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Sample records for a2b copolymer melts

  1. Morphology diagrams for A2B copolymer melts: real-space self-consistent field theory

    SciTech Connect

    Kumar, Rajeev; Sides, Scott; Mays, Jimmy; Li, Yige; Sumpter, Bobby G

    2012-01-01

    Morphology diagrams for A2B copolymer melts are constructed using real-space self-consistent field theory (SCFT). In particular, the effect of architectural asymmetry on the morphology diagram is studied. It is shown that asymmetry in the lengths of A arms in the A2B copolymer melts aids in the microphase separation. As a result, the disorder-order transition boundaries for the A2B copolymer melts are shown to shift downward in terms of N, and N being the Flory s chi parameter and the total number of the Kuhn segments,respectively, in comparison with the A2B copolymers containing symmetric A arms. Furthermore, perforated lamellar (PL) and a micelle-like (M) microphase segregated morphologies are found to compete with the classical morphologies namely, lamellar, cylinders, spheres and gyroid. The PL morphology is found to be stable for A2B copolymers containing asymmetric A arms and M is found to be metastable for the parameter range explored in this work.

  2. Melt structure and self-nucleation of ethylene copolymers

    NASA Astrophysics Data System (ADS)

    Alamo, Rufina G.

    A strong memory effect of crystallization has been observed in melts of random ethylene copolymers well above the equilibrium melting temperature. These studies have been carried out by DSC, x-ray, TEM and optical microscopy on a large number of model, narrow, and broad copolymers with different comonomer types and contents. Melt memory is correlated with self-seeds that increase the crystallization rate of ethylene copolymers. The seeds are associated with molten ethylene sequences from the initial crystals that remain in close proximity and lower the nucleation barrier. Diffusion of all sequences to a randomized melt state is a slow process, restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. Self-seeds dissolve above a critical melt temperature that demarcates homogeneity of the copolymer melt. There is a critical threshold level of crystallinity to observe the effect of melt memory on crystallization rate, thus supporting the correlation between melt memory and the change in melt structure during copolymer crystallization. Unlike binary blends, commercial ethylene-1-alkene copolymers with a range in inter-chain comonomer composition between 1 and about 15 mol % display an inversion of the crystallization rate in a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. With decreasing the initial melt temperature, broadly distributed copolymers show enhanced crystallization followed by a decrease of crystallization rate. The inversion demarcates the onset of liquid-liquid phase separation (LLPS) and a reduction of self-nuclei due to the strong thermodynamic drive for molecular segregation inside the binodal. The strong effect of melt memory on crystallization rate can be used to identify liquid-liquid phase separation in broadly distributed copolymers, and offers strategies to control the state of copolymer melts in ways of

  3. Effect of Crystallinity on Melt Memory of Random Ethylene Copolymers

    NASA Astrophysics Data System (ADS)

    Chen, Xuejian; Mamun, Al; Rufina, Alamo G.

    2015-03-01

    A strong melt memory effect of crystallization has been observed in random ethylene copolymers even above the equilibrium melting temperature. Melt memory is associated with seeds that increase the crystallization rate of copolymers in a range of comonomer content between 0.5 and 4.5 mol%. The seeds are taken as molten ethylene sequences that remain in close proximity and are unable to diffuse fast to the randomized melt state. Fast diffusion is restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. The molten nature of the self-seeds is supported by a linear variation of T2H with Tmelt n NMR experiments in a range from 180 °C to 100 °C, covering both the homogeneous and heterogeneous melt regions. The effect of topological constraints on melt memory, or on number of seeds that remain in the melt, was analyzed studying copolymers with different levels of crystallinity. There is a threshold level of crystallinity, which depends on type and concentration of comonomer, below which copolymers do not display strong melt memory. Increasing 1-hexene content from 0.5 to 3.5 mol%, the crystallinity threshold decreases from 39 to 4%, while decreasing branch length from hexyl to ethyl, the threshold crystallinity decreases from 18% to 5% in agreement with stronger melt memory in copolymers with increasing comonomer content and with shorter branches.

  4. Effective Interactions and Miscibility of Nanoparticles in Multiblock Copolymer Melts

    DOE PAGESBeta

    Banerjee, Debapriya; Schweizer, Kenneth S

    2015-01-01

    The microscopic Polymer Reference Interaction Site Model theory is employed to study, for the first time, the effective interactions, spatial organization, and miscibility of dilute spherical nanoparticles in non-microphase separating, chemically heterogeneous, compositionally symmetric AB multiblock copolymer melts of varying monomer sequence or architecture. The dependence of nanoparticle wettability on copolymer sequence and chemistry results in interparticle potentials-of-mean force that are qualitatively different from homopolymers. An important prediction is the ability to improve nanoparticle dispersion via judicious choice of block length and monomer adsorption-strengths which control both local surface segregation and chain connectivity induced packing constraints and frustration. The degreemore » of dispersion also depends strongly on nanoparticle diameter relative to the block contour length. Small particles in copolymers with longer block lengths experience a more homopolymer-like environment which renders them relatively insensitive to copolymer chemical heterogeneity and hinders dispersion. Larger particles (sufficiently larger than the monomer diameter) in copolymers of relatively short block lengths provide better dispersion than either a homopolymer or random copolymer. The theory also predicts a novel widening of the miscibility window for large particles upon increasing the overall molecular weight of copolymers composed of relatively long blocks. The influence of a positive chi-parameter in the pure copolymer melt is briefly studied. Quantitative application to fullerenes in specific copolymers of experimental interest is performed, and miscibility predictions are made.« less

