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Sample records for semiflexible polymer networks

  1. Modeling semiflexible polymer networks

    NASA Astrophysics Data System (ADS)

    Broedersz, C. P.; MacKintosh, F. C.

    2014-07-01

    This is an overview of theoretical approaches to semiflexible polymers and their networks. Such semiflexible polymers have large bending rigidities that can compete with the entropic tendency of a chain to crumple up into a random coil. Many studies on semiflexible polymers and their assemblies have been motivated by their importance in biology. Indeed, cross-linked networks of semiflexible polymers form a major structural component of tissue and living cells. Reconstituted networks of such biopolymers have emerged as a new class of biological soft matter systems with remarkable material properties, which have spurred many of the theoretical developments discussed here. Starting from the mechanics and dynamics of individual semiflexible polymers, the physics of semiflexible bundles, entangled solutions, and disordered cross-linked networks are reviewed. Finally, recent developments on marginally stable fibrous networks, which exhibit critical behavior similar to other marginal systems such as jammed soft matter, are discussed.

  2. Viscoelasticity of reversibly crosslinked networks of semiflexible polymers.

    PubMed

    Plagge, Jan; Fischer, Andreas; Heussinger, Claus

    2016-06-01

    We present a theoretical framework for the linear and nonlinear viscoelastic properties of reversibly crosslinked networks of semiflexible polymers. In contrast to affine models where network strain couples to the polymer end-to-end distance, in our model strain rather serves to locally distort the network structure. This induces bending modes in the polymer filaments, the properties of which are slaved to the surrounding network structure. Specifically, we investigate the frequency-dependent linear rheology, in particular in combination with crosslink binding-unbinding processes. We also develop schematic extensions to describe the nonlinear response during creep measurements as well as during constant strain-rate ramps. PMID:27415312

  3. Viscoelasticity of reversibly crosslinked networks of semiflexible polymers

    NASA Astrophysics Data System (ADS)

    Plagge, Jan; Fischer, Andreas; Heussinger, Claus

    2016-06-01

    We present a theoretical framework for the linear and nonlinear viscoelastic properties of reversibly crosslinked networks of semiflexible polymers. In contrast to affine models where network strain couples to the polymer end-to-end distance, in our model strain rather serves to locally distort the network structure. This induces bending modes in the polymer filaments, the properties of which are slaved to the surrounding network structure. Specifically, we investigate the frequency-dependent linear rheology, in particular in combination with crosslink binding-unbinding processes. We also develop schematic extensions to describe the nonlinear response during creep measurements as well as during constant strain-rate ramps.

  4. Nonaffine behavior of three-dimensional semiflexible polymer networks

    NASA Astrophysics Data System (ADS)

    Hatami-Marbini, Hamed

    2016-04-01

    Three-dimensional semiflexible polymer networks are the structural building blocks of various biological and structural materials. Previous studies have primarily used two-dimensional models for understanding the behavior of these networks. In this paper, we develop a three-dimensional nonaffinity measure capable of providing direct comparison with continuum level homogenized quantities, i.e., strain field. The proposed nonaffinity measure is capable of capturing possible anisotropic microstructures of the filamentous networks. This strain-based nonaffinity measure is used to probe the mechanical behavior at different length scales and investigate the effects of network mechanical and microstructural properties. Specifically, it is found that although all nonaffinity measure components have a power-law variation with the probing length scale, the degree of nonaffinity decreases with increasing the length scale of observation. Furthermore, the amount of nonaffinity is a function of network fiber density, bending stiffness of the constituent filaments, and the network architecture. Finally, it is found that the two power-law scaling regimes previously reported for two-dimensional systems do not appear in three-dimensional networks. Also, unlike two-dimensional models, the exponent of the power-law relation depends weakly on the density of the three-dimensional networks.

  5. Discontinuous bundling transition in semiflexible polymer networks induced by Casimir interactions

    NASA Astrophysics Data System (ADS)

    Kachan, Devin; Müller, Kei W.; Wall, Wolfgang A.; Levine, Alex J.

    2016-09-01

    Fluctuation-induced interactions are an important organizing principle in a variety of soft matter systems. We investigate the role of fluctuation-based or thermal Casimir interactions between cross linkers in a semiflexible network. One finds that, by integrating out the polymer degrees of freedom, there is an attractive logarithmic potential between nearest-neighbor cross linkers in a bundle, with a significantly weaker next-nearest-neighbor interaction. Here we show that a one-dimensional gas of these strongly interacting linkers in equilibrium with a source of unbound ones admits a discontinuous phase transition between a sparsely and a densely bound bundle. This discontinuous transition induced by the long-ranged nature of the Casimir interaction allows for a similarly abrupt structural transition in semiflexible filament networks between a low cross linker density isotropic phase and a higher cross link density bundle network. We support these calculations with the results of finite element Brownian dynamics simulations of semiflexible filaments and transient cross linkers.

  6. Curvature-induced crosshatched order in two-dimensional semiflexible polymer networks

    NASA Astrophysics Data System (ADS)

    Vrusch, Cyril; Storm, Cornelis

    2015-12-01

    A recurring motif in the organization of biological tissues are networks of long, fibrillar protein strands effectively confined to cylindrical surfaces. Often, the fibers in such curved, quasi-two-dimensional (2D) geometries adopt a characteristic order: the fibers wrap around the central axis at an angle which varies with radius and, in several cases, is strongly bimodally distributed. In this Rapid Communication, we investigate the general problem of a 2D crosslinked network of semiflexible fibers confined to a cylindrical substrate, and demonstrate that in such systems the trade-off between bending and stretching energies, very generically, gives rise to crosshatched order. We discuss its general dependency on the radius of the confining cylinder, and present an intuitive model that illustrates the basic physical principle of curvature-induced order. Our findings shed new light on the potential origin of some curiously universal fiber orientational distributions in tissue biology, and suggests novel ways in which synthetic polymeric soft materials may be instructed or programmed to exhibit preselected macromolecular ordering.

  7. Cylindrical confinement of semiflexible polymers

    NASA Astrophysics Data System (ADS)

    Vázquez-Montejo, Pablo; McDargh, Zachary; Deserno, Markus; Guven, Jemal

    2015-06-01

    Equilibrium states of a closed semiflexible polymer binding to a cylinder are described. This may be either by confinement or by constriction. Closed completely bound states are labeled by two integers: the number of oscillations, n , and the number of times it winds the cylinder, p , the latter being a topological invariant. We examine the behavior of these states as the length of the loop is increased by evaluating the energy, the conserved axial torque, and the contact force. The ground state for a given p is the state with n =1 ; a short loop with p =1 is an elliptic deformation of a parallel circle; as its length increases it elongates along the cylinder axis with two hairpin ends. Excited states with n ≥2 and p =1 possess n -fold axial symmetry. Short (long) loops possess energies ≈p E0 (n E0 ), with E0 the energy of a circular loop with same radius as the cylinder; in long loops the axial torque vanishes. Confined bound excited states are initially unstable; however, above a critical length each n -fold state becomes stable: The folded hairpin cannot be unfolded. The ground state for each p is also initially unstable with respect to deformations rotating the loop off the surface into the interior. A closed planar elastic curve aligned along the cylinder axis making contact with the cylinder on its two sides is identified as the ground state of a confined loop. Exterior bound states behave very differently, if free to unbind, as signaled by the reversal in the sign of the contact force. If p =1 , all such states are unstable. If p ≥2 , however, a topological obstruction to complete unbinding exists. If the loop is short, the bound state with p =2 and n =1 provides a stable constriction of the cylinder, partially unbinding as the length is increased. This motif could be relevant to an understanding of the process of membrane fission mediated by dynamin rings.

  8. Free energy of twisted semiflexible polymers

    NASA Astrophysics Data System (ADS)

    Sinha, Supurna

    2008-06-01

    We investigate the role of fluctuations in single-molecule measurements of torque-link (t-lk) curves. For semiflexible polymers of finite persistence length (i.e., polymers with contour length L comparable to the persistence length LP ), the torque versus link curve in the constant-torque (isotorque) ensemble is distinct from the one in the constant-link (isolink) ensemble. Thus, one encounters the conceptually interesting issue of a “free energy of transition” in switching ensembles while making torque-link measurements. We predict the dependence on the semiflexibility parameter β=L/LP of this extra contribution to the free energy, which shows up as an area in the torque-link plane. This can be tested against future torque-link experiments with single biopolymers. We bring out the inequivalence of torque-link curves for a stiff polymer and present explicit analytical expressions for the distinct torque-link relations in the two ensembles and the free-energy difference in switching ensembles in this context. The predictions of our work can be tested against single-molecule experiments on torsionally constrained biopolymers.

  9. Cluster Glasses of Semiflexible Ring Polymers

    PubMed Central

    2014-01-01

    We present computer simulations of concentrated solutions of unknotted nonconcatenated semiflexible ring polymers. Unlike in their flexible counterparts, shrinking involves a strong energetic penalty, favoring interpenetration and clustering of the rings. We investigate the slow dynamics of the centers-of-mass of the rings in the amorphous cluster phase, consisting of disordered columns of oblate rings penetrated by bundles of prolate ones. Scattering functions reveal a striking decoupling of self- and collective motions. Correlations between centers-of-mass exhibit slow relaxation, as expected for an incipient glass transition, indicating the dynamic arrest of the cluster positions. However, self-correlations decay at much shorter time scales. This feature is a manifestation of the fast, continuous exchange and diffusion of the individual rings over the matrix of clusters. Our results reveal a novel scenario of glass formation in a simple monodisperse system, characterized by self-collective decoupling, soft caging, and mild dynamic heterogeneity. PMID:25083314

  10. End-monomer Dynamics in Semiflexible Polymers

    PubMed Central

    Hinczewski, Michael; Schlagberger, Xaver; Rubinstein, Michael; Krichevsky, Oleg; Netz, Roland R.

    2009-01-01

    Spurred by an experimental controversy in the literature, we investigate the end-monomer dynamics of semiflexible polymers through Brownian hydrodynamic simulations and dynamic mean-field theory. Precise experimental observations over the last few years of end-monomer dynamics in the diffusion of double-stranded DNA have given conflicting results: one study indicated an unexpected Rouse-like scaling of the mean squared displacement (MSD) 〈r2(t)〉 ~ t1/2 at intermediate times, corresponding to fluctuations at length scales larger than the persistence length but smaller than the coil size; another study claimed the more conventional Zimm scaling 〈r2(t)〉 ~ t2/3 in the same time range. Using hydrodynamic simulations, analytical and scaling theories, we find a novel intermediate dynamical regime where the effective local exponent of the end-monomer MSD, α(t) = d log〈r2(t)〉/d log t, drops below the Zimm value of 2/3 for sufficiently long chains. The deviation from the Zimm prediction increases with chain length, though it does not reach the Rouse limit of 1/2. The qualitative features of this intermediate regime, found in simulations and in an improved mean-field theory for semiflexible polymers, in particular the variation of α(t) with chain and persistence lengths, can be reproduced through a heuristic scaling argument. Anomalously low values of the effective exponent α are explained by hydrodynamic effects related to the slow crossover from dynamics on length scales smaller than the persistence length to dynamics on larger length scales. PMID:21359118

  11. Phase behavior of semiflexible polymer systems

    NASA Astrophysics Data System (ADS)

    Moonay, David Jordan

    Phase behavior of semiflexible poly(n-hexyl isocyanate) (PHIC) and flexible coil poly(cyclohexyl methacrylate) (PCHMA) were investigated. Room-temperature solubility screenings showed that PCHMA behavior in various solvents agreed with that predicted by Flory-Huggins theory: solvents had interaction parameter values chi1 < 0.5, i.e., less than the critical value for incipient phase separation, while nonsolvents had chi1 > 1, well within the thermodynamically-poor solvency region. PHIC, on the other hand, had interactions which were not in accord with the simple enthalpic theory. A high-boiling solvent, 1-chloronaphthalene, was chosen as suitable for binary and ternary phase behavior work, as a result of the screenings. PCHMA was found to be soluble at all concentrations at room temperature. However, PHIC crystallized at about 5 wt.% a result not previously reported in the literature. The crystallinity, and degradation, interfered with liquid crystalline expression up to the PHIC melting point in binary solution. The novel room-temperature ternary phase diagram, PHIC/PCHMA/CLN, was developed. Particularly striking is its 5 wt.% total polymer solubility limit, which extended to 90:1 (w/w) ratios of PCHMA:PI-HC in CLN, as verified by serial dilution experiments. Novel gels were prepared with PHIC longer-pendant-group homologs poly(n-nonylisocyanate) and poly(n-undecylisocyanate), to investigate their heightened solubility relative to PHIC, in high-boiling alkylaromatic solvents. Apparently homogeneous isotropic gels in two structurally similar solvents, were found. Lengthening pendant groups in the alkyl isocyanate polymers increases solubility in high-boiling solvents, although gelation occurs when the solutions are cooled to room temperature. Elongational flow apparati were constructed. Trumpet-shaped tube experiments indicated no flow-induced crystallinity of isotropic PHIC/CLN solutions. A planar-elongational flow system was constructed and tested, and its central

  12. Self-organization in suspensions of end-functionalized semiflexible polymers under shear flow.

    PubMed

    Myung, Jin Suk; Winkler, Roland G; Gompper, Gerhard

    2015-12-28

    The nonequilibrium dynamical behavior and structure formation of end-functionalized semiflexible polymer suspensions under flow are investigated by mesoscale hydrodynamic simulations. The hybrid simulation approach combines the multiparticle collision dynamics method for the fluid, which accounts for hydrodynamic interactions, with molecular dynamics simulations for the semiflexible polymers. In equilibrium, various kinds of scaffold-like network structures are observed, depending on polymer flexibility and end-attraction strength. We investigate the flow behavior of the polymer networks under shear and analyze their nonequilibrium structural and rheological properties. The scaffold structure breaks up and densified aggregates are formed at low shear rates, while the structural integrity is completely lost at high shear rates. We provide a detailed analysis of the shear- rate-dependent flow-induced structures. The studies provide a deeper understanding of the formation and deformation of network structures in complex materials.

  13. Self-organization in suspensions of end-functionalized semiflexible polymers under shear flow

    NASA Astrophysics Data System (ADS)

    Myung, Jin Suk; Winkler, Roland G.; Gompper, Gerhard

    2015-12-01

    The nonequilibrium dynamical behavior and structure formation of end-functionalized semiflexible polymer suspensions under flow are investigated by mesoscale hydrodynamic simulations. The hybrid simulation approach combines the multiparticle collision dynamics method for the fluid, which accounts for hydrodynamic interactions, with molecular dynamics simulations for the semiflexible polymers. In equilibrium, various kinds of scaffold-like network structures are observed, depending on polymer flexibility and end-attraction strength. We investigate the flow behavior of the polymer networks under shear and analyze their nonequilibrium structural and rheological properties. The scaffold structure breaks up and densified aggregates are formed at low shear rates, while the structural integrity is completely lost at high shear rates. We provide a detailed analysis of the shear- rate-dependent flow-induced structures. The studies provide a deeper understanding of the formation and deformation of network structures in complex materials.

  14. Nonlinear elasticity of semiflexible filament networks.

    PubMed

    Meng, Fanlong; Terentjev, Eugene M

    2016-08-10

    We develop a continuum theory for equilibrium elasticity of a network of crosslinked semiflexible filaments, spanning the full range between flexible entropy-driven chains to stiff athermal rods. We choose the 3-chain constitutive model of network elasticity over several plausible candidates, and derive analytical expressions for the elastic energy at arbitrary strain, with the corresponding stress-strain relationship. The theory fits well to a wide range of experimental data on simple shear in different filament networks, quantitatively matching the differential shear modulus variation with stress, with only two adjustable parameters (which represent the filament stiffness and the pre-tension in the network, respectively). The general theory accurately describes the crossover between the positive and negative Poynting effect (normal stress on imposed shear) on increasing the stiffness of filaments forming the network. We discuss the network stability (the point of marginal rigidity) and the phenomenon of tensegrity, showing that filament pre-tension on crosslinking into the network determines the magnitude of linear modulus G0. PMID:27444846

  15. Nonlinear elasticity of semiflexible filament networks.

    PubMed

    Meng, Fanlong; Terentjev, Eugene M

    2016-08-10

    We develop a continuum theory for equilibrium elasticity of a network of crosslinked semiflexible filaments, spanning the full range between flexible entropy-driven chains to stiff athermal rods. We choose the 3-chain constitutive model of network elasticity over several plausible candidates, and derive analytical expressions for the elastic energy at arbitrary strain, with the corresponding stress-strain relationship. The theory fits well to a wide range of experimental data on simple shear in different filament networks, quantitatively matching the differential shear modulus variation with stress, with only two adjustable parameters (which represent the filament stiffness and the pre-tension in the network, respectively). The general theory accurately describes the crossover between the positive and negative Poynting effect (normal stress on imposed shear) on increasing the stiffness of filaments forming the network. We discuss the network stability (the point of marginal rigidity) and the phenomenon of tensegrity, showing that filament pre-tension on crosslinking into the network determines the magnitude of linear modulus G0.

  16. Distinct Tensile Response of Model Semi-flexible Elastomer Networks

    NASA Astrophysics Data System (ADS)

    Aguilera-Mercado, Bernardo M.; Cohen, Claude; Escobedo, Fernando A.

    2011-03-01

    Through coarse-grained molecular modeling, we study how the elastic response strongly depends upon nanostructural heterogeneities in model networks made of semi-flexible chains exhibiting both regular and realistic connectivity. Idealized regular polymer networks have been shown to display a peculiar elastic response similar to that of super-tough natural materials (e.g., organic adhesives inside abalone shells). We investigate the impact of chain stiffness, and the effect of including tri-block copolymer chains, on the network's topology and elastic response. We find in some systems a dual tensile response: a liquid-like behavior at small deformations, and a distinct saw-tooth shaped stress-strain curve at moderate to large deformations. Additionally, stiffer regular networks exhibit a marked hysteresis over loading-unloading cycles that can be deleted by heating-cooling cycles or by performing deformations along different axes. Furthermore, small variations of chain stiffness may entirely change the nature of the network's tensile response from an entropic to an enthalpic elastic regime, and micro-phase separation of different blocks within elastomer networks may significantly enhance their mechanical strength. This work was supported by the American Chemical Society.

  17. Semiflexible polymer dynamics with a bead-spring model

    NASA Astrophysics Data System (ADS)

    Barkema, Gerard T.; Panja, Debabrata; van Leeuwen, J. M. J.

    2014-11-01

    We study the dynamical properties of semiflexible polymers with a recently introduced bead-spring model. We focus on double-stranded DNA (dsDNA). The two parameters of the model, T* and ν, are chosen to match its experimental force-extension curve. In comparison to its groundstate value, the bead-spring Hamiltonian is approximated in the first order by the Hessian that is quadratic in the bead positions. The eigenmodes of the Hessian provide the longitudinal (stretching) and transverse (bending) eigenmodes of the polymer, and the corresponding eigenvalues match well with the established phenomenology of semiflexible polymers. At the Hessian approximation of the Hamiltonian, the polymer dynamics is linear. Using the longitudinal and transverse eigenmodes, for the linearized problem, we obtain analytical expressions of (i) the autocorrelation function of the end-to-end vector, (ii) the autocorrelation function of a bond (i.e. a spring, or a tangent) vector at the middle of the chain, and (iii) the mean-square displacement of a tagged bead in the middle of the chain, as the sum over the contributions from the modes—the so-called ‘mode sums’. We also perform simulations with the full dynamics of the model. The simulations yield numerical values of the correlations functions (i-iii) that agree very well with the analytical expressions for the linearized dynamics. This does not however mean that the nonlinearities are not present. In fact, we also study the mean-square displacement of the longitudinal component of the end-to-end vector that showcases strong nonlinear effects in the polymer dynamics, and we identify at least an effective t7/8 power-law regime in its time-dependence. Nevertheless, in comparison to the full mean-square displacement of the end-to-end vector the nonlinear effects remain small at all times—it is in this sense we state that our results demonstrate that the linearized dynamics suffices for dsDNA fragments that are shorter than or

  18. Ordered structures of small numbers of nanorods induced by semiflexible star polymers.

    PubMed

    Zhang, Dong; He, Lilin; Zhang, Linxi

    2014-09-14

    The ordered structures of nanorods (NRs) in the semiflexible star polymer/NR mixtures are explored by employing molecular dynamics simulation. The structures of small numbers of NRs can be well controlled by varying the stiffness of semiflexible star polymers. At a moderate binding energy between star polymers and NRs, four completely different structures of small numbers of NRs are observed, including that the side-to-side hexagonal aggregation structures of NRs for flexible star polymers, the partly parallel aggregation structures of NRs and the end-to-end contact parallel aggregation structures of NRs for semiflexible star polymers, and the partial dispersion of NRs for rigid star polymers. Helical conformations of semiflexible star polymers binding with NRs are responsible for the formation of the end-to-end contact parallel aggregation structures for small numbers of NRs. This investigation may provide a possible pathway to develop ''smart'' medium to construct novel materials with high performance.

  19. Dynamics of a semiflexible polymer or polymer ring in shear flow.

    PubMed

    Lang, Philipp S; Obermayer, Benedikt; Frey, Erwin

    2014-02-01

    Polymers exposed to shear flow exhibit a remarkably rich tumbling dynamics. While rigid rods rotate on Jeffery orbits, a flexible polymer stretches and coils up during tumbling. Theoretical results show that in both of these asymptotic regimes the corresponding tumbling frequency f(c) in a linear shear flow of strength γ scales as a power law Wi(2/3) in the Weissenberg number Wi = γτ, where τ is a characteristic time of the polymer's relaxational dynamics. For a flexible polymer these theoretical results are well confirmed by a large body of experimental single molecule studies. However, for the intermediate semiflexible regime, especially relevant for cytoskeletal filaments like F-actin and microtubules, the situation is less clear. While recent experiments on single F-actin filaments are still interpreted within the classical Wi(2/3) scaling law, theoretical results indicated deviations from it. Here we perform extensive Brownian dynamics simulations to explore the tumbling dynamics of semiflexible polymers over a broad range of shear strength and the polymer's persistence length l(p). We find that the Weissenberg number alone does not suffice to fully characterize the tumbling dynamics, and the classical scaling law breaks down. Instead, both the polymer's stiffness and the shear rate are relevant control parameters. Based on our Brownian dynamics simulations we postulate that in the parameter range most relevant for cytoskeletal filaments there is a distinct scaling behavior with f(c) τ* = Wi(3/4)f(c)(x) with Wi = γτ* and the scaling variable x = (l(p)/L)(Wi)(-1/3); here τ* is the time the polymer's center of mass requires to diffuse its own contour length L. Comparing these results with experimental data on F-actin we find that the Wi(3/4) scaling law agrees quantitatively significantly better with the data than the classical Wi(2/3) law. Finally, we extend our results to single ring polymers in shear flow, and find similar results as for linear

  20. Dynamics of a semiflexible polymer or polymer ring in shear flow

    NASA Astrophysics Data System (ADS)

    Lang, Philipp S.; Obermayer, Benedikt; Frey, Erwin

    2014-02-01

    Polymers exposed to shear flow exhibit a remarkably rich tumbling dynamics. While rigid rods rotate on Jeffery orbits, a flexible polymer stretches and coils up during tumbling. Theoretical results show that in both of these asymptotic regimes the corresponding tumbling frequency fc in a linear shear flow of strength γ scales as a power law Wi2/3 in the Weissenberg number Wi=γτ, where τ is a characteristic time of the polymer's relaxational dynamics. For a flexible polymer these theoretical results are well confirmed by a large body of experimental single molecule studies. However, for the intermediate semiflexible regime, especially relevant for cytoskeletal filaments like F-actin and microtubules, the situation is less clear. While recent experiments on single F-actin filaments are still interpreted within the classical Wi2/3 scaling law, theoretical results indicated deviations from it. Here we perform extensive Brownian dynamics simulations to explore the tumbling dynamics of semiflexible polymers over a broad range of shear strength and the polymer's persistence length lp. We find that the Weissenberg number alone does not suffice to fully characterize the tumbling dynamics, and the classical scaling law breaks down. Instead, both the polymer's stiffness and the shear rate are relevant control parameters. Based on our Brownian dynamics simulations we postulate that in the parameter range most relevant for cytoskeletal filaments there is a distinct scaling behavior with fcτ*=Wi3/4f ̂c(x) with Wi =γτ* and the scaling variable x =(lp/L)(Wi)-1/3; here τ* is the time the polymer's center of mass requires to diffuse its own contour length L. Comparing these results with experimental data on F-actin we find that the Wi3/4 scaling law agrees quantitatively significantly better with the data than the classical Wi2/3 law. Finally, we extend our results to single ring polymers in shear flow, and find similar results as for linear polymers with slightly different

  1. Equilibrium properties of DNA and other semiflexible polymers confined in nanochannels

    NASA Astrophysics Data System (ADS)

    Muralidhar, Abhiram

    Recent developments in next-generation sequencing (NGS) techniques have opened the door for low-cost, high-throughput sequencing of genomes. However, these developments have also exposed the inability of NGS to track large scale genomic information, which are extremely important to understand the relationship between genotype and phenotype. Genome mapping offers a reliable way to obtain information about large-scale structural variations in a given genome. A promising variant of genome mapping involves confining single DNA molecules in nanochannels whose cross-sectional dimensions are approximately 50 nm. Despite the development and commercialization of nanochannel-based genome mapping technology, the polymer physics of DNA in confinement is only beginning to be understood. Apart from its biological relevance, DNA is also used as a model polymer in experiments by polymer physicists. Indeed, the seminal experiments by Reisner et al. (2005) of DNA confined in nanochannels of different widths revealed discrepancies with the classical theories of Odijk and de Gennes for polymer confinement. Picking up from the conclusions of the dissertation of Tree (2014), this dissertation addresses a number of key outstanding problems in the area of nanoconfined DNA. Adopting a Monte Carlo chain growth technique known as the pruned-enriched Rosenbluth method, we examine the equilibrium and near-equilibrium properties of DNA and other semiflexible polymers in nanochannel confinement. We begin by analyzing the dependence of molecular weight on various thermodynamic properties of confined semiflexible polymers. This allows us to point out the finite size effects that can occur when using low molecular weight DNA in experiments. We then analyze the statistics of backfolding and hairpin formation in the context of existing theories and discuss how our results can be used to engineer better conditions for genome mapping. Finally, we elucidate the diffusion behavior of confined

  2. Stiffness dependence of critical exponents of semiflexible polymer chains situated on two-dimensional compact fractals.

    PubMed

    Zivić, Ivan; Elezović-Hadzić, Suncica; Milosević, Sava

    2009-12-01

    We present an exact and Monte Carlo renormalization group (MCRG) study of semiflexible polymer chains on an infinite family of the plane-filling (PF) fractals. The fractals are compact, that is, their fractal dimension df is equal to 2 for all members of the fractal family enumerated by the odd integer b(3polymer chain) and gamma (associated with the total number of different polymer chains). In addition, we calculate nu and gamma through the MCRG approach for b up to 201. Our results show that for each particular b, critical exponents are stiffness dependent functions, in such a way that the stiffer polymer chains (with smaller values of s) display enlarged values of nu, and diminished values of gamma. On the other hand, for any specific s, the critical exponent nu monotonically decreases, whereas the critical exponent gamma monotonically increases, with the scaling parameter b. We reflect on a possible relevance of the criticality of semiflexible polymer chains on the PF family of fractals to the same problem on the regular Euclidean lattices.

  3. Effect of Conformation in Charge Transport for Semiflexible Polymers

    NASA Astrophysics Data System (ADS)

    Noriega, Rodrigo; Salleo, Alberto; Spakowitz, Andrew

    2014-03-01

    Current models for the electronic properties of semiconducting conjugated polymers do not include the hierarchical connectivity between charge transport units that results from the physical makeup of the materials. Concepts like on-chain vs. interchain mobility anisotropy have been known for a long time, yet they must be artificially incorporated into simulations. Models that achieve remarkable predictive power but provide limited physical insight when applied to this new class of materials are of limited use for the rational design of new conjugated polymers. Here we present a new model in which the morphology of individual polymer chains is determined by well-known statistical models and the electronic coupling between units is described using Marcus theory. Combining knowledge from polymer physics and semiconducting materials into an analytical and computational model that realistically incorporates the structural and electronic properties of conjugated polymers, it is possible to explain observations that previously relied on phenomenological models. The multi-scale behavior of charges in these materials (high mobility at short scales, low mobility at long scales) can be naturally described with our framework.

  4. From Semi-Flexible Polymers to Membranes: Anomalous Diffusion and Reptation

    NASA Astrophysics Data System (ADS)

    Granek, R.

    1997-12-01

    The dynamics of semi-flexible polymers and membranes is discussed. The effect of thermal undulations on both the transversal and longitudinal Mean Square Displacement (MSD) of a tagged “monomer” is studied in free polymers and membranes. The two MSDs are found to be proportional to one another, and behave as sim t^{3/4} for polymers and sim t^{2/3} for membranes on the short time scale. The longitudinal motion is shown to be linked to the dynamics of fluctuations of the projected length (area) of the polymer (membrane). We demonstrate how, at long times, these fluctuations lead to reptation motion of the polymer (membrane) in the longitudinal direction. We generalize this approach to investigate the motion of a membrane between two plates and a polymer in a tube. The latter problem is used as a model for polymer motion in semi-dilute solutions in which the persistence length is longer than the entanglement length. Such systems are not suitable for the classical reptation model of de-Gennes and of Doi and Edwards, which was designed for chains that are flexible on the entanglement distance. The reptation diffusion coefficient and relaxation times that we obtain have the same scaling with chain length L as in the classical reptation model, but differ greatly in factors that are dependent on the ratio of persistence length to entanglement length. We also discuss the diffusion of a tagged “monomer” under imposed tension and liquid crystalline order.

  5. 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.

  6. 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

  7. Entropic forces exerted on a rough wall by a grafted semiflexible polymer.

    PubMed

    Bayati, Parvin; Ghassab, Leila; Najafi, Ali

    2014-10-01

    We study the entropic force due to a fluctuating semiflexible polymer that is grafted from one end and confined by a rigid and rough wall from the other end. We show how roughness of the wall modifies the entropic force. In addition to the perpendicular force that is present in the case of a flat wall, roughness of the wall adds a lateral component to the force. Both perpendicular and lateral components of the force are examined for different values of amplitude and wavelength of the roughness and at different temperatures. The lateral force is controlled by the local slope of the wall while the perpendicular force is only sensitive to the curvature of the wall. We show that for small compression, the entropic force is increased by increasing the curvature of the confining wall. In addition to the biophysical relevance, the results may also be useful in developing an AFM-based experimental technique for probing the roughness of surfaces. PMID:25315449

  8. Brushes of semiflexible polymers in equilibrium and under flow in a super-hydrophobic regime.

    PubMed

    Speyer, K; Pastorino, C

    2015-07-21

    We performed molecular dynamics simulations to study the equilibrium and flow properties of a liquid in a nano-channel with confining surfaces coated with a layer of grafted semiflexible polymers. The coverage spans a wide range of grafting densities from essentially isolated chains to dense brushes. The end-grafted polymers were described by a bead spring model with a harmonic potential to include the bond stiffness of the chains. We varied the rigidity of the chains, from fully flexible polymers to rigid rods, in which the configurational entropy of the chains is negligible. The brush-liquid interaction was tuned to obtain a super-hydrophobic channel, in which the liquid did not penetrate the polymer brush, giving rise to a Cassie-Baxter state. Equilibrium properties such as brush height and bending energy were measured, varying the grafting density and the stiffness of the polymers. We also studied the characteristics of the brush-liquid interface and the morphology of the polymer chains supporting the liquid for different bending rigidities. Non-equilibrium simulations were performed, moving the walls of the channel in opposite directions at constant speed, obtaining a Couette velocity profile in the bulk liquid. The molecular degrees of freedom of the polymers were studied as a function of the Weissenberg number. Also, the violation of the no-slip boundary condition and the slip properties were analyzed as a function of the shear rate, grafting density and bending stiffness. At high grafting densities, a finite slip length independent of the shear rate or bending constant was found, while at low grafting densities a very interesting non-monotonic dependence on the bending constant is observed.

  9. Cooperative buckling and the nonlinear mechanics of nematic semiflexible networks

    NASA Astrophysics Data System (ADS)

    Foucard, L. C.; Price, J. K.; Klug, W. S.; Levine, A. J.

    2015-09-01

    We review the nonlinear mechanics of cross-linked networks of stiff filaments with a quenched anisotropic (nematic) alignment. A combination of numerical simulations and analytic calculations shows that the broken rotational symmetry of the filament orientational distribution leads to a dramatic nonlinear softening of the network at very small strain (on the order of 0.1%). We argue that one can understand this softening in terms of Euler buckling, i.e. the loss of further load-carrying capacity in compression within the network. With increasing shear strain, this source of geometric nonlinearity appears as heterogeneous nucleation (originating in particularly fragile regions, which may be identified by a linear stability analysis) and subsequently grows into ‘buckling scars’ that eventually spread throughout the system. We develop a simple mean-field model for the nonlinear mechanics of such networks and suggest applications of these ideas to a variety of fiber networks and biopolymer systems.

  10. Anisotropic effective interactions and stack formation in mixtures of semiflexible ring polymers.

    PubMed

    Poier, Peter; Bačová, Petra; Moreno, Angel J; Likos, Christos N; Blaak, Ronald

    2016-05-25

    By means of extensive computer simulations, we investigate the formation of columnar structures (stacks) in concentrated solutions of semiflexible ring polymers. To characterize the stacks we employ an algorithm that identifies tube-like structures in the simulation cell. Stacks are found both in the real system and in the fluid of soft disks interacting through the effective anisotropic pair potential derived for the rings [P. Poier et al., Macromolecules, 2015, 48, 4983-4997]. Furthermore, we investigate binary mixtures of cluster-forming and non-cluster-forming rings. We find that monodispersity is not a requirement for stack formation. The latter is found for a broad range of mixture compositions, though the columns in the mixtures exhibit important differences to those observed in the monodisperse case. We extend the anisotropic effective model to mixtures. We show that it correctly predicts stack formation and constitutes a significant improvement with respect to the usual isotropic effective description based only on macromolecular centers-of-mass.

  11. Universal Crossover Dynamics of a Semi-Flexible Polymer in Two Dimensions

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Aniket; Huang, Aiqun; Adhikari, Ramesh; Binder, Kurt

    2014-03-01

    We present a unified scaling theory for the dynamics of monomers for dilute solutions of semiflexible polymers under good solvent conditions in the free draining limit. Our theory encompasses the well-known regime of mean square displacements (MSDs) of stiff chains growing like t 3 / 4 with time (R. Granek, J. Phys. II (Paris) 7, 1767 (1997); E. Farge and A. C. Maggs, Macromolecules 26, 5041 (1993)) due to bending motions, and the Rouse regime t 2 ν /(1 + 2 ν) where ν is the Flory exponent describing the radius R of a swollen flexible coil. We identify how the prefactors of these laws scale with the persistence length lp, and show that a crossover from stiff to flexible behavior occurs at a MSD of order lp2 (at a time proportional to lp3), a second crossover (to diffusive motion) occurs when the MSD is of order R2. We also provide compelling evidence for the theory by carrying out large scale Molecular Dynamics simulations in d = 2 dimensions. Partially supported by UCF Office of Research and Commercialization & College of Science SEED grant.

  12. Mesoscale simulation of semiflexible chains. II. Evolution dynamics and stability of fiber bundle networks.

    PubMed

    Groot, Robert D

    2013-06-14

    Network formation of associative semiflexible fibers and mixtures of fibers and colloidal particles is simulated for the Johnson-Kendall-Roberts model of elastic contacts, and a phase diagram in terms of particle elasticity and surface energy is presented. When fibers self-assemble, they form a network for sufficiently large fiber-solvent surface energy. If the surface energy is above the value where single particles crystallize, the adhesion forces drive diffusion-limited aggregation. Two mechanisms contribute to coarsening: non-associated chains joining existing bundles, and fiber bundles merging. Coarsening stops when the length of the network connections is roughly the persistence length, independent of surface energy. If the surface energy is below the value where single particles crystallize, a network can still be formed but at a much slower (reaction limited) rate. Loose (liquid-like) assemblies between chains form when they happen to run more-or-less parallel. These assemblies grow by diffusion and aggregation and form a loose network, which sets in micro-phase separation, i.e., syneresis. Only when the clusters crystallize, the coarsening process stops. In this case, the length of the network connections is larger than the persistence length of a single chain, and depends on the value of the surface energy. All networks of semiflexible homopolymers in this study show syneresis. Mixtures of fibers and colloid particles also form fiber bundle networks, but by choosing the colloid volume fraction sufficiently low, swelling gels are obtained. Applications of this model are in biological systems where fibers self-assemble into cell walls and bone tissue.

  13. Mesoscale simulation of semiflexible chains. II. Evolution dynamics and stability of fiber bundle networks.

    PubMed

    Groot, Robert D

    2013-06-14

    Network formation of associative semiflexible fibers and mixtures of fibers and colloidal particles is simulated for the Johnson-Kendall-Roberts model of elastic contacts, and a phase diagram in terms of particle elasticity and surface energy is presented. When fibers self-assemble, they form a network for sufficiently large fiber-solvent surface energy. If the surface energy is above the value where single particles crystallize, the adhesion forces drive diffusion-limited aggregation. Two mechanisms contribute to coarsening: non-associated chains joining existing bundles, and fiber bundles merging. Coarsening stops when the length of the network connections is roughly the persistence length, independent of surface energy. If the surface energy is below the value where single particles crystallize, a network can still be formed but at a much slower (reaction limited) rate. Loose (liquid-like) assemblies between chains form when they happen to run more-or-less parallel. These assemblies grow by diffusion and aggregation and form a loose network, which sets in micro-phase separation, i.e., syneresis. Only when the clusters crystallize, the coarsening process stops. In this case, the length of the network connections is larger than the persistence length of a single chain, and depends on the value of the surface energy. All networks of semiflexible homopolymers in this study show syneresis. Mixtures of fibers and colloid particles also form fiber bundle networks, but by choosing the colloid volume fraction sufficiently low, swelling gels are obtained. Applications of this model are in biological systems where fibers self-assemble into cell walls and bone tissue. PMID:23781818

  14. Mesoscale simulation of semiflexible chains. II. Evolution dynamics and stability of fiber bundle networks

    NASA Astrophysics Data System (ADS)

    Groot, Robert D.

    2013-06-01

    Network formation of associative semiflexible fibers and mixtures of fibers and colloidal particles is simulated for the Johnson-Kendall-Roberts model of elastic contacts, and a phase diagram in terms of particle elasticity and surface energy is presented. When fibers self-assemble, they form a network for sufficiently large fiber-solvent surface energy. If the surface energy is above the value where single particles crystallize, the adhesion forces drive diffusion-limited aggregation. Two mechanisms contribute to coarsening: non-associated chains joining existing bundles, and fiber bundles merging. Coarsening stops when the length of the network connections is roughly the persistence length, independent of surface energy. If the surface energy is below the value where single particles crystallize, a network can still be formed but at a much slower (reaction limited) rate. Loose (liquid-like) assemblies between chains form when they happen to run more-or-less parallel. These assemblies grow by diffusion and aggregation and form a loose network, which sets in micro-phase separation, i.e., syneresis. Only when the clusters crystallize, the coarsening process stops. In this case, the length of the network connections is larger than the persistence length of a single chain, and depends on the value of the surface energy. All networks of semiflexible homopolymers in this study show syneresis. Mixtures of fibers and colloid particles also form fiber bundle networks, but by choosing the colloid volume fraction sufficiently low, swelling gels are obtained. Applications of this model are in biological systems where fibers self-assemble into cell walls and bone tissue.

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

    NASA Astrophysics Data System (ADS)

    Hsu, Hsiao-Ping; Binder, Kurt

    2012-01-01

    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 ɛb for chain bending. In the absence of excluded volume interactions, the persistence length ℓp of the polymers would then simply be ℓ _p=ℓ _b(2d-2)^{-1}q_b^{-1} with qb = exp (-ɛb/kBT), the bond length ℓb being the lattice spacing, and kBT is the thermal energy. Using Monte Carlo simulations applying the pruned-enriched Rosenbluth method (PERM), both qb and the chain length N are varied over a wide range (0.005 ⩽ qb ⩽ 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 ℓp) 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 qb ≪ 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.

  16. Multiple time scale dynamics of distance fluctuations in a semiflexible polymer: a one-dimensional generalized Langevin equation treatment.

    PubMed

    Debnath, Pallavi; Min, Wei; Xie, X Sunney; Cherayil, Binny J

    2005-11-22

    Time-dependent fluctuations in the distance x(t) between two segments along a polymer are one measure of its overall conformational dynamics. The dynamics of x(t), modeled as the coordinate of a particle moving in a one-dimensional potential well in thermal contact with a reservoir, is treated with a generalized Langevin equation whose memory kernel K(t) can be calculated from the time-correlation function of distance fluctuations C(t) identical with x(0)x(t). We compute C(t) for a semiflexible continuum model of the polymer and use it to determine K(t) via the GLE. The calculations demonstrate that C(t) is well approximated by a Mittag-Leffler function and K(t) by a power-law decay on time scales of several decades. Both functions depend on a number of parameters characterizing the polymer, including chain length, degree of stiffness, and the number of intervening residues between the two segments. The calculations are compared with the recent observation of a nonexponential C(t) and a power law K(t) in the conformational dynamics within single molecule proteins [Min et al., Phys. Rev. Lett. 94, 198302 (2005)].

  17. Using an effective dimensionality to map the force-extension relation for a semi-flexible polymer in a nanoslit

    NASA Astrophysics Data System (ADS)

    de Haan, Hendrick

    2015-03-01

    The force-extension relation for a semi-flexible polymer is well described by the Marko-Siggia equation in both two and three dimensions. However, while of interest for experimental systems such as DNA in nanopits, the behaviour between these limiting dimensionalities is less understood. I will present results from simulations of a polymer subject to a stretching force F confined in nanoslits of varying heights h. Going from the 3D case to the 2D case, both the coefficients of the equation and the relevant persistence length are shown to change. This observation leads to the definition of an effective dimensionality, deff, to characterize the system. At low F, using deff in a generalized form of the Marko-Siggia relation provides good agreement with the simulation curves. However, at high F, deff drifts back towards d = 3 . 0 . The reason behind this F dependence is discussed. Semi-empirical forms for strong and weak confinement regimes will be presented and shown to give good agreement across all slit heights and stretching forces. deff is thus dependent on h and F and provides a cohesive physical picture for all regimes.

  18. 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

  19. Uncoupling shear and uniaxial elastic moduli of semiflexible biopolymer networks: compression-softening and stretch-stiffening

    PubMed Central

    van Oosten, Anne S. G.; Vahabi, Mahsa; Licup, Albert J.; Sharma, Abhinav; Galie, Peter A.; MacKintosh, Fred C.; Janmey, Paul A.

    2016-01-01

    Gels formed by semiflexible filaments such as most biopolymers exhibit non-linear behavior in their response to shear deformation, e.g., with a pronounced strain stiffening and negative normal stress. These negative normal stresses suggest that networks would collapse axially when subject to shear stress. This coupling of axial and shear deformations can have particularly important consequences for extracellular matrices and collagenous tissues. Although measurements of uniaxial moduli have been made on biopolymer gels, these have not directly been related to the shear response. Here, we report measurements and simulations of axial and shear stresses exerted by a range of hydrogels subjected to simultaneous uniaxial and shear strains. These studies show that, in contrast to volume-conserving linearly elastic hydrogels, the Young’s moduli of networks formed by the biopolymers are not proportional to their shear moduli and both shear and uniaxial moduli are strongly affected by even modest degrees of uniaxial strain. PMID:26758452

  20. 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.

  1. 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.

  2. Simulated Associating Polymer Networks

    NASA Astrophysics Data System (ADS)

    Billen, Joris

    Telechelic associating polymer networks consist of polymer chains terminated by endgroups that have a different chemical composition than the polymer backbone. When dissolved in a solution, the endgroups cluster together to form aggregates. At low temperature, a strongly connected reversible network is formed and the system behaves like a gel. Telechelic networks are of interest since they are representative for biopolymer networks (e.g. F-actin) and are widely used in medical applications (e.g. hydrogels for tissue engineering, wound dressings) and consumer products (e.g. contact lenses, paint thickeners). In this thesis such systems are studied by means of a molecular dynamics/Monte Carlo simulation. At first, the system in rest is studied by means of graph theory. The changes in network topology upon cooling to the gel state, are characterized. Hereto an extensive study of the eigenvalue spectrum of the gel network is performed. As a result, an in-depth investigation of the eigenvalue spectra for spatial ER, scale-free, and small-world networks is carried out. Next, the gel under the application of a constant shear is studied, with a focus on shear banding and the changes in topology under shear. Finally, the relation between the gel transition and percolation is discussed.

  3. Strongly anisotropic polymer networks

    NASA Astrophysics Data System (ADS)

    Ulrich, Stephan; Zippelius, Annette; Benetatos, Panayotis

    2011-03-01

    We investigate a network of worm-like chains, which are strongly oriented along a preferred direction due to an external field, boundary conditions, or a nematic environment. We discuss the effects of random permanent cross-links, whose density may follow an arbitrary distribution along the alignment direction. We show that the tilt modulus is unaffected by cross-links. As the cross-link density is increased beyond the gel point, the network develops a stiffness to in-plane shear deformations. Results for the shear elasticity and fluctuations of the polymer chains are presented. The case of cross-linking the chains on one end only is highlighted, it constitutes a simple model for polymer brushes. Moreover force-extension curves are presented for a toy model that consists of two cross-linked chains.

  4. Semi-Interpenetrating Polymer Networks

    NASA Technical Reports Server (NTRS)

    St. Clair, T. L.; Egli, A. O.

    1987-01-01

    Desirable qualities achieved by "networking" aromatic and addition polyimides. Novel semi-interpenetrating network (semi-ipn) prepared from two types of polyimides. Semi-ipn results when linear polymer synthesized in presence of cross-linked polymer or vice-versa. Semi-ipn attains certain properties better than those of either polymer alone.

  5. Semiflexible filamentous composites.

    PubMed

    Huisman, E M; Heussinger, C; Storm, C; Barkema, G T

    2010-09-10

    Inspired by the ubiquity of composite filamentous networks in nature, we investigate models of biopolymer networks that consist of interconnected floppy and stiff filaments. Numerical simulations carried out in three dimensions allow us to explore the microscopic partitioning of stresses and strains between the stiff and floppy fractions cs and cf and reveal a nontrivial relationship between the mechanical behavior and the relative fraction of stiff polymer: when there are few stiff polymers, nonpercolated stiff "inclusions" are protected from large deformations by an encompassing floppy matrix, while at higher fractions of stiff material the stiff network is independently percolated and dominates the mechanical response. PMID:20867610

  6. Flows in Polymer Networks

    NASA Astrophysics Data System (ADS)

    Tanaka, Fumihiko

    A simple transient network model is introduced to describe creation and annihilation of junctions in the networks of associating polymers. Stationary non-linear viscosity is calculated by the theory and by Monte Carlo simulation to study shear thickening. The dynamic mechanical moduli are calculated as functions of the frequency and the chain disengagement rate. From the peak of the loss modulus, the lifetime τx of the junction is estimated, and from the high frequency plateau of the storage modulus, the number of elastically effective chains in the network is found. Transient phenomena such as stress relaxation and stress overshoot are also theoretically studied. Results are compared with the recent experimental reports on the rheological study of hydrophobically modified water-soluble polymeters.

  7. Electroelasticity of polymer networks

    NASA Astrophysics Data System (ADS)

    Cohen, Noy; Dayal, Kaushik; deBotton, Gal

    2016-07-01

    A multiscale analysis of the electromechanical coupling in elastic dielectrics is conducted, starting from the discrete monomer level through the polymer chain and up to the macroscopic level. Three models for the local relations between the molecular dipoles and the electric field that can fit a variety of dipolar monomers are considered. The entropy of the network is accounted for within the framework of statistical mechanics with appropriate kinematic and energetic constraints. At the macroscopic level closed-form explicit expressions for the behaviors of amorphous dielectrics and isotropic polymer networks are determined, none of which admits the commonly assumed linear relation between the polarization and the electric field. The analysis reveals the dependence of the macroscopic coupled behavior on three primary microscopic parameters: the model assumed for the local behavior, the intensity of the local dipole, and the length of the chain. We show how these parameters influence the directional distributions of the monomers and the hence the resulting overall response of the network. In particular, the dependences of the polarization and the polarization induced stress on the deformation of the dielectric are illustrated. More surprisingly, we also reveal a dependence of the stress on the electric field which stems from the kinematic constraint imposed on the chains.

  8. Competing dynamic phases of active polymer networks

    NASA Astrophysics Data System (ADS)

    Freedman, Simon; Banerjee, Shiladitya; Dinner, Aaron R.

    Recent experiments on in-vitro reconstituted assemblies of F-actin, myosin-II motors, and cross-linking proteins show that tuning local network properties can changes the fundamental biomechanical behavior of the system. For example, by varying cross-linker density and actin bundle rigidity, one can switch between contractile networks useful for reshaping cells, polarity sorted networks ideal for directed molecular transport, and frustrated networks with robust structural properties. To efficiently investigate the dynamic phases of actomyosin networks, we developed a coarse grained non-equilibrium molecular dynamics simulation of model semiflexible filaments, molecular motors, and cross-linkers with phenomenologically defined interactions. The simulation's accuracy was verified by benchmarking the mechanical properties of its individual components and collective behavior against experimental results at the molecular and network scales. By adjusting the model's parameters, we can reproduce the qualitative phases observed in experiment and predict the protein characteristics where phase crossovers could occur in collective network dynamics. Our model provides a framework for understanding cells' multiple uses of actomyosin networks and their applicability in materials research. Supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

  9. Network dynamics in nanofilled polymers.

    PubMed

    Baeza, Guilhem P; Dessi, Claudia; Costanzo, Salvatore; Zhao, Dan; Gong, Shushan; Alegria, Angel; Colby, Ralph H; Rubinstein, Michael; Vlassopoulos, Dimitris; Kumar, Sanat K

    2016-01-01

    It is well accepted that adding nanoparticles (NPs) to polymer melts can result in significant property improvements. Here we focus on the causes of mechanical reinforcement and present rheological measurements on favourably interacting mixtures of spherical silica NPs and poly(2-vinylpyridine), complemented by several dynamic and structural probes. While the system dynamics are polymer-like with increased friction for low silica loadings, they turn network-like when the mean face-to-face separation between NPs becomes smaller than the entanglement tube diameter. Gel-like dynamics with a Williams-Landel-Ferry temperature dependence then result. This dependence turns particle dominated, that is, Arrhenius-like, when the silica loading increases to ∼31 vol%, namely, when the average nearest distance between NP faces becomes comparable to the polymer's Kuhn length. Our results demonstrate that the flow properties of nanocomposites are complex and can be tuned via changes in filler loading, that is, the character of polymer bridges which 'tie' NPs together into a network. PMID:27109062

  10. Network dynamics in nanofilled polymers

    NASA Astrophysics Data System (ADS)

    Baeza, Guilhem P.; Dessi, Claudia; Costanzo, Salvatore; Zhao, Dan; Gong, Shushan; Alegria, Angel; Colby, Ralph H.; Rubinstein, Michael; Vlassopoulos, Dimitris; Kumar, Sanat K.

    2016-04-01

    It is well accepted that adding nanoparticles (NPs) to polymer melts can result in significant property improvements. Here we focus on the causes of mechanical reinforcement and present rheological measurements on favourably interacting mixtures of spherical silica NPs and poly(2-vinylpyridine), complemented by several dynamic and structural probes. While the system dynamics are polymer-like with increased friction for low silica loadings, they turn network-like when the mean face-to-face separation between NPs becomes smaller than the entanglement tube diameter. Gel-like dynamics with a Williams-Landel-Ferry temperature dependence then result. This dependence turns particle dominated, that is, Arrhenius-like, when the silica loading increases to ~31 vol%, namely, when the average nearest distance between NP faces becomes comparable to the polymer's Kuhn length. Our results demonstrate that the flow properties of nanocomposites are complex and can be tuned via changes in filler loading, that is, the character of polymer bridges which `tie' NPs together into a network.

  11. Network dynamics in nanofilled polymers

    PubMed Central

    Baeza, Guilhem P.; Dessi, Claudia; Costanzo, Salvatore; Zhao, Dan; Gong, Shushan; Alegria, Angel; Colby, Ralph H.; Rubinstein, Michael; Vlassopoulos, Dimitris; Kumar, Sanat K.

    2016-01-01

    It is well accepted that adding nanoparticles (NPs) to polymer melts can result in significant property improvements. Here we focus on the causes of mechanical reinforcement and present rheological measurements on favourably interacting mixtures of spherical silica NPs and poly(2-vinylpyridine), complemented by several dynamic and structural probes. While the system dynamics are polymer-like with increased friction for low silica loadings, they turn network-like when the mean face-to-face separation between NPs becomes smaller than the entanglement tube diameter. Gel-like dynamics with a Williams–Landel–Ferry temperature dependence then result. This dependence turns particle dominated, that is, Arrhenius-like, when the silica loading increases to ∼31 vol%, namely, when the average nearest distance between NP faces becomes comparable to the polymer's Kuhn length. Our results demonstrate that the flow properties of nanocomposites are complex and can be tuned via changes in filler loading, that is, the character of polymer bridges which ‘tie' NPs together into a network. PMID:27109062

  12. Self-Healing Polymer Networks

    NASA Astrophysics Data System (ADS)

    Tournilhac, Francois

    2012-02-01

    Supramolecular chemistry teaches us to control non-covalent interactions between organic molecules, particularly through the use of optimized building blocks able to establish several hydrogen bonds in parallel. This discipline has emerged as a powerful tool in the design of new materials through the concept of supramolecular polymers. One of the fascinating aspects of such materials is the possibility of controlling the structure, adding functionalities, adjusting the macroscopic properties of and taking profit of the non-trivial dynamics associated to the reversibility of H-bond links. Applications of these compounds may include adhesives, coatings, rheology additives, high performance materials, etc. However, the synthesis of such polymers at the industrial scale still remains a challenge. Our first ambition is to design supramolecular polymers with original properties, the second ambition is to devise simple and environmentally friendly methods for their industrial production. In our endeavours to create novel supramolecular networks with rubbery elasticity, self-healing ability and as little as possible creep, the strategy to prolongate the relaxation time and in the same time, keep the system flexible was to synthesize rather than a single molecule, an assembly of randomly branched H-bonding oligomers. We propose a strategy to obtain through a facile one-pot synthesis a large variety of supramolecular materials that can behave as differently as associating low-viscosity liquids, semi-crystalline or amorphous thermoplastics, viscoelastic melts or self-healing rubbers.

  13. Persistent draining crossover in DNA and other semi-flexible polymers: Evidence from hydrodynamic models and extensive measurements on DNA solutions.

    PubMed

    Mansfield, Marc L; Tsortos, Achilleas; Douglas, Jack F

    2015-09-28

    Although the scaling theory of polymer solutions has had many successes, this type of argument is deficient when applied to hydrodynamic solution properties. Since the foundation of polymer science, it has been appreciated that measurements of polymer size from diffusivity, sedimentation, and solution viscosity reflect a convolution of effects relating to polymer geometry and the strength of the hydrodynamic interactions within the polymer coil, i.e., "draining." Specifically, when polymers are expanded either by self-excluded volume interactions or inherent chain stiffness, the hydrodynamic interactions within the coil become weaker. This means there is no general relationship between static and hydrodynamic size measurements, e.g., the radius of gyration and the hydrodynamic radius. We study this problem by examining the hydrodynamic properties of duplex DNA in solution over a wide range of molecular masses both by hydrodynamic modeling using a numerical path-integration method and by comparing with extensive experimental observations. We also considered how excluded volume interactions influence the solution properties of DNA and confirm that excluded volume interactions are rather weak in duplex DNA in solution so that the simple worm-like chain model without excluded volume gives a good leading-order description of DNA for molar masses up to 10(7) or 10(8) g/mol or contour lengths between 5 μm and 50 μm. Since draining must also depend on the detailed chain monomer structure, future work aiming to characterize polymers in solution through hydrodynamic measurements will have to more carefully consider the relation between chain molecular structure and hydrodynamic solution properties. In particular, scaling theory is inadequate for quantitative polymer characterization.

  14. Supramolecular polymer networks: hydrogels and bulk materials.

    PubMed

    Voorhaar, Lenny; Hoogenboom, Richard

    2016-07-21

    Supramolecular polymer networks are materials crosslinked by reversible supramolecular interactions, such as hydrogen bonding or electrostatic interactions. Supramolecular materials show very interesting and useful properties resulting from their dynamic nature, such as self-healing, stimuli-responsiveness and adaptability. Here we will discuss recent progress in polymer-based supramolecular networks for the formation of hydrogels and bulk materials. PMID:27206244

  15. Four 1-D metal-organic polymers self-assembled from semi-flexible benzimidazole-based ligand: Syntheses, structures and fluorescent properties

    NASA Astrophysics Data System (ADS)

    Zhou, Chun-lin; Wang, Shi-min; Liu, Sai-nan; Yu, Tian-tian; Li, Rui-ying; Xu, Hong; Liu, Zhong-yi; Sun, Huan; Cheng, Jia-jia; Li, Jin-peng; Hou, Hong-wei; Chang, Jun-biao

    2016-08-01

    Four one-dimensional (1-D) metal-organic polymers based on methylene-bis(1,1‧-benzimidazole)(mbbz), namely, {[Hg(mbbz)(SCN)2]·1/3H2O}n (1), [Co(mbbz)(Cl)2]n (2), {[Co(mbbz)(SO4)]·CH3OH}n (3) and {[Zn(mbbz)(SO4)]·CH3OH}n (4) have been successfully synthesized and structurally characterized. Single-crystal X-ray diffraction reveals that polymers 1 and 2 exhibit interesting 1-D double helical chain structures, while polymers 3 and 4 are 1-D double chain structures due to the bridging effect of mbbz ligands and sulfate anions. These polymers containing the mbbz-based ligand have a high degree of dependence on the corresponding counter anions. Furthermore, the fluorescence properties of the four polymers were also investigated in the solid state, showing the fluorescence signal changes in comparing with that of free ligand mbbz.

  16. Building polymer fiber optic network

    NASA Astrophysics Data System (ADS)

    Bienias, P.; Bereś-Pawlik, E.

    2015-09-01

    The paper describes an investigation of transmission in LAN with using polymer optical fiber (POF). There were used two kinds of POF, step index plastic optical fiber (SI-POF) and graded index plastic optical fiber (GI-POF). Furthermore, the paper include a comparison between SI-POF and GI-POF and possibilities of using them. For the project's needs, new type of couplers has been designed and built, optimization has been performed to obtain the best parameters for designed couplers. Additionally, the coupler has been built from the same material, which GI-POF - PMMA is made of. Moreover, CWDM (Coarse Wavelength Division Multiplexing) transmissions is investigated to improve the network capacity.

  17. Viscoelastic properties of semiflexible filamentous bacteriophage fd.

    PubMed

    Schmidt, F G; Hinner, B; Sackmann, E; Tang, J X

    2000-10-01

    The cytoskeletal protein filament F-actin has been treated in a number of recent studies as a model physical system for semiflexible filaments. In this work, we studied the viscoelastic properties of entangled solutions of the filamentous bacteriophage fd as an alternative to F-actin with similar physical parameters. We present both microrheometric and macrorheometric measurements of the viscoelastic storage and loss moduli, G'(f ) and G"(f ), respectively, in a frequency range 0.01semiflexible filament networks. For the dynamic viscosity at the low shear rate limit, a concentration dependence of eta(0) approximately c(2.6) was found. Finally, a linear scaling of the terminal relaxation time with concentration, tau(d) approximately c, was observed. PMID:11089110

  18. Universal Cyclic Topology in Polymer Networks

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Alexander-Katz, Alfredo; Johnson, Jeremiah A.; Olsen, Bradley D.

    2016-05-01

    Polymer networks invariably possess topological defects: loops of different orders which have profound effects on network properties. Here, we demonstrate that all cyclic topologies are a universal function of a single dimensionless parameter characterizing the conditions for network formation. The theory is in excellent agreement with both experimental measurements of hydrogel loop fractions and Monte Carlo simulations without any fitting parameters. We demonstrate the superposition of the dilution effect and chain-length effect on loop formation. The one-to-one correspondence between the network topology and primary loop fraction demonstrates that the entire network topology is characterized by measurement of just primary loops, a single chain topological feature. Different cyclic defects cannot vary independently, in contrast to the intuition that the densities of all topological species are freely adjustable. Quantifying these defects facilitates studying the correlations between the topology and properties of polymer networks, providing a key step in overcoming an outstanding challenge in polymer physics.

  19. Universal Cyclic Topology in Polymer Networks.

    PubMed

    Wang, Rui; Alexander-Katz, Alfredo; Johnson, Jeremiah A; Olsen, Bradley D

    2016-05-01

    Polymer networks invariably possess topological defects: loops of different orders which have profound effects on network properties. Here, we demonstrate that all cyclic topologies are a universal function of a single dimensionless parameter characterizing the conditions for network formation. The theory is in excellent agreement with both experimental measurements of hydrogel loop fractions and Monte Carlo simulations without any fitting parameters. We demonstrate the superposition of the dilution effect and chain-length effect on loop formation. The one-to-one correspondence between the network topology and primary loop fraction demonstrates that the entire network topology is characterized by measurement of just primary loops, a single chain topological feature. Different cyclic defects cannot vary independently, in contrast to the intuition that the densities of all topological species are freely adjustable. Quantifying these defects facilitates studying the correlations between the topology and properties of polymer networks, providing a key step in overcoming an outstanding challenge in polymer physics.

  20. Universal monomer dynamics of a two-dimensional semi-flexible chain

    NASA Astrophysics Data System (ADS)

    Huang, Aiqun; Adhikari, Ramesh; Bhattacharya, Aniket; Binder, Kurt

    2014-01-01

    We present a unified scaling theory for the dynamics of monomers for dilute solutions of semi-flexible polymers under good solvent conditions in the free draining limit. Our theory encompasses the well-known regimes of mean square displacements (MSDs) of stiff chains growing like t^{3/4} with time due to bending motions, and the Rouse-like regime t^{2\

  1. Nanoscale glucan polymer network causes pathogen resistance

    PubMed Central

    Eggert, Dennis; Naumann, Marcel; Reimer, Rudolph; Voigt, Christian A.

    2014-01-01

    Successful defence of plants against colonisation by fungal pathogens depends on the ability to prevent initial penetration of the plant cell wall. Here we report that the pathogen-induced (1,3)-β-glucan cell wall polymer callose, which is deposited at sites of attempted penetration, directly interacts with the most prominent cell wall polymer, the (1,4)-β-glucan cellulose, to form a three-dimensional network at sites of attempted fungal penetration. Localisation microscopy, a super-resolution microscopy technique based on the precise localisation of single fluorescent molecules, facilitated discrimination between single polymer fibrils in this network. Overexpression of the pathogen-induced callose synthase PMR4 in the model plant Arabidopsis thaliana not only enlarged focal callose deposition and polymer network formation but also resulted in the exposition of a callose layer on the surface of the pre-existing cellulosic cell wall facing the invading pathogen. The importance of this previously unknown polymeric defence network is to prevent cell wall hydrolysis and penetration by the fungus. We anticipate our study to promote nanoscale analysis of plant-microbe interactions with a special focus on polymer rearrangements in and at the cell wall. Moreover, the general applicability of localisation microscopy in visualising polymers beyond plant research will help elucidate their biological function in complex networks. PMID:24561766

  2. Stress Relaxation of Entangled Polymer Networks

    SciTech Connect

    EVERAERS,RALF; GREST,GARY S.; KREMER,KURT; PUTZ,MATHIAS

    1999-10-22

    The non-linear stress-strain relation for crosslinked polymer networks is studied using molecular dynamics simulations. Previously we demonstrated the importance of trapped entanglements in determining the elastic and relaxational properties of networks. Here we present new results for the stress versus strain for both dry and swollen networks. Models which limit the fluctuations of the network strands like the tube model are shown to describe the stress for both elongation and compression. For swollen networks, the total modulus is found to decrease like (V{sub o}/V){sup 2/3} and goes to the phantom model result only for short strand networks.

  3. Interfacial welding of dynamic covalent network polymers

    NASA Astrophysics Data System (ADS)

    Yu, Kai; Shi, Qian; Li, Hao; Jabour, John; Yang, Hua; Dunn, Martin L.; Wang, Tiejun; Qi, H. Jerry

    2016-09-01

    Dynamic covalent network (or covalent adaptable network) polymers can rearrange their macromolecular chain network by bond exchange reactions (BERs) where an active unit replaces a unit in an existing bond to form a new bond. Such macromolecular events, when they occur in large amounts, can attribute to unusual properties that are not seen in conventional covalent network polymers, such as shape reforming and surface welding; the latter further enables the important attributes of material malleability and powder-based reprocessing. In this paper, a multiscale modeling framework is developed to study the surface welding of thermally induced dynamic covalent network polymers. At the macromolecular network level, a lattice model is developed to describe the chain density evolution across the interface and its connection to bulk stress relaxation due to BERs. The chain density evolution rule is then fed into a continuum level interfacial model that takes into account surface roughness and applied pressure to predict the effective elastic modulus and interfacial fracture energy of welded polymers. The model yields particularly accessible results where the moduli and interfacial strength of the welded samples as a function of temperature and pressure can be predicted with four parameters, three of which can be measured directly. The model identifies the dependency of surface welding efficiency on the applied thermal and mechanical fields: the pressure will affect the real contact area under the consideration of surface roughness of dynamic covalent network polymers; the chain density increment on the real contact area of interface is only dependent on the welding time and temperature. The modeling approach shows good agreement with experiments and can be extended to other types of dynamic covalent network polymers using different stimuli for BERs, such as light and moisture etc.

  4. Force distribution in a semiflexible loop

    NASA Astrophysics Data System (ADS)

    Waters, James T.; Kim, Harold D.

    2016-04-01

    Loops undergoing thermal fluctuations are prevalent in nature. Ringlike or cross-linked polymers, cyclic macromolecules, and protein-mediated DNA loops all belong to this category. Stability of these molecules are generally described in terms of free energy, an average quantity, but it may also be impacted by local fluctuating forces acting within these systems. The full distribution of these forces can thus give us insights into mechanochemistry beyond the predictive capability of thermodynamics. In this paper, we study the force exerted by an inextensible semiflexible polymer constrained in a looped state. By using a simulation method termed "phase-space sampling," we generate the equilibrium distribution of chain conformations in both position and momentum space. We compute the constraint forces between the two ends of the loop in this chain ensemble using Lagrangian mechanics, and show that the mean of these forces is equal to the thermodynamic force. By analyzing kinetic and potential contributions to the forces, we find that the mean force acts in the direction of increasing extension not because of bending stress, but in spite of it. Furthermore, we obtain a distribution of constraint forces as a function of chain length, extension, and stiffness. Notably, increasing contour length decreases the average force, but the additional freedom allows fluctuations in the constraint force to increase. The force distribution is asymmetric and falls off less sharply than a Gaussian distribution. Our work exemplifies a system where large-amplitude fluctuations occur in a way unforeseen by a purely thermodynamic framework, and offers computational tools useful for efficient, unbiased simulation of a constrained system.

  5. Modeling heterogeneous polymer-grafted nanoparticle networks

    NASA Astrophysics Data System (ADS)

    Zhang, Tao; Mbanga, Badel; Yashin, Victor; Balazs, Anna

    Via a dynamic 3D computational approach, we simulate the heterogeneous polymer-grafted nanoparticle networks. The nanoparticles rigid cores are decorated with a corona of grafted polymers, which contain reactive functional groups at the chain ends. With the overlap of grafted polymers, these reactive groups can form weak labile bonds, which can reform after breakage, or stronger bonds, which rupture irreversibly and thus, the nanoparticles are interconnected by dual cross-links. Previous work has been done on homogeneous networks, while we introduce the heterogeneity by considering two types of particles having different reactive functional groups, so that the labile bond energy varies depending on types of the two end reactive groups. We study the effect of tensile and rotational deformations on the network morphology, and observe, in particular, the phase separation of two types of particles. Our results will provide guidelines for designing transformable material that can controllably change structure under mechanical action.

  6. Deformation propagation in responsive polymer network films

    NASA Astrophysics Data System (ADS)

    Ghosh, Surya K.; Cherstvy, Andrey G.; Metzler, Ralf

    2014-08-01

    We study the elastic deformations in a cross-linked polymer network film triggered by the binding of submicron particles with a sticky surface, mimicking the interactions of viral pathogens with thin films of stimulus-responsive polymeric materials such as hydrogels. From extensive Langevin Dynamics simulations we quantify how far the network deformations propagate depending on the elasticity parameters of the network and the adhesion strength of the particles. We examine the dynamics of the collective area shrinkage of the network and obtain some simple relations for the associated characteristic decay lengths. A detailed analysis elucidates how the elastic energy of the network is distributed between stretching and compression modes in response to the particle binding. We also examine the force-distance curves of the repulsion or attraction interactions for a pair of sticky particles in the polymer network film as a function of the particle-particle separation. The results of this computational study provide new insight into collective phenomena in soft polymer network films and may, in particular, be applied to applications for visual detection of pathogens such as viruses via a macroscopic response of thin films of cross-linked hydrogels.

  7. Estimation of intermolecular interactions in polymer networks

    SciTech Connect

    Subrananian, P.R.; Galiatsatos, V.

    1993-12-31

    Strain-birefringence measurements have been used to estimate intermolecular interactions in polymer networks. The intensity of the interaction has been quantified through a theoretical scheme recently proposed by Erman. The results show that these interactions diminish with decreasing molecular weight between cross-links and decreasing cross-link functionality.

  8. Scattering from deformed polymer networks

    NASA Astrophysics Data System (ADS)

    Müller-Nedebock, Kristian K.; Edwards, Sam F.; McLeish, Tom C. B.

    1999-11-01

    The structure factor of chains dissolved in a stretched, geometrically quenched network is computed in the framework of the replica theory for networks. A variational ansatz is used. The structure factor shows features, due to the quenched disorder, leading to "lozenge"-like and the so-called "butterfly" isointensity structure factor plots. The latter patterns increase in size in the momentum transfer vector space as the degree of affinity of the network is increased, until they disappear to be replaced by the elliptical patterns.

  9. Rubber elasticity for incomplete polymer networks.

    PubMed

    Nishi, Kengo; Chijiishi, Masashi; Katsumoto, Yukiteru; Nakao, Toshio; Fujii, Kenta; Chung, Ung-il; Noguchi, Hiroshi; Sakai, Takamasa; Shibayama, Mitsuhiro

    2012-12-14

    We investigated the relationship between the elastic modulus, G and the reaction probability, p for polymer networks. First, we pointed out that the elastic modulus is expressed by G = {(fp∕2 - 1) + O((p - 1)(2))} Nk(B)T∕V (percolated network law), which does not depend on the local topology of the network structure or the existence of the loops. Here, N is the number of lattice point, V is the system volume, f is the functionality of the cross-link, k(B) is the Boltzmann constant, and T is the absolute temperature. We also conducted simulations for polymer networks with triangular and diamond lattices, and mechanical testing experiments on tetra-poly(ethylene glycol) (PEG) gel with systematically tuning the reaction probability. Here, the tetra-PEG gel was confirmed to be a potential candidate for ideal polymer networks consisting of unimodal strands free from defects and entanglements. From the results of simulations and experiments, it was revealed, for the first time, that the elastic modulus obeys this law in the wide range of p (p(c) ≪ p ≤ 1), where p(c) is the reaction probability at gelation threshold.

