranes at 80 °C under fully humidified conditions was found between 0.02 and 0.2 S/cm and appeared to depend primarily on the Tg. PMID:21138250

  15. Nanoscale confinement and interfacial effects on the dynamics and glass transition/crystallinity of thin adsorbed films on silica nanoparticles

    NASA Astrophysics Data System (ADS)

    Madathingal, Rajesh Raman

    The research investigated in this dissertation has focused on understanding the structure-property-function relationships of polymer nanocomposites. The properties of composite systems are dictated by the properties of their components, typically fillers in a polymer matrix. In nanocomposites, the polymer near an interface has significantly different properties compared with the bulk polymer, and the contribution of the adsorbed polymer to composite properties becomes increasingly important as the filler size decreases. Despite many reports of highly favorable properties, the behavior of polymer nanocomposites is not generally predictable, and thus requires a better understanding of the interfacial region. The ability to tailor the filler/matrix interaction and an understanding of the impact of the interface on macroscopic properties are keys in the design of nanocomposite properties. In this original work the surface of silica nanoparticles was tailored by: (a) Changing the number of sites for polymer attachment by varying the surface silanols and, (b) By varying the size/curvature of nanoparticles. The effect of surface tailoring on the dynamic properties after the adsorption of two model polymers, amorphous polymethyl methacrylate (PMMA) and semicrystalline polyethylene oxide (PEO) was observed. The interphase layer of polymers adsorbed to silica surfaces is affected by the surface silanol density as well as the relative size of the polymer compared with the size of the adsorbing substrate. The non-equilibrium adsorption of PMMA onto individual colloidal Stober silica (SiO2) particles, where Rparticle (100nm) > RPMMA (˜6.5nm) was compared with the adsorption onto fumed silica, where Rparticle (7nm) ˜ RPMMA (6.5nm) < Raggregate (˜1000nm), both as a function of silanol density [SiOH] and hydrophobility. In the former case, TEM images showed that the PMMA adsorbed onto individual nanoparticles, so that the number of PMMA chains/bead could be calculated, whereas

  16. RADIOLYSIS OF ORGANIC COMPOUNDS IN THE ADSORBED STATE

    DOEpatents

    Sutherland, J.W.; Allen, A.O.

    1961-10-01

    >A method of forming branch chained hydrocarbons by means of energetic penetrating radiation is described. A solid zeolite substrate is admixed with a cobalt ion and is irradiated with a hydrocarbon adsorbed therein. Upon irradiation with gamma rays, there is an increased yield of branched and lower molecular straight chain compounds. (AEC)

  17. Influence of chain length and polymer concentration on the gelation of (amidated) low-methoxyl pectin induced by calcium.

    PubMed

    Capel, François; Nicolai, Taco; Durand, Dominique; Boulenguer, Patrick; Langendorff, Virginie

    2005-01-01

    The gelation of low-methoxyl pectin (LMP) induced by addition of Ca2+ was studied by measuring the storage modulus as a function of temperature during cooling. Samples with different molar masses were prepared by mechanical degradation. The effect of the molar mass and the pectin concentration on the gelation properties was investigated. The effect of partial amidation was studied by comparing LMP and partially amidated LMP with the same molar mass and degree of methylation. The results are compared to those from a model developed for Ca2+-induced pectin gelation, and good agreement is found except at low concentrations and low molar masses where the gels are weaker than predicted. At low concentrations intrachain bonding weakens the gel, while the presence of small pectin chains weakens the gel because it neutralizes binding sites on larger chains. PMID:16283714

  18. A simple strategy to the side chain functionalization on the quinoxaline unit for efficient polymer solar cells.

    PubMed

    Yuan, Jun; Qiu, Lixia; Zhang, Zhiguo; Li, Yongfang; He, Yuehui; Jiang, Lihui; Zou, Yingping

    2016-05-25

    A new tetrafluoridequinoxaline electron accepting block from a quinoxaline core, which is substituted with a fluorine atom onto its backbone and side chains, was designed. A new copolymer (PBDTT-ffQx) was synthesized from tetrafluoridequinoxaline and benzodithiophene. The copolymer was characterized in detail. The photovoltaic properties were well investigated. A high PCE of 8.6% based on the single junction device was obtained. PMID:27025274

  19. Insight from molecular modelling: does the polymer side chain length matter for transport properties of perfluorosulfonic acid membranes?