  5. Effective Interactions and Miscibility of Nanoparticles in Multiblock Copolymer Melts

    SciTech Connect

    Banerjee, Debapriya; Schweizer, Kenneth S

    2015-01-01

    The microscopic Polymer Reference Interaction Site Model theory is employed to study, for the first time, the effective interactions, spatial organization, and miscibility of dilute spherical nanoparticles in non-microphase separating, chemically heterogeneous, compositionally symmetric AB multiblock copolymer melts of varying monomer sequence or architecture. The dependence of nanoparticle wettability on copolymer sequence and chemistry results in interparticle potentials-of-mean force that are qualitatively different from homopolymers. An important prediction is the ability to improve nanoparticle dispersion via judicious choice of block length and monomer adsorption-strengths which control both local surface segregation and chain connectivity induced packing constraints and frustration. The degree of dispersion also depends strongly on nanoparticle diameter relative to the block contour length. Small particles in copolymers with longer block lengths experience a more homopolymer-like environment which renders them relatively insensitive to copolymer chemical heterogeneity and hinders dispersion. Larger particles (sufficiently larger than the monomer diameter) in copolymers of relatively short block lengths provide better dispersion than either a homopolymer or random copolymer. The theory also predicts a novel widening of the miscibility window for large particles upon increasing the overall molecular weight of copolymers composed of relatively long blocks. The influence of a positive chi-parameter in the pure copolymer melt is briefly studied. Quantitative application to fullerenes in specific copolymers of experimental interest is performed, and miscibility predictions are made.

  6. Microphase Ordering in Melts of Randomly Grafted Copolymers

    SciTech Connect

    Qi, S.; Chakraborty, A.K.; Wang, H.; Lefebvre, A.A.; Balsara, N.P.; Shakhnovich, E.I.; Xenidou, M.; Hadjichristidis, N.

    1999-04-01

    Using optical birefringence, small-angle neutron scattering, and field-theoretic methods, we study the effects of frustrating quenched randomness and connectivity on microphase ordering in copolymer melts. Our results show that randomly grafted copolymers are good model systems to examine these effects, and we find that these materials exhibit behavior different from that observed heretofore for other types of molten polymers. {copyright} {ital 1999} {ital The American Physical Society}

  7. Theory of the Miscibility of Fullerenes in Random Copolymer Melts

    SciTech Connect

    Dadmun, Mark D; Sumpter, Bobby G; Schweizer, Kenneth; Banerjee, Debapriya

    2013-01-01

    We combine polymer integral equation theory and computational chemistry methods to study the interfacial structure, effective interactions, miscibility and spatial dispersion mechanism of fullerenes dissolved in specific random AB copolymer melts characterized by strong non-covalent electron donor-acceptor interactions with the nanofiller. A statistical mechanical basis is developed for designing random copolymers to optimize fullerene dispersion at intermediate copolymer compositions. Pair correlation calculations reveal a strong sensitivity of interfacial packing near the fullerene to copolymer composition and adsorption energy mismatch. The potential of mean force between fullerenes displays rich trends, often non-monotonic with copolymer composition, reflecting a non-additive competition between direct filler attractions and polymer-mediated bridging and steric stabilization. The spinodal phase diagrams are in qualitative agreement with recent solubility limit experimental observations on three systems, and testable predictions are made for other random copolymers. The distinctive non-monotonic variation of miscibility with copolymer composition is found to be primarily a consequence of composition-dependent, spatially short-range attractions between the A and B monomers with the fullerene. A remarkably rich, polymer-specific temperature dependence of the spinodal diagram is predicted which reflects the thermal sensitivity of spatial correlations which can result in fullerene miscibility either increasing or decreasing with cooling. The calculations are contrasted with a simpler effective homopolymer model and the random structure Flory-Huggins model. The former appears to be qualitatively reasonable but can incur large quantitative errors since it misses preferential packing of monomers near nanoparticles, while the latter appears to fail qualitatively due to its neglect of all spatial correlations.