  10. Bio-inspired network optimization in soft materials--insights from the plant cell wall.

    PubMed

    Vincent, R R; Cucheval, A; Hemar, Y; Williams, M A K

    2009-01-01

    The dynamic-mechanical responses of ionotropic gels made from the biopolymer pectin have recently been investigated by microrheological experiments and found to exhibit behaviour indicative of semi-flexible polymer networks. In this work we investigate the gelling behaviour of pectin systems in which an enzyme (pectinmethylesterase, PME) is used to liberate ion-binding sites on initially inert polymers, while in the presence of ions. This is in contrast to the previous work, where it was the release of ions (rather than ion-binding groups) that was controlled and the polymers had pre-existing cross-linkable moieties. In stark contrast to the semi-flexible network paradigm of biological gels and the previous work on pectin, the gels studied herein exhibit the properties of chemically cross-linked networks of flexible polymers.

  11. Mechanics of light-activated network polymers

    NASA Astrophysics Data System (ADS)

    Long, Kevin Nicholas

    Mechanically responsive, environmentally activated polymers can undergo large, complex deformation in response to external stimuli such as thermal, luminous, and chemical changes to the environment. Light as a stimulus provides unique application potential because it allows for remote, rapid, and isothermal activation of the material with precise spatial control via existing optical technologies. While certain systems have received considerable attention, the state of the art of most light-activated polymers is limited to basic characterization and demonstrations. To make such materials available to the engineering and scientific communities, physically based theoretical and computational tools are required to guide experimental and design efforts that capitalize on their complex photo-mechanical couplings. The central objective of this thesis is to develop a multi-physics constitutive modeling framework to simulate the continuum scale, photo mechanical behavior of light-activated polymers and implement it into a finite element analysis setting. This framework is independent of specific underlying photo-stimulation mechanisms and is discussed in the context of photo-activated shape memory polymers and network rearranging polymers. Next, the framework is applied to the light-activated network rearranging polymer system, which is relaxed of stress upon irradiation with UV light, and a suite of characterization and application oriented experiments are carried out to calibrate and validate the model's predictive capabilities. The calibrated model is used to investigate several applications such as photo-activated stress relaxation of notched specimens, bending actuation, creep, the buckling of equi-biaxially deformed and irradiated films, and photomechanically formed 1D channels and ridges. Modeling creep involves additional complexity through simultaneous deformation and irradiation, and so the model framework is extended to cover such scenarios. Experiments, finite

  12. Coupled biopolymer networks

    NASA Astrophysics Data System (ADS)

    Schwarz, J. M.; Zhang, Tao

    2015-03-01

    The actin cytoskeleton provides the cell with structural integrity and allows it to change shape to crawl along a surface, for example. The actin cytoskeleton can be modeled as a semiflexible biopolymer network that modifies its morphology in response to both external and internal stimuli. Just inside the inner nuclear membrane of a cell exists a network of filamentous lamin that presumably protects the heart of the cell nucleus--the DNA. Lamins are intermediate filaments that can also be modeled as semiflexible biopolymers. It turns out that the actin cytoskeletal biopolymer network and the lamin biopolymer network are coupled via a sequence of proteins that bridge the outer and inner nuclear membranes. We, therefore, probe the consequences of such a coupling via numerical simulations to understand the resulting deformations in the lamin network in response to perturbations in the cytoskeletal network. Such study could have implications for mechanical mechanisms of the regulation of transcription, since DNA--yet another semiflexible polymer--contains lamin-binding domains, and, thus, widen the field of epigenetics.

  13. Biomimetic oral mucin from polymer micelle networks

    NASA Astrophysics Data System (ADS)

    Authimoolam, Sundar Prasanth

    -functional implant coats. KEYWORDS: Biomimic, Bioapplication, Drug delivery, Filomicelle, Mucin, Polymer networks.

  14. Scattering from polymer networks under elongational strain

    NASA Astrophysics Data System (ADS)

    Svaneborg, C.; Grest, G. S.; Everaers, R.

    2005-12-01

    Molecular-dynamics simulations are used to sample the single-chain form factor of labelled sub-chains in model polymer networks under elongational strain. We observe very similar results for randomly cross-linked and for randomly end-linked networks with the same average strand length and see no indication of lozenge-like scattering patterns reported for some experimental systems. Our data analysis shows that a recent variant of the tube model quantitatively describes scattering in the Guinier regime as well as the macroscopic elastic properties. The observed failure of the theory outside the Guinier regime is shown to be due to non-Gaussian pair-distance distributions.

  15. Scattering from polymer networks under elongational strain.

    SciTech Connect

    Grest, Gary Stephen; Svaneborg, Carsten; Everaers, Ralf

    2005-06-01

    Molecular-dynamics simulations are used to sample the single-chain form factor of labelled sub-chains in model polymer networks under elongational strain. We observe very similar results for randomly cross-linked and for randomly end-linked networks with the same average strand length and see no indication of lozenge-like scattering patterns reported for some experimental systems. Our data analysis shows that a recent variant of the tube model quantitatively describes scattering in the Guinier regime as well as the macroscopic elastic properties. The observed failure of the theory outside the Guinier regime is shown to be due to non-Gaussian pair-distance distributions.

  16. Structure of entangled polymer network from primitive chain network simulations

    NASA Astrophysics Data System (ADS)

    Masubuchi, Yuichi; Uneyama, Takashi; Watanabe, Hiroshi; Ianniruberto, Giovanni; Greco, Francesco; Marrucci, Giuseppe

    2010-04-01

    The primitive chain network (PCN) model successfully employed to simulate the rheology of entangled polymers is here tested versus less coarse-grained (lattice or atomistic) models for what concerns the structure of the network at equilibrium (i.e., in the absence of flow). By network structure, we mean the distributions of some relevant quantities such as subchain length in space or in monomer number. Indeed, lattice and atomistic simulations are obviously more accurate, but are also more difficult to use in nonequilibrium flow situations, especially for long entangled polymers. Conversely, the coarse-grained PCN model that deals more easily with rheology lacks, strictly speaking, a rigorous foundation. It is therefore important to verify whether or not the equilibrium structure of the network predicted by the PCN model is consistent with the results recently obtained by using lattice and atomistic simulations. In this work, we focus on single chain properties of the entangled network. Considering the significant differences in modeling the polymer molecules, the results here obtained appear encouraging, thus providing a more solid foundation to Brownian simulations based on the PCN model. Comparison with the existing theories also proves favorable.

  17. Undulatory Swimming in Fluids with Polymer Networks

    NASA Astrophysics Data System (ADS)

    Gagnon, David; Shen, Xiaoning; Arratia, Paulo

    2013-11-01

    In this talk, we systematically investigate the motility behavior of the nematode Caenorhabditis elegans in polymeric solutions of varying concentration using tracking and velocimetry methods. As the polymer concentration is increased, the solution undergoes a transition from the semi-dilute to the concentrated regime, where these rod-like polymers entangle, align, and form networks. Remarkably, we find an enhancement in the nematode's swimming speed of approximately 65 percent in concentrated solutions compared to semi-dilute solutions. Using velocimetry methods, we show that the undulatory swimming motion of the nematode induces an anisotropic mechanical response in the fluid. This anisotropy, which arises from the fluid micro-structure, is responsible for the observed increase in swimming speed. This work was supported by NSF CAREER (CBET) 0954084.

  18. Undulatory swimming in fluids with polymer networks

    NASA Astrophysics Data System (ADS)

    Gagnon, D. A.; Shen, X. N.; Arratia, P. E.

    2013-10-01

    The motility behavior of the nematode Caenorhabditis elegans in polymeric solutions of varying concentrations is systematically investigated in experiments using tracking and velocimetry methods. As the polymer concentration is increased, the solution undergoes a transition from the semi-dilute to the concentrated regime, where these rod-like polymers entangle, align, and form networks. Remarkably, we find an enhancement in the nematode's swimming speed of approximately 65% in concentrated solutions compared to semi-dilute solutions. Using velocimetry methods, we show that the undulatory swimming motion of the nematode induces an anisotropic mechanical response in the fluid. This anisotropy, which arises from the fluid micro-structure, is responsible for the observed increase in swimming speed.

  19. Polymer networks and gels: Simulation and theory

    NASA Astrophysics Data System (ADS)

    Kenkare, Nirupama Ramamurthy

    1998-12-01

    The purpose of this research is to understand the molecular origins of the dynamic and swelling properties of polymer networks and gels. Our approach has been to apply computer simulations techniques to off-lattice, near-perfect, trifunctional and tetrafunctional network models. The networks are constructed by endlinking freely-jointed, tangent-hard-sphere chains. Equilibrium discontinuous molecular dynamics techniques are employed to simulate the relaxation of large networks of chain lengths ranging from N = 20 to N = 150 at a packing fraction of 0.43. The simulation trajectories are used to calculate the radius of gyration and end-to-end distance of the network chains, the static structure factor of the crosslinks, the mean-squared displacement of the crosslinks and chain inner segments, the intermediate scattering function of the chains and the elastic modulus of the network. The structure and properties of the networks are shown to depend heavily on the manner in which the network is initially constructed. The dynamics of the network crosslinks and chain inner segments are similar to those of melt chains at short times and show evidence of spatial localization at long times. The results from the elastic moduli and long-time crosslink and chain displacement calculations indicate that entanglement constraints act in conjunction with crosslink constraints to reduce crosslink and chain mobility. The presence of entanglements appears to cause the magnitude of the elastic modulus to be larger than the affine/phantom model predictions. The pressure-volume behavior and the chain configurational properties of deformed networks are investigated over a range of packing fractions. The variation of network pressure with density is found to be similar to that of uncrosslinked chain systems of the same chain length, except at low densities where the network pressures become negative due to elastic effects. We derive a simple, mean-field network equation of state in which the

  20. Universal aspects of conformations and transverse fluctuations of a two-dimensional semi-flexible chain

    NASA Astrophysics Data System (ADS)

    Hsu, Hsiao-Ping; Huang, Aiqun; Bhattacharya, Aniket; Binder, Kurt

    2015-03-01

    In this talk we compare the results obtained from Monte Carlo (MC) and Brownian dynamics (BD) simulation for the universal properties of a semi-flexible chain. Specifically we compare MC results obtained using pruned-enriched Rosenbluth method (PERM) with those obtained from BD simulation. We find that the scaled plot of root-mean-square (RMS) end-to-end distance / 2 Llp and RMS transverse transverse fluctuations √{ } /lp as a function of L /lp (where L and lp are the contour length, and the persistence length respectively) are universal and independent of the definition of the persistence length used in MC and BD schemes. We further investigate to what extent these results agree for a semi-flexible polymer confined in a quasi one dimensional channel.

  1. Acrylamide Polymer Double-Network Hydrogels

    PubMed Central

    Arnold, Markus P.; Daniels, Alma U.; Ronken, Sarah; García, Helena Ardura; Friederich, Niklaus F.; Kurokawa, Takayuki; Gong, Jian P.; Wirz, Dieter

    2011-01-01

    Background: In focal repair of joint cartilage and meniscus, initial stiffness and strength of repairs are generally much less than surrounding tissue. This increases early failure potential. Secure primary fixation of the repair material is also a problem. Acrylamide polymer double-network (DN) hydrogels are candidate-improved repair materials. DN gels have exceptional strength and toughness compared to ordinary gels. This stems from the double-network structure in which there is a high molar ratio of the second network to the first network, with the first network highly crosslinked and the second loosely crosslinked. Previous studies of acrylic PAMPS/PDMAAm and PAMPS/PAAm DN gels demonstrated physicochemical stability and tissue compatibility as well as the ability to foster cartilage formation. Methods: Mechanical properties related to surgical use were tested in 2 types of DN gels. Results: Remarkably, these >90%-water DN gels exhibited dynamic impact stiffness (E*) values (~1.1 and ~1.5 MPa) approaching swine meniscus (~2.9 MPa). Dynamic impact energy-absorbing capability was much lower (median loss angles of ~2°) than swine meniscus (>10°), but it is intriguing that >90%-water materials can efficiently store energy. Also, fine 4/0 suture tear-out strength approached cartilage (~2.1 and ~7.1 N v. ~13.5 N). Initial strength of attachment of DN gels to cartilage with acrylic tissue adhesive was also high (~0.20 and ~0.15 N/mm2). Conclusions: DN gel strength and toughness properties stem from optimized entanglement of the 2 network components. DN gels thus have obvious structural parallels with cartilaginous tissues, and their surgical handling properties make them ideal candidates for clinical use. PMID:26069595

  2. Covalently crosslinked diels-alder polymer networks.

    SciTech Connect

    Bowman, Christopher; Adzima, Brian J.; Anderson, Benjamin John

    2011-09-01

    This project examines the utility of cycloaddition reactions for the synthesis of polymer networks. Cycloaddition reactions are desirable because they produce no unwanted side reactions or small molecules, allowing for the formation of high molecular weight species and glassy crosslinked networks. Both the Diels-Alder reaction and the copper-catalyzed azide-alkyne cycloaddition (CuAAC) were studied. Accomplishments include externally triggered healing of a thermoreversible covalent network via self-limited hysteresis heating, the creation of Diels-Alder based photoresists, and the successful photochemical catalysis of CuAAC as an alternative to the use of ascorbic acid for the generation of Cu(I) in click reactions. An analysis of the results reveals that these new methods offer the promise of efficiently creating robust, high molecular weight species and delicate three dimensional structures that incorporate chemical functionality in the patterned material. This work was performed under a Strategic Partnerships LDRD during FY10 and FY11 as part of a Sandia National Laboratories/University of Colorado-Boulder Excellence in Science and Engineering Fellowship awarded to Brian J. Adzima, a graduate student at UC-Boulder. Benjamin J. Anderson (Org. 1833) was the Sandia National Laboratories point-of-contact for this fellowship.

  3. Mesoscopic Simulations of Crosslinked Polymer Networks

    NASA Astrophysics Data System (ADS)

    Megariotis, Grigorios; Vogiatzis, Georgios G.; Schneider, Ludwig; Müller, Marcus; Theodorou, Doros N.

    2016-08-01

    A new methodology and the corresponding C++ code for mesoscopic simulations of elastomers are presented. The test system, crosslinked ds-1’4-polyisoprene’ is simulated with a Brownian Dynamics/kinetic Monte Carlo algorithm as a dense liquid of soft, coarse-grained beads, each representing 5-10 Kuhn segments. From the thermodynamic point of view, the system is described by a Helmholtz free-energy containing contributions from entropic springs between successive beads along a chain, slip-springs representing entanglements between beads on different chains, and non-bonded interactions. The methodology is employed for the calculation of the stress relaxation function from simulations of several microseconds at equilibrium, as well as for the prediction of stress-strain curves of crosslinked polymer networks under deformation.

  4. Physics in Cell Biology: Actin as a Model System for Polymer Physics

    NASA Astrophysics Data System (ADS)

    Frey, Erwin

    Living cells are soft bodies of a characteristic form, but endowed with a capacity for a steady turnover of their structures. Both of these material properties, i.e. recovery of the shape after an external stress has been imposed and dynamic structural reorganization, are essential for many cellular phenomena. The structural element responsible for the extraordinary mechanical and dynamical properties of eukaryotic cells is a three-dimensional assembly of protein fibers, the cytoskeleton. These fibers are semiflexible polymers with a stiffness intermediate between rigid rods and freely jointed chains. We discuss the statistical mechanics of individual semiflexible polymers and analyze the viscoelastic properties of solutions and cross linked networks of these biopolymers.

  5. Wavelength selective polymer network formation of end-functional star polymers.

    PubMed

    Kaupp, Michael; Hiltebrandt, Kai; Trouillet, Vanessa; Mueller, Patrick; Quick, Alexander S; Wegener, Martin; Barner-Kowollik, Christopher

    2016-01-31

    A wavelength selective technique for light-induced network formation based on two photo-active moieties, namely ortho-methylbenzaldehyde and tetrazole is introduced. The network forming species are photo-reactive star polymers generated via reversible activation fragmentation chain transfer (RAFT) polymerization, allowing the network to be based on almost any vinylic monomer. Direct laser writing (DLW) allows to form any complex three-dimensional structure based on the photo-reactive star polymers.

  6. Porous polymer networks and ion-exchange media and metal-polymer composites made therefrom

    DOEpatents

    Kanatzidis, Mercouri G.; Katsoulidis, Alexandros

    2016-10-18

    Porous polymeric networks and composite materials comprising metal nanoparticles distributed in the polymeric networks are provided. Also provided are methods for using the polymeric networks and the composite materials in liquid- and vapor-phase waste remediation applications. The porous polymeric networks, are highly porous, three-dimensional structures characterized by high surface areas. The polymeric networks comprise polymers polymerized from aldehydes and phenolic molecules.

  7. Porous polymer networks and ion-exchange media and metal-polymer composites made therefrom

    DOEpatents

    Kanatzidis, Mercouri G; Katsoulidis, Alexandros

    2015-03-10

    Porous polymeric networks and composite materials comprising metal nanoparticles distributed in the polymeric networks are provided. Also provided are methods for using the polymeric networks and the composite materials in liquid- and vapor-phase waste remediation applications. The porous polymeric networks, are highly porous, three-dimensional structures characterized by high surface areas. The polymeric networks comprise polymers polymerized from aldehydes and phenolic molecules.

  8. Hydrodynamics of diatom chains and semiflexible fibres.

    PubMed

    Nguyen, Hoa; Fauci, Lisa

    2014-07-01

    Diatoms are non-motile, unicellular phytoplankton that have the ability to form colonies in the form of chains. Depending upon the species of diatoms and the linking structures that hold the cells together, these chains can be quite stiff or very flexible. Recently, the bending rigidities of some species of diatom chains have been quantified. In an effort to understand the role of flexibility in nutrient uptake and aggregate formation, we begin by developing a three-dimensional model of the coupled elastic-hydrodynamic system of a diatom chain moving in an incompressible fluid. We find that simple beam theory does a good job of describing diatom chain deformation in a parabolic flow when its ends are tethered, but does not tell the whole story of chain deformations when they are subjected to compressive stresses in shear. While motivated by the fluid dynamics of diatom chains, our computational model of semiflexible fibres illustrates features that apply widely to other systems. The use of an adaptive immersed boundary framework allows us to capture complicated buckling and recovery dynamics of long, semiflexible fibres in shear. PMID:24789565

  9. Self-assembled polymer nanocomposites and their networks

    NASA Astrophysics Data System (ADS)

    Patil, Nitin Vikas

    This dissertation describes new routes to synthesize polymer nanocomposite networks via self-assembly. Polymerizable structure directing agents (referred to as surfmers) obtained by end-group functionalization preserves the structure-directing capabilities of the surfactant for templating ordered mesoporous silica particle growth, while simultaneously generating a reactive matrix for polymer network formation through reactive end groups in the presence of intimately mixed mesoporous silicates. A combination of small angle X-ray scattering, surface area, and microscopy experiments on mesoporous silica indicated the structure directing capabilities of surfmers. Free-radical polymerization of the surfmer leads to novel crosslinked nanocomposites networks. Multiple experiments, including gel permeation chromatography, swelling, and solid state NMR experiments on polymer nanocomposites gave evidence of the polymerization of surfmer leading to formation of crosslink networks. Polymer nanocomposites with varied silica content were prepared. Effects of silica content on polymer nanocomposites were studied on rheometer. Results obtained from rheological experiments indicate that the storage (G') and loss modulus (G") increases with increase in the content of mesoporous silica. In this way, the nanocomposites networks obtained via self-assembly shows independent behavior with respect to frequency in rheological experiments. Additionally, this self-assembled route was extended to synthesize biodegradable and biocompatible polymer nanocomposites networks. The nanocomposite networks obtained with 15% of silica content showed the increase in storage modulus by two orders of magnitude in rheological experiments.

  10. Polysiloxane Based Interpenetrating Polymer Networks: synthesis and Properties

    NASA Astrophysics Data System (ADS)

    Fichet, Odile; Vidal, Frédéric; Darras, Vincent; Boileau, Sylvie; Teyssié, Dominique

    This article summarizes a large amount of work carried out in our laboratory on polysiloxane based Interpenetrating Polymer Networks (IPNs). First, a polydimethylsiloxane (PDMS) network has been combined with a cellulose acetate butyrate (CAB) network in order to improve its mechanical properties. Second, a PDMS network was combined with a fluorinated polymer network. Thanks to a perfect control of the respective rates of formation of each network it has been possible to avoid polymer phase separation during the IPN synthesis. Physico-chemical analyses of these materials led to classify them as "true" IPNs according to Sperling's definition. In addition, synergy of the mechanical properties, on the one hand, and of the surface properties, on the other hand, was displayed.

  11. 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.

  12. Porous networks derived from synthetic polymer-clay complexes

    SciTech Connect

    Carrado, K.A.; Thiyagarajan, P.; Elder, D.L.

    1995-05-12

    Synthetic hectorites were hydrothermally crystallized with direct incorporation of a cationic polymer poly(dimethyl diallyl ammonium chloride) (PDDA), and two neutral cellulosic polymers hydroxypropyl methylcellulose (HPMC) and hydroxyethyl cellulose (HEC). Synthetic PDDA-hectorite displays the lowest d-spacing at 15.8 {Angstrom} along with less polymer incorporation (7.8 wt % organic) than the neutral polymers (18--22 wt % organic). Thermal analysis and small angle neutron scattering were used to further examine the polymer-clay systems. Clay platelets of the largest size and best stacking order occur when cationic PDDA polymer is used. PDDA also enhances these properties over the crystallites prepared for a control mineral, where no polymer is used. HEC acts to aggregate the silica, leaving less to react to form clay. The clay platelets which result from HEC are small, not stacked to a large degree, and oriented randomly. Neutral HPMC acts more like cationic PDDA in that larger clay platelets are allowed to form. The extended microstructure of the clay network remains undisturbed after polymer is removed by calcination. When no polymer is used, the synthetic hectorite has a N{sub 2} BET surface area of 200 M{sup 2}/gm, even after calcination. This increases by 20--50% for the synthetic polymer-hectorites after the polymer is removed by calcination.

  13. Polymer electrolyte gating of carbon nanotube network transistors.

    PubMed

    Ozel, Taner; Gaur, Anshu; Rogers, John A; Shim, Moonsub

    2005-05-01

    Network behavior in single-walled carbon nanotubes (SWNTs) is examined by polymer electrolyte gating. High gate efficiencies, low voltage operation, and the absence of hysteresis in polymer electrolyte gating lead to a convenient and effective method of analyzing transport in SWNT networks. Furthermore, the ability to control carrier type with chemical groups of the host polymer allows us to examine both electron and hole conduction. Comparison to back gate measurements is made on channel length scaling. Frequency measurements are also made giving an upper limit of approximately 300 Hz switching speed for poly(ethylene oxide)/LiClO(4) gated SWNT thin film transistors. PMID:15884892

  14. Phase diagram of hopping conduction mechanisms in polymer nanofiber network

    SciTech Connect

    Li, Jeng-Ting; Lu, Yu-Cheng; Jiang, Shiau-Bin; Zhong, Yuan-Liang; Yeh, Jui-Ming

    2015-12-07

    Network formation by nanofiber crosslinking is usually in polymer materials as application in organic semiconductor devices. Electron hopping transport mechanisms depend on polymer morphology in network. Conducting polymers morphology in a random network structure is modeled by a quasi-one-dimensional system coupled of chains or fibers. We observe the varying hopping conduction mechanisms in the polyaniline nanofibers of the random network structure. The average diameter d of the nanofibers is varied from approximately 10 to 100 nm. The different dominant hopping mechanisms including Efros-Shklovskii variable-range hopping (VRH), Mott VRH, and nearest-neighbor hopping are dependent on temperature range and d in crossover changes. The result of this study is first presented in a phase diagram of hopping conduction mechanisms based on the theories of the random network model. The hopping conduction mechanism is unlike in normal semiconductor materials.

  15. Polymer-Fullerene Network Formation via Light-Induced Crosslinking.

    PubMed

    Sugawara, Yuuki; Hiltebrandt, Kai; Blasco, Eva; Barner-Kowollik, Christopher

    2016-09-01

    A facile and efficient methodology for the formation of polymer-fullerene networks via a light-induced reaction is reported. The photochemical crosslinking is based on a nitrile imine-mediated tetrazole-ene cycloaddition reaction, which proceeds catalyst-free under UV-light irradiation (λmax = 320 nm) at ambient temperature. A tetrazole-functionalized polymer (Mn = 6500 g mol(-1) , Ð = 1.3) and fullerene C60 are employed for the formation of the hybrid networks. The tetrazole-functionalized polymer as well as the fullerene-containing networks are carefully characterized by NMR spectrometry, size exclusion chromatography, infrared spectroscopy, and elemental analysis. Furthermore, thermal analysis of the fullerene networks and their precursors is carried out. The current contribution thus induces an efficient platform technology for fullerene-based network formation. PMID:27336692

  16. Phase diagram of hopping conduction mechanisms in polymer nanofiber network

    NASA Astrophysics Data System (ADS)

    Li, Jeng-Ting; Lu, Yu-Cheng; Jiang, Shiau-Bin; Zhong, Yuan-Liang; Yeh, Jui-Ming

    2015-12-01

    Network formation by nanofiber crosslinking is usually in polymer materials as application in organic semiconductor devices. Electron hopping transport mechanisms depend on polymer morphology in network. Conducting polymers morphology in a random network structure is modeled by a quasi-one-dimensional system coupled of chains or fibers. We observe the varying hopping conduction mechanisms in the polyaniline nanofibers of the random network structure. The average diameter d of the nanofibers is varied from approximately 10 to 100 nm. The different dominant hopping mechanisms including Efros-Shklovskii variable-range hopping (VRH), Mott VRH, and nearest-neighbor hopping are dependent on temperature range and d in crossover changes. The result of this study is first presented in a phase diagram of hopping conduction mechanisms based on the theories of the random network model. The hopping conduction mechanism is unlike in normal semiconductor materials.

  17. SANS Study of Static Structure of The Double Network Polymers

    NASA Astrophysics Data System (ADS)

    Tominaga, Taiki; Takata, Shin-ichi; Suzuki, Jun-ichi; Aizawa, Kazuya; Seto, Hideki; Arai, Masatoshi

    The freeze-dried double-network hydrogels (DN-polymers) have cross-linked aqueous polymer networks giving unique mechanical properties [1]. The Young's modulus of the DN-polymers is nearly unchanged around 102 MPa in the relative humidity (RH) between 0 and 80%. The DN-polymers also show maximum values in both Young's modulus and fracture stress around 30% RH, which corresponds to the water content of about 7 wt.%, in contrast with the plastics for which tinny amount of water causes significant decrease of mechanical properties. Small-angle neutron scattering (SANS) measurements were carried out to investigate the humidity dependence of the nanoscaled structure of the DN-polymers. Several SANS profiles obtained for un-deformed DN-polymers made of poly- (2-acrylamido-2-methylpropane sulfonic acid) sodium salt (PNaAMPS) and polyacrylamide (PAAm) are compared with each other. The SANS results show that water is adsorbed on the structure larger than a mesh-size of the polymer network at low RH but is adsorbed gradually also on the structure in a scale of the segment of the polymer with increasing RH.

  18. The spatial response of nonlinear strain propagation in response to actively driven microspheres through entangled actin networks

    NASA Astrophysics Data System (ADS)

    Falzone, Tobias; Blair, Savanna; Robertson-Anderson, Rae

    2015-03-01

    The semiflexible biopolymer actin, a ubiquitous component of nearly all biological organisms, plays an important role in many mechanically-driven processes such as muscle contraction, cancer invasion and cell motility. As such, entangled actin networks, which possess unique and complex viscoelastic properties, have been the subject of much theoretical and experimental work. However, due to this viscoelastic complexity, much is still unknown regarding the correlation of the applied stress on actin networks to the induced filament strain at the molecular and micro scale. Here, we use simultaneous optical trapping and fluorescence microscopy to characterize the link between applied microscopic forces and strain propagation as a function of strain rate and concentration. Specifically, we track fiduciary markers on entangled actin filaments before, during and after actively driving embedded microspheres through the network. These measurements provide much needed insight into the molecular-level dynamics connecting stress and strain in semiflexible polymer networks.

  19. Synthetic Oral Mucin Mimic from Polymer Micelle Networks

    PubMed Central

    2015-01-01

    Mucin networks are formed in the oral cavity by complexation of glycoproteins with other salivary proteins, yielding a hydrated lubricating barrier. The function of these networks is linked to their structural, chemical, and mechanical properties. Yet, as these properties are interdependent, it is difficult to tease out their relative importance. Here, we demonstrate the ability to recreate the fibrous like network through a series of complementary rinses of polymeric worm-like micelles, resulting in a 3-dimensional (3D) porous network that can be deposited layer-by-layer onto any surface. In this work, stability, structure, and microbial capture capabilities were evaluated as a function of network properties. It was found that network structure alone was sufficient for bacterial capture, even with networks composed of the adhesion-resistant polymer, poly(ethylene glycol). The synthetic networks provide an excellent, yet simple, means of independently characterizing mucin network properties (e.g., surface chemistry, stiffness, and pore size). PMID:24992241

  20. Fluorinated Azobenzenes for Shape-Persistent Liquid Crystal Polymer Networks.

    PubMed

    Iamsaard, Supitchaya; Anger, Emmanuel; Aßhoff, Sarah Jane; Depauw, Alexis; Fletcher, Stephen P; Katsonis, Nathalie

    2016-08-16

    Liquid crystal polymer networks respond with an anisotropic deformation to a range of external stimuli. When doped with molecular photoswitches, these materials undergo complex shape modifications under illumination. As the deformations are reversed when irradiation stops, applications where the activated shape is required to have thermal stability have been precluded. Previous attempts to incorporate molecular switches into thermally stable photoisomers were unsuccessful at photogenerating macroscopic shapes that are retained over time. Herein, we show that to preserve photoactivated molecular deformation on the macroscopic scale, it is important not only to engineer the thermal stability of the photoswitch but also to adjust the cross-linking density in the polymer network and to optimize the molecular orientations in the material. Our strategy resulted in materials containing fluorinated azobenzenes that retain their photochemical shape for more than eight days, which constitutes the first demonstration of long-lived photomechanical deformation in liquid-crystal polymer networks. PMID:27430357

  1. Off-Lattice Monte Carlo Simulation of Supramolecular Polymer Architectures

    NASA Astrophysics Data System (ADS)

    Amuasi, H. E.; Storm, C.

    2010-12-01

    We introduce an efficient, scalable Monte Carlo algorithm to simulate cross-linked architectures of freely jointed and discrete wormlike chains. Bond movement is based on the discrete tractrix construction, which effects conformational changes that exactly preserve fixed-length constraints of all bonds. The algorithm reproduces known end-to-end distance distributions for simple, analytically tractable systems of cross-linked stiff and freely jointed polymers flawlessly, and is used to determine the effective persistence length of short bundles of semiflexible wormlike chains, cross-linked to each other. It reveals a possible regulatory mechanism in bundled networks: the effective persistence of bundles is controlled by the linker density.

  2. Viscoelasticity of Solutions of Semiflexible Rods

    NASA Astrophysics Data System (ADS)

    Morse, David

    2001-03-01

    I will discuss theoretical studies and Brownian dynamics simulationsof the linear viscoelasticity of solutions of wormlike chains. The relaxation modulus G(t) in dilute solutions of relatively short chains, with lengths L less than the persistence length L_p, is found to exhibit three time regimes: At very early times, before an initially affine longitudinal deformation has begun to relax, G(t) ∝ t-3/4. Over a broad range of intermediate times, during which the end-to-end length relaxes, G(t) ∝ t-5/4. In these first two regimes, the stress is dominated by longitudinal forces (i.e., tension) induced by the deformation. At long times, G(t) mimics the exponential decay found for solutions of rods, due to the rotational diffusion of the overall chain orientation. An analytically solvable model of the mechanically inextensible semiflexible chain as an effectively extensible rod, with an effective modulus B(ω) ∝ ω^3/4, is shown to quantitatively describe G(t) for all L <= Lp throughout the first two time regimes. In tightly-entangled solutions, a additional plateau in G(t) appears, in which the stress is dominated by transverse forces, due to stress arising from the disturbance of the equilibrium distribution of transverse fluctuations, which, in this regime, can relax only by reptation. Predictions are compared to experiments with dilute solutions of poly(benzyl glutamate) and tightly-entangled solutions of F-actin.

  3. Helix-like structure formation of a semi-flexible chain confined in a cylinder channel

    NASA Astrophysics Data System (ADS)

    Wen, Xiaohui; Sun, Tieyu; Zhang, Wei-Bing; Lam, Chi-Hang; Zhang, Linxi; Zang, Huaping

    2016-09-01

    Molecular dynamics method is used to study the conformation behavior of a semi-flexible polymer chain confined in a cylinder channel. A novel helix-like structure is found to form during the simulation. Moreover, the detailed characteristic parameters and formation probability of these helix-like structures under moderate conditions are investigated. We find that the structure is not a perfect helix, but a bundle of elliptical turns. In addition, we conduct a statistical analysis for the chain monomer distribution along the radial direction. This research contributes to our understanding of the microscopic conformation of polymer chains in confined environments filled with a solvent. Project supported by the National Natural Science Foundation of China (Grant Nos. 11504033 and 11404290) and the General Research Fund of Hong Kong Research Council of China (Grant No. 15301014).

  4. Helix-like structure formation of a semi-flexible chain confined in a cylinder channel

    NASA Astrophysics Data System (ADS)

    Wen, Xiaohui; Sun, Tieyu; Zhang, Wei-Bing; Lam, Chi-Hang; Zhang, Linxi; Zang, Huaping

    2016-09-01

    Molecular dynamics method is used to study the conformation behavior of a semi-flexible polymer chain confined in a cylinder channel. A novel helix-like structure is found to form during the simulation. Moreover, the detailed characteristic parameters and formation probability of these helix-like structures under moderate conditions are investigated. We find that the structure is not a perfect helix, but a bundle of elliptical turns. In addition, we conduct a statistical analysis for the chain monomer distribution along the radial direction. This research contributes to our understanding of the microscopic conformation of polymer chains in confined environments filled with a solvent. Project supported by the National Natural Science Foundation of China (Grant Nos. 11504033 and 11404290) and the General Research Fund of Hong Kong Research Council of China (Grant No. 15301014).

  5. Direct detection of RDX vapor using a conjugated polymer network.

    PubMed

    Gopalakrishnan, Deepti; Dichtel, William R

    2013-06-01

    1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) is a principal component of plastic explosives used in acts of terrorism and within improvised explosive devices, among others. Approaches to detect RDX compatible with remote, "stand-off" sampling that do not require preconcentration strategies, such as the swabs commonly employed in airports, will benefit military and civilian security. Such detection remains a significant challenge because RDX is 10(3) less volatile than 1,3,5-trinitrotoluene (TNT), corresponding to a parts-per-trillion vapor pressure under ambient conditions. Therefore, while fluorescence quenching of conjugated polymers is sufficiently sensitive to detect TNT vapors, RDX vapor detection is undemonstrated. Here we report a cross-linked phenylene vinylene polymer network whose fluorescence is quenched by trace amounts of RDX introduced from solution or the vapor phase. Fluorescence quenching is reduced, but remains significant, when partially degraded RDX is employed, suggesting that the polymer responds to RDX itself. The polymer network also responds to TNT and PETN similarly introduced from solution or the vapor phase. Pure solvents, volatile amines, and the outgassed vapors from lipstick or sunscreen do not quench polymer fluorescence. The established success of TNT sensors based on fluorescence quenching makes this a material of interest for real-world explosive sensors and will motivate further interest in cross-linked polymers and framework materials for sensing applications. PMID:23641956

  6. Advancing reversible shape memory by tuning the polymer network architecture

    DOE PAGESBeta

    Li, Qiaoxi; Zhou, Jing; Vatankhah-Varnoosfaderani, Mohammad; Nykypanchuk, Dmytro; Gang, Oleg; Sheiko, Sergei S.

    2016-02-02

    Because of counteraction of a chemical network and a crystalline scaffold, semicrystalline polymer networks exhibit a peculiar behavior—reversible shape memory (RSM), which occurs naturally without applying any external force and particular structural design. There are three RSM properties: (i) range of reversible strain, (ii) rate of strain recovery, and (iii) decay of reversibility with time, which can be improved by tuning the architecture of the polymer network. Different types of poly(octylene adipate) networks were synthesized, allowing for control of cross-link density and network topology, including randomly cross-linked network by free-radical polymerization, thiol–ene clicked network with enhanced mesh uniformity, and loosemore » network with deliberately incorporated dangling chains. It is shown that the RSM properties are controlled by average cross-link density and crystal size, whereas topology of a network greatly affects its extensibility. In conclusion, we have achieved 80% maximum reversible range, 15% minimal decrease in reversibility, and fast strain recovery rate up to 0.05 K–1, i.e., ca. 5% per 10 s at a cooling rate of 5 K/min.« less

  7. Controlled architecture for improved macromolecular memory within polymer networks.

    PubMed

    DiPasquale, Stephen A; Byrne, Mark E

    2016-08-01

    This brief review analyzes recent developments in the field of living/controlled polymerization and the potential of this technique for creating imprinted polymers with highly structured architecture with macromolecular memory. As a result, it is possible to engineer polymers at the molecular level with increased homogeneity relating to enhanced template binding and transport. Only recently has living/controlled polymerization been exploited to decrease heterogeneity and substantially improve the efficiency of the imprinting process for both highly and weakly crosslinked imprinted polymers. Living polymerization can be utilized to create imprinted networks that are vastly more efficient than similar polymers produced using conventional free radical polymerization, and these improvements increase the role that macromolecular memory can play in the design and engineering of new drug delivery and sensing platforms. PMID:27322505

  8. Semi-2-interpenetrating polymer networks of high temperature systems

    NASA Technical Reports Server (NTRS)

    Hanky, A. O.; St. Clair, T. L.

    1985-01-01

    A semi-interpenetrating (semi-IPN) polymer system of the semi-2-IPN type is described in which a polymer of acetylene-terminated imidesulfone (ATPISO2) is cross linked in the presence of polyimidesulfone (PISO2). Six different formulations obtained by mixing of either ATPISO2-1n or ATPISO2-3n with PISO2 in three different proportions were characterized in terms of glass transition temperature, thermooxidative stability, inherent viscosity, and dynamic mechanical properties. Adhesive (lap shear) strength was tested at elevated temperatures on aged samples of adhesive scrim cloth prepared from each resin. Woven graphite (Celion 1000)/polyimide composites were tested for flexural strength, flexural modulus, and shear strength. The network polymers have properties intermediate between those of the component polymers alone, have greatly improved processability over either polyimide, and are able to form good adhesive bonds and composites, making the semi-2-IPN systems superior materials for aerospace structures.

  9. Macro- and microphase separation in multifunctional supramolecular polymer networks

    NASA Astrophysics Data System (ADS)

    Mester, Zoltan; Mohan, Aruna; Fredrickson, Glenn

    2011-03-01

    We develop a field-based model for a binary melt of multifunctional polymers that can reversibly bond to form copolymer networks. The mean-field phase separation behavior of several model networks with heterogeneous bonding is calculated via the random phase approximation (RPA). The extent of bonding between polymers is controlled by specified bond energies. The phase boundary calculated via RPA is the stability limit of the homogeneous disordered phase to coexisting homogeneous macrophases, for low bond strengths, and to microphases, for high bond strengths. An isotropic Lifshitz point separates these two regions along the spindodal boundary. It is demonstrated that higher functionality and higher bond strength suppresses macrophase separation due to greater connectivity between unlike species. Gelation first occurs at a bond strength higher than the Lifshitz point for tri- or higher functional polymer components.

  10. Constitutive Equation for Polymer Networks with Phonon Fluctuations

    NASA Astrophysics Data System (ADS)

    Hansen, Rasmus; Hassager, Ole; Skov, Anne Ladegaard

    2008-07-01

    Recent research by Xing et al. [Phys. Rev. Lett. 98, 075502, 2007] has provided an expression for the Helmholtz free energy related to phonon fluctuations in polymer networks. We extend this result by constructing the corresponding nonlinear constitutive equation, usable for entirely general, volume conserving deformation fields. Constitutive equations for the sliplink and the tube model are applied. The three models are examined by comparison with each other and with data from Xu and Mark [Rubber Chem. Technol. 63, 276, 1990] and Wang and Mark [J. Polym. Sci. Part B: Polym. Phys. 30, 801, 1992] on end-linked polydimethylsiloxane networks. Elastic moduli are derived for the three models and compared with the moduli determined from the chemical stoichiometry. We conclude that the sliplink model and the phonon fluctuation model are relatively consistent with each other and also with the data. The tube model seems consistent neither with the other models nor with the data.

  11. Stress relaxation of polymer networks containing low concentrations of dangling chains and star shaped polymers

    NASA Astrophysics Data System (ADS)

    Vega, Daniel A.; Gómez, Leopoldo R.

    2005-03-01

    We analyze the influence of low concentrations of star and dangling polymer chains on the stress relaxation process of model polymer networks. Model PDMS networks with well defined structure were obtained by the hydrosylilation reaction, based on the addition of hydrogen silanes from a trifunctional cross- linker to end vinyl groups of α- φ polydimethylsiloxane chains. Rheological characterization was carried out in a rotational rheometer by dynamic and stress relaxation tests. Viscoelastic properties of the networks depend strongly on the molecular weight of the stars or pendant chains. It was found that a modified Pearson-Helfand model provides a very good fit to the behavior of these networks. This model incorporates the effect of higher Rouse modes on the arm retraction [Milner and McLeish, Macromolecules, 1997] and the potential for arm retraction originally proposed by Doi and Kuzuu.

  12. ``Lozenge'' Contour Plots in Scattering from Polymer Networks

    NASA Astrophysics Data System (ADS)

    Read, D. J.; McLeish, T. C. B.

    1997-07-01

    We present a consistent explanation for the appearance of ``lozenge'' shapes in contour plots of the two dimensional scattering intensity from stretched polymer networks. By explicitly averaging over quenched variables in a tube model, we show that lozenge patterns arise as a result of chain material that is not directly deformed by the stretch. We obtain excellent agreement with experimental data.

  13. Dependence of physical and mechanical properties on polymer architecture for model polymer networks

    NASA Astrophysics Data System (ADS)

    Guo, Ruilan

    Effect of architecture at nanoscale on the macroscopic properties of polymer materials has long been a field of major interest, as evidenced by inhomogeneities in networks, multimodal network topologies, etc. The primary purpose of this research is to establish the architecture-property relationship of polymer networks by studying the physical and mechanical responses of a series of topologically different PTHF networks. Monodispersed allyl-tenninated PTHF precursors were synthesized through "living" cationic polymerization and functional end-capping. Model networks of various crosslink densities and inhomogeneities levels (unimodal, bimodal and clustered) were prepared by endlinking precursors via thiol-ene reaction. Thermal characteristics, i.e., glass transition, melting point, and heat of fusion, of model PTHF networks were investigated as functions of crosslink density and inhomogeneities, which showed different dependence on these two architectural parameters. Study of freezing point depression (FPD) of solvent confined in swollen networks indicated that the size of solvent microcrystals is comparable to the mesh size formed by intercrosslink chains depending on crosslink density and inhomogeneities. Relationship between crystal size and FPD provided a good reflection of the existing architecture facts in the networks. Mechanical responses of elastic chains to uniaxial strains were studied through SANS. Spatial inhomogeneities in bimodal and clustered networks gave rise to "abnormal butterfly patterns", which became more pronounced as elongation ratio increases. Radii of gyration of chains were analyzed at directions parallel and perpendicular to stretching axis. Dependence of Rg on lambda was compared to three rubber elasticity models and the molecular deformation mechanisms for unimodal, bimodal and clustered networks were explored. The thesis focused its last part on the investigation of evolution of free volume distribution of linear polymer (PE

  14. Polymer Solar Cells: Solubility Controls Fiber Network Formation.

    PubMed

    van Franeker, Jacobus J; Heintges, Gaël H L; Schaefer, Charley; Portale, Giuseppe; Li, Weiwei; Wienk, Martijn M; van der Schoot, Paul; Janssen, René A J

    2015-09-16

    The photoactive layer of polymer solar cells is commonly processed from a four-component solution, containing a semiconducting polymer and a fullerene derivative dissolved in a solvent-cosolvent mixture. The nanoscale dimensions of the polymer-fullerene morphology that is formed upon drying determines the solar cell performance, but the fundamental processes that govern the size of the phase-separated polymer and fullerene domains are poorly understood. Here, we investigate morphology formation of an alternating copolymer of diketopyrrolopyrrole and a thiophene-phenyl-thiophene oligomer (PDPPTPT) with relatively long 2-decyltetradecyl (DT) side chains blended with [6,6]-phenyl-C71-butyric acid methyl ester. During solvent evaporation the polymer crystallizes into a fibrous network. The typical width of these fibers is analyzed by quantification of transmission electron microscopic images, and is mainly determined by the solubility of the polymer in the cosolvent and the molecular weight of the polymer. A higher molecular weight corresponds to a lower solubility and film processing results in a smaller fiber width. Surprisingly, the fiber width is not related to the drying rate or the amount of cosolvent. We have made solar cells with fiber widths ranging from 28 to 68 nm and found an inverse relation between fiber width and photocurrent. Finally, by mixing two cosolvents, we develop a ternary solvent system to tune the fiber width. We propose a model based on nucleation-and-growth which can explain these measurements. Our results show that the width of the semicrystalline polymer fibers is not the result of a frozen dynamical state, but determined by the nucleation induced by the polymer solubility.

  15. Green polymer chemistry: Synthesis of poly(disulfide) polymers and networks

    NASA Astrophysics Data System (ADS)

    Rosenthal-Kim, Emily Quinn

    The disulfide group is unique in that it presents a covalent bond that is easily formed and cleaved under certain biological conditions. While the ease of disulfide bond cleavage is often harnessed as a method of biodegradation, the ease of disulfide bond formation as a synthetic strategy is often overlooked. The objective this research was to synthesize poly(disulfide) polymers and disulfide crosslinked networks from a green chemistry approach. The intent of the green chemistry approach was to take advantage of the mild conditions applicable to disulfide bond synthesis from thiols. With anticipated use as biomaterials, it was also desired that the polymer materials could be degraded under biological conditions. Here, a new method of poly(disulfide) polymer synthesis is introduced which was inspired by the reaction conditions and reagents found in Nature. Ambient temperatures and aqueous mixtures were used in the new method. Hydrogen peroxide, one of the Nature's most powerful oxidizing species was used as the oxidant in the new polymerization reaction. The dithiol monomer, 3,6-dioxa-1,8-octanedithiol was first solubilized in triethylamine, which activated the thiol groups and made the monomer water soluble. At room temperature, the organic dithiol/amine solution was then mixed with dilute aqueous hydrogen peroxide (3% by weight) to make the poly(disulfide) polymers. The presence of a two phase system (organic and aqueous phases) was critical to the polymerization reaction. As the reaction progresses, a third, polymer phase appeared. At ambient temperatures and above, this phase separated from the reaction mixture and the polymer product was easily removed from the reaction solution. These polymers reach Mn > 250,000 g/mol in under two hours. Molecular weight distributions were between 1.5 and 2.0. Reactions performed in an ice bath which remain below room temperature contain high molecular weight polymers with Mn ≈ 120,000 g/mol and have a molecular weight

  16. Quantifying the impact of molecular defects on polymer network elasticity.

    PubMed

    Zhong, Mingjiang; Wang, Rui; Kawamoto, Ken; Olsen, Bradley D; Johnson, Jeremiah A

    2016-09-16

    Elasticity, one of the most important properties of a soft material, is difficult to quantify in polymer networks because of the presence of topological molecular defects in these materials. Furthermore, the impact of these defects on bulk elasticity is unknown. We used rheology, disassembly spectrometry, and simulations to measure the shear elastic modulus and count the numbers of topological "loop" defects of various order in a series of polymer hydrogels, and then used these data to evaluate the classical phantom and affine network theories of elasticity. The results led to a real elastic network theory (RENT) that describes how loop defects affect bulk elasticity. Given knowledge of the loop fractions, RENT provides predictions of the shear elastic modulus that are consistent with experimental observations. PMID:27634530

  17. Molecular dynamics in polymers, polymer networks, and model compounds by dielectric relaxation spectroscopy

    NASA Astrophysics Data System (ADS)

    Fitz, Benjamin David

    Segmental dynamics are investigated in model compounds, polymers, and network-forming polymers. Two aspects of these materials are investigated: (1) the role of molecular structure and connectivity on determining the characteristics of the segmental relaxation, and (2) monitoring the variations in the segmental dynamics during network-forming chemical reactions. We quantify the most important aspects of the dynamics: the relaxation shape, the relaxation strength, the relaxation time, and the temperature dependencies of these properties. Additionally, two general segmental dynamics issues of interest are the length-scale and the homogeneous/heterogeneous aspects. A judicious choice of network-forming polymer provides for the determination of an upper bound on the length-scale. A comparison of relaxation characteristics between dynamic light scattering (measuring density fluctuations) and dielectric relaxation spectroscopy (measuring segmental dipolar reorientation) provides one evaluation of the heterogeneity issue. Dipole dynamics in small molecule model compounds show the influence of molecular connectivity on the cooperative molecular response associated with the glass transition. A rigid, nonpolar, cyanate ester network is shown to develop an anomalous relaxation process during crosslinking. A specific local mode of motion is assigned. Additionally, the main relaxation becomes extraordinarily broad during the course of the network formation, due to markedly increased segmental rigidity and loss of configurational entropy.

  18. Semi-interpenetrating polymer network's of polyimides: Fracture toughness

    NASA Technical Reports Server (NTRS)

    Hansen, Marion Glenn

    1988-01-01

    The objective was to improve the fracture toughness of the PMR-15 thermosetting polyimide by co-disolving LaRC-TPI, a thermoplastic polyimide. The co-solvation of a thermoplastic into a thermoset produces an interpenetration of the thermoplastic polymer into the thermoset polyimide network. A second research program was planned around the concept that to improve the fracture toughness of a thermoset polyimide polymer, the molecular weight between crosslink points would be an important macromolecular topological parameter in producing a fracture toughened semi-IPN polyimide.

  19. High-Performance, Semi-Interpenetrating Polymer Network

    NASA Technical Reports Server (NTRS)

    Pater, Ruth H.; Lowther, Sharon E.; Smith, Janice Y.; Cannon, Michelle S.; Whitehead, Fred M.; Ely, Robert M.

    1992-01-01

    High-performance polymer made by new synthesis in which one or more easy-to-process, but brittle, thermosetting polyimides combined with one or more tough, but difficult-to-process, linear thermoplastics to yield semi-interpenetrating polymer network (semi-IPN) having combination of easy processability and high tolerance to damage. Two commercially available resins combined to form tough, semi-IPN called "LaRC-RP49." Displays improvements in toughness and resistance to microcracking. LaRC-RP49 has potential as high-temperature matrix resin, adhesive, and molding resin. Useful in aerospace, automotive, and electronic industries.

  20. Design and Application of Nanogel-Based Polymer Networks

    NASA Astrophysics Data System (ADS)

    Dailing, Eric Alan

    Crosslinked polymer networks have wide application in biomaterials, from soft hydrogel scaffolds for cell culture and tissue engineering to glassy, high modulus dental restoratives. Composite materials formed with nanogels as a means for tuning network structure on the nanoscale have been reported, but no investigation into nanogels as the primary network component has been explored to this point. This thesis was dedicated to studying network formation from the direct polymerization of nanogels and investigating applications for these unique materials. Covalently crosslinked polymer networks were synthesized from polymerizable nanogels without the use of reactive small monomers or oligomers. Network properties were controlled by the chemical and physical properties of the nanogel, allowing for materials to be designed from nanostructured macromolecular precursors. Nanogels were synthesized from a thermally initiated solution free radical polymerization of a monomethacrylate, a dimethacrylate, and a thiol-based chain transfer agent. Monomers with a range of hydrophilic and hydrophobic character were copolymerized, and polymerizable groups were introduced through an alcohol-isocyanate click reaction. Nanogels were dispersible in water up to 75 wt%, including nanogels that contained a relatively high fraction of a conventionally water-insoluble component. Nanogels with molecular weights that ranged from 10's to 100's of kDa and hydrodynamic radii between 4 and 10 nm were obtained. Macroscopic crosslinked polymer networks were synthesized from the photopolymerization of methacrylate-functionalized nanogels in inert solvent, which was typically water. The nanogel composition and internal branching density affected both covalent and non-covalent interparticle interactions, which dictated the final mechanical properties of the networks. Nanogels with progressively disparate hydrophilic and hydrophobic character were synthesized to explore the potential for creating

  1. Semi-flexible sockets for amputation below the knee.

    PubMed

    Symington, D C; Lowe, P J; Mackay, S

    1975-09-01

    A semi-flexible socket fitted to a series of 47 consecutive below-knee amputees is evaluated, and the problems in assessing prosthetic components and appropriate methodology are discussed. The results suggest that this type of socket deserves wider use and further evaluation in active amputees, where comfort, perspiration control or the condition of the skin is interfering with the patient's function.

  2. Shape memory polymer network with thermally distinct elasticity and plasticity.

    PubMed

    Zhao, Qian; Zou, Weike; Luo, Yingwu; Xie, Tao

    2016-01-01

    Stimuli-responsive materials with sophisticated yet controllable shape-changing behaviors are highly desirable for real-world device applications. Among various shape-changing materials, the elastic nature of shape memory polymers allows fixation of temporary shapes that can recover on demand, whereas polymers with exchangeable bonds can undergo permanent shape change via plasticity. We integrate the elasticity and plasticity into a single polymer network. Rational molecular design allows these two opposite behaviors to be realized at different temperature ranges without any overlap. By exploring the cumulative nature of the plasticity, we demonstrate easy manipulation of highly complex shapes that is otherwise extremely challenging. The dynamic shape-changing behavior paves a new way for fabricating geometrically complex multifunctional devices. PMID:26824077

  3. An easily fabricated high performance ionic polymer based sensor network

    NASA Astrophysics Data System (ADS)

    Zhu, Zicai; Wang, Yanjie; Hu, Xiaopin; Sun, Xiaofei; Chang, Longfei; Lu, Pin

    2016-08-01

    Ionic polymer materials can generate an electrical potential from ion migration under an external force. For traditional ionic polymer metal composite sensors, the output voltage is very small (a few millivolts), and the fabrication process is complex and time-consuming. This letter presents an ionic polymer based network of pressure sensors which is easily and quickly constructed, and which can generate high voltage. A 3 × 3 sensor array was prepared by casting Nafion solution directly over copper wires. Under applied pressure, two different levels of voltage response were observed among the nine nodes in the array. For the group producing the higher level, peak voltages reached as high as 25 mV. Computational stress analysis revealed the physical origin of the different responses. High voltages resulting from the stress concentration and asymmetric structure can be further utilized to modify subsequent designs to improve the performance of similar sensors.

  4. Shape memory polymer network with thermally distinct elasticity and plasticity

    PubMed Central

    Zhao, Qian; Zou, Weike; Luo, Yingwu; Xie, Tao

    2016-01-01

    Stimuli-responsive materials with sophisticated yet controllable shape-changing behaviors are highly desirable for real-world device applications. Among various shape-changing materials, the elastic nature of shape memory polymers allows fixation of temporary shapes that can recover on demand, whereas polymers with exchangeable bonds can undergo permanent shape change via plasticity. We integrate the elasticity and plasticity into a single polymer network. Rational molecular design allows these two opposite behaviors to be realized at different temperature ranges without any overlap. By exploring the cumulative nature of the plasticity, we demonstrate easy manipulation of highly complex shapes that is otherwise extremely challenging. The dynamic shape-changing behavior paves a new way for fabricating geometrically complex multifunctional devices. PMID:26824077

  5. Multiple relaxation modes in associative polymer networks with varying connectivity

    NASA Astrophysics Data System (ADS)

    Bohdan, M.; Sprakel, J.; van der Gucht, J.

    2016-09-01

    The dynamics and mechanics of networks depend sensitively on their spatial connectivity. To explore the effect of connectivity on local network dynamics, we prepare transient polymer networks in which we systematically cut connecting bonds. We do this by creating networks formed from hydrophobically modified difunctionalized polyethylene glycol chains. These form physical gels, consisting of flowerlike micelles that are transiently cross-linked by connecting bridges. By introducing monofunctionalized chains, we can systematically reduce the number of bonds between micelles and thus lower the network connectivity, which strongly reduces the network elasticity and relaxation time. Dynamic light scattering reveals a complex relaxation dynamics that are not apparent in bulk rheology. We observe three distinct relaxation modes. First we find a fast diffusive mode that does not depend on the number of bridges and is attributed to the diffusion of micelles within a cage formed by neighboring micelles. A second, intermediate mode depends strongly on network connectivity but surprisingly is independent of the scattering vector q . We attribute this viscoelastic mode to fluctuations in local connectivity of the network. The third, slowest mode is also diffusive and is attributed to the diffusion of micelle clusters through the viscoelastic matrix. These results shed light on the microscopic dynamics in weakly interconnected transient networks.

  6. Shape memory polymers based on uniform aliphatic urethane networks

    SciTech Connect

    Wilson, T S; Bearinger, J P; Herberg, J L; Marion III, J E; Wright, W J; Evans, C L; Maitland, D J

    2007-01-19

    Aliphatic urethane polymers have been synthesized and characterized, using monomers with high molecular symmetry, in order to form amorphous networks with very uniform supermolecular structures which can be used as photo-thermally actuable shape memory polymers (SMPs). The monomers used include hexamethylene diisocyanate (HDI), trimethylhexamethylenediamine (TMHDI), N,N,N{prime},N{prime}-tetrakis(hydroxypropyl)ethylenediamine (HPED), triethanolamine (TEA), and 1,3-butanediol (BD). The new polymers were characterized by solvent extraction, NMR, XPS, UV/VIS, DSC, DMTA, and tensile testing. The resulting polymers were found to be single phase amorphous networks with very high gel fraction, excellent optical clarity, and extremely sharp single glass transitions in the range of 34 to 153 C. Thermomechanical testing of these materials confirms their excellent shape memory behavior, high recovery force, and low mechanical hysteresis (especially on multiple cycles), effectively behaving as ideal elastomers above T{sub g}. We believe these materials represent a new and potentially important class of SMPs, and should be especially useful in applications such as biomedical microdevices.

  7. Reconfigurable Polymer Networks for Improved Treatment of Intracranial Aneurysms

    NASA Astrophysics Data System (ADS)

    Ninh, Chi Suze Q.

    Endovascular embolization of intracranial aneurysms is a minimally invasive treatment in which an implanted material forms a clot to isolate the weakened vessel. Current strategy suffers from long-term potential failure modes. These potential failure modes include (1) enzymatic degradation of the fibrin clot that leads to compaction of the embolic agent, (2) incomplete filling of the aneurysm sac by embolic agent, and (3) challenging geometry of wide neck aneurysms. In the case of wide neck aneurysms, usually an assisting metal stent is used to help open the artery. However, metal stents with much higher modulus in comparison to the soft blood vessel can cause biocompatibilities issues in the long term such as infection and scarring. Motivated to solve these challenges associated with endovascular embolization, strategies to synthesize and engineer reconfigurable and biodegradable polymers as alternative therapies are evaluated in this thesis. (1) Reconfiguration of fibrin gel's modulus was achieved through crosslinking with genipin released from a biodegradable polymer matrix. (2) Reconfigurability can also be achieved by transforming triblock co-polymer hydrogel into photoresponsive material through incorporation of melanin nanoparticles as efficient photosensitizers. (3) Finally, reconfigurability can be conferred on biodegradable polyester networks via Diels-Alder coupling of furan pendant groups and dimaleimide crosslinking agent. Taken all together, this thesis describes strategies to transform a broad class of polymer networks into reconfigurable materials for improved treatment of intracranial aneurysms as well as for other biomedical applications.

  8. Flash freezing route to mesoporous polymer nanofibre networks

    PubMed Central

    Samitsu, Sadaki; Zhang, Rui; Peng, Xinsheng; Krishnan, Mohan Raj; Fujii, Yoshihisa; Ichinose, Izumi

    2013-01-01

    There are increasing requirements worldwide for advanced separation materials with applications in environmental protection processes. Various mesoporous polymeric materials have been developed and they are considered as potential candidates. It is still challenging, however, to develop economically viable and durable separation materials from low-cost, mass-produced materials. Here we report the fabrication of a nanofibrous network structure from common polymers, based on a microphase separation technique from frozen polymer solutions. The resulting polymer nanofibre networks exhibit large free surface areas, exceeding 300 m2 g−1, as well as small pore radii as low as 1.9 nm. These mesoporous polymer materials are able to rapidly adsorb and desorb a large amount of carbon dioxide and are also capable of condensing organic vapours. Furthermore, the nanofibres made of engineering plastics with high glass transition temperatures over 200 °C exhibit surprisingly high, temperature-dependent adsorption of organic solvents from aqueous solution. PMID:24145702

  9. Interpenetrating Polymer Networks as Innovative Drug Delivery Systems

    PubMed Central

    Lohani, Alka; Singh, Garima; Bhattacharya, Shiv Sankar; Verma, Anurag

    2014-01-01

    Polymers have always been valuable excipients in conventional dosage forms, also have shown excellent performance into the parenteral arena, and are now capable of offering advanced and sophisticated functions such as controlled drug release and drug targeting. Advances in polymer science have led to the development of several novel drug delivery systems. Interpenetrating polymer networks (IPNs) have shown superior performances over the conventional individual polymers and, consequently, the ranges of applications have grown rapidly for such class of materials. The advanced properties of IPNs like swelling capacity, stability, biocompatibility, nontoxicity and biodegradability have attracted considerable attention in pharmaceutical field especially in delivering bioactive molecules to the target site. In the past few years various research reports on the IPN based delivery systems showed that these carriers have emerged as a novel carrier in controlled drug delivery. The present review encompasses IPNs, their types, method of synthesis, factors which affects the morphology of IPNs, extensively studied IPN based drug delivery systems, and some natural polymers widely used for IPNs. PMID:24949205

  10. Interpenetrating polymer networks as innovative drug delivery systems.

    PubMed

    Lohani, Alka; Singh, Garima; Bhattacharya, Shiv Sankar; Verma, Anurag

    2014-01-01

    Polymers have always been valuable excipients in conventional dosage forms, also have shown excellent performance into the parenteral arena, and are now capable of offering advanced and sophisticated functions such as controlled drug release and drug targeting. Advances in polymer science have led to the development of several novel drug delivery systems. Interpenetrating polymer networks (IPNs) have shown superior performances over the conventional individual polymers and, consequently, the ranges of applications have grown rapidly for such class of materials. The advanced properties of IPNs like swelling capacity, stability, biocompatibility, nontoxicity and biodegradability have attracted considerable attention in pharmaceutical field especially in delivering bioactive molecules to the target site. In the past few years various research reports on the IPN based delivery systems showed that these carriers have emerged as a novel carrier in controlled drug delivery. The present review encompasses IPNs, their types, method of synthesis, factors which affects the morphology of IPNs, extensively studied IPN based drug delivery systems, and some natural polymers widely used for IPNs.

  11. A simple model for the swelling of polymer networks

    SciTech Connect

    Painter, P.C.; Shenoy, S.L. )

    1993-07-15

    The Flory--Rehner approach to the solvent swelling of polymer networks is modified so as to abandon the affine deformation assumption. Instead, it is assumed that swelling occurs by a process of disinterspersion of cross-link junctions, and relationships between chain expansion and segment concentration are established using the ideas of de Gennes. Using this approach, we also examine osmotic deswelling, aspects of phase equilibria, and the maximum observed in differential swelling measurements.

  12. Liquid Crystalline Polymers and Networks -- orientation, molecular shape change, mechanics

    NASA Astrophysics Data System (ADS)

    Warner, Mark

    2008-03-01

    In a prescient paper of 1969, Pierre-Gilles de Gennes envisaged both liquid crystal polymers and elastomers. 10 years later, these systems were realised. After 25 years, monodomain elastomers were prepared and displayed phenomena he had predicted: rods incorporated into polymers induce liquid crystallinity in polymer melts and elastomers; orientational order causes shape changes in the back bones of such polymers; mechanical ramifications follow in networks, e.g. spontaneous elongations and contractions on changing order. The latter are proposed as the basis of micro-actuation and artificial muscles, both heat and light-driven. In 1969, de Gennes already described ideal networks heated through the nematic-isotropic transition losing all their order by mechanical relaxation. It is not obvious, but is true in theory and largely in experiment, even in highly non-ideal networks. He also envisaged that a cholesteric network, where there is a topological memory of chirality imprinted by crosslinking chains in a twisted state. Chirality cannot relax away on entering the isotropic phase, even in systems without molecular chirality (for instance those crosslinked in the presence of chiral solvent that is subsequently exchanged away). His chiral elastomers have found application as mechanically-tuneable, rubber lasers. De Gennes also constructed the first continuum elastic theories of nematic elastomers (1982), though distortions are generally very large. His elasticity has informed non-linear elasticity that works even at large amplitudes. I shall describe de Gennes' many contributions, and the current state of a field that has since yielded still more remarkable phenomena.

  13. Microstructure and rheology of microfibril-polymer networks.

    PubMed

    Veen, Sandra J; Versluis, Peter; Kuijk, Anke; Velikov, Krassimir P

    2015-12-14

    By using an adsorbing polymer in combination with mechanical de-agglomeration, the microstructure and rheological properties of networks of microfibrils could be controlled. By the addition of sodium carboxymethyl cellulose during de-agglomeration of networks of bacterial cellulose, the microstructure could be changed from an inhomogeneous network with bundles of microfibrils and voids to a more homogeneous spread and alignment of the particles. As a result the macroscopic rheological properties were altered. Although still elastic and gel-like in nature, the elasticity and viscous behavior of the network as a function of microfibril concentration is altered. The microstructure is thus changed by changing the surface properties of the building blocks leading to a direct influence on the materials macroscopic behavior. PMID:26434637

  14. Microstructure and rheology of microfibril-polymer networks.

    PubMed

    Veen, Sandra J; Versluis, Peter; Kuijk, Anke; Velikov, Krassimir P

    2015-12-14

    By using an adsorbing polymer in combination with mechanical de-agglomeration, the microstructure and rheological properties of networks of microfibrils could be controlled. By the addition of sodium carboxymethyl cellulose during de-agglomeration of networks of bacterial cellulose, the microstructure could be changed from an inhomogeneous network with bundles of microfibrils and voids to a more homogeneous spread and alignment of the particles. As a result the macroscopic rheological properties were altered. Although still elastic and gel-like in nature, the elasticity and viscous behavior of the network as a function of microfibril concentration is altered. The microstructure is thus changed by changing the surface properties of the building blocks leading to a direct influence on the materials macroscopic behavior.

  15. Phase stability of weakly crosslinked interpenetrating polymer networks

    NASA Astrophysics Data System (ADS)

    Binder, K.; Frisch, H. L.

    1984-08-01

    A phenomenological theory is formulated for chemically quenched binary interpenetrating polymer networks, considering both simultaneously crosslinked networks and sequentially crosslinked networks, as well as pseudointerpenetrating networks (where only one component is crosslinked and the other is a linear polymer). We construct free energy functionals for these systems, starting from the classical Flory theory of rubber elasticity, and study their properties as a function of the volume fraction φ of one component and of the Flory-Huggins interaction parameter v. It is suggested that in the limit of small crosslink density the contribution to the free energy due to the mutual entanglement of the networks is small and can be neglected, provided that the spatially homogeneous phase is thermodynamically stable. The stability limit (spinodals) of this phase for the various cases are derived, and also predictions are made for the initial growth of inhomogeneous modes in the unstable regions of the phase diagrams, within the framework of the linearized theory of spinodal decomposition. We also discuss how the predictions of this theory could be checked experimentally.

  16. Energy localization and shape transformations in semiflexible polymer rings.

    PubMed

    Gaididei, Yu B; Archilla, J F R; Sánchez-Morcillo, V J; Gorria, C

    2016-06-01

    Shape transformations in driven and damped molecular chains are considered. Closed chains of weakly coupled molecular subunits under the action of spatially homogeneous time-periodic external field are studied. The coupling between the internal excitations and the bending degrees of freedom of the chain modifies the local bending rigidity of the chain. In the absence of driving the array takes a circular shape. When the energy pumped into the system exceeds some critical value the chain undergoes a nonequilibrium phase transition: The circular shape of the aggregate becomes unstable and the chain takes the shape of an ellipse or, in general, of a polygon. The excitation energy distribution becomes spatially nonuniform: It localizes in such places where the chain is more flat. The weak interaction of the chain with a flat surface restricts the dynamics to a flat manifold. PMID:27415273

  17. Energy localization and shape transformations in semiflexible polymer rings

    NASA Astrophysics Data System (ADS)

    Gaididei, Yu. B.; Archilla, J. F. R.; Sánchez-Morcillo, V. J.; Gorria, C.

    2016-06-01

    Shape transformations in driven and damped molecular chains are considered. Closed chains of weakly coupled molecular subunits under the action of spatially homogeneous time-periodic external field are studied. The coupling between the internal excitations and the bending degrees of freedom of the chain modifies the local bending rigidity of the chain. In the absence of driving the array takes a circular shape. When the energy pumped into the system exceeds some critical value the chain undergoes a nonequilibrium phase transition: The circular shape of the aggregate becomes unstable and the chain takes the shape of an ellipse or, in general, of a polygon. The excitation energy distribution becomes spatially nonuniform: It localizes in such places where the chain is more flat. The weak interaction of the chain with a flat surface restricts the dynamics to a flat manifold.

  18. Backfolded Odijk regime for semiflexible polymers confined in nanochannels

    NASA Astrophysics Data System (ADS)

    Muralidhar, Abhiram; Tree, Douglas; Dorfman, Kevin

    2015-03-01

    The description of properties of DNA confined in a nanochannel with size close to its persistence length has attracted significant attention recently due to its relevance to genome mapping technology. However, clear consensus between existing theories, simulations and experiments in this range of confinement is still lacking. In this talk, we show via Pruned-Enriched Rosebluth Method (PERM) simulations that Odijk's scaling theory based on hairpin formation describes the properties of confined wormlike chains when the confinement size is commensurate with the persistence length. This was made possible by our calculation of the global persistence length, which characterizes the length scale between hairpin bends in the confined molecule. We find that the range of this ``backfolded'' Odijk regime increases with the monomer anisotropy ratio lp / w , where lp and w are the persistence length and width of the molecule respectively. We are thus able to predict the experimental conditions under which one could observe these hairpins for various stiff molecules such as DNA and actin. This information can be used to engineer favorable conditions for genome mapping technology.