    SciTech Connect

    Devanathan, Ramaswami; Dupuis, Michel

    2012-08-28

    We present a detailed analysis of the nanostructure of short side chain (SSC) perfluorosulfonic acid membrane and its effect on H{sub 2}O network percolation, H{sub 3}O{sup +} and H{sub 2}O diffusion, and mean residence times of H{sub 3}O{sup +} and H{sub 2}O near SO{sub 3}{sup -} groups based on molecular dynamics simulations. We studied a range of hydration levels ({lambda}) at temperatures of 300 and 360 K, and compare the results to our previous findings in the benchmark Nafion membrane at 300 K. The water channel diameter is about 20% larger in Nafion, while the extent of SO3- clustering is more in SSC membrane. The calculated channel diameter is in excellent agreement with the recently proposed cylindrical water channel model of these membranes. The H{sub 2}O network percolation occurs at comparable hydration levels, and the diffusion coefficients of H{sub 2}O and H{sub 3}O{sup +} are similar in SSC and Nafion membranes. Raising the temperature of the SSC membrane from 300 to 360 K provides a much bigger increase in proton vehicular diffusion coefficient (by a factor of about 4) than changing the side chain length. H3O+ ions are found to exchange more frequently with SO{sub 3}{sup -} partners at the higher temperature. Our key findings are that (a) the hydrophobic-hydrophilic separation in the two membranes is surprisingly similar; (b) at all hydration levels studied, the longer side chain of Nafion is bent and is effectively equivalent to a short side chain in terms of extension into the water domain; and (c) proton transport along the centre of the channel is improbable and vehicular proton transport occurs between SO{sub 3}{sup -} groups. The simulations are validated by good agreement with corresponding experimental values for the simulated membrane density and diffusion coefficients of H{sub 2}O.

  20. From polymers to proteins: the effect of side chains and broken symmetry on the formation of secondary structures within a Wang-Landau approach.

    PubMed

    Škrbić, Tatjana; Badasyan, Artem; Hoang, Trinh Xuan; Podgornik, Rudolf; Giacometti, Achille

    2016-05-25

    We use a micro-canonical Wang-Landau technique to study the equilibrium properties of a single flexible homopolymer where consecutive monomers are represented by impenetrable hard spherical beads tangential to each other, and non-consecutive monomers interact via a square-well potential. To mimic the characteristics of a protein-like system, the model is then refined in two different directions. Firstly, by allowing partial overlap between consecutive beads, we break the spherical symmetry and thus provide a severe constraint on the possible conformations of the chain. Alternatively, we introduce additional spherical beads at specific positions in the direction normal to the backbone, to represent the steric hindrance of the side chains in real proteins. Finally, we consider also a combination of these two ingredients. In all three systems, we obtain the full phase diagram in the temperature-interaction range plane and find the presence of helicoidal structures at low temperatures in the intermediate range of interactions. The effect of the range of the square-well attraction is highlighted, and shown to play a role similar to that found in simple liquids and polymers. Perspectives in terms of protein folding are finally discussed. PMID:27137225

  1. Inter-Ring and Hexyl Chain Torsional Potentials in Poly (3-HEXYLTHIOPHENE) Oligomers: Scaling with the Length of the Conjugted Polymer Backbone

    NASA Astrophysics Data System (ADS)

    Bhatta, Ram S.; Perry, David S.; Yimer, Yeneneh; Tsige, Mesfin

    2011-06-01

    Density functional theory calculations are presented for the equilibrium structures and torsional potentials for isolated Poly (3-Hexylthiophene) (P3HT) oligomers up to 12 monomer units (up to 302 atoms). Calculations were performed at B3LYP/6-31++G(d,p) treating both the backbone of thiophene rings and the hexyl chains explicitly. One-dimensional inter-ring torsional potentials were calculated by rotating backbone around the central inter-ring bond and hexyl torsional potentials were calculated rotating n-hexyl group adjacent to the central inter-ring bond for each oligomer. The torsional and electronic properties change significantly for oligomers with 2 to 8 units but reach asymptotic values for a 10 unit P3HT chain, thereby suggesting the 10 unit long oligomer as a molecular model for the extended polymer. For P3HT oligomers having 10 or more units, all the rings and the hexyl groups are approximately coplanar except for one hexyl group at head end. The principal interaction that promotes the coplanarity of the hexyl groups is the attraction of the proximal methylene hydrogens to the sulfur on the adjacent thiophene ring. The cis conformation of the backbone is about 2kT higher than the trans minimum at room temperature. The gauche conformation of the hexyl group is within about half kT of the planar minimum. Therefore conformational polymorphisms of both types will likely be significant in the heterogeneous environment of photovoltaic devices.