  8. Chirality in block copolymer melts: mesoscopic helicity from intersegment twist.

    PubMed

    Zhao, Wei; Russell, Thomas P; Grason, Gregory M

    2013-02-01

    We study the effects of chirality at the segment scale on the thermodynamics of block copolymer melts using self-consistent field theory. In linear diblock melts where segments of one block prefer a twisted, or cholesteric, texture, we show that melt assembly is critically sensitive to the ratio of random coil size to the preferred pitch of cholesteric twist. For weakly chiral melts (large pitch), mesophases remain achiral, while below a critical value of pitch, two mesoscopically chiral phases are stable: an undulated lamellar phase and a phase of hexagonally ordered helices. We show that the nonlinear sensitivity of mesoscale chiral order to preferred pitch derives specifically from the geometric and thermodynamic coupling of the helical mesodomain shape to the twisted packing of chiral segments within the core, giving rise to a second-order cylinder-to-helix transition. PMID:23414052

  9. Structural investigations of block copolymer melts and solutions

    NASA Astrophysics Data System (ADS)

    Kossuth, Mary Beth

    1999-11-01

    Block copolymers have been observed to spontaneously self-assemble into a variety of ordered liquid crystalline phases, much like surfactant and lipid solutions. Among these structures are two cubic morphologies: spheres packed on a body-centered cubic lattice and a bicontinuous structure known as the gyroid. The viscoelastic behavior of these two microstructures was examined in detail for nine chemically distinct systems using oscillatory shear. Remarkable similarities were seen in the rheological responses of the two phases, and a universal picture of the viscoelastic behavior of cubic phases was proposed. Two features were observed in every system: a low frequency crossover of the storage and loss moduli, oxx, and a frequency independent plateau in the storage modulus, Gcubic°. The plateau modulus is related experimentally to the characteristic domain spacing d* of the microstructures by Gcubic °˜d*-3, while theory predicts a d*-2 dependence. There are similarities between the phase behavior of melt-state block copolymers and surfactant solutions both in the phases that appear and the order in which they occur. The phase behavior for a series of low molecular weight block copolymers of poly(ethylene oxide)-poly(ethyl ethylene) (PEO-PEE) was examined in the presence of water and both water and dodecane (oil) using small-angle x-ray scattering. In the binary aqueous solutions, phase behavior similar to that of nonionic surfactants was observed, with evidence of lamellae, hexagonally packed cylinders, and body-centered cubic spheres; however, no gyroid phase was seen. The phases were remarkably robust; ordered structures persisted even to high temperatures. Above a critical concentration only lyotropic phase behavior was seen; below this composition thermotropic behavior was evident. Addition of dodecane to a symmetric block copolymer produced a very different phase diagram than its aqueous counterpart. Face-centered cubic spheres and a small window of the

  10. The packing of soft materials: Molecular asymmetry, geometric frustration and optimal lattices in block copolymer melts

    NASA Astrophysics Data System (ADS)

    Grason, Gregory M.

    Melts of block copolymers provide an ideal route to engineering well-controlled structures on nanometer length scales. Through the control of only a few thermodynamic parameters, these systems can be tuned to self-assemble into periodic structures of an astounding variety. It is known that geometry plays a particularly important role in determining equilibrium structure since phase behavior of copolymer melts is generically insensitive to detail at the monomeric scale. Here, we explore a particular way in which the geometry of packing objects in three dimensions frustrates the internal configurations of segregated block copolymer domains. In particular, we find that lattices of spherical micelles are sensitive to the periodic structure of the lattice arrangement because these micelles are forced to occupy the non-ideal, polyhedral unit cells of the lattice. By analyzing the energetics of block copolymer melts in the limit of strongly-segregated domains, we find that the interfaces which separate unlike polymer domains tend to adopt the polyhedral shape of the lattice unit cell, and this tendency is entirely controlled by the specific copolymer architecture. Furthermore, in the limit where interfaces are perfectly polyhedral, a remarkable simplicity emerges, and the relative stability of competing lattice arrangements of micelles can be assessed purely in terms of geometric measures of the two-dimensional lattice unit cell. From this analysis we predict the stability of a novel cubic arrangement spherical micelles in block copolymer melts, the A15 lattice. To corroborate our geometric arguments we develop and implement a numerical self-consistent field theory for melts of highly asymmetric block copolymers. This field theory allows us to systematically and efficiently explore the equilibrium phase behavior of asymmetric copolymer melts as a function of molecular architecture. These numerical results bear out the predictions of our geometric analysis and confirm that

  11. Molecular Simulation of Bicontinuous Phases in Diblock Copolymer Melts

    NASA Astrophysics Data System (ADS)

    Martinez-Veracoechea, Francisco; Escobedo, Fernando

    2008-03-01

    Molecular simulations are used to study the stabilization of different bicontinuous phases in diblock copolymer (DBC) melts. The stabilization approach entails attempting to reduce the packing frustration inside the bicontinuous phases nodes by the addition of a ``filler'' with affinity for the A component. Two different strategies are considered: 1) addition of selective-solvent particles, and 2) addition of homopolymer. Approximate phase boundaries were found via free-energy calculations. A very dissimilar phase behavior is observed upon increasing the amount of the ``additive'' in the two different strategies. While with the first strategy (i.e., addition of selective solvent) we observed the progression Gyroid (G) -> Perforated Lamella -> Lamella -> Reversed-Gyroid. With the second strategy (i.e., addition of homopolymer) we observed the progression of morphologies G -> Cylinder -> Double Diamond (DD) -> Plumber's Nightmare (P). In both the DD and the P phases, the homopolymer concentrates preferentially in the nodes, suggesting the reduction of the nodes' packing frustration. In addition, a novel morphology was observed, wherein cylinders of two different diameters alternate in a tetragonal packing. The contrasting difference in the phase behavior observed for the two strategies is understood as a consequence of the difference in mixing entropy exhibited by the two additives.