  19. Inferential estimation of polymer quality using bootstrap aggregated neural networks.

    PubMed

    Zhang, J

    1999-07-01

    Inferential estimation of polymer quality in a batch polymerisation reactor using bootstrap aggregated neural networks is studied in this paper. Number average molecular weight and weight average molecular weight are estimated from the on-line measurements of reactor temperature, jacket inlet and outlet temperatures, coolant flow rate through the jacket, monomer conversion, and the initial batch conditions. Bootstrap aggregated neural networks are used to enhance the accuracy and robustness of neural network models built from a limited amount of training data. The training data set is re-sampled using bootstrap re-sampling with replacement to form several sets of training data. For each set of training data, a neural network model is developed. The individual neural networks are then combined together to form a bootstrap aggregated neural network. Determination of appropriate weights for combining individual networks using principal component regression is proposed in this paper. Confidence bounds for neural network predictions can also be obtained using the bootstrapping technique. The techniques have been successfully applied to the simulation of a batch methyl methacrylate polymerisation reactor.

  20. Divergent Shear Thinning and Shear Thickening Behavior of Supramolecular Polymer Networks in Semidilute Entangled Polymer Solutions

    PubMed Central

    Xu, Donghua; Liu, Chen-Yang; Craig, Stephen L.

    2011-01-01

    The steady shear behavior of metallo-supramolecular polymer networks formed by bis-Pd(II) cross-linkers and semidilute entangled solutions of poly(4-vinylpyridine) (PVP) in dimethyl sulfoxide (DMSO) or N,N-dimethyl formamide (DMF) is reported. The steady shear behavior of the networks depends on the dissociation rate and association rate of the cross-linkers, the concentration of cross-linkers, and the concentration of the polymer solution. The divergent steady shear behavior—shear thinning versus shear thickening—of samples with identical structure but different cross-linker dynamics (J. Phys. Chem. Lett. 2010, 1, 1683-1686) is further explored in this paper. The divergent steady shear behavior for networks with different cross-linkers is connected to a competition between different time scales: the average time that a cross-linker remains open (τ1) and the local relaxation time of a segment of polymer chain (τsegment). When τ1 is larger than τsegment, shear thickening is observed. When τ1 is smaller than τsegment, only shear thinning is observed. PMID:21547008

  1. Carchesium stalk fibrillar matrix as a highly filled polymer network.

    PubMed

    Hawkes, R

    1977-01-01

    Glycerolated stalks of the sessile peritrich ciliate Carchesium sp. were treated with 10(-6) g ion/1 Ca2+ to disrupt the contractile spasmoneme. The resulting preparation consisted primarily of the fibrillar matrix, a dense extra-cellular meshwork of microfibrils. Some mechanical properties of this preparation have been investigated. The matrix tensile force-extension ratio relation for an initial stretch was characteristic of a soft, swollen polymer network, elastic modulus in young stalks 1.7 X 10(5) Nm-2, in mature stalks 4.0 X 10(5) Nm-2. The higher elastic modulus in mature stalks implies an increase in the interchain cross-link frequency. In young stalks, elastic modulus was found to be independent of the ambient Ca2+ concentration in the threshold range for spasmonemal contraction. Stalk relaxation was pronouncedly irreversible, showing stress softening and permanent hysteresis on repeated loading. Hysteresis was time independent and stiffness was not recovered after four hours at zero strain. Hysteresis was enhanced by repeated loading to the same tensile force. Stress-strain hysteresis at a low extension is characteristic of highly filled polymer networks in which polymer chains are interconnected via rigid filler particles as well as directly cross-linked.

  2. Electropolymerization on wireless electrodes towards conducting polymer microfibre networks

    PubMed Central

    Koizumi, Yuki; Shida, Naoki; Ohira, Masato; Nishiyama, Hiroki; Tomita, Ikuyoshi; Inagi, Shinsuke

    2016-01-01

    Conducting polymers can be easily obtained by electrochemical oxidation of aromatic monomers on an electrode surface as a film state. To prepare conducting polymer fibres by electropolymerization, templates such as porous membranes are necessary in the conventional methods. Here we report the electropolymerization of 3,4-ethylenedioxythiophene and its derivatives by alternating current (AC)-bipolar electrolysis. Poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives were found to propagate as a fibre form from the ends of Au wires used as bipolar electrodes (BPEs) parallel to an external electric field, without the use of templates. The effects of applied frequency and of the solvent on the morphology, growth rate and degree of branching of these PEDOT fibres were investigated. In addition, a chain-growth model for the formation of conductive material networks was also demonstrated. PMID:26804140

  3. Tough, processable semi-interpenetrating polymer networks from monomer reactants

    NASA Technical Reports Server (NTRS)

    Pater, Ruth H. (Inventor)

    1994-01-01

    A high temperature semi-interpenetrating polymer network (semi-IPN) was developed which had significantly improved processability, damage tolerance, and mechanical performance, when compared to the commercial Thermid materials. This simultaneous semi-IPN was prepared by mixing the monomer precursors of Thermid AL-600 (a thermoset) and NR-150B2 (a thermoplastic) and allowing the monomers to react randomly upon heating. This reaction occurs at a rate which decreases the flow and broadens the processing window. Upon heating at a higher temperature, there is an increase in flow. Because of the improved flow properties, broadened processing window and enhanced toughness, high strength polymer matrix composites, adhesives and molded articles can now be prepared from the acetylene end-capped polyimides which were previously inherently brittle and difficult to process.

  4. An electroactive polymer energy harvester for wireless sensor networks

    NASA Astrophysics Data System (ADS)

    McKay, T. G.; Rosset, S.; Anderson, I. A.; Shea, H.

    2013-12-01

    This paper reports the design, fabrication, and testing of a soft electroactive polymer power generator that has a volume of 1cm3. The generator provides an opportunity to harvest energy from environmental sources to power wireless sensor networks because it can harvest from low frequency motions, is compact, and lightweight. Electroactive polymers are highly stretchable variable capacitors. Electrical energy is produced when the deformation of a stretched, charged electroactive polymer is relaxed; like-charges are compressed together and opposite-charges are pushed apart, resulting in an increased voltage. Although electroactive polymers have impressively displayed energy densities as high as 550 mJ/g, they have been based on films with thicknesses of tens to hundreds of micrometers, thus a generator covering a large area would be required to provide useful power. Energy harvesters covering large areas are inconvenient to deploy in a wireless sensor network with a large number of nodes, so a generator that is compact in all three dimensions is required. In this work we fabricated a generator that can fit within a 11×11×9 mm envelope by stacking 42, 11mm diameter generator films on top of each other. When compressed cyclically at a rate of 0.5 Hz our generator produced 300 uW of power which is a sufficient amount of power for a low power wireless sensor node. The combination of our generator's small form factor and ability to harvest useful energy from low frequency motions provides an opportunity to deploy large numbers of wireless sensor nodes without the need for periodic, costly battery replacement.

  5. Surprising high hydrophobicity of polymer networks from hydrophilic components.

    PubMed

    Attanasio, Agnese; Bayer, Ilker S; Ruffilli, Roberta; Ayadi, Farouk; Athanassiou, Athanassia

    2013-06-26

    We report a simple and inexpensive method of fabricating highly hydrophobic novel materials based on interpenetrating networks of polyamide and poly(ethyl cyanoacrylate) hydrophilic components. The process is a single-step solution casting from a common solvent, formic acid, of polyamide and ethyl cyanoacrylate monomers. After casting and subsequent solvent evaporation, the in situ polymerization of ethyl cyanoacrylate monomer forms polyamide-poly(ethyl cyanoacrylate) interpenetrating network films. The interpenetrating networks demonstrate remarkable waterproof properties allowing wettability control by modulating the concentration of the components. In contrast, pure polyamide and poly(ethyl cyanoacrylate) films obtained from formic acid solutions are highly hygroscopic and hydrophilic, respectively. The polymerization of ethyl cyanoacrylate in the presence of polyamide promotes molecular interactions between the components, which reduce the available hydrophilic moieties and render the final material hydrophobic. The wettability, morphology, and thermo-physical properties of the polymeric coatings were characterized. The materials developed in this work take advantage of the properties of both polymers in a single blend and above all, due to their hydrophobic nature and minimal water uptake, can extend the application range of the individual polymers where water repellency is required. PMID:23713478

  6. Self-Healing of Polymer Networks with Reversible Bonds

    NASA Astrophysics Data System (ADS)

    Rubinstein, Michael

    2015-03-01

    Self-healing polymeric materials are systems that after damage can revert to their original state with full or partial recovery of mechanical strength. Using scaling theory we study a simple model of autonomic self-healing of polymer networks. In this model one of the two end monomers of each polymer chain is fixed in space mimicking dangling chains attachment to a polymer network, while the sticky monomer at the other end of each chain can form pairwise reversible bond with the sticky end of another chain. We study the reaction kinetics of reversible bonds in this simple model and analyze the different stages in the self-repair process. The formation of bridges and the recovery of the material strength across the fractured interface during the healing period occur appreciably faster after shorter waiting time, during which the fractured surfaces are kept apart. We observe the slowest formation of bridges for self-adhesion after bringing into contact two bare surfaces with equilibrium (very low) density of open stickers in comparison with self-healing. The primary role of anomalous diffusion in material self-repair for short waiting times is established, while at long waiting times the recovery of bonds across fractured interface is due to hopping diffusion of stickers between different bonded partners. Acceleration in bridge formation for self-healing compared to self-adhesion is due to excess nonequilibrium concentration of open stickers. Full recovery of reversible bonds across fractured interface (formation of bridges) occurs after appreciably longer time than the equilibration time of the concentration of reversible bonds in the bulk. The model is extended to describe enhanced toughness of dual networks with both permanent and reversible cross-links. This work was done in collaboration with Drs. Ludwik Leibler, Li-Heng Cai, Evgeny B. Stukalin, N. Arun Kumar and supported by the National Science Foundation.

  7. Time dependent mechanical modeling for polymers based on network theory

    NASA Astrophysics Data System (ADS)

    Billon, Noëlle

    2016-05-01

    Despite of a lot of attempts during recent years, complex mechanical behaviour of polymers remains incompletely modelled, making industrial design of structures under complex, cyclic and hard loadings not totally reliable. The non linear and dissipative viscoelastic, viscoplastic behaviour of those materials impose to take into account non linear and combined effects of mechanical and thermal phenomena. In this view, a visco-hyperelastic, viscoplastic model, based on network description of the material has recently been developed and designed in a complete thermodynamic frame in order to take into account those main thermo-mechanical couplings. Also, a way to account for coupled effects of strain-rate and temperature was suggested. First experimental validations conducted in the 1D limit on amorphous rubbery like PMMA in isothermal conditions led to pretty goods results. In this paper a more complete formalism is presented and validated in the case of a semi crystalline polymer, a PA66 and a PET (either amorphous or semi crystalline) are used. Protocol for identification of constitutive parameters is described. It is concluded that this new approach should be the route to accurately model thermo-mechanical behaviour of polymers using a reduced number of parameters of some physicl meaning.

  8. Interpenetrating polymer network ion exchange membranes and method for preparing same

    DOEpatents

    Alexandratos, Spiro D.; Danesi, Pier R.; Horwitz, E. Philip

    1989-01-01

    Interpenetrating polymer network ion exchange membranes include a microporous polymeric support film interpenetrated by an ion exchange polymer and are produced by absorbing and polymerizing monomers within the support film. The ion exchange polymer provides ion exchange ligands at the surface of and throughout the support film which have sufficient ligand mobility to extract and transport ions across the membrane.

  9. Characterization of a polymer-infiltrated ceramic-network material

    PubMed Central

    Corazza, Pedro H.; Zhang, Yu

    2015-01-01

    Objectives To characterize the microstructure and determine some mechanical properties of a polymer-ingfiltrated ceramic-network (PICN) material (Vita Enamic, Vita Zahnfabrik) available for CAD–CAM systems. Methods Specimens were fabricated to perform quantitative and qualitative analyses of the material’s microstructure and to determine the fracture toughness (KIc), density (ρ), Poisson’s ratio (v) and Young’s modulus (E). KIc was determined using V-notched specimens and the short beam toughness method, where bar-shaped specimens were notched and 3-point loaded to fracture. ρ was calculated using Archimedes principle, and v and E were measured using an ultrasonic thickness gauge with a combination of a pulse generator and an oscilloscope. Results Microstructural analyses showed a ceramic- and a polymer-based interpenetrating network. Mean and standard deviation values for the properties evaluated were: KIc = 1.09 ± 0.05 MPa m1/2, ρ = 2.09 ± 0.01 g/cm3, v = 0.23 ± 0.002 and E = 37.95 ± 0.34 GPa. Significance The PICN material showed mechanical properties between porcelains and resin-based composites, reflecting its microstructural components. PMID:24656471

  10. Modular and Orthogonal Synthesis of Hybrid Polymers and Networks

    PubMed Central

    Liu, Shuang; Dicker, Kevin T.; Jia, Xinqiao

    2015-01-01

    Biomaterials scientists strive to develop polymeric materials with distinct chemical make-up, complex molecular architectures, robust mechanical properties and defined biological functions by drawing inspirations from biological systems. Salient features of biological designs include (1) repetitive presentation of basic motifs; and (2) efficient integration of diverse building blocks. Thus, an appealing approach to biomaterials synthesis is to combine synthetic and natural building blocks in a modular fashion employing novel chemical methods. Over the past decade, orthogonal chemistries have become powerful enabling tools for the modular synthesis of advanced biomaterials. These reactions require building blocks with complementary functionalities, occur under mild conditions in the presence of biological molecules and living cells and proceed with high yield and exceptional selectivity. These chemistries have facilitated the construction of complex polymers and networks in a step-growth fashion, allowing facile modulation of materials properties by simple variations of the building blocks. In this review, we first summarize features of several types of orthogonal chemistries. We then discuss recent progress in the synthesis of step growth linear polymers, dendrimers and networks that find application in drug delivery, 3D cell culture and tissue engineering. Overall, orthogonal reactions and modulular synthesis have not only minimized the steps needed for the desired chemical transformations but also maximized the diversity and functionality of the final products. The modular nature of the design, combined with the potential synergistic effect of the hybrid system, will likely result in novel hydrogel matrices with robust structures and defined functions. PMID:25572255

  11. Self-Healing of Unentangled Polymer Networks with Reversible Bonds

    PubMed Central

    Stukalin, Evgeny B.; Cai, Li-Heng; Kumar, N. Arun; Leibler, Ludwik; Rubinstein, Michael

    2013-01-01

    Self-healing polymeric materials are systems that after damage can revert to their original state with full or partial recovery of mechanical strength. Using scaling theory we study a simple model of autonomic self-healing of unentangled polymer networks. In this model one of the two end monomers of each polymer chain is fixed in space mimicking dangling chains attachment to a polymer network, while the sticky monomer at the other end of each chain can form pairwise reversible bond with the sticky end of another chain. We study the reaction kinetics of reversible bonds in this simple model and analyze the different stages in the self-repair process. The formation of bridges and the recovery of the material strength across the fractured interface during the healing period occur appreciably faster after shorter waiting time, during which the fractured surfaces are kept apart. We observe the slowest formation of bridges for self-adhesion after bringing into contact two bare surfaces with equilibrium (very low) density of open stickers in comparison with self-healing. The primary role of anomalous diffusion in material self-repair for short waiting times is established, while at long waiting times the recovery of bonds across fractured interface is due to hopping diffusion of stickers between different bonded partners. Acceleration in bridge formation for self-healing compared to self-adhesion is due to excess non-equilibrium concentration of open stickers. Full recovery of reversible bonds across fractured interface (formation of bridges) occurs after appreciably longer time than the equilibration time of the concentration of reversible bonds in the bulk. PMID:24347684

  12. Copper-catalyzed azide alkyne cycloaddition polymer networks

    NASA Astrophysics Data System (ADS)

    Alzahrani, Abeer Ahmed

    The click reaction concept, introduced in 2001, has since spurred the rapid development and reexamination of efficient, high yield reactions which proceed rapidly under mild conditions. Prior to the discovery of facile copper catalysis in 2002, the thermally activated azide-alkyne or Huisgen cycloaddition reaction was largely ignored following its discovery in large part due to its slow kinetics, requirement for elevated temperature and limited selectivity. Now, arguably, the most prolific and capable of the click reactions, the copper-catalyzed azide alkyne cycloaddition (CuAAC) reaction is extremely efficient and affords exquisite control of the reaction. The orthogonally and chemoselectivity of this reaction enable its wide utility across varied scientific fields. Despite numerous inherent advantages and widespread use for small molecule synthesis and solution-based polymer chemistry, it has only recently and rarely been utilized to form polymer networks. This work focuses on the synthesis, mechanisms, and unique attributes of the CuAAC reaction for the fabrication of functional polymer networks. The photo-reduction of a series of copper(II)/amine complexes via ligand metal charge transfer was examined to determine their relative efficiency and selectivity in catalyzing the CuAAC reaction. The aliphatic amine ligands were used as an electron transfer species to reduce Cu(II) upon irradiation with 365 nm light while also functioning as an accelerating agent and as protecting ligands for the Cu(I) that was formed. Among the aliphatic amines studied, tertiary amines such as triethylamine (TEA), tetramethyldiamine (TMDA), N,N,N',N",N"-pentamethyldiethylenetriamine (PMDTA), and hexamethylenetetramine (HMTETA) were found to be the most effective. The reaction kinetics were accelerated by increasing the PMDETA : Cu(II) ratio with a ratio of ligand to Cu(II) of 4:1 yielding the maximum conversion in the shortest time. The sequential and orthogonal nature of the photo

  13. Use of Semiflexible Applicators for Radiofrequency Ablation of Liver Tumors

    SciTech Connect

    Gaffke, G. Gebauer, B.; Knollmann, F.D.; Helmberger, T.; Ricke, J.; Oettle, H.; Felix, R.; Stroszczynski, C.

    2006-04-15

    Purpose. To evaluate the feasibility and potential advantages of the radiofrequency ablation of liver tumors using new MRI-compatible semiflexible applicators in a closed-bore high-field MRI scanner. Methods. We treated 8 patients with 12 malignant liver tumors of different origin (5 colorectal carcinoma, 2 cholangiocellular carcinoma, 1 breast cancer) under MRI guidance. Radiofrequency ablation (RFA) was performed using 5 cm Rita Starburst Semi-Flex applicators (Rita Medical Systems, Milwaukee, WI, USA) which are suitable for MR- and CT-guided interventions and a 150 W RF generator. All interventions were performed in a closed-bore 1.5 T high-field MRI scanner for MRI-guided RFA using fast T1-weighted gradient echo sequences and T2-weighted ultra-turbo spin echo sequences. Control and follow-up MRI examinations were performed on the next day, at 6 weeks, and every 3 months after RFA. Control MRI were performed as double-contrast MRI examinations (enhancement with iron oxide and gadopentetate dimeglumine). All interventions were performed with the patient under local anesthesia and analgo-sedation. Results. The mean diameter of the treated hepatic tumors was 2.4 cm ({+-}0.6 cm, range 1.0-3.2 cm). The mean diameter of induced necrosis was 3.1 cm ({+-}0.4 cm). We achieved complete ablation in all patients. Follow-up examinations over a duration of 7 months ({+-}1.3 months, range 4-9 month) showed a local control rate of 100% in this group of patients. All interventions were performed without major complications; only 2 subcapsular hematomas were documented. Conclusion. RFA of liver tumors using semiflexible applicators in closed-bore 1.5 T scanner systems is feasible. These applicators might simplify the RFA of liver tumors under MRI control. The stiff distal part of the applicator facilitates its repositioning.

  14. Tetraarylborate polymer networks as single-ion conducting solid electrolytes

    DOE PAGESBeta

    Van Humbeck, Jeffrey F.; Aubrey, Michael L.; Alsbaiee, Alaaeddin; Ameloot, Rob; Coates, Geoffrey W.; Dichtel, William R.; Long, Jeffrey R.

    2015-06-23

    A new family of solid polymer electrolytes based upon anionic tetrakis(phenyl)borate tetrahedral nodes and linear bis-alkyne linkers is reported. Sonogashira polymerizations using tetrakis(4-iodophenyl)borate, tetrakis(4-iodo-2,3,5,6-tetrafluorophenyl)borate and tetrakis(4-bromo-2,3,5,6-tetrafluorophenyl)borate delivered highly cross-linked polymer networks with both 1,4-diethynylbeznene and a tri(ethylene glycol) substituted derivative. Promising initial conductivity metrics have been observed, including high room temperature conductivities (up to 2.7 × 10-4 S cm-1), moderate activation energies (0.25–0.28 eV), and high lithium ion transport numbers (up to tLi+ = 0.93). Initial investigations into the effects of important materials parameters such as bulk morphology, porosity, fluorination, and other chemical modification, provide starting design parameters for furthermore » development of this new class of solid electrolytes.« less

  15. Tailoring Patterns of Surface-Attached Multiresponsive Polymer Networks.

    PubMed

    Chollet, Benjamin; D'Eramo, Loïc; Martwong, Ekkachai; Li, Mengxing; Macron, Jennifer; Mai, Thuy Quyen; Tabeling, Patrick; Tran, Yvette

    2016-09-21

    A new strategy for the fabrication of micropatterns of surface-attached hydrogels with well-controlled chemistry is reported. The "grafting onto" approach is preferred to the "grafting from" approach. It consists of cross-linking and grafting preformed and functionalized polymer chains through thiol-ene click chemistry. The advantage is a very good control without adding initiators. A powerful consequence of thiol-ene click reaction by UV irradiation is the facile fabrication of micropatterned hydrogel thin films by photolithography. It is achieved either with photomasks using common UV lamp or without photomasks by direct drawing due to laser technology. Our versatile approach allows the fabrication of various chemical polymer networks on various solid substrates. It is demonstrated here with silicon wafers, glass and gold surfaces as substrates, and two responsive hydrogels, poly(N-isopropylacrylamide) for its responsiveness to temperature and poly(acrylic acid) for its pH-sensitivity. We also demonstrate the fabrication of stable hydrogel multilayers (or stacked layers) in which each elementary layer height can widely range from a few nanometers to several micrometers, providing an additional degree of freedom to the internal architecture of hydrogel patterns. This facile route for the synthesis of micrometer-resolute hydrogel patterns with tailored architecture and multiresponsive properties should have a strong impact. PMID:27560306

  16. Tetraarylborate polymer networks as single-ion conducting solid electrolytes

    SciTech Connect

    Van Humbeck, Jeffrey F.; Aubrey, Michael L.; Alsbaiee, Alaaeddin; Ameloot, Rob; Coates, Geoffrey W.; Dichtel, William R.; Long, Jeffrey R.

    2015-06-23

    A new family of solid polymer electrolytes based upon anionic tetrakis(phenyl)borate tetrahedral nodes and linear bis-alkyne linkers is reported. Sonogashira polymerizations using tetrakis(4-iodophenyl)borate, tetrakis(4-iodo-2,3,5,6-tetrafluorophenyl)borate and tetrakis(4-bromo-2,3,5,6-tetrafluorophenyl)borate delivered highly cross-linked polymer networks with both 1,4-diethynylbeznene and a tri(ethylene glycol) substituted derivative. Promising initial conductivity metrics have been observed, including high room temperature conductivities (up to 2.7 × 10-4 S cm-1), moderate activation energies (0.25–0.28 eV), and high lithium ion transport numbers (up to tLi+ = 0.93). Initial investigations into the effects of important materials parameters such as bulk morphology, porosity, fluorination, and other chemical modification, provide starting design parameters for further development of this new class of solid electrolytes.

  17. Cascade synthesis of a gold nanoparticle-network polymer composite

    NASA Astrophysics Data System (ADS)

    Grubjesic, Simonida; Ringstrand, Bryan S.; Jungjohann, Katherine L.; Brombosz, Scott M.; Seifert, Sönke; Firestone, Millicent A.

    2016-01-01

    The multi-step, cascade synthesis of a self-supporting, hierarchically-structured gold nanoparticle hydrogel composite is described. The composite is spontaneously prepared from a non-covalent, lamellar lyotropic mesophase composed of amphiphiles that support the reactive constituents, a mixture of hydroxyl- and acrylate-end-derivatized PEO117-PPO47-PEO117 and [AuCl4]-. The reaction sequence begins with the auto-reduction of aqueous [AuCl4]- by PEO117-PPO47-PEO117 which leads to both the production of Au NPs and the free radical initiated polymerization and crosslinking of the acrylate end-derivatized PEO117-PPO47-PEO117 to yield a network polymer. Optical spectroscopy and TEM monitored the reduction of [AuCl4]-, formation of large aggregated Au NPs and oxidative etching into a final state of dispersed, spherical Au NPs. ATR/FT-IR spectroscopy and thermal analysis confirms acrylate crosslinking to yield the polymer network. X-ray scattering (SAXS and WAXS) monitored the evolution of the multi-lamellar structured mesophase and revealed the presence of semi-crystalline PEO confined within the water layers. The hydrogel could be reversibly swollen without loss of the well-entrained Au NPs with full recovery of composite structure. Optical spectroscopy shows a notable red shift (Δλ ~ 45 nm) in the surface plasmon resonance between swollen and contracted states, demonstrating solvent-mediated modulation of the internal NP packing arrangement.The multi-step, cascade synthesis of a self-supporting, hierarchically-structured gold nanoparticle hydrogel composite is described. The composite is spontaneously prepared from a non-covalent, lamellar lyotropic mesophase composed of amphiphiles that support the reactive constituents, a mixture of hydroxyl- and acrylate-end-derivatized PEO117-PPO47-PEO117 and [AuCl4]-. The reaction sequence begins with the auto-reduction of aqueous [AuCl4]- by PEO117-PPO47-PEO117 which leads to both the production of Au NPs and the free radical

  18. Modeling Methane Adsorption in Interpenetrating Porous Polymer Networks

    SciTech Connect

    Martin, RL; Shahrak, MN; Swisher, JA; Simon, CM; Sculley, JP; Zhou, HC; Smit, B; Haranczyk, M

    2013-10-03

    Porous polymer networks (PPNs) are a class of porous materials of particular interest in a variety of energy-related applications because of their stability, high surface areas, and gas uptake capacities. Computationally derived structures for five recently synthesized PPN frameworks, PPN-2, -3, -4, -5, and -6, were generated for various topologies, optimized using semiempirical electronic structure methods, and evaluated using classical grand canonical Monte Carlo simulations. We show that a key factor in modeling the methane uptake performance of these materials is whether, and how, these material frameworks interpenetrate and demonstrate a computational approach for predicting the presence, degree, and nature of interpenetration in PPNs that enables the reproduction of experimental adsorption data.

  19. Defects on semiflexible filaments: Kinks and twist kinks

    NASA Astrophysics Data System (ADS)

    Lee, Nam-Kyung; Johner, Albert

    2016-04-01

    Due to local interactions with ligands or to global constraints, semiflexible filaments can exhibit localized defects. We focus on filaments laying flat on a surface. The two lowest order singularities are addressed: discontinuities of the orientation, which are called kink, and discontinuities of the curvature. The latter are called twist kinks in flattened helical filaments where they can form spontaneously. We calculate the partition functions for a given defect fugacity and discuss some often measured quantities like the correlation of the orientation along the filament.

  20. Recycling of textile dye using double network polymer from sodium alginate and superabsorbent polymer.

    PubMed

    Dhanapal, V; Subramanian, K

    2014-08-01

    Double network polymers (DNP) of different compositions were photosynthesized using sodium alginate (NaAlg) and superabsorbent polymer (SAP). They were characterized by FT-IR, thermal stability (TG), morphology by scanning electron microscopy (SEM), and its mechanical properties were also evaluated for their dye adsorption-desorption characteristics via adsorption isotherms at different temperature and pH values. The spectrophotometric determination of adsorbed dye indicated that the maximum dye uptake in column mode was 439 mg/g. The nearly identical visible absorption spectra of the fabrics dyed with virgin and recovered dyes indicated that the recovered dye retained its structural stability during column recovery and the dyed fabrics possess good color fastness properties. Dye adsorption kinetic and de-sorption mechanism were found to be pseudo-first-order and non-Fickian, respectively. The adsorption showed best fit for Langmuir adsorption isotherm. The changes in the thermodynamic parameters namely Gibbs free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°) for the dye-adsorbent systems inferred that the adsorption process was spontaneous and exothermic.

  1. Structural Properties and Phase Behavior of Crosslinked Networks in Polymer Solutions

    PubMed Central

    Benmouna, Farida; Zemmour, Samira; Benmouna, Mustapha

    2016-01-01

    ABSTRACT Structural properties and phase behavior of crosslinked networks embedded in polymer solutions are theoretically investigated. The partial structure factor of the network is calculated using a matrix formulation of the random phase approximation and the forward scattering limit is correlated with the phase behavior. Swelling and deswelling processes are analyzed in terms of the polymer concentration, the mismatch of solvent quality with respect to polymer and network, the polymers incompatibility and their characteristic sizes. Most studies reported so far in the literature have focussed on the swelling of crosslinked networks and gels in pure solvents but the correlation of the structural properties with the phase behavior in the presence of high molecular weight polymers in solution has not been given sufficient attention. The present work is intended to fill this gap in view of the current efforts to develop novel drug encapsulating and targeted delivery devices. PMID:27134310

  2. Cooperative motion of intrinsic and actuated semiflexible swimmers

    NASA Astrophysics Data System (ADS)

    Llopis, I.; Pagonabarraga, I.; Cosentino Lagomarsino, M.; Lowe, C. P.

    2013-03-01

    We examine the phenomenon of hydrodynamic-induced cooperativity for pairs of flagellated micro-organism swimmers, of which spermatozoa cells are an example. We consider semiflexible swimmers, where inextensible filaments are driven by an internal intrinsic force and torque-free mechanism (intrinsic swimmers). The velocity gain for swimming cooperatively, which depends on both the geometry and the driving, develops as a result of the near-field coupling of bending and hydrodynamic stresses. We identify the regimes where hydrodynamic cooperativity is advantageous and quantify the change in efficiency. When the filaments' axes are parallel, hydrodynamic interaction induces a directional instability that causes semiflexible swimmers that profit from swimming together to move apart from each other. Biologically, this implies that flagella need to select different synchronized collective states and to compensate for directional instabilities (e.g., by binding) in order to profit from swimming together. By analyzing the cooperative motion of pairs of externally actuated filaments, we assess the impact that stress distribution along the filaments has on their collective displacements.

  3. Dynamic assembly of polymer nanotube networks via kinesin powered microtubule filaments

    NASA Astrophysics Data System (ADS)

    Paxton, Walter F.; Bouxsein, Nathan F.; Henderson, Ian M.; Gomez, Andrew; Bachand, George D.

    2015-06-01

    We describe for the first time how biological nanomotors may be used to actively self-assemble mesoscale networks composed of diblock copolymer nanotubes. The collective force generated by multiple kinesin nanomotors acting on a microtubule filament is large enough to overcome the energy barrier required to extract nanotubes from polymer vesicles comprised of poly(ethylene oxide-b-butadiene) in spite of the higher force requirements relative to extracting nanotubes from lipid vesicles. Nevertheless, large-scale polymer networks were dynamically assembled by the motors. These networks displayed enhanced robustness, persisting more than 24 h post-assembly (compared to 4-5 h for corresponding lipid networks). The transport of materials in and on the polymer membranes differs substantially from the transport on analogous lipid networks. Specifically, our data suggest that polymer mobility in nanotubular structures is considerably different from planar or 3D structures, and is stunted by 1D confinement of the polymer subunits. Moreover, quantum dots adsorbed onto polymer nanotubes are completely immobile, which is related to this 1D confinement effect and is in stark contrast to the highly fluid transport observed on lipid tubules.We describe for the first time how biological nanomotors may be used to actively self-assemble mesoscale networks composed of diblock copolymer nanotubes. The collective force generated by multiple kinesin nanomotors acting on a microtubule filament is large enough to overcome the energy barrier required to extract nanotubes from polymer vesicles comprised of poly(ethylene oxide-b-butadiene) in spite of the higher force requirements relative to extracting nanotubes from lipid vesicles. Nevertheless, large-scale polymer networks were dynamically assembled by the motors. These networks displayed enhanced robustness, persisting more than 24 h post-assembly (compared to 4-5 h for corresponding lipid networks). The transport of materials in and on

  4. Polymer network/carbon layer on monolith support and monolith catalytic reactor

    DOEpatents

    Nordquist, Andrew Francis; Wilhelm, Frederick Carl; Waller, Francis Joseph; Machado, Reinaldo Mario

    2003-08-26

    The present invention relates to an improved monolith catalytic reactor and a monolith support. The improvement in the support resides in a polymer network/carbon coating applied to the surface of a porous substrate and a catalytic metal, preferably a transition metal catalyst applied to the surface of the polymer network/carbon coating. The monolith support has from 100 to 800 cells per square inch and a polymer network/carbon coating with surface area of from 0.1 to 15 m.sup.2 /gram as measured by adsorption of N.sub.2 or Kr using the BET method.

  5. From ribbons to networks: hierarchical organization of DNA-grafted supramolecular polymers.

    PubMed

    Vyborna, Yuliia; Vybornyi, Mykhailo; Häner, Robert

    2015-11-11

    DNA-grafted supramolecular polymers (SPs) allow the programmed organization of DNA in a highly regular, one-dimensional array. Oligonucleotides are arranged along the edges of pyrene-based helical polymers. Addition of complementary oligonucleotides triggers the assembly of individual nanoribbons resulting in the development of extended supramolecular networks. Network formation is enabled by cooperative coaxial stacking interactions of terminal GC base pairs. The process is accompanied by structural changes in the pyrene polymer core that can be followed spectroscopically. Network formation is reversible, and disassembly into individual ribbons is realized either via thermal denaturation or by addition of a DNA separator strand.

  6. From ribbons to networks: hierarchical organization of DNA-grafted supramolecular polymers.

    PubMed

    Vyborna, Yuliia; Vybornyi, Mykhailo; Häner, Robert

    2015-11-11

    DNA-grafted supramolecular polymers (SPs) allow the programmed organization of DNA in a highly regular, one-dimensional array. Oligonucleotides are arranged along the edges of pyrene-based helical polymers. Addition of complementary oligonucleotides triggers the assembly of individual nanoribbons resulting in the development of extended supramolecular networks. Network formation is enabled by cooperative coaxial stacking interactions of terminal GC base pairs. The process is accompanied by structural changes in the pyrene polymer core that can be followed spectroscopically. Network formation is reversible, and disassembly into individual ribbons is realized either via thermal denaturation or by addition of a DNA separator strand. PMID:26491956

  7. Trimethylene carbonate and epsilon-caprolactone based (co)polymer networks: mechanical properties and enzymatic degradation.

    PubMed

    Bat, Erhan; Plantinga, Josée A; Harmsen, Martin C; van Luyn, Marja J A; Zhang, Zheng; Grijpma, Dirk W; Feijen, Jan

    2008-11-01

    High molecular weight trimethylene carbonate (TMC) and epsilon-caprolactone (CL) (co)polymers were synthesized. Melt pressed (co)polymer films were cross-linked by gamma irradiation (25 kGy or 50 kGy) in vacuum, yielding gel fractions of up to 70%. The effects of copolymer composition and irradiation dose on the cytotoxicity, surface properties, degradation behavior, and mechanical and thermal properties of these (co)polymers and networks were investigated. Upon incubation with cell culture medium containing extracts of (co)polymers and networks, human foreskin fibroblasts remained viable. For all (co)polymers and networks, cell viabilities were determined to be higher than 94%. The formed networks were flexible, with elastic moduli ranging from 2.7 to 5.8 MPa. Moreover, these form-stable networks were creep resistant under dynamic conditions. The permanent deformation after 2 h relaxation was as low as 1% after elongating to 50% strain for 20 times. The in vitro enzymatic erosion behavior of these hydrophobic (co)polymers and networks was investigated using aqueous lipase solutions. The erosion rates in lipase solution could be tuned linearly from 0.8 to 45 mg/(cm (2) x day) by varying the TMC to CL ratio and the irradiation dose. The copolymers and networks degraded essentially by a surface erosion mechanism. PMID:18855440

  8. SANS measurements of semiflexible xyloglucan polysaccharide chains in water reveal their self-avoiding statistics.

    PubMed

    Muller, François; Manet, Sabine; Jean, Bruno; Chambat, Gérard; Boué, François; Heux, Laurent; Cousin, Fabrice

    2011-09-12

    We explored the behavior and the characteristics of xyloglucan polysaccharide chains extracted from tamarind seeds in aqueous media. The initial solubilization is achieved by using a 0.01 M NaOH solution. The absence of compact aggregates in the solution and the average molecular mass of the individual chains were unambiguously demonstrated by size exclusion chromatography with multi-angle light scattering detection. The composition and the stability of the solution were quantitatively checked over weeks by using liquid state nuclear magnetic resonance with DMSO as internal standard. The conformational characteristics of the chains were measured using nondestructive small-angle neutron scattering (SANS). The unambiguous determination of the Flory exponent (ν = 0.588) by SANS enabled us to directly prove that xyloglucan chains in water behave like semiflexible worm-like chains with excluded volume statistics (good solvent), contrary to most of the neutral water-soluble polymer chains that rather exhibit Gaussian statistics (θ-solvent). In addition to the Flory exponent, the persistence length l(p) and the cross section of the chains were also determined by SANS with utmost precision, with values of 80 and of 7 Å, respectively, which provides a complete description of the conformational characteristics of XG chains at all relevant length scales.

  9. SANS measurements of semiflexible xyloglucan polysaccharide chains in water reveal their self-avoiding statistics.

    PubMed

    Muller, François; Manet, Sabine; Jean, Bruno; Chambat, Gérard; Boué, François; Heux, Laurent; Cousin, Fabrice

    2011-09-12

    We explored the behavior and the characteristics of xyloglucan polysaccharide chains extracted from tamarind seeds in aqueous media. The initial solubilization is achieved by using a 0.01 M NaOH solution. The absence of compact aggregates in the solution and the average molecular mass of the individual chains were unambiguously demonstrated by size exclusion chromatography with multi-angle light scattering detection. The composition and the stability of the solution were quantitatively checked over weeks by using liquid state nuclear magnetic resonance with DMSO as internal standard. The conformational characteristics of the chains were measured using nondestructive small-angle neutron scattering (SANS). The unambiguous determination of the Flory exponent (ν = 0.588) by SANS enabled us to directly prove that xyloglucan chains in water behave like semiflexible worm-like chains with excluded volume statistics (good solvent), contrary to most of the neutral water-soluble polymer chains that rather exhibit Gaussian statistics (θ-solvent). In addition to the Flory exponent, the persistence length l(p) and the cross section of the chains were also determined by SANS with utmost precision, with values of 80 and of 7 Å, respectively, which provides a complete description of the conformational characteristics of XG chains at all relevant length scales. PMID:21806009

  10. Synthesis and characterization of polymers and interpenetrating polymer networks (IPNs) with nonlinear optical (NLO) properties and related numerical studies

    NASA Astrophysics Data System (ADS)

    Sharma, P. R. Srikanth

    Copolymers of methyl methacrylate (MMA) and 2-propenoic acid, 2-methyl-, 2-[[[[4-methyl-3-[[[2-methyl-4-nitrophenyl)amino]carbonyl]aminophenyl]carbonyl]oxy]ethyl ester (PAMEE) exhibiting nonlinear optical (NLO) properties have been synthesized. Two kinds of urethane containing interpenetrating polymer networks (IPNs), consisting of nonlinear optical (NLO) chromophore, 2-methyl-4-nitroaniline (MNA) or Disperse Red1 (DR1) have been synthesized. The IPN systems consist of either aliphatic polycarbonate urethane (PCU) or 2,6-dimethyl-1,4-phenylene oxide (PPO) as one network and crosslinked poly (MMA-co-PAMEE) or poly (MMA-co-PMNEE) as the second network. Copolymers and interpenetrating polymer networks (IPNs) were characterized by IR spectroscopy, UV-VIS spectroscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and second harmonic generation (SHG) measurements. The thin films of copolymers and IPNs were optically transparent and the corona poled polymers produced relatively large and stable SHG signals at room temperature. To understand the polarization decay of our NLO polymer we studied a simple theoretical model which can account for the main features which we observe. The addition of an apparent "chemical" reaction with a reaction activation energy EAB to the neighbor-facilitated Fredrickson-Anderson model shows the existence of a beta relaxation occurring simultaneously with the main alpha process. The combination of an Ising-model with antiferromagnetic interaction and the neighbor-facilitated Fredrickson-Anderson model allows a description of the polarization decay of polarized materials, such as our polymers, below the glass transition temperature Tg. The relaxation time for the polarization scales with the relaxation time of the alpha-process of the glass transition, and shows a typical curvature in the ln tau versus T-1 plot. Real polymers, such as poly(MMA-co-PAMEE) which we study possess both of these features and its

  11. Patterned silver nanoparticles embedded in a nanoporous smectic liquid crystalline polymer network.

    PubMed

    Dasgupta, Debarshi; Shishmanova, Ivelina K; Ruiz-Carretero, Amparo; Lu, Kangbo; Verhoeven, Martinus; van Kuringen, Huub P C; Portale, Giuseppe; Leclère, Philippe; Bastiaansen, Cees W M; Broer, Dirk J; Schenning, Albertus P H J

    2013-07-31

    A nanoporous smectic liquid crystalline polymer network has been exploited to fabricate photo patternable organic-inorganic hybrid materials, wherein, the nanoporous channels control the diameter and orientational order of the silver nanoparticles.

  12. Template-mediated nano-crystallite networks in semiconducting polymers

    NASA Astrophysics Data System (ADS)

    Kwon, Sooncheol; Yu, Kilho; Kweon, Kyoungchun; Kim, Geunjin; Kim, Junghwan; Kim, Heejoo; Jo, Yong-Ryun; Kim, Bong-Joong; Kim, Jehan; Lee, Seoung Ho; Lee, Kwanghee

    2014-06-01

    Unlike typical inorganic semiconductors with a crystal structure, the charge dynamics of π-conjugated polymers (π-CPs) are severely limited by the presence of amorphous portions between the ordered crystalline regions. Thus, the formation of interconnected pathways along crystallites of π-CPs is desired to ensure highly efficient charge transport in printable electronics. Here we report the formation of nano-crystallite networks in π-CP films by employing novel template-mediated crystallization (TMC) via polaron formation and electrostatic interaction. The lateral and vertical charge transport of TMC-treated films increased by two orders of magnitude compared with pristine π-CPs. In particular, because of the unprecedented room temperature and solution-processing advantages of our TMC method, we achieve a field-effect mobility of 0.25 cm2 V-1 s-1 using a plastic substrate, which corresponds to the highest value reported thus far. Because our findings can be applied to various π-conjugated semiconductors, our approach is universal and is expected to yield high-performance printable electronics.

  13. Pattern Formations in Polymer-Molecular Motor Networks

    NASA Astrophysics Data System (ADS)

    Smith, David; Humphrey, David; Duggan, Cynthia; Käs, Josef

    2001-03-01

    In previous studies with the microtubule-kinesin system, organized patterns such as asters and rotating vortices have been seen (Nedelec et al, Nature 1997), which were of a dynamic nature and dependent on active motors. A similar system was constructed using actin and myosin, which displays similar patterns, however, with drastically different dynamics. These patterns arise independent of the initial amount of immediate use energy (in the form of ATP), assembling only upon the near exhaustion of available ATP. Further studies have clearly shown that in fact these patterns are not dependent upon the motor activity of the myosin but its propensity to serve as a cross-linking element in an actin network, with the motor activity serving to prevent the arising of order in the system. We believe the dynamic differences inherent between the two polymer-motor systems studied lies primarily in the structural nature of the motor complexes, with the kinesin complex ordering the system by pushing multiple filaments in a parallel direction, and the myosin complexes disordering the system by pushing filaments in an antiparallel manner.

  14. Cytotoxicity and genotoxicity of superporous hydrogel containing interpenetrating polymer networks.

    PubMed

    Yin, Lichen; Zhao, Xin; Cui, Liming; Ding, Jieying; He, Miao; Tang, Cui; Yin, Chunhua

    2009-06-01

    The superporous hydrogel containing poly(acrylic acid-co-acrylamide)/O-carboxymethyl chitosan (O-CMC) interpenetrating polymer networks (SPH-IPN) that had been developed as an oral delivery vehicle for protein drugs was subject to cytotoxicity and genotoxicity testing, thus evaluating its biological safety in use. In a battery of cytotoxicity assays on RBL-2H3 and Caco-2 cells, the SPH-IPN caused minimal damage towards cell viability, lysosomal activity, and metabolic activity following both direct and indirect treatment. The SPH-IPN did not induce cell apoptosis or DNA breakage in the above cell lines; it did not increase micronucleus (MN) incidence in mouse bone marrow, either. Therefore, the SPH-IPN was preliminarily considered to be biocompatible and might be a safe carrier for protein drugs. In addition, using the HPLC method, residual acrylic acid, acrylamide, and glutaraldehyde in the SPH-IPN were quantified to be 1.4, 2.0, and below 0.2 ppm, respectively. Lack of these low molecular monomers and crosslinker that were mainly responsible for the toxicity provided evidence for the good biocompatibility of the SPH-IPN. PMID:19425232

  15. Probing Rubber Cross-Linking Generation of Industrial Polymer Networks at Nanometer Scale.

    PubMed

    Gabrielle, Brice; Gomez, Emmanuel; Korb, Jean-Pierre

    2016-06-23

    We present improved analyses of rheometric torque measurements as well as (1)H double-quantum (DQ) nuclear magnetic resonance (NMR) buildup data on polymer networks of industrial compounds. This latter DQ NMR analysis allows finding the distribution of an orientation order parameter (Dres) resulting from the noncomplete averaging of proton dipole-dipole couplings within the cross-linked polymer chains. We investigate the influence of the formulation (filler and vulcanization systems) as well as the process (curing temperature) ending to the final polymer network. We show that DQ NMR follows the generation of the polymer network during the vulcanization process from a heterogeneous network to a very homogeneous one. The time variations of microscopic Dres and macroscopic rheometric torques present power-law behaviors above a threshold time scale with characteristic exponents of the percolation theory. We observe also a very good linear correlation between the kinetics of Dres and rheometric data routinely performed in industry. All these observations confirm the description of the polymer network generation as a critical phenomenon. On the basis of all these results, we believe that DQ NMR could become a valuable tool for investigating in situ the cross-linking of industrial polymer networks at the nanometer scale. PMID:27254797

  16. Probing Rubber Cross-Linking Generation of Industrial Polymer Networks at Nanometer Scale.

    PubMed

    Gabrielle, Brice; Gomez, Emmanuel; Korb, Jean-Pierre

    2016-06-23

    We present improved analyses of rheometric torque measurements as well as (1)H double-quantum (DQ) nuclear magnetic resonance (NMR) buildup data on polymer networks of industrial compounds. This latter DQ NMR analysis allows finding the distribution of an orientation order parameter (Dres) resulting from the noncomplete averaging of proton dipole-dipole couplings within the cross-linked polymer chains. We investigate the influence of the formulation (filler and vulcanization systems) as well as the process (curing temperature) ending to the final polymer network. We show that DQ NMR follows the generation of the polymer network during the vulcanization process from a heterogeneous network to a very homogeneous one. The time variations of microscopic Dres and macroscopic rheometric torques present power-law behaviors above a threshold time scale with characteristic exponents of the percolation theory. We observe also a very good linear correlation between the kinetics of Dres and rheometric data routinely performed in industry. All these observations confirm the description of the polymer network generation as a critical phenomenon. On the basis of all these results, we believe that DQ NMR could become a valuable tool for investigating in situ the cross-linking of industrial polymer networks at the nanometer scale.

  17. - and Two-Bead Microrheology in Semiflexible Biopolymer Solutions

    NASA Astrophysics Data System (ADS)

    Schmidt, Christoph

    2002-03-01

    We have used one and two-particle microrheology, employing micron-sized embedded beads and laser interferometric displacement detection, to study the rheological properties of entangled solutions of semiflexible biopolymers. Microrheology has distinct advantages over conventional macrorheology, particularly in expanding the bandwidth of detection, in probing true linear response, and in making it possible to measure solvent draining compressional elastic modes. Experiments on the filamentous fd virus will be reported. Thermal fluctuations of the embedded probes were measured and the viscoelastic parameters of the embedding medium were derived. In two-particle microrheology the correlated motions of two identical particles separated by a varying distance in the medium are analyzed, which can avoid biased results due to surface depletion effects near the probes. Particular emphasis was placed on the comparison between the one- and two-particle results.

  18. Biodegradability of regenerated cellulose films coated with polyurethane/natural polymers interpenetrating polymer networks

    SciTech Connect

    Zhang, L.; Zhou, J.; Huang, J.; Gong, P. Zhou, Q.; Zheng, L.; Du, Y.

    1999-11-01

    Interpenetrating polymer network (IPN) coatings synthesized from castor-oil-based polyurethane (PU) with chitosan, nitrocellulose, or elaeostearin were coated on regenerated cellulose (RC) film for curing at 80--100 C for 2--5 min, providing biodegradable, water-resistant cellulose films coded, respectively, as RCCH, RCNC, and RCEs. The coated films were buried in natural soil for decaying and inoculated with a spore suspension of fungi on the agar medium, respectively, to test biodegradability. The viscosity-average molecular weight, M{sub {eta}}, and the weight of the degraded films decreased sharply with the progress of degradation. The degradation half-lifes, t{sub 1/2}, of the films in soil at 30 C were found to be 19 days for RC, 25 days for RCNC, 32 days for RCCH, and 45 days for the RCEs films. Scanning electron microscopy (SEM) showed that the extent of decay followed in the order RC {gt} RCNC {gt} RCCH {gt} RCEs. SEM, infrared (IR), high-performance liquid chromatography (HPLC), and CO{sub 2} evolution results indicated that the microorganisms directly attacked the water-resistant coating layer and then penetrated into the cellulose to speedily metabolize, while accompanying with producing CO{sub 2}, H{sub 2}O, glucose cleaved from cellulose, and small molecules decomposed from the coatings.

  19. Hybrid polymer networks as ultra low `k` dielectric layers

    DOEpatents

    Lewicki, James; Worsley, Marcus A.

    2016-02-16

    According to one embodiment, a polymeric material includes at least one polydimethylsiloxane (PDMS) polymer, and at least one polyhedral oligomericsilsequioxane (POSS) molecule. According to another embodiment, a method includes providing at least one polydimethylsiloxane (PDMS) polymer, providing at least one polyhedral oligomericsilsequioxane (POSS) molecule, and coupling the at least one PDSM polymer to the at least one POSS molecule to form a hybrid polymeric material.

  20. Interpenetrating polymer network approach to tougher and more microcracking resistant high temperature polymers. I - LaRC-RP40

    NASA Technical Reports Server (NTRS)

    Pater, Ruth H.; Morgan, Cassandra D.

    1988-01-01

    Interpenetrating polymer networks in the form of the LaRC-RP40 resin, prepared by the in situ polymerization of a thermosetting imide prepolymer and thermoplastic monomer reactants, are presently used to obtain toughness and microcracking resistance in a high-temperature polymer. Attention is presently given to the processing, physical, and mechanical properties, as well as the thermooxidative stability, of both the neat resin and the resin as a graphite fiber-reinforced matrix. Microcracking after thermal cycling was also tested. LaRC-RP40 exhibits significant resin fracture toughness improvements over the PMR-15 high-temperature matrix resin.

  1. Analytical theory of polymer-network-mediated interaction between colloidal particles.

    PubMed

    Di Michele, Lorenzo; Zaccone, Alessio; Eiser, Erika

    2012-06-26

    Nanostructured materials based on colloidal particles embedded in a polymer network are used in a variety of applications ranging from nanocomposite rubbers to organic-inorganic hybrid solar cells. Further, polymer-network-mediated colloidal interactions are highly relevant to biological studies whereby polymer hydrogels are commonly employed to probe the mechanical response of living cells, which can determine their biological function in physiological environments. The performance of nanomaterials crucially relies upon the spatial organization of the colloidal particles within the polymer network that depends, in turn, on the effective interactions between the particles in the medium. Existing models based on nonlocal equilibrium thermodynamics fail to clarify the nature of these interactions, precluding the way toward the rational design of polymer-composite materials. In this article, we present a predictive analytical theory of these interactions based on a coarse-grained model for polymer networks. We apply the theory to the case of colloids partially embedded in cross-linked polymer substrates and clarify the origin of attractive interactions recently observed experimentally. Monte Carlo simulation results that quantitatively confirm the theoretical predictions are also presented. PMID:22679289

  2. Dynamic assembly of polymer nanotube networks via kinesin powered microtubule filaments

    DOE PAGESBeta

    Paxton, Walter F.; Bachand, George D.; Gomez, Andrew; Henderson, Ian M.; Bouxsein, Nathan F.

    2015-04-24

    In this study, we describe for the first time how biological nanomotors may be used to actively self-assemble mesoscale networks composed of diblock copolymer nanotubes. The collective force generated by multiple kinesin nanomotors acting on a microtubule filament is large enough to overcome the energy barrier required to extract nanotubes from polymer vesicles comprised of poly(ethylene oxide-b-butadiene) in spite of the higher force requirements relative to extracting nanotubes from lipid vesicles. Nevertheless, large-scale polymer networks were dynamically assembled by the motors. These networks displayed enhanced robustness, persisting more than 24 h post-assembly (compared to 4–5 h for corresponding lipid networks).more » The transport of materials in and on the polymer membranes differs substantially from the transport on analogous lipid networks. Specifically, our data suggest that polymer mobility in nanotubular structures is considerably different from planar or 3D structures, and is stunted by 1D confinement of the polymer subunits. Moreover, quantum dots adsorbed onto polymer nanotubes are completely immobile, which is related to this 1D confinement effect and is in stark contrast to the highly fluid transport observed on lipid tubules.« less

  3. Dynamic assembly of polymer nanotube networks via kinesin powered microtubule filaments.

    PubMed

    Paxton, Walter F; Bouxsein, Nathan F; Henderson, Ian M; Gomez, Andrew; Bachand, George D

    2015-07-01

    We describe for the first time how biological nanomotors may be used to actively self-assemble mesoscale networks composed of diblock copolymer nanotubes. The collective force generated by multiple kinesin nanomotors acting on a microtubule filament is large enough to overcome the energy barrier required to extract nanotubes from polymer vesicles comprised of poly(ethylene oxide-b-butadiene) in spite of the higher force requirements relative to extracting nanotubes from lipid vesicles. Nevertheless, large-scale polymer networks were dynamically assembled by the motors. These networks displayed enhanced robustness, persisting more than 24 h post-assembly (compared to 4-5 h for corresponding lipid networks). The transport of materials in and on the polymer membranes differs substantially from the transport on analogous lipid networks. Specifically, our data suggest that polymer mobility in nanotubular structures is considerably different from planar or 3D structures, and is stunted by 1D confinement of the polymer subunits. Moreover, quantum dots adsorbed onto polymer nanotubes are completely immobile, which is related to this 1D confinement effect and is in stark contrast to the highly fluid transport observed on lipid tubules.

  4. Dynamic assembly of polymer nanotube networks via kinesin powered microtubule filaments

    SciTech Connect

    Paxton, Walter F.; Bachand, George D.; Gomez, Andrew; Henderson, Ian M.; Bouxsein, Nathan F.

    2015-04-24

    In this study, we describe for the first time how biological nanomotors may be used to actively self-assemble mesoscale networks composed of diblock copolymer nanotubes. The collective force generated by multiple kinesin nanomotors acting on a microtubule filament is large enough to overcome the energy barrier required to extract nanotubes from polymer vesicles comprised of poly(ethylene oxide-b-butadiene) in spite of the higher force requirements relative to extracting nanotubes from lipid vesicles. Nevertheless, large-scale polymer networks were dynamically assembled by the motors. These networks displayed enhanced robustness, persisting more than 24 h post-assembly (compared to 4–5 h for corresponding lipid networks). The transport of materials in and on the polymer membranes differs substantially from the transport on analogous lipid networks. Specifically, our data suggest that polymer mobility in nanotubular structures is considerably different from planar or 3D structures, and is stunted by 1D confinement of the polymer subunits. Moreover, quantum dots adsorbed onto polymer nanotubes are completely immobile, which is related to this 1D confinement effect and is in stark contrast to the highly fluid transport observed on lipid tubules.

  5. Tuning the Photoinduced Motion of Glassy Azobenzene Polymers and Networks

    NASA Astrophysics Data System (ADS)

    Vaia, R. A.

    2013-03-01

    Continual innovation at the forefront of soft-matter, in areas such as liquid crystal networks, nano-composites and bio-molecules, is providing exciting opportunities to create smart materials systems that exhibit a controlled, reproducible and reversible modulation of physical properties. These material systems evoke the adaptivity of natural organisms, and inspire radical aerospace notions. A key example is photo-responsive polymers, which convert a light stimulus input into a mechanical output (work). Photoinduced conformational changes, such as within azobenzene, dictate molecular-level distortions that summate into a macroscopic strain, which often manifests as a shape change or motion. The transduction of the molecular-level response to a macroscale effect is regulated by mesoscopic features, such as chain packing, free volume, and local molecular order - factors which depend on chemical composition as well as the process history of the material. For example, physical aging increases the density of the glass, reduces local free volume, and thus decreases the minima in local conformation space which strongly influences the azobenzene photochemistry (trans-cis-trans isomerization). The subsequent change in the energy landscape of the system reduces the fraction of azobenzene able to undergo reconfiguration as well as increases the probability that those photoinduced conformations will relax back to the initial local environment. The result is a tuning of the magnitude of macroscopic strain and the ability to shift from shape fixing to shape recovery, respectively. Work done in collaboration with H. Koerner, K.M. Lee, M. Smith, D. Wang, L-S. Tan. and T. White, Air Force Research Laboratory.

  6. Morphological control of inter-penetrating polymer networks

    NASA Technical Reports Server (NTRS)

    Hansen, Marion

    1989-01-01

    Synthetic organic polymer chemistry has been successful in producing composition of matter with thermal oxidation stability and progressively higher glass transition temperatures. In part, this was done by increasing the steric-hindrance of moieties in the chain of a macromolecule. The resulting polymers are usually quite insoluble and produce molten polymers of very high viscosities. These types of polymers are not easily processed into graphite fiber prepregs by melt or solution impregnation methods. Hence, a technological need exists to produce new knowledge of how to produce polymer-fiber composites from this class of polymers. The concept of freeze drying amic-acid prepolymers with reactive thermoplastic was proposed as a research topic for the ASEE/NASA Summer Faculty Program of 1989 as a means of producing polymer-fiber composites. This process scheme has the thermodynamic attribute that the magnitude of phase separation due to differences in solubility of two organic constituents in solution will be greatly reduced by removing a solvent not by evaporation but by sublimation. Progress to date on evaluating this polymer processing concept is briefly outlined.

  7. Enhancement and restriction of chain motion in polymer networks.

    PubMed

    Hudson, Sarah P; Owens, Eleanor; Hughes, Helen; McLoughlin, Peter

    2012-07-01

    Sevelamer carbonate, a polymeric drug, adsorbs phosphate ions from the gastro intestine of patients suffering from chronic kidney disease. Polymer chain mobility becomes critical during its manufacture and storage. How the polymer chain mobility in sevelamer carbonate is quantitatively controlled by small molecular species, in this case by water molecules and bicarbonate anions, is demonstrated here. Spin-lattice relaxation times of the protons in the hydrogel, detected by solid state NMR, are indicative of mobility within the polymer. They decreased with increasing water content but increased as the bicarbonate anion content increased. As the water content increased, the glass transition temperature decreased but increasing the bicarbonate anion content had the opposite effect. FTIR analysis indicated that the anions were involved in bonding while the water molecules were not. The stability and physicochemical properties of polymers during storage and formulation depend on the polymeric structure and the dynamic behaviour of the polymer chains.

  8. A multiple-responsive self-healing supramolecular polymer gel network based on multiple orthogonal interactions.

    PubMed

    Zhan, Jiayi; Zhang, Mingming; Zhou, Mi; Liu, Bin; Chen, Dong; Liu, Yuanyuan; Chen, Qianqian; Qiu, Huayu; Yin, Shouchun

    2014-08-01

    Supramolecular polymer networks have attracted considerable attention not only due to their topological importance but also because they can show some fantastic properties such as stimuli-responsiveness and self-healing. Although various supramolecular networks are constructed by supramolecular chemists based on different non-covalent interactions, supramolecular polymer networks based on multiple orthogonal interactions are still rare. Here, a supramolecular polymer network is presented on the basis of the host-guest interactions between dibenzo-24-crown-8 (DB24C8) and dibenzylammonium salts (DBAS), the metal-ligand coordination interactions between terpyridine and Zn(OTf)2 , and between 1,2,3-triazole and PdCl2 (PhCN)2 . The topology of the networks can be easily tuned from monomer to main-chain supramolecular polymer and then to the supramolecular networks. This process is well studied by various characterization methods such as (1) H NMR, UV-vis, DOSY, viscosity, and rheological measurements. More importantly, a supramolecular gel is obtained at high concentrations of the supramolecular networks, which demonstrates both stimuli-responsiveness and self-healing properties. PMID:24943122

  9. Amphiphilic semi-interpenetrating polymer networks using pulverized rubber

    NASA Astrophysics Data System (ADS)

    Shahidi, Nima

    Scrap rubber materials provide a significant challenge to either reuse or safe disposal. Every year, millions of tires are discarded to landfills in the United States, consuming a staggering amount of land space, creating a high risk for large fires, breeding mosquitoes that spread diseases, and wasting the planet's natural resources. This situation cannot be sustained. The challenge of reusing scrap rubber materials is mainly due to the crosslinked structure of vulcanized rubber that prevent them from melting and further processing for reuse. The most feasible recycling approach is believed to be a process in which the vulcanized rubber is first pulverized into a fine powder and then incorporated into new products. The production of fine rubber particles is generally accomplished through the use of a cryogenic process that is costly. Therefore, development of a cost effective technology that utilizes a large quantity of the scrap rubber materials to produce high value added materials is an essential element in maintaining a sustainable solution to rubber recycling. In this research, a cost effective pulverization process, solid state shear extrusion (SSSE), was modified and used for continuous pulverization of the rubber into fine particles. In the modified SSSE process, pulverization takes place at high compressive shear forces and a controlled temperature. Furthermore, an innovative particle modification process was developed to enhance the chemical structure and surface properties of the rubber particles for manufacturing of high value added products. Modification of rubber particles was accomplished through the polymerization of a hydrophilic monomer mixture within the intermolecular structure of the hydrophobic rubber particles. The resulting composite particles are considered as amphiphilic particulate phase semi-interpenetrating polymer networks (PPSIPNs). The modified rubber particles are water dispersible and suitable for use in a variety of aqueous media

  10. Precursor polymer approach towards functional conjugated polymer networks and ultrathin film electro-optical applications

    NASA Astrophysics Data System (ADS)

    Taranekar, Prasad

    Conjugated polymers are organic semiconductors which are of interest to a wide variety of optical, electronic, opto-electronic, and sensory applications; including light emitting diodes, thin film transistors, photovoltaic cells, and chemical sensors. While conducting polymers have some similarities to conventional polymeric materials, it is clearly the extensive main chain pi-conjugated structure and its implicit electro-optical properties that make it distinct. The same structure, however, gives it "chain stiffness" that affects its physical behavior. As a direct consequence of this, virtually all unsubstituted conducting polymers are found to be intractable and insoluble. This dissertation details the issue of tailoring the electro-optical properties and processability of conjugated polymers via a novel "precursor polymer approach". In this approach, electroactive side group units of either similar or different kind are tethered to a polymeric backbone. This combination determines the eventual electro-optical and electrochemical properties of these polymers including their ability to form ultrathin films. Thus, the desired macroscopic property is transformed by designing new precursor polymer structures, manipulating polymer-based compositions and blends, and the exploration and exploitation of their electrochemical processing conditions. In Chapters 2, 3, and 4, we have used single or binary electroactive compositions of species such as pyrrole, thiophene, carbazole and terthiophene are tethered to a linear polymeric backbone. Besides, the linear approach, in Chapters 5 and 6, we have also explored the use of generational dendrimers as backbone with carbazole units attached as peripheral electroactive groups. These precursor polymers were then subjected to electrochemical cross-linking to generate high optical quality ultrathin films on a conducting substrate such as indium tin oxide (ITO) or Au surfaces. The reaction of such electroactive species inimically

  11. Light-emitting conjugated polymers with microporous network architecture: interweaving scaffold promotes electronic conjugation, facilitates exciton migration, and improves luminescence.

    PubMed

    Xu, Yanhong; Chen, Long; Guo, Zhaoqi; Nagai, Atsushi; Jiang, Donglin

    2011-11-01

    Herein we report a strategy for the design of highly luminescent conjugated polymers by restricting rotation of the polymer building blocks through a microporous network architecture. We demonstrate this concept using tetraphenylethene (TPE) as a building block to construct a light-emitting conjugated microporous polymer. The interlocked network successfully restricted the rotation of the phenyl units, which are the major cause of fluorescence deactivation in TPE, thus providing intrinsic luminescence activity for the polymers. We show positive "CMP effects" that the network promotes π-conjugation, facilitates exciton migration, and improves luminescence activity. Although the monomer and linear polymer analogue in solvents are nonemissive, the network polymers are highly luminescent in various solvents and the solid state. Because emission losses due to rotation are ubiquitous among small chromophores, this strategy can be generalized for the de novo design of light-emitting materials by integrating the chromophores into an interlocked network architecture.

  12. Ferroelectric polymer networks with high energy density and improved discharged efficiency for dielectric energy storage.

    PubMed

    Khanchaitit, Paisan; Han, Kuo; Gadinski, Matthew R; Li, Qi; Wang, Qing

    2013-01-01

    Ferroelectric polymers are being actively explored as dielectric materials for electrical energy storage applications. However, their high dielectric constants and outstanding energy densities are accompanied by large dielectric loss due to ferroelectric hysteresis and electrical conduction, resulting in poor charge-discharge efficiencies under high electric fields. To address this long-standing problem, here we report the ferroelectric polymer networks exhibiting significantly reduced dielectric loss, superior polarization and greatly improved breakdown strength and reliability, while maintaining their fast discharge capability at a rate of microseconds. These concurrent improvements lead to unprecedented charge-discharge efficiencies and large values of the discharged energy density and also enable the operation of the ferroelectric polymers at elevated temperatures, which clearly outperforms the melt-extruded ferroelectric polymer films that represents the state of the art in dielectric polymers. The simplicity and scalability of the described method further suggest their potential for high energy density capacitors.

  13. Recyclable Crosslinked Polymer Networks via One-Step Controlled Radical Polymerization.

    PubMed

    Jin, Kailong; Li, Lingqiao; Torkelson, John M

    2016-08-01

    A nitroxide-mediated polymerization strategy allows one-step synthesis of recyclable crosslinked polymeric materials from any monomers or polymers that contain carbon-carbon double bonds amenable to radical polymerization. The resulting materials with dynamic covalent bonds can show full property recovery after multiple melt-reprocessing recycles. This one-step strategy provides for both robust, relatively sustainable recyclability of crosslinked polymers and design of networks for advanced technologies.

  14. Significance of bending restraints for the stability of helical polymer conformations.

    PubMed

    Williams, Matthew J; Bachmann, Michael

    2016-06-01

    We performed parallel-tempering Monte Carlo simulations to investigate the formation and stability of helical tertiary structures for flexible and semiflexible polymers, employing a generic coarse-grained model. Structural conformations exhibit helical order with tertiary ordering into single helices, multiple helical segments organized into bundles, and disorganized helical arrangements. For both bending-restrained semiflexible and bending-unrestrained flexible helical polymers, the stability of the structural phases is discussed systematically by means of hyperphase diagrams parametrized by suitable order parameters, temperature, and torsion strength. This exploration lends insight into the restricted flexibility of biological polymers such as double-stranded DNA and proteins.

  15. Significance of bending restraints for the stability of helical polymer conformations.

    PubMed

    Williams, Matthew J; Bachmann, Michael

    2016-06-01

    We performed parallel-tempering Monte Carlo simulations to investigate the formation and stability of helical tertiary structures for flexible and semiflexible polymers, employing a generic coarse-grained model. Structural conformations exhibit helical order with tertiary ordering into single helices, multiple helical segments organized into bundles, and disorganized helical arrangements. For both bending-restrained semiflexible and bending-unrestrained flexible helical polymers, the stability of the structural phases is discussed systematically by means of hyperphase diagrams parametrized by suitable order parameters, temperature, and torsion strength. This exploration lends insight into the restricted flexibility of biological polymers such as double-stranded DNA and proteins. PMID:27415311

  16. Significance of bending restraints for the stability of helical polymer conformations

    NASA Astrophysics Data System (ADS)

    Williams, Matthew J.; Bachmann, Michael

    2016-06-01

    We performed parallel-tempering Monte Carlo simulations to investigate the formation and stability of helical tertiary structures for flexible and semiflexible polymers, employing a generic coarse-grained model. Structural conformations exhibit helical order with tertiary ordering into single helices, multiple helical segments organized into bundles, and disorganized helical arrangements. For both bending-restrained semiflexible and bending-unrestrained flexible helical polymers, the stability of the structural phases is discussed systematically by means of hyperphase diagrams parametrized by suitable order parameters, temperature, and torsion strength. This exploration lends insight into the restricted flexibility of biological polymers such as double-stranded DNA and proteins.

  17. Network of nano-droplets by a tri-block polymer

    NASA Astrophysics Data System (ADS)

    Sharifi, Soheil; Doodman, Esmaeil

    2014-11-01

    Mixtures of oil in water nano-droplets with two molecular weights of a tri-block polymer was studied by quasi elastic light scattering and small angle X-ray scattering. The results showed that the size and interaction of droplets didn't change with increase of the tri-block polymer length but the order parameters increased. The increase of length of the tri-block biopolymer changed the dynamics of the droplets. A network formation is resulted with increase of the amount of tri-block polymer in the microemulsions.

  18. Confinement dynamics of a semiflexible chain inside nano-spheres

    NASA Astrophysics Data System (ADS)

    Fathizadeh, A.; Heidari, Maziar; Eslami-Mossallam, B.; Ejtehadi, M. R.

    2013-07-01

    We study the conformations of a semiflexible chain, confined in nano-scaled spherical cavities, under two distinct processes of confinement. Radial contraction and packaging are employed as two confining procedures. The former method is performed by gradually decreasing the diameter of a spherical shell which envelopes a confined chain. The latter procedure is carried out by injecting the chain inside a spherical shell through a hole on the shell surface. The chain is modeled with a rigid body molecular dynamics simulation and its parameters are adjusted to DNA base-pair elasticity. Directional order parameter is employed to analyze and compare the confined chain and the conformations of the chain for two different sizes of the spheres are studied in both procedures. It is shown that for the confined chains in the sphere sizes of our study, they appear in spiral or tennis-ball structures, and the tennis-ball structure is more likely to be observed in more compact confinements. Our results also show that the dynamical procedure of confinement and the rate of the confinement are influential parameters of the structure of the chain inside spherical cavities.