  2. Accessing conjugated polymers with precisely controlled heterobisfunctional chain ends via post-polymerization modification of the OTf group and controlled Pd(0)/t-Bu3P-catalyzed Suzuki cross-coupling polymerization

    SciTech Connect

    Hu, Qiao -Sheng; Hong, Kunlun; Zhang, Hong -Hai

    2015-08-12

    In this study, a general strategy toward the synthesis of well-defined conjugated polymers with controlled heterobisfunctional chain ends via combination of controlled Pd(0)/t-Bu3P Suzuki cross-coupling polymerization with the post-polymerization modification of the triflate (OTf) group was disclosed.

  3. Accessing conjugated polymers with precisely controlled heterobisfunctional chain ends via post-polymerization modification of the OTf group and controlled Pd(0)/t-Bu3P-catalyzed Suzuki cross-coupling polymerization

    DOE PAGESBeta

    Hu, Qiao -Sheng; Hong, Kunlun; Zhang, Hong -Hai

    2015-08-12

    In this study, a general strategy toward the synthesis of well-defined conjugated polymers with controlled heterobisfunctional chain ends via combination of controlled Pd(0)/t-Bu3P Suzuki cross-coupling polymerization with the post-polymerization modification of the triflate (OTf) group was disclosed.

  4. Regenerative adsorbent heat pump

    NASA Technical Reports Server (NTRS)

    Jones, Jack A. (Inventor)

    1991-01-01

    A regenerative adsorbent heat pump process and system is provided which can regenerate a high percentage of the sensible heat of the system and at least a portion of the heat of adsorption. A series of at least four compressors containing an adsorbent is provided. A large amount of heat is transferred from compressor to compressor so that heat is regenerated. The process and system are useful for air conditioning rooms, providing room heat in the winter or for hot water heating throughout the year, and, in general, for pumping heat from a lower temperature to a higher temperature.

  5. In-situ ultrasonic compatibilization of binary blends of flexible chain polyesters and aromatic liquid crystalline polymers

    NASA Astrophysics Data System (ADS)

    Gunes, Kaan

    The objective of this research was to improve the properties of immiscible polymer blends by developing a new ultrasonic extrusion process. The ability of ultrasonic treatment to induce recombination reactions in polymer blends was anticipated to result in fast in-situ compatibilization of immiscible blends. In order to test this hypothesis, a new ultrasonic extruder operating at a frequency of 20 kHz at amplitudes of 5, 7.5, and 10 mum was developed. Polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and wholly aromatic liquid crystalline copolyesters (LCPs) were selected to illustrate the effect of ultrasonic treatment on copolymerization of components through transesterification reactions in blends. The LCPs studied were a copolymer of hydroxybenzoic and hydroxynaphthoic acid (LCP1) and a copolymer of dioxydiphenyl, terephthalic and isophthalic acid (LCP2). PET/PEN, PET/LCP1, PEN/LCP1, and LCP1/LCP2 blends and their components were subsequently injection molded and spun into fibers. PET underwent homopolymerization and degradation, respectively, at ultrasonic amplitudes of 7.5 mum and 10 mum, while PEN underwent degradation at all amplitudes. MALDI-TOF mass spectroscopy revealed greater amounts of hydroxyl and carboxyl terminated oligomers in ultrasonically treated PET and PEN. Transesterification (copolymer formation) was observed in PET/PEN blends, which was enhanced with ultrasonic treatment, as indicated by 1H NMR and MALDI-TOF. Oxygen permeability of compression molded films of untreated and ultrasonically treated PET/PEN blends followed theoretical predictions for miscible blends. Ultrasonic treatment of LCP1 at amplitudes of 7.5 and 10 mum led to improved mechanical properties of its injection moldings. On the other hand, LCP2 underwent degradation with treatment, leading to a reduction of mechanical properties of LCP2 and LCP1/LCP2 blends. However, due to enhanced fibrillation, these blends retained synergism such that moldings exhibited

  6. Adsorbent and adsorbent bed for materials capture and separation processes

    SciTech Connect

    Liu, Wei

    2011-01-25

    A method device and material for performing adsorption wherein a fluid mixture is passed through a channel in a structured adsorbent bed having a solid adsorbent comprised of adsorbent particles having a general diameter less than 100 um, loaded in a porous support matrix defining at least one straight flow channel. The adsorbent bed is configured to allow passage of a fluid through said channel and diffusion of a target material into said adsorbent under a pressure gradient driving force. The targeted molecular species in the fluid mixture diffuses across the porous support retaining layer, contacts the adsorbent, and adsorbs on the adsorbent, while the remaining species in the fluid mixture flows out of the channel.