  12. Dodecagonal Quasicrystal Phase in a Diblock Copolymer Melt

    NASA Astrophysics Data System (ADS)

    Bates, Frank; Gillard, Timothy; Lee, Sangwoo

    Recent experiments with low molecular weight asymmetric poly(isoprene- b-lactide) (PI-PLA) diblock copolymers have established an equilibrium Frank-Kasper σ-phase at compositions between 18 and 22 percent by volume PLA, which transforms to a BCC phase followed by disordering with increasing temperature. This presentation will describe synchrotron small-angle x-ray scattering and dynamic mechanical spectroscopy experiments conducted following rapid temperature quenches from the disordered state to temperatures associated with the σ-phase. We document the development of a long-lived dodecagonal quasicrystalline (DQC) phase that transforms with time into the associated quasicrystal approximate σ-phase at a rate that is highly temperature dependent. Remarkably, the DQC does not form from either the σ-phase or BCC state. These finding will be discussed in the context of an apparent spontaneous structural transition that occurs when the disordered melt is supercooled below a threshold temperature coincident with the BCC to σ-phase order-order transition temperature. Support provided by the National Science Foundation (1104368).

  13. Theory of Chirality Transfer in Block Copolymer Melts

    NASA Astrophysics Data System (ADS)

    Prasad, Ishan; Grason, Gregory

    Block copolymers assemble into a rich spectrum of ordered phases, with complexity driven by asymmetry in copolymer architecture. Despite decades of study, influence of intrinsic chirality on equilibrium mesophase assembly of block copolymers is not well understood and largely unexplored. Self-consistent field theory has been largely instrumental in prediction of physical properties of polymeric systems. Recently, a polar orientational self-consistent field (oSCF) theory was adopted to model chiral block copolymers having a thermodynamic preference for cholesteric ordering in chiral segments, and which confirmed the equilibrium stability of a helical cylinder morphology observed for chiral diblocks. Here, I describe a newly developed oSCF theory for chiral nematic copolymers, where segment orientations are characterized by quadrupolar interactions, and focus our study on intra-domain nematic ordering in flexible block copolymer assemblies, and in particular, mechanisms of transfer of segment chirality to mesochiral symmetries of self-assembled bicontinuous network morphologies.

  14. Dodecagonal quasicrystalline order in a diblock copolymer melt.

    PubMed

    Gillard, Timothy M; Lee, Sangwoo; Bates, Frank S

    2016-05-10

    We report the discovery of a dodecagonal quasicrystalline state (DDQC) in a sphere (micelle) forming poly(isoprene-b-lactide) (IL) diblock copolymer melt, investigated as a function of time following rapid cooling from above the order-disorder transition temperature (TODT = 66 °C) using small-angle X-ray scattering (SAXS) measurements. Between TODT and the order-order transition temperature TOOT = 42 °C, an equilibrium body-centered cubic (BCC) structure forms, whereas below TOOT the Frank-Kasper σ phase is the stable morphology. At T < 40 °C the supercooled disordered state evolves into a metastable DDQC that transforms with time to the σ phase. The times required to form the DDQC and σ phases are strongly temperature dependent, requiring several hours and about 2 d at 35 °C and more than 10 and 200 d at 25 °C, respectively. Remarkably, the DDQC forms only from the supercooled disordered state, whereas the σ phase grows directly when the BCC phase is cooled below TOOT and vice versa upon heating. A transition in the rapidly supercooled disordered material, from an ergodic liquid-like arrangement of particles to a nonergodic soft glassy-like solid, occurs below ∼40 °C, coincident with the temperature associated with the formation of the DDQC. We speculate that this stiffening reflects the development of particle clusters with local tetrahedral or icosahedral symmetry that seed growth of the temporally transient DDQC state. This work highlights extraordinary opportunities to uncover the origins and stability of aperiodic order in condensed matter using model block polymers. PMID:27118844

  15. Investigation of Universal Behavior in Symmetric Diblock Copolymer Melts

    NASA Astrophysics Data System (ADS)