  19. Relaxation dynamics of small-world degree-distributed treelike polymer networks

    NASA Astrophysics Data System (ADS)

    Galiceanu, Mircea; Oliveira, Edieliton S.; Dolgushev, Maxim

    2016-11-01

    Hyperbranched polymers are typically treelike macromolecules with a very disordered structure. Here we construct hyperbranched polymers based on the degree distribution of the small-world networks. This algorithm allows us to study a transition from monodisperse linear chains to structurally-disordered dendritic polymers by varying the parameter p (0 ≤ p ≤ 1), which measures the randomness and the degree of branching of the network. Employing the framework of generalized Gaussian structures, we determine for the obtained structures the relaxation spectra, which are exemplified on the mechanical relaxation moduli (storage and loss moduli). We monitor these physical quantities for networks of different sizes and for various values of the parameter p. In the intermediate frequency domain, we encounter macroscopically distinguishable behaviours.

  20. Relationships between specific surface area and pore size in electrospun polymer fibre networks

    PubMed Central

    Eichhorn, S. J.; Sampson, W. W.

    2010-01-01

    From consideration of the extent of contact between fibres in electrospun polymer networks, we provide theory relating the specific surface area of the network to the characteristic dimensions of interfibre voids. We show that these properties are strongly influenced by the cross-sectional morphologies of fibres. Whereas porosity has a strong influence on pore dimensions, in the range of porosities typically obtained in real networks, its influence on specific surface area is weak. By considering reference geometries of collapsed ribbons and fibres with circular cross sections, we demonstrate that at a given network porosity, fibre parameters that increase the specific surface area reduce the characteristic dimensions of voids. The implications of the theory, mainly in the context of cell proliferation on electrospun polymer scaffolds, are discussed; the theory has relevance also to future applications of these materials in composites. PMID:19812071

  1. Dendritic polyglycerol-poly(ethylene glycol)-based polymer networks for biosensing application.

    PubMed

    Dey, Pradip; Adamovski, Miriam; Friebe, Simon; Badalyan, Artavazd; Mutihac, Radu-Cristian; Paulus, Florian; Leimkühler, Silke; Wollenberger, Ulla; Haag, Rainer

    2014-06-25

    This work describes the formation of a new dendritic polyglycerol-poly(ethylene glycol)-based 3D polymer network as a matrix for immobilization of the redox enzyme periplasmatic aldehyde oxidoreductase to create an electrochemical biosensor. The novel network is built directly on the gold surface, where it simultaneously stabilizes the enzyme for up to 4 days. The prepared biosensors can be used for amperometric detection of benzaldehyde in the range of 0.8-400 μM. PMID:24882361

  2. Modeling of polymer networks for application to solid propellant formulating

    NASA Technical Reports Server (NTRS)

    Marsh, H. E.

    1979-01-01

    Methods for predicting the network structural characteristics formed by the curing of pourable elastomers were presented; as well as the logic which was applied in the development of mathematical models. A universal approach for modeling was developed and verified by comparison with other methods in application to a complex system. Several applications of network models to practical problems are described.

  3. Mechanical and swelling properties of PDMS interpenetrating polymer networks

    NASA Astrophysics Data System (ADS)

    Cohen, Claude; Yoo, Seong Hyun

    2006-03-01

    Poly(dimethylsiloxane) (PDMS) interpenetrating networks (IPNs) of a large and a small molar mass PDMS were prepared. Six series of IPNs were obtained by first tetra-functionally end-linking long vinyl-terminated PDMS neat or in a 50 per cent solution with unreactive PDMS chains. These networks were then dried and swollen with short reactive telechelic PDMS that were subsequently end-linked. We found that the correlation between modulus (E) and equilibrium swelling (Q) in toluene of the PDMS IPNs obeys a scaling relation identical to that of normal uni-modal PDMS networks. The results of the toughness of the networks represented by the energy required to rupture them were analyzed in terms of a recent model by Okumura (Europhysics Letters 67(3), 470, 2004). A modified version of this model that assumes each component of the double network to be subjected to an equal stress gives a good representation of the data.

  4. Polymorphism of highly cross-linked F-actin networks: Probing multiple length scales

    NASA Astrophysics Data System (ADS)

    Nguyen, Lam T.; Hirst, Linda S.

    2011-03-01

    The assembly properties of F-actin filaments in the presence of different biological cross-linker concentrations and types have been investigated using a combined approach of fluorescence confocal microscopy and coarse-grained molecular dynamics simulation. In particular for highly cross-linked regimes, new network morphologies are observed. Complex network formation and the details of the resulting structure are strongly dependent on the ratio of cross-linkers to actin monomers and cross-linker shape but only weakly dependent on overall actin concentration and filament length. The work presented here may help to provide some fundamental understanding of how excessive cross-linkers interact with the actin filament solution, creating different structures in the cell under high cross-linker concentrations. F-actin is not only of biological importance but also, as an example of a semiflexible polymer, has attracted significant interest in its physical behavior. In combination with different cross-linkers semiflexible filaments may provide new routes to bio-materials development and act as the inspiration for new hierarchical network-based materials.

  5. Antimicrobial Efficacy of Synthesized Quaternary Ammonium Polyamidoamine Dendrimers and Dendritic Polymer Network.

    PubMed

    Zainul Abid, C K V; Jackeray, Richa; Jain, Swati; Chattopadhyay, Sruti; Asif, S; Singh, Harpal

    2016-01-01

    Water treatment to mitigate microbial contaminants is a major challenge across globe paving the way to develop novel antimicrobial compounds. We aim at architecting antibacterial moiety eventually catering to vast water treatment industry. In this research study, quaternary ammonium functionalized polyamidoamine (PAMAM) dendrimer and PAMAM-ethyleneglycol dimethacrylate (EGDMA) dendritic polymer network were synthesized. These materials were characterized by various analytical techniques like ATR-FTIR, 1HNMR, DSC etc. Water soluble generation (G) 1.0 PAMAM dendrimer and water insoluble PAMAM G1.0 EGDMA dendritic polymer network were quaternized by reacting with dilute hydrochloric acid (HCI) and octyl iodide (01) respectively. Both quaternary ammonium dendrimer products were found to exhibit potent bactericidal activity against a group of common Gram-negative and Gram-positive bacteria. 10 mg/L concentration of liquid PAMAM G1.0 QHCI was efficient to kill 100% bacteria rapidly within an incubation time of just 2 minutes. In addition, quaternary ammonium dendritic polymer network PAMAM G1.0-EGDMA Q OI demonstrated good contact killing antimicrobial property without releasing any active molecule into the surrounding medium and disinfected contaminated water within 5 minutes. Both quaternary ammonium dendrimer and dendritic polymer network showed negligible cytotoxicity in MTT assay indicating their potential as a viable antimicrobial agent. PMID:27398560

  6. Thermoreversible associating polymer networks. I. Interplay of thermodynamics, chemical kinetics, and polymer physics

    NASA Astrophysics Data System (ADS)

    Hoy, Robert S.; Fredrickson, Glenn H.

    2009-12-01

    Hybrid molecular dynamics/Monte Carlo simulations are used to study melts of unentangled, thermoreversibly associating supramolecular polymers. In this first of a series of papers, we describe and validate a model that is effective in separating the effects of thermodynamics and chemical kinetics on the dynamics and mechanics of these systems, and is extensible to arbitrarily nonequilibrium situations and nonlinear mechanical properties. We examine the model's quiescent (and heterogeneous) dynamics, nonequilibrium chemical dynamics, and mechanical properties. Many of our results may be understood in terms of the crossover from diffusion-limited to kinetically limited sticky bond recombination, which both influences and is influenced by polymer physics, i.e., the connectivity of the parent chains.

  7. Structural properties of end-linked polymer networks: Monte Carlo simulation and neutron scattering studies

    NASA Astrophysics Data System (ADS)

    Gilra, Nisha

    2000-12-01

    In this work, computational and experimental approaches were taken to elucidate the structural behavior of end- linked polymer networks. Monte Carlo simulations with the bond fluctuation model were used to study the formation and structure of 10-, 20-, and 50-mer networks cured with various ratios of cross-link sites to chain ends, r. The simulations confirmed experimental results that optimum r values for structural properties are found at non- stoichiometric ratios, increase with increasing precursor polymer chain length, and increase with side reaction. The same structural properties were determined for 50-mer networks formed in the presence of a series of concentrations of 50-mer unreactive linear chain diluent. A slight maximum in the fraction of elastic material was observed at a small degree of dilution and was explained in terms of entanglement effects. The conformational behavior of a small fraction of 50-mer linear probe chains was studied in various polymer network mesh sizes, where mesh size is the number of monomers between cross- links. The radius of gyration, R g, of the probe chains decreased by less than 6% for all mesh sizes studied. Uniaxial network deformation was studied using constant pressure simulations. A new methodology to perform volume change moves was developed. The equation of state of 10- mer athermal network system was determined and found to be similar to the corresponding athermal linear polymer equation of state at high volume fractions, but approached a region of negative pressures at low volume fractions. The chain segment orientational correlation was determined for probe free chains trapped in isotropic and deformed networks. Increased correlation was observed at small distances, whereas no orientational preference was evident at larger distances. The study of probe free chains trapped in polymer networks was also performed using small-angle neutron scattering. The conformational behavior of 70K poly(dimethylsiloxane) (PDMS

  8. A statistical model for the length distribution of meshes in a polymer network

    NASA Astrophysics Data System (ADS)

    Lang, M.; Michalke, W.; Kreitmeier, S.

    2001-05-01

    A statistical model is introduced which allows estimation of the length distribution of meshes in a unimodal polymer network. The length distribution is responsible for the type and number of entanglements in a network and can thus provide information about the deformation behavior of polymers. The model can also predict the influence of certain simulation parameters such as the degree of cross linkage, the chain length, or the density of the melt from which the network is built. Both a reaction- and a diffusion-controlled cross-linking process can be mapped. We found that a shorter chain length implies a smaller number of chains per mesh. An increase of the degree of cross linkage as well as a lowering of the density of the melt also leads to a smaller average length of the meshes.

  9. Self-supported fibrin-polyvinyl alcohol interpenetrating polymer networks: an easily handled and rehydratable biomaterial.

    PubMed

    Bidault, Laurent; Deneufchatel, Marie; Vancaeyzeele, Cédric; Fichet, Odile; Larreta-Garde, Véronique

    2013-11-11

    A fibrin hydrogel at physiological concentration (5 mg/mL) was associated with polyvinyl alcohol (PVA) inside an interpenetrating polymer networks (IPN) architecture. Previously, PVA has been modified with methacrylate functions in order to cross-link it by free-radical polymerization. The fibrin network was synthesized by the enzymatic hydrolysis of fibrinogen by thrombin. The resulting self-supported materials simultaneously exhibit the properties of the fibrin hydrogel and those of the synthetic polymer network. Their storage modulus is 50-fold higher than that of the fibrin hydrogel and they are completely rehydratable. These materials are noncytotoxic toward human fibroblast and the fibrin present on the surface of PVAm-based IPNs favors cell development.

  10. Kinetics of microphase separation in interpenetrated polymer networks in solution.

    PubMed

    Derouiche, A; Benhamou, M; Bettachy, A

    2005-04-01

    We present here a theoretical study of the early kinetics of the microphase separation in crosslinked polymer blends, made of two incompatible polymers A and B, dissolved in a common good solvent. Use is made of an extended blob model used previously for the investigation of the static properties of such a transition. We are interested in the variation of the relaxation rate, tau(q), versus the wave number q, in the vicinity of the spinodal temperature. We first show that kinetics is entirely dominated by local motions, which are of Rouse type. Slow motions are absent, because of the permanent presence of crosslinks. Second, we find that the characteristic frequency, omega (q) = tau(q)(-1), increases with increasing wave number q according to a sixth power law, that is omega (q) approximately q6 phi(-9/4), where phi is the overall monomer volume fraction. Therefore, the swelling of strands due to the excluded-volume forces leads to a renormalization of the characteristic frequency by a multiplicative factor scaling as phi(-9/4). The main conclusion is that the presence of a good solvent necessitates relaxation rates less important than those relative to crosslinked mixtures in the molten state.

  11. Effects of molecular architecture on fluid ingress behavior of glassy polymer networks

    NASA Astrophysics Data System (ADS)

    Jaskson, Matthew Blaine

    This manuscript demonstrates the synthesis of glassy polymer network isomers to control morphological variations and study solvent ingress behavior independent of chemical affinity. Well-controlled network architectures with varying free volume average hole-sizes have been shown to substantially influence solvent ingress within glassy polymer networks. Bisphenol-A diglycidyl ether (DGEBA), bisphenol-F diglycidyl ether (DGEBF), Triglycidyl p-aminophenol (pAP, MY0510), Triglycidyl maminophenol (mAP, MY0610), and tetraglydicyl-4,4'-diamino-diphenyl methane (TGDDM, MY721) were cured with 3,3'- and 4,4'-diaminodiphenyl sulfone (DDS) at a stoichiometric ratio of 1:1 oxirane to amine active hydrogen to generate a series of network architectures with an average free volume hole-size (Vh) ranging between 54-82 A3. Polymer networks were exposed to water and a broad range of organic solvents ranging in van der Waals (vdW) volumes from 18-88 A3 for up to 10,000h time. A clear relationship between glassy polymer network Vh and fluid penetration has been established. As penetrant vdW volume approached Vh, uptake kinetics significantly decreased, and as penetrant vdW volume exceeded Vh, a blocking mechanism dominated ingress and prevented penetrant transport. These results suggest that reducing the free volume hole-size is a reasonable approach to control solvent properties for glassy polymer networks. New techniques to monitor and predict the diffusion behavior of liquids through glassy networks are also presented. Digital Image Correlation (DIC) was employed to accurately measure the strain developed during case II diffusion. This technique also presented a new theory for a relationship between sample topology and irreversible macroscopic brittle failure induced by solvent absorption. A new modeling technique has been developed which can accurately predict the chemical and physical interactions a solvent may have with a glassy network. This new model can be used as a

  12. Pt-Free Counter Electrodes with Carbon Black and 3D Network Epoxy Polymer Composites

    PubMed Central

    Kang, Gyeongho; Choi, Jongmin; Park, Taiho

    2016-01-01

    Carbon black (CB) and a 3D network epoxy polymer composite, representing dual functions for conductive corrosion protective layer (CCPL) and catalytic layer (CL) by the control of CB weight ratio against polymer is developed. Our strategy provides a proper approach which applies high catalytic ability and chemical stability of CB in corrosive triiodide/iodide (I3−/I−) redox electrolyte system. The CB and a 3D network epoxy polymer composite coated on the stainless steel (SS) electrode to alternate counter electrodes in dye sensitized solar cells (DSSCs). A two-step spray pyrolysis process is used to apply a solution containing epoxy monomers and a polyfunctional amine hardener with 6 wt% CB to a SS substrate, which forms a CCPL. Subsequently, an 86 wt% CB is applied to form a CL. The excellent catalytic properties and corrosion protective properties of the CB and 3D network epoxy polymer composites produce efficient counter electrodes that can replace fluorine-doped tin oxide (FTO) with CCPL/SS and Pt/FTO with CL/CCPL/SS in DSSCs. This approach provides a promising approach to the development of efficient, stable, and cheap solar cells, paving the way for large-scale commercialization. PMID:26961256

  13. Pt-Free Counter Electrodes with Carbon Black and 3D Network Epoxy Polymer Composites

    NASA Astrophysics Data System (ADS)

    Kang, Gyeongho; Choi, Jongmin; Park, Taiho

    2016-03-01

    Carbon black (CB) and a 3D network epoxy polymer composite, representing dual functions for conductive corrosion protective layer (CCPL) and catalytic layer (CL) by the control of CB weight ratio against polymer is developed. Our strategy provides a proper approach which applies high catalytic ability and chemical stability of CB in corrosive triiodide/iodide (I3‑/I‑) redox electrolyte system. The CB and a 3D network epoxy polymer composite coated on the stainless steel (SS) electrode to alternate counter electrodes in dye sensitized solar cells (DSSCs). A two-step spray pyrolysis process is used to apply a solution containing epoxy monomers and a polyfunctional amine hardener with 6 wt% CB to a SS substrate, which forms a CCPL. Subsequently, an 86 wt% CB is applied to form a CL. The excellent catalytic properties and corrosion protective properties of the CB and 3D network epoxy polymer composites produce efficient counter electrodes that can replace fluorine-doped tin oxide (FTO) with CCPL/SS and Pt/FTO with CL/CCPL/SS in DSSCs. This approach provides a promising approach to the development of efficient, stable, and cheap solar cells, paving the way for large-scale commercialization.

  14. Pt-Free Counter Electrodes with Carbon Black and 3D Network Epoxy Polymer Composites.

    PubMed

    Kang, Gyeongho; Choi, Jongmin; Park, Taiho

    2016-01-01

    Carbon black (CB) and a 3D network epoxy polymer composite, representing dual functions for conductive corrosion protective layer (CCPL) and catalytic layer (CL) by the control of CB weight ratio against polymer is developed. Our strategy provides a proper approach which applies high catalytic ability and chemical stability of CB in corrosive triiodide/iodide (I3(-)/I(-)) redox electrolyte system. The CB and a 3D network epoxy polymer composite coated on the stainless steel (SS) electrode to alternate counter electrodes in dye sensitized solar cells (DSSCs). A two-step spray pyrolysis process is used to apply a solution containing epoxy monomers and a polyfunctional amine hardener with 6 wt% CB to a SS substrate, which forms a CCPL. Subsequently, an 86 wt% CB is applied to form a CL. The excellent catalytic properties and corrosion protective properties of the CB and 3D network epoxy polymer composites produce efficient counter electrodes that can replace fluorine-doped tin oxide (FTO) with CCPL/SS and Pt/FTO with CL/CCPL/SS in DSSCs. This approach provides a promising approach to the development of efficient, stable, and cheap solar cells, paving the way for large-scale commercialization. PMID:26961256

  15. Equilibrium & Nonequilibrium Fluctuation Effects in Biopolymer Networks

    NASA Astrophysics Data System (ADS)

    Kachan, Devin Michael

    Fluctuation-induced interactions are an important organizing principle in a variety of soft matter systems. In this dissertation, I explore the role of both thermal and active fluctuations within cross-linked polymer networks. The systems I study are in large part inspired by the amazing physics found within the cytoskeleton of eukaryotic cells. I first predict and verify the existence of a thermal Casimir force between cross-linkers bound to a semi-flexible polymer. The calculation is complicated by the appearance of second order derivatives in the bending Hamiltonian for such polymers, which requires a careful evaluation of the the path integral formulation of the partition function in order to arrive at the physically correct continuum limit and properly address ultraviolet divergences. I find that cross linkers interact along a filament with an attractive logarithmic potential proportional to thermal energy. The proportionality constant depends on whether and how the cross linkers constrain the relative angle between the two filaments to which they are bound. The interaction has important implications for the synthesis of biopolymer bundles within cells. I model the cross-linkers as existing in two phases: bound to the bundle and free in solution. When the cross-linkers are bound, they behave as a one-dimensional gas of particles interacting with the Casimir force, while the free phase is a simple ideal gas. Demanding equilibrium between the two phases, I find a discontinuous transition between a sparsely and a densely bound bundle. This discontinuous condensation transition induced by the long-ranged nature of the Casimir interaction allows for a similarly abrupt structural transition in semiflexible filament networks between a low cross linker density isotropic phase and a higher cross link density bundle network. This work is supported by the results of finite element Brownian dynamics simulations of semiflexible filaments and transient cross-linkers. I

  16. Effect of Network Structure/Topology on Mechanical Properties of Crosslinked Polymers

    NASA Astrophysics Data System (ADS)

    Sharifi, Majid

    The interest in epoxy thermosetting polymers is widespread (e.g. Boeing 787 Dreamliner, windmill blades, automobiles, coatings, adhesives, etc.), and a demand still exists for improving toughness of these materials without degrading advantageous properties such as strength, modulus, and Tg. This study introduces novel approaches for improving the intrinsic mechanical characteristics of these polymers. The designed synthetic techniques focus on developing polymer materials with the same overall compositions but varying in network topologies, with distinct topological features in the size range of 5-50 nm, measured by SAXS and SEM. It was found that without altering chemical structure, the network topology of a dense thermoset can be engineered such that, under mechanical deformation, nano-cavities open and dissipate energy before rupturing covalent bonds, producing a tougher material without sacrificing strength, modulus, and even glass transition temperature. Modified structures also revealed higher resistance to fracture than the corresponding control structures. The major fracture mechanism responsible for the increased energy dissipation was found to be nano-cavitation. SEM images from the fracture surfaces showed clear cavities on the modified samples whereas none were seen on the fracture surface of the control samples. Overall, it was demonstrated that network topology can be used to tailor thermal and mechanical properties of thermosetting polymers. The experimental methodologies in this dissertation can directly and economically be applied to design polymeric materials with improved properties for desired applications. Although topology-based toughening was investigated on epoxy-amine polymers, the concept can be extended to most thermoset chemistries and perhaps to other brittle network forming materials.

  17. 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)

  18. Strain-dependent characterization of electrode and polymer network of electrically activated polymer actuators

    NASA Astrophysics Data System (ADS)

    Töpper, Tino; Osmani, Bekim; Weiss, Florian M.; Winterhalter, Carla; Wohlfender, Fabian; Leung, Vanessa; Müller, Bert

    2015-04-01

    Fecal incontinence describes the involuntary loss of bowel content and affects about 45 % of retirement home residents and overall more than 12 % of the adult population. Artificial sphincter implants for treating incontinence are currently based on mechanical systems with failure rates resulting in revision after three to five years. To overcome this drawback, artificial muscle sphincters based on bio-mimetic electro-active polymer (EAP) actuators are under development. Such implants require polymer films that are nanometer-thin, allowing actuation below 24 V, and electrodes that are stretchable, remaining conductive at strains of about 10 %. Strain-dependent resistivity measurements reveal an enhanced conductivity of 10 nm compared to 30 nm sputtered Au on silicone for strains higher than 5 %. Thus, strain-dependent morphology characterization with optical microscopy and atomic force microscopy could demonstrate these phenomena. Cantilever bending measurements are utilized to determine elastic/viscoelastic properties of the EAP films as well as their long-term actuation behavior. Controlling these properties enables the adjustment of growth parameters of nanometer-thin EAP actuators.

  19. Ion pair reinforced semi-interpenetrating polymer network for direct methanol fuel cell applications.

    PubMed

    Fang, Chunliu; Julius, David; Tay, Siok Wei; Hong, Liang; Lee, Jim Yang

    2012-06-01

    This paper describes the synthesis of ion-pair-reinforced semi-interpenetrating polymer networks (SIPNs) as proton exchange membranes (PEMs) for the direct methanol fuel cells (DMFCs). Specifically, sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO), a linear polymer proton source, was immobilized in a brominated PPO (BPPO) network covalently cross-linked by ethylenediamine (EDA). The immobilization of SPPO in the SIPN network was accomplished not only by the usual means of mechanical interlocking but also by ion pair formation between the sulfonic acid groups of SPPO and the amine moieties formed during the cross-linking reaction of BPPO with EDA. Through the ion pair interactions, the immobilization of SPPO polymer in the BPPO network was made more effective, resulting in a greater uniformity of sulfonic acid cluster distribution in the membrane. The hydrophilic amine-containing cross-links also compensated for some of the decrease in proton conductivity caused by ion pair formation. The SIPN membranes prepared as such showed good proton conductivity, low methanol permeability, good mechanical properties, and dimensional stability. Consequently, the PPO based SIPN membranes were able to deliver a higher maximum power density than Nafion, demonstrating the potential of the SIPN structure for PEM designs.

  20. Field-effect Flow Control in Polymer Microchannel Networks

    NASA Technical Reports Server (NTRS)

    Sniadecki, Nathan; Lee, Cheng S.; Beamesderfer, Mike; DeVoe, Don L.

    2003-01-01

    A new Bio-MEMS electroosmotic flow (EOF) modulator for plastic microchannel networks has been developed. The EOF modulator uses field-effect flow control (FEFC) to adjust the zeta potential at the Parylene C microchannel wall. By setting a differential EOF pumping rate in two of the three microchannels at a T-intersection with EOF modulators, the induced pressure at the intersection generated pumping in the third, field-free microchannel. The EOF modulators are able to change the magnitude and direction of the pressure pumping by inducing either a negative or positive pressure at the intersection. The flow velocity is tracked by neutralized fluorescent microbeads in the microchannels. The proof-of-concept of the EOF modulator described here may be applied to complex plastic ,microchannel networks where individual microchannel flow rates are addressable by localized induced-pressure pumping.

  1. A family of reworkable polymer networks by the incorporation of sterically hindered urea linkages

    NASA Astrophysics Data System (ADS)

    Malik, Jitendra

    2002-01-01

    Crosslinked polymer networks are excellent materials for multiple applications. However, while their crosslinked structure gives the networks many positive attributes, it also makes them essentially intractable after the covalent crosslinks are formed. Therefore, it is exceedingly difficult to reprocess polymer networks once crosslinked without exposure to extreme degradation conditions. The first part of this work focuses in creating crosslinked networks that could show controlled disassembly upon stimulus. It was found that a controlled network disassembly process could be invoked by the incorporation of sterically hindered urea linkages into the polymer network. This network was shown to disassemble upon exposure to heat, whereas in the absence of heat, the network was found to maintain its crosslinked structure. The disassembly temperature could be varied by careful selection of the cleaving agent based on controllable considerations. This work focuses on showing controlled network disassembly of a crosslinked polymer matrix. Herein, we describe the factors that control the disassembly temperature and conclude with a possible mechanism for the disassembly process based on experimental data. Once disassembly could be shown to occur using sterically hindered urea linkages, polymer molecules were incorporated directly into the reworkable network. The presence of the polymer was found to significantly effect the reworkable behavior and these effects were detailed and an explanation for the behavior was provided. The work then focused on the effects of sterics along the length of the reworkable crosslinker. It was found that sterics along the length of the chain did have an effect. Specifically, as the steric hindrance increased around the urea linkage the rework temperature was found to decrease. Our focus then shifted to study the effects of changing the number of reworkable linkages per crosslinker. As the number per crosslinker changed from two to one the

  2. Conductivity and properties of polysiloxane-polyether cluster-LiTFSI networks as hybrid polymer electrolytes

    NASA Astrophysics Data System (ADS)

    Boaretto, Nicola; Joost, Christine; Seyfried, Mona; Vezzù, Keti; Di Noto, Vito

    2016-09-01

    This report describes the synthesis and the properties of a series of polymer electrolytes, composed of a hybrid inorganic-organic matrix doped with LiTFSI. The matrix is based on ring-like oligo-siloxane clusters, bearing pendant, partially cross-linked, polyether chains. The dependency of the thermo-mechanic and of the transport properties on several structural parameters, such as polyether chains' length, cross-linkers' concentration, and salt concentration is studied. Altogether, the materials show good thermo-mechanical and electrochemical stabilities, with conductivities reaching, at best, 8·10-5 S cm-1 at 30 °C. In conclusion, the cell performances of one representative sample are shown. The scope of this report is to analyze the correlations between structure and properties in networked and hybrid polymer electrolytes. This could help the design of optimized polymer electrolytes for application in lithium metal batteries.

  3. Probe surface chemistry dependence and local polymer network structure in F-actin microrheology.

    PubMed

    Chae, Byeong Seok; Furst, Eric M

    2005-03-29

    We investigate the dependence of F-actin microrheology on probe surface chemistry using diffusing wave spectroscopy. Polystyrene probe particles exhibit subdiffusive mean-squared displacements, where Deltar(2)(t) approximately t(0.77)(+/-)(0.03) consistent with previous experiments and theory. However, polystyrene probes preadsorbed with bovine serum albumin (BSA) interact weakly with the surrounding polymer network and exhibit a scaling exponent similar to pure diffusion Deltar(2)(t) approximately t, which decreases as particle size and actin concentration increases. Using models of particle diffusion in locally heterogeneous viscoelastic microenvironments, we find that the microrheological response of BSA-treated particles is consistent with the formation of a polymer-depleted shell surrounding the probes. The shell thickness scales with particle size but not polymer concentration. These results suggest that the depletion is caused by exclusion or orientation of actin filaments near probes due to their long length and rigidity.

  4. AB-polymer networks based on oligo(epsilon-caprolactone) segments showing shape-memory properties.

    PubMed

    Lendlein, A; Schmidt, A M; Langer, R

    2001-01-30

    Although shape-memory metal alloys have wide use in medicine and other areas, improved properties, particularly easy shaping, high shape stability, and adjustable transition temperature, are realizable only by polymer systems. In this paper, a polymer system of shape-memory polymer networks based on oligo(epsilon-caprolactone) dimethacrylate as crosslinker and n-butyl acrylate as comonomer was introduced. The influence of two structural parameters, the molecular weight of oligo(epsilon-caprolactone) dimethacrylate and the weight content of n-butyl acrylate, on macroscopic properties of polymer networks such as thermal and mechanical properties has been investigated. Tensile tests above and below melting temperature showed a decrease in the elastic modulus with increasing comonomer weight content. The crystallization behavior of the new materials has been investigated, and key parameters for the programming procedure of the temporary shape have been evaluated. Shape-memory properties have been quantified by thermocyclic experiments. All samples reached uniform deformation properties with recovery rates above 99% after 3 cycles. Whereas strain recovery increased with increasing n-butyl acrylate content, strain fixity decreased, reflecting the decreasing degree of crystallinity of the material. PMID:11158558

  5. AB-polymer networks based on oligo(epsilon-caprolactone) segments showing shape-memory properties.

    PubMed

    Lendlein, A; Schmidt, A M; Langer, R

    2001-01-30

    Although shape-memory metal alloys have wide use in medicine and other areas, improved properties, particularly easy shaping, high shape stability, and adjustable transition temperature, are realizable only by polymer systems. In this paper, a polymer system of shape-memory polymer networks based on oligo(epsilon-caprolactone) dimethacrylate as crosslinker and n-butyl acrylate as comonomer was introduced. The influence of two structural parameters, the molecular weight of oligo(epsilon-caprolactone) dimethacrylate and the weight content of n-butyl acrylate, on macroscopic properties of polymer networks such as thermal and mechanical properties has been investigated. Tensile tests above and below melting temperature showed a decrease in the elastic modulus with increasing comonomer weight content. The crystallization behavior of the new materials has been investigated, and key parameters for the programming procedure of the temporary shape have been evaluated. Shape-memory properties have been quantified by thermocyclic experiments. All samples reached uniform deformation properties with recovery rates above 99% after 3 cycles. Whereas strain recovery increased with increasing n-butyl acrylate content, strain fixity decreased, reflecting the decreasing degree of crystallinity of the material.

  6. 3D networked graphene-ferromagnetic hybrids for fast shape memory polymers with enhanced mechanical stiffness and thermal conductivity.

    PubMed

    Lee, Sang-Heon; Jung, Jung-Hwan; Oh, Il-Kwon

    2014-10-15

    A novel 3D networked graphene-ferromagnetic hybrid can be easily fabricated using one-step microwave irradiation. By incorporating this hybrid material into shape memory polymers, the synergistic effects of fast speed and the enhancement of thermal conductivity and mechanical stiffness can be achieved. This can be broadly applicable to designing magneto-responsive shape memory polymers for multifunction applications.

  7. Facile one-pot synthesis of porphyrin based porous polymer networks (PPNs) as biomimetic catalysts

    SciTech Connect

    Zou, LF; Feng, DW; Liu, TF; Chen, YP; Fordham, S; Yuan, S; Tian, J; Zhou, HC

    2015-01-01

    Stable porphyrin based porous polymer networks, PPN-23 and PPN-24, have been synthesized through a facile one-pot approach by the aromatic substitution reactions of pyrrole and aldehydes. PPN-24(Fe) shows high catalytic efficiency as a biomimetic catalyst in the oxidation reaction of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) in the presence of H2O2.

  8. Hysteresis-free and submillisecond-response polymer network liquid crystal.

    PubMed

    Lee, Yun-Han; Gou, Fangwang; Peng, Fenglin; Wu, Shin-Tson

    2016-06-27

    We demonstrate a polymer network liquid crystal (PNLC) with negligible hysteresis while keeping submillisecond response time. By doping about 1% dodecyl acrylate (C12A) into the liquid crystal/monomer precursor, both hysteresis and residual birefringence are almost completely eliminated. The operating voltage and scattering properties remain nearly intact, but the tradeoff is enhanced double relaxation. This hysteresis-free PNLC should find applications in spatial light modulators, laser beam control, and optical communications in infrared region.

  9. Hysteresis-free and submillisecond-response polymer network liquid crystal.

    PubMed

    Lee, Yun-Han; Gou, Fangwang; Peng, Fenglin; Wu, Shin-Tson

    2016-06-27

    We demonstrate a polymer network liquid crystal (PNLC) with negligible hysteresis while keeping submillisecond response time. By doping about 1% dodecyl acrylate (C12A) into the liquid crystal/monomer precursor, both hysteresis and residual birefringence are almost completely eliminated. The operating voltage and scattering properties remain nearly intact, but the tradeoff is enhanced double relaxation. This hysteresis-free PNLC should find applications in spatial light modulators, laser beam control, and optical communications in infrared region. PMID:27410631

  10. Polymer-assisted direct deposition of uniform carbon nanotube bundle networks for high performance transparent electrodes.

    PubMed

    Hellstrom, Sondra L; Lee, Hang Woo; Bao, Zhenan

    2009-06-23

    Flexible transparent electrodes are crucial for touch screen, flat panel display, and solar cell technologies. While carbon nanotube network electrodes show promise, characteristically poor dispersion properties have limited their practicality. We report that addition of small amounts of conjugated polymer to nanotube dispersions enables straightforward fabrication of uniform network electrodes by spin-coating and simultaneous tuning of parameters such as bundle size and density. After treatment in thionyl chloride, electrodes have sheet resistances competitive with other reported carbon nanotube based transparent electrodes to date. PMID:19422197

  11. Stimuli Responses of Topology-Controlled Polymer Networks and Liquid Crystalline Gels

    NASA Astrophysics Data System (ADS)

    Urayama, Kenji

    2006-03-01

    In this talk I will present and discuss the stimulus-response relationships of topology-controlled polymer networks and liquid crystalline gels. I will assess several modern entanglement theories of rubber elasticity on the basis of the multi-axial stress-strain data of end-linked polydimethylsiloxane (PDMS) networks with well-characterized structures. The dynamics of guest linear PDMS in host PDMS networks will also been discussed as a function of mesh size and molecular mass of guest chains. I will also demonstrate the highly extensible or damping elastomers of PDMS by simply controlling the topological characteristics such as the conformation of network chains, the amount of trapped entanglement and pendant chain. Furthermore, I will present the volume transition accompanying the shape variation induced by nematic-isotropic transition in liquid crystalline gels. I will also reveal the electrically-driven deformation coupled to director rotation in nematic gels.

  12. Fabrication of interpenetrating polymer network chitosan/gelatin porous materials and study on dye adsorption properties.

    PubMed

    Cui, Li; Xiong, Zihao; Guo, Yi; Liu, Yun; Zhao, Jinchao; Zhang, Chuanjie; Zhu, Ping

    2015-11-01

    One kind of adsorbent based on chitosan and gelatin with interpenetrating polymer networks (IPN) and porous dual structures was prepared using genipin as the cross-linker. These dual structures were demonstrated by means of Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Adsorptions of acid orange II dye from aqueous solution were carried out at different genipin contents, adsorption times and pH values. The results showed that this material was put up the largest adsorption capacity when the genipin content is 0.25 mmol/L, meanwhile, the lower the solution pH value the greater the adsorption capacity. The chitosan/gelatin interpenetrating polymer networks porous material displayed pH-sensitive and rapidly response in adsorption and desorption to pH altered. It is indicated that the cross-linked chitosan/gelatin interpenetrating polymer networks porous material could be used as a recyclable adsorbent in removal or separation of anionic dyes as environmental pH condition changed.

  13. Stability in alkaline aqueous electrolyte of air electrode protected with fluorinated interpenetrating polymer network membrane

    NASA Astrophysics Data System (ADS)

    Bertolotti, Bruno; Messaoudi, Houssam; Chikh, Linda; Vancaeyzeele, Cédric; Alfonsi, Séverine; Fichet, Odile

    2015-01-01

    We developed original anion exchange membranes to protect air electrodes operating in aqueous lithium-air battery configuration, i.e. supplied with atmospheric air and in concentrated aqueous lithium hydroxide. These protective membranes have an interpenetrating polymer network (IPN) architecture combining a hydrogenated cationic polyelectrolyte network based on poly(epichlorohydrin) (PECH) and a fluorinated neutral network based on perfluoropolyether (Fluorolink® MD700). Two phases, each one rich in one of the polymer, are co-continuous in the materials. This morphology allows combining their properties according to the weight proportions of each polymer. Thus, PECH/Fluorolink IPNs show ionic conductivity varying from 1 to 2 mS cm-1, water uptake from 30 to 90 wt.% and anionic transport number from 0.65 to 0.80 when the PECH proportion varies from 40 to 90 wt.%. These membranes have been systematically assembled on air electrodes. Air electrode protected with PECH/Fluorolink 70/30 IPN shows outstanding stability higher than 1000 h, i.e. a 20-fold increase in the lifetime of the non-modified electrode. This efficient membrane/air electrode assembly is promising for development of alkaline electrolyte based storage or production energy systems, such as metal air batteries or alkaline fuel cells.

  14. Ionically Cross-Linked Polymer Networks for the Multiple-Month Release of Small Molecules.

    PubMed

    Lawrence, Patrick G; Patil, Pritam S; Leipzig, Nic D; Lapitsky, Yakov

    2016-02-01

    Long-term (multiple-week or -month) release of small, water-soluble molecules from hydrogels remains a significant pharmaceutical challenge, which is typically overcome at the expense of more-complicated drug carrier designs. Such approaches are payload-specific and include covalent conjugation of drugs to base materials or incorporation of micro- and nanoparticles. As a simpler alternative, here we report a mild and simple method for achieving multiple-month release of small molecules from gel-like polymer networks. Densely cross-linked matrices were prepared through ionotropic gelation of poly(allylamine hydrochloride) (PAH) with either pyrophosphate (PPi) or tripolyphosphate (TPP), all of which are commonly available commercial molecules. The loading of model small molecules (Fast Green FCF and Rhodamine B dyes) within these polymer networks increases with the payload/network binding strength and with the PAH and payload concentrations used during encapsulation. Once loaded into the PAH/PPi and PAH/TPP ionic networks, only a few percent of the payload is released over multiple months. This extended release is achieved regardless of the payload/network binding strength and likely reflects the small hydrodynamic mesh size within the gel-like matrices. Furthermore, the PAH/TPP networks show promising in vitro cytocompatibility with model cells (human dermal fibroblasts), though slight cytotoxic effects were exhibited by the PAH/PPi networks. Taken together, the above findings suggest that PAH/PPi and (especially) PAH/TPP networks might be attractive materials for the multiple-month delivery of drugs and other active molecules (e.g., fragrances or disinfectants).

  15. Ionically Cross-Linked Polymer Networks for the Multiple-Month Release of Small Molecules.

    PubMed

    Lawrence, Patrick G; Patil, Pritam S; Leipzig, Nic D; Lapitsky, Yakov

    2016-02-01

    Long-term (multiple-week or -month) release of small, water-soluble molecules from hydrogels remains a significant pharmaceutical challenge, which is typically overcome at the expense of more-complicated drug carrier designs. Such approaches are payload-specific and include covalent conjugation of drugs to base materials or incorporation of micro- and nanoparticles. As a simpler alternative, here we report a mild and simple method for achieving multiple-month release of small molecules from gel-like polymer networks. Densely cross-linked matrices were prepared through ionotropic gelation of poly(allylamine hydrochloride) (PAH) with either pyrophosphate (PPi) or tripolyphosphate (TPP), all of which are commonly available commercial molecules. The loading of model small molecules (Fast Green FCF and Rhodamine B dyes) within these polymer networks increases with the payload/network binding strength and with the PAH and payload concentrations used during encapsulation. Once loaded into the PAH/PPi and PAH/TPP ionic networks, only a few percent of the payload is released over multiple months. This extended release is achieved regardless of the payload/network binding strength and likely reflects the small hydrodynamic mesh size within the gel-like matrices. Furthermore, the PAH/TPP networks show promising in vitro cytocompatibility with model cells (human dermal fibroblasts), though slight cytotoxic effects were exhibited by the PAH/PPi networks. Taken together, the above findings suggest that PAH/PPi and (especially) PAH/TPP networks might be attractive materials for the multiple-month delivery of drugs and other active molecules (e.g., fragrances or disinfectants). PMID:26811936

  16. Synthesis and redox activity of "clicked" triazolylbiferrocenyl polymers, network encapsulation of gold and silver nanoparticles and anion sensing.

    PubMed

    Rapakousiou, Amalia; Deraedt, Christophe; Irigoyen, Joseba; Wang, Yanlan; Pinaud, Noël; Salmon, Lionel; Ruiz, Jaime; Moya, Sergio; Astruc, Didier

    2015-03-01

    The design of redox-robust polymers is called for in view of interactions with nanoparticles and surfaces toward applications in nanonetwork design, sensing, and catalysis. Redox-robust triazolylbiferrocenyl (trzBiFc) polymers have been synthesized with the organometallic group in the side chain by ring-opening metathesis polymerization using Grubbs-III catalyst or radical polymerization and with the organometallic group in the main chain by Cu(I) azide alkyne cycloaddition (CuAAC) catalyzed by [Cu(I)(hexabenzyltren)]Br. Oxidation of the trzBiFc polymers with ferricenium hexafluorophosphate yields the stable 35-electron class-II mixed-valent biferrocenium polymer. Oxidation of these polymers with Au(III) or Ag(I) gives nanosnake-shaped networks (observed by transmission electron microscopy and atomic force microscopy) of this mixed-valent Fe(II)Fe(III) polymer with encapsulated metal nanoparticles (NPs) when the organoiron group is located on the side chain. The factors that are suggested to be synergistically responsible for the NP stabilization and network formation are the polymer bulk, the trz coordination, the nearby cationic charge of trzBiFc, and the inter-BiFc distance. For instance, reduction of such an oxidized trzBiFc-AuNP polymer to the neutral trzBiFc-AuNP polymer with NaBH4 destroys the network, and the product flocculates. The polymers easily provide modified electrodes that sense, via the oxidized Fe(II)Fe(III) and Fe(III)Fe(III) polymer states, respectively, ATP(2-) via the outer ferrocenyl units of the polymer and Pd(II) via the inner Fc units; this recognition works well in dichloromethane, but also to a lesser extent in water with NaCl as the electrolyte.

  17. Modeling heterogeneous polymer-grafted nanoparticle networks having biomimetic core-shell structure

    NASA Astrophysics Data System (ADS)

    Mbanga, Badel L.; Yashin, Victor V.; Holten-Andersen, Niels; Balazs, Anna C.

    Inspired by the remarkable mechanical properties of such biological structures as mussel adhesive fibers, we use 3D computational modeling to study the behavior of heterogeneous polymer-grafted nanoparticle (PGN) networks under tensile deformation. The building block of a PGN network is a nanoparticle with grafted polymer chains whose free ends' reactive groups can form both permanent and labile bonds with the end chains on the nearby particles. The tunable behavior of cross-linked PGN networks makes them excellent candidates for designing novel materials with enhanced mechanical properties. Here, we consider the PGN networks having the core-shell structures, in which the type and strength of the inter-particle bonds in the outer shell differ from those in the core. Using the computer simulations, we obtain and compare the ultimate tensile properties (strength, toughness, ductility) and the strain recovery properties for the uniform samples and various core-shell structures. We demonstrate that the core-shell structures could be designed to obtain highly resilient self-healing materials

  18. Effect of crystals and fibrous network polymer additives on cellular morphology of microcellular foams

    NASA Astrophysics Data System (ADS)

    Miyamoto, Ryoma; Utano, Tatsumi; Yasuhara, Shunya; Ishihara, Shota; Ohshima, Masahiro

    2015-05-01

    In this study, the core-back foam injection molding was used for preparing microcelluar polypropylene (PP) foam with either a 1,3:2,4 bis-O-(4-methylbenzylidene)-D-sorbitol gelling agent (Gel-all MD) or a fibros network polymer additive (Metablen 3000). Both agent and addiive could effectively control the celluar morphology in foams but somehow different ways. In course of cooling the polymer with Gel-all MD in the mold caity, the agent enhanced the crystal nucleation and resulted in the large number of small crystals. The crystals acted as effective bubble nucleation agent in foaming process. Thus, the agent reduced the cell size and increased the cell density, drastically. Furthermore, the small crystals provided an inhomogenuity to the expanding cell wall and produced the high open cell content with nano-scale fibril structure. Gell-all as well as Metablene 3000 formed a gel-like fibrous network in melt. The network increased the elongational viscosity and tended to prevent the cell wall from breaking up. The foaming temperature window was widened by the presence of the network. Especially, the temperature window where the macro-fibrous structure was formed was expanded to the higher temperature. The effects of crystal nucleating agent and PTFE on crystals' size and number, viscoelsticity, rheological propreties of PP and cellular morphology were compared and thorougly investigated.

  19. Chemical compatibility of PU/PAN interpenetrating polymer network membrane with substituted aromatic solvents.

    PubMed

    Kumar, H; Siddaramaiah

    2007-09-01

    Polyethylene glycol (PEG)-based polyurethane/polyacrylonitrile (PU/PAN, 50/50) semi-interpenetrating polymer network (SIPN) membrane has been studied from sorption/desorption cycles and diffusion behaviour with substituted aromatic probe molecules at 20, 40 and 60 degrees C. Sorption/desorption cycles have been repeated to evaluate polymer-solvent interaction. Organic solvents taken up or given out by IPN are measured periodically till equilibrium. Using these data, sorption (S), diffusion (D) and permeation (P) coefficients have been calculated from Fick's equation. Sorption data is correlated with solubility parameter of solvents and polymer. It was found that solvents of comparable solubility parameter with IPN interact more and thus there is an increase in sorption. Molecular mass between cross-link has been calculated using Flory Rehner equation. The cross-link density and degree of cross-linking of the membrane is calculated. From the temperature dependence of sorption and diffusion coefficients, the Arrhenius activation parameters like activation energy for diffusion (E(D)) and permeation (E(P)) processes have been calculated. Furthermore, the sorption results have been interpreted in terms of thermodynamic parameters such as change in enthalpy (DeltaH) and entropy (DeltaS). Concentration profiles of penetrants at different penetration depths in the polymer sample at different time intervals have also been calculated theoretically from a solution of Fick's equation under appropriate initial boundary conditions. PMID:17418943

  20. Thermoreversible Morphology and Conductivity of a Conjugated Polymer Network Embedded in Block Copolymer Self-Assemblies

    DOE PAGESBeta

    Han, Youngkyu; Carrillo, Jan-Michael Y.; Zhang, Zhe; Li, Yunchao; Hong, Kunlun; Sumpter, Bobby G.; Ohl, Michael; Paranthaman, Mariappan Parans; Smith, Gregory S.; Do, Changwoo

    2016-07-19

    Self-assembly of block copolymers provides numerous opportunities to create functional materials, utilizing self-assembled microdomains with a variety of morphology and periodic architectures as templates for functional nanofillers. Here new progress is reported toward the fabrication of thermally responsive and electrically conductive polymeric self-assemblies made from a water-soluble poly(thiophene) derivative with short poly(ethylene oxide) side chains and Pluronic L62 block copolymer solution in water. The structural and electrical properties of conjugated polymer-embedded self-assembled architectures are investigated by combining small-angle neutron and X-ray scattering, coarse-grained molecular dynamics simulations, and impedance spectroscopy. The L62 solution template organizes the conjugated polymers by stably incorporatingmore » them into the hydrophilic domains thus inhibiting aggregation. The changing morphology of L62 during the micellarto- lamellar phase transition defines the embedded conjugated polymer network. As a result, the conductivity is strongly coupled to the structural change of the templating L62 phase and exhibits thermally reversible behavior with no signs of quenching of the conductivity at high temperature. In conclusion, this study shows promise for enabling more flexibility in processing and utilizing water-soluble conjugated polymers in aqueous solutions for self-assembly based fabrication of stimuli-responsive nanostructures and sensory materials.« less

  1. Photomechanical bending mechanics of polydomain azobenzene liquid crystal polymer network films

    SciTech Connect

    Cheng Liang; Torres, Yanira; Oates, William S.; Lee, Kyung Min; McClung, Amber J.; Baur, Jeffery; White, Timothy J.

    2012-07-01

    Glassy, polydomain azobenzene liquid crystal polymer networks (azo-LCNs) have been synthesized, characterized, and modeled to understand composition dependence on large amplitude, bidirectional bending, and twisting deformation upon irradiation with linearly polarized blue-green (440-514 nm) light. These materials exhibit interesting properties for adaptive structure applications in which the shape of the photoresponsive material can be rapidly reconfigured with light. The basis for the photomechanical output observed in these materials is absorption of actinic light by azobenzene, which upon photoisomerization dictates an internal stress within the local polymer network. The photoinduced evolution of the underlying liquid crystal microstructure is manifested as macroscopic deformation of the glassy polymer film. Accordingly, this work examines the polarization-controlled bidirectional bending of highly concentrated azo-LCN materials and correlates the macroscopic output (observed as bending) to measured blocked stresses upon irradiation with blue-green light of varying polarization. The resulting photomechanical output is highly dependent on the concentration of crosslinked azobenzene mesogens employed in the formulation. Experiments that quantify photomechanical bending and photogenerated stress are compared to a large deformation photomechanical shell model to quantify the effect of polarized light interactions with the material during static and dynamic polarized light induced deformation. The model comparisons illustrate differences in internal photostrain and deformation rates as a function of composition and external mechanical constraints.

  2. Multifunctional supramolecular polymer networks as next-generation consolidants for archaeological wood conservation

    PubMed Central

    Walsh, Zarah; Janeček, Emma-Rose; Hodgkinson, James T.; Sedlmair, Julia; Koutsioubas, Alexandros; Spring, David R.; Welch, Martin; Hirschmugl, Carol J.; Toprakcioglu, Chris; Nitschke, Jonathan R.; Jones, Mark; Scherman, Oren A.

    2014-01-01

    The preservation of our cultural heritage is of great importance to future generations. Despite this, significant problems have arisen with the conservation of waterlogged wooden artifacts. Three major issues facing conservators are structural instability on drying, biological degradation, and chemical degradation on account of Fe3+-catalyzed production of sulfuric and oxalic acid in the waterlogged timbers. Currently, no conservation treatment exists that effectively addresses all three issues simultaneously. A new conservation treatment is reported here based on a supramolecular polymer network constructed from natural polymers with dynamic cross-linking formed by a combination of both host-guest complexation and a strong siderophore pendant from a polymer backbone. Consequently, the proposed consolidant has the ability to chelate and trap iron while enhancing structural stability. The incorporation of antibacterial moieties through a dynamic covalent linkage into the network provides the material with improved biological resistance. Exploiting an environmentally compatible natural material with completely reversible chemistries is a safer, greener alternative to current strategies and may extend the lifetime of many culturally relevant waterlogged artifacts around the world. PMID:25385610

  3. Effect of Supramolecular Interchain Sticking on the Low-Frequency Relaxation of Transient Polymer Networks.

    PubMed

    Seiffert, Sebastian

    2016-02-01

    Supramolecular polymer networks and gels often exhibit three effects in rheology as a function of increasing strength and extent of transient chain interlinkage: (i) the longest relaxation time increases, (ii) the elastic part of the complex shear modulus on timescales longer than that increases, and (iii) the frequency-dependent power-law scaling of this modulus gets shallower in this regime. In a recent report, these effects have been systematically assessed by comparing transient polymer networks derived from a common precursor modified with different extents of a common hydrogen-bonding supramolecular sticker. In this communication, complementary studies are discussed that are based on a set of polymers also derived from a common precursor but all modified with the same extent (4.8%) of very different supramolecular crosslinking motifs. This comparison reveals that effect (iii) can be rationalized by exacerbation of polydispersity effects to the relaxation time spectrum if supramolecular interchain sticking is present. In addition, effect (ii) is addressable to a simple thermodynamic argument that appraises the supramolecular sticking contribution to the elastic part of the shear modulus in the relaxation regime. PMID:26641417

  4. Multifunctional supramolecular polymer networks as next-generation consolidants for archaeological wood conservation.

    PubMed

    Walsh, Zarah; Janeček, Emma-Rose; Hodgkinson, James T; Sedlmair, Julia; Koutsioubas, Alexandros; Spring, David R; Welch, Martin; Hirschmugl, Carol J; Toprakcioglu, Chris; Nitschke, Jonathan R; Jones, Mark; Scherman, Oren A

    2014-12-16

    The preservation of our cultural heritage is of great importance to future generations. Despite this, significant problems have arisen with the conservation of waterlogged wooden artifacts. Three major issues facing conservators are structural instability on drying, biological degradation, and chemical degradation on account of Fe(3+)-catalyzed production of sulfuric and oxalic acid in the waterlogged timbers. Currently, no conservation treatment exists that effectively addresses all three issues simultaneously. A new conservation treatment is reported here based on a supramolecular polymer network constructed from natural polymers with dynamic cross-linking formed by a combination of both host-guest complexation and a strong siderophore pendant from a polymer backbone. Consequently, the proposed consolidant has the ability to chelate and trap iron while enhancing structural stability. The incorporation of antibacterial moieties through a dynamic covalent linkage into the network provides the material with improved biological resistance. Exploiting an environmentally compatible natural material with completely reversible chemistries is a safer, greener alternative to current strategies and may extend the lifetime of many culturally relevant waterlogged artifacts around the world. PMID:25385610

  5. Destruction and recovery of a nanorod conductive network in polymer nanocomposites via molecular dynamics simulation.

    PubMed

    Gao, Yangyang; Cao, Dapeng; Wu, Youping; Liu, Jun; Zhang, Liqun

    2016-03-28

    By adopting coarse-grained molecular dynamics simulation, we investigate the effects of end-functionalization and shear flow on the destruction and recovery of a nanorod conductive network in a functionalized polymer matrix. We find that the end-functionalization of polymeric chains can enhance the electrical conductivity of nanorod filled polymer nanocomposites, indicated by the decrease of the percolation threshold. However, there exists an optimal end-functionalization extent to reach the maximum electrical conductivity. In the case of steady shear flow, both homogeneous conductive probability and directional conductive probability perpendicular to the shear direction decrease with the shear rate, while the directional conductive probability parallel to the shear direction increases. Importantly, we develop a semi-empirical equation to describe the change of the homogeneous conductive probability as a function of the shear rate. Meanwhile, we obtain an empirical formula describing the relationship between the anisotropy of the conductive probability and the orientation of the nanorods. In addition, the conductivity stability increases with increasing nanorod volume fraction. During the recovery process of the nanorod conductive network, it can be fitted well by the model combining classical percolation theory and a time-dependent nanorod aggregation kinetic equation. The fitted recovery rate is similar for different nanorod volume fractions. In summary, this work provides some rational rules for fabricating polymer nanocomposites with excellent performance of electrical conductivity. PMID:26895557

  6. Destruction and recovery of a nanorod conductive network in polymer nanocomposites via molecular dynamics simulation.

    PubMed

    Gao, Yangyang; Cao, Dapeng; Wu, Youping; Liu, Jun; Zhang, Liqun

    2016-03-28

    By adopting coarse-grained molecular dynamics simulation, we investigate the effects of end-functionalization and shear flow on the destruction and recovery of a nanorod conductive network in a functionalized polymer matrix. We find that the end-functionalization of polymeric chains can enhance the electrical conductivity of nanorod filled polymer nanocomposites, indicated by the decrease of the percolation threshold. However, there exists an optimal end-functionalization extent to reach the maximum electrical conductivity. In the case of steady shear flow, both homogeneous conductive probability and directional conductive probability perpendicular to the shear direction decrease with the shear rate, while the directional conductive probability parallel to the shear direction increases. Importantly, we develop a semi-empirical equation to describe the change of the homogeneous conductive probability as a function of the shear rate. Meanwhile, we obtain an empirical formula describing the relationship between the anisotropy of the conductive probability and the orientation of the nanorods. In addition, the conductivity stability increases with increasing nanorod volume fraction. During the recovery process of the nanorod conductive network, it can be fitted well by the model combining classical percolation theory and a time-dependent nanorod aggregation kinetic equation. The fitted recovery rate is similar for different nanorod volume fractions. In summary, this work provides some rational rules for fabricating polymer nanocomposites with excellent performance of electrical conductivity.

  7. Conformational Statistics of Semi-Flexible Macromolecular Chains with Internal Joints

    PubMed Central

    Zhou, Yu

    2010-01-01

    Fluctuations in the bending angles at internal irregularities of DNA and RNA (such as symmetric loops, bulges, and nicks/gaps) have been observed from various experiments. However, little effort has been made to computationally predict and explain the statistical behavior of semi-flexible chains with internal defects. In this paper, we describe the general structure of these macromolecular chains as inextensible elastic chains with one or more internal joints which have limited ranges of rotation, and propose a method to compute the probability density functions of the end-to-end pose of these macromolecular chains. Our method takes advantage of the operational properties of the non-commutative Fourier transform for the group of rigid-body motions in three-dimensional space, SE(3). Two representative types of joints, the hinge for planar rotation and the ball joint for spatial rotation, are discussed in detail. The proposed method applies to various stiffness models of semi-flexible chain-like macromolecules. Examples are calculated using the Kratky-Porod model with specified stiffness, angular fluctuation, and joint locations. Entropic effects associated with internal angular fluctuations of semi-flexible macromolecular chains with internal joints can be computed using this formulation. Our method also provides a potential tool to detect the existence of internal irregularities. PMID:21243113

  8. The Reverse Thermal Effect in Epoxy Resins and Moisture Absorption in Semi-Interpenetrating Polymer Networks.

    NASA Astrophysics Data System (ADS)

    El-Sa'Ad, Leila

    1989-12-01

    Available from UMI in association with The British Library. Requires signed TDF. Epoxy resins exhibit many desirable properties which make them ideal subjects for use as matrices of composite materials in many commercial, military and space applications. However, due to their high cross-link density they are often brittle. Epoxy resin networks have been modified by incorporating tough, ductile thermoplastics. Such systems are referred to as Semi-Interpenetrating Polymer Networks (Semi-IPN). Systematic modification to the thermoplastics backbone allowed the morphology of the blend to be controlled from a homogeneous one-phase structure to fully separated structures. The moisture absorption by composites in humid environments has been found to lead to a deterioration in the physical and mechanical properties of the matrix. Therefore, in order to utilize composites to their full potential, their response to hot/wet environments must be known. The aims of this investigation were two-fold. Firstly, to study the effect of varying the temperature of exposure at different stages in the absorption process on the water absorption behaviour of a TGDDM/DDS epoxy resin system. Secondly, to study water absorption characteristics, under isothermal conditions, of Semi-Interpenetrating Polymer Networks possessing different morphologies, and develop a theoretical model to evaluate the diffusion coefficients of the two-phase structures. The mathematical treatment used in this analysis was based on Fick's second law of diffusion. Tests were performed on specimens immersed in water at 10 ^circ, 40^circ and 70^circC, their absorption behaviour and swelling behaviour, as a consequence of water absorption, were investigated. The absorption results of the variable temperature absorption tests indicated a saturation dependence on the absorption behaviour. Specimens saturated at a high temperature will undergo further absorption when transferred to a lower temperature. This behaviour was

  9. Interpenetrating polymer network of locust bean gum-poly (vinyl alcohol) for controlled release drug delivery.

    PubMed

    Kaity, Santanu; Isaac, Jinu; Ghosh, Animesh

    2013-04-15

    A novel interpenetrating polymer network (IPN) microspheres of locust bean gum (LBG) and poly (vinyl alcohol) (PVA) was developed for oral controlled release of buflomedil hydrochloride (BH) by emulsion crosslinking method using glutaraldehyde as crosslinker. The effects of gum-polymer ratio, concentration of crosslinker and internal phase viscosity were evaluated thoroughly. Drug entrapment efficiency, particle size distribution, swelling property and in vitro release characteristics with kinetic modelling of microspheres were evaluated. The microspheres were characterised by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), solid state C(13) NMR, X-ray diffraction study (XRD) and differential scanning colorimetry (DSC). The microspheres showed control release property without showing any incompatibility in IPN device. Hence, IPN microspheres of LBG and PVA can be used as a potential carrier for controlled oral delivery of highly water soluble drugs like BH.

  10. Radiation synthesis and characterisation of the network structure of natural/synthetic double-network superabsorbent polymers

    NASA Astrophysics Data System (ADS)

    Şen, Murat; Hayrabolulu, Hande

    2012-09-01

    In this study radiation synthesis and characterisation of the network structure of acrylic acid sodium salt/locust bean gum, (AAcNa/LBG) natural/synthetic double-network super absorbent polymers were investigated. Quartet systems composed of acrylic acid sodium salt/locust bean gum/N,N methylene bis acrylamide/water (AAcNa/LBG/MBAAm/water) were prepared at varying degree of neutralisations (DN) by controlling the DN value of AAc and irradiated with gamma rays at ambient temperature at a very low dose rate. The influences of the DN on the swelling and network properties were examined. It was observed that the DN strongly affected the gelation and super absorption properties of the gels. Molecular weight between crosslinks (M), effective crosslink density (νe) and mesh size (ξ) of SAPs were calculated from swelling and shear modules data obtained from compression and oscillatory frequency sweep tests. M values obtained from the uniaxial deformation experiments were very close to those obtained from the oscillatory shear experiments excluding the completely neutralised gel system. It was concluded that the uniaxial compression technique could be used for the characterisation of the network structure of a hydrogel as along with the rheological analyses; however, a very precise control of the gel size was also needed.

  11. Bismaleimide and cyanate ester based sequential interpenetrating polymer networks for high temperature application

    NASA Astrophysics Data System (ADS)

    Geng, Xing

    2005-07-01

    A research area of high activity in connection with aerospace engineering has been the development of polymer thermosetting resins that can withstand temperature as high as 300°C while maintaining adequate toughness and providing ease of processing to enable low temperature and low cost composite fabrication methods. In order to meet such requirements, sequential interpenetrating polymer networks (IPNs) based on bismaleimide (BMI) and cyanate ester (CE) monomers were investigated. In these systems, a polycyanurate network is first formed in the presence of BMI and appropriate reactive diluent monomers and, in a second step, a network based on the BMI is created in the presence of a fully formed polycyanurate network. The materials developed can be processed at relatively low temperature (<150°C) and with the aid of electron beam (EB) curing. Of major importance to the success of this work was the identification of a reactive diluent that improves ease of processing and has tailored reactivity to allow for the controlled synthesis of CE-BMI sequential IPNs. Based on solubility and reactivity of a number of reactive diluents, N-acryloylmorpholine (AMP) was selected as a co-monomer for BMI copolymerization. A donor-acceptor reaction mechanism was suggested to explain the relative reactivity of a variety of reactive diluents towards maleimide functionality. The optimum processing parameters for the formation of the first network were determined through the study of metal catalyzed cure and hydrolysis of cyanate esters, whereas the reaction behavior for second network formation in terms of the influence of EB dose rate and temperature was elucidated through an in-situ kinetics study of maleimide and AMP copolymerization. Structure-property relationships were developed which allowed for the design of improved resin systems. In particular, an appropriate network coupler possessing cyanate ester and maleimide functionality was synthesized to link the polycyanurate first

  12. Simple one-step process for immobilization of biomolecules on polymer substrates based on surface-attached polymer networks.

    PubMed

    Rendl, Martin; Bönisch, Andreas; Mader, Andreas; Schuh, Kerstin; Prucker, Oswald; Brandstetter, Thomas; Rühe, Jürgen

    2011-05-17

    For the miniaturization of biological assays, especially for the fabrication of microarrays, immobilization of biomolecules at the surfaces of the chips is the decisive factor. Accordingly, a variety of binding techniques have been developed over the years to immobilize DNA or proteins onto such substrates. Most of them require rather complex fabrication processes and sophisticated surface chemistry. Here, a comparatively simple immobilization technique is presented, which is based on the local generation of small spots of surface attached polymer networks. Immobilization is achieved in a one-step procedure: probe molecules are mixed with a photoactive copolymer in aqueous buffer, spotted onto a solid support, and cross-linked as well as bound to the substrate during brief flood exposure to UV light. The described procedure permits spatially confined surface functionalization and allows reliable binding of biological species to conventional substrates such as glass microscope slides as well as various types of plastic substrates with comparable performance. The latter also permits immobilization on structured, thermoformed substrates resulting in an all-plastic biochip platform, which is simple and cheap and seems to be promising for a variety of microdiagnostic applications. PMID:21491877

  13. Simple one-step process for immobilization of biomolecules on polymer substrates based on surface-attached polymer networks.

    PubMed

    Rendl, Martin; Bönisch, Andreas; Mader, Andreas; Schuh, Kerstin; Prucker, Oswald; Brandstetter, Thomas; Rühe, Jürgen

    2011-05-17

    For the miniaturization of biological assays, especially for the fabrication of microarrays, immobilization of biomolecules at the surfaces of the chips is the decisive factor. Accordingly, a variety of binding techniques have been developed over the years to immobilize DNA or proteins onto such substrates. Most of them require rather complex fabrication processes and sophisticated surface chemistry. Here, a comparatively simple immobilization technique is presented, which is based on the local generation of small spots of surface attached polymer networks. Immobilization is achieved in a one-step procedure: probe molecules are mixed with a photoactive copolymer in aqueous buffer, spotted onto a solid support, and cross-linked as well as bound to the substrate during brief flood exposure to UV light. The described procedure permits spatially confined surface functionalization and allows reliable binding of biological species to conventional substrates such as glass microscope slides as well as various types of plastic substrates with comparable performance. The latter also permits immobilization on structured, thermoformed substrates resulting in an all-plastic biochip platform, which is simple and cheap and seems to be promising for a variety of microdiagnostic applications.

  14. Evaluation of Metal-Organic Frameworks and Porous Polymer Networks for CO2 -Capture Applications.

    PubMed

    Verdegaal, Wolfgang M; Wang, Kecheng; Sculley, Julian P; Wriedt, Mario; Zhou, Hong-Cai

    2016-03-21

    This manuscript presents experimental data for 20 adsorption materials (metal-organic frameworks, porous polymer networks, and Zeolite-5A), including CO2 and N2 isotherms and heat capacities. With input from only experimental data, working capacities per energy for each material were calculated. Furthermore, by running seven different carbon-capture scenarios in which the initial flue-gas composition and process temperature was systematically changed, we present a range of performances for each material and quantify how sensitive each is to these varying parameters. The presented calculations provide researchers with a tool to investigate promising carbon-capture materials more easily and completely.

  15. Reactive molecular dynamics of network polymers: Generation, characterization and mechanical properties

    NASA Astrophysics Data System (ADS)

    Shankar, Chandrashekar

    The goal of this research was to gain a fundamental understanding of the properties of networks created by the ring opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) used in self-healing materials. To this end we used molecular simulation methods to generate realistic structures of DCPD networks, characterize their structures, and determine their mechanical properties. Density functional theory (DFT) calculations, complemented by structural information derived from molecular dynamics simulations were used to reconstruct experimental Raman spectra and differential scanning calorimetry (DSC) data. We performed coarse-grained simulations comparing networks generated via the ROMP reaction process and compared them to those generated via a RANDOM process, which led to the fundamental realization that the polymer topology has a unique influence on the network properties. We carried out fully atomistic simulations of DCPD using a novel algorithm for recreating ROMP reactions of DCPD molecules. Mechanical properties derived from these atomistic networks are in excellent agreement with those obtained from coarse-grained simulations in which interactions between nodes are subject to angular constraints. This comparison provides self-consistent validation of our simulation results and helps to identify the level of detail necessary for the coarse-grained interaction model. Simulations suggest networks can classified into three stages: fluid-like, rubber-like or glass-like delineated by two thresholds in degree of reaction alpha: The onset of finite magnitudes for the Young's modulus, alphaY, and the departure of the Poisson ration from 0.5, alphaP. In each stage the polymer exhibits a different predominant mechanical response to deformation. At low alpha < alphaY it flows. At alpha Y < alpha < alphaP the response is entropic with no change in internal energy. At alpha > alphaP the response is enthalpic change in internal energy. We developed graph theory

  16. Tailoring the Structure of Polymer Networks with Photo-Controlled Radical Polymerization

    NASA Astrophysics Data System (ADS)

    Singh, Awaneesh; Kuksenok, Olga; Johnson, Jeremiah A.; Balazs, Anna C.

    Using dissipative particle dynamics (DPD) approach, we developed a novel computational model to study the photo-controlled radical polymerization (photo-CRP) within polymer networks with embedded iniferters. The polymerization process can be turned ``on'' or ``off'' in response to light and the polymerization rate can be modulated by altering the light intensity. This ``photo-growth'' approach allows us to impart changes in the gel network pore size and composition to form photo-tunable smart materials. For example, our approach allows us to design gel composites that are comprised of two distinct layers made of two compatible components at low photo-iniferter concentrations or gel composites that are comprised of two incompatible components that are relatively well intermixed at high photo-iniferter concentration.

  17. Exploiting Dynamic Bonds in Polymer-grafted Nanoparticle Networks to Create Mechanomutable, Reconfigurable Composites

    NASA Astrophysics Data System (ADS)

    Balazs, Anna C.; Hamer, Matthew J.; Iyer, Balaji V. S.; Yashin, Victor V.

    2015-03-01

    Via a new dynamic, three-dimensional computer model, we simulate the tensile deformation of polymer-grafted nanoparticles (PGNs) that are cross-linked by labile bonds, which can readily rupture and reform. For a range of relatively high strains, the network does not fail, but rather restructures into a stable, ordered structure. Within this network, the reshuffling of the labile bonds enables the formation of this new morphology. The studies reveal that the appropriate combination of stress-responsive hybrid materials and applied stress can yield distinct opportunities to dynamically switch between different structures, and thus, the properties of the material. Thus, the results provide guidelines for designing mechano-responsive hybrid materials that undergo controllable structural transitions through the application of applied forces.

  18. Interfacial fracture between highly crosslinked polymer networks and a solid surface: Effect of interfacial bond density

    SciTech Connect

    STEVENS,MARK J.

    2000-03-23

    For highly crosslinked, polymer networks bonded to a solid surface, the effect of interfacial bond density as well as system size on interfacial fracture is studied molecular dynamics simulations. The correspondence between the stress-strain curve and the sequence of molecular deformations is obtained. The failure strain for a fully bonded surface is equal to the strain necessary to make taut the average minimal path through the network from the bottom solid surface to the top surface. At bond coverages less than full, nanometer scale cavities form at the surface yielding an inhomogeneous strain profile. The failure strain and stress are linearly proportional to the number of bonds at the interface unless the number of bonds is so few that van der Waals interactions dominate. The failure is always interfacial due to fewer bonds at the interface than in the bulk.

  19. Full eigenvalues of the Markov matrix for scale-free polymer networks

    NASA Astrophysics Data System (ADS)

    Zhang, Zhongzhi; Guo, Xiaoye; Lin, Yuan

    2014-08-01

    Much important information about the structural and dynamical properties of complex systems can be extracted from the eigenvalues and eigenvectors of a Markov matrix associated with random walks performed on these systems, and spectral methods have become an indispensable tool in the complex system analysis. In this paper, we study the Markov matrix of a class of scale-free polymer networks. We present an exact analytical expression for all the eigenvalues and determine explicitly their multiplicities. We then use the obtained eigenvalues to derive an explicit formula for the random target access time for random walks on the studied networks. Furthermore, based on the link between the eigenvalues of the Markov matrix and the number of spanning trees, we confirm the validity of the obtained eigenvalues and their corresponding degeneracies.