  7. Polymer composites containing nanotubes

    NASA Technical Reports Server (NTRS)

    Bley, Richard A. (Inventor)

    2008-01-01

    The present invention relates to polymer composite materials containing carbon nanotubes, particularly to those containing singled-walled nanotubes. The invention provides a polymer composite comprising one or more base polymers, one or more functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers and carbon nanotubes. The invention also relates to functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers, particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having side chain functionalization, and more particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having olefin side chains and alkyl epoxy side chains. The invention further relates to methods of making polymer composites comprising carbon nanotubes.

  8. Modeling the Assembly of Polymer-Grafted Nanoparticles at Oil-Water Interfaces.

    PubMed

    Yong, Xin

    2015-10-27

    Using dissipative particle dynamics (DPD), I model the interfacial adsorption and self-assembly of polymer-grafted nanoparticles at a planar oil-water interface. The amphiphilic core-shell nanoparticles irreversibly adsorb to the interface and create a monolayer covering the interface. The polymer chains of the adsorbed nanoparticles are significantly deformed by surface tension to conform to the interface. I quantitatively characterize the properties of the particle-laden interface and the structure of the monolayer in detail at different surface coverages. I observe that the monolayer of particles grafted with long polymer chains undergoes an intriguing liquid-crystalline-amorphous phase transition in which the relationship between the monolayer structure and the surface tension/pressure of the interface is elucidated. Moreover, my results indicate that the amorphous state at high surface coverage is induced by the anisotropic distribution of the randomly grafted chains on each particle core, which leads to noncircular in-plane morphology formed under excluded volume effects. These studies provide a fundamental understanding of the interfacial behavior of polymer-grafted nanoparticles for achieving complete control of the adsorption and subsequent self-assembly. PMID:26439456

  9. Electrospun regenerated cellulose nanofibrous membranes surface-grafted with polymer chains/brushes via the atom transfer radical polymerization method for catalase immobilization.

    PubMed

    Feng, Quan; Hou, Dayin; Zhao, Yong; Xu, Tao; Menkhaus, Todd J; Fong, Hao

    2014-12-10

    In this study, an electrospun regenerated cellulose (RC) nanofibrous membrane with fiber diameters of ∼200-400 nm was prepared first; subsequently, 2-hydroxyethyl methacrylate (HEMA), 2-dimethylaminoethyl methacrylate (DMAEMA), and acrylic acid (AA) were selected as the monomers for surface grafting of polymer chains/brushes via the atom transfer radical polymerization (ATRP) method. Thereafter, four nanofibrous membranes (i.e., RC, RC-poly(HEMA), RC-poly(DMAEMA), and RC-poly(AA)) were explored as innovative supports for immobilization of an enzyme of bovine liver catalase (CAT). The amount/capacity, activity, stability, and reusability of immobilized catalase were evaluated, and the kinetic parameters (Vmax and Km) for immobilized and free catalase were determined. The results indicated that the respective amounts/capacities of immobilized catalase on RC-poly(HEMA) and RC-poly(DMAEMA) nanofibrous membranes reached 78 ± 3.5 and 67 ± 2.7 mg g(-1), which were considerably higher than the previously reported values. Meanwhile, compared to that of free CAT (i.e., 18 days), the half-life periods of RC-CAT, RC-poly(HEMA)-CAT, RC-poly(DMAEMA)-CAT, and RC-poly(AA)-CAT were 49, 58, 56, and 60 days, respectively, indicating that the storage stability of immobilized catalase was also significantly improved. Furthermore, the immobilized catalase exhibited substantially higher resistance to temperature variation (tested from 5 to 70 °C) and lower degree of sensitivity to pH value (tested from 4.0 and 10.0) than the free catalase. In particular, according to the kinetic parameters of Vmax and Km, the nanofibrous membranes of RC-poly(HEMA) (i.e., 5102 μmol mg(-1) min(-1) and 44.89 mM) and RC-poly(DMAEMA) (i.e., 4651 μmol mg(-1) min(-1) and 46.98 mM) had the most satisfactory biocompatibility with immobilized catalase. It was therefore concluded that the electrospun RC nanofibrous membranes surface-grafted with 3-dimensional nanolayers of polymer chains/brushes would be