    Medapuram, Pavani

    Coarse-grained theories of dense polymer liquids such as block copolymer melts predict a universal dependence of equilibrium properties on a few dimensionless parameters. For symmetric diblock copolymer melts, such theories predict a universal dependence on only chieN and N¯, where chie is an effective interaction parameter, N is the degree of polymerization, and N¯ is a measure of overlap. This thesis focuses on testing the universal behavior hypothesis by comparing results for various properties obtained from different coarse-grained simulation models to each other. Specifically, results from pairs of simulations of different models that have been designed to have matched values of N¯ are compared over a range of values of chiN. The use of vastly different simulation models allows us to cover a vast range of chi eN ≃ 200 - 8000 that includes most of the experimentally relevant range. Properties studied here include collective and single-chain correlations in the disordered phase, block and chain radii of gyration in the disordered phase, the value of chieN at the order-disorder transition (ODT), the free energy per chain, the latent heat of transition, the layer spacing, the composition profile, and compression modulus in the ordered phase. All results strongly support the universal scaling hypothesis, even for rather short chains, confirming that it is indeed possible to give an accurate universal description of simulation models that differ in many details. The underlying universality becomes apparent, however, only if data are analyzed using an adequate estimate of chie, which we obtained by fitting the structure factor S( q) in the disordered state to predictions of the recently developed renormalized one-loop (ROL) theory. The ROL theory is shown to provide an excellent description of the dependence of S(q on chain length and thermodynamic conditions for all models, even for very short chains, if we allow for the existence of a nonlinear dependence of

  16. Order and Disorder in Polydisperse Block Copolymer Melts

    NASA Astrophysics Data System (ADS)

    Lynd, Nathaniel; Hillmyer, Marc

    2007-03-01

    Utilizing creative strategies for the synthesis of model controlled-polydispersity poly(ethylene-alt-propylene)-b-poly(d,l-lactide)(PEP-PLA) and polystyrene-b-polyisoprene(PS-PI) block copolymers, the effects of increased breadth in the molecular weight distribution on block copolymer self-assembly were investigated. Small-angle x-ray scattering and rheological measurements were carried out to characterize the morphological details of these self-assembled materials as a function of their polydispersity, interaction strengths, and compositions. A number of surprising consequences of increased breadth in the molecular weight distribution emerged; the domain spacing of the ordered structures increased, changes in morphology occurred, and the degree of segregation at the order-disorder transitions changed as well, particularly for asymmetric block copolymers. The change in the degree of segregation at the order-disorder transition as the polydispersity was increased was found to be dependent on the block copolymer composition, e.g., for PEP-PLA and PS-PI at asymmetric compositions, when the polydispersity was increased in the minority component, the degree of segregation at the order-disorder transition decreased, whereas when the polydispersity was increased in the majority component, the degree of segregation at the order-disorder transition increased.

  17. Synthesis and Melt Self-Assembly of PS-PMMA-PLA Triblock Bottlebrush Copolymers

    SciTech Connect

    Bolton, Justin; Rzayev, Javid

    2014-07-03

    Polystyrene–poly(methyl methacrylate)–polylactide (PS–PMMA–PLA) triblock bottlebrush copolymer with nearly symmetric volume fractions was synthesized by grafting from a symmetrical triblock backbone and the resulting melt was characterized by scanning electron microscopy and small-angle X-ray scattering. The copolymer backbone was prepared by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization of solketal methacrylate (SM), 2-(bromoisobutyryl)ethyl methacrylate (BIEM), and 5-(trimethylsilyl)-4-pentyn-1-ol methacrylate (TPYM). PMMA branches were grafted by atom transfer radical polymerization from the poly(BIEM) segment, PS branches were grafted by RAFT polymerization from the poly(TPYM) block after installment of the RAFT agents, while PLA side chains were grafted from the deprotected poly(SM) block. The resulting copolymer was found to exhibit a lamellae morphology with a domain spacing of 79 nm. Differential scanning calorimetry analysis indicated that PMMA was preferentially mixing with PS while phase separating from PLA domains.

  18. Architectural effect on the self-assembly of supramolecular triblock copolymer melts

    NASA Astrophysics Data System (ADS)

    Lee, Won Bo; Elliott, Richard; Katsov, Kirill; Fredrickson, Glenn H.

    2007-03-01

    Thermoreversible, supramolecular self-assembly in multi-block copolymer melts is studied within the framework of self-consistent field theory. This approach is adapted to study a system composed of two chemically distinct, but reactive homopolymer species: a linear A-homopolymer with a single reactive group at one of the ends, and a linear B-homopolymer with reactive groups at both ends. Reversible bonding occurs between the functional groups from different polymer species so that the reacting system can contain A, B, AB and ABA (co)polymer species whose overall volume fractions are controlled by the segmental incompatibility, bonding strength and homopolymer chain lengths. Architectural variations of these copolymers, arising from the differing lengths of A and B homopolymers, have a dramatic effect on not only the micro-phase separation but also on the extent of reversible bonding. Two characteristic phase diagrams are constructed to illustrate this behavior and possible technological applications are discussed.

  19. Dissipative particle dynamics of triblock copolymer melts: A midblock conformational study at moderate segregation

    NASA Astrophysics Data System (ADS)

    Tallury, Syamal S.; Spontak, Richard J.; Pasquinelli, Melissa A.