  20. Sulfonate-grafted porous polymer networks for preferential CO2 adsorption at low pressure.

    PubMed

    Lu, Weigang; Yuan, Daqiang; Sculley, Julian; Zhao, Dan; Krishna, Rajamani; Zhou, Hong-Cai

    2011-11-16

    A porous polymer network (PPN) grafted with sulfonic acid (PPN-6-SO(3)H) and its lithium salt (PPN-6-SO(3)Li) exhibit significant increases in isosteric heats of CO(2) adsorption and CO(2)-uptake capacities. IAST calculations using single-component-isotherm data and a 15/85 CO(2)/N(2) ratio at 295 K and 1 bar revealed that the sulfonate-grafted PPN-6 networks show exceptionally high adsorption selectivity for CO(2) over N(2) (155 and 414 for PPN-6-SO(3)H and PPN-6-SO(3)Li, respectively). Since these PPNs also possess ultrahigh physicochemical stability, practical applications in postcombustion capture of CO(2) lie well within the realm of possibility.

  1. Microstructural Characterization of Semi-Interpenetrating Polymer Networks by Positron Lifetime Spectroscopy

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Pater, Ruth H.; Eftekhari, Abe

    1996-01-01

    Thermoset and thermoplastic polyimides have complementary physical and mechanical properties. Whereas thermoset polyimides are brittle and generally easier to process, thermoplastic polyimides are tough but harder to process. A combination of these two types of polyimides may help produce polymers more suitable for aerospace applications. Semi-Interpenetrating Polymer Networks (S-IPN) of thermoset LaRC(TM)-RP46 and thermoplastic LaRC(TM)-IA polyimides were prepared in weight percent ratios ranging from 100:0 to 0:100. Positron lifetime measurements were made in these samples to correlate their free volume features with physical and mechanical properties. As expected, positronium atoms are not formed in these samples. The second lifetime component has been used to infer the positron trap dimensions. The 'free volume' goes through a minimum at a ratio of about 50:50, and this suggests that S-IPN samples are not merely solid solutions of the two polymers. These data and related structural properties of the S-IPN samples are discussed.

  2. Light-triggered conducting properties of a random carbon nanotubes network in a photochromic polymer matrix

    NASA Astrophysics Data System (ADS)

    Castagna, R.; Sciascia, C.; Srimath Kandada, A. R.; Meneghetti, M.; Lanzani, G.; Bertarelli, C.

    2011-10-01

    Photochromic materials reversibly change their colour due to a photochemical reaction that takes place when the material is irradiated with photons of suitable energy. This peculiar feature has been extensively exploited to develop smart sunglasses, filters and inks. With a proper molecular design it is possible to enable modulation not only of colour but also of other properties such as refractive index, dipole moment, nonlinear optical properties or conductivity by a photoswitching of the molecular structure. The approach herein developed consists in modifying, upon irradiation, the properties of a molecular component coupled with the photochromic molecule. In particular, the switching features of photochromic systems are matched with the intriguing peculiar properties of carbon nanotubes (CNTs). A photochromic polyester has been properly synthesised to be used as switching polymer matrix coupled with a network of CNTs. Irradiation of the polymer/CNTs blend results into a light-triggered conductance switching. The reversible electrocyclization of the polymer under UV-vis illumination results into a modification of the inter-tube charge mobility, and accordingly, of the overall resistance of the blend. Solution techniques allow us to obtain blended films with sheet resistance modulation larger than 150%, good thermal stability and fatigue resistance at room conditions, in an easier, faster and scalable way as respect to the single-molecule approach.ÿ

  3. Relaxation of non-equilibrium entanglement networks in thin polymer films.

    PubMed

    McGraw, Joshua D; Fowler, Paul D; Ferrari, Melissa L; Dalnoki-Veress, Kari

    2013-01-01

    It is known that polymer films, prepared by spin coating, inherit non-equilibrium configurations which can affect macroscopic film properties. Here we present the results of crazing experiments that support this claim; our measurements indicate that the as-cast chain configurations are strongly stretched as compared to equilibrium Gaussian configurations. The results of our experiments also demonstrate that the entanglement network equilibrates on a time scale comparable to one reptation time. Having established that films can be prepared with an equilibrium entanglement network, we proceed by confining polymers to films in which the thickness is comparable to the molecular size. By stacking two such films, a bilayer is created with a buried entropic interface. Such an interface has no enthalpic cost, only an entropic penalty associated with the restricted configurations of molecules that cannot cross the mid-plane of the bilayer. In the melt, the entropic interface heals as chains from the two layers mix and entangle with one another; crazing measurements allow us to probe the dynamics of two films becoming one. Healing of the entropic interface is found to take less than one bulk reptation time.

  4. Nanocasting Design and Spatially Selective Sulfonation of Polystyrene-Based Polymer Networks as Solid Acid Catalysts.

    PubMed

    Richter, Felix H; Sahraoui, Laila; Schüth, Ferdi

    2016-09-12

    Nanocasting is a general and widely applied method in the generation of porous materials during which a sacrificial solid template is used as a mold on the nanoscale. Ideally, the resulting structure is the inverse of the template. However, replication is not always as direct as anticipated, so the influences of the degree of pore filling and of potential restructuring processes after removal of the template need to be considered. These apparent limitations give rise to opportunities in the synthesis of poly(styrene-co-divinylbenzene) (PSD) polymer networks of widely varying porosities (BET surface area=63-562 m(2)  g(-1) ; Vtot =0.18-1.05 cm(3)  g(-1) ) by applying a single synthesis methodology. In addition, spatially selective sulfonation on the nanoscale seems possible. Together, nanocasting and sulfonation enable rational catalyst design. The highly porous nanocast and predominantly surface-sulfonated PSD networks approach the activity of the corresponding molecular catalyst, para-toluenesulfonic acid, and exceed those of commercial ion-exchange polymers in the depolymerization of macromolecular inulin.

  5. Light-induced stress relief to improve flaw tolerance in network polymers

    SciTech Connect

    Long, Kevin N.; Dunn, Martin L.; Scott, Timothy F.; Turpin, Lucas P.; Qi, H. Jerry

    2010-03-15

    We demonstrate the ability to use photoactivated stress relaxation to improve flaw tolerance in network polymers. Unlike most self-healing polymers, which effectively close flaws by locally introducing healing agents (such as uncured resins), here light is used to relax elevated stresses around a flaw before it reaches a critical state, which reduces the threat that the flaw poses to the structural integrity of the material. In this study, we fabricate specimens with well-defined flaws and uniaxially stretch them to failure. By irradiating the specimens with UV light (365 nm) before failure, the nominal strain at failure is increased by 70% and the corresponding nominal stress is increased by 30% compared with nonirradiated specimens. To better understand the phenomena that occur at the multiaxial stress state at the flaw, we model the photomechanics using a recently developed finite element approach that accurately describes the light propagation, photochemistry, radical-induced network evolution, and the mechanical behavior of the material. Model predictions agree well with the experimental results and elucidate the role that photoinduced stress relaxation has on improving flaw tolerance.

  6. Nanocasting Design and Spatially Selective Sulfonation of Polystyrene-Based Polymer Networks as Solid Acid Catalysts.

    PubMed

    Richter, Felix H; Sahraoui, Laila; Schüth, Ferdi

    2016-09-12

    Nanocasting is a general and widely applied method in the generation of porous materials during which a sacrificial solid template is used as a mold on the nanoscale. Ideally, the resulting structure is the inverse of the template. However, replication is not always as direct as anticipated, so the influences of the degree of pore filling and of potential restructuring processes after removal of the template need to be considered. These apparent limitations give rise to opportunities in the synthesis of poly(styrene-co-divinylbenzene) (PSD) polymer networks of widely varying porosities (BET surface area=63-562 m(2)  g(-1) ; Vtot =0.18-1.05 cm(3)  g(-1) ) by applying a single synthesis methodology. In addition, spatially selective sulfonation on the nanoscale seems possible. Together, nanocasting and sulfonation enable rational catalyst design. The highly porous nanocast and predominantly surface-sulfonated PSD networks approach the activity of the corresponding molecular catalyst, para-toluenesulfonic acid, and exceed those of commercial ion-exchange polymers in the depolymerization of macromolecular inulin. PMID:27561365

  7. Molecular template-directed synthesis of microporous polymer networks for highly selective CO2 capture.

    PubMed

    Shi, Yao-Qi; Zhu, Jing; Liu, Xiao-Qin; Geng, Jian-Cheng; Sun, Lin-Bing

    2014-11-26

    Porous polymer networks have great potential in various applications including carbon capture. However, complex monomers and/or expensive catalysts are commonly used for their synthesis, which makes the process complicated, costly, and hard to scale up. Herein, we develop a molecular template strategy to fabricate new porous polymer networks by a simple nucleophilic substitution reaction of two low-cost monomers (i.e., chloromethylbenzene and ethylene diamine). The polymerization reactions can take place under mild conditions in the absence of any catalysts. The resultant materials are interconnected with secondary amines and show well-defined micropores due to the structure-directing role of solvent molecules. These properties make our materials highly efficient for selective CO2 capture, and unusually high CO2/N2 and CO2/CH4 selectivities are obtained. Furthermore, the adsorbents can be completely regenerated under mild conditions. Our materials may provide promising candidates for selective capture of CO2 from mixtures such as flue gas and natural gas.

  8. Strain Hardening and Strain Softening of Reversibly Cross-linked Supramolecular Polymer Networks.

    PubMed

    Xu, Donghua; Craig, Stephen L

    2011-09-27

    The large amplitude oscillatory shear behavior of metallo-supramolecular polymer networks formed by adding bis-Pd(II) cross-linkers to poly(4-vinylpyridine) (PVP) in dimethyl sulfoxide (DMSO) solution is reported. The influence of scanning frequency, dissociation rate of cross-linkers, concentration of cross-linkers, and concentration of PVP solution on the large amplitude oscillatory shear behavior is explored. In semidilute unentangled PVP solutions, above a critical scanning frequency, strain hardening of both storage moduli and loss moduli is observed. In the semidilute entangled regime of PVP solution, however, strain softening is observed for samples with faster cross-linkers (k(d) ∼ 1450 s(-1)), whereas strain hardening is observed for samples with slower cross-linkers (k(d) ∼ 17 s(-1)). The mechanism of strain hardening is attributed primarily to a strain-induced increase in the number of elastically active chains, with possible contributions from non-Gaussian stretching of polymer chains at strains approaching network fracture. The divergent strain softening of samples with faster cross-linkers in semidilute entangled PVP solutions, relative to the strain hardening of samples with slower cross-linkers, is consistent with observed shear thinning/shear thickening behavior reported previously and is attributed to the fact that the average time that a cross-linker remains detached is too short to permit the local relaxation of polymer chain segments that is necessary for a net conversion of elastically inactive to elastically active cross-linkers. These and other observations paint a picture in which strain softening and shear thinning arise from the same set of molecular mechanisms, conceptually uniting the two nonlinear responses for this system.

  9. Strain Hardening and Strain Softening of Reversibly Cross-linked Supramolecular Polymer Networks

    PubMed Central

    Xu, Donghua; Craig, Stephen L.

    2011-01-01

    The large amplitude oscillatory shear behavior of metallo-supramolecular polymer networks formed by adding bis-Pd(II) cross-linkers to poly(4-vinylpyridine) (PVP) in dimethyl sulfoxide (DMSO) solution is reported. The influence of scanning frequency, dissociation rate of cross-linkers, concentration of cross-linkers, and concentration of PVP solution on the large amplitude oscillatory shear behavior is explored. In semidilute unentangled PVP solutions, above a critical scanning frequency, strain hardening of both storage moduli and loss moduli is observed. In the semidilute entangled regime of PVP solution, however, strain softening is observed for samples with faster cross-linkers (kd ∼ 1450 s−1), whereas strain hardening is observed for samples with slower cross-linkers (kd ∼ 17 s−1). The mechanism of strain hardening is attributed primarily to a strain-induced increase in the number of elastically active chains, with possible contributions from non-Gaussian stretching of polymer chains at strains approaching network fracture. The divergent strain softening of samples with faster cross-linkers in semidilute entangled PVP solutions, relative to the strain hardening of samples with slower cross-linkers, is consistent with observed shear thinning/shear thickening behavior reported previously and is attributed to the fact that the average time that a cross-linker remains detached is too short to permit the local relaxation of polymer chain segments that is necessary for a net conversion of elastically inactive to elastically active cross-linkers. These and other observations paint a picture in which strain softening and shear thinning arise from the same set of molecular mechanisms, conceptually uniting the two nonlinear responses for this system. PMID:22043083

  10. Aneesur Rahman Prize Talk: Dynamics of Entangled Polymer Melts: Perceptive from Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Grest, Gary S.

    2008-03-01

    Twenty years ago at the APS March Meeting, Kurt Kremer and I presented the first numerical evidence from computer simulations that the reptation model of Edwards and de Gennes correctly describes the dynamics of entangled linear polymer melts. For chains longer than the entanglement length Ne, the monomers of a chain move predominantly along their own contour. The distinctive signature of reptation dynamics, which we observed, was that on intermediate time scales, the mean squared displacement of a monomer increases with time as t^ 1/4. Though these early simulations were limited to chains of a few Ne, they demonstrated the potential of computer simulations to contribute to our understanding of polymer dynamics. Here I will review the progress over the past twenty years and present an outlook for the future in modeling entangled polymer melts and networks. With present day computers coupled with efficient parallel molecular dynamics codes, it is now possible to follow the equilibrium dynamics of chains of length 10-20Ne from the early Rouse regime to the long time diffusive regime. Result of these simulations support the earlier results obtained on chains of only a few Ne. Further evidence for the tube models of polymer dynamics has been obtained by identifying the primitive path mesh that characterizes the microscopic topological state of the computer- generated conformations of the chains. In particular, the plateau moduli derived on the basis of this analysis quantitatively reproduce experimental data for a wide spectrum of entangled polymer liquids including semi-dilute theta solutions of synthetic polymers, the corresponding dense melts, and solutions of semi-flexible (bio)polymers such as f-actin or suspensions of rodlike viruses. We also find that in agreement with the reptation model, the stress, end-to-end distance and entanglement length of an entangled melt subjected to uniaxial elongation, all relax on the same time scale.

  11. 1,2,3-Triazolium-Based Epoxy-Amine Networks: Ion-Conducting Polymer Electrolytes.

    PubMed

    Ly Nguyen, Thi Khanh; Obadia, Mona Marie; Serghei, Anatoli; Livi, Sébastien; Duchet-Rumeau, Jannick; Drockenmuller, Eric

    2016-07-01

    A diepoxy-functionalized 1,2,3-triazolium ionic liquid is synthesized in three steps and used in combination with a poly(propylene glycol) diamine to obtain ion-conducting epoxy-amine networks (EANs). The curing kinetics are followed by Fourier transform infrared spectroscopy, while the physical, mechanical, and ion-conducting properties of the resulting networks are studied by swelling experiments, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical thermal analysis, and broadband dielectric spectroscopy. The curing kinetics and thermomechanical properties of this system are relatively similar to those of conventional DGEBA- (bisphenol A diglycidyl ether)-based EANs with low glass transition temperature (Tg = -44 and -52 °C, respectively) characteristic of rubbery polymer networks. The anhydrous ionic conductivity of the pure network at 30 °C reaches a remarkably high value of 2 × 10(-7) S cm(-1) that could be further increased to 10(-6) S cm(-1) by the addition of 10 wt% LiTFSI.

  12. Assessing the Strength Enhancement of Heterogeneous Networks of Miscible Polymer Blends

    NASA Astrophysics Data System (ADS)

    Giller, Carl; Roland, Mike

    2013-03-01

    At the typical crosslink densities of elastomers, the failure properties vary inversely with mechanical stiffness, so that compounding entails a compromise between stiffness and strength. Our approach to circumvent this conventional limitation is by forming networks of two polymers that: (i) are thermodynamically miscible, whereby the chemical composition is uniform on the segmental level; and (ii) have markedly different reactivities for network formation. The resulting elastomer consists of one highly crosslinked component and one that is lightly or uncrosslinked. This disparity in crosslinking causes their respective contributions to the network mechanical response to differ diametrically. Earlier results showed some success with this approach for thermally crosslinked blends of 1,2-polybutadiene (PVE) and polyisoprene (PI), as well as ethylene-propylene copolymer (EPM) and ethylene-propylene-diene random terpolymer (EPDM), taking advantage of their differing reactivities to sulfur. In this work we demonstrate the miscibility of polyisobutylene (PIB) with butyl rubber (BR) (a copolymer of PIB and polyisoprene) and show that networks in which only the BR is crosslinked possess greater tensile strengths than neat BR over the same range of moduli. Office of Naval Research

  13. 1,2,3-Triazolium-Based Epoxy-Amine Networks: Ion-Conducting Polymer Electrolytes.

    PubMed

    Ly Nguyen, Thi Khanh; Obadia, Mona Marie; Serghei, Anatoli; Livi, Sébastien; Duchet-Rumeau, Jannick; Drockenmuller, Eric

    2016-07-01

    A diepoxy-functionalized 1,2,3-triazolium ionic liquid is synthesized in three steps and used in combination with a poly(propylene glycol) diamine to obtain ion-conducting epoxy-amine networks (EANs). The curing kinetics are followed by Fourier transform infrared spectroscopy, while the physical, mechanical, and ion-conducting properties of the resulting networks are studied by swelling experiments, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical thermal analysis, and broadband dielectric spectroscopy. The curing kinetics and thermomechanical properties of this system are relatively similar to those of conventional DGEBA- (bisphenol A diglycidyl ether)-based EANs with low glass transition temperature (Tg = -44 and -52 °C, respectively) characteristic of rubbery polymer networks. The anhydrous ionic conductivity of the pure network at 30 °C reaches a remarkably high value of 2 × 10(-7) S cm(-1) that could be further increased to 10(-6) S cm(-1) by the addition of 10 wt% LiTFSI. PMID:26924313

  14. The Configuration and Dynamics of Self-Attractive Flexible and Semi-Flexible Polymers

    NASA Astrophysics Data System (ADS)

    Larson, Ronald; Saha Dalal, Indranil; Kong, Miqiu

    2014-03-01

    We study ``bead-rod'' chains containing stiff Fraenkel springs with nearly fixed Kuhn length, but with varying numbers of rods representing each Kuhn length, Nr,K, modeled by incorporating a bending potential between consecutive rods. We find converged results as we increase the number of rods per Kuhn step. We find that at high ɛ*Nr,K, where ɛ* is the attractive interaction strength per bead normalized by kT, collapsed globules are produced at moderate dimensionless chain diameter σ* = 1/4, while for σ* = 1, helices are formed, and for σ* = 1/16, tori, folded bundles, and finally globules, are formed as ɛ*Nr,K increases. Under shear, a universal tumbling state is found where chain width in the shear gradient direction is independent of chain length and proportion to shear rate to the fourth power.

  15. Incorporation of network in synthesis of zircon-imprinted polymer and its effect on zircon ion extraction

    NASA Astrophysics Data System (ADS)

    Aladin, S.; Amran, M. B.; Buchari, B.; Arcana, I. M.

    2014-03-01

    The material polymer functionalized on SPE have been developed by ion- imprinted polymer. The ion-polymer with zircon ion as imprint ions were synthesized via bulk polymerization methods by forming binary complex Zr-Xylenol orange in 2-methoxy ethanol and copolymerizing in the presence of styrene as a monomer functional, divinyl benzene as a monomer cross-linker, and peroxide as an initiator. The zircon-imprinted polymer produced the porous polymer. It was indicated that zircon ion imprints were released under conditioning. The polymer particles both prior to and after leaching have been characterized by IR, SEM-EDS, TEM, and pore size. Incorporation of network polymer using divinyl benzene as the cross-linker were performances tested on zircon ion extraction, and the optimum of the mole ratio of styrene/DVB was observed about 1. The decrease of percent extraction of zircon ion when the mole ration of styrene/divinyl benzene < 1, due to the pores as binding sites of polymers were covered, and it was evidenced by the decrease in total pore volume.

  16. Electroactive semi-interpenetrating polymer networks architecture with tunable IR reflectivity

    NASA Astrophysics Data System (ADS)

    Chevrot, C.; Teyssié, D.; Verge, P.; Goujon, L.; Tran-Van, F.; Vidal, F.; Aubert, P. H.; Peralta, S.; Sauques, L.

    2011-04-01

    A promising alternative of multi-layered devices showing electrochromic properties results from the design of a self-supported semi-interpenetrating polymer network (semi-IPN) including an electronic conductive polymer (ECP) formed within. The formation of the ECP in the network has already been described by oxidative polymerization using iron trichloride as an oxidant and leading to conducting semi-IPN with mixed electronic and ionic conductivities as well as convenient mechanical properties. This presentation relates to the elaboration of such semi-IPN using polyethyleneoxide (PEO) network or a PEO/NBR (Nitrile Butadiene Rubber) IPN in which a linear poly (3,4-ethylenedioxythiophene) (PEDOT) is formed symmetrically and selectively as very thin layers very next to the two main faces of the film matrix. PEO/PEDOT semi-IPNs lead to interesting optical reflective properties in the IR between 0.8 and 25 μm. Reflectance contrasts up to 35 % is observed when, after swelling in an ionic liquid, a low voltage is applied between the two main faces of the film. However the low flexibility and brittleness of the film and a slow degradation in air at temperature up from 60°C prompted to replace the PEO matrix by a flexible PEO/NBR IPN one. Indeed, the combination of NBR and PEO in an IPN leads to materials possessing flexible properties, good ionic conductivity at 25°C as well as a better resistance to thermal ageing. Finally, NBR/PEO/PEDOT semi-IPNs allow observing comparable reflectance contrast in the IR range than those shown by PEO/PEDOT semi-IPNs.

  17. Influence of polydispersity on the isotropic-nematic boundary in melt of semiflexible diblock copolymer

    NASA Astrophysics Data System (ADS)

    Aliev, M. A.

    2015-12-01

    The analytical expressions have been obtained to describe the dependence of spinodal curve at which isotropic state of polydisperse melt of semiflexible diblock copolymer becomes unstable with respect to formation of nematic state on the polydispersity indices of the blocks, parameters of anisotropic interactions, and flexibility of blocks. The flexibility of blocks is taken into account within discrete worm-like chain model, lengths of blocks are assumed to be distributed by the Schulz-Zimm distribution. It is shown that increase of degree of polydispersity of blocks yields the increase of nematic spinodal temperature.

  18. New frontiers in single polymer dynamics

    NASA Astrophysics Data System (ADS)

    Schroeder, Charles

    2015-03-01

    Single molecule techniques allow for the direct observation of polymer dynamics under highly non-equilibrium conditions. Until recently, however, these methods have been largely confined to linear semi-flexible DNA molecules as ``model'' polymer chains. This talk will show recent work from our group in extending the field of single polymer dynamics to new materials, including branched polymers and truly flexible polymer chains. In this way, we explore new questions in classical polymer physics such as the role of architecture, topology, and backbone flexibility on chain dynamics at the molecular level. Recently, we used single molecule methods to directly visualize comb-shaped DNA polymers. Macromolecular DNA combs are synthesized utilizing a hybrid enzymatic-synthetic approach, wherein chemically modified DNA branches and DNA backbones are generated in separate polymerase chain reactions, followed by graft-onto reactions via ``click'' chemistry. This method allows for the synthesis of dual-color DNA combs, such that the backbone and side branches can be tracked independently using single molecule fluorescence microscopy. In this way, we study the dynamic properties of single comb polymers under flow, including conformational and stretching dynamics for highly branched chains and polymer relaxation following cessation of flow. In related work, we also study the dynamics of flexible polymer chains using fluorescently-labeled single stranded DNA. We observe that truly flexible polymers exhibit key differences in dynamics compared to semi-flexible DNA. Overall, our work highlights the ways in which single molecule methods can be brought to bear on fundamental problems in polymer physics.

  19. Probing the subglass relaxation behavior in model heterocyclic polymer networks by dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Kramarenko, V. Yu.; Ezquerra, T. A.; Privalko, V. P.

    2001-11-01

    The subglass relaxation (β) in model heterocyclic polymer networks (HPNs) with a controlled ratio of trimerized mono- and diisocyanates was characterized by dielectric spectroscopy in the frequency domain. The β relaxation in the investigated HPNs follows the Arrhenius law with unusually low values of the preexponential factor (10-17<τβ0<10-15 s). However, little influence of the local environment, as characterized by the network density, on the apparent activation energies ΔEβ is observed. This fact, combined with their fairly low absolute values (50.4-58.3 kJ/mol), were considered as typical of a noncooperative relaxation in loosely packed regions of a glassy quasilattice. Both the intensity and dielectric strength of the β relaxation in HPNs increase with increasing apparent network density (i.e., with lower ratios of linear and network structures in the system, L/N). This effect was explained by a model assuming that the total, composition-invariant, free volume available was distributed between densely packed domains comprising linear, two-arm isocyanurate heterocycles (ISHs) and loosely packed, three-arm ISHs, which form continuous, three-dimensional network structures. The experimental data for HPNs confirm Ngai's correlation between the logarithm of the secondary β-relaxation time and the Kohlrausch-Williams-Watts stretching exponent for the primary α relaxation. It is suggested that the absence of conjugated bonds within isocyanurate heterocycles makes them sufficiently flexible to allow for specific conformational transitions, like the ``chair-boat-chair'' transition in the structurally similar cyclohexyl ring.

  20. Mechanism of Shear Thickening in Reversibly Cross-linked Supramolecular Polymer Networks

    PubMed Central

    Xu, Donghua; Hawk, Jennifer L.; Loveless, David M.; Jeon, Sung Lan; Craig, Stephen L.

    2010-01-01

    We report here the nonlinear rheological properties of metallo-supramolecular networks formed by the reversible cross-linking of semi-dilute unentangled solutions of poly(4-vinylpyridine) (PVP) in dimethyl sulfoxide (DMSO). The reversible cross-linkers are bis-Pd(II) or bis-Pt(II) complexes that coordinate to the pyridine functional groups on the PVP. Under steady shear, shear thickening is observed above a critical shear rate, and that critical shear rate is experimentally correlated with the lifetime of the metal-ligand bond. The onset and magnitude of the shear thickening depend on the amount of cross-linkers added. In contrast to the behavior observed in most transient networks, the time scale of network relaxation is found to increase during shear thickening. The primary mechanism of shear thickening is ascribed to the shear-induced transformation of intrachain cross-linking to interchain cross-linking, rather than nonlinear high tension along polymer chains that are stretched beyond the Gaussian range. PMID:20479956

  1. Persistence-length renormalization of polymers in a crowded environment of hard disks.

    PubMed

    Schöbl, S; Sturm, S; Janke, W; Kroy, K

    2014-12-01

    The most conspicuous property of a semiflexible polymer is its persistence length, defined as the decay length of tangent correlations along its contour. Using an efficient stochastic growth algorithm to sample polymers embedded in a quenched hard-disk fluid, we find apparent wormlike chain statistics with a renormalized persistence length. We identify a universal form of the disorder renormalization that suggests itself as a quantitative measure of molecular crowding. PMID:25526167

  2. Fluorescent nanoparticles based on a microporous organic polymer network: fabrication and efficient energy transfer to surface-bound dyes.

    PubMed

    Patra, Abhijit; Koenen, Jan-Moritz; Scherf, Ullrich

    2011-09-14

    Well-defined nanoparticles composed of a tetraphenylmethane-based microporous polymer network with an average particle diameter of 30-60 nm were fabricated by a miniemulsion polymerization technique. Strong green emission was observed and efficient excitation energy transfer from nanoparticles to surface-bound dye molecules was explored. PMID:21805006

  3. Diffusion processes of single fluorescent molecules in a polymer-based thin material with three-dimensional network.

    PubMed

    Ito, Syoji; Kusumi, Takatsugu; Takei, Satoshi; Miyasaka, Hiroshi

    2009-11-01

    Single-molecule imaging revealed the hierarchical mobility change of guest dyes in a polymer-based thin film under network formation: at the early stage of the reaction, only the translational diffusion was inhibited while keeping the rotational diffusion active, the fraction of translationally immobilized dyes increased with increasing crosslinking, and at the last stage both motions stopped.

  4. Novel biobased photo-crosslinked polymer networks prepared from vegetable oil and 2,5-furan diacrylate

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Novel biobased crosslinked polymer networks were prepared from vegetable oil with 2,5-furan diacrylate as a difunctional stiffener through UV photopolymerization, and the mechanical properties of the resulting films were evaluated. The vegetable oil raw materials used were acrylated epoxidized soybe...

  5. In silico design of porous polymer networks: high-throughput screening for methane storage materials.

    PubMed

    Martin, Richard L; Simon, Cory M; Smit, Berend; Haranczyk, Maciej

    2014-04-01

    Porous polymer networks (PPNs) are a class of advanced porous materials that combine the advantages of cheap and stable polymers with the high surface areas and tunable chemistry of metal-organic frameworks. They are of particular interest for gas separation or storage applications, for instance, as methane adsorbents for a vehicular natural gas tank or other portable applications. PPNs are self-assembled from distinct building units; here, we utilize commercially available chemical fragments and two experimentally known synthetic routes to design in silico a large database of synthetically realistic PPN materials. All structures from our database of 18,000 materials have been relaxed with semiempirical electronic structure methods and characterized with Grand-canonical Monte Carlo simulations for methane uptake and deliverable (working) capacity. A number of novel structure-property relationships that govern methane storage performance were identified. The relationships are translated into experimental guidelines to realize the ideal PPN structure. We found that cooperative methane-methane attractions were present in all of the best-performing materials, highlighting the importance of guest interaction in the design of optimal materials for methane storage.

  6. Liquid crystal polymer networks: preparation, properties, and applications of films with patterned molecular alignment.

    PubMed

    Liu, Danqing; Broer, Dirk J

    2014-11-18

    Monolithically ordered liquid crystal polymer networks are formed by the photoinitiated polymerization of multifunctional liquid crystal monomers. This paper describes the relevant principles and methods, the basic structure-property relationships in terms of mesogenic properties of the monomers, and the mechanical and optical properties of the polymers. Strategies are discussed to control the molecular orientation by various means and in all three dimensions. The versatility of the process is demonstrated by two examples of films with a patterned molecular order. It is shown that patterned retarders can be made by a two-step polymerization process which is successfully employed in a transflective display principle. A transflective display is a liquid crystal display that operates in both a reflective mode using ambient light and a transmissive mode with light coming from a backlight system. Furthermore, a method is discussed to create a patterned film in a single polymerization process. This film has alternating planar chiral nematic areas next to perpendicularly oriented (so-called homeotropic) areas. When applied as a coating to a substrate, the film changes its surface texture. During exposure to UV light, it switches from a flat to a corrugated state. PMID:24707811

  7. Dynamic swelling behavior of interpenetrating polymer networks in response to temperature and pH

    PubMed Central

    Slaughter, Brandon V.; Blanchard, Aaron T.; Maass, Katie F.; Peppas, Nicholas A.

    2015-01-01

    Temperature responsive hydrogels based on ionic polymers exhibit swelling transitions in aqueous solutions as a function of shifting pH and ionic strength, in addition to temperature. Applying these hydrogels to useful applications, particularly for biomedical purposes such as drug delivery and regenerative medicine, is critically dependent on understanding the hydrogel solution responses as a function of all three parameters together. In this work, interpenetrating polymer network (IPN) hydrogels of polyacrylamide and poly(acrylic acid) were formulated over a broad range of synthesis variables using a fractional factorial design, and were examined for equilibrium temperature responsive swelling in a variety of solution conditions. Due to the acidic nature of these IPN hydrogels, usable upper critical solution temperature (UCST) responses for this system occur in mildly acidic environments. Responses were characterized in terms of maximum equilibrium swelling and temperature-triggered swelling using turbidity and gravimetric measurements. Additionally, synthesis parameters critical to achieving optimal overall swelling, temperature-triggered swelling, and sigmoidal temperature transitions for this IPN system were analyzed based on the fractional factorial design used to formulate these hydrogels. PMID:26405349

  8. Polymer-sorted semiconducting carbon nanotube networks for high-performance ambipolar field-effect transistors.

    PubMed

    Schiessl, Stefan P; Fröhlich, Nils; Held, Martin; Gannott, Florentina; Schweiger, Manuel; Forster, Michael; Scherf, Ullrich; Zaumseil, Jana

    2015-01-14

    Efficient selection of semiconducting single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples is crucial for their application as printable and flexible semiconductors in field-effect transistors (FETs). In this study, we use atactic poly(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative with asymmetric side-chains, for the selective dispersion of semiconducting SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs. Lowering the molecular weight of the dispersing polymer leads to a significant improvement of selectivity. Combining dense semiconducting SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide hybrid dielectric enables transistors with balanced ambipolar, contact resistance-corrected mobilities of up to 50 cm(2)·V(-1)·s(-1), low ohmic contact resistance, steep subthreshold swings (0.12-0.14 V/dec) and high on/off ratios (10(6)) even for short channel lengths (<10 μm). These FETs operate at low voltages (<3 V) and show almost no current hysteresis. The resulting ambipolar complementary-like inverters exhibit gains up to 61. PMID:25493421

  9. The synthesis of hydrogels with controlled distribution of polymer brushes in hydrogel network

    NASA Astrophysics Data System (ADS)

    Sun, YuWei; Zhou, Chao; Zhang, AoKai; Xu, LiQun; Yao, Fang; Cen, Lian; Fu, Guo-Dong

    2014-11-01

    Poly(ethylene glycol) (PEG) hydrogels with 3-dimensionally controlled well-defined poly(N-isopropylacrylamide) (poly(NIPAAm)) brushes were prepared by combined copper(I)-catalyzed azide-alkyne cycloaddition ("Click Chemistry") and atom transfer radical polymerization (ATRP). The resulting hydrogels were presented as representatives with their detailed synthesis routes and characterization. HPEG-S-poly(NIPAAm) is a hydrogel with poly(NIPAAm) brushes mainly grafted on surface, whereas HPEG-G-poly(NIPAAm) has a gradiently decreased poly(NIPAAm) brushes in their chain length from surface to inside. On the other hand, poly(NIPAAm) brushes in HPEG-U-poly(NIPAAm) are uniformly dispersed throughout the whole hydrogel network. Successful preparation of HPEG-S-poly(NIPAAm), HPEG-G-poly(NIPAAm) and HPEG-U-poly(NIPAAm) were ascertained by X-ray photoelectron spectroscopy (XPS) and water contact angle measurement. Optical properties and thermal behaviors of these hydrogels were evaluated by UV-visible transmittance spectra and differential scanning calorimetry (DSC). Hence, the flexibility and controllability of the synthetic strategy in varying the distribution of polymer brushes and hydrogel properties was demonstrated. Hydrogels with tunable and well-defined 3-dimensional poly(NIPAAm) polymer brushes could be tailor-designed to find potential applications in smart devices or skin dressing, such as for diabetics as they have special optical and thermal behaviors.

  10. Polymer-Sorted Semiconducting Carbon Nanotube Networks for High-Performance Ambipolar Field-Effect Transistors

    PubMed Central

    2014-01-01

    Efficient selection of semiconducting single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples is crucial for their application as printable and flexible semiconductors in field-effect transistors (FETs). In this study, we use atactic poly(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative with asymmetric side-chains, for the selective dispersion of semiconducting SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs. Lowering the molecular weight of the dispersing polymer leads to a significant improvement of selectivity. Combining dense semiconducting SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide hybrid dielectric enables transistors with balanced ambipolar, contact resistance-corrected mobilities of up to 50 cm2·V–1·s–1, low ohmic contact resistance, steep subthreshold swings (0.12–0.14 V/dec) and high on/off ratios (106) even for short channel lengths (<10 μm). These FETs operate at low voltages (<3 V) and show almost no current hysteresis. The resulting ambipolar complementary-like inverters exhibit gains up to 61. PMID:25493421

  11. Liquid crystal polymer networks: preparation, properties, and applications of films with patterned molecular alignment.

    PubMed

    Liu, Danqing; Broer, Dirk J

    2014-11-18

    Monolithically ordered liquid crystal polymer networks are formed by the photoinitiated polymerization of multifunctional liquid crystal monomers. This paper describes the relevant principles and methods, the basic structure-property relationships in terms of mesogenic properties of the monomers, and the mechanical and optical properties of the polymers. Strategies are discussed to control the molecular orientation by various means and in all three dimensions. The versatility of the process is demonstrated by two examples of films with a patterned molecular order. It is shown that patterned retarders can be made by a two-step polymerization process which is successfully employed in a transflective display principle. A transflective display is a liquid crystal display that operates in both a reflective mode using ambient light and a transmissive mode with light coming from a backlight system. Furthermore, a method is discussed to create a patterned film in a single polymerization process. This film has alternating planar chiral nematic areas next to perpendicularly oriented (so-called homeotropic) areas. When applied as a coating to a substrate, the film changes its surface texture. During exposure to UV light, it switches from a flat to a corrugated state.

  12. Semi-interpenetrating polymer networks of poly(3-hydroxybutyrate) prepared by radiation-induced polymerization

    NASA Astrophysics Data System (ADS)

    Martellini, Flavia; Innocentini Mei, Lúcia H.; Lora, Silvano; Carenza, Mario

    2004-09-01

    Semi-interpenetrating polymer networks (IPNs) based on bacterial poly(3-hydroxy butyrate) with a hydrophilic monomer at different compositions were prepared by radiation-induced polymerization using γ-rays from a 60Co source with a total dose of 10-100 kGy. The swelling behaviour was determined by water content at equilibrium, while thermal properties and crystallinity were studied by differential scanning calorimetry. Extraction of the soluble part of PHB from the films at low and high temperature with water or chloroform as well as FTIR data indicate the occurrence of the crosslinking reaction in the hydrogels. The results show a water uptake increasing with the hydrophilic component until 25%.

  13. 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

  14. Segmenting delaminations in carbon fiber reinforced polymer composite CT using convolutional neural networks

    NASA Astrophysics Data System (ADS)

    Sammons, Daniel; Winfree, William P.; Burke, Eric; Ji, Shuiwang

    2016-02-01

    Nondestructive evaluation (NDE) utilizes a variety of techniques to inspect various materials for defects without causing changes to the material. X-ray computed tomography (CT) produces large volumes of three dimensional image data. Using the task of identifying delaminations in carbon fiber reinforced polymer (CFRP) composite CT, this work shows that it is possible to automate the analysis of these large volumes of CT data using a machine learning model known as a convolutional neural network (CNN). Further, tests on simulated data sets show that with a robust set of experimental data, it may be possible to go beyond just identification and instead accurately characterize the size and shape of the delaminations with CNNs.

  15. Synthesis of hybrid polymer networks of irradiated chitosan/poly(vinyl alcohol) for biomedical applications

    NASA Astrophysics Data System (ADS)

    Islam, Atif; Yasin, Tariq; Rehman, Ihtesham ur

    2014-03-01

    Hybrid polymer network (HPN) of chitosan (CS) with poly(vinyl alcohol) (PVA) was prepared by using radiation degraded chitosan. The chemical structure of chitosan promoted chain scission reactions upon irradiation which lowered its molecular weight and also changed its hydrophilic balance. The effect of molecular weight and hydrophilicity of irradiated chitosan on structural, thermal and surface properties of the HPN were studied. The increased hydrophilicity of irradiated chitosan lowered the crystallinity of the HPN. The endothermic peak was shifted towards higher temperatures in HPN having irradiated chitosan. The decreased value of contact angle with increasing dose, further confirmed the increased hydrophilicity of the HPN. The cytotoxicity results of HPN showed the viability of human fibroblast cells and their non-toxic nature making it suitable for tissue engineering and other biomedical applications.

  16. Improving processing and toughness of a high performance composite matrix through an interpenetrating polymer network. VI

    NASA Technical Reports Server (NTRS)

    Pater, Ruth H.

    1990-01-01

    A simultaneous semi-interpenetrating polymer network (semi-IPN) concept is presented which combines easy-to-process, but brittle, thermosetting polyimides with tough, but difficult to process, linear thermoplastic polyimides. The combination results in a semi-IPN with the easy processability of a thermoset and good toughness of a thermoplastic. Four simultaneous semi-IPN systems were developed from commercially available NR-150B2 combined with each of the four Thermid materials (LR-600, AL-600, MC-600, and FA-700). It is concluded that there is a significant improvement in resin fracture toughness of Thermid-polyimide-based semi-IPN systems and some improvement in composite microcracking resistance compared to Thermid LR-600. Excellent composite mechanical properties have been achieved. These new semi-IPN materials have the potential to be used as composite matrices, adhesives, and molding materials.

  17. Multifunctional membranes for solvent resistant nanofiltration and pervaporation applications based on segmented polymer networks.

    PubMed

    Li, Xianfeng; Basko, Malgorzata; Du Prez, S Filip; Vankelecom, Ivo F J

    2008-12-25

    Hydrophilic bis(acrylate)-terminated poly(ethylene oxide) was used as macromolecular cross-linker of different hydrophobic polyacrylates for the synthesis of amphiphilic segmented polymer networks (SPNs). Multifunctional composite membranes with thin SPN toplayers were prepared by in situ polymerization. As the support consisted of hydrolyzed polyacrylonitrile, the high chemical resistance of the composite membrane allowed applications of the SPN-based membranes in solvent-resistant nanofiltration (SRNF) and pervaporation (PV). The membranes show very high retention on Rose Bengal (RB) in different solvents, especially in strong swelling solvents such as tetrahydrofuran (THF) and dimethylformamide (DMF). The membranes were also tested in pervaporation for dehydration of ethanol and isopropanol (IPA). The selectivity of the membranes greatly depends on the composition or the ratio of the hydrophilic and hydrophobic phases of the SPN. PMID:19055387

  18. Improving processing and toughness of a high performance composite matrix through an interpenetrating polymer network. VI

    NASA Technical Reports Server (NTRS)

    Pater, Ruth H.

    1990-01-01

    The use of a semiinterpenetrating polymer network (SIPN) of the high-performance polyimide NR-150B2 to reduce brittleness and improve processability in the highly crosslinked acetylene-terminated polyimides Thermid LR-600, AL-600, MC-600, and FA-700 is described. The theoretical basis of the SIPN process is reviewed; the preparation and characterization of the neat SIPN resins and unidirectional graphite-fiber composites are explained; and the results are presented in extensive tables, graphs, and micrographs and discussed in detail. Significant increases in fracture energy were observed with SIPN, from 93 J/sq m for unmodified LR-600 to 283-603 J/sq m for the SIPN materials; the room-temperature flexural strength of the unidirectional composites also increased, from 1344 MPa for an unmodified MC-600 composite to 2020-1751 MPa for the SIPN composites. The potential applicability of SIPN-based composites to aerospace structures and electronic components is indicated.

  19. Free-energy calculations for semi-flexible macromolecules: Applications to DNA knotting and looping

    SciTech Connect

    Giovan, Stefan M.; Scharein, Robert G.; Hanke, Andreas; Levene, Stephen D.

    2014-11-07

    We present a method to obtain numerically accurate values of configurational free energies of semiflexible macromolecular systems, based on the technique of thermodynamic integration combined with normal-mode analysis of a reference system subject to harmonic constraints. Compared with previous free-energy calculations that depend on a reference state, our approach introduces two innovations, namely, the use of internal coordinates to constrain the reference states and the ability to freely select these reference states. As a consequence, it is possible to explore systems that undergo substantially larger fluctuations than those considered in previous calculations, including semiflexible biopolymers having arbitrary ratios of contour length L to persistence length P. To validate the method, high accuracy is demonstrated for free energies of prime DNA knots with L/P = 20 and L/P = 40, corresponding to DNA lengths of 3000 and 6000 base pairs, respectively. We then apply the method to study the free-energy landscape for a model of a synaptic nucleoprotein complex containing a pair of looped domains, revealing a bifurcation in the location of optimal synapse (crossover) sites. This transition is relevant to target-site selection by DNA-binding proteins that occupy multiple DNA sites separated by large linear distances along the genome, a problem that arises naturally in gene regulation, DNA recombination, and the action of type-II topoisomerases.

  20. Multi-stage freezing of HEUR polymer networks with magnetite nanoparticles.

    PubMed

    Campanella, A; Holderer, O; Raftopoulos, K N; Papadakis, C M; Staropoli, M P; Appavou, M S; Müller-Buschbaum, P; Frielinghaus, H

    2016-04-01

    We observe a change in the segmental dynamics of hydrogels based on hydrophobically modified ethoxylated urethanes (HEUR) when hydrophobic magnetite nanoparticles (MNPs) are embedded in the hydrogels. The dynamics of the nanocomposite hydrogels is investigated using dielectric relaxation spectroscopy (DRS) and neutron spin echo (NSE) spectroscopy. The magnetic nanoparticles within the hydrophobic domains of the HEUR polymer network increase the size of these domains and their distance. The size increase leads to a dilution of the polymers close to the hydrophobic domain, allowing higher mobility of the smallest polymer blobs close to the "center". This is reflected in the decrease of the activation energy of the β-process detected in the DRS data. The increase in distance leads to an increase of the size of the largest hydrophilic polymer blobs. Therefore, the segmental dynamics of the largest blobs is slowed down. At short time scales, i.e. 10(-9) s < τ < 10(-3) s, the suppression of the segmental dynamics is reflected in the α-relaxation processes detected in the DRS data and in the decrease of the relaxation rate Γ of the segmental motion in the NSE data with increasing concentration of magnetic nanoparticles. The stepwise (multi-stage) freezing of the small blobs is only visible for the pure hydrogel at low temperatures. On the other hand, the glass transition temperature (Tg) decreases upon increasing the MNP loading, indicating an acceleration of the segmental dynamics at long time scales (τ∼ 100 s). Therefore, it would be possible to tune the Tg of the hydrogels by varying the MNP concentration. The contribution of the static inhomogeneities to the total scattering function Sst(q) is extracted from the NSE data, revealing a more ordered gel structure than the one giving rise to the total scattering function S(q), with a relaxed correlation length ξNSE = (43 ± 5) Å which is larger than the fluctuating correlation length from a static investigation

  1. An annulus fibrosus closure device based on a biodegradable shape-memory polymer network.

    PubMed

    Sharifi, Shahriar; van Kooten, Theo G; Kranenburg, Hendrik-Jan C; Meij, Björn P; Behl, Marc; Lendlein, Andreas; Grijpma, Dirk W

    2013-11-01

    Injuries to the intervertebral disc caused by degeneration or trauma often lead to tearing of the annulus fibrosus (AF) and extrusion of the nucleus pulposus (NP). This can compress nerves and cause lower back pain. In this study, the characteristics of poly(D,L-lactide-co-trimethylene carbonate) networks with shape-memory properties have been evaluated in order to prepare biodegradable AF closure devices that can be implanted minimally invasively. Four different macromers with (D,L-lactide) to trimethylene carbonate (DLLA:TMC) molar ratios of 80:20, 70:30, 60:40 and 40:60 with terminal methacrylate groups and molecular weights of approximately 30 kg mol(-1) were used to prepare the networks by photo-crosslinking. The mechanical properties of the samples and their shape-memory properties were determined at temperatures of 0 °C and 40 °C by tensile tests- and cyclic, thermo-mechanical measurements. At 40 °C all networks showed rubber-like behavior and were flexible with elastic modulus values of 1.7-2.5 MPa, which is in the range of the modulus values of human annulus fibrosus tissue. The shape-memory characteristics of the networks were excellent with values of the shape-fixity and the shape-recovery ratio higher than 98 and 95%, respectively. The switching temperatures were between 10 and 39 °C. In vitro culture and qualitative immunocytochemistry of human annulus fibrosus cells on shape-memory films with DLLA:TMC molar ratios of 60:40 showed very good ability of the networks to support the adhesion and growth of human AF cells. When the polymer network films were coated by adsorption of fibronectin, cell attachment, cell spreading, and extracellular matrix production was further improved. Annulus fibrosus closure devices were prepared from these AF cell-compatible materials by photo-polymerizing the reactive precursors in a mold. Insertion of the multifunctional implant in the disc of a cadaveric canine spine showed that these shape-memory devices could be

  2. High internal quantum efficiency in fullerene solar cells based on crosslinked polymer donor networks

    NASA Astrophysics Data System (ADS)

    Liu, Bo; Png, Rui-Qi; Zhao, Li-Hong; Chua, Lay-Lay; Friend, Richard H.; Ho, Peter K. H.

    2012-12-01

    The power conversion efficiency of organic photovoltaic cells depends crucially on the morphology of their donor-acceptor heterostructure. Although tremendous progress has been made to develop new materials that better cover the solar spectrum, this heterostructure is still formed by a primitive spontaneous demixing that is rather sensitive to processing and hence difficult to realize consistently over large areas. Here we report that the desired interpenetrating heterostructure with built-in phase contiguity can be fabricated by acceptor doping into a lightly crosslinked polymer donor network. The resultant nanotemplated network is highly reproducible and resilient to phase coarsening. For the regioregular poly(3-hexylthiophene):phenyl-C61-butyrate methyl ester donor-acceptor model system, we obtained 20% improvement in power conversion efficiency over conventional demixed biblend devices. We reached very high internal quantum efficiencies of up to 0.9 electron per photon at zero bias, over an unprecedentedly wide composition space. Detailed analysis of the power conversion, power absorbed and internal quantum efficiency landscapes reveals the separate contributions of optical interference and donor-acceptor morphology effects.

  3. High internal quantum efficiency in fullerene solar cells based on crosslinked polymer donor networks.

    PubMed

    Liu, Bo; Png, Rui-Qi; Zhao, Li-Hong; Chua, Lay-Lay; Friend, Richard H; Ho, Peter K H

    2012-01-01

    The power conversion efficiency of organic photovoltaic cells depends crucially on the morphology of their donor-acceptor heterostructure. Although tremendous progress has been made to develop new materials that better cover the solar spectrum, this heterostructure is still formed by a primitive spontaneous demixing that is rather sensitive to processing and hence difficult to realize consistently over large areas. Here we report that the desired interpenetrating heterostructure with built-in phase contiguity can be fabricated by acceptor doping into a lightly crosslinked polymer donor network. The resultant nanotemplated network is highly reproducible and resilient to phase coarsening. For the regioregular poly(3-hexylthiophene):phenyl-C(61)-butyrate methyl ester donor-acceptor model system, we obtained 20% improvement in power conversion efficiency over conventional demixed biblend devices. We reached very high internal quantum efficiencies of up to 0.9 electron per photon at zero bias, over an unprecedentedly wide composition space. Detailed analysis of the power conversion, power absorbed and internal quantum efficiency landscapes reveals the separate contributions of optical interference and donor-acceptor morphology effects.

  4. Synthesis and characterization of photocrosslinkable gelatin and silk fibroin interpenetrating polymer network hydrogels

    PubMed Central

    Xiao, Wenqian; He, Jiankang; Nichol, Jason W.; Wang, Lianyong; Hutson, Ché B.; Wang, Ben; Du, Yanan; Fan, Hongsong; Khademhosseini, Ali

    2011-01-01

    To effectively repair or replace damaged tissues, it is necessary to design scaffolds with tunable structural and biomechanical properties that closely mimic the host tissue. In this paper, we describe a newly synthesized photocrosslinkable interpenetrating polymer network (IPN) hydrogel based on gelatin methacrylate (GelMA) and silk fibroin (SF) formed by sequential polymerization, which possesses tunable structural and biological properties. Experimental results revealed that IPNs, where both the GelMA and SF were independently crosslinked in interpenetrating networks, demonstrated a lower swelling ratio, higher compressive modulus and lower degradation rate as compared to the GelMA and semi-IPN hydrogels, where only GelMA was crosslinked. These differences were likely caused by a higher degree of overall crosslinking due to the presence of crystallized SF in the IPN hydrogels. NIH-3T3 fibroblasts readily attached to, spread, and proliferated on the surface of IPN hydrogels as demonstrated by F-actin staining and analysis of mitochondrial activity (MTT). In addition, photolithography combined with lyophilization techniques was used to fabricate 3D micropatterned and porous micro-scaffolds from GelMA-SF IPN hydrogels, furthering their versatility for use in various microscale tissue engineering applications. Overall, this study introduces a class of photocrosslinkable, mechanically robust and tunable IPN hydrogels that could be useful for various tissue engineering and regenerative medicine applications. PMID:21295165

  5. Synthesis and characterization of photocrosslinkable gelatin and silk fibroin interpenetrating polymer network hydrogels.

    PubMed

    Xiao, Wenqian; He, Jiankang; Nichol, Jason W; Wang, Lianyong; Hutson, Ché B; Wang, Ben; Du, Yanan; Fan, Hongsong; Khademhosseini, Ali

    2011-06-01

    To effectively repair or replace damaged tissues, it is necessary to design scaffolds with tunable structural and biomechanical properties that closely mimic the host tissue. In this paper, we describe a newly synthesized photocrosslinkable interpenetrating polymer network (IPN) hydrogel based on gelatin methacrylate (GelMA) and silk fibroin (SF) formed by sequential polymerization, which possesses tunable structural and biological properties. Experimental results revealed that IPNs, where both the GelMA and SF were independently crosslinked in interpenetrating networks, demonstrated a lower swelling ratio, higher compressive modulus and lower degradation rate as compared to the GelMA and semi-IPN hydrogels, where only GelMA was crosslinked. These differences were likely caused by a higher degree of overall crosslinking due to the presence of crystallized SF in the IPN hydrogels. NIH-3T3 fibroblasts readily attached to, spread and proliferated on the surface of IPN hydrogels, as demonstrated by F-actin staining and analysis of mitochondrial activity (MTT). In addition, photolithography combined with lyophilization techniques was used to fabricate three-dimensional micropatterned and porous microscaffolds from GelMA-SF IPN hydrogels, furthering their versatility for use in various microscale tissue engineering applications. Overall, this study introduces a class of photocrosslinkable, mechanically robust and tunable IPN hydrogels that could be useful for various tissue engineering and regenerative medicine applications.

  6. Controlling Phase Separation of Interpenetrating Polymer Networks by Addition of Block Copolymers

    NASA Astrophysics Data System (ADS)

    Rohde, Brian; Krishnamoorti, Ramanan; Robertson, Megan

    2015-03-01

    Interpenetrating polymer networks (IPNs) offer a unique way to produce mechanically superior thermoset blends relative to the neat components. In this study, IPNs were prepared consisting of polydicyclopentadiene (polyDCPD), contributing high fracture toughness, and an epoxy resin (the diglycidyl ether of bisphenol A cured with nadic methyl anhydride), contributing high tensile strength and modulus. In the absence of compatibilization, the simultaneous curing of the networks leads to a macroscopically phase separated blend that exhibits poor mechanical behavior. To control phase separation and drive the system towards more mechanically robust nanostructured IPNs, block copolymers were designed to compatibilize this system, where one block possesses affinity to polyDCPD (polynorbornene in this study) and the other block possesses affinity to DGEBA (poly(ɛ-caprolactone) in this study). The influence of the block copolymer composition on the degree of phase separation and interfacial adhesion in the IPN was studied using a combination of small-angle scattering and imaging techniques. The resultant mechanical properties were explored and structure-property relationships were developed in this blend system.

  7. Preparation and characterization of shape memory composite foams with interpenetrating polymer networks

    NASA Astrophysics Data System (ADS)

    Yao, Yongtao; Zhou, Tianyang; Yang, Cheng; Liu, Yanju; Leng, Jinsong

    2016-03-01

    The present study reports a feasible approach of fabricating shape memory composite foams with an interpenetrating polymer network (IPN) based on polyurethane (PU) and shape memory epoxy resin (SMER) via a simultaneous polymerization technique. The PU component is capable of constructing a foam structure and the SMER is grafted on the PU network to offer its shape memory property in the final IPN foams. A series of IPN foams without phase separation were produced due to good compatibility and a tight chemical interaction between PU and SMER components. The relationships of the geometry of the foam cell were investigated via varying compositions of PU and SMER. The physical property and shape memory property were also evaluated. The stimulus temperature of IPN shape memory composite foams, glass temperature (Tg), could be tunable by varying the constituents and Tg of PU and SMER. The mechanism of the shape memory effect of IPN foams has been proposed. The shape memory composite foam with IPN developed in this study has the potential to extend its application field.

  8. Soft hydrogels interpenetrating silicone--A polymer network for drug-releasing medical devices.

    PubMed

    Steffensen, Søren L; Vestergaard, Merete H; Møller, Eva H; Groenning, Minna; Alm, Martin; Franzyk, Henrik; Nielsen, Hanne M

    2016-02-01

    Materials for the next generation of medical devices will require not only the mechanical stability of current devices, but must also possess other properties such as sustained release of drugs in a controlled manner over a prolonged period of time. This work focuses on creating such a sophisticated material by forming an interpenetrating polymer network (IPN) material through modification of silicone elastomers with a poly(2-hydroxyethyl methacrylate) (PHEMA)-based hydrogel. IPN materials with a PHEMA content in the range of 13%-38% (w/w) were synthesized by using carbon dioxide-based solvent mixtures under high pressure. These IPNs were characterized with regard to microstructure as well as ability of the hydrogel to form a surface-connected hydrophilic carrier network inside the silicone. A critical limit for hydrogel connectivity was found both via simulation and by visualization of water uptake in approximately 25% (w/w) PHEMA, indicating that entrapment of gel occurs at low gel concentrations. The optimized IPN material was loaded with the antibiotic ciprofloxacin, and the resulting drug release was shown to inhibit bacterial growth when placed on agar, thus demonstrating the potential of this IPN material for future applications in drug-releasing medical devices.

  9. The semi-interpenetrating polymer network matrix of fiber-reinforced composite and its effect on the surface adhesive properties.

    PubMed

    Lastumäki, T M; Lassila, L V J; Vallittu, P K

    2003-09-01

    This aim of this study was to examine the effect of further-impregnation time of polymer pre-impregnated fiber-reinforcement on polymer matrix structure of the fiber-reinforced composite (FRC) used in dental applications. In addition, shear bond strength between the FRC and veneering composite after various length of further-impregnation was studied. Polymethyl methacrylate (PMMA) pre-impregnated glass fiber-reinforcement was further-impregnated with a diacrylate monomer resin by using five lengths of further-impregnation from 10 min to 24 h. The test specimens (n=5) from each five groups were treated with the solvent tetrahydrofuran and examined with a scanning electron microscope (SEM) to determinate the existence of linear PMMA in the polymer matrix of the FRC. The same lengths of further-impregnation were used to form an adhesive substrate for veneering composite and to measure the shear bond strength (n=8). The SEM examination showed that linear PMMA-polymer and cross-linked diacrylate polymer formed two independent networks for the polymer matrix of FRC. The highest mean shear bond strength value (18.7+/-2.9 MPa) was achieved when the fiber reinforcement was further-impregnated for 24 h. The shortest further-impregnation, 10 min, resulted in the lowest mean shear bond strength (12.7+/-2.9 MPa). A correlation between increased shear bond strength and longer further-impregnation was found (0.689, p<0.001). The results revealed that linear PMMA network of the polymer matrix of the FRC remained in the structure regardless of the various lengths of the further-impregnation with diacrylate resin. PMID:15348401

  10. Ice-Templated Assembly Strategy to Construct 3D Boron Nitride Nanosheet Networks in Polymer Composites for Thermal Conductivity Improvement.

    PubMed

    Zeng, Xiaoliang; Yao, Yimin; Gong, Zhengyu; Wang, Fangfang; Sun, Rong; Xu, Jianbin; Wong, Ching-Ping

    2015-12-01

    Owing to the growing heat removal issue of modern electronic devices, polymer composites with high thermal conductivity have drawn much attention in the past few years. However, a traditional method to enhance the thermal conductivity of the polymers by addition of inorganic fillers usually creates composite with not only limited thermal conductivity but also other detrimental effects due to large amount of fillers required. Here, novel polymer composites are reported by first constructing 3D boron nitride nanosheets (3D-BNNS) network using ice-templated approach and then infiltrating them with epoxy matrix. The obtained polymer composites exhibit a high thermal conductivity (2.85 W m(-1) K(-1)), a low thermal expansion coefficient (24-32 ppm K(-1)), and an increased glass transition temperature (T(g)) at relatively low BNNSs loading (9.29 vol%). These results demonstrate that this approach opens a new avenue for design and preparation of polymer composites with high thermal conductivity. The polymer composites are potentially useful in advanced electronic packaging techniques, namely, thermal interface materials, underfill materials, molding compounds, and organic substrates. PMID:26479262

  11. Ice-Templated Assembly Strategy to Construct 3D Boron Nitride Nanosheet Networks in Polymer Composites for Thermal Conductivity Improvement.

    PubMed

    Zeng, Xiaoliang; Yao, Yimin; Gong, Zhengyu; Wang, Fangfang; Sun, Rong; Xu, Jianbin; Wong, Ching-Ping

    2015-12-01

    Owing to the growing heat removal issue of modern electronic devices, polymer composites with high thermal conductivity have drawn much attention in the past few years. However, a traditional method to enhance the thermal conductivity of the polymers by addition of inorganic fillers usually creates composite with not only limited thermal conductivity but also other detrimental effects due to large amount of fillers required. Here, novel polymer composites are reported by first constructing 3D boron nitride nanosheets (3D-BNNS) network using ice-templated approach and then infiltrating them with epoxy matrix. The obtained polymer composites exhibit a high thermal conductivity (2.85 W m(-1) K(-1)), a low thermal expansion coefficient (24-32 ppm K(-1)), and an increased glass transition temperature (T(g)) at relatively low BNNSs loading (9.29 vol%). These results demonstrate that this approach opens a new avenue for design and preparation of polymer composites with high thermal conductivity. The polymer composites are potentially useful in advanced electronic packaging techniques, namely, thermal interface materials, underfill materials, molding compounds, and organic substrates.

  12. Fluorescence microscopy techniques for characterizing the microscale mechanical response of entangled actin networks

    NASA Astrophysics Data System (ADS)

    Blair, Savanna; Falzone, Tobias; Robertson-Anderson, Rae

    2015-03-01

    Actin filaments are semiflexible polymers that display complex viscoelastic properties when entangled in networks. In order to characterize the molecular-level physical and mechanical properties of entangled actin networks it is important to know the in-network length distribution and the response of entangled filaments to local forcing. Here we describe two single-molecule microscopy protocols developed to investigate these properties. Using confocal fluorescence microscopy and ImageJ image analysis we have developed a protocol to accurately measure the in-network actin length distribution. To characterize the deformation of actin filaments in response to perturbation, we trap micron size beads embedded in the network with optical tweezers and propagate the beads through the entangled filaments while simultaneously recording images of fluorescent-labeled filaments in the network. A sparse number of labeled filaments dispersed throughout the network allow us to visualize the movement of individual filaments during perturbation. Analysis of images taken during forcing is carried out using a combination of vector mapping and skeletonization techniques to directly reveal the deformation and subsequent relaxation modes induced in entangled actin filaments by microscale strains. We also determine the dependence of deformation modes on the relative filament position relative to the strain.

  13. Multicomponent polymer materials

    SciTech Connect

    Paul, D.R.; Sperling, L.H.

    1986-01-01

    Interpenetrating polymer networks are discussed, taking into account interpenetrating polymer networks based on polybutadiene and polystyrene, polyurethane-polysiloxane simultaneous interpenetrating polymer networks, extraction studies and morphology of physical-chemical interpenetrating polymer networks based on block polymer and polystyrene, twoand three-component interpenetrating polymer networks, and poly(acrylourethane)-polyepoxide semiinterpenetrating networks formed by electron-beam curing. Other topics studied are related to the characterization of polymer blends, the characterization of block copolymers, the mechanical behavior, and rheology and applications. Attention is given to a new silicone flame-retardant system for thermoplastics, recent developments in interpenetrating polymer networks and related materials, miscibility in random copolymer blends, crystallization and melting in compatible polymer blends, and fatigue in rubber-modified epoxies and other polyblends.

  14. Enhanced performance of polymer solar cell with ZnO nanoparticle electron transporting layer passivated by in situ cross-linked three-dimensional polymer network

    NASA Astrophysics Data System (ADS)

    Wu, Zhongwei; Song, Tao; Xia, Zhouhui; Wei, Huaixin; Sun, Baoquan

    2013-12-01

    An in situ cross-linked three-dimensional polymer network has been developed to passivate ZnO nanoparticles as an electron transporting layer (ETL) to improve the performance of inverted organic solar cells. The passivated ZnO ETL-based devices achieve efficiencies of 3.26% for poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and 7.37% for poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b‧]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl

  15. Comparative characterization of a novel cad-cam polymer-infiltrated-ceramic-network

    PubMed Central

    Pascual, Agustín; Camps, Isabel; Grau-Benitez, María

    2015-01-01

    Background The field of dental ceramics for CAD-CAM is enriched with a new innovative material composition having a porous three-dimensional structure of feldspathic ceramic infiltrated with acrylic resins.The aim of this study is to determine the mechanical properties of Polymer-Infiltrated-Ceramic-Network (PICN) and compare its performance with other ceramics and a nano-ceramic resin available for CAD-CAM systems. Material and Methods In this study a total of five different materials for CAD-CAM were investigated. A polymer-infiltrated ceramic (Vita Enamic), a nano-ceramic resin (Lava Ultimate), a feldspathic ceramic (Mark II), a lithium disilicate ceramic (IPS-e max CAD) and finally a Leucite based ceramic (Empress - CAD). From CAD-CAM blocks, 120 bars (30 for each material cited above) were cut to measure the flexural strength with a three-point-bending test. Strain at failure, fracture stress and Weibull modulus was calculated. Vickers hardness of each material was also measured. Results IPS-EMAX presents mechanical properties significantly better from the other materials studied. Its strain at failure, flexural strength and hardness exhibited significantly higher values in comparison with the others. VITA ENAMIC and LAVA ULTIMATE stand out as the next most resistant materials. Conclusions The flexural strength, elastic modulus similar to a tooth as well as having less hardness than ceramics make PICN materials an option to consider as a restorative material. Key words:Ceramic infiltrated with resin, CAD-CAM, Weibull modulus, flexural strength, micro hardness. PMID:26535096

  16. Photothermal triggering of self-healing processes applied to the reparation of bio-based polymer networks

    NASA Astrophysics Data System (ADS)

    Altuna, F. I.; Antonacci, J.; Arenas, G. F.; Pettarin, V.; Hoppe, C. E.; Williams, R. J. J.

    2016-04-01

    Green laser irradiation successfully activated self-healing processes in epoxy-acid networks modified with low amounts of gold nanoparticles (NPs). A bio-based polymer matrix, obtained by crosslinking epoxidized soybean oil (ESO) with an aqueous citric acid (CA) solution, was self-healed through molecular rearrangements produced by transesterification reactions of β-hydroxyester groups generated in the polymerization reaction. The temperature increase required for the triggering of these thermally activated reactions was attained by green light irradiation of the damaged area. Compression force needed to assure a good contact between crack faces was achieved by volume dilatation generated by the same temperature rise. Gold NPs dispersed in the polymer efficiently generated heat in the presence of electromagnetic radiation under plasmon resonance, acting as nanometric heating sources and allowing remote activation of the self-healing in the crosslinked polymer.

  17. Thiophene-based oligomers, polymers and dendrimers for organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Zhang, Yong

    Demand for inexpensive renewable energy sources has stimulated new approaches for the production of efficient, low cost photovoltaic (PV) solar cell devices. This thesis research has focused on developing thiophene-based oligomers, polymers and dendrimers for this purpose. The key results are summarized as follows: First, three fully characterized polynorbornenes with electronically active pendant oligothiophene side chains have been synthesized and incorporated as active electronic components into single-layer photovoltaic cells. The device tests along with the electrochemical experiments demonstrate that incorporating chemically stable end-groups on the oligothiophene unit is responsible for the improvement of operation stability under ambient conditions. Second, in-situ surface-initiated polymerization of thiophene inside nanoporous networks has been realized. The resulting organic-inorganic hybrids with polythiophene covalently bound inside nanopores can achieve better interface contact, larger surface coverage and more complete filling of the pores. These result in more efficient photoinjection of electrons into the conduction band of nanocrystalline TiO2 than an analogous nanoporous structure infiltrated by polymer synthesized outside the network. The last part of this thesis covers the synthesis and characterization of a new series of semi-flexible oligothiophene-based dendrimers, which show pronounced solvatochromic and thermochromic properties. Microscopic fluorescence investigation of such surface adhered dendrimers provides the evidence that the intramolecular interactions inside these dendritic structures mainly account for the origin of the morphology-related chromism properties. This architecture is promising to make processable light harvesting structures having scaffolded donors covalently integrated with acceptors such as fullerenes in order to fabricate photovoltaics where phase segregation is suppressed.

  18. Phase behavior and crystal nucleation and growth in a system of short semi-flexible chains

    NASA Astrophysics Data System (ADS)

    Vorselaars, Bart; Quigley, David

    2014-03-01

    A system of semi-flexible short chains is simulated to study its phase behavior and ability to crystallize, by using a combination of molecular dynamics and other techniques. For calculating the free energy of the liquid phase a new method is introduced. It is very simple to implement in practice and leads to accurate computation of the melting curve. Furthermore we determine the rate of nucleation and crystal growth in this system via a combination of path-sampling and brute-force simulation techniques. By comparing these quantities, we infer the initial microstructure of the solid phase. Due to the strong anisotropy in the crystal growth rate grains no thicker than a single chain are common, even at moderate supercoolings. This work is supported by the UK Engineering and Physical Sciences Research Council (EPSRC).

  19. Diagram of states and morphologies of flexible-semiflexible copolymer chains: A Monte Carlo simulation.

    PubMed

    Zablotskiy, Sergey V; Martemyanova, Julia A; Ivanov, Viktor A; Paul, Wolfgang

    2016-06-28

    A single copolymer chain consisting of multiple flexible (F) and semiflexible (S) blocks has been studied using a continuum bead-spring model by Stochastic Approximation Monte Carlo simulations, which determine the density of states of the model. The only difference between F and S blocks is the intramolecular bending potential, all non-bonded interactions are equal. The state diagrams for this class of models display multiple nematic phases in the collapsed state, characterized through a demixing of the blocks of different stiffness and orientational ordering of the stiff blocks. We observe dumbbell-like morphologies, lamellar phases, and for the larger block lengths also Saturn-like structures with a core of flexible segments and the stiff segments forming a ring around the core. PMID:27369540

  20. Diagram of states and morphologies of flexible-semiflexible copolymer chains: A Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Zablotskiy, Sergey V.; Martemyanova, Julia A.; Ivanov, Viktor A.; Paul, Wolfgang

    2016-06-01

    A single copolymer chain consisting of multiple flexible (F) and semiflexible (S) blocks has been studied using a continuum bead-spring model by Stochastic Approximation Monte Carlo simulations, which determine the density of states of the model. The only difference between F and S blocks is the intramolecular bending potential, all non-bonded interactions are equal. The state diagrams for this class of models display multiple nematic phases in the collapsed state, characterized through a demixing of the blocks of different stiffness and orientational ordering of the stiff blocks. We observe dumbbell-like morphologies, lamellar phases, and for the larger block lengths also Saturn-like structures with a core of flexible segments and the stiff segments forming a ring around the core.

  1. Development of novel multifunctional biobased polymer composites with tailored conductive network of micro-and-nano-fillers

    NASA Astrophysics Data System (ADS)

    Leung, Siu N.; Ghaffari, Shahriar; Naguib, Hani E.