  10. Existence of global weak solutions to compressible isentropic finitely extensible nonlinear bead-spring chain models for dilute polymers: The two-dimensional case

    NASA Astrophysics Data System (ADS)

    Barrett, John W.; Süli, Endre

    2016-07-01

    We prove the existence of global-in-time weak solutions to a general class of models that arise from the kinetic theory of dilute solutions of nonhomogeneous polymeric liquids, where the polymer molecules are idealized as bead-spring chains with finitely extensible nonlinear elastic (FENE) type spring potentials. The class of models under consideration involves the unsteady, compressible, isentropic, isothermal Navier-Stokes system in a bounded domain Ω in Rd, d = 2, for the density ρ, the velocity u ˜ and the pressure p of the fluid, with an equation of state of the form p (ρ) =cpργ, where cp is a positive constant and γ > 1. The right-hand side of the Navier-Stokes momentum equation includes an elastic extra-stress tensor, which is the classical Kramers expression. The elastic extra-stress tensor stems from the random movement of the polymer chains and is defined through the associated probability density function that satisfies a Fokker-Planck-type parabolic equation, a crucial feature of which is the presence of a centre-of-mass diffusion term. This extends the result in our paper J.W. Barrett and E. Süli (2016) [9], which established the existence of global-in-time weak solutions to the system for d ∈ { 2 , 3 } and γ >3/2, but the elastic extra-stress tensor required there the addition of a quadratic interaction term to the classical Kramers expression to complete the compactness argument on which the proof was based. We show here that in the case of d = 2 and γ > 1 the existence of global-in-time weak solutions can be proved in the absence of the quadratic interaction term. Our results require no structural assumptions on the drag term in the Fokker-Planck equation; in particular, the drag term need not be corotational. With a nonnegative initial density ρ0 ∈L∞ (Ω) for the continuity equation; a square-integrable initial velocity datum u˜0 for the Navier-Stokes momentum equation; and a nonnegative initial probability density function ψ0

  11. Star Polymers.

    PubMed

    Ren, Jing M; McKenzie, Thomas G; Fu, Qiang; Wong, Edgar H H; Xu, Jiangtao; An, Zesheng; Shanmugam, Sivaprakash; Davis, Thomas P; Boyer, Cyrille; Qiao, Greg G

    2016-06-22

    Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings. PMID:27299693

  12. Synthesis of 4-vinylpyridine-divinylbenzene copolymer adsorbents for microwave-assisted desorption of benzene.

    PubMed

    Meng, Qing Bo; Yang, Go-Su; Lee, Youn-Sik

    2012-02-29

    Reports on the development of polymer adsorbents for microwave-assisted desorption of nonpolar volatile organic compounds (VOCs) are rare. In this study, we synthesized macroporous polymeric adsorbents with hydrophilic methyl pyridinium units for microwave-assisted desorption of nonpolar VOCs. The benzene adsorption and desorption properties of the adsorbents were investigated under both dry and humid conditions. Under humid conditions, as the content of the hydrophilic methyl pyridinium units in the adsorbents increased from 0 to 20%, the adsorption capacity of benzene decreased from about 21 to 7 mg/g, while the desorption efficiency of benzene increased significantly from 48 to 87%. The maximum concentration of desorbate also increased significantly as the content of the hydrophilic units was increased under humid conditions. We attributed the enhanced desorption efficiency mainly to more adsorbed moisture, which indirectly allowed heating of the polymer adsorbents to higher temperatures upon irradiation with 600 W microwaves. PMID:22236950

  13. Well-defined oxide core-polymer shell nanoparticles: interfacial interactions, peculiar dynamics, and transitions in polymer nanolayers.