    2014-12-01

    As thermoplastic elastomers, triblock copolymers constitute an immensely important class of shape-memory soft materials due to their unique ability to form molecular networks stabilized by physical, rather than chemical, cross-links. The extent to which such networks develop in triblock and higher-order multiblock copolymers is sensitive to the formation of midblock bridges, which serve to connect neighboring microdomains. In addition to bridges, copolymer molecules can likewise form loops and dangling ends upon microphase separation or they can remain unsegregated. While prior theoretical and simulation studies have elucidated the midblock bridging fraction in triblock copolymer melts, most have only considered strongly segregated systems wherein dangling ends and unsegregated chains become relatively insignificant. In this study, simulations based on dissipative particle dynamics are performed to examine the self-assembly and networkability of moderately segregated triblock copolymers. Utilizing a density-based cluster-recognition algorithm, we demonstrate how the simulations can be analyzed to extract information about microdomain formation and permit explicit quantitation of the midblock bridging, looping, dangling, and unsegregated fractions for linear triblock copolymers varying in chain length, molecular composition, and segregation level. We show that midblock conformations can be sensitive to variations in chain length, molecular composition, and bead repulsion, and that a systematic investigation can be used to identify the onset of strong segregation where the presence of dangling and unsegregated fractions are minimal. In addition, because this clustering approach is robust, it can be used with any particle-based simulation method to quantify network formation of different morphologies for a wide range of triblock and higher-order multiblock copolymer systems.

  20. Dissipative particle dynamics of triblock copolymer melts: a midblock conformational study at moderate segregation.

    PubMed

    Tallury, Syamal S; Spontak, Richard J; Pasquinelli, Melissa A

    2014-12-28

    As thermoplastic elastomers, triblock copolymers constitute an immensely important class of shape-memory soft materials due to their unique ability to form molecular networks stabilized by physical, rather than chemical, cross-links. The extent to which such networks develop in triblock and higher-order multiblock copolymers is sensitive to the formation of midblock bridges, which serve to connect neighboring microdomains. In addition to bridges, copolymer molecules can likewise form loops and dangling ends upon microphase separation or they can remain unsegregated. While prior theoretical and simulation studies have elucidated the midblock bridging fraction in triblock copolymer melts, most have only considered strongly segregated systems wherein dangling ends and unsegregated chains become relatively insignificant. In this study, simulations based on dissipative particle dynamics are performed to examine the self-assembly and networkability of moderately segregated triblock copolymers. Utilizing a density-based cluster-recognition algorithm, we demonstrate how the simulations can be analyzed to extract information about microdomain formation and permit explicit quantitation of the midblock bridging, looping, dangling, and unsegregated fractions for linear triblock copolymers varying in chain length, molecular composition, and segregation level. We show that midblock conformations can be sensitive to variations in chain length, molecular composition, and bead repulsion, and that a systematic investigation can be used to identify the onset of strong segregation where the presence of dangling and unsegregated fractions are minimal. In addition, because this clustering approach is robust, it can be used with any particle-based simulation method to quantify network formation of different morphologies for a wide range of triblock and higher-order multiblock copolymer systems. PMID:25554184

  1. Local Dynamics of Acid- and Ion-containing Copolymer Melts

    NASA Astrophysics Data System (ADS)

    Winey, Karen; Middleton, Robert; Tarver, Jacob; Tyagi, Madhusudan; Soles, Christopher; Frischknecht, Amalie

    Interest in acid- and ion-containing polymers arises in part from applications as single-ion conductors for selectively transporting a counter ion for battery applications. Structurally, the low dielectric constant of organic polymers and strong ionic interactions leads to ionic aggregation. Here the polymer backbone motion was investigated through quasi-elastic neutron scattering measurements (QENS) and compared with fully atomistic molecular dynamic simulations of precise poly(ethylene-acrylic acid) copolymers and their ionomers (pxAA-y%Li). The effect of carbon spacer length (x =9, 15, 21) between the acid groups and the degree of neutralization (y) with Li on PE backbone dynamics were considered. Systematic slowing in chain dynamics were observed with increasing neutralization where polymer dynamics appear constrained due to anchoring effects. Simulations provide complementary viewpoints indicating a gradient in chain dynamics as a distance away from acid groups. These results indicate that the addition of pendant acid groups inhibit typical PE backbone motion and the neutralized forms strongly suppress the fraction of mobile PE chain.

  2. Neutron spin echo investigation of the concentration fluctuation dynamics in melts of diblock copolymers

    NASA Astrophysics Data System (ADS)

    Montes, H.; Monkenbusch, M.; Willner, L.; Rathgeber, S.; Fetters, L.; Richter, D.