    2013-04-01

    Biobased/green polymers and nanotechnology warrant a multidisciplinary approach to promote the development of the next generation of materials, products, and processes that are environmentally sustainable. The scientific challenge is to find the suitable applications, and thereby to create the demand for large scale production of biobased/green polymers that would foster sustainable development of these eco-friendly materials in contrast to their petroleum/fossil fuel derived counterparts. In this context, this research aims to investigate the synergistic effect of green materials and nanotechnology to develop a new family of multifunctional biobased polymer composites with promoted thermal conductivity. For instance, such composite can be used as a heat management material in the electronics industry. A series of parametric studies were conducted to elucidate the science behind materials behavior and their structure-toproperty relationships. Using biobased polymers (e.g., polylactic acid (PLA)) as the matrix, heat transfer networks were developed and structured by embedding hexagonal boron nitride (hBN) and graphene nanoplatelets (GNP) in the PLA matrix. The use of hybrid filler system, with optimized material formulation, was found to promote the composite's effective thermal conductivity by 10-folded over neat PLA. This was achieved by promoting the development of an interconnected thermally conductive network through structuring hybrid fillers. The thermally conductive composite is expected to afford unique opportunities to injection mold three-dimensional, net-shape, lightweight, and eco-friendly microelectronic enclosures with superior heat dissipation performance.

  2. Characterization of nanocellulose reinforced semi-interpenetrating polymer network of poly(vinyl alcohol) & polyacrylamide composite films.

    PubMed

    Mandal, Arup; Chakrabarty, Debabrata

    2015-12-10

    Semi-interpenetrating polymer network (semi-IPN) of poly(vinyl alcohol)/polyacrylamide was reinforced with various doses of nanocellulose. The different composite films thus prepared were characterized with respect to their mechanical, thermal, morphological and barrier properties. The composite film containing 5 wt.% of nanocellulose showed the highest tensile strength. The semi-interpenetrating polymer network of poly(vinyl alcohol)/polyacrylamide; and its various composites with nanocellulose were almost identical in their thermal stability. Each of the composites however exhibited much superior stability with respect to the linear poly(vinyl alcohol) and crosslinked polyacrylamide. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies exhibited phase separated morphology where agglomerates of nanocellulose were found to be dispersed in the matrix of the semi-IPN. The moisture vapor transmission rate (MVTR) was the lowest for the film containing 5 wt.% of nanocellulose. PMID:26428121

  3. Reversible formation of supramolecular polymer networks via orthogonal pillar[10]arene-based host-guest interactions and metal ion coordinations.

    PubMed

    Wu, Lintao; Han, Chun; Wu, Xi; Wang, Lei; Caochen, Yaozi; Jing, Xiaobi

    2015-12-21

    Supramolecular polymer networks, assembled via the combination of orthogonal terpyridine-Zn(2+), carbene-Ag(+), and pillar[10]arene/alkyl chain recognition motifs, exhibit dynamic properties responsive to various external stimuli. PMID:26569051

  4. Real-time observation of polymer network formation by liquid- and solid-state NMR revealing multistage reaction kinetics.

    PubMed

    Kovermann, Michael; Saalwächter, Kay; Chassé, Walter

    2012-06-28

    The reaction rate for the end-cross-linking process of vinyl-terminated poly(dimethylsiloxane) by a cross-linker with four Si-H functionalities in the presence of solvent was studied by (1)H liquid-state NMR in dependence of the reaction temperature. The properties of the resulting polymer networks, i.e., the gel-point and the formation of the elastically effective network, were monitored in situ during the reaction by single-evolution-time (1)H double-quantum (SET-DQ) low-field NMR. It was found that the cross-linking kinetics shows no uniform reaction order for the conversions of the functional groups before the topological gelation threshold of the polymer network. The two NMR methods are combined to investigate the formation of the elastically effective network in dependence of the conversion of the functional groups of the precursor polymers and the cross-linker. The high chemical and time resolution of the experiments enabled an in-depth analysis of the reaction kinetics, allowing us to conclude on a multistage model for PDMS network formation by hydrosilylation-based end-linking in the presence of solvent. We found that the nonuniform network formation kinetics originates from a dependence of the apparent reaction rate on the number of the Si-H groups of the cross-linker that have already reacted during the progress of the reaction. The fastest overall reaction rate is observed in a range until each cross-linker has reacted once on average, and a uniform apparent overall reaction order of unity with respect to cross-linker concentration is only found at a later stage, when multiply reacted cross-linker molecules with similar reactivity dominate. PMID:22650309

  5. Microphase separation in cross-linked polymer blends. Efficient replica RPA post-processing of simulation data for homopolymer networks.

    PubMed

    Klopper, A V; Svaneborg, Carsten; Everaers, Ralf

    2009-01-01

    We investigate the behaviour of randomly cross-linked (co)polymer blends using a combination of replica theory and large-scale molecular dynamics simulations. In particular, we derive the analogue of the random phase approximation for systems with quenched disorder and show how the required correlation functions can be calculated efficiently. By post-processing simulation data for homopolymer networks we are able to describe neutron scattering measurements in heterogeneous systems without resorting to microscopic detail and otherwise unphysical assumptions. We obtain structure function data which illustrate the expected microphase separation and contain system-specific information relating to the intrinsic length scales of our networks.

  6. Size-exclusion partitioning of neutral solutes in crosslinked polymer networks: a Monte Carlo simulation study.

    PubMed

    Quesada-Pérez, Manuel; Adroher-Benítez, Irene; Maroto-Centeno, José Alberto

    2014-05-28

    In this work, the size-exclusion partitioning of neutral solutes in crosslinked polymer networks has been studied through Monte Carlo simulations. Two models that provide user-friendly expressions to predict the partition coefficient have been tested over a wide range of volume fractions: Ogston's model (especially devised for fibrous media) and the pore model. The effects of crosslinking and bond stiffness have also been analyzed. Our results suggest that the fiber model can acceptably account for size-exclusion effects in crosslinked gels. Its predictions are good for large solutes if the fiber diameter is assumed to be the effective monomer diameter. For solutes sizes comparable to the monomer dimensions, a smaller fiber diameter must be used. Regarding the pore model, the partition coefficient is poorly predicted when the pore diameter is estimated as the distance between adjacent crosslinker molecules. On the other hand, our results prove that the pore sizes obtained from the pore model by fitting partitioning data of swollen gels are overestimated. PMID:24880328

  7. Investigation of the growth mechanisms of diglyme plasma polymers on amyloid fibril networks

    NASA Astrophysics Data System (ADS)

    Li, Yali; Reynolds, Nicholas P.; Styan, Katie E.; Muir, Benjamin W.; Forsythe, John S.; Easton, Christopher D.

    2016-01-01

    Within the area of biomaterials research, the ability to tailor a materials surface chemistry while presenting a biomimetic topography is a useful tool for studying cell-surface and cell-cell interactions. For the study reported here we investigated the deposition of diglyme plasma polymer films (DGpp) onto amyloid fibril networks (AFNs), which have morphologies that mimic the extracellular matrix. We extend our previous work to observe that the nanoscale contours of the AFNs are well preserved even under thick layers of DGpp. The width of the surface features is positively correlated to the DGpp thickness. DGpp film growth conformed to the underlying fibril features, with a gradual smoothing out of the resultant surface topography. Further, to understand how the films grow on top of AFNs, X-ray photoelectron spectroscopy depth profiling was employed to determine the elemental composition within the coating, perpendicular to the plane of the substrate. It was found that AFNs partially fragment during the initial stage of plasma polymerisation, and these fragments then mix with the growing DGpp to form an intermixed interface region above the AFN. The findings in this study are likely applicable to situations where plasma polymerisation is used to apply an overcoat to adsorbed organic and/or biological molecules.

  8. Highly sensitive gas-phase explosive detection by luminescent microporous polymer networks

    PubMed Central

    Räupke, André; Palma-Cando, Alex; Shkura, Eugen; Teckhausen, Peter; Polywka, Andreas; Görrn, Patrick; Scherf, Ullrich; Riedl, Thomas

    2016-01-01

    We propose microporous networks (MPNs) of a light emitting spiro-carbazole based polymer (PSpCz) as luminescent sensor for nitro-aromatic compounds. The MPNs used in this study can be easily synthesized on arbitrarily sized/shaped substrates by simple and low-cost electrochemical deposition. The resulting MPN afford an extremely high specific surface area of 1300 m2/g, more than three orders of magnitude higher than that of the thin films of the respective monomer. We demonstrate, that the luminescence of PSpCz is selectively quenched by nitro-aromatic analytes, e.g. nitrobenzene, 2,4-DNT and TNT. In striking contrast to a control sample based on non-porous spiro-carbazole, which does not show any luminescence quenching upon exposure to TNT at levels of 3 ppm and below, the microporous PSpCz shows a clearly detectable response even at TNT concentrations as low as 5 ppb, clearly demonstrating the advantage of microporous films as luminescent sensors for traces of explosive analytes. This level states the vapor pressure of TNT at room temperature. PMID:27373905

  9. Highly sensitive gas-phase explosive detection by luminescent microporous polymer networks

    NASA Astrophysics Data System (ADS)

    Räupke, André; Palma-Cando, Alex; Shkura, Eugen; Teckhausen, Peter; Polywka, Andreas; Görrn, Patrick; Scherf, Ullrich; Riedl, Thomas

    2016-07-01

    We propose microporous networks (MPNs) of a light emitting spiro-carbazole based polymer (PSpCz) as luminescent sensor for nitro-aromatic compounds. The MPNs used in this study can be easily synthesized on arbitrarily sized/shaped substrates by simple and low-cost electrochemical deposition. The resulting MPN afford an extremely high specific surface area of 1300 m2/g, more than three orders of magnitude higher than that of the thin films of the respective monomer. We demonstrate, that the luminescence of PSpCz is selectively quenched by nitro-aromatic analytes, e.g. nitrobenzene, 2,4-DNT and TNT. In striking contrast to a control sample based on non-porous spiro-carbazole, which does not show any luminescence quenching upon exposure to TNT at levels of 3 ppm and below, the microporous PSpCz shows a clearly detectable response even at TNT concentrations as low as 5 ppb, clearly demonstrating the advantage of microporous films as luminescent sensors for traces of explosive analytes. This level states the vapor pressure of TNT at room temperature.

  10. In vivo dynamical behavior of yeast chromatin modeled as an entangled polymer network with constraint release

    NASA Astrophysics Data System (ADS)

    Wang, Chenxi; Kilfoil, Maria L.

    2013-03-01

    The high fidelity segregation of chromatin is the central problem in cell mitosis. The role of mechanics underlying this, however, is undetermined. Work in this area has largely focused on cytoskeletal elements of the process. Preliminary work in our lab suggests the mechanical properties of chromatin are fundamental in this process. Nevertheless, the mechanical properties of chromatin in the cellular context are not well-characterized. For better understanding of the role of mechanics in this cellular process, and of the chromatin mechanics in vivo generally, a systematic dynamical description of chromatin in vivo is required. Accordingly, we label specific sites on chromatin with fluorescent proteins of different wave lengths, enabling us to detect multiple spots separately in 3D and track their displacements in time inside living yeast cells. We analyze the pairwise cross-correlated motion between spots as a function of relative distance along the DNA contour. Comparison between the reptation model and our data serves to test our conjecture that chromatin in the cell is basically an entangled polymer network under constraints to thermal motion, and removal of constraints by non-thermal cellular processes is expected to affect its dynamic behavior.

  11. Highly sensitive gas-phase explosive detection by luminescent microporous polymer networks.

    PubMed

    Räupke, André; Palma-Cando, Alex; Shkura, Eugen; Teckhausen, Peter; Polywka, Andreas; Görrn, Patrick; Scherf, Ullrich; Riedl, Thomas

    2016-01-01

    We propose microporous networks (MPNs) of a light emitting spiro-carbazole based polymer (PSpCz) as luminescent sensor for nitro-aromatic compounds. The MPNs used in this study can be easily synthesized on arbitrarily sized/shaped substrates by simple and low-cost electrochemical deposition. The resulting MPN afford an extremely high specific surface area of 1300 m(2)/g, more than three orders of magnitude higher than that of the thin films of the respective monomer. We demonstrate, that the luminescence of PSpCz is selectively quenched by nitro-aromatic analytes, e.g. nitrobenzene, 2,4-DNT and TNT. In striking contrast to a control sample based on non-porous spiro-carbazole, which does not show any luminescence quenching upon exposure to TNT at levels of 3 ppm and below, the microporous PSpCz shows a clearly detectable response even at TNT concentrations as low as 5 ppb, clearly demonstrating the advantage of microporous films as luminescent sensors for traces of explosive analytes. This level states the vapor pressure of TNT at room temperature. PMID:27373905

  12. Size-exclusion partitioning of neutral solutes in crosslinked polymer networks: A Monte Carlo simulation study

    SciTech Connect

    Quesada-Pérez, Manuel; Maroto-Centeno, José Alberto; Adroher-Benítez, Irene

    2014-05-28

    In this work, the size-exclusion partitioning of neutral solutes in crosslinked polymer networks has been studied through Monte Carlo simulations. Two models that provide user-friendly expressions to predict the partition coefficient have been tested over a wide range of volume fractions: Ogston's model (especially devised for fibrous media) and the pore model. The effects of crosslinking and bond stiffness have also been analyzed. Our results suggest that the fiber model can acceptably account for size-exclusion effects in crosslinked gels. Its predictions are good for large solutes if the fiber diameter is assumed to be the effective monomer diameter. For solutes sizes comparable to the monomer dimensions, a smaller fiber diameter must be used. Regarding the pore model, the partition coefficient is poorly predicted when the pore diameter is estimated as the distance between adjacent crosslinker molecules. On the other hand, our results prove that the pore sizes obtained from the pore model by fitting partitioning data of swollen gels are overestimated.

  13. Size-exclusion partitioning of neutral solutes in crosslinked polymer networks: a Monte Carlo simulation study.

    PubMed

    Quesada-Pérez, Manuel; Adroher-Benítez, Irene; Maroto-Centeno, José Alberto

    2014-05-28

    In this work, the size-exclusion partitioning of neutral solutes in crosslinked polymer networks has been studied through Monte Carlo simulations. Two models that provide user-friendly expressions to predict the partition coefficient have been tested over a wide range of volume fractions: Ogston's model (especially devised for fibrous media) and the pore model. The effects of crosslinking and bond stiffness have also been analyzed. Our results suggest that the fiber model can acceptably account for size-exclusion effects in crosslinked gels. Its predictions are good for large solutes if the fiber diameter is assumed to be the effective monomer diameter. For solutes sizes comparable to the monomer dimensions, a smaller fiber diameter must be used. Regarding the pore model, the partition coefficient is poorly predicted when the pore diameter is estimated as the distance between adjacent crosslinker molecules. On the other hand, our results prove that the pore sizes obtained from the pore model by fitting partitioning data of swollen gels are overestimated.

  14. Theoretical analysis on ion transport through polymer networks in electrochemical capacitors

    NASA Astrophysics Data System (ADS)

    Zwanikken, Jos W.; Jing, Yufei; Jadhao, Vikram; Sing, Charles E.; Boon, Niels; Olvera de La Cruz, Monica

    2014-03-01

    The development of predictive methods for deformable electronics calls for an equally composite theoretical foundation that unites traditionally separated fields. We are pioneering theoretical methods that unite polymer physics with liquid state theory, and develop a dynamical algorithm for inhomogeneous polarizable media between capacitor plates. By a quantitative study of the local molecular correlations we can explain the macroscopic behavior and the induced (non-equilibrium) potentials of mean force between the ions, the supporting medium, and the electrodes. Several timescales are found that correspond to different relaxation processes, related to ion diffusion, double layer formation, and the elastic response of the network. The application of an alternating current reveals a complex frequency-dependent response, by which the relative importance of the different underlying processes can be tuned. Typical non-equilibrium forces, generated by the applied field, are found to arise between regions with sharp gradients in the molecular structure or supporting background. The results may inform experimental efforts on noise reduction in soft capacitors, and suggest new functionality based on frequency-dependent non-equilibrium forces.

  15. Electrogenerated thin films of microporous polymer networks with remarkably increased electrochemical response to nitroaromatic analytes.

    PubMed

    Palma-Cando, Alex; Scherf, Ullrich

    2015-06-01

    Thin films of microporous polymer networks (MPNs) have been generated by electrochemical polymerization of a series of multifunctional carbazole-based monomers. The microporous films show high Brunauer-Emmett-Teller (BET) surface areas up to 1300 m2 g(-1) as directly measured by krypton sorption experiments. A correlation between the number of polymerizable carbazole units of the monomer and the resulting surface area is observed. Electrochemical sensing experiments with 1,3,5-trinitrobenzene as prototypical nitroaromatic analyte demonstrate an up to 180 times increased current response of MPN-modified glassy carbon electrodes in relation to the nonmodified electrode. The phenomenon probably involves intermolecular interactions between the electron-poor nitroaromatic analytes and the electron-rich, high surface area microporous deposits, with the electrochemical reduction at the MPN-modified electrodes being an adsorption-controlled process for low scan rates. We expect a high application potential of such MPN-modified electrodes for boosting the sensitivity of electrochemical sensor devices. PMID:25946727

  16. Controlling Phase Separation of Tough Interpenetrating Polymer Networks via Addition of Amphiphilic Block Copolymers

    NASA Astrophysics Data System (ADS)

    Rohde, Brian; Krishnamoorti, Ramanan; Robertson, Megan

    Interpenetrating polymer networks (IPNs) offer a unique way to combine the mechanical properties of two thermoset systems. Often used to create a material that possesses both high toughness and tensile properties, here we use polydicyclopentadiene, cured via ring opening metathesis polymerization, to contribute high toughness and diglycidyl ether of bisphenol A cured via anhydride chemistry to contribute high tensile strength and modulus. As the uncompatibilized system reacts in the presence of one another, mesoscopic phase separation occurs and dictates the overall efficacy of combining mechanical properties. To control phase separation and drive the system towards more mechanically robust nanostructed IPNs, amphiphilic block copolymers of polybutadiene- b-polyethylene oxide, where one block possesses strong affinity to polyDCPD and the other the DGEBA, were added to the system. Here we present a systematic study of the influence of block copolymer composition in the overall blend on degree of phase separation and morphology using a combination of small-angle x-ray scattering (SAXS) and scanning electron microscopy (SEM) techniques. The resultant mechanical properties are then explored in an effort to link mechanical properties to blend morphology.

  17. Directing colloidal assembly and a metal-insulator transition using quenched-disordered polymeric networks

    NASA Astrophysics Data System (ADS)

    Phan, Anh; Jadrich, Ryan; Schweizer, Kenneth

    2015-03-01

    Replica integral equation and effective medium theory methods are employed to elucidate how to massively reconfigure a colloidal assembly and realize equilibrium states of high electrical conductivity at low physical volume fractions. This is achieved by employing variable mesh size networks of rigid rod or semiflexible polymers as a templating internal field. By exploiting bulk phase separation frustration and the tunable competing processes of colloid adsorption on the low dimensional network and fluctuation-driven colloid clustering in the pore spaces, distinct spatial organizations of greatly enhanced particle contacts can be achieved. As a result, a continuous, but very abrupt, transition from an insulating to metallic-like state can be realized via a small change of either the colloid-template or colloid-colloid attraction strength. Polymer conformational fluctuations are found to significantly modify the physical adsorption process and hence the ability of colloids to organize along the filamentary network strands. Qualitatively new physical behavior can emerge as the pore size approaches the colloid diameter, reflecting strong frustrating constraints of the template on colloidal assembly.

  18. Nanoscale Charge Percolation Analysis in Polymer-Sorted (7,5) Single-Walled Carbon Nanotube Networks.

    PubMed

    Bottacchi, Francesca; Bottacchi, Stefano; Späth, Florian; Namal, Imge; Hertel, Tobias; Anthopoulos, Thomas D

    2016-08-01

    The current percolation in polymer-sorted semiconducting (7,5) single-walled carbon nanotube (SWNT) networks, processed from solution, is investigated using a combination of electrical field-effect measurements, atomic force microscopy (AFM), and conductive AFM (C-AFM) techniques. From AFM measurements, the nanotube length in the as-processed (7,5) SWNTs network is found to range from ≈100 to ≈1500 nm, with a SWNT surface density well above the percolation threshold and a maximum surface coverage ≈58%. Analysis of the field-effect charge transport measurements in the SWNT network using a 2D homogeneous random-network stick-percolation model yields an exponent coefficient for the transistors OFF currents of 16.3. This value is indicative of an almost ideal random network containing only a small concentration of metallic SWNTs. Complementary C-AFM measurements on the other hand enable visualization of current percolation pathways in the xy plane and reveal the isotropic nature of the as-spun (7,5) SWNT networks. This work demonstrates the tremendous potential of combining advanced scanning probe techniques with field-effect charge transport measurements for quantification of key network parameters including current percolation, metallic nanotubes content, surface coverage, and degree of SWNT alignment. Most importantly, the proposed approach is general and applicable to other nanoscale networks, including metallic nanowires as well as hybrid nanocomposites. PMID:27375031

  19. Evolution of non-equilibrium entanglement networks in spincast thin polymer films

    NASA Astrophysics Data System (ADS)

    Dalnoki-Veress, Kari; McGraw, Joshua; Fowler, Paul

    2012-02-01

    Measuring the rheology of non-equilibrium thin polymer films has received significant attention recently. Experiments are typically performed on thin polymer films that inherit their structure from spin coating. While the results of several rheological experiments paint a clear picture, details of molecular configurations in spincast polymer films are still unknown. Here we present the results of crazing measurements which demonstrate that the effective entanglement density of thin polymer films changes as a function of annealing toward a stable equilibrium value. The effective entanglement density plateaus with a time scale on the same order as the bulk reptation time.

  20. Polymer Optical Fiber Sensor and the Prediction of Sensor Response Utilizing Artificial Neural Networks

    NASA Astrophysics Data System (ADS)

    Haroglu, Derya

    characteristics: reproducibility, accuracy, selectivity, aging, and resolution. Artificial neural network (ANN), a mathematical model formed by mimicking the human nervous system, was used to predict the sensor response. Qwiknet (version 2.23) software was used to develop ANNs and according to the results of Qwiknet the prediction performances for training and testing data sets were 75%, and 83.33% respectively. In this dissertation, Chapter 1 describes the worldwide plastic optical fiber (POF) and fiber optic sensor markets, and the existing textile structures used in fiber optic sensing design particularly for the applications of biomedical and structural health monitoring (SHM). Chapter 2 provides a literature review in detail on polymer optical fibers, fiber optic sensors, and occupancy sensing in the passenger seats of automobiles. Chapter 3 includes the research objectives. Chapter 4 presents the response of POF to tensile loading, bending, and cyclic tensile loading with discussion parts. Chapter 5 includes an e-mail based survey to prioritize customer needs in a Quality Function Deployment (QFD) format utilizing Analytic Hierarchy Process (AHP) and survey results. Chapter 6 describes the POF sensor design and the behavior of it under pressure. Chapter 7 provides a data analysis based on the experimental results of Chapter 6. Chapter 8 presents the summary of this study and recommendations for future work.

  1. Fast-response IR spatial light modulators with a polymer network liquid crystal

    NASA Astrophysics Data System (ADS)

    Peng, Fenglin; Chen, Haiwei; Tripathi, Suvagata; Twieg, Robert J.; Wu, Shin-Tson

    2015-03-01

    Liquid crystals (LC) have widespread applications for amplitude modulation (e.g. flat panel displays) and phase modulation (e.g. beam steering). For phase modulation, a 2π phase modulo is required. To extend the electro-optic application into infrared region (MWIR and LWIR), several key technical challenges have to be overcome: 1. low absorption loss, 2. high birefringence, 3. low operation voltage, and 4. fast response time. After three decades of extensive development, an increasing number of IR devices adopting LC technology have been demonstrated, such as liquid crystal waveguide, laser beam steering at 1.55μm and 10.6 μm, spatial light modulator in the MWIR (3~5μm) band, dynamic scene projectors for infrared seekers in the LWIR (8~12μm) band. However, several fundamental molecular vibration bands and overtones exist in the MWIR and LWIR regions, which contribute to high absorption coefficient and hinder its widespread application. Therefore, the inherent absorption loss becomes a major concern for IR devices. To suppress IR absorption, several approaches have been investigated: 1) Employing thin cell gap by choosing a high birefringence liquid crystal mixture; 2) Shifting the absorption bands outside the spectral region of interest by deuteration, fluorination and chlorination; 3) Reducing the overlap vibration bands by using shorter alkyl chain compounds. In this paper, we report some chlorinated LC compounds and mixtures with a low absorption loss in the near infrared and MWIR regions. To achieve fast response time, we have demonstrated a polymer network liquid crystal with 2π phase change at MWIR and response time less than 5 ms.

  2. Scleral reinforcement through host tissue integration with biomimetic enzymatically degradable semi-interpenetrating polymer network.

    PubMed

    Su, James; Wall, Samuel T; Healy, Kevin E; Wildsoet, Christine F

    2010-03-01

    Enzymatically degradable semi-interpenetrating polymer networks (edsIPNs) were explored for their biocompatibility and ability to promote new scleral tissue growth, as a means of reinforcing the posterior wall of the eye. The edsIPNs comprised thermoresponsive poly(N-isopropylacrylamide-co-acrylic acid), customizable peptide crosslinkers cleavable by matrix metalloproteinases, and interpenetrating linear poly(acrylic acid)-graft-peptide chains to engage with cell surface receptors. Rheological studies revealed an increase in stiffness at body temperature; the complex shear modulus |G*| was 14.13 +/- 6.13 Pa at 22 degrees C and 63.18 +/- 12.24 Pa at 37 degrees C, compatible with injection at room temperature. Primary chick scleral fibroblasts and chondrocytes cultured on edsIPN increased by 15.1- and 11.1-fold, respectively, over 11 days; both exhibited delayed onset of exponential growth compared with the cells plated on tissue culture polystyrene. The edsIPN was delivered by retrobulbar injection (100 microL) to nine 2-week-old chicks to assess biocompatibility in vivo. Ocular axial dimensions were assessed using A-scan ultrasonography over 28 days, after which eyes were processed for histological analysis. Although edsIPN injections did not affect the rate of ocular elongation, the outer fibrous sclera showed significant thickening. The demonstration that injectable biomimetic edsIPNs stimulate scleral fibrous tissue growth represents proof-of-principle for a novel approach for scleral reinforcement and a potential therapy for high myopia. PMID:19814587

  3. Influence of polymer network parameters of tragacanth gum-based pH responsive hydrogels on drug delivery.

    PubMed

    Singh, Baljit; Sharma, Vikrant

    2014-01-30

    The present article deals with design of tragacanth gum-based pH responsive hydrogel drug delivery systems. The characterization of hydrogels has been carried out by SEMs, EDAX, FTIR, (13)C NMR, XRD, TGA/DTA/DTG and swelling studies. The correlation between reaction conditions and structural parameters of polymer networks such as polymer volume fraction in the swollen state (ϕ), Flory-Huggins interaction parameter (χ), molecular weight of the polymer chain between two neighboring cross links (M¯c), crosslink density (ρ) and mesh size (ξ) has been determined. The different kinetic models such as zero order, first order, Higuchi square root law, Korsmeyer-Peppas model and Hixson-Crowell cube root model were applied and it has been observed that release profile of amoxicillin best followed the first order model for the release of drug from the polymer matrix. The swelling of the hydrogels and release of drug from the drug loaded hydrogels occurred through non-Fickian diffusion mechanism in pH 7.4 solution.

  4. Thermo-reversible morphology and conductivity of a conjugated polymer network embedded in polymeric self-assembly

    NASA Astrophysics Data System (ADS)

    Han, Youngkyu; Carrillo, Jan-Michael Y.; Zhang, Zhe; Li, Yunchao; Hong, Kunlun; Sumpter, Bobby G.; Ohl, Michael; Paranthaman, Mariappan Parans; Smith, Gregory S.; Do, Changwoo

    Self-assembly of block copolymers provides opportunities to create nano hybrid materials, utilizing self-assembled micro-domains with a variety of morphology and periodic architectures as templates for functional nano-fillers. Here we report new progress towards the fabrication of a thermally responsive conducting polymer self-assembly made from a water-soluble poly(thiophene) derivative with short PEO side chains and Pluronic L62 solution in water. The structural and electrical properties of conjugated polymer-embedded nanostructures were investigated by combining SANS, SAXS, CGMD simulations, and impedance spectroscopy. The L62 solution template organizes the conjugated polymers by stably incorporating them into the hydrophilic domains thus inhibiting aggregation. The changing morphology of L62 during the micellar-to-lamellar phase transition defines the embedded conjugated polymer network. The conductivity is strongly coupled to the structural change of the templating L62 phase and exhibits thermally reversible behavior with no signs of quenching of the conductivity at high temperature. The research was sponsored by the Scientific User Facilities Division, Office of BES, U.S. DOE and Laboratory Directed Research and Development Program of ORNL, managed by UT-Battelle, LLC.

  5. Influence of polymer network parameters of tragacanth gum-based pH responsive hydrogels on drug delivery.

    PubMed

    Singh, Baljit; Sharma, Vikrant

    2014-01-30

    The present article deals with design of tragacanth gum-based pH responsive hydrogel drug delivery systems. The characterization of hydrogels has been carried out by SEMs, EDAX, FTIR, (13)C NMR, XRD, TGA/DTA/DTG and swelling studies. The correlation between reaction conditions and structural parameters of polymer networks such as polymer volume fraction in the swollen state (ϕ), Flory-Huggins interaction parameter (χ), molecular weight of the polymer chain between two neighboring cross links (M¯c), crosslink density (ρ) and mesh size (ξ) has been determined. The different kinetic models such as zero order, first order, Higuchi square root law, Korsmeyer-Peppas model and Hixson-Crowell cube root model were applied and it has been observed that release profile of amoxicillin best followed the first order model for the release of drug from the polymer matrix. The swelling of the hydrogels and release of drug from the drug loaded hydrogels occurred through non-Fickian diffusion mechanism in pH 7.4 solution. PMID:24299858

  6. Entropic attraction: Polymer compaction and expansion induced by nano-particles in confinement

    NASA Astrophysics Data System (ADS)

    Liao, Guo-Jun; Chien, Fan-Tso; Luzhbin, Dmytro; Chen, Yeng-Long

    2015-05-01

    We investigated nanoparticle (NP)-induced coil-to-globule transition of a semi-flexible polymer in a confined suspension of ideal NP using Langevin dynamics. DNA molecules are often found to be highly compact, bound with oppositely charged proteins in a crowded environment within cells and viruses. Recent studies found that high concentration of electrostatically neutral NP also condenses DNA due to entropically induced depletion attraction between DNA segments. Langevin dynamics simulations with a semi-flexible chain under strong confinement were performed to investigate the competition between NP-induced monomer-monomer and monomer-wall attraction under different confinement heights and NP volume fractions. We found that whether NP induce polymer segments to adsorb to the walls and swell or to attract one another and compact strongly depends on the relative strength of the monomer-wall and the NP-wall interactions.

  7. Computational analysis of cartilage implants based on an interpenetrated polymer network for tissue repairing.

    PubMed

    Manzano, Sara; Poveda-Reyes, Sara; Ferrer, Gloria Gallego; Ochoa, Ignacio; Hamdy Doweidar, Mohamed

    2014-10-01

    Interpenetrated polymer networks (IPNs), composed by two independent polymeric networks that spatially interpenetrate, are considered as valuable systems to control permeability and mechanical properties of hydrogels for biomedical applications. Specifically, poly(ethyl acrylate) (PEA)-poly(2-hydroxyethyl acrylate) (PHEA) IPNs have been explored as good hydrogels for mimicking articular cartilage. These lattices are proposed as matrix implants in cartilage damaged areas to avoid the discontinuity in flow uptake preventing its deterioration. The permeability of these implants is a key parameter that influences their success, by affecting oxygen and nutrient transport and removing cellular waste products to healthy cartilage. Experimental try-and-error approaches are mostly used to optimize the composition of such structures. However, computational simulation may offer a more exhaustive tool to test and screen out biomaterials mimicking cartilage, avoiding expensive and time-consuming experimental tests. An accurate and efficient prediction of material's permeability and internal directionality and magnitude of the fluid flow could be highly useful when optimizing biomaterials design processes. Here we present a 3D computational model based on Sussman-Bathe hyperelastic material behaviour. A fluid structure analysis is performed with ADINA software, considering these materials as two phases composites where the solid part is saturated by the fluid. The model is able to simulate the behaviour of three non-biodegradable hydrogel compositions, where percentages of PEA and PHEA are varied. Specifically, the aim of this study is (i) to verify the validity of the Sussman-Bathe material model to simulate the response of the PEA-PHEA biomaterials; (ii) to predict the fluid flux and the permeability of the proposed IPN hydrogels and (iii) to study the material domains where the passage of nutrients and cellular waste products is reduced leading to an inadequate flux

  8. Conformal organic-inorganic hybrid network polymer thin films by molecular layer deposition using trimethylaluminum and glycidol.

    PubMed

    Gong, Bo; Peng, Qing; Parsons, Gregory N

    2011-05-19

    Growing interest in nanoscale organic-inorganic hybrid network polymer materials is driving exploration of new bulk and thin film synthesis reaction mechanisms. Molecular layer deposition (MLD) is a vapor-phase deposition process, based on atomic layer deposition (ALD) which proceeds by exposing a surface to an alternating sequence of two or more reactant species, where each surface half-reaction goes to completion before the next reactant exposure. This work describes film growth using trimethyl aluminum and heterobifunctional glycidol at moderate temperatures (90-150 °C), producing a relatively stable organic-inorganic network polymer of the form (-Al-O-(C(4)H(8))-O-)(n). Film growth rate and in situ reaction analysis indicate that film growth does not initially follow a steady-state rate, but increases rapidly during early film growth. The mechanism is consistent with subsurface species transport and trapping, previously documented during MLD and ALD on polymers. A water exposure step after the TMA produces a more linear growth rate, likely by blocking TMA subsurface diffusion. Uniform and conformal films are formed on complex nonplanar substrates. Upon postdeposition annealing, films transform into microporous metal oxides with ∼5 Å pore size and surface area as high as ∼327 m(2)/g, and the resulting structures duplicate the shape of the original substrate. These hybrid films and porous materials could find uses in several research fields including gas separations and diffusion barriers, biomedical scaffolds, high surface area coatings, and others.

  9. Shear-induced clustering of Brownian colloids in associative polymer networks at moderate Péclet number

    NASA Astrophysics Data System (ADS)

    Kim, Juntae; Helgeson, Matthew E.

    2016-08-01

    We investigate shear-induced clustering and its impact on fluid rheology in polymer-colloid mixtures at moderate colloid volume fraction. By employing a thermoresponsive system that forms associative polymer-colloid networks, we present experiments of rheology and flow-induced microstructure on colloid-polymer mixtures in which the relative magnitudes of the time scales associated with relaxation of viscoelasticity and suspension microstructure are widely and controllably varied. In doing so, we explore several limits of relative magnitude of the relevant dimensionless shear rates, the Weissenberg number Wi and the Péclet number Pe. In all of these limits, we find that the fluid exhibits two distinct regimes of shear thinning at relatively low and high shear rates, in which the rheology collapses by scaling with Wi and Pe, respectively. Using three-dimensionally-resolved flow small-angle neutron scattering measurements, we observe clustering of the suspension above a critical shear rate corresponding to Pe ˜0.1 over a wide range of fluid conditions, having anisotropy with projected orientation along both the vorticity and compressional axes of shear. The degree of anisotropy is shown to scale with Pe. From this we formulate an empirical model for the shear stress and viscosity, in which the viscoelastic network stress is augmented by an asymptotic shear thickening contribution due to hydrodynamic clustering. Overall, our results elucidate the significant role of hydrodynamic interactions in contributing to shear-induced clustering of Brownian suspensions in viscoelastic liquids.

  10. Extremely stretchable thermosensitive hydrogels by introducing slide-ring polyrotaxane cross-linkers and ionic groups into the polymer network

    PubMed Central

    Bin Imran, Abu; Esaki, Kenta; Gotoh, Hiroaki; Seki, Takahiro; Ito, Kohzo; Sakai, Yasuhiro; Takeoka, Yukikazu

    2014-01-01

    Stimuli-sensitive hydrogels changing their volumes and shapes in response to various stimulations have potential applications in multiple fields. However, these hydrogels have not yet been commercialized due to some problems that need to be overcome. One of the most significant problems is that conventional stimuli-sensitive hydrogels are usually brittle. Here we prepare extremely stretchable thermosensitive hydrogels with good toughness by using polyrotaxane derivatives composed of α-cyclodextrin and polyethylene glycol as cross-linkers and introducing ionic groups into the polymer network. The ionic groups help the polyrotaxane cross-linkers to become well extended in the polymer network. The resulting hydrogels are surprisingly stretchable and tough because the cross-linked α-cyclodextrin molecules can move along the polyethylene glycol chains. In addition, the polyrotaxane cross-linkers can be used with a variety of vinyl monomers; the mechanical properties of the wide variety of polymer gels can be improved by using these cross-linkers. PMID:25296246

  11. Tracer diffusion in a polymer gel: simulations of static and dynamic 3D networks using spherical boundary conditions

    NASA Astrophysics Data System (ADS)

    Kamerlin, Natasha; Elvingson, Christer

    2016-11-01

    We have investigated an alternative to the standard periodic boundary conditions for simulating the diffusion of tracer particles in a polymer gel by performing Brownian dynamics simulations using spherical boundary conditions. The gel network is constructed by randomly distributing tetravalent cross-linking nodes and connecting nearest pairs. The final gel structure is characterised by the radial distribution functions, chain lengths and end-to-end distances, and the pore size distribution. We have looked at the diffusion of tracer particles with a wide range of sizes, diffusing in both static and dynamic networks of two different volume fractions. It is quantitatively shown that the dynamical effect of the network becomes more important in facilitating the diffusional transport for larger particle sizes, and that one obtains a finite diffusion also for particle sizes well above the maximum in the pore size distribution.

  12. Tracer diffusion in a polymer gel: simulations of static and dynamic 3D networks using spherical boundary conditions.

    PubMed

    Kamerlin, Natasha; Elvingson, Christer

    2016-11-30

    We have investigated an alternative to the standard periodic boundary conditions for simulating the diffusion of tracer particles in a polymer gel by performing Brownian dynamics simulations using spherical boundary conditions. The gel network is constructed by randomly distributing tetravalent cross-linking nodes and connecting nearest pairs. The final gel structure is characterised by the radial distribution functions, chain lengths and end-to-end distances, and the pore size distribution. We have looked at the diffusion of tracer particles with a wide range of sizes, diffusing in both static and dynamic networks of two different volume fractions. It is quantitatively shown that the dynamical effect of the network becomes more important in facilitating the diffusional transport for larger particle sizes, and that one obtains a finite diffusion also for particle sizes well above the maximum in the pore size distribution. PMID:27662260

  13. A polarization-independent liquid crystal phase modulation using polymer-network liquid crystal with orthogonal alignment layers

    NASA Astrophysics Data System (ADS)

    Chen, Ming-Syuan; Lin, Wei-Chih; Tsou, Yu-Shih; Lin, Yi-Hsin

    2012-10-01

    A polarization-independent liquid crystal (LC) phase modulation using polymer-network liquid crystals with orthogonal alignments layers (T-PNLC) is demonstrated. T-PNLC consists of three layers. LC directors in the two layers near glass substrates are orthogonal to each other. In the middle layer, LC directors are perpendicular to the glass substrate. The advantages of such T-PNLC include polarizer-free, larger phase shift (~0.4π rad) than the residual phase type (<0.05π rad), and low operating voltage (< 30Vrms). It does not require bias voltage for avoiding scattering because the refractive index of liquid crystals matches that of polymers. The phase shift of T-PNLC is affected by the cell gap and the curing voltages. The potential applications are laser beam steering, spatial light modulators and electrically tunable micro-lens arrays.

  14. Real-Time Monitoring of Chemical and Topological Rearrangements in Solidifying Amphiphilic Polymer Co-Networks: Understanding Surface Demixing.

    PubMed

    Guzman, Gustavo; Nugay, Turgut; Kennedy, Joseph P; Cakmak, Mukerrem

    2016-04-12

    Amphiphilic polymer co-networks provide a unique route to integrating contrasting attributes of otherwise immiscible components within a bicontinuous percolating morphology and are anticipated to be valuable for applications such as biocatalysis, sensing of metabolites, and dual dialysis membranes. These co-networks are in essence chemically forced blends and have been shown to selectively phase-separate at surfaces during film formation. Here, we demonstrate that surface demixing at the air-film interface in solidifying polymer co-networks is not a unidirectional process; instead, a combination of kinetic and thermodynamic interactions leads to dynamic molecular rearrangement during solidification. Time-resolved gravimetry, low contact angles, and negative out-of-plane birefringence provided strong experimental evidence of the transitory trapping of thermodynamically unfavorable hydrophilic moieties at the air-film interface due to fast asymmetric solvent depletion. We also find that slow-drying hydrophobic elements progressively substitute hydrophilic domains at the surface as the surface energy is minimized. These findings are broadly applicable to common-solvent bicontinuous systems and open the door for process-controlled performance improvements in diverse applications. Similar observations could potentially be coupled with controlled polymerization rates to maximize the intermingling of bicontinuous phases at surfaces, thus generating true three-dimensional, bicontinuous, and undisturbed percolation pathways throughout the material.

  15. Modification of Polymer Network Properties through the Addition of Functional Nanogel Particles

    NASA Astrophysics Data System (ADS)

    Liu, JianCheng

    Multifunctional acrylic and methacrylic monomers have been widely applied in many photopolymerization applications to produce crosslinked polymers with advantages such as rapid curing, broad choices of commercially available monomers and desirable physical and mechanical properties. However, there still remain critical challenges for these materials during polymerization including limited conversion and early onset of gelation as well as the generation of significant polymerization shrinkage and stress. This thesis explores the effects of network property modification through the addition of polymeric nanoparticles or nanogels. In order to understand the relationship between nanogel structure and composite material properties, nanogels with different architectures and functionalities were studied during polymerization in terms of kinetics, shrinkage and stress reduction, mechanical performance and reaction mechanisms. Nanogel composite formulations were evaluated to understand the interaction between nanogel structure with the resin matrix during polymerization through adjustment of nanogel branching densities and reactivity of polymer chain ends. It was found that both the chemical crosslinking from reactive chain ends and physical entanglements of high branching density nanogels with the resin matrix dramatically could improve final material mechanical strength. The reductions in overall volumetric shrinkage and shrinkage stress were found to follow at least proportional behavior with respect to nanogel loading concentration while maintaining similar final conversion and modulus results compared with the control resin. Nanogels containing unique functionalities were designed in order to modify reaction mechanism during secondary polymerization. A nanogel containing an integrated photoinitiator and active chain-end RAFT groups was able to initiate secondary polymerization from the nanogel phase so that localized polymerization was achieved from the beginning of

  16. The effect of molecular mobility on electronic transport in carbon nanotube-polymer composites and networks

    SciTech Connect

    Shenogin, Sergei; Lee, Jonghoon; Voevodin, Andrey A.; Roy, Ajit K.

    2014-12-21

    A multiscale modeling approach to the prediction of electrical conductivity in carbon nanotube (CNT)–polymer composite materials is developed, which takes into account thermally activated molecular mobility of the matrix and the CNTs. On molecular level, a tight-binding density functional theory and non-equilibrium Green's function method are used to calculate the static electron transmission function in the contact between two metallic carbon nanotubes that corresponds to electron transport at 0 K. For higher temperatures, the statistical distribution of effective contact resistances is considered that originates from thermal fluctuations of intermolecular distances caused by molecular mobility of carbon nanotube and the polymer matrix. Based on this distribution and using effective medium theory, the temperature dependence of macroscopic electrical resistivity for CNT-polymer composites and CNT mats is calculated. The predicted data indicate that the electrical conductivity of the CNT-polymer composites increases linearly with temperature above 50 K, which is in a quantitative agreement with the experiments. Our model predicts a slight nonlinearity in temperature dependence of electric conductivity at low temperatures for percolated composites with small CNT loading. The model also explains the effect of glass transition and other molecular relaxation processes in the polymer matrix on the composite electrical conductivity. The developed multiscale approach integrates the atomistic charge transport mechanisms in percolated CNT-polymer composites with the macroscopic response and thus enables direct comparison of the prediction with the measurements of macroscopic material properties.

  17. Synthesis and gas adsorption properties of tetra-armed microporous organic polymer networks based on triphenylamine.

    PubMed

    Yang, Xiao; Yao, Shuwen; Yu, Miao; Jiang, Jia-Xing

    2014-04-01

    Two novel tetra-armed microporous organic polymers have been designed and synthesized via a nickel-catalyzed Yamamoto-type Ullmann cross-coupling reaction or Suzuki cross-coupling polycondensation. These polymers are stable in various solvents, including concentrated hydrochloric acid, and are thermally stable. The homocoupled polymer YPTPA shows much higher Brunauer-Emmet-Teller-specific surface area up to 1557 m(2) g(-1) than the copolymer SPTPA (544 m(2) g(-1)), and a high CO2 uptake ability of 3.03 mmol g(-1) (1.13 bar/273 K) with a CO2 /N2 sorption selectivity of 17.3:1. Both polymers show high isosteric heats of CO2 adsorption (22.7-26.5 kJ mol(-1)) because the incorporation of nitrogen atoms into the skeleton of microporous organic polymers enhances the interaction between the pore wall and the CO2 molecules. The values are higher than those of the porous aromatic frameworks, which contain neither additional polar functional groups nor nitrogen atoms, and are rather close to those of previously reported microporous organic polymers containing the nitrogen atoms on the pore wall. These data show that these materials would be potential candidates for applications in post-combustion CO2 capture and sequestration technology.

  18. The effect of molecular mobility on electronic transport in carbon nanotube-polymer composites and networks

    NASA Astrophysics Data System (ADS)

    Shenogin, Sergei; Lee, Jonghoon; Voevodin, Andrey A.; Roy, Ajit K.

    2014-12-01

    A multiscale modeling approach to the prediction of electrical conductivity in carbon nanotube (CNT)-polymer composite materials is developed, which takes into account thermally activated molecular mobility of the matrix and the CNTs. On molecular level, a tight-binding density functional theory and non-equilibrium Green's function method are used to calculate the static electron transmission function in the contact between two metallic carbon nanotubes that corresponds to electron transport at 0 K. For higher temperatures, the statistical distribution of effective contact resistances is considered that originates from thermal fluctuations of intermolecular distances caused by molecular mobility of carbon nanotube and the polymer matrix. Based on this distribution and using effective medium theory, the temperature dependence of macroscopic electrical resistivity for CNT-polymer composites and CNT mats is calculated. The predicted data indicate that the electrical conductivity of the CNT-polymer composites increases linearly with temperature above 50 K, which is in a quantitative agreement with the experiments. Our model predicts a slight nonlinearity in temperature dependence of electric conductivity at low temperatures for percolated composites with small CNT loading. The model also explains the effect of glass transition and other molecular relaxation processes in the polymer matrix on the composite electrical conductivity. The developed multiscale approach integrates the atomistic charge transport mechanisms in percolated CNT-polymer composites with the macroscopic response and thus enables direct comparison of the prediction with the measurements of macroscopic material properties.

  19. Facile preparation of carbon nanotube-conducting polymer network for sensitive electrochemical immunoassay of Hepatitis B surface antigen in serum.

    PubMed

    Hu, Yaogai; Zhao, Zhengyu; Wan, Qianqian

    2011-06-01

    A novel electrochemical immunosensor built on three dimensional carbon nanotube-conducting polymer (CNT-CP) network is reported for detection of Hepatitis B surface antigen (HBsAg) in human serum. The CNT-CP network is prepared by drop-drying of CNT solution on glassy carbon electrode, followed by electrochemical polymerization of poly (pyrrole propionic acid) (pPPA) film to crosslink and stabilize the CNTs, wherein the CNTs form the backbone of the network, and offer great specific surface areas for antibody attachment, and confer good conductivity for electrochemical detection, while the conducting film integrates the carbon nanotubes into a stable network due to its self-limiting growth behavior and provides abundant carboxyl groups for covalent immobilization of probe proteins. As a unique matrix, the CNT-CP network enables sensitive electrochemical detection of HBsAg biomarker by using alkaline phosphatase (ALP)-conjugated secondary antibodies under sandwich format coupling with the ALP substrate solution, p-aminophenyl phosphate (PAPP), reaching a detection limit of 0.01ng/mL with a dynamic range of 5 orders of magnitude.

  20. Equilibrium & Nonequilibrium Fluctuation Effects in Biopolymer Networks

    NASA Astrophysics Data System (ADS)

    Kachan, Devin Michael

    Fluctuation-induced interactions are an important organizing principle in a variety of soft matter systems. In this dissertation, I explore the role of both thermal and active fluctuations within cross-linked polymer networks. The systems I study are in large part inspired by the amazing physics found within the cytoskeleton of eukaryotic cells. I first predict and verify the existence of a thermal Casimir force between cross-linkers bound to a semi-flexible polymer. The calculation is complicated by the appearance of second order derivatives in the bending Hamiltonian for such polymers, which requires a careful evaluation of the the path integral formulation of the partition function in order to arrive at the physically correct continuum limit and properly address ultraviolet divergences. I find that cross linkers interact along a filament with an attractive logarithmic potential proportional to thermal energy. The proportionality constant depends on whether and how the cross linkers constrain the relative angle between the two filaments to which they are bound. The interaction has important implications for the synthesis of biopolymer bundles within cells. I model the cross-linkers as existing in two phases: bound to the bundle and free in solution. When the cross-linkers are bound, they behave as a one-dimensional gas of particles interacting with the Casimir force, while the free phase is a simple ideal gas. Demanding equilibrium between the two phases, I find a discontinuous transition between a sparsely and a densely bound bundle. This discontinuous condensation transition induced by the long-ranged nature of the Casimir interaction allows for a similarly abrupt structural transition in semiflexible filament networks between a low cross linker density isotropic phase and a higher cross link density bundle network. This work is supported by the results of finite element Brownian dynamics simulations of semiflexible filaments and transient cross-linkers. I

  1. Highly dispersed pd catalyst locked in knitting aryl network polymers for Suzuki-Miyaura coupling reactions of aryl chlorides in aqueous media.

    PubMed

    Li, Buyi; Guan, Zhenhong; Wang, Wei; Yang, Xinjia; Hu, Jianglin; Tan, Bien; Li, Tao

    2012-07-01

    Highly dispersed palladium chloride catalysts locked in triphenylphosphine-functionalized knitting aryl network polymers (KAPs) are developed and exhibit excellent activity under mild conditions in the Suzuki-Miyaura cross-coupling reactions of aryl chlorides in aqueous media. This work highlights that the microporous polymers not only play the role of support materials, but also protect the Pd species from aggregation and precipitation, hence, positively effect the catalysis activity.

  2. Conductive network formation of carbon nanotubes in elastic polymer microfibers and its effect on the electrical conductance: Experiment and simulation

    NASA Astrophysics Data System (ADS)

    Cho, Hyun Woo; Kim, Sang Won; Kim, Jeongmin; Kim, Un Jeong; Im, Kyuhyun; Park, Jong-Jin; Sung, Bong June

    2016-05-01

    We investigate how the electrical conductance of microfibers (made of polymers and conductive nanofillers) decreases upon uniaxial deformation by performing both experiments and simulations. Even though various elastic conductors have been developed due to promising applications for deformable electronic devices, the mechanism at a molecular level for electrical conductance change has remained elusive. Previous studies proposed that the decrease in electrical conductance would result from changes in either distances or contact numbers between conductive fillers. In this work, we prepare microfibers of single walled carbon nanotubes (SWCNTs)/polyvinyl alcohol composites and investigate the electrical conductance and the orientation of SWCNTs upon uniaxial deformation. We also perform extensive Monte Carlo simulations, which reproduce experimental results for the relative decrease in conductance and the SWCNTs orientation. We investigate the electrical networks of SWCNTs in microfibers and find that the decrease in the electrical conductance upon uniaxial deformation should be attributed to a subtle change in the topological structure of the electrical network.

  3. Interfacial reaction of silver ultra-thin film deposited on interpenetrating polymer network substrate by liquor-phase reduction

    NASA Astrophysics Data System (ADS)

    Tang, Dongyan; Guo, Yudi; Zhang, Xiaohong; Yin, Yuelong

    2010-08-01

    The interfacial reaction, metal transformations, and nonmetal bond types of silver ultra-thin film deposited on polyurethane (PU) based interpenetrating polymer networks (IPN) substrate by the liquor-phase reduction at room temperatures were studied by atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The IPN substrate was prepared by dip-pulling precursors onto a silicon wafer or a glass plate, followed by solidification at room temperature. The interpenetrate structures of IPN with two crosslinked networks restricted the aggregation of silver during the reduction and deposition. The devised -OH terminal group in PU simplified the determination of reactive site in IPN and reinforced the adhesion between IPN and silver through interfacial reaction. The XPS results, which matched well with the ATR-FTIR results, verified the chemical reactive site of PU in IPN with silver in the oxide state.

  4. Strong electroactive biodegradable shape memory polymer networks based on star-shaped polylactide and aniline trimer for bone tissue engineering.

    PubMed

    Xie, Meihua; Wang, Ling; Ge, Juan; Guo, Baolin; Ma, Peter X

    2015-04-01

    Preparation of functional shape memory polymer (SMP) for tissue engineering remains a challenge. Here the synthesis of strong electroactive shape memory polymer (ESMP) networks based on star-shaped polylactide (PLA) and aniline trimer (AT) is reported. Six-armed PLAs with various chain lengths were chemically cross-linked to synthesize SMP. After addition of an electroactive AT segment into the SMP, ESMP was obtained. The polymers were characterized by (1)H NMR, GPC, FT-IR, CV, DSC, DMA, tensile test, and degradation test. The SMP and ESMP exhibited strong mechanical properties (modulus higher than GPa) and excellent shape memory performance: short recovery time (several seconds), high recovery ratio (over 94%), and high fixity ratio (almost 100%). Moreover, cyclic voltammetry test confirmed the electroactivity of the ESMP. The ESMP significantly enhanced the proliferation of C2C12 cells compared to SMP and linear PLA (control). In addition, the ESMP greatly improved the osteogenic differentiation of C2C12 myoblast cells compared to PH10 and PLA in terms of ALP enzyme activity, immunofluorescence staining, and relative gene expression by quantitative real-time polymerase chain reaction (qRT-PCR). These intelligent SMPs and electroactive SMP with strong mechanical properties, tunable degradability, good electroactivity, biocompatibility, and enhanced osteogenic differentiation of C2C12 cells show great potential for bone regeneration.

  5. Solution-Processed Donor-Acceptor Polymer Nanowire Network Semiconductors For High-Performance Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Lei, Yanlian; Deng, Ping; Li, Jun; Lin, Ming; Zhu, Furong; Ng, Tsz-Wai; Lee, Chun-Sing; Ong, Beng S.

    2016-04-01

    Organic field-effect transistors (OFETs) represent a low-cost transistor technology for creating next-generation large-area, flexible and ultra-low-cost electronics. Conjugated electron donor-acceptor (D-A) polymers have surfaced as ideal channel semiconductor candidates for OFETs. However, high-molecular weight (MW) D-A polymer semiconductors, which offer high field-effect mobility, generally suffer from processing complications due to limited solubility. Conversely, the readily soluble, low-MW D-A polymers give low mobility. We report herein a facile solution process which transformed a lower-MW, low-mobility diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene (I) into a high crystalline order and high-mobility semiconductor for OFETs applications. The process involved solution fabrication of a channel semiconductor film from a lower-MW (I) and polystyrene blends. With the help of cooperative shifting motion of polystyrene chain segments, (I) readily self-assembled and crystallized out in the polystyrene matrix as an interpenetrating, nanowire semiconductor network, providing significantly enhanced mobility (over 8 cm2V‑1s‑1), on/off ratio (107), and other desirable field-effect properties that meet impactful OFET application requirements.

  6. Solution-Processed Donor-Acceptor Polymer Nanowire Network Semiconductors For High-Performance Field-Effect Transistors.

    PubMed

    Lei, Yanlian; Deng, Ping; Li, Jun; Lin, Ming; Zhu, Furong; Ng, Tsz-Wai; Lee, Chun-Sing; Ong, Beng S

    2016-01-01

    Organic field-effect transistors (OFETs) represent a low-cost transistor technology for creating next-generation large-area, flexible and ultra-low-cost electronics. Conjugated electron donor-acceptor (D-A) polymers have surfaced as ideal channel semiconductor candidates for OFETs. However, high-molecular weight (MW) D-A polymer semiconductors, which offer high field-effect mobility, generally suffer from processing complications due to limited solubility. Conversely, the readily soluble, low-MW D-A polymers give low mobility. We report herein a facile solution process which transformed a lower-MW, low-mobility diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene (I) into a high crystalline order and high-mobility semiconductor for OFETs applications. The process involved solution fabrication of a channel semiconductor film from a lower-MW (I) and polystyrene blends. With the help of cooperative shifting motion of polystyrene chain segments, (I) readily self-assembled and crystallized out in the polystyrene matrix as an interpenetrating, nanowire semiconductor network, providing significantly enhanced mobility (over 8 cm(2)V(-1)s(-1)), on/off ratio (10(7)), and other desirable field-effect properties that meet impactful OFET application requirements. PMID:27091315

  7. Solution-Processed Donor-Acceptor Polymer Nanowire Network Semiconductors For High-Performance Field-Effect Transistors

    PubMed Central

    Lei, Yanlian; Deng, Ping; Li, Jun; Lin, Ming; Zhu, Furong; Ng, Tsz-Wai; Lee, Chun-Sing; Ong, Beng S.

    2016-01-01

    Organic field-effect transistors (OFETs) represent a low-cost transistor technology for creating next-generation large-area, flexible and ultra-low-cost electronics. Conjugated electron donor-acceptor (D-A) polymers have surfaced as ideal channel semiconductor candidates for OFETs. However, high-molecular weight (MW) D-A polymer semiconductors, which offer high field-effect mobility, generally suffer from processing complications due to limited solubility. Conversely, the readily soluble, low-MW D-A polymers give low mobility. We report herein a facile solution process which transformed a lower-MW, low-mobility diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene (I) into a high crystalline order and high-mobility semiconductor for OFETs applications. The process involved solution fabrication of a channel semiconductor film from a lower-MW (I) and polystyrene blends. With the help of cooperative shifting motion of polystyrene chain segments, (I) readily self-assembled and crystallized out in the polystyrene matrix as an interpenetrating, nanowire semiconductor network, providing significantly enhanced mobility (over 8 cm2V−1s−1), on/off ratio (107), and other desirable field-effect properties that meet impactful OFET application requirements. PMID:27091315

  8. Thermosetting polyimide resin matrix composites with interpenetrating polymer networks for precision foil resistor chips based on special mechanical performance requirements

    NASA Astrophysics Data System (ADS)

    Wang, X. Y.; Ma, J. X.; Li, C. G.; Wang, H. X.

    2014-04-01

    Based on interpenetrating networks (IPNs) different macromolecular materials such as epoxy, phenolic, and silicone resin were chosen to modify thermosetting polyimide (TSPI) resin to solve the lack of performance when used for protecting precision foil resistor chips. Copolymerization modification, controlled at curing stage, was used to prepare TSPI composites considering both performance and process requirements. The mechanical properties related to trimming process were mainly studied due to the special requirements of the regularity of scratch edges caused by a tungsten needle. The analysis on scratch edges reveals that the generation and propagation of microcracks caused by scratching together with crack closure effect may lead to regular scratch traces. Experiments show that the elongation at break of TSPI composites is the main reason that determines the special mechanical properties. The desired candidate materials should have proper hardness and toughness, and the specific mechanical data are that the mean elongation at break and tensile strength of polymer materials are in the range of 9.2-10.4% and 100-107 MPa, respectively. Possible reasons for the effect of the modifiers chosen on TSPI polymers, the reaction mechanisms on modified TSPI resin and the IPN structure in TSPI composite polymers were discussed based on IR and TG analysis.

  9. Fast Triggering of Shape Memory Polymers using an Embedded Carbon Nanotube Sponge Network.

    PubMed

    Zhou, Guoxiang; Zhang, Heng; Xu, Shuping; Gui, Xuchun; Wei, Hongqiu; Leng, Jinsong; Koratkar, Nikhil; Zhong, Jing

    2016-01-01

    In this work, a 3-D porous carbon nanotube sponge (CNTS) was embedded within a shape memory polymer (SMPs) matrix. We demonstrate complete infiltration and filling of the SMPs into the CNTS by capillary force without any damage to the CNTS structure. With only ~0.2 wt% carbon nanotube loading, the glass transition temperature is increased by ~20 °C, indicating strong interaction between CNTS and the SMPs matrix. Further, we find that the uniform distribution of the carbon nanotubes in the nanocomposite results in high electrical conductivity, and thus highly effective electricity triggering capability. The carbon nanotube sponge shape memory polymer (CNTS/SMPs) nanocomposite could be triggered within ~10 seconds by the application of ~10 volts. Results from finite element simulations showed good agreement with the experimental results, and indicated that for our system the interface thermal energy loss does not have a significant effect on the heating rate of the polymer matrix.

  10. Fast Triggering of Shape Memory Polymers using an Embedded Carbon Nanotube Sponge Network.

    PubMed

    Zhou, Guoxiang; Zhang, Heng; Xu, Shuping; Gui, Xuchun; Wei, Hongqiu; Leng, Jinsong; Koratkar, Nikhil; Zhong, Jing

    2016-01-01

    In this work, a 3-D porous carbon nanotube sponge (CNTS) was embedded within a shape memory polymer (SMPs) matrix. We demonstrate complete infiltration and filling of the SMPs into the CNTS by capillary force without any damage to the CNTS structure. With only ~0.2 wt% carbon nanotube loading, the glass transition temperature is increased by ~20 °C, indicating strong interaction between CNTS and the SMPs matrix. Further, we find that the uniform distribution of the carbon nanotubes in the nanocomposite results in high electrical conductivity, and thus highly effective electricity triggering capability. The carbon nanotube sponge shape memory polymer (CNTS/SMPs) nanocomposite could be triggered within ~10 seconds by the application of ~10 volts. Results from finite element simulations showed good agreement with the experimental results, and indicated that for our system the interface thermal energy loss does not have a significant effect on the heating rate of the polymer matrix. PMID:27052451

  11. Model systems for single molecule polymer dynamics

    PubMed Central

    Latinwo, Folarin

    2012-01-01

    Double stranded DNA (dsDNA) has long served as a model system for single molecule polymer dynamics. However, dsDNA is a semiflexible polymer, and the structural rigidity of the DNA double helix gives rise to local molecular properties and chain dynamics that differ from flexible chains, including synthetic organic polymers. Recently, we developed single stranded DNA (ssDNA) as a new model system for single molecule studies of flexible polymer chains. In this work, we discuss model polymer systems in the context of “ideal” and “real” chain behavior considering thermal blobs, tension blobs, hydrodynamic drag and force–extension relations. In addition, we present monomer aspect ratio as a key parameter describing chain conformation and dynamics, and we derive dynamical scaling relations in terms of this molecular-level parameter. We show that asymmetric Kuhn segments can suppress monomer–monomer interactions, thereby altering global chain dynamics. Finally, we discuss ssDNA in the context of a new model system for single molecule polymer dynamics. Overall, we anticipate that future single polymer studies of flexible chains will reveal new insight into the dynamic behavior of “real” polymers, which will highlight the importance of molecular individualism and the prevalence of non-linear phenomena. PMID:22956980

  12. Shape memory polymers

    SciTech Connect

    Wilson, Thomas S.; Bearinger, Jane P.

    2015-06-09

    New shape memory polymer compositions, methods for synthesizing new shape memory polymers, and apparatus comprising an actuator and a shape memory polymer wherein the shape memory polymer comprises at least a portion of the actuator. A shape memory polymer comprising a polymer composition which physically forms a network structure wherein the polymer composition has shape-memory behavior and can be formed into a permanent primary shape, re-formed into a stable secondary shape, and controllably actuated to recover the permanent primary shape. Polymers have optimal aliphatic network structures due to minimization of dangling chains by using monomers that are symmetrical and that have matching amine and hydroxyl groups providing polymers and polymer foams with clarity, tight (narrow temperature range) single transitions, and high shape recovery and recovery force that are especially useful for implanting in the human body.

  13. Viscoelasticity and primitive path analysis of entangled polymer liquids: From F-actin to polyethylene

    NASA Astrophysics Data System (ADS)

    Uchida, Nariya; Grest, Gary S.; Everaers, Ralf

    2008-01-01

    We combine computer simulations and scaling arguments to develop a unified view of polymer entanglement based on the primitive path analysis of the microscopic topological state. Our results agree with experimentally measured plateau moduli for three different polymer classes over a wide range of reduced polymer densities: (i) semidilute theta solutions of synthetic polymers, (ii) the corresponding dense melts above the glass transition or crystallization temperature, and (iii) solutions of semiflexible (bio)polymers such as F-actin or suspensions of rodlike viruses. Together, these systems cover the entire range from loosely to tightly entangled polymers. In particular, we argue that the primitive path analysis renormalizes a loosely to a tightly entangled system and provide a new explanation of the successful Lin-Noolandi packing conjecture for polymer melts.

  14. Fast flexoelectric switching in a cholesteric liquid crystal cell with surface-localized polymer network

    NASA Astrophysics Data System (ADS)

    Kim, Sang Hwa; Shi, Lei; Chien, Liang-Chy

    2009-10-01

    We developed an electro-optical device based on the flexoelectric effect of a polymer-stabilized cholesteric liquid crystal with a uniform lying helix. Using a dual-frequency switchable nematic, a small amount of chiral dopant and a small amount of phase-separated polymer localized at the substrate surfaces, we were able to create a device that operates in both the amplitude (flexoelectric) and phase (dielectric) modes. Using a high-frequency voltage we were able to suppress the phase mode and preserve the amplitude mode.

  15. Attractive interactions among intermediate filaments determine network mechanics in vitro.

    PubMed

    Pawelzyk, Paul; Mücke, Norbert; Herrmann, Harald; Willenbacher, Norbert

    2014-01-01

    Mechanical and structural properties of K8/K18 and vimentin intermediate filament (IF) networks have been investigated using bulk mechanical rheometry and optical microrheology including diffusing wave spectroscopy and multiple particle tracking. A high elastic modulus G0 at low protein concentration c, a weak concentration dependency of G0 (G0 ∼ c(0.5 ± 0.1)) and pronounced strain stiffening are found for these systems even without external crossbridgers. Strong attractive interactions among filaments are required to maintain these characteristic mechanical features, which have also been reported for various other IF networks. Filament assembly, the persistence length of the filaments and the network mesh size remain essentially unaffected when a nonionic surfactant is added, but strain stiffening is completely suppressed, G0 drops by orders of magnitude and exhibits a scaling G0 ∼ c(1.9 ± 0.2) in agreement with microrheological measurements and as expected for entangled networks of semi-flexible polymers. Tailless K8Δ/K18ΔT and various other tailless filament networks do not exhibit strain stiffening, but still show high G0 values. Therefore, two binding sites are proposed to exist in IF networks. A weaker one mediated by hydrophobic amino acid clusters in the central rod prevents stretched filaments between adjacent cross-links from thermal equilibration and thus provides the high G0 values. Another strong one facilitating strain stiffening is located in the tail domain with its high fraction of hydrophobic amino acid sequences. Strain stiffening is less pronounced for vimentin than for K8/K18 due to electrostatic repulsion forces partly compensating the strong attraction at filament contact points.

  16. Synthesis of chiral networks for polymer stabilized cholesteric texture (PSCT) displays

    SciTech Connect

    Rego, J.A.; Cahill, P.A.

    1997-03-01

    New mono- and di-functional polymerizable twist agents for formation of polymer stabilized cholesteric texture liquid crystal displays have been synthesized. Degree of crosslinking has a pronounced effect on electrooptic response of the cell and the stability of oriented states.

  17. Elasticity of F-actin networks

    NASA Astrophysics Data System (ADS)

    Gardel, Margaret Lise

    This thesis presents a study of the elasticity and microstructure of three filamentous actin (F-actin) based materials. Using bulk rheology, microrheology, multiple particle tracking and imaging techniques, we study the microscopic origins of the mechanical properties of F-actin networks. We briefly introduce aspects of F-actin and rheology essential to provide a background for and motivate this thesis in Chapter 1. In Chapter 2, we describe the materials and methods used. An introduction to microrheology is given in Chapter 3. In Chapter 4, we study solutions of entangled F-actin. We elucidate the microscopic origins of bulk elasticity using microrheology techniques. We also show that multiple particle tracking can also probe the dynamics of the F-actin solution microstructure. We explore the effect of rigid, incompliant chemical cross-links between actin filaments in Chapter 5. We explore changes in the network microstructure as the concentration of cross-links is varied. We find that the elastic stiffness of these networks is extremely sensitive to small changes in cross-link density. Despite this large variation, the linear viscoelasticity of all networks can be scaled onto a universal master curve; this scaling reveals that the mechanical dissipation of the networks is due to thermal fluctuations of F-actin. At large stresses, the mechanical stiffness of these networks diverges. The form of this stress stiffening response is consistent with the non-linear force extension of a single semi-flexible polymer. Thus, over a large range of conditions, the linear and nonlinear mechanical response of rigidly cross-linked networks is entropic in origin. Finally, at very low cross-link and filament densities, we observe a transition to a qualitatively different type of elasticity; this is consistent with a transition to an enthalpic network elasticity dominated by bending of F-actin. In Chapter 6, we study the elastic properties of F-actin networks assembled with a

  18. 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.

  19. Effects of polymer stiffness on surface tension and pressure in confinement

    NASA Astrophysics Data System (ADS)

    Milchev, Andrey

    2015-08-01

    We study the effect of chain rigidity on the behavior of semiflexible polymers in the vicinity of flat walls in a slit, and of surfactants at the liquid-liquid interface between immiscible liquids. Using molecular dynamics simulations, it is demonstrated that the impact of bending angle forces is particularly strong within the depletion layer at the phase boundary whereas at distance Re away from the interface, where Re is the mean distance between the ends of a semiflexible chain, the contribution of these non-local triplet interactions to pressure tensor virtually disappears. The present study also demonstrates that growing stiffness of the macromolecules leads to an increase in surface tension and total pressure.

  20. Progress in simulating semi-flexible glass fiber orientation in an injection molded end-gated plaque

    NASA Astrophysics Data System (ADS)

    Cieslinski, Mark J.; Meyer, Kevin J.; Baird, Donald G.

    2014-05-01

    The use of long fiber reinforced thermoplastics has gained increasing interest as a means to enhance a part's mechanical properties created through traditional melt processing techniques. Injection molding creates a complex microstructure to develop caused by flow field within the mold. Accurate predictions of fiber orientation can allow for mold design to be tailored to achieve a desired microstructure and mechanical properties. Simulations utilize the Bead-Rod orientation model adapted for concentrated suspensions to account for semi-flexible fibers by representing a fiber as two adjoined vectors that are free to rotate around the connecting point. This work uses orientation model parameters extracted from orientation data taken along the center plane at the transition between the gate and plaque. The entire mold cavity is simulated under non-isothermal conditions including the entry region to the plaque and the fountain flow behavior at the advancing front. Simulations of the semi-flexible model are compared to the Strain Reduction Factor (SRF) model developed for rigid fibers following the same simulation procedure. Predictions are compared to experimental data measured along and away from the plane of symmetry. Improvement in orientation predictions are obtained from the Bead-Rod model which greatly out performs the rigid fiber model away from the center plane.