    PubMed

    Bershtein, V A; Gun'ko, V M; Egorova, L M; Guzenko, N V; Pakhlov, E M; Ryzhov, V A; Zarko, V I

    2010-07-01

    Interfacial interactions, chain dynamics, and glass and melting transitions were studied in well-defined core-shell nanoparticles with amorphous silica or crystalline alumina cores and noncrystallizable poly(vinyl pyrrolidone) (PVP) or crystallizable poly(ethylene glycol) (PEG) shells. Varying particle composition caused regular changes in the shell thickness from 1 to 2 nm (monomolecular layer) up to 90 nm. Far- and mid-IR spectroscopy allowed us to register hydrogen bonding and, tentatively, Lewis/Brønsted (LB) interfacial interactions as well as changes in the dynamics and conformational state of the polymer chains as a function of the nanoshell thickness. Their most pronounced peculiarities were found for the monomolecular polymer layers. The LB interactions were stronger with the alumina substrate than silica. DSC analysis was performed, and the data obtained were in agreement with the spectroscopic data. Unlike the bulk polymer, the PVP monolayer was characterized with an extraordinarily large dynamic heterogeneity within the glass transition while broadening the transition range and varying the activation energy by an order of magnitude. The PEG monolayer adsorbed on silica was totally amorphous, whereas a highly crystalline one with the anomalously thin lamellae, down to 3 nm thick, was adsorbed on an alumina surface, presumably as a result of the quasi-heteroepitaxial crystallization process. PMID:20415443

  14. Analysis of Adsorbate-Adsorbate and Adsorbate-Adsorbent Interactions to Decode Isosteric Heats of Gas Adsorption.

    PubMed

    Madani, S Hadi; Sedghi, Saeid; Biggs, Mark J; Pendleton, Phillip

    2015-12-21

    A qualitative interpretation is proposed to interpret isosteric heats of adsorption by considering contributions from three general classes of interaction energy: fluid-fluid heat, fluid-solid heat, and fluid-high-energy site (HES) heat. Multiple temperature adsorption isotherms are defined for nitrogen, T=(75, 77, 79) K, argon at T=(85, 87, 89) K, and for water and methanol at T=(278, 288, 298) K on a well-characterized polymer-based, activated carbon. Nitrogen and argon are subjected to isosteric heat analyses; their zero filling isosteric heats of adsorption are consistent with slit-pore, adsorption energy enhancement modelling. Water adsorbs entirely via specific interactions, offering decreasing isosteric heat at low pore filling followed by a constant heat slightly in excess of water condensation enthalpy, demonstrating the effects of micropores. Methanol offers both specific adsorption via the alcohol group and non-specific interactions via its methyl group; the isosteric heat increases at low pore filling, indicating the predominance of non-specific interactions. PMID:26538339

  15. Selective adsorption and efficient regeneration via smart adsorbents possessing thermo-controlled molecular switches.

    PubMed

    Jiang, Yao; Tan, Peng; Cheng, Lei; Shan, Shu-Feng; Liu, Xiao-Qin; Sun, Lin-Bing

    2016-04-21

    Adsorption and desorption are equally important in an adsorptive separation process, while conventional adsorbents with fixed pores benefit only one of them rather than both. Here, a new generation of adsorbents was fabricated by incorporating thermo-responsive polymers (TRPs) into pores. The TRPs act as molecular switches, making pore spaces and active sites responsive to adsorption/desorption conditions. The adsorbents can thus realize both selective adsorption and efficient desorption, which are extremely desirable for adsorptive separation. PMID:26883022

  16. Self-assembly of silver(I) coordination polymers from aminopyrimidyl derivatives and malonate acid: From 1D chain to 2D layer

    NASA Astrophysics Data System (ADS)

    Sun, Di; Zhang, Na; Xu, Qin-Juan; Luo, Geng-Geng; Huang, Rong-Bin; Zheng, Lan-Sun

    2010-04-01

    Two new silver(I) coordination polymers (CPs) of the formula [Ag 2(dmapym) 4(mal)·H 2O] n ( 1) and [Ag 3(apym) 3(mal)NO 3] n ( 2) (dmapym = 2-amino-4,6-dimethylprimidine, apym = 2-aminopyrimidine, H 2mal = malonate) have been synthesized by reactions of AgNO 3 and 2-aminopyrimidyl ligands with malonate under the ammoniacal condition. Both complexes have been characterized by element analysis, IR and single-crystal X-ray diffraction. The monodentate dmapym and tridentate mal ligands link Ag(I) ions to give complex 1 a one-dimensional (1D) H-shaped chain structure. The complex 2 is a two-dimensional (2D) double sheet struc