    1999-05-01

    Diblock copolymers in the melt exhibit order-disorder phase transitions (ODT), which are accompanied by strong concentration fluctuations. These transitions are generally described in terms of the random phase approximation (RPA) of Leibler and Fredrickson, which is able to explain small angle scattering results in the neighborhood of the ODT, in particular around the correlation peak at q*. The RPA theory has been extended to include dynamical phenomena, predicting the short time relaxation of the dynamic structure factor in polymeric multicomponent systems. We report small angle neutron scattering and neutron spin echo experiments on polyethylene-block-polyethylethylene (PE-PEE) and poly(ethylene-propylene)-block-polyethylethylene (PEP-PEE) copolymers with molecular weights of 16.500 and 68.000 g/mol, which explore the structure and dynamics of these block copolymers. Studying melts with different hydrogen/deuterium labeling it was possible to observe experimentally the different relaxation modes of such systems separately. In particular the collective relaxation behavior as well as the single chain motion were accessed. The experimental results were quantitatively compared with the RPA predictions, which were based solely on the dynamical properties of the corresponding homopolymers and the static structure factors. The collective dynamics exhibits an unanticipated fast relaxation mode. This mode is most visible at low wave numbers (q⩾q*) but extends to length scales considerably shorter than the radius of gyration. Furthermore, the dynamical RPA yields expressions for the mobilities of chain segments in the block copolymer melt. These combination rules are at variance with the experimental findings for the single chain dynamics, while they hold for the collective response.

  3. Melt and Solid-State Structures of Polydisperse Polyolefin Multiblock Copolymers

    SciTech Connect

    Li, Sheng; Register, Richard A.; Weinhold, Jeffrey D.; Landes, Brian G.

    2012-10-23

    Crystallization in polydisperse ethylene-octene multiblock copolymers, polymerized via chain shuttling chemistry, is examined using two-dimensional synchrotron small- and wide-angle X-ray scattering on flow-aligned specimens. The multiblocks are composed of alternating crystalline (hard) blocks of low 1-octene content and amorphous (soft) blocks of high 1-octene content; the block lengths and the number of blocks per chain are characterized by most-probable distributions. These polymers self-assemble into lamellar domain morphologies in the melt, and the melt morphology is retained in the solid state. Despite extensive mixing between hard and soft blocks, the high crystallinity (>50%) of the hard blocks leads to an alignment of the crystallites within the domain structure, with the orthorhombic polyethylene c-axis generally perpendicular to the lamellar domain normal. The interlamellar domain spacings exhibited by the multiblocks, which exceed 100 nm, are estimated to be 5 times larger than those in near-monodisperse block copolymers having a similar chemical composition and a number-average molecular weight equivalent to the multiblock's 'constituent diblock' repeating unit. This swelling factor exceeds the value of 3 previously reported for analogous polydisperse olefin diblock copolymers, due to the lower segregation strength and enhanced phase mixing of the multiblocks studied here.

  4. Melt and Solid-State Structures of Polydisperse Polyolefin Block Copolymers

    NASA Astrophysics Data System (ADS)

    Register, Richard; Li, Sheng

    2013-03-01

    Recent developments in coordinative chain transfer polymerization have enabled the synthesis of ethylene-co-octene block copolymers, where the blocks are either crystallizable (an ethylene-co-octene random copolymer block with low octene content) or amorphous (analogous block with high octene content). With a suitable choice of catalyst type(s) and reactor train configuration, accessible chain architectures include diblock, where each block ideally has the most-probable distribution of chain lengths, and multiblock, where both the individual blocks and the number of blocks per chain follow the most-probable distribution. With a sufficiently large interblock octene differential, block copolymers of both architectures, containing roughly equal masses of the two types of block, self-assemble in the melt into well-ordered lamellar structures, despite the large polydispersity. Interblock mixing, induced by the modest Flory interaction parameter and the broad distribution of block lengths, yields an enormous domain spacing (> 100 nm) despite the relatively low average block molecular weights (< 50 kg/mol). Extensive interblock mixing also allows the polyethylene crystals to grow freely and nearly isotropically across the domain interfaces, while preserving the domain structure present in the melt; in the solid state, the optical and x-ray contrasts between dissimilar domains are greatly enhanced due to their different levels of crystallinity. (Work conducted in collaboration with Jeffrey Weinhold, Philip Hustad, and Brian Landes of Dow Chemical Core R&D.) Support from the NSF Polymers Program (DMR-1003942).

  5. The Tricontinuous 3ths(5) Phase: A New Morphology in Copolymer Melts

    NASA Astrophysics Data System (ADS)

    Fischer, Michael; de Campo, Liliana; Kirkensgaard, Jacob; Hyde, Stephen; Schroeder-Turk, Gerd

    2015-03-01

    Self-assembly remains one of the most efficient routes to the formation of ordered nanostructures, including the double gyroid network phase in diblock copolymers based on two intergrown network domains. This talk demonstrates the use of self-consistent field theory to show that a tricontinuous structure with monoclinic symmetry, called 3ths(5), based on the intergrowth of three distorted ths nets, is an equilibrium phase of triblock star-copolymer melts when an extended molecular core is introduced. The introduction of the core enhances the role of chain stretching by enforcing larger structural length scales, thus destabilizing the hexagonal columnar phase in favor of morphologies with less packing frustration. This study further demonstrates that the introduction of molecular cores is a general concept for tuning the relative importance of entropic and enthalpic free energy contributions, hence providing a tool to stabilize an extended repertoire of self-assembled nanostructured materials.