  1. Unveiling the molecular mechanism of self-healing in a telechelic, supramolecular polymer network

    PubMed Central

    Yan, Tingzi; Schröter, Klaus; Herbst, Florian; Binder, Wolfgang H.; Thurn-Albrecht, Thomas

    2016-01-01

    Reversible polymeric networks can show self-healing properties due to their ability to reassemble after application of stress and fracture, but typically the relation between equilibrium molecular dynamics and self-healing kinetics has been difficult to disentangle. Here we present a well-characterized, self-assembled bulk network based on supramolecular assemblies, that allows a clear distinction between chain dynamics and network relaxation. Small angle x-ray scattering and rheological measurements provide evidence for a structurally well-defined, dense network of interconnected aggregates giving mechanical strength to the material. Different from a covalent network, the dynamic character of the supramolecular bonds enables macroscopic flow on a longer time scale and the establishment of an equilibrium structure. A combination of linear and nonlinear rheological measurements clearly identifies the terminal relaxation process as being responsible for the process of self-healing. PMID:27581380

  2. Unveiling the molecular mechanism of self-healing in a telechelic, supramolecular polymer network

    NASA Astrophysics Data System (ADS)

    Yan, Tingzi; Schröter, Klaus; Herbst, Florian; Binder, Wolfgang H.; Thurn-Albrecht, Thomas

    2016-09-01

    Reversible polymeric networks can show self-healing properties due to their ability to reassemble after application of stress and fracture, but typically the relation between equilibrium molecular dynamics and self-healing kinetics has been difficult to disentangle. Here we present a well-characterized, self-assembled bulk network based on supramolecular assemblies, that allows a clear distinction between chain dynamics and network relaxation. Small angle x-ray scattering and rheological measurements provide evidence for a structurally well-defined, dense network of interconnected aggregates giving mechanical strength to the material. Different from a covalent network, the dynamic character of the supramolecular bonds enables macroscopic flow on a longer time scale and the establishment of an equilibrium structure. A combination of linear and nonlinear rheological measurements clearly identifies the terminal relaxation process as being responsible for the process of self-healing.

  3. Unveiling the molecular mechanism of self-healing in a telechelic, supramolecular polymer network.

    PubMed

    Yan, Tingzi; Schröter, Klaus; Herbst, Florian; Binder, Wolfgang H; Thurn-Albrecht, Thomas

    2016-01-01

    Reversible polymeric networks can show self-healing properties due to their ability to reassemble after application of stress and fracture, but typically the relation between equilibrium molecular dynamics and self-healing kinetics has been difficult to disentangle. Here we present a well-characterized, self-assembled bulk network based on supramolecular assemblies, that allows a clear distinction between chain dynamics and network relaxation. Small angle x-ray scattering and rheological measurements provide evidence for a structurally well-defined, dense network of interconnected aggregates giving mechanical strength to the material. Different from a covalent network, the dynamic character of the supramolecular bonds enables macroscopic flow on a longer time scale and the establishment of an equilibrium structure. A combination of linear and nonlinear rheological measurements clearly identifies the terminal relaxation process as being responsible for the process of self-healing. PMID:27581380

  4. Gene networks in the synthesis and deposition of protein polymers during grain development of wheat.

    PubMed

    She, Maoyun; Ye, Xingguo; Yan, Yueming; Howit, C; Belgard, M; Ma, Wujun

    2011-03-01

    As the amino acid storing organelle, the protein bodies provide nutrients for embryo development, seed germination and early seedling growth through storage proteolysis in cereal plants, such as wheat and rice. In protein bodies, the monomeric and polymeric prolamins, i.e. gliadins and glutenins, form gluten and play a key role in determining dough functionality and end-product quality of wheat. The formation of intra- and intermolecular bonds, including disulphide and tyrosine bonds, in and between prolamins confers cohesivity, viscosity, elasticity and extensibility to wheat dough during mixing and processing. In this review, we summarize recent progress in wheat gluten research with a focus on the fundamental molecular biological aspects, including transcriptional regulation on genes coding for prolamin components, biosynthesis, deposition and secretion of protein polymers, formation of protein bodies, genetic control of seed storage proteins, the transportation of the protein bodies and key enzymes for determining the formation of disulphide bonds of prolamin polymers.

  5. Experimental and modelling studies of the shape memory properties of amorphous polymer network composites

    NASA Astrophysics Data System (ADS)

    Arrieta, J. S.; Diani, J.; Gilormini, P.

    2014-09-01

    Shape memory polymer composites (SMPCs) have become an important way to leverage improvements in the development of applications featuring shape memory polymers (SMPs). In this study, an amorphous SMP matrix has been filled with different types of reinforcements. An experimental set of results is presented and then compared to three-dimensional (3D) finite-element simulations. Thermomechanical shape memory cycles were performed in uniaxial tension. The fillers effect was studied in stress-free and constrained-strain recoveries. Experimental observations indicate complete shape recovery and put in evidence the increased sensitivity of constrained length stress recoveries to the heating ramp on the tested composites. The simulations reproduced a simplified periodic reinforced composite and used a model for the matrix material that has been previously tested on regular SMPs. The latter combines viscoelasticity at finite strain and time-temperature superposition. The simulations easily allow representation of the recovery properties of a reinforced SMP.

  6. Coupled ion and network dynamics in polymer electrolytes: Monte Carlo study of a lattice model

    NASA Astrophysics Data System (ADS)

    Dürr, O.; Dieterich, W.; Nitzan, A.

    2004-12-01

    Monte Carlo simulations are used to study ion and polymer chain dynamic properties in a simplified lattice model with only one species of mobile ions. The ions interact attractively with specific beads in the host chains, while polymer beads repel each other. Cross linking of chains by the ions reduces chain mobilities which in turn suppresses ionic diffusion. Diffusion constants for ions and chains as a function of temperature follow the Vogel-Tammann-Fulcher (VTF) law with a common VTF temperature at low ion concentration, but both decouple at higher concentrations, in agreement with experimental observations. Our model allows us to introduce pressure as an independent variable through calculations of the equation of state using the quasichemical approximation, and to detect an exponential pressure dependence of the ionic diffusion.

  7. Conjugated polymer network films of poly(p-phenylene vinylene) with hole-transporting carbazole pendants: dual photoluminescence and electrochromic behavior.

    PubMed

    Ponnapati, Ramakrishna; Felipe, Mary Jane; Muthalagu, Vetrichelvan; Puno, Katherine; Wolff, Birte; Advincula, Rigoberto

    2012-03-01

    A series of poly(p-phenylene vinylene) (PPV) copolymers functionalized with hole-transport and electrochemically active carbazole units as pendant moieties is reported. These polymers exhibit photoluminescence properties by virtue of the PPV analogous backbone. They were also designed as precursor polymer bearing the electroactive carbazole group to form conjugated polymer network (CPN) films by electrodeposition. The electrochemical polymerization of the pendant units eventually lead to a dual property electro-optically active thin film - photoluminescence (PL) behavior that can be attenuated with CPN formation, and a reversible doping and dedoping processes at controlled potentials that lead to an electrochromic behavior. This reveals the ability to incorporate complementary optical and electro-optical properties within the same film using the CPN approach. It should be possible to design and synthesize other PPV π-conjugated polymers with efficient pendant hole-transport groups exhibiting tunable PL and electrochromism with cross-linking. PMID:22329863

  8. Conjugated polymer network films of poly(p-phenylene vinylene) with hole-transporting carbazole pendants: dual photoluminescence and electrochromic behavior.

    PubMed

    Ponnapati, Ramakrishna; Felipe, Mary Jane; Muthalagu, Vetrichelvan; Puno, Katherine; Wolff, Birte; Advincula, Rigoberto

    2012-03-01

    A series of poly(p-phenylene vinylene) (PPV) copolymers functionalized with hole-transport and electrochemically active carbazole units as pendant moieties is reported. These polymers exhibit photoluminescence properties by virtue of the PPV analogous backbone. They were also designed as precursor polymer bearing the electroactive carbazole group to form conjugated polymer network (CPN) films by electrodeposition. The electrochemical polymerization of the pendant units eventually lead to a dual property electro-optically active thin film - photoluminescence (PL) behavior that can be attenuated with CPN formation, and a reversible doping and dedoping processes at controlled potentials that lead to an electrochromic behavior. This reveals the ability to incorporate complementary optical and electro-optical properties within the same film using the CPN approach. It should be possible to design and synthesize other PPV π-conjugated polymers with efficient pendant hole-transport groups exhibiting tunable PL and electrochromism with cross-linking.

  9. Localised polymer networks in chiral nematic liquid crystals for high speed photonic switching

    NASA Astrophysics Data System (ADS)

    Tartan, Chloe C.; Salter, Patrick S.; Booth, Martin J.; Morris, Stephen M.; Elston, Steve J.

    2016-05-01

    Self-assembled periodic structures based upon chiral liquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to low-threshold lasers. The flexoelectro-optic effect, which is observed in chiral nematic liquid crystals (LCs) when an electric field is applied perpendicular to the helical axis, has significant potential as it exhibits analogue switching in 10-100 μs. However, the major technological barrier that prohibits the commercial realisation of this electro-optic effect is the requirement of a uniform, in-plane alignment of the helix axis between glass substrates. Here, it is shown that periodic polymer structures engineered in the nematic phase of a chiral nematic LC device using direct laser writing can result in the spontaneous formation of the necessary uniform lying helix (ULH) state. Specifically, two-photon polymerization is used in conjunction with a spatial light modulator so as to correct for aberrations introduced by the bounding glass substrates enabling the polymer structures to be fabricated directly into the device. The ULH state appears to be stable in the absence of an externally applied electric field, and the optimum contrast between the bright and dark states is obtained using polymer structures that have periodicities of the order of the device thickness.

  10. Fast Triggering of Shape Memory Polymers using an Embedded Carbon Nanotube Sponge Network

    NASA Astrophysics Data System (ADS)

    Zhou, Guoxiang; Zhang, Heng; Xu, Shuping; Gui, Xuchun; Wei, Hongqiu; Leng, Jinsong; Koratkar, Nikhil; Zhong, Jing

    2016-04-01

    In this work, a 3-D porous carbon nanotube sponge (CNTS) was embedded within a shape memory polymer (SMPs) matrix. We demonstrate complete infiltration and filling of the SMPs into the CNTS by capillary force without any damage to the CNTS structure. With only ~0.2 wt% carbon nanotube loading, the glass transition temperature is increased by ~20 °C, indicating strong interaction between CNTS and the SMPs matrix. Further, we find that the uniform distribution of the carbon nanotubes in the nanocomposite results in high electrical conductivity, and thus highly effective electricity triggering capability. The carbon nanotube sponge shape memory polymer (CNTS/SMPs) nanocomposite could be triggered within ~10 seconds by the application of ~10 volts. Results from finite element simulations showed good agreement with the experimental results, and indicated that for our system the interface thermal energy loss does not have a significant effect on the heating rate of the polymer matrix.

  11. Fast Triggering of Shape Memory Polymers using an Embedded Carbon Nanotube Sponge Network

    PubMed Central

    Zhou, Guoxiang; Zhang, Heng; Xu, Shuping; Gui, Xuchun; Wei, Hongqiu; Leng, Jinsong; Koratkar, Nikhil; Zhong, Jing

    2016-01-01

    In this work, a 3-D porous carbon nanotube sponge (CNTS) was embedded within a shape memory polymer (SMPs) matrix. We demonstrate complete infiltration and filling of the SMPs into the CNTS by capillary force without any damage to the CNTS structure. With only ~0.2 wt% carbon nanotube loading, the glass transition temperature is increased by ~20 °C, indicating strong interaction between CNTS and the SMPs matrix. Further, we find that the uniform distribution of the carbon nanotubes in the nanocomposite results in high electrical conductivity, and thus highly effective electricity triggering capability. The carbon nanotube sponge shape memory polymer (CNTS/SMPs) nanocomposite could be triggered within ~10 seconds by the application of ~10 volts. Results from finite element simulations showed good agreement with the experimental results, and indicated that for our system the interface thermal energy loss does not have a significant effect on the heating rate of the polymer matrix. PMID:27052451

  12. Conjugated polymer-assisted dispersion of single-wall carbon nanotubes: the power of polymer wrapping.

    PubMed

    Samanta, Suman Kalyan; Fritsch, Martin; Scherf, Ullrich; Gomulya, Widianta; Bisri, Satria Zulkarnaen; Loi, Maria Antonietta

    2014-08-19

    The future application of single-walled carbon nanotubes (SWNTs) in electronic (nano)devices is closely coupled to the availability of pure, semiconducting SWNTs and preferably, their defined positioning on suited substrates. Commercial carbon nanotube raw mixtures contain metallic as well as semiconducting tubes of different diameter and chirality. Although many techniques such as density gradient ultracentrifugation, dielectrophoresis, and dispersion by surfactants or polar biopolymers have been developed, so-called conjugated polymer wrapping is one of the most promising and powerful purification and discrimination strategies. The procedure involves debundling and dispersion of SWNTs by wrapping semiflexible conjugated polymers, such as poly(9,9-dialkylfluorene)s (PFx) or regioregular poly(3-alkylthiophene)s (P3AT), around the SWNTs, and is accompanied by SWNT discrimination by diameter and chirality. Thereby, the π-conjugated backbone of the conjugated polymers interacts with the two-dimensional, graphene-like π-electron surface of the nanotubes and the solubilizing alkyl side chains of optimal length support debundling and dispersion in organic solvents. Careful structural design of the conjugated polymers allows for a selective and preferential dispersion of both small and large diameter SWNTs or SWNTs of specific chirality. As an example, with polyfluorenes as dispersing agents, it was shown that alkyl chain length of eight carbons are favored for the dispersion of SWNTs with diameters of 0.8-1.2 nm and longer alkyls with 12-15 carbons can efficiently interact with nanotubes of increased diameter up to 1.5 nm. Polar side chains at the PF backbone produce dispersions with increased SWNT concentration but, unfortunately, cause reduction in selectivity. The selectivity of the dispersion process can be monitored by a combination of absorption, photoluminescence, and photoluminescence excitation spectroscopy, allowing identification of nanotubes with specific

  13. Thermally cured semi-interpenetrating electrolyte networks (s-IPN) for safe and aging-resistant secondary lithium polymer batteries

    NASA Astrophysics Data System (ADS)

    Nair, Jijeesh R.; Destro, Matteo; Bella, Federico; Appetecchi, Giovanni B.; Gerbaldi, Claudio

    2016-02-01

    Truly solid polymer electrolyte membranes are designed by thermally induced free radical polymerisation. The overall membrane architecture is built on a semi-interpenetrating polymer network (s-IPN) structure, where a di-methacrylate oligomer is cross-linked (in situ) in the presence of a long thermoplastic linear PEO chain and a supporting lithium salt to obtain a freestanding, flexible and non-tacky film. In the envisaged systems, the di-methacrylate functions as a soft cross-linker, thus avoiding physico-mechanical deformation of the s-IPNs at elevated temperature, without hampering the ionic conductivity. s-IPNs exhibit remarkable stability towards lithium metal and no traces of impurity are detected while testing their oxidation stability (4.7 V vs. Li/Li+) towards anodic potential. The newly elaborated system is also successfully tested at moderately high temperature in Li metal cells in which LiFePO4/C is used as the cathode active material, showing excellent indications of safe and highly durable electrolyte separator (i.e., 2000 cycles at reasonably high 1C rate).

  14. Semi-interpenetrating polymer networks composed of silk fibroin and poly(ethylene glycol) for wound dressing.

    PubMed

    Kweon, Haeyong; Yeo, Joo-hong; Lee, Kwang-gill; Lee, Hyun Chul; Na, Hee Sam; Won, Young Ho; Cho, Chong Su

    2008-09-01

    Semi-interpenetrating polymer networks (SIPNs) composed of silk fibroin (SF) and poly(ethylene glycol) (PEG) were prepared by photopolymerization of a PEG macromer in the presence of SF to improve the mechanical properties of SF sponge as wound dressing. The morphological structure of the SF/PEG SIPNs was observed to be composed of an interconnected microporous surface and a cross-sectional area. SF/PEG SIPNs showed non-cytotoxicity evaluated by a cell proliferation method using L929 fibroblasts. Wound contraction treated with SF/PEG SIPNs sponges was faster than that of Vaseline gauze as a control. Histological observation confirmed that the deposition of collagen in the dermis was organized by covering the wound area with SF/PEG SIPNs. The above results indicated that SF/PEG SIPNs could be used as wound dressing.

  15. Capillary zone electrophoresis in polymer networks of polymerase chain reaction-amplified oligonucleotides: the case of congenital adrenal hyperplasia.

    PubMed

    Gelfi, C; Orsi, A; Righetti, P G; Zanussi, M; Carrera, P; Ferrari, M

    1994-07-01

    The use of capillary zone electrophoresis (CZE) in polymer networks for the analysis of an 8 bp (base pair) deletion in congenital adrenal hyperplasia was investigated. Separations were performed in Tris-borate-EDTA buffer (pH 8.3) containing 6% liquid linear polyacrylamide as a sieving dynamic matrix and 10 microM ethidium bromide for improving DNA fragment separation. Easy analysis and detection of the 127 and 135 bp amplified fragments was accomplished. The capillary column can be used for > 50 analyses before degradation and loss of resolution. The results are comparable to those obtained by gel-slab zone electrophoresis in a 12%T, 4%C polyacrylamide matrix. The sensitivity, by simple UV absorption at 254 nm, is similar to that obtained in gel slabs by dye intercalation staining. PMID:7952069

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    Xu, Wen-Sheng; Freed, Karl F.

    2015-07-01

    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.

  18. 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.

  19. Synthesis, physical characterization, and biological performance of sequential homointerpenetrating polymer network sponges based on poly(2-hydroxyethyl methacrylate).

    PubMed

    Lou, X; Vijayasekaran, S; Chirila, T V; Maley, M A; Hicks, C R; Constable, I J

    1999-12-01

    A limitation in the use of hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) sponges as implantable devices is their inherently poor mechanical strength. This precludes proper surgical manipulation, especially in the eye where the size of the implant is usually small. In this study a new method was developed to produce mechanically stronger PHEMA sponges. Sequential homointerpenetrating polymer network (homo-IPN) sponges were made by using HEMA as the precursor for generating both the first network and the successive interpenetrated networks. Following the formation of network I, the sponge was squeezed to remove the interstitial water, soaked in the second monomer (also HEMA), and squeezed again to remove the excess monomer from the pores before being subjected to the second polymerization leading to the formation of network II. Two two-component IPN sponges (K2 and K4) with increasing HEMA content in the network II and a three-component IPN sponge (K3) were produced, and their properties were compared to those of a homopolymer PHEMA sponge (control). Apart from elongation, the tensile properties were all significantly enhanced in the IPN sponges; the water content was the same as in the control sponge, except for sponge K4, which was lower. Light microscopy revealed similar pore morphologies of the control and IPN sponges K2 and K3, and the majority of the pores were around 25 microm. Sponge K4 displayed smaller pores of around 10 microm. Cellular invasion into the sponges was examined in vitro (incubation with 3T3 fibroblasts) and in vivo (implantation in rabbit corneas). Although the in vitro assay detected a change in the cell behavior in the early stage of invasion, which was probably due to the formation of IPNs, such changes were not reflected in the longer term in vivo experiment. There was a proper integration of sponges K2 and K3 with the corneal stroma, but much less cellular invasion and no neovascularization in sponge K4. We concluded that IPN

  20. A semi-flexible model prediction for the polymerization force exerted by a living F-actin filament on a fixed wall.

    PubMed

    Pierleoni, Carlo; Ciccotti, Giovanni; Ryckaert, Jean-Paul

    2015-10-14

    We consider a single living semi-flexible filament with persistence length ℓp in chemical equilibrium with a solution of free monomers at fixed monomer chemical potential μ1 and fixed temperature T. While one end of the filament is chemically active with single monomer (de)polymerization steps, the other end is grafted normally to a rigid wall to mimic a rigid network from which the filament under consideration emerges. A second rigid wall, parallel to the grafting wall, is fixed at distance L < < ℓp from the filament seed. In supercritical conditions where monomer density ρ1 is higher than the critical density ρ1c, the filament tends to polymerize and impinges onto the second surface which, in suitable conditions (non-escaping filament regime), stops the filament growth. We first establish the grand-potential Ω(μ1, T, L) of this system treated as an ideal reactive mixture, and derive some general properties, in particular the filament size distribution and the force exerted by the living filament on the obstacle wall. We apply this formalism to the semi-flexible, living, discrete Wormlike chain model with step size d and persistence length ℓp, hitting a hard wall. Explicit properties require the computation of the mean force f̄i(L) exerted by the wall at L and associated potential f̄i(L)=-dWi(L)/dL on a filament of fixed size i. By original Monte-Carlo calculations for few filament lengths in a wide range of compression, we justify the use of the weak bending universal expressions of Gholami et al. [Phys. Rev. E 74, 041803 (2006)] over the whole non-escaping filament regime. For a filament of size i with contour length Lc = (i - 1) d, this universal form is rapidly growing from zero (non-compression state) to the buckling value fb(Lc,ℓp)=π(2)kBTℓp4Lc (2) over a compression range much narrower than the size d of a monomer. Employing this universal form for living filaments, we find that the average force exerted by a living filament on a wall at

  1. Conformational Analysis of Stiff Chiral Polymers with End-Constraints

    PubMed Central

    Kim, Jin Seob; Chirikjian, Gregory S.

    2010-01-01

    We present a Lie-group-theoretic method for the kinematic and dynamic analysis of chiral semi-flexible polymers with end constraints. The first is to determine the minimum energy conformations of semi-flexible polymers with end constraints, and the second is to perform normal mode analysis based on the determined minimum energy conformations. In this paper, we use concepts from the theory of Lie groups and principles of variational calculus to model such polymers as inextensible or extensible chiral elastic rods with coupling between twisting and bending stiffnesses, and/or between twisting and extension stiffnesses. This method is general enough to include any stiffness and chirality parameters in the context of elastic filament models with the quadratic elastic potential energy function. As an application of this formulation, the analysis of DNA conformations is discussed. We demonstrate our method with examples of DNA conformations in which topological properties such as writhe, twist, and linking number are calculated from the results of the proposed method. Given these minimum energy conformations, we describe how to perform the normal mode analysis. The results presented here build both on recent experimental work in which DNA mechanical properties have been measured, and theoretical work in which the mechanics of non-chiral elastic rods has been studied. PMID:20198114

  2. Biologically Derived Soft Conducting Hydrogels Using Heparin-Doped Polymer Networks

    PubMed Central

    2015-01-01

    The emergence of flexible and stretchable electronic components expands the range of applications of electronic devices. Flexible devices are ideally suited for electronic biointerfaces because of mechanically permissive structures that conform to curvilinear structures found in native tissue. Most electronic materials used in these applications exhibit elastic moduli on the order of 0.1–1 MPa. However, many electronically excitable tissues exhibit elasticities in the range of 1–10 kPa, several orders of magnitude smaller than existing components used in flexible devices. This work describes the use of biologically derived heparins as scaffold materials for fabricating networks with hybrid electronic/ionic conductivity and ultracompliant mechanical properties. Photo-cross-linkable heparin–methacrylate hydrogels serve as templates to control the microstructure and doping of in situ polymerized polyaniline structures. Macroscopic heparin-doped polyaniline hydrogel dual networks exhibit impedances as low as Z = 4.17 Ω at 1 kHz and storage moduli of G′ = 900 ± 100 Pa. The conductivity of heparin/polyaniline networks depends on the oxidation state and microstructure of secondary polyaniline networks. Furthermore, heparin/polyaniline networks support the attachment, proliferation, and differentiation of murine myoblasts without any surface treatments. Taken together, these results suggest that heparin/polyaniline hydrogel networks exhibit suitable physical properties as an electronically active biointerface material that can match the mechanical properties of soft tissues composed of excitable cells. PMID:24738911

  3. 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

  4. Synthesis and characterization of semi-interpenetrating polymer networks based on polyurethane and N-isopropylacrylamide for wound dressing.

    PubMed

    Reddy, Thatiparti Thimma; Kano, Arihiro; Maruyama, Atsushi; Hadano, Michiko; Takahara, Atsushi

    2009-01-01

    Thermosensitive semi-interpenetrating polymer networks (semi-IPNs) composed of crosslinked poly(N-isopropylacrylamide) (PNiPAAm) and linear segmented polyurethane urea (SPUU) were synthesized via thermal initiated free radical polymerization. Synthesized semi-IPNs of various compositions were characterized by Fourier transform infrared spectroscopy, water equilibrium swelling at different temperatures, drug lading, drug release, cell adhesion, and detachment. The semi-IPN films of all the compositions were transparent in dry state and negative thermosensitivity in their swelling ratio, that is, lower swelling levels with increasing temperature. The drug release study revealed that the rate of drug release is fast in case of pure SPUU compared to PNiPAAm and semi-IPN film. Drug release depended mainly on solubility of the drugs and physical networks between SPUU and PNiPAAm. Finally NIH3T3 cells were seeded on the semi-IPN films and found that cells were securely attached and proliferated to confluence. Upon cooling, cells were detached from the semi-IPN films. Therefore, the semi-IPN films may be good candidate materials for wound dressing applications. PMID:18780359

  5. Surface-Directed Assembly of Sequence-Defined Synthetic Polymers into Networks of Hexagonally Patterned Nanoribbons with Controlled Functionalities.

    PubMed

    Chen, Chun-Long; Zuckermann, Ronald N; DeYoreo, James J

    2016-05-24

    The exquisite self-assembly of proteins and peptides in nature into highly ordered functional materials has inspired innovative approaches to the design and synthesis of biomimetic materials. While sequence-defined polymers hold great promise to mimic proteins and peptides for functions, controlled assembly of them on surfaces still remains underdeveloped. Here, we report the assembly of 12-mer peptoids containing alternating acidic and aromatic monomers into networks of hexagonally patterned nanoribbons on mica surfaces. Ca(2+)-carboxylate coordination creates peptoid-peptoid and peptoid-mica interactions that control self-assembly. In situ atomic force microscopy (AFM) shows that peptoids first assemble into discrete nanoparticles; these particles then transform into hexagonally patterned nanoribbons on mica surfaces. AFM-based dynamic force spectroscopy studies show that peptoid-mica interactions are much stronger than peptoid-peptoid interactions, illuminating the driving forces for mica-directed peptoid assembly. We further demonstrate the display of functional domains at the N-terminus of assembling peptoids to produce extended networks with similar hierarchical structures. This research demonstrates that surface-directed peptoid assembly can be used as a robust platform to develop biomimetic coating materials for applications. PMID:27136277

  6. Spatial and Temporal Control of Thiol-Michael Addition via Photocaged Superbase in Photopatterning and Two-Stage Polymer Networks Formation

    PubMed Central

    2015-01-01

    Photochemical processes enable spatial and temporal control of reactions, which can be implemented as an accurate external control approach in both polymer synthesis and materials applications. “Click” reactions have also been employed as efficient tools in the same field. Herein, we combined photochemical processes and thiol-Michael “click” reactions to achieve a “photo-click” reaction that can be used in surface patterning and controlled polymer network formation, owing to the ease of spatial and temporal control through use of photolabile amines as appropriate catalysts. PMID:25264379

  7. A model of cell wall expansion based on thermodynamics of polymer networks

    NASA Technical Reports Server (NTRS)

    Veytsman, B. A.; Cosgrove, D. J.

    1998-01-01

    A theory of cell wall extension is proposed. It is shown that macroscopic properties of cell walls can be explained through the microscopic properties of interpenetrating networks of cellulose and hemicellulose. The qualitative conclusions of the theory agree with the existing experimental data. The dependence of the cell wall yield threshold on the secretion of the wall components is discussed.

  8. Effect of hydrodynamic interaction on partially stretched polymers.

    PubMed

    Sain, Anirban

    2008-06-01

    We compute the effect of hydrodynamic interaction and stretching on the fluctuation properties of a polymer, with its end points held fixed. Computing the preaveraged hydrodynamic tensor exactly for this geometry, we study both flexible and semiflexible polymer chains, such as Zimm, freely jointed chain, and wormlike chain (WLC) models. We compare the spectra of relaxation-time scales for the effective normal modes of these models. The spectra differ across models with respect to the degree of stretch, but their power-law scaling with low mode numbers turns out to be the same. The characteristics of the transverse modes of WLC agree very well with the experimental data on DNA. The crossover scaling function for (1/r), the inverse of the distance along the polymer contour, yields a modified formula for the size of a "Pincus blob," appropriate for the fixed-end boundary condition.

  9. A novel structure and photochromism of heteropolyoxometalates dispersed in polymer networks

    SciTech Connect

    Bao Xinjian; Feng Wei; Chen Jie; Liu Xiaoyang

    2012-07-15

    Nanocomposites based on Keggin structure tungstophosphate acid (PWA) with 'branch-like' nanometer well dispersed in poly(acrylamide-co-vinylamine) (PAM-co-PVAm) were fabricated. The microstructure and photochromic properties were studied via Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM), ultraviolet-visible spectra (UV-vis) and electron resonance spectra (ESR). FT-IR results showed that the Keggin geometry of polyoxometalates was still preserved inside the composites and hydrogen bonding and salt formation were built between PWA and polymer matrix. SEM and TEM images showed that PWA nanoparticles were finely dispersed in polymer matrix with 'branch-like' shape. Under UV irradiation, the film was reduced photochemically to yield a glaucous species. After UV light turned off, the color of film became green. Two photo-reduction processes (one was between acylamino and heteropoly acid, another was between amidocyanogen and heteropoly acid) occurred at the same time in PWA/PAM-co-PVAm system, which resulted in the formation of heteropolygreen. - Graphical abstract: Two absorption bands appeared after UV irradiated. In bleaching process, the peaks at 620-820 nm disappeared and those at 420 nm still presented. Due to synergies happened between heteropolyacid and PAM-co-PVAm, heteropolygreen was formed. Highlights: Black-Right-Pointing-Pointer 'Branch-like' composites were fabricated by dispersed PWA into PAM-co-PVAm system. Black-Right-Pointing-Pointer Two photo-reduction processes occurred simultaneously in PWA/PAM-co-PVAm system. Black-Right-Pointing-Pointer Heteropolygreen was formed by synergies of hydrogen bonding and salt formation.

  10. Hard-sphere-chain Equations of State for Lyotropic Polymer LiquidCrystals

    SciTech Connect

    Hino, T.; Prausnitz, John M.

    1998-06-01

    Using Parsons-type scaling, the Onsager theory for theisotropic-nematic (I-N) transition of rigid-rod lyotropic polymer liquidcrystals is combined with the equation of state for hard-sphere-chainfluids of Chapman et al. and that of Hu et al. The equation of Hu et al.gives the I-N transition pressure and density in good agreement withcomputer simulation by Wilson and Allen for a semi-flexible hard-spherechain consisting of seven segments. For real semi-flexible polymers, wefollow the Khokhlov-Semenov theory of persistent chains that introduceschain flexibility into the Onsager theory. Using a consistent procedureto regress the equation-of-state parameters, the equations of Chapman etal. and Hu et al. are also compared with the theory of DuPre and Yangthat uses the equation of Lee for hard spherocylinders. These models arecompared with experiment for two binary polymer solutions containingpoly(hexyl isocyanate) and another solution containing polysaccharideschizophyllan. The concentration of polymer at the I-N transition ispredicted as a function of the molecular weight of polymer. All modelsperform similarly and show semi-quantitative agreement withexperiment.

  11. Continuous Paranematic Ordering of Rigid and Semiflexible Amyloid-Fe3O4 Hybrid Fibrils in an External Magnetic Field.

    PubMed

    Zhao, Jianguo; Bolisetty, Sreenath; Isabettini, Stéphane; Kohlbrecher, Joachim; Adamcik, Jozef; Fischer, Peter; Mezzenga, Raffaele

    2016-08-01

    External magnetic field is a powerful approach to induce orientational order in originally disordered suspensions of magneto-responsive anisotropic particles. By small angle neutron scattering and optical birefringence measurement technology, we investigated the effect of magnetic field on the spatial ordering of hybrid amyloid fibrils with different aspect ratios (length-to-diameter) and flexibilities decorated by spherical Fe3O4 nanoparticles. A continuous paranematic ordering from an initially isotropic suspension was observed upon increasing magnetic field strength, with spatial orientation increasing with colloidal volume fraction. At constant dimensionless concentration, stiff hybrid fibrils with varying aspect ratios and volume fractions, fall on the same master curve, with equivalent degrees of ordering at identical magnetic fields. However, the semiflexible hybrid fibrils with contour length close to persistence length exhibit a lower degree of alignment. This is consistent with Khokhlov-Semenov theoretical predictions. These findings sharpen the experimental toolbox to design colloidal systems with controllable degree of orientational ordering. PMID:27304090

  12. High performance of transferring lithium ion for polyacrylonitrile-interpenetrating crosslinked polyoxyethylene network as gel polymer electrolyte.

    PubMed

    Kuo, Ping-Lin; Wu, Ching-An; Lu, Chung-Yu; Tsao, Chin-Hao; Hsu, Chun-Han; Hou, Sheng-Shu

    2014-03-12

    A polyacrylonitrile (PAN)-interpenetrating cross-linked polyoxyethylene (PEO) network (named XANE) was synthesized acting as separator and as gel polymer electrolytes simultaneously. SEM images show that the surface of the XANE membrane is nonporous, comparing to the surface of the commercial separator to be porous. This property results in excellent electrolyte uptake amount (425 wt %), and electrolyte retention for XANE membrane, significantly higher than that of commercial separator (200 wt %). The DSC result indicates that the PEO crystallinity is deteriorated by the cross-linked process and was further degraded by the interpenetration of the PAN. The XANE membrane shows significantly higher ionic conductivity (1.06-8.21 mS cm(-1)) than that of the commercial Celgard M824 separator (0.45-0.90 mS cm(-1)) ascribed to the high electrolyte retention ability of XANE (from TGA), the deteriorated PEO crystallinity (from DSC) and the good compatibility between XANE and electrode (from measuring the interfacial-resistance). For battery application, under all charge/discharge rates (from 0.1 to 3 C), the specific half-cell capacities of the cell composed of the XANE membrane are all higher than those of the aforementioned commercial separator. More specifically, the cell composed of the XANE membrane has excellent cycling stability, that is, the half-cell composed of the XANE membrane still exhibited more than 97% columbic efficiency after 100 cycles at 1 C. The above-mentioned advantageous properties and performances of the XANE membrane allow it to act as both an ionic conductor as well as a separator, so as to work as separator-free gel polymer electrolytes.

  13. High performance of transferring lithium ion for polyacrylonitrile-interpenetrating crosslinked polyoxyethylene network as gel polymer electrolyte.

    PubMed

    Kuo, Ping-Lin; Wu, Ching-An; Lu, Chung-Yu; Tsao, Chin-Hao; Hsu, Chun-Han; Hou, Sheng-Shu

    2014-03-12

    A polyacrylonitrile (PAN)-interpenetrating cross-linked polyoxyethylene (PEO) network (named XANE) was synthesized acting as separator and as gel polymer electrolytes simultaneously. SEM images show that the surface of the XANE membrane is nonporous, comparing to the surface of the commercial separator to be porous. This property results in excellent electrolyte uptake amount (425 wt %), and electrolyte retention for XANE membrane, significantly higher than that of commercial separator (200 wt %). The DSC result indicates that the PEO crystallinity is deteriorated by the cross-linked process and was further degraded by the interpenetration of the PAN. The XANE membrane shows significantly higher ionic conductivity (1.06-8.21 mS cm(-1)) than that of the commercial Celgard M824 separator (0.45-0.90 mS cm(-1)) ascribed to the high electrolyte retention ability of XANE (from TGA), the deteriorated PEO crystallinity (from DSC) and the good compatibility between XANE and electrode (from measuring the interfacial-resistance). For battery application, under all charge/discharge rates (from 0.1 to 3 C), the specific half-cell capacities of the cell composed of the XANE membrane are all higher than those of the aforementioned commercial separator. More specifically, the cell composed of the XANE membrane has excellent cycling stability, that is, the half-cell composed of the XANE membrane still exhibited more than 97% columbic efficiency after 100 cycles at 1 C. The above-mentioned advantageous properties and performances of the XANE membrane allow it to act as both an ionic conductor as well as a separator, so as to work as separator-free gel polymer electrolytes. PMID:24521309

  14. Effective conductivity of particulate polymer composite electrolytes using random resistor network method

    SciTech Connect

    Kalnaus, Sergiy; Sabau, Adrian S; Newman, Sarah M; Tenhaeff, Wyatt E; Daniel, Claus; Dudney, Nancy J

    2011-01-01

    The effective DC conductivity of particulate composite electrolytes was obtained by solving electrostatics equations using random resistors network method in three dimensions. The composite structure was considered to consist of three phases: matrix, particulate filler, and conductive shell that surrounded each particle; each phase possessing a different conductivity. Different particle size distributions were generated using Monte Carlo simulations. Unlike effective medium formulations, it was shown that the random resistors network method was able to predict percolation thresholds for the effective composite conductivity. It was found that the mean particle radius has a higher influence on the effective composite conductivity compared to the effect of type of the particle size distributions that were considered. The effect of the shell thickness on the composite conductivity has been investigated. It was found that the conductivity enhancement due to the presence of the conductive shell phase becomes less evident as the shell thickness increases.

  15. Assembling supramolecular networks by halogen bonding in coordination polymers driven by 5-bromonicotinic acid

    SciTech Connect

    Gu, Jin-Zhong; Wu, Jiang; Kirillov, Alexander M.; Lv, Dong-Yu; Tang, Yu; Wu, Jin-Cai

    2014-05-01

    A series of six coordination compounds ([Zn(5-Brnic){sub 2}]·1.5H{sub 2}O){sub n} (1), [Cd(5-Brnic){sub 2}]{sub n} (2), [Co(5-Brnic){sub 2}(H{sub 2}O){sub 2}]{sub n} (3), [Zn(5-Brnic){sub 2}(H{sub 2}biim)]{sub n} (4), ([Cd(5-Brnic){sub 2}(phen)]·H{sub 2}O){sub n} (5), and [Pb(5-Brnic){sub 2}(phen)] (6) have been generated by the hydrothermal method from the metal(II) nitrates, 5-bromonicotinic acid (5-BrnicH), and an optional ancillary 1,10-phenanthroline (phen) or 2,2′-biimidazole (H{sub 2}biim) ligand. All the products 1–6 have been characterized by IR spectroscopy, elemental, thermal, powder and single-crystal X-ray diffraction analyses. Their 5-bromonicotinate-driven structures vary from the 3D metal-organic framework with the seh-3,5-P21/c topology (in 2) and the 2D interdigitated layers with the sql topology (in 1 and 3), to the 1D chains (in 4 and 5) and the 0D discrete monomers (in 6). The 5-bromonicotinate moiety acts as a versatile building block and its tethered bromine atom plays a key role in reinforcing and extending the structures into diverse 3D supramolecular networks via the various halogen bonding Br⋯O, Br⋯Br, and Br⋯π interactions, as well as the N–H⋯O and C–H⋯O hydrogen bonds. The obtained results demonstrate a useful guideline toward engineering the supramolecular architectures in the coordination network assembly under the influence of various halogen bonding interactions. The luminescent (for 1, 2, 4, 5, and 6) and magnetic (for 3) properties have also been studied and discussed in detail. - Graphical abstract: Six coordination compounds driven by 5-bromonicotinic acid have been generated and structurally characterized, revealing diverse metal-organic networks that are further reinforced and extended via various halogen bonding interactions. - Highlights: • 5-Bromonicotinic acid is a versatile ligand for Zn, Cd, Co and Pb derivatives. • Careful selection of co-ligands and metals resulted in different network

  16. Rupture Orientation and Strain-induced Crystallization of Polymer Chain and Network in Vulcanized Polyisoprene During Uniaxial Deformation by in-situ Electron Spin Resonance(ESR) and Synchrotron X-ray Analysis

    SciTech Connect

    S Toki; R Takagi; M Ito; B Hsiao

    2011-12-31

    Different network structures of vulcanized polyisoprene rubbers were studied by in-situ ESR and synchrotron X-ray during deformation to analyze the rupture, orientation, and strain-induced crystallization of polymer chains and network points. Rupture of network points occur, depending on network structure, and create an un-reversible change in vulcanized rubber. The flexibility of network points affects the possibility of rupture, polymer orientation and strain-induced crystallization. Peroxide vulcanized network is rigid and un-rupturable. Poly-sulfide rich vulcanized network is more flexible and less rupturable than mono-sulfide rich vulcanized network. Chain flexibility and rupturability of network points affect the strain-induced crystallization and stress-strain relation.

  17. Static and dynamic properties of large polymer melts in equilibrium

    NASA Astrophysics Data System (ADS)

    Hsu, Hsiao-Ping; Kremer, Kurt

    2016-04-01

    We present a detailed study of the static and dynamic behaviors of long semiflexible polymer chains in a melt. Starting from previously obtained fully equilibrated high molecular weight polymer melts [G. Zhang et al., ACS Macro Lett. 3, 198 (2014)], we investigate their static and dynamic scaling behaviors as predicted by theory. We find that for semiflexible chains in a melt, results of the mean square internal distance, the probability distributions of the end-to-end distance, and the chain structure factor are well described by theoretical predictions for ideal chains. We examine the motion of monomers and chains by molecular dynamics simulations using the ESPResSo++ package. The scaling predictions of the mean squared displacement of inner monomers, center of mass, and relations between them based on the Rouse and the reptation theory are verified, and related characteristic relaxation times are determined. Finally, we give evidence that the entanglement length Ne,PPA as determined by a primitive path analysis (PPA) predicts a plateau modulus, GN 0 = /4 5 ( ρ k B T / N e ) , consistent with stresses obtained from the Green-Kubo relation. These comprehensively characterized equilibrium structures, which offer a good compromise between flexibility, small Ne, computational efficiency, and small deviations from ideality, provide ideal starting states for future non-equilibrium studies.

  18. Freeze drying for morphological control of inter-penetrating polymer networks

    NASA Technical Reports Server (NTRS)

    Hansen, Marion G.; Pater, Ruth H.

    1990-01-01

    The intrinsic brittleness of BMI resins can be reduced through the creation of an interpenetrating network (IPN) of BMI with a reactive-encapped thermoplastic, such as the presently considered polyimidesulfone, PISO2. The PISO2 and BMI were dissolved in a common solvent, which was then removed from the constituents by freeze drying; in an alternative method, an IPN was formed through dissolution of the constituent in a common solvent with either high or low melting point, followed by evaporative removal of the solvent. The effectiveness of the freeze-drying approach for morphological control is evaluated.

  19. Building artificial networks of neuronal cells with light-assisted polymer surface functionalization

    NASA Astrophysics Data System (ADS)

    Nicolau, Dan V.; Taniguchi, Hideo; Taguchi, Takahisa; Yoshikawa, Susumu

    1997-11-01

    The surface of photosensible diazo-naphto-quinone/novolak film was chemically manipulated through UV exposure and subsequent functionalization processes to obtain surfaces with different chemistries (DNQ, carboxylic, and peptidic groups). The neuronal cell attachment is controlled by three pairs of antagonistic surface variables: charged/uncharged species, amino/carboxylic groups and hydrophilic/hydrophobic balance, in which the former promote the adhesion. The study proves that microlithographic techniques in connection with surface functionalization with specific neuro-peptides can be used to build artificial networks with neuronal cells.

  20. Polymer stabilization of the smectic C-alpha* liquid crystal phase—Over tenfold thermal stabilization by confining networks of photo-polymerized reactive mesogens

    NASA Astrophysics Data System (ADS)

    Labeeb, A.; Gleeson, H. F.; Hegmann, T.

    2015-12-01

    The smectic C*-alpha (SmCα*) phase is one of the sub-phases of ferroelectric liquid crystals that has drawn much interest due to its electro-optical properties and ultrafast switching. Generally observed above the ferroelectric SmC* phase in temperature, the SmCα* commonly shows only very narrow phase temperature range of a few degree Celsius. To broaden the SmCα* phase, polymer stabilization was investigated for thermal phase stabilization. Two different reactive monomers were tested in three mixtures, and all three broadened the temperature range of the SmCα* phase from 3 °C to 39 °C. The current reversal method was used to determine the phase existence versus temperature. Moreover, the texture and network structure was studied by polarized optical microscopy and scanning electron microscopy, with the latter revealing the confinement of the smectic layer structure within the porous polymer network.

  1. Broken Detailed Balance of Filament Dynamics in Active Networks

    NASA Astrophysics Data System (ADS)

    Gladrow, J.; Fakhri, N.; MacKintosh, F. C.; Schmidt, C. F.; Broedersz, C. P.

    2016-06-01

    Myosin motor proteins drive vigorous steady-state fluctuations in the actin cytoskeleton of cells. Endogenous embedded semiflexible filaments such as microtubules, or added filaments such as single-walled carbon nanotubes are used as novel tools to noninvasively track equilibrium and nonequilibrium fluctuations in such biopolymer networks. Here, we analytically calculate shape fluctuations of semiflexible probe filaments in a viscoelastic environment, driven out of equilibrium by motor activity. Transverse bending fluctuations of the probe filaments can be decomposed into dynamic normal modes. We find that these modes no longer evolve independently under nonequilibrium driving. This effective mode coupling results in nonzero circulatory currents in a conformational phase space, reflecting a violation of detailed balance. We present predictions for the characteristic frequencies associated with these currents and investigate how the temporal signatures of motor activity determine mode correlations, which we find to be consistent with recent experiments on microtubules embedded in cytoskeletal networks.

  2. Hydrogels of collagen/chondroitin sulfate/hyaluronan interpenetrating polymer network for cartilage tissue engineering.

    PubMed

    Guo, Yan; Yuan, Tun; Xiao, Zhanwen; Tang, Pingping; Xiao, Yumei; Fan, Yujiang; Zhang, Xingdong

    2012-09-01

    The network structure of a three-dimensional hydrogel scaffold dominates its performance such as mechanical strength, mass transport capacity, degradation rate and subsequent cellular behavior. The hydrogels scaffolds with interpenetrating polymeric network (IPN) structure have an advantage over the individual component gels and could simulate partly the structure of native extracellular matrix of cartilage tissue. In this study, to develop perfect cartilage tissue engineering scaffolds, IPN hydrogels of collagen/chondroitin sulfate/hyaluronan were prepared via two simultaneous processes of collagen self-assembly and cross linking polymerization of chondroitin sulfate-methacrylate (CSMA) and hyaluronic acid-methacrylate. The degradation rate, swelling performance and compressive modulus of IPN hydrogels could be adjusted by varying the degree of methacrylation of CSMA. The results of proliferation and fluorescence staining of rabbit articular chondrocytes in vitro culture demonstrated that the IPN hydrogels possessed good cytocompatibility. Furthermore, the IPN hydrogels could upregulate cartilage-specific gene expression and promote the chondrocytes secreting glycosaminoglycan and collagen II. These results suggested that IPN hydrogels might serve as promising hydrogel scaffolds for cartilage tissue engineering. PMID:22639153

  3. Multifunctional semi-interpenetrating polymer network-nanoencapsulated cathode materials for high-performance lithium-ion batteries

    PubMed Central

    Kim, Ju-Myung; Park, Jang-Hoon; Lee, Chang Kee; Lee, Sang-Young

    2014-01-01

    As a promising power source to boost up advent of next-generation ubiquitous era, high-energy density lithium-ion batteries with reliable electrochemical properties are urgently requested. Development of the advanced lithium ion-batteries, however, is staggering with thorny problems of performance deterioration and safety failures. This formidable challenge is highly concerned with electrochemical/thermal instability at electrode material-liquid electrolyte interface, in addition to structural/chemical deficiency of major cell components. Herein, as a new concept of surface engineering to address the abovementioned interfacial issue, multifunctional conformal nanoencapsulating layer based on semi-interpenetrating polymer network (semi-IPN) is presented. This unusual semi-IPN nanoencapsulating layer is composed of thermally-cured polyimide (PI) and polyvinyl pyrrolidone (PVP) bearing Lewis basic site. Owing to the combined effects of morphological uniqueness and chemical functionality (scavenging hydrofluoric acid that poses as a critical threat to trigger unwanted side reactions), the PI/PVP semi-IPN nanoencapsulated-cathode materials enable significant improvement in electrochemical performance and thermal stability of lithium-ion batteries. PMID:24710575

  4. A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell

    NASA Astrophysics Data System (ADS)

    Lin, Yi-Hsin; Chen, Ming-Syuan; Lin, Wei-Chih; Tsou, Yu-Shih

    2012-07-01

    A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell (T-PNLC) is demonstrated. T-PNLC consists of three layers. Liquid crystal (LC) directors in the two layers near glass substrates are orthogonal to each other and those two layers modulate two eigen-polarizations of an incident light. As a result, two eigen-polarizations of an incident light experience the same phase shift. In the middle layer, LC directors are perpendicular to the glass substrate and contribute no phase shift. The phase shift of T-PNLC is electrically tunable and polarization-independent. T-PNLC does not require any bias voltage for operation. The phase shift is 0.28 π rad for the voltage of 30 Vrms. By measuring and analyzing the optical phase shift of T-PNLC at the oblique incidence of transverse magnetic wave, the pretilt angle of LC directors and the effective thickness of three layers are obtained and discussed. The potential applications are spatial light modulators, laser beam steering, and micro-lens arrays.

  5. Multifunctional semi-interpenetrating polymer network-nanoencapsulated cathode materials for high-performance lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Kim, Ju-Myung; Park, Jang-Hoon; Lee, Chang Kee; Lee, Sang-Young

    2014-04-01

    As a promising power source to boost up advent of next-generation ubiquitous era, high-energy density lithium-ion batteries with reliable electrochemical properties are urgently requested. Development of the advanced lithium ion-batteries, however, is staggering with thorny problems of performance deterioration and safety failures. This formidable challenge is highly concerned with electrochemical/thermal instability at electrode material-liquid electrolyte interface, in addition to structural/chemical deficiency of major cell components. Herein, as a new concept of surface engineering to address the abovementioned interfacial issue, multifunctional conformal nanoencapsulating layer based on semi-interpenetrating polymer network (semi-IPN) is presented. This unusual semi-IPN nanoencapsulating layer is composed of thermally-cured polyimide (PI) and polyvinyl pyrrolidone (PVP) bearing Lewis basic site. Owing to the combined effects of morphological uniqueness and chemical functionality (scavenging hydrofluoric acid that poses as a critical threat to trigger unwanted side reactions), the PI/PVP semi-IPN nanoencapsulated-cathode materials enable significant improvement in electrochemical performance and thermal stability of lithium-ion batteries.

  6. Characterization of submillisecond response optical addressing phase modulator based on low light scattering polymer network liquid crystal

    SciTech Connect

    Xiangjie, Zhao E-mail: zxjdouble@gmail.com; Cangli, Liu; Jiazhu, Duan; Dayong, Zhang; Yongquan, Luo

    2015-01-07

    Optically addressed conventional nematic liquid crystal spatial light modulator has attracted wide research interests. But the slow response speed limited its further application. In this paper, polymer network liquid crystal (PNLC) was proposed to replace the conventional nematic liquid crystal to enhance the response time to the order of submillisecond. The maximum light scattering of the employed PNLC was suppressed to be less than 2% at 1.064 μm by optimizing polymerization conditions and selecting large viscosity liquid crystal as solvent. The occurrence of phase ripple phenomenon due to electron diffusion and drift in photoconductor was found to deteriorate the phase modulation effect of the optical addressed PNLC phase modulator. The wavelength effect and AC voltage frequency effect on the on state dynamic response of phase change was investigated by experimental methods. These effects were interpreted by electron diffusion and drift theory based on the assumption that free electron was inhomogeneously distributed in accordance with the writing beam intensity distribution along the incident direction. The experimental results indicated that the phase ripple could be suppressed by optimizing the wavelength of the writing beam and the driving AC voltage frequency when varying the writing beam intensity to generate phase change in 2π range. The modulation transfer function was also measured.

  7. Dehydration induced 2D-to-3D crystal-to-crystal network re-assembly and ferromagnetism tuning within two chiral copper(II)-tartrate coordination polymers.

    PubMed

    Liu, Yen-Hsiang; Lee, Szu-Hsuan; Chiang, Jung-Chun; Chen, Po-Chen; Chien, Po-Hsiu; Yang, Chen-I

    2013-12-28

    The synthesis of two homochiral l-tartrate-copper(II) coordination polymers, [Cu2(C4H4O6)2(H2O)2·xH2O]n (1), and [Cu(C4H4O6)]n (2), under hydrothermal conditions, is reported. Compound 1 adopts a 2D layered network structure with a space group of P21, while compound 2 features a 3D network structure with a space group P21212. Interestingly, the 2D layered structure of compound 1 can undergo a crystal-to-crystal network reassembly, with the formation of the 3D network structure of compound 2 under dehydration conditions. Variable temperature and field magnetic studies reveal the existence of a distinct ferromagnetic interaction between Cu(2+) ions as the result of distinct syn-anti carboxylate bridging coordination modes.

  8. Development of Hierarchical Polymer@Pd Nanowire‐Network: Synthesis and Application as Highly Active Recyclable Catalyst and Printable Conductive Ink

    PubMed Central

    Mir, Sajjad Husain

    2016-01-01

    Abstract A facile one‐pot approach for preparing hierarchical nanowire‐networks of hollow polymer@Pd nanospheres is reported. First, polymer@Pd hollow nanospheres were produced through metal‐complexation‐induced phase separation with functionalized graft copolymers and subsequent self‐assembly of PdNPs. The nanospheres hierarchically assembled into the nanowire‐network upon drying. The Pd nanowire‐network served as an active catalyst for Mizoroki–Heck and Suzuki–Miyaura coupling reactions. As low as 500 μmol % Pd was sufficient for quantitative reactions, and the origin of the high activity is ascribed to the highly active sites originating from high‐index facets, kinks, and coalesced structures. The catalyst can be recycled via simple filtration and washing, maintaining its high activity owing to the micrometer‐sized hierarchical structure of the nanomaterial. The polymer@Pd nanosphere also served as a printable conductive ink for a translucent grid pattern with excellent horizontal conductivity (7.5×105 S m−1). PMID:27551657

  9. Development of Hierarchical Polymer@Pd Nanowire-Network: Synthesis and Application as Highly Active Recyclable Catalyst and Printable Conductive Ink.

    PubMed

    Mir, Sajjad Husain; Ochiai, Bungo

    2016-06-01

    A facile one-pot approach for preparing hierarchical nanowire-networks of hollow polymer@Pd nanospheres is reported. First, polymer@Pd hollow nanospheres were produced through metal-complexation-induced phase separation with functionalized graft copolymers and subsequent self-assembly of PdNPs. The nanospheres hierarchically assembled into the nanowire-network upon drying. The Pd nanowire-network served as an active catalyst for Mizoroki-Heck and Suzuki-Miyaura coupling reactions. As low as 500 μmol % Pd was sufficient for quantitative reactions, and the origin of the high activity is ascribed to the highly active sites originating from high-index facets, kinks, and coalesced structures. The catalyst can be recycled via simple filtration and washing, maintaining its high activity owing to the micrometer-sized hierarchical structure of the nanomaterial. The polymer@Pd nanosphere also served as a printable conductive ink for a translucent grid pattern with excellent horizontal conductivity (7.5×10(5) S m(-1)). PMID:27551657

  10. Pore Network Modeling and Synchrotron Imaging of Liquid Water in the Gas Diffusion Layer of Polymer Electrolyte Membrane Fuel Cells

    NASA Astrophysics Data System (ADS)

    Hinebaugh, James Thomas

    Polymer electrolyte membrane (PEM) fuel cells operate at levels of high humidity, leading to condensation throughout the cell components. The porous gas diffusion layer (GDL) must not become over-saturated with liquid water, due to its responsibility in providing diffusion pathways to and from the embedded catalyst sites. Due to the opaque and microscale nature of the GDL, a current challenge of the fuel cell industry is to identify the characteristics that make the GDL more or less robust against flooding. Modeling the system as a pore network is an attractive investigative strategy; however, for flooding simulations to provide meaningful material comparisons, accurate GDL topology and condensation distributions must be provided. The focus of this research is to provide the foundational tools with which to capture both of these requirements. The method of pore network modeling on topologically representative pore networks is demonstrated to describe flooding phenomena within GDL materials. A stochastic modeling algorithm is then developed to create pore spaces with the relevant features of GDL materials. Then, synchrotron based X-ray visualization experiments are developed and conducted to provide insight into condensation conditions. It was found that through-plane porosity distributions have significant effects on the GDL saturation levels. Some GDL manufacturing processes result in high porosity regions which are predicted to become heavily saturated with water if they are positioned between the condensation sites and the exhaust channels. Additionally, it was found that fiber diameter and the volume fraction of binding material applied to the GDL have significant impacts on the GDL heterogeneity and pore size distribution. Representative stochastic models must accurately describe these three material characteristics. In situ, dynamic liquid water behavior was visualized at the Canadian Light source, Inc. synchrotron using imaging and image processing

  11. Photo-Reactive Nanogel as a Means to Tune Properties during Polymer Network Formation

    PubMed Central

    Liu, JianCheng; Rad, Ima Y.; Sun, Fang; Stansbury, Jeffrey W.

    2013-01-01

    Photo-reactive nanogels with an integrated photoinitiator-based functionality were synthesized via a Reversible Addition-Fragmentation Chain Transfer (RAFT) process. Without additional free initiators, this nanogel is capable of radical generation and initiating polymerization of a secondary monomer (i.e. dimethacrylate) that infiltrates and disperses the nanogel particles. Due to the presence of RAFT functionality and the fact that all initiating sites are initially located within the nanogel structure, gelation can be delayed by sequencing the polymerization from the nanogel to the bulk matrix. During polymerization of a nanogel-filled resin system, a progressive delay of gelation conversion from about 2 % for conventional chain growth polymerization to 18 % for the same monomer containing 20 wt% nanogel additive was achieved. A significant delay of stress development was also observed with much lower final stress achieved with the nanogel-modified systems due to the change of network formation mechanics. Compared with the nanogel-free dimethacrylate control, which contained uniformly distributed free initiator, the flexural modulus and mechanical strength results were maintained for the photopolymers with nanogel contents greater than 10 wt%. There appears to be a critical interparticle spacing of the photo-reactive nanogel that provides effective photopolymerization while providing delayed gelation and substantial stress reduction. PMID:24348753

  12. Preparation of semi-interpenetrating polymer networks composed of silk fibroin and poloxamer macromer.

    PubMed

    Yoo, Mi-Kyong; Kweon, Hae Yong; Lee, Kwang-Gill; Lee, Hyun-Chul; Cho, Chong-Su

    2004-08-01

    A system was designed to utilize silk fibroin (SF) as a matrix for wound dressing. For this system, we prepared a sponge type of porous semi-interpenetrating networks (SIPNs) hydrogel composed of SF and poloxamer 407 macromer to enhance the mechanical and functional properties of SF. The thermal and mechanical properties of the hydrogels as well as their swelling behaviors were studied by means of differential scanning calorimetry, compressive modulus measurement, and gravimetric method, respectively. The morphology and crystalline structure of these SIPN hydrogels were also investigated by scanning electron microscopy (SEM) and wide-angle diffractometry, respectively. Conformational change of SF from random coil to beta-sheet structure was accelerated by formation of SIPNs with poloxamer. The melting temperature of poloxamer in the SIPNs decreased due to the prevention of crystallization by the incorporation of SF. The mechanical strength of SIPNs hydrogel was much higher than those of SF itself or SF/poloxamer blend and increased with the poloxamer content. The equilibrium water content of SF was remarkably increased by formation of SIPNs with poloxamer due to the hydrophilicity of poloxamer. The crystallinity and morphology of SIPNs hydrogel were affected by SIPNs hydrogel composition. PMID:15374683

  13. Role of hydrodynamic interactions in dynamics of semi-flexible polyelectrolytes

    NASA Astrophysics Data System (ADS)

    Kekre, Rahul

    Experiments have shown that DNA molecules in capillary electrophoresis migrate across field lines if a pressure gradient is applied simultaneously. We suggest that this migration results from an electrically driven flow field around the polyelectrolyte, which generates additional contributions to the center-of-mass velocity if the overall polymer conformation is asymmetric. Numerical simulations and experiments have demonstrated that confined polymers migrate towards the center of the channel in response to both external forces and uniaxial flows. Yet, migration towards the walls has been observed with combinations of external force and flow. In this work, the kinetic theory for an elastic dumbbell developed by Ma and Graham [Phys. Fluids 17, 083103 (2005)] has been extended to account for the effects of an external body force. Further modifications account for counterion screening within a Debye-Huckel approximation for the specific case of applied electric field. The theory qualitatively reproduces results of both experiments for the migration of neutral polymers and polyelectrolytes. The favorable comparison supports the contention [Long et al., Phys. Rev. Lett. 76, 3858 (1996)] that the hydrodynamic interactions in polyelectrolytes decay algebraically, as 1/r 3, rather than exponentially. A coarse-grained polymer model, without explicit charges, is developed and integrated using Brownian-dynamics simulations in analogy with the kinetic theory. The novel feature of the simulations is the inclusion of hydrodynamic interactions induced by the electric field. This model quantitatively captures experimental observations [Zheng and Yeung, Anal. Chem. 75, 3675 (2003)] of DNA migration under combined electric and pressure-driven flow fields in absence of any adjusted parameters. In addition the model predicts dependence of electrophoretic velocity on the instantaneous length of the polyelectrolyte which has been verified by experiments of Lee et. al. [Electrophoresis

  14. Construction of a lithium ion transport network in cathode with lithiated bis(benzene sulfonyl)imide based single ion polymer ionomers

    NASA Astrophysics Data System (ADS)

    Pan, Qiyun; Zhang, Wenchao; Pan, Meize; Zhang, Baodan; Zeng, Danli; Sun, Yubao; Cheng, Hansong

    2015-06-01

    We demonstrate a novel method to construct a lithium ion transport network in cathode materials by replacing PVDF with lithiated poly(bis(4-carbonyl benzene sulfonyl)imide-co-bis(4-amino benzene sulfonyl)imide) as the binder. The single ion conducting polymer was synthesized via polycondensation of bis(4-carbonyl benzene sulfonyl)imide and bis(4-amino benzene sulfonyl)imide followed by lithium ion exchange. By blending the ionomers with LiFePO4 and acetylene carbon, the ionic network was well constructed, resulting in a maximum use of active cathode material inside the cathode. The membrane of the polymer electrolyte exhibits an ionic conductivity of 0.14 mS cm-1 at room temperature, a high ion transference number of 0.92 and a wide electrochemical window of 4.5 V (vs. Li+/Li). A lithium ion battery assembled with the single ion conducting polymer electrolyte delivers excellent performance at room temperature with various C-rates.

  15. On the use of the activation energy concept to investigate analyte and network deformations in entangled polymer solution capillary electrophoresis of synthetic polyelectrolytes.

    PubMed

    Cottet, H; Gareil, P

    2001-01-01

    The activation energy associated with the electrophoretic migration of an analyte under given electrolyte conditions can be accessed through the determination of the analyte electrophoretic mobility at various temperatures. In the case of the electrophoretic separation of polyelectrolytes in the presence of an entangled polymer network, activation energy can be regarded as the energy needed by the analyte to overcome the obstacles created by the separating network. Any deformation undergone by the analyte or the network is expected to induce a decrease in the activation energy. In this work, the electrophoretic mobilities of poly(styrenesulfonates) (PSSs) of various molecular weights (Mr 16 x 10(3) to 990 x 10(3)) were determined in entangled polyethylene oxide (PEO) solutions as a function of temperature (in the 17-60 degrees C range) and the PSS activation energies were calculated. The influences of the PSS molecular weight, blob sizes zetab of the separating network (related to the PEO concentration), ionic strength of the electrolyte and electric field strength (75-600 V/cm) were investigated. The results were interpreted in terms of analyte and network deformations and were confronted with those previously obtained for DNA migration in polymer solutions and chemical gels. For a radius of gyration Rgzetab, suggesting PSS and network deformations in the latter case. Increasing ionic strength resulted in an increase in the PSS activation energy, because of the decrease of their radii of gyration, which makes them less deformable. Finally, the activation energies of all the PSSs are a decreasing function of field strength and at high field strength tend to reach a constant value close to that for a small molecule.

  16. Translational and rotational diffusion of a single nanorod in unentangled polymer melts

    NASA Astrophysics Data System (ADS)

    Kim, Min Jung; Cho, Hyun Woo; Kim, Jeongmin; Kim, Heesuk; Sung, Bong June

    2015-10-01

    Polymer nanocomposites have been an issue of both academic and industrial interest due to promising electrical, mechanical, optical, and magnetic properties. The dynamics of nanoparticles in polymer nanocomposites is a key to understanding those properties of polymer nanocomposites and is important for applications such as self-healing nanocomposites. In this article we investigate the translational and the rotational dynamics of a single nanorod in unentangled polymer melts by employing extensive molecular dynamics simulations. A nanorod and polymers are modeled as semiflexible tangent chains of spherical beads. The stiffness of a nanorod is tuned by changing the bending potential between chemical bonds. When polymers are sufficiently long and the nanorod is stiff, the nanorod translates in an anisotropic fashion along the nanorod axis within time scales of translational relaxation times even in unentangled polymer melts. The rotational diffusion is suppressed more significantly than the translational diffusion as the polymer chain length is increased, thus the translational and rotational diffusion of the nanorod are decoupled. We also estimate the winding numbers of polymers, i.e., how many times a polymer winds the nanorod. The winding number increases with longer polymers but is relatively insensitive to the nanorod stiffness.

  17. Elasticity of a semiflexible filament with a discontinuous tension due to a cross-link or a molecular motor

    NASA Astrophysics Data System (ADS)

    Razbin, Mohammadhosein; Benetatos, Panayotis; Zippelius, Annette

    2016-05-01

    We analyze the stretching elasticity of a wormlike chain with a tension discontinuity resulting from a Hookean spring connecting its backbone to a fixed point. The elasticity of isolated semiflexible filaments has been the subject in a significant body of literature, primarily because of its relevance to the mechanics of biological matter. In real systems, however, these filaments are usually part of supramolecular structures involving cross-linkers or molecular motors, which cause tension discontinuities. Our model is intended as a minimal structural element incorporating such a discontinuity. We obtain analytical results in the weakly bending limit of the filament, concerning its force-extension relation and the response of the two parts in which the filament is divided by the spring. For a small tension discontinuity, the linear response of the filament extension to this discontinuity strongly depends on the external tension. For large external tension f , the spring force contributes a subdominant correction ˜1 /f3 /2 to the well-known ˜1 /√{f } -dependence of the end-to-end extension.

  18. Self-assembly of octapod-shaped colloidal nanocrystals into a hexagonal ballerina network embedded in a thin polymer film.

    PubMed

    Arciniegas, Milena P; Kim, Mee R; De Graaf, Joost; Brescia, Rosaria; Marras, Sergio; Miszta, Karol; Dijkstra, Marjolein; van Roij, René; Manna, Liberato

    2014-02-12

    Nanoparticles with unconventional shapes may exhibit different types of assembly architectures that depend critically on the environmental conditions under which they are formed. Here, we demonstrate how the presence of polymer (polymethyl methacrylate, PMMA) molecules in a solution, in which CdSe(core)/CdS(pods) octapods are initially dispersed, affects the octapod-polymer organization upon solvent evaporation. We show that a fast drop-drying process can induce a remarkable two-dimensional (2D) self-assembly of octapods at the polymer/air interface. In the resulting structure, each octapod is oriented like a "ballerina", that is, only one pod sticks out of the polymer film and is perpendicular to the polymer-air interface, while the opposite pod (with respect to the octapod's center) is fully immersed in the film and points toward the substrate, like a ballerina performing a grand battement. In some areas, a hexagonal-like pattern is formed by the ballerinas in which the six nonvertical pods, which are all embedded in the film, maintain a pod-pod parallel configuration with respect to neighboring particles. We hypothesize that the mechanism responsible for such a self-assembly is based on a fast adsorption of the octapods from bulk solution to the droplet/air interface during the early stages of solvent evaporation. At this interface, the octapods maintain enough rotational freedom to organize mutually in a pod-pod parallel configuration between neighboring octapods. As the solvent evaporates, the octapods form a ballerina-rich octapod-polymer composite in which the octapods are in close contact with the substrate. Finally, we found that the resulting octapod-polymer composite is less hydrophilic than the polymer-only film.

  19. 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

  20. Enhanced contrast ratio and viewing angle of polymer-stabilized liquid crystal via refractive index matching between liquid crystal and polymer network.

    PubMed

    Lee, Ji-Hoon; Lee, Jung Jin; Lim, Young Jin; Kundu, Sudarshan; Kang, Shin-Woong; Lee, Seung Hee

    2013-11-01

    Long standing electro-optic problems of a polymer-dispersed liquid crystal (PDLC) such as low contrast ratio and transmittances decrease in oblique viewing angle have been challenged with a mixture of dual frequency liquid crystal (DFLC) and reactive mesogen (RM). The DFLC and RM molecules were vertically aligned and then photo-polymerized using a UV light. At scattering state under 50 kHz electric field, DFLC was switched to planar state, giving greater extraordinary refractive index than the normal PDLC cell. Consequently, the scattering intensity and the contrast ratio were increased compared to the conventional PDLC cell. At transparent state under 1 kHz electric field, the extraordinary refractive index of DFLC was simultaneously matched with the refractive index of vertically aligned RM so that the light scattering in oblique viewing angles was minimized, giving rise to high transmittance in all viewing angles.

  1. Enhanced contrast ratio and viewing angle of polymer-stabilized liquid crystal via refractive index matching between liquid crystal and polymer network.

    PubMed

    Lee, Ji-Hoon; Lee, Jung Jin; Lim, Young Jin; Kundu, Sudarshan; Kang, Shin-Woong; Lee, Seung Hee

    2013-11-01

    Long standing electro-optic problems of a polymer-dispersed liquid crystal (PDLC) such as low contrast ratio and transmittances decrease in oblique viewing angle have been challenged with a mixture of dual frequency liquid crystal (DFLC) and reactive mesogen (RM). The DFLC and RM molecules were vertically aligned and then photo-polymerized using a UV light. At scattering state under 50 kHz electric field, DFLC was switched to planar state, giving greater extraordinary refractive index than the normal PDLC cell. Consequently, the scattering intensity and the contrast ratio were increased compared to the conventional PDLC cell. At transparent state under 1 kHz electric field, the extraordinary refractive index of DFLC was simultaneously matched with the refractive index of vertically aligned RM so that the light scattering in oblique viewing angles was minimized, giving rise to high transmittance in all viewing angles. PMID:24216913

  2. Functionalized chitosan/NIPAM (HEMA) hybrid polymer networks as inserts for ocular drug delivery: synthesis, in vitro assessment, and in vivo evaluation.