  6. 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.

  7. Stable Freestanding Thin Films of Copolymer Melts Far from the Glass Transition

    PubMed Central

    2015-01-01

    Thin polymer films have attracted attention because of both their broad range of applications and of the fundamental questions they raise regarding the dynamic response of confined polymers. These films are unstable if the temperature is above their glass transition temperature Tg. Here, we describe freestanding thin films of centimetric dimensions made of a comb copolymer melt far from its glass transition that are stable for more than a day. These long lifetimes allowed us to characterize the drainage dynamics and the thickness profile of the films. Stratified regions appear as the film drains. We have evidence that the stability, thinning dynamics, and thickness profile of the films result from structural forces in the melt. Understanding the key mechanisms behind our observations may lead to new developments in polymeric thin films, foams, and emulsions without the use of stabilizing agents. PMID:26527410

  8. Melt-Miscibility in Block Copolymers Containing Polyethylene and Substituted Polynorbornene Blocks

    NASA Astrophysics Data System (ADS)

    Mulhearn, William; Register, Richard

    2015-03-01

    Block copolymers containing a crystallizable block, such as polyethylene (PE), and a high-Tg amorphous block are potentially interesting materials since the rigid glassy block can mitigate the poor yield strength of the PE crystals. However, chemical incompatibility between blocks, quantified by the Flory interaction parameter χ or the interaction energy density X, drives microphase separation at low temperatures or high chain lengths. To prepare a high molecular weight PE-containing block copolymer that is easy to process (i.e. with a disordered low-viscosity melt) it is necessary to select amorphous blocks that have low mixing energies with PE. The only suitable polymers currently known are chemically similar to PE and therefore have similarly low glass transition temperatures. We investigate a series of both low- and high-Tg polymers based on substituted norbornene monomers, polymerized via ring-opening metathesis polymerization (ROMP). Several ROMP polymers of this type exhibit high Tg and low interaction energy against PE. For example, hydrogenated poly(cyclohexyl norbornene) has Tg = 88 oC and has interaction energy density XhPCyN - PE ~ 0.8 MPa, comparable to the interaction energy density between PE and hydrogenated polyisoprene. The miscibility of an amorphous block can be further tuned by statistical copolymerization of norbornene units with aromatic side-groups (high Hildebrand solubility parameter) and norbornene units with aliphatic side-groups (low Hildebrand solubility parameter).

  9. Phase diagram of rod-coil diblock copolymer melts by self-consistent field theory

    NASA Astrophysics Data System (ADS)

    Yan, Dadong; Tang, Jiuzhou; Jiang, Ying; Zhang, Xinghua; Chen, Jeff

    A unified phase diagram is presented for rod-coil diblock copolymer melts in the isotropic phase regime as a function of the asymmetric parameter. The study is based on free-energy calculation, which incorporates three-dimensional spatial variations of the volume fraction with angular dependence. The wormlike-chain model is used in a self-consistent field treatment. Body-centered cubic, A15, hexagonal, gyroid, and lamellar structures where the rod segments are packed inside the convex rod-coil interface are found stable. As the conformational asymmetric parameter increases, the A15 phase region expands and the gyroid phase region reduces. The stability of the structures is analyzed by concepts such as packing frustration, spinodal limit, and interfacial curvature.

  10. Deviations from the mean-field predictions for the phase behaviour of random copolymers melts

    NASA Astrophysics Data System (ADS)

    Houdayer, J.; Müller, M.

    2002-06-01

    We investigate the phase behaviour of random copolymers melts via large-scale Monte Carlo simulations. We observe macrophase separation into A- and B-rich phases as predicted by the mean-field theory only for systems with a very large correlation λ of blocks along the polymer chains, far away from the Lifshitz point. For smaller values of λ, we find that a locally segregated, disordered microemulsion-like structure gradually forms as the temperature decreases. As we increase the number of blocks in the polymers, the region of macrophase separation further shrinks. The results of our Monte Carlo simulation are in agreement with a Ginzburg criterium, which suggests that the mean-field theory becomes worse as the number of blocks in polymers increases.

  11. Deformation of Inclusions and Lamellae during Melt Elongation of Blends of a Styrene-Butadiene Block Copolymer with Polystyrene

    NASA Astrophysics Data System (ADS)

    Handge, U. A.; Buschnakowski, M.; Michler, G. H.

    2008-07-01

    In this study, we investigated the development of the morphology in melt extension of blends of a linear styrene-butadiene block copolymer (LN3) and polystyrene (PS 158K). After melt mixing, PS 158K and LN3 formed two-phase polymer blends. The block copolymer was arranged in a lamellar phase. Our rheological experiments in shear and elongation clearly showed that the complex modulus, the transient extensional viscosity and the recovered stretch of the blends mainly resulted from a superposition of the properties of the neat blend components. The melt elongation experiments revealed that pure LN3