    PubMed

    Verestiuc, Liliana; Nastasescu, Oana; Barbu, Eugen; Sarvaiya, Indrajeetsinh; Green, Keith L; Tsibouklis, John

    2006-06-15

    A series of hybrid polymeric hydrogels, prepared by the reaction of acrylic acid-functionalized chitosan with either N-isopropylacrylamide or 2-hydroxyethyl methacrylate monomers, were synthesized, pressed into minitablets, and investigated for their ability to act as controlled release vehicles for ophthalmic drug delivery. For comparison, interpolymeric complex analogues synthesized using the same monomers and pure, unfunctionalized chitosan were examined by means of an identical characterization protocol. The effects of network structure and composition upon the swelling properties, adhesion behavior, and drug release characteristics were investigated. Comparative in vitro studies employing chloramphenicol, atropine, norfloxacin, or pilocarpine informed the selection of drug-specific carrier compositions for the controlled delivery of these compounds. In addition, in vivo (rabbit model) experiments involving the delivery of pilocarpine indicated that chitosan-based hybrid polymer networks containing 2-hydroxyethyl methacrylate are useful carriers for the delivery of this therapeutic agent. PMID:16555266

  3. Nuclear Instruments and Methods in Physics Research. Section B; Microstructural Characterization of Semi-Interpenetrating Polymer Networks by Positron Lifetime Spectroscopy

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Pater, Ruth H.; Eftekhari, Abe

    1998-01-01

    Thermoset and thermoplastic polyimides have complementary physical/mechanical properties. Whereas thermoset polyimides are brittle and generally easier to process, thermoplastic polyimides are tough but harder to process. It is expected that a combination of these two types of polyimides may help produce polymers more suitable for aerospace applications. Semi-Interpenetrating Polymer Networks (S-IPNs) of thermoset LaRC(Trademark)-RP46 and thermoplastic LARC(Trademark)-IA polyimides were prepared in weight percent ratios ranging from 100:0 to 0: 100. Positron lifetime measurements were made in these samples to correlate their free volume features with physical/mechanical properties. As expected, positronium atoms are not formed in these samples. The second life time component has been used to infer the positron trap dimensions. The "free volume" goes through a minimum at about 50:50 ratio, suggesting that S-IPN samples are not merely solid solutions of the two polymers. These data and related structural properties of the S-IPN samples have been discussed in this paper.

  4. Efficient ibuprofen delivery from anhydrous semisolid formulation based on a novel cross-linked silicone polymer network: an in vitro and in vivo study.

    PubMed

    Aliyar, Hyder; Huber, Robert; Loubert, Gary; Schalau, Gerald

    2014-07-01

    The use of silicone as a primary polymer in topical semisolid pharmaceutical formulations is infrequent. Recent development of novel silicone materials provides an opportunity to investigate their drug delivery efficiencies. In this study, an anhydrous semisolid formulation was prepared using a novel cross-linked silicone polymer network swollen in isododecane. Similar formulations were prepared using petrolatum, an acrylic, or a cellulose polymer. All formulations contained 5% ibuprofen (IBP). In vitro permeability was evaluated for all formulations and a commercial product using human cadaver epidermis. The silicone formulation delivered IBP more efficiently than all other formulations in terms of flux, cumulative amount, and percent drug release. The silicone formulation showed the maximum flux of 85.9 μg . cm(-2) . h(-1) and a cumulative IBP release of 261.6 μg in 8 h, whereas the benchmark showed 20.1 μg . cm(-2) . h(-1) and 30.9 μg, respectively. An in vivo study conducted on rats showed calculated blood AUCs of 59.2 and 17.6 μg . h/g (p < 0.003) for the silicone formulation and the benchmark, respectively. The IBP in excised rat skin was 264 ± 59 μg/g for the silicone formulation and 102 ± 5 μg/g for the benchmark. The results obtained from the in vitro and in vivo studies demonstrate efficient topical IBP delivery by the silicone formulation.

  5. Effect of polyacrylonitrile on triethylene glycol diacetate-2-propenoic acid butyl ester gel polymer electrolytes with interpenetrating crosslinked network for flexible lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Wang, Qiujun; Song, Wei-Li; Fan, Li-Zhen; Shi, Qiao

    2015-11-01

    A new flexible gel polymer electrolytes (GPE) with interpenetrating cross-linked network is fabricated by blending long-chain polyacrylonitrile (PAN) polymer matrix and short-chain triethylene glycol diacetate-2-propenoic acid butyl ester (TEGDA-BA) framework, with the purpose of enhancing the mechanical stability of the GPE frameworks via synergistic effects of the linear polymers and crosslinked monomers. The as fabricated frameworks enable the liquid electrolytes to be firmly entrapped in the polymeric matrices, which significantly improves the mechanical bendability and interface stability of the resultant GPE. The GPE with 5 wt% PAN exhibits high ionic conductivity up to 5.9 × 10-3 S cm-1 at 25 °C with a stable electrochemical window observed (>5.0 V vs. Li/Li+). The Li|GPE|LiFePO4 half cells demonstrate remarkably stable capacity retention and rate ability during cycling tests. As expected, the LiFePO4|GPE|Li4Ti5O12 full cells also exhibit discharge capacity of 125.2 mAh g-1 coupled with high columbic efficiency greater than 98% after 100 cycles. The excellent mechanical flexibility and charge/discharge performance suggest that the GPE holds great application potential in flexible LIBs.

  6. Strain-induced crystallization in elastomeric polymer networks prepared in solution and sol-gel derived high-temperature organic-inorganic hybrid materials

    NASA Astrophysics Data System (ADS)

    Premachandra, Jagath Kumara

    Cross-linking polymer chains in solution should bring about fewer inter-chain entanglements in the resulting network. The subsequent drying of this network should compress the chains into a "super-contracted" state. The opposing effects of these changes on strain-induced crystallization in cis-1,4-polyisoprene networks formed in solution were investigated. Higher elongations were required to achieve strain-induced crystallinity in the networks prepared at higher dilutions, suggesting that in this regard the compressed states of the chains was more important than their reduced entangling. The constrained-junction theory was applied to strain-induced crystallization in the above networks. The stress-strain isotherms generated from this theory were in satisfactory agreement with experiment. It was found that the constraint parameter kappa decreases with increase in dilution during cross-linking mainly due to the fact that cross-linking in solution decreases chain interpenetration. The dependence of hydrolysis and condensation of gamma-ureidopropyltrimethoxysilane on pH in the water-methanol system at 23sp°C was investigated by FTIR spectroscopy. Quantitative analysis of rates of hydrolysis showed that gamma-ureidopropyltrimethoxysilane is most stable in the water-methanol system at pH 7.7. The rate of overall condensation of silanols produced by the hydrolysis was qualitatively analyzed. These silanol groups are relatively more stable around pH 4.87. The mechanical properties, thermal stability and water absorption of high-temperature sulfopolybenzobisthiazole-silica hybrid materials were investigated. The use of a bonding agent N,N-diethylaminopropyltrimethoxysilane facilitated the interfacial bonding between the organic and inorganic phases in these materials prepared through the sol-gel process. Tensile modulus, thermal stability and the resistant to water absorption were increased with increase in silica content in the resulting composites

  7. Thermoresponsive semicrystalline poly(ε-caprolactone) networks: exploiting cross-linking with cinnamoyl moieties to design polymers with tunable shape memory.

    PubMed

    Garle, Amit; Kong, Sany; Ojha, Umaprassana; Budhlall, Bridgette M

    2012-02-01

    The overall goal of this study was to synthesize semicrystalline poly(ε-caprolactone) (PCL) copolymer networks with stimuli-responsive shape memory behavior. Herein, we investigate the influence of a cinnamoyl moiety to design shape memory polymer networks with tunable transition temperatures. The effect of various copolymer architectures (random or ABA triblock), the molecular weight of the crystalline domains, PCL diol, (M(w) 1250 or 2000 g mol(-1)) and its composition in the triblock (50 or 80 mol %) were also investigated. The polymer microstructures were confirmed by NMR, DSC, WAXS and UV-vis spectroscopic techniques. The thermal and mechanical properties and the cross-linking density of the networks were characterized by DSC, tensile testing and solvent swelling, respectively. Detailed thermomechanical investigations conducted using DMA showed that shape memory behavior was obtained only in the ABA triblock copolymers. The best shape memory fixity, R(f) of ~99% and shape recovery, R(r) of ~99% was obtained when PCL diol with M(w) 2000 g mol(-1) was incorporated in the triblock copolymer at a concentration of 50 mol %. The series of triblock copolymers with PCL at 50 mol % also showed mechanical properties with tunable shape memory transition temperatures, ranging from 54 °C to close to body temperature. Our work establishes a general design concept for inducing a shape memory effect into any semicrystalline polyester network. More specifically, it can be applied to systems which have the highest transition temperature closest to the application temperature. An advantage of our novel copolymers is their ability to be cross-linked with UV radiation without any initiator or chemical cross-linker. Possible applications are envisioned in the area of endovascular treatment of ischemic stroke and cerebrovascular aneurysms, and for femoral stents.

  8. Flexible star polymer chain adsorption by a flat surface: a molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Zenak, Siham; Guenachi, Aicha; Sabeur, Sid Ahmed

    2016-08-01

    In this work, we have studied the adsorption of a single flexible star polymer chain by a flat surface. The molecular dynamics simulation has been validated for the case of a free star polymer chain using the diffusion experiment. The scaling laws found are in agreement with the Flory theory predictions and the Rouse model. For the adsorption, preliminary results were obtained for chains of different sizes N=31 to N=199 and different functionalities (f=3,4,6,8,10). For the case of semi-flexible star polymer chains, further investigation is needed to locate the critical point of adsorption when varying the potential interaction strength between the chain and the surface.

  9. Polymer films

    DOEpatents

    Granick, Steve; Sukhishvili, Svetlana A.

    2008-12-30

    A film contains a first polymer having a plurality of hydrogen bond donating moieties, and a second polymer having a plurality of hydrogen bond accepting moieties. The second polymer is hydrogen bonded to the first polymer.

  10. Polymer films

    DOEpatents

    Granick, Steve; Sukhishvili, Svetlana A.

    2004-05-25

    A film contains a first polymer having a plurality of hydrogen bond donating moieties, and a second polymer having a plurality of hydrogen bond accepting moieties. The second polymer is hydrogen bonded to the first polymer.

  11. Molecular Level Insights into Thermally Induced [alpha]-Chymotrypsinogen A Amyloid Aggregation Mechanism and Semiflexible Protofibril Morphology

    SciTech Connect

    Zhang, Aming; Jordan, Jacob L.; Ivanova, Magdalena I.; Weiss, IV., William F.; Roberts, Christopher J.; Fernandez, Erik J.

    2010-12-07

    Understanding nonnative protein aggregation is critical not only to a number of amyloidosis disorders but also for the development of effective and safe biopharmaceuticals. In a series of previous studies [Weiss et al. (2007) Biophys. J. 93, 4392-4403; Andrews et al. (2007) Biochemistry 46, 7558-7571; Andrews et al. (2008) Biochemistry 47, 2397-2403], {alpha}-chymotrypsinogen A (aCgn) and bovine granulocyte colony stimulating factor (bG-CSF) have been shown to exhibit the kinetic and morphological features of other nonnative aggregating proteins at low pH and ionic strength. In this study, we investigated the structural mechanism of aCgn aggregation. The resultant aCgn aggregates were found to be soluble and exhibited semiflexible filamentous aggregate morphology under transmission electron microscopy. In addition, the filamentous aggregates were demonstrated to possess amyloid characteristics by both Congo red binding and X-ray diffraction. Peptide level hydrogen exchange (HX) analysis suggested that a buried native {beta}-sheet comprised of three peptide segments (39-46, 51-64, and 106-114) reorganizes into the cross-{beta} amyloid core of aCgn aggregates and that at least 50% of the sequence adopts a disordered structure in the aggregates. Furthermore, the equimolar, bimodal HX labeling distribution observed for three reported peptides (65-102, 160-180, and 229-245) suggested a heterogeneous assembly of two molecular conformations in aCgn aggregates. This demonstrates that extended {beta}-sheet interactions typical of the amyloid are sufficiently strong that a relatively small fraction of polypeptide sequence can drive formation of filamentous aggregates even under conditions favoring colloidal stability.

  12. Polymer stabilization of the smectic C-alpha* liquid crystal phase—Over tenfold thermal stabilization by confining networks of photo-polymerized reactive mesogens

    SciTech Connect

    Labeeb, A.; Gleeson, H. F.; Hegmann, T.

    2015-12-07

    The smectic C*-alpha (SmC{sub α}*) phase is one of the sub-phases of ferroelectric liquid crystals that has drawn much interest due to its electro-optical properties and ultrafast switching. Generally observed above the ferroelectric SmC* phase in temperature, the SmC{sub α}* commonly shows only very narrow phase temperature range of a few degree Celsius. To broaden the SmC{sub α}* phase, polymer stabilization was investigated for thermal phase stabilization. Two different reactive monomers were tested in three mixtures, and all three broadened the temperature range of the SmC{sub α}* phase from 3 °C to 39 °C. The current reversal method was used to determine the phase existence versus temperature. Moreover, the texture and network structure was studied by polarized optical microscopy and scanning electron microscopy, with the latter revealing the confinement of the smectic layer structure within the porous polymer network.

  13. Polymers with pendant ferrocenes.

    PubMed

    Pietschnig, Rudolf

    2016-10-01

    The tailoring of smart material properties is one of the challenges in materials science. The unique features of polymers with pendant ferrocene units, either as ferrocenyl or ferrocenediyl groups, provide electrochemical, electronic, optoelectronic, catalytic, and biological properties with potential for applications as smart materials. The possibility to tune or to switch the properties of such materials relies mostly on the redox activity of the ferrocene/ferricenium couple. By switching the redox state of ferrocenyl units - separately or in a cooperative fashion - charge, polarity, color (UV-vis range) and hydrophilicity of polymers, polymer functionalized surfaces and polymer derived networks (sol-gel) may be controlled. In turn, also the vicinity of such polymers influences the redox behavior of the pendant ferrocenyl units allowing for sensing applications by using polymer bound enzymes as triggering units. In this review the focus is set mainly on the literature of the past five years.

  14. Silver nanowire percolation network soldered with graphene oxide at room temperature and its application for fully stretchable polymer light-emitting diodes.

    PubMed

    Liang, Jiajie; Li, Lu; Tong, Kwing; Ren, Zhi; Hu, Wei; Niu, Xiaofan; Chen, Yongsheng; Pei, Qibing

    2014-02-25

    Transparent conductive electrodes with high surface conductivity, high transmittance in the visible wavelength range, and mechanical compliance are one of the major challenges in the fabrication of stretchable optoelectronic devices. We report the preparation of a transparent conductive electrode (TCE) based on a silver nanowire (AgNW) percolation network modified with graphene oxide (GO). The monatomic thickness, mechanical flexibility, and strong bonding with AgNWs enable the GO sheets to wrap around and solder the AgNW junctions and thus dramatically reduce the inter-nanowire contact resistance without heat treatment or high force pressing. The GO-soldered AgNW network has a figure-of-merit sheet resistance of 14 ohm/sq with 88% transmittance at 550 nm. Its storage stability is improved compared to a conventional high-temperature annealed AgNW network. The GO-soldered AgNW network on polyethylene terephthalate films was processed from solutions using a drawdown machine at room temperature. When bent to 4 mm radius, its sheet resistance was increased by only 2-3% after 12,000 bending cycles. GO solder can also improve the stretchability of the AgNW network. Composite TCE fabricated by inlaying a GO-soldered AgNW network in the surface layer of polyurethane acrylate films is stretchable, by greater than 100% linear strain without losing electrical conductivity. Fully stretchable white polymer light-emitting diodes (PLEDs) were fabricated for the first time, employing the stretchable TCE as both the anode and cathode. The PLED can survive after 100 stretching cycles between 0 and 40% strain and can be stretched up to 130% linear strain at room temperature. PMID:24471886

  15. Encoding Mechano-Memories in Actin Networks

    NASA Astrophysics Data System (ADS)

    Foucard, Louis; Majumdar, Sayantan; Levine, Alex; Gardel, Margaret

    The ability of cells to sense and adapt to external mechanical stimuli is vital to many of its biological functions. A critical question is therefore to understand how mechanosensory mechanisms arise in living matter, with implications in both cell biology and smart materials design. Experimental work has demonstrated that the mechanical properties of semiflexible actin networks in Eukaryotic cells can be modulated (either transiently or irreversibly) via the application of external forces. Previous work has also shown with a combination of numerical simulations and analytic calculations shows that the broken rotational symmetry of the filament orientational distribution in semiflexible networks leads to dramatic changes in the mechanical response. Here we demonstrate with a combination of numerical and analytic calculations that the observed long-lived mechano-memory in the actin networks arise from changes in the nematic order of the constituent filaments. These stress-induced changes in network topology relax slowly under zero stress and can be observed through changes in the nonlinear mechanics. Our results provide a strategy for designing a novel class of materials and demonstrate a new putative mechanism of mechanical sensing in eukaryotic cells.

  16. Understanding Local and Macroscopic Electron Mobilities in the Fullerene Network of Conjugated Polymer-based Solar Cells. Time-Resolved Microwave Conductivity and Theory

    SciTech Connect

    Aguirre, Jordan C.; Arntsen, Christopher D.; Hernandez, Samuel; Huber, Rachel; Nardes, Alexandre M.; Halim, Merissa; Kilbride, Daniel; Rubin, Yves; Tolbert, Sarah H.; Kopidakis, Nikos; Schwartz, Benjamin J.; Neuhauser, Daniel

    2013-09-23

    The efficiency of bulk heterojunction (BHJ) organic photovoltaics is sensitive to the morphology of the fullerene network that transports electrons through the device. This sensitivity makes it difficult to distinguish the contrasting roles of local electron mobility (how easily electrons can transfer between neighboring fullerene molecules) and macroscopic electron mobility (how well-connected is the fullerene network on device length scales) in solar cell performance. In this work, a combination of density functional theory (DFT) calculations, flash-photolysis time-resolved microwave conductivity (TRMC) experiments, and space-charge-limit current (SCLC) mobility estimates are used to examine the roles of local and macroscopic electron mobility in conjugated polymer/fullerene BHJ photovoltaics. The local mobility of different pentaaryl fullerene derivatives (so-called ‘shuttlecock’ molecules) is similar, so that differences in solar cell efficiency and SCLC mobilities result directly from the different propensities of these molecules to self-assemble on macroscopic length scales. These experiments and calculations also demonstrate that the local mobility of phenyl-C60 butyl methyl ester (PCBM) is an order of magnitude higher than that of other fullerene derivatives, explaining why PCBM has been the acceptor of choice for conjugated polymer BHJ devices even though it does not form an optimal macroscopic network. The DFT calculations indicate that PCBM's superior local mobility comes from the near-spherical nature of its molecular orbitals, which allow strong electronic coupling between adjacent molecules. In combination, DFT and TRMC techniques provide a tool for screening new fullerene derivatives for good local mobility when designing new molecules that can improve on the macroscopic electron mobility offered by PCBM.

  17. A study of ferrocene diffusion dynamics in network poly(ethylene oxide) polymer electrolyte by solid-state voltammetry

    SciTech Connect

    Watanabe, M.; Longmire, M.L.; Murray, R.W. )

    1990-03-22

    The diffusion rates of five ferrocene derivatives dissolved in an amorphous, cross-linked poly(ethylene oxide) (PEO) polymer electrolyte are measured by an electrochemical technique which detects the rate of their transport to an oxidizing microdisk electrode. The diffusion coefficients in dilute ferrocene/polymer solutions at 65{degree}C vary from 3 {times} 10{sup {minus}7} to 2 {times} 10{sup {minus}8} cm{sup 2} s{sup {minus}1} depending on the size of the ferrocene derivative. The diffusion coefficients decrease with increasing ferrocene concentration, increasing LiClO{sub 4} electrolyte concentration, and decreasing temperature; values approaching 10{sup {minus}10} cm{sup 2} s{sup {minus}1} are encountered at room temperature.

  18. Mesoporous polymer networks-ultraporous DVB resins by hard-templating of close-packed silica spheres.

    PubMed

    Wilke, Antje; Weber, Jens

    2012-05-14

    The preparation of ultraporous polymer resins using a straightforward hard-templating synthesis is presented. Self-assembly of silica nanospheres into densely packed glasses allows an easy preparation of templates. Polydivinylbenzene resins with surface areas of up to 1000 m(2) g(-1) are synthesized as a model system and porosity analysis reveals bimodal porosity (spherical mesopores and micropores within the pore walls). The prepared systems can be further functionalized without loss of porosity as demonstrated by sulfonation. Because of their large pore sizes (13-28 nm), they are efficient adsorbents also for large molecules. Finally, the systems can also be used as model systems for the study of the pore drying and collapse process, which is of crucial importance for any application of mesoporous polymers.

  19. Tube-type coordination polymers: two- and four-silver(I)-mediated linear networking of calix[4]arene tetracarboxylates.

    PubMed

    Park, Ki-Min; Lee, Eunji; Park, Chul Soon; Lee, Shim Sung

    2011-12-01

    Two calix[4]arene tetracarboxylates, [calix[4]arene tetraacetate (K(4)CTA) and calix[4]arene tetrabenzoate (K(4)CTB)] as their potassium salts, have been prepared. Employing these as precursors, two Ag(I) coordination polymers incorporating calix[4]arene units have been successfully prepared and their X-ray crystal structures have been determined. In these, the CTA and CTB derivatives are linearly bound to two and four silver atoms, respectively, to generate unusual tubular nanostructures. A comparative NMR study was undertaken to investigate the nature of the metal ion blocking of the tube as observed in the CTA-derived structure. The thermal properties for both coordination polymers were also examined.

  20. Dynamics of Hydrogen-Bonded Supramolecular Polymers

    NASA Astrophysics Data System (ADS)

    Buhler, Eric; Candau, Jean; Kolomiets, Elena; Lehn, Jean-Marie

    2010-03-01

    Supramolecular polymers formed from molecular recognition directed association between monomers bearing complementary hydrogen bonding groups were studied by rheology, small-angle neutron and light scattering experiments. The semiflexible fibers consist of few aggregated monomolecular wires. At T= 25 C the formation of branched aggregates occurs around the crossover concentration, C^*, between the dilute and semi-dilute regimes, whereas the classical behaviour of equilibrium polymers is observed at T=65 C. For semi-dilute solutions the steady-state flow curves showed a shear banding type instability, namely the occurrence of a stress plateau σp above a critical shear rate γ̂c. The values of σp and γ̂c were found to be of the same order of magnitude as those of the elastic plateau modulus and the inverse stress relaxation time, respectively. The above features are in agreement with the theoretical predictions based on the reptation model. Dynamic light scattering experiments showed the presence in the autocorrelation function of the concentration fluctuations of a slow viscoelastic relaxation process that is likely to be of Rouse type.

  1. Polymer relaxation and stretching dynamics in semi-dilute DNA solutions: a single molecule study

    NASA Astrophysics Data System (ADS)

    Hsiao, Kai-Wen; Brockman, Christopher; Schroeder, Charles

    2015-03-01

    In this work, we study polymer relaxation and stretching dynamics in semi-dilute DNA solutions using single molecule techniques. Using this approach, we uncover a unique scaling relation for longest polymer relaxation time that falls in the crossover regime described by semi-flexible polymer solutions, which is distinct from truly flexible polymer chains. In addition, we performed a series of step-strain experiments on single polymers in semi-dilute solutions in planar extensional flow using an automated microfluidic trap. In this way, we are able to precisely control the flow strength and the amount of strain applied to single polymer chains, thereby enabling direct observation of the full stretching and relaxation process in semi-dilute solutions during transient start-up and flow cessation. Interestingly, we observe polymer individualism in the conformation of single chains in semi-dilute solutions, which to our knowledge has not yet been observed. In addition, we observe the relaxation data can be explained by a multi-exponential decay process after flow cessation in semi-dilute solutions. Overall, our work reports key advance in non-dilute polymer systems from a molecular perspective via direct observation of dynamics in strong flows. DOW fellowship.

  2. Reconfigurable thermo-optic polymer switch based true-time-delay network utilizing imprinting and inkjet printing

    NASA Astrophysics Data System (ADS)

    Pan, Zeyu; Subbaraman, Harish; Zhang, Cheng; Panday, Ashwin; Li, Qiaochu; Zhang, Xingyu; Zou, Yi; Xu, Xiaochuan; Guo, L. J.; Chen, Ray T.

    2015-03-01

    Previously, we introduced a novel and an etch-free solution based procedure utilizing a combination of imprinting and inkjet printing for developing polymer photonic devices to overcome the limitations of conventional polymer photonic device fabrication techniques, such as RIE or direct pattern writing. In this work, we demonstrate the feasibility of developing very large-area photonic systems on both rigid and flexible substrates. Specifically, a complete reconfigurable 4-bit true-time-delay module, comprising of an array of five interconnected TO switches and polymer delay lines, with a dimension of 25 mm × 18 mm is developed. Because of the roll-to-roll (R2R) compatibility of the employed solution processing techniques, photonic system development over large areas at high-throughput on rigid or flexible substrates is possible, which will lead to tremendous cost savings. Moreover, these devices can be integrated with other printed photonic and electronic components, such as light sources, modulators, antennas, etc., on the same substrate, thus enabling integrated systems that can be conformably integrated on any platform.

  3. Heparin as a Bundler in a Self-Assembled Fibrous Network of Functionalized Protein-Based Polymers.

    PubMed

    Włodarczyk-Biegun, Małgorzata K; Slingerland, Cornelis J; Werten, Marc W T; van Hees, Ilse A; de Wolf, Frits A; de Vries, Renko; Stuart, Martien A Cohen; Kamperman, Marleen

    2016-06-13

    Nature shows excellent control over the mechanics of fibrous hydrogels by assembling protein fibers into bundles of well-defined dimensions. Yet, obtaining artificial materials displaying controlled bundling remains a challenge. Here, we developed genetically engineered protein-based polymers functionalized with heparin-binding KRSR domains and show controlled bundling using heparin as a binder. The protein polymer forms fibers upon increasing the pH to physiological values and at higher concentrations fibrous gels. We show that addition of heparin to the protein polymer with incorporated KRSR domains, induces bundling, which results in faster gel formation and stiffer gels. The interactions are expected to be primarily electrostatic and fiber bundling has an optimum when the positive charges of KRSR are approximately in balance with the negative charges of the heparin. Our study suggests that, generally, a straightforward method to control the properties of fibrous gels is to prepare a fiber former with specific binding domains and then simply adding an appropriate amount of binder. PMID:27129090

  4. On the origin of Gaussian network theory in the thermo/chemo-responsive shape memory effect of amorphous polymers undergoing photo-elastic transition

    NASA Astrophysics Data System (ADS)

    Lu, Haibao; Huang, Wei Min; Leng, Jinsong

    2016-06-01

    Amorphous polymers are normally isotropic in their physical properties, however, upon stress their structural randomness is disturbed and they become anisotropic. There is a close connection between the optical anisotropy and the elastic (or mechanical) anisotropy, since both are related to the type of symmetry exhibited by the molecular structure. On the origin of Gaussian network theory, a phenomenological constitutive framework was proposed to study the photo-elastic transition and working mechanism of the thermo-/chemo-responsive shape-memory effect (SME) in amorphous shape memory polymers (SMPs). Optically refractive index was initially employed to couple the stress, strain and the anisotropy of the random link in macromolecule chain. Based on the Arrhenius law, a constitutive framework was then applied for the temperature dependence of optical (or elastic or mechanical) anisotropy according to the fictive temperature parameter. Finally, the phenomenological photo-elastic model was proposed to quantitatively identify the influential factors behind the thermo-/chemo-responsive SME in SMPs, of which the shape recovery behavior is predicted and verified by the available experimental data reported in the literature.

  5. Adsorption of ammonium and phosphate by feather protein based semi-interpenetrating polymer networks hydrogel as a controlled-release fertilizer.

    PubMed

    Su, Yuan; Liu, Jia; Yue, Qinyan; Li, Qian; Gao, Baoyu

    2014-01-01

    A new feather protein-grafted poly(potassium acrylate)/polyvinyl alcohol (FP-g-PKA/PVA) semi-interpenetrating polymer networks (semi-IPNs) hydrogel was produced through graft copolymerization with FP as a basic macromolecular skeletal material, acrylic acid as a monomer and PVA as a semi-IPNs polymer. The adsorption of ammonium and phosphate ions from aqueous solution using the new hydrogel as N and P controlled-release fertilizer with water-retention capacity was studied. The effects of pH value, concentration, contact time and ion strength on NH4+ and PO3-4 removal by FP-g-PKA/PVA semi-IPNs hydrogel were investigated using batch adsorption experiments. The results indicated that the hydrogel had high adsorption capacities and fast adsorption rates for NH4+ and PO3-4 in wide pH levels ranging from 4.0 to 9.0. Kinetic analysis presented that both NH4+ and PO3-4 removal were closely fitted with the pseudo-second-order model. Furthermore, the adsorption isotherms of hydrogel were best represented by the Freundlich model. The adsorption-desorption experimental results showed the sustainable stability of FP-g-PKA/PVA semi-IPNs hydrogel for NH4+ and PO3-4 removal. Overall, FP-g-PKA/PVA could be considered as an efficient material for the removal and recovery of nitrogen and phosphorus with the agronomic reuse as a fertilizer. PMID:24600885

  6. Bio-based Interpenetrating Network Polymer Composites from Locust Sawdust as Coating Material for Environmentally Friendly Controlled-Release Urea Fertilizers.

    PubMed

    Zhang, Shugang; Yang, Yuechao; Gao, Bin; Wan, Yongshan; Li, Yuncong C; Zhao, Chenhao

    2016-07-20

    A novel polymer-coated nitrogen (N) fertilizer was developed using bio-based polyurethane (PU) derived from liquefied locust sawdust as the coating material. The bio-based PU was successfully coated on the surface of the urea fertilizer prills to form polymer-coated urea (PCU) fertilizer for controlled N release. Epoxy resin (EP) was also used to further modify the bio-based PU to synthesize the interpenetrating network (IPN), enhancing the slow-release properties of the PCU. The N release characteristics of the EP-modified PCU (EMPCU) in water were determine at 25 °C and compared to that of PCU and EP-coated urea (ECU). The results showed that the EP modification reduced the N release rate and increased the longevity of the fertilizer coated with bio-based PU. A corn growth study was conducted to further evaluate the filed application of the EMPCU. In comparison to commercial PCU and conventional urea fertilizer, EMPCU was more effective and increased the yield and total dry matter accumulation of the corn. Findings from this work indicated that bio-based PU derived from sawdust can be used as coating materials for PCU, particularly after EP modification. The resulting EMPCU was more environmentally friendly and cost-effective than conventional urea fertilizers coated by EP. PMID:27352017

  7. Bio-based Interpenetrating Network Polymer Composites from Locust Sawdust as Coating Material for Environmentally Friendly Controlled-Release Urea Fertilizers.

    PubMed

    Zhang, Shugang; Yang, Yuechao; Gao, Bin; Wan, Yongshan; Li, Yuncong C; Zhao, Chenhao

    2016-07-20

    A novel polymer-coated nitrogen (N) fertilizer was developed using bio-based polyurethane (PU) derived from liquefied locust sawdust as the coating material. The bio-based PU was successfully coated on the surface of the urea fertilizer prills to form polymer-coated urea (PCU) fertilizer for controlled N release. Epoxy resin (EP) was also used to further modify the bio-based PU to synthesize the interpenetrating network (IPN), enhancing the slow-release properties of the PCU. The N release characteristics of the EP-modified PCU (EMPCU) in water were determine at 25 °C and compared to that of PCU and EP-coated urea (ECU). The results showed that the EP modification reduced the N release rate and increased the longevity of the fertilizer coated with bio-based PU. A corn growth study was conducted to further evaluate the filed application of the EMPCU. In comparison to commercial PCU and conventional urea fertilizer, EMPCU was more effective and increased the yield and total dry matter accumulation of the corn. Findings from this work indicated that bio-based PU derived from sawdust can be used as coating materials for PCU, particularly after EP modification. The resulting EMPCU was more environmentally friendly and cost-effective than conventional urea fertilizers coated by EP.

  8. Adsorption of ammonium and phosphate by feather protein based semi-interpenetrating polymer networks hydrogel as a controlled-release fertilizer.

    PubMed

    Su, Yuan; Liu, Jia; Yue, Qinyan; Li, Qian; Gao, Baoyu

    2014-01-01

    A new feather protein-grafted poly(potassium acrylate)/polyvinyl alcohol (FP-g-PKA/PVA) semi-interpenetrating polymer networks (semi-IPNs) hydrogel was produced through graft copolymerization with FP as a basic macromolecular skeletal material, acrylic acid as a monomer and PVA as a semi-IPNs polymer. The adsorption of ammonium and phosphate ions from aqueous solution using the new hydrogel as N and P controlled-release fertilizer with water-retention capacity was studied. The effects of pH value, concentration, contact time and ion strength on NH4+ and PO3-4 removal by FP-g-PKA/PVA semi-IPNs hydrogel were investigated using batch adsorption experiments. The results indicated that the hydrogel had high adsorption capacities and fast adsorption rates for NH4+ and PO3-4 in wide pH levels ranging from 4.0 to 9.0. Kinetic analysis presented that both NH4+ and PO3-4 removal were closely fitted with the pseudo-second-order model. Furthermore, the adsorption isotherms of hydrogel were best represented by the Freundlich model. The adsorption-desorption experimental results showed the sustainable stability of FP-g-PKA/PVA semi-IPNs hydrogel for NH4+ and PO3-4 removal. Overall, FP-g-PKA/PVA could be considered as an efficient material for the removal and recovery of nitrogen and phosphorus with the agronomic reuse as a fertilizer.

  9. Physical properties of a high molecular weight hydroxyl-terminated polydimethylsiloxane modified castor oil based polyurethane/epoxy interpenetrating polymer network composites

    NASA Astrophysics Data System (ADS)

    Chen, Shoubing; Wang, Qihua; Wang, Tingmei

    2011-06-01

    A series of polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites modified by a high molecular weight hydroxyl-terminated polydimethylsiloxane (HTPDMS) were prepared. The effects of HTPDMS content on the phase structure, damping properties and the glass transition temperature ( Tg) of the HTPDMS-modified PU/EP IPN composites were studied by scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). Thermogravimetric analysis (TGA) showed that the thermal decomposition temperature of the composites increased with the increase of HTPDMS content. The tensile strength and impact strength of the IPN composites were also significantly improved, especially when the HTPDMS content was 10%. The modified IPN composites were expected to be used as structural damping materials in the future.

  10. Three-dimensional activated graphene network-sulfonate-terminated polymer nanocomposite as a new electrode material for the sensitive determination of dopamine and heavy metal ions.

    PubMed

    Yuan, Xiaoyan; Zhang, Yijia; Yang, Lu; Deng, Wenfang; Tan, Yueming; Ma, Ming; Xie, Qingji

    2015-03-01

    We report here that three-dimensional activated graphene networks (3DAGNs) are a better matrix to prepare graphene-polymer nanocomposites for sensitive electroanalysis than two-dimensional graphene nanosheets (2DGNs). 3DAGNs were synthesized in advance by the direct carbonization and simultaneous chemical activation of a cobalt ion-impregnated D113-type ion exchange resin, which showed an interconnected network structure and a large specific surface area. Then, the 3DAGN-sulfonate-terminated polymer (STP) nanocomposite was prepared via the in situ chemical co-polymerization of m-aminobenzene sulfonic acid and aniline in the presence of 3DAGNs. The 3DAGN-STP nanocomposite can adsorb dopamine (DA) and heavy metal ions, which was confirmed by quartz crystal microbalance studies. The 3DAGN-STP modified glassy carbon electrode (GCE) was used for the electrochemical detection of DA in the presence of ascorbic acid and uric acid, with a linear response range of 0.1-32 μM and a limit of detection of 10 nM. In addition, differential pulse voltammetry was used for the simultaneous determination of Cd(2+) and Pb(2+) at the 3DAGN-STP/GCE further modified with a bismuth film, exhibiting linear response ranges of 1-70 μg L(-1) for Cd(2+) and 1-80 μg L(-1) for Pb(2+) with limits of detection of 0.1 μg L(-1) for Cd(2+) and 0.2 μg L(-1) for Pb(2+). Because the 3DAGN-STP can integrate the advantages of 3DAGNs with STPs, the 3DAGN-STP/GCE was more sensitive than the bare GCE, 3DAGN/GCE, and 2DGN-STP/GCE for the determination of DA and heavy metal ions. PMID:25611429

  11. Physical Organic Chemistry of Supramolecular Polymers

    PubMed Central

    Serpe, Michael J.; Craig, Stephen L.

    2008-01-01

    Unlike the case of traditional covalent polymers, the entanglements that determine properties of supramolecular polymers are defined by very specific, intermolecular interactions. Recent work using modular molecular platforms to probe the mechanisms underlying mechanical response of supramolecular polymers is reviewed. The contributions of supramolecular kinetics, thermodynamics, and conformational flexibility to supramolecular polymer properties in solutions of discrete polymers, in networks, and at interfaces, are described. Molecule-to-material relationships are established through methods reminiscent of classic physical organic chemistry. PMID:17279638

  12. Porous polymer media

    DOEpatents

    Shepodd, Timothy J.

    2002-01-01

    Highly crosslinked monolithic porous polymer materials for chromatographic applications. By using solvent compositions that provide not only for polymerization of acrylate monomers in such a fashion that a porous polymer network is formed prior to phase separation but also for exchanging the polymerization solvent for a running buffer using electroosmotic flow, the need for high pressure purging is eliminated. The polymer materials have been shown to be an effective capillary electrochromatographic separations medium at lower field strengths than conventional polymer media. Further, because of their highly crosslinked nature these polymer materials are structurally stable in a wide range of organic and aqueous solvents and over a pH range of 2-12.

  13. Formulation and characterisation of tetracycline-containing bioadhesive polymer networks designed for the treatment of periodontal disease.

    PubMed

    Jones, David S; Lawlor, Michelle S; Woolfson, A David

    2004-01-01

    This study described the drug release, rheological (dynamic and flow) and textural/mechanical properties of a series of formulations composed of 15% w/w polymethylvinylether-co-maleic anhydride (PMVE-MA), 0-9% w/w polyvinylpyrrolidone (PVP) and containing 1-5% w/w tetracycline hydrochloride, designed for the treatment of periodontal disease. All formulations exhibited pseudoplastic flow with minimal thixotropy. Increasing the concentration of PVP sequentially increased the zero-rate viscosity (derived from the Cross model) and the hardness and compressibility of the formulations (derived from texture profile analysis). These affects may be accredited to increased polymer entanglement and, in light of the observed synergy between the two polymers with respect to their textural and rheological properties, interaction between PVP and PMVE-MA. Increasing the concentration of PVP increased the storage and loss moduli yet decreased the loss tangent of all formulations, indicative of increased elastic behaviour. Synergy between the two polymers with respect to their viscoelastic properties was observed. Increased adhesiveness, associated with increased concentrations of PVP was ascribed to the increasing bioadhesion and tack of the formulations. The effect of increasing drug concentration on the rheological and textural properties was dependent on PVP concentration. At lower concentrations (0, 3% w/w) no effect was observed whereas, in the presence of 9% w/w PVP, increasing drug concentration increased formulation elasticity, zero rate viscosity, hardness and compressibility. These observations were ascribed to the greater mass of suspended drug in formulations containing the highest concentration of PVP. Drug release from formulations containing 6 and 9% PVP (and 5% w/w drug) was prolonged and swelling/diffusion controlled. Based on the drug release, rheological and textural properties, it is suggested that the formulation containing 15% w/w PMVE-MA, 6% w/w PVP and

  14. Confined polymers in the extended de Gennes regime

    NASA Astrophysics Data System (ADS)

    Mehlig, Bernhard

    In the ''extended de Gennes regime'' the problem of describing the conformations of a semiflexible polymer confined to a channel can be mapped onto the weakly self-avoiding random-walk model. For large contour lengths the asymptotically exact solution of this model predicts how the conformational fluctuations of the confined polymer depend upon the channel dimensions and upon the physical properties of the polymer, its effective width and persistence length. The extended de Gennes regime (where the polymer is neither weakly nor strongly confined) has recently been studied intensively experimentally and by means of computer simulations of worm-like chain models. In this talk I explain the mapping, summarise the predictions derived from the exact solution, and compare the predictions to results of computer simulations [Dorfman et al.] and experiments [Westerlund et al.] of DNA molecules confined to nanochannels. I conclude by summarising open questions. This talk is mainly based on joint work with E. Werner [Phys Rev. E 90 (2014) 062602].

  15. Finite-size corrections for confined polymers in the extended de Gennes regime

    NASA Astrophysics Data System (ADS)

    Smithe, Toby St Clere; Iarko, Vitalii; Muralidhar, Abhiram; Werner, Erik; Dorfman, Kevin D.; Mehlig, Bernhard

    2015-12-01

    Theoretical results for the extension of a polymer confined to a channel are usually derived in the limit of infinite contour length. But experimental studies and simulations of DNA molecules confined to nanochannels are not necessarily in this asymptotic limit. We calculate the statistics of the span and the end-to-end distance of a semiflexible polymer of finite length in the extended de Gennes regime, exploiting the fact that the problem can be mapped to a one-dimensional weakly self-avoiding random walk. The results thus obtained compare favorably with pruned-enriched Rosenbluth method (PERM) simulations of a three-dimensional discrete wormlike chain model of DNA confined in a nanochannel. We discuss the implications for experimental studies of linear λ -DNA confined to nanochannels at the high ionic strengths used in many experiments.

  16. 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.

  17. Synthesis and water absorption transport mechanism of a pH-sensitive polymer network structured on vinyl-functionalized pectin.

    PubMed

    Guilherme, Marcos R; Moia, Thais A; Reis, Adriano V; Paulino, Alexandre T; Rubira, Adley F; Mattoso, Luiz H C; Muniz, Edvani C; Tambourgi, Elias B

    2009-01-12

    Polysaccharide-structured copolymer hydrogel having excellent pH-sensitivity was developed from N,N-dimethylacrylamide (DMAc) and vinyl-functionalized Pectin (Pec). The Pec was vinyl-functionalized by way of chemical reaction with glycidyl metacrylate (GMA) in water under acidic and thermal stimuli. 13C NMR, 1H NMR, and FT-IR spectra revealed that the vinyl groups coming from the GMA were attached onto backbone of the polysaccharide. The hydrogels were obtained by polymerization of the Pec-vinyl with the DMAc. 13C-CP/MAS NMR and FTIR spectra confirmed that the gelling process occurred by way of the vinyl groups attached on Pec-vinyl backbone. The values of apparent swelling rate constant (k) decreased appreciably for pH greater than 6, demonstrating the swelling process of the hydrogel becomes slower at more alkaline conditions. There was an increase of diffusional exponent (n) with increasing pH of the surrounding liquid. This means the water absorption profile becomes more dependent on the polymer relaxation in basified swelling media. In this condition, a longer water absorption half-time (t1/2) was verified, suggesting the polymer relaxation mechanism of the hydrogel would have a considerable effect on the t1/2.

  18. Hydrogel-elastomer composite biomaterials: 2. Effects of aging methacrylated gelatin solutions on the preparation and physical properties of interpenetrating polymer networks.

    PubMed

    Peng, Henry T; Mok, Michelle; Martineau, Lucie; Shek, Pang N

    2007-06-01

    This study was conducted to understand the effects of aging methacrylated gelatin solutions on the properties of gelatin-HydroThane Interpenetrating Polymer Network (IPN) films. The latter were prepared from methacrylated gelatin solutions that were either freshly made or stored at different concentrations and temperatures for various periods. The morphology, swelling stability and mechanical properties of the IPNs were then accordingly characterized. The IPNs prepared with aged solutions showed a reduced phase separation; changed from a network-like structure to a continuous phase structure; and demonstrated higher swelling stabilities and higher elasticity under optimal aging conditions, compared to the IPN prepared with a fresh methacrylated gelatin solution. An increase in viscosity and a change in phase transition of aged methacrylated gelatin solutions were also observed, presumably due to the physical structuring of methacrylated gelatin chains (e.g., by the formation of a helix structure), thus altering the resulting IPN characteristics. A better understanding of the effects of aging methacrylated gelatin solution on the formation and properties of gelatin-HydroThane IPNs should enable us to further develop our composite biomaterials for different dressing applications.

  19. All-silicone prestrain-locked interpenetrating polymer network elastomers: free-standing silicone artificial muscles with improved performance and robustness

    NASA Astrophysics Data System (ADS)

    Brochu, P.; Stoyanov, H.; Niu, X.; Pei, Q.

    2013-05-01

    We present a novel all-silicone prestrain-locked interpenetrating polymer network (all-S-IPN) elastomer for use as a muscle-like actuator. The elastomer is fabricated using a combination of two silicones: a soft room temperature vulcanizing (RTV) silicone that serves as the host elastomer matrix, and a more rigid high temperature vulcanizing (HTV) silicone that acts to preserve the prestrain in the host network. In our novel S-IPN fabrication procedure we co-dissolve the RTV and HTV silicones in a common solvent, cast thin films, and allow the RTV silicone to cure before applying prestrain and finally curing the HTV silicone to lock in the prestrain. The free-standing prestrain-locked silicones show a performance improvement over standard free-standing silicone films, with a linear strain of 25% and an area strain of 45% when tested in a diaphragm configuration. We show that the process can also be used to improve electrode adhesion and stability as well as improve the interlayer adhesion in multilayer actuators. We demonstrate that, when coupled with carbon nanotube electrodes, fault-tolerance through self-clearing can be observed. We use the fault-tolerance and improved interlayer adhesion to demonstrate stable long-life (>30 000 cycles at >20% strain) actuation and repeated high-performance actuation (>500 cycles at ∼40% strain) of prestrained free-standing multilayer actuators driving a load.

  20. Effects of Using Silica Fume and Polycarboxylate-Type Superplasticizer on Physical Properties of Cementitious Grout Mixtures for Semiflexible Pavement Surfacing

    PubMed Central

    Karim, Mohamed Rehan; Mahmud, Hilmi; Mashaan, Nuha S.; Katman, Herdayati; Husain, Nadiah Md

    2014-01-01

    Semi-flexible pavement surfacing is a composite pavement that utilizes the porous pavement structure of the flexible bituminous pavement, which is subsequently grouted with appropriate cementitious materials. This study aims to investigate the compressive strength, flexural strength, and workability performance of cementitious grout. The grout mixtures are designed to achieve high strength and maintain flow properties in order to allow the cement slurries to infiltrate easily through unfilled compacted skeletons. A paired-sample t-test was carried out to find out whether water/cement ratio, SP percentages, and use of silica fume influence the cementitious grout performance. The findings showed that the replacement of 5% silica fume with an adequate amount of superplasticizer and water/cement ratio was beneficial in improving the properties of the cementitious grout. PMID:24526911

  1. Transport properties of rigid bent-rod macromolecules and of semiflexible broken rods in the rigid-body treatment. Analysis of the flexibility of myosin rod.

    PubMed Central

    Iniesta, A; Díaz, F G; García de la Torre, J

    1988-01-01

    The translational diffusion coefficients, rotational relaxation times and intrinsic viscosities of rigid bent rods, composed by two rodlike arms joined rigidly at an angle alpha, have been evaluated for varying conformation using the latest advances in hydrodynamic theory. We have considered semiflexible rods in which the joint is an elastic hinge or swivel, with a potential V(alpha) = 1/2Q alpha 2 with constant Q. Accepting the rigid-body treatment, we calculate properties of broken rods by averaging alpha-dependent values for rigid rods. The results are finally used to interpret literature values of the properties of myosin rod. Q is regarded as an adjustable parameter, and the value fitted is such that the average bending angle of myosin rod is approximately 60 degrees. PMID:3207825

  2. Effects of using silica fume and polycarboxylate-type superplasticizer on physical properties of cementitious grout mixtures for semiflexible pavement surfacing.

    PubMed

    Koting, Suhana; Karim, Mohamed Rehan; Mahmud, Hilmi; Mashaan, Nuha S; Ibrahim, Mohd Rasdan; Katman, Herdayati; Husain, Nadiah Md

    2014-01-01

    Semi-flexible pavement surfacing is a composite pavement that utilizes the porous pavement structure of the flexible bituminous pavement, which is subsequently grouted with appropriate cementitious materials. This study aims to investigate the compressive strength, flexural strength, and workability performance of cementitious grout. The grout mixtures are designed to achieve high strength and maintain flow properties in order to allow the cement slurries to infiltrate easily through unfilled compacted skeletons. A paired-sample t-test was carried out to find out whether water/cement ratio, SP percentages, and use of silica fume influence the cementitious grout performance. The findings showed that the replacement of 5% silica fume with an adequate amount of superplasticizer and water/cement ratio was beneficial in improving the properties of the cementitious grout.

  3. Effects of using silica fume and polycarboxylate-type superplasticizer on physical properties of cementitious grout mixtures for semiflexible pavement surfacing.

    PubMed

    Koting, Suhana; Karim, Mohamed Rehan; Mahmud, Hilmi; Mashaan, Nuha S; Ibrahim, Mohd Rasdan; Katman, Herdayati; Husain, Nadiah Md

    2014-01-01

    Semi-flexible pavement surfacing is a composite pavement that utilizes the porous pavement structure of the flexible bituminous pavement, which is subsequently grouted with appropriate cementitious materials. This study aims to investigate the compressive strength, flexural strength, and workability performance of cementitious grout. The grout mixtures are designed to achieve high strength and maintain flow properties in order to allow the cement slurries to infiltrate easily through unfilled compacted skeletons. A paired-sample t-test was carried out to find out whether water/cement ratio, SP percentages, and use of silica fume influence the cementitious grout performance. The findings showed that the replacement of 5% silica fume with an adequate amount of superplasticizer and water/cement ratio was beneficial in improving the properties of the cementitious grout. PMID:24526911

  4. The development of a high-throughput gradient array apparatus for the study of porous polymer networks.

    SciTech Connect

    Majumdar, Partha; Lee, Elizabeth; Chisholm, Bret J.; Dirk, Shawn M.; Weisz, Michael; Bahr, James; Schiele, Kris

    2010-01-01

    A gradient array apparatus was constructed for the study of porous polymers produced using the process of chemically-induced phase separation (CIPS). The apparatus consisted of a 60 element, two-dimensional array in which a temperature gradient was placed in the y-direction and composition was varied in the x-direction. The apparatus allowed for changes in opacity of blends to be monitored as a function of temperature and cure time by taking images of the array with time. The apparatus was validated by dispense a single blend composition into all 60 wells of the array and curing them for 24 hours and doing the experiment in triplicate. Variations in micron scale phase separation were readily observed as a function of both curing time and temperature and there was very good well-to-well consistency as well as trial-to-trial consistency. Poragen of samples varying with respect to cure temperature was removed and SEM images were obtained. The results obtained showed that cure temperature had a dramatic affect on sample morphology, and combining data obtained from visual observations made during the curing process with SEM data can enable a much better understanding of the CIPS process and provide predictive capability through the relatively facile generation of composition-process-morphology relationships. Data quality could be greatly enhanced by making further improvements in the apparatus. The primary improvements contemplated include the use of a more uniform light source, an optical table, and a CCD camera with data analysis software. These improvements would enable quantification of the amount of scattered light generated from individual elements as a function of cure time. In addition to the gradient array development, porous composites were produced by incorporating metal particles into a blend of poragen, epoxy resin, and crosslinker. The variables involved in the experiment were metal particle composition, primary metal particle size, metal concentration

  5. Soft-materials: From colloids on templates to polymers in nematics

    NASA Astrophysics Data System (ADS)

    Zhang, Jian

    We describe two major experimental studies on colloidal systems. We demonstrate that square two-dimensional grating templates can drive the growth of three-dimensional, face-centered-cubic (fcc) colloidal crystals by convective assembly. The square symmetry [i.e. (100) planes parallel to the substrate] of the underlying templates was transferred to the colloidal crystals and maintained throughout their growth of ˜50 layers. We characterized crystals grown on flat and on templated substrates using electron microscopy and small-angle x-ray scattering (SAXS). SAXS measurements of the templated samples clearly revealed four-fold diffraction patterns that arise from fcc domains without stacking faults. In a different vein, we investigated how polymers behave in colloidal nematic liquid crystals. Semi-flexible polymers with persistence lengths varying from 0.05 to 16 mum were dissolved in a nematic liquid crystal of rod-like virus fd. The polymers were directly visualized with fluorescence optical microscopy and their fluctuations were quantitatively analyzed. A coil-to-rod transition of the semiflexible polymers was observed when the background phase evolved from isotropic to the nematic phase. We found that semiflexible filaments' long wavelength fluctuations were the result of the tight coupling to the background nematic field's fluctuation. The Odijk deflection length and the elastic constant of the background nematic phase were extracted from our experimental data. In addition to the experimental work described above, we have developed a wide range of particle synthesis capabilities in the laboratory. While all of these procedures were based on previous work, in many cases we developed techniques to improve yield and/or generate new kinds of colloidal particles. We used emulsion polymerization and sol-gel process to synthesize organic PMMA colloid particles and inorganic silica and Zinc Sulfide (ZnS) colloid particles. For the PMMA (polymethyl methacrylate

  6. Process for controlling morphology and improving thermal mechanical performance of high performance interpenetrating and semiinterpenetrating polymer networks

    NASA Technical Reports Server (NTRS)

    Pater, Ruth H. (Inventor); Hansen, Marion G. (Inventor)

    1998-01-01

    In the process of the present invention, a non-polar, aprotic solvent is removed from an oligomer/polymer solution by freeze-drying in order to produce IPNs and semi-IPNs. By thermally quenching the solution to a solid in a short length of time, the size of the minor constituent-rich regions is greatly reduced as they are excluded along with the major constituent from the regions of crystallizing solvent. The use of this process sequence of controlling phase morphology provides IPNs and semi-IPNs with improved fracture toughness, microcracking resistance, and other physical-mechanical properties as compared to IPNs and semi-IPNs formed when the solvent is evaporated rather than sublimed.

  7. Process for controlling morphology and improving thermal-mechanical performance of high performance interpenetrating and semi-interpenetrating polymer networks

    NASA Technical Reports Server (NTRS)

    Pater, Ruth H. (Inventor); Hansen, Marion G. (Inventor)

    1997-01-01

    In the process of the present invention, a non-polar, aprotic solvent is removed from an oligomer/polymer solution by freeze-drying in order to produce IPNs and semi-IPNs. By thermally quenching the solution to a solid in a short length of time, the size of the minor constituent-rich regions is greatly reduced as they are excluded along with the major constituent from the regions of crystallizing solvent. The use of this process sequence of controlling phase morphology provides IPNs and semi-IPNs with improved fracture toughness, microcracking resistance, and other physical-mechanical properties as compared to IPNs and semi-IPNs formed when the solvent is evaporated rather than sublimed.

  8. Microgravity Polymers

    NASA Technical Reports Server (NTRS)

    1986-01-01

    A one-day, interactive workshop considering the effects of gravity on polymer materials science was held in Cleveland, Ohio, on May 9, 1985. Selected programmatic and technical issues were reviewed to introduce the field to workshop participants. Parallel discussions were conducted in three disciplinary working groups: polymer chemistry, polymer physics, and polymer engineering. This proceedings presents summaries of the workshop discussions and conclusions.

  9. Oil and fat absorbing polymers

    NASA Technical Reports Server (NTRS)

    Marsh, H. E., Jr. (Inventor)

    1977-01-01

    A method is described for forming a solid network polymer having a minimal amount of crosslinking for use in absorbing fats and oils. The polymer remains solid at a swelling ratio in oil or fat of at least ten and provides an oil absorption greater than 900 weight percent.

  10. Highly enhanced dynamics of microdomains ordering by solvent vapor annealing of thin block copolymer films on polymer network supports

    NASA Astrophysics Data System (ADS)

    Tsarkova, Larisa; Stenbock-Fermor, Anja; Böker, Alexander; Knoll, Armin; IBM Reserach Collaboration; DWI Team

    2014-03-01

    We studied the solvent driven ordering dynamics of block copolymer films supported by a densely cross-linked organic hard mask (HM) designed for lithographic fabrication. We found that the ordering of microphase separated domains on the HM layer proceeds significantly faster as compared to similar films on silicon wafers. This leads to a pronounced enhancement of the dynamics of both the terrace-formation as well as the long-range lateral ordering of the microdomains. The effect is independent on the chemical structure and volume composition of the studied block copolymers (cylinder-/ lamella-forming). Importantly, enhanced ordering is achieved even at a reduced degree of swelling corresponding to an intermediate to strong segregation regime, when similar films on conventional substrate show very limited ordering. In-situ ellipsometric measurements of the swollen films revealed an insignificant increase by 1-3 vol. % in the solvent up-take by HM-supported films. Therefore we attribute the enhanced dynamics to reduced interactions at the block copolymer/HM-support interface. Apart from immediate technological impact in block copolymer-assisted nanolithography, our findings convey novel insight into effects of molecular architecture on polymer-solvent interactions. Forckenbeckstr. 50 52056 Aachen, Germany.

  11. Glass-like dynamics of the strain-induced coil/helix transition on a permanent polymer network

    NASA Astrophysics Data System (ADS)

    Ronsin, O.; Caroli, C.; Baumberger, T.

    2016-02-01

    We study the stress response to a step strain of covalently bonded gelatin gels in the temperature range where triple helix reversible crosslink formation is prohibited. We observe slow stress relaxation towards a T-dependent finite asymptotic level. We show that this is assignable to the strain-induced coil → helix transition, previously evidenced by Courty et al. [Proc. Natl. Acad. Sci. U. S. A. 102, 13457 (2005)], of a fraction of the polymer strands. Relaxation proceeds, in a first stage, according to a stretched exponential dynamics, then crosses over to a terminal simple exponential decay. The respective characteristic times τK and τf exhibit an Arrhenius-like T-dependence with an associated energy E incompatibly larger than the activation barrier height for the isomerisation process which sets the clock for an elementary coil → helix transformation event. We tentatively assign this glass-like slowing down of the dynamics to the long-range couplings due to the mechanical noise generated by the local elementary events in this random elastic medium.

  12. Monte Carlo simulations of lattice models for single polymer systems

    SciTech Connect

    Hsu, Hsiao-Ping

    2014-10-28

    Single linear polymer chains in dilute solutions under good solvent conditions are studied by Monte Carlo simulations with the pruned-enriched Rosenbluth method up to the chain length N∼O(10{sup 4}). Based on the standard simple cubic lattice model (SCLM) with fixed bond length and the bond fluctuation model (BFM) with bond lengths in a range between 2 and √(10), we investigate the conformations of polymer chains described by self-avoiding walks on the simple cubic lattice, and by random walks and non-reversible random walks in the absence of excluded volume interactions. In addition to flexible chains, we also extend our study to semiflexible chains for different stiffness controlled by a bending potential. The persistence lengths of chains extracted from the orientational correlations are estimated for all cases. We show that chains based on the BFM are more flexible than those based on the SCLM for a fixed bending energy. The microscopic differences between these two lattice models are discussed and the theoretical predictions of scaling laws given in the literature are checked and verified. Our simulations clarify that a different mapping ratio between the coarse-grained models and the atomistically realistic description of polymers is required in a coarse-graining approach due to the different crossovers to the asymptotic behavior.

  13. Polymer-facilitated low temperature fusing of spray-coated silver nanowire networks as transparent top and bottom electrodes in small molecule organic photovoltaics (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Selzer, Franz; Weiß, Nelli; Kneppe, David; Bormann, Ludwig; Sachse, Christoph; Gaponik, Nikolai; Eychmüller, Alexander; Leo, Karl; Müller-Meskamp, Lars

    2015-10-01

    Networks of silver nanowires (AgNWs) are promising candidates for transparent conducting electrodes in organic photovoltaics (OPV), as they achieve similar performance as the commonly used indium tin oxide (ITO) at lower cost and increased flexibility. The initial sheet resistance (Rs) of AgNW electrodes typically needs to be reduced by a post-annealing step (90 min@200 °C), being detrimental for processing on polymeric substrates. We present novel low temperature-based methods to integrate AgNWs in organic small molecule-based photovoltaics, either as transparent and highly conductive bottom-electrode or, for the first time, as spray-coated AgNW top-electrode. The bottom-electrodes are prepared by organic matrix assisted low-temperature fusing. Here, selected polymers are coated below the AgNWs to increase the interaction between NWs and substrate. In comparison to networks without these polymeric sublayers, the Rs is reduced by two orders of magnitude. AgNW top-electrodes are realized by dispersing modified high-quality AgNWs in inert solvents, which do not damage small molecule layers. Accordingly, our AgNW dispersion can be spray-coated onto all kind of OPV devices. Both bottom- and top-electrodes show a Rs of <11 Ω/ at >87 % transparency directly after spray-coating at very low substrate temperatures of <80 °C. We also demonstrate the implementation of our AgNW electrodes in organic solar cells. The corresponding devices show almost identical performance compared to organic solar cells exploiting ITO as bottom or thermally evaporated thin-metal as top-electrode.

  14. Polyvinylpyrrolidone-based semi-interpenetrating polymer networks as highly selective and chemically stable membranes for all vanadium redox flow batteries

    NASA Astrophysics Data System (ADS)

    Zeng, L.; Zhao, T. S.; Wei, L.; Zeng, Y. K.; Zhang, Z. H.

    2016-09-01

    Vanadium redox flow batteries (VRFBs) with their high flexibility in configuration and operation, as well as long cycle life are competent for the requirement of future energy storage systems. Nevertheless, due to the application of perfluorinated membranes, VRFBs are plagued by not only the severe migration issue of vanadium ions, but also their high cost. Herein, we fabricate semi-interpenetrating polymer networks (SIPNs), consisting of cross-linked polyvinylpyrrolidone (PVP) and polysulfone (PSF), as alternative membranes for VRFBs. It is demonstrated that the PVP-based SIPNs exhibit extremely low vanadium permeabilities, which contribute to the well-established hydrophilic/hydrophobic microstructures and the Donnan exclusion effect. As a result, the coulombic efficiencies of VRFBs with PVP-based SIPNs reach almost 100% at 40 mA cm-2 to 100 mA cm-2; the energy efficiencies are more than 3% higher than those of VRFBs with Nafion 212. More importantly, the PVP-based SIPNs exhibit a superior chemical stability, as demonstrated both by an ex situ immersion test and continuously cycling test. Hence, all the characterizations and performance tests reported here suggest that PVP-based SIPNs are a promising alternative membrane for redox flow batteries to achieve superior cell performance and excellent cycling stability at the fraction of the cost of perfluorinated membranes.

  15. Nanoscale control of the network morphology of high efficiency polymer fullerene solar cells by the use of high material concentration in the liquid phase.

    PubMed

    Radbeh, R; Parbaile, E; Bouclé, J; Di Bin, C; Moliton, A; Coudert, V; Rossignol, F; Ratier, B

    2010-01-22

    Despite the constant improvement of their power conversion efficiencies, organic solar cells based on an interpenetrating network of a conjugated polymer as donor and fullerene derivatives as acceptor materials still need to be improved for commercial use. In this context, we present a study on the optimization of solar cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) by varying a specific cell parameter, namely the concentration of the active layer components in the liquid phase before blend film deposition, in order to improve device performance and to better understand the relation between morphology and device operation. Our study shows a significant increase of the short-circuit current, open-circuit voltage and cell efficiency by properly choosing the formulation of the initial blend before film deposition. We demonstrate that the active layer morphology, which is strongly dependent on the initial material concentrations and the processing conditions, can greatly impact the electronic characteristics of the device, especially regarding charge recombination dynamics at the donor-acceptor interface. Our optimized P3HT:PCBM device exhibits both slow recombination and high photocurrent generation associated with an overall power conversion efficiency of 4.25% under 100 mW cm(-2) illumination (AM1.5G).

  16. Nanoscale control of the network morphology of high efficiency polymer fullerene solar cells by the use of high material concentration in the liquid phase

    NASA Astrophysics Data System (ADS)

    Radbeh, R.; Parbaile, E.; Bouclé, J.; Di Bin, C.; Moliton, A.; Coudert, V.; Rossignol, F.; Ratier, B.

    2010-01-01

    Despite the constant improvement of their power conversion efficiencies, organic solar cells based on an interpenetrating network of a conjugated polymer as donor and fullerene derivatives as acceptor materials still need to be improved for commercial use. In this context, we present a study on the optimization of solar cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) by varying a specific cell parameter, namely the concentration of the active layer components in the liquid phase before blend film deposition, in order to improve device performance and to better understand the relation between morphology and device operation. Our study shows a significant increase of the short-circuit current, open-circuit voltage and cell efficiency by properly choosing the formulation of the initial blend before film deposition. We demonstrate that the active layer morphology, which is strongly dependent on the initial material concentrations and the processing conditions, can greatly impact the electronic characteristics of the device, especially regarding charge recombination dynamics at the donor-acceptor interface. Our optimized P3HT:PCBM device exhibits both slow recombination and high photocurrent generation associated with an overall power conversion efficiency of 4.25% under 100 mW cm-2 illumination (AM1.5G).

  17. Interpenetrating polymer networks containing gelatin modified with PEGylated RGD and soluble KGF: synthesis, characterization, and application in in vivo critical dermal wound.

    PubMed

    Waldeck, Heather; Chung, Amy S; Kao, Weiyuan John

    2007-09-15

    The purpose of this study was to evaluate the biocompatibility and the efficacy in wound healing of a gelatin-based interpenetrating polymer network (IPN) containing poly(ethylene glycol) (PEG)-ylated RGD and soluble KGF-1 (RGD-IPN+KGF). IPNs were applied to full-thickness wounds on a rat model. Wound healing was assessed through histological grading of the host response and percent area contraction at 2 days, 1 week, 2 weeks, and 3 weeks. A control IPN containing unmodified gelatin (unmod-IPN) and a conventional clinical bandage were applied to similar wounds and also evaluated. During the first week of healing, the unmod-IPN and conventional dressing wound showed a greater amount of contraction than that of RGD-IPN+KGF. However, by 3 weeks the extent of wound contraction was comparable between treatments. The RGD-IPN+KGF treated wound demonstrated lower macrophage and fibroblast densities at 3 weeks as compared to unmod-IPN treated wounds. RGD-IPN+KGF acted as a tissue scaffold while preventing the entry of foreign bodies, advantages not seen with the conventional dressing. The extent of cellularity and extracellular matrix organization was higher for wounds healed with RGD-IPN+KGF than those healed with unmod-IPN. These results indicate that both soluble and immobilized bioactive factors can be incorporated into our IPN platform to enhance the rate and the quality of dermal wound healing.

  18. Ultra-Durable and Transparent Self-Cleaning Surfaces by Large-Scale Self-Assembly of Hierarchical Interpenetrated Polymer Networks.

    PubMed

    Wong, William S Y; Stachurski, Zbigniew H; Nisbet, David R; Tricoli, Antonio

    2016-06-01

    In nature, durable self-cleaning surfaces such as the Lotus leaf rely on the multiscale architecture and cohesive regenerative properties of organic tissue. Real-world impact of synthetic replicas has been limited by the poor mechanical and chemical stability of the ultrafine hierarchical textures required for attaining a highly dewetting superhydrophobic state. Here, we present the low-cost synthesis of large-scale ultradurable superhydrophobic coatings by rapid template-free micronano texturing of interpenetrated polymer networks (IPNs). A highly transparent texture of soft yielding marshmallow-like pillars with an ultralow surface energy is obtained by sequential spraying of a novel polyurethane-acrylic colloidal suspension and a superhydrophobic nanoparticle solution. The resulting coatings demonstrate outstanding antiabrasion resistance, maintaining superhydrophobic water contact angles and a pristine lotus effect with sliding angles of below 10° for up to 120 continuous abrasion cycles. Furthermore, they also have excellent chemical- and photostability, preserving the initial performance upon more than 50 h exposure to intense UVC light (254 nm, 3.3 mW cm(-2)), 24 h of oil contamination, and highly acidic conditions (1 M HCl). This sprayable polyurethane-acrylic colloidal suspension and surface texture provide a rapid and low-cost approach for the substrate-independent fabrication of ultradurable transparent self-cleaning surfaces with superior abrasion, chemical, and UV-resistance.

  19. Interplay between viscoelastic and chemical tunings in fatty-acid-based polyester adhesives: engineering biomass toward functionalized step-growth polymers and soft networks.

    PubMed

    Vendamme, Richard; Olaerts, Katrien; Gomes, Monica; Degens, Marc; Shigematsu, Takayuki; Eevers, Walter

    2012-06-11

    This Article describes the synthesis and characterization of renewable self-adhesive coatings with tunable viscoelastic properties and equipped with well-defined amounts of carboxylic acid "sticker" groups with adhesion promoting characteristics. Hydroxyl-ended polyesters with various architectures (linear, branched) were synthesized by melt polycondensation of dimerized fatty acids and fatty diols and then cured with maleic anhydride-modified triglycerides (such as maleinized soybean oil) in the presence of the amidine catalyst 1,8-diazabicyclo[5.4.0]undec-7-ene. The curing reaction of alcoholysis has the dual effect of chain extending/cross-linking the base polymers via creation of polymeric half-esters linkages while introducing carboxylic acid functions within the gel structure. We demonstrated how the adhesion properties can be finely tuned from molecular design and formulation of the network precursors and how the rheology and functionality of the coatings influence the adhesive bond formation and development. These renewable polyester adhesives proved to be suitable materials for pressure-sensitive adhesives applications with respect to adhesion strength, viscoelasticity, and functionality. In addition, the environmental benefits of such materials are briefly discussed.

  20. Ultra-Durable and Transparent Self-Cleaning Surfaces by Large-Scale Self-Assembly of Hierarchical Interpenetrated Polymer Networks.

    PubMed

    Wong, William S Y; Stachurski, Zbigniew H; Nisbet, David R; Tricoli, Antonio

    2016-06-01

    In nature, durable self-cleaning surfaces such as the Lotus leaf rely on the multiscale architecture and cohesive regenerative properties of organic tissue. Real-world impact of synthetic replicas has been limited by the poor mechanical and chemical stability of the ultrafine hierarchical textures required for attaining a highly dewetting superhydrophobic state. Here, we present the low-cost synthesis of large-scale ultradurable superhydrophobic coatings by rapid template-free micronano texturing of interpenetrated polymer networks (IPNs). A highly transparent texture of soft yielding marshmallow-like pillars with an ultralow surface energy is obtained by sequential spraying of a novel polyurethane-acrylic colloidal suspension and a superhydrophobic nanoparticle solution. The resulting coatings demonstrate outstanding antiabrasion resistance, maintaining superhydrophobic water contact angles and a pristine lotus effect with sliding angles of below 10° for up to 120 continuous abrasion cycles. Furthermore, they also have excellent chemical- and photostability, preserving the initial performance upon more than 50 h exposure to intense UVC light (254 nm, 3.3 mW cm(-2)), 24 h of oil contamination, and highly acidic conditions (1 M HCl). This sprayable polyurethane-acrylic colloidal suspension and surface texture provide a rapid and low-cost approach for the substrate-independent fabrication of ultradurable transparent self-cleaning surfaces with superior abrasion, chemical, and UV-resistance. PMID:27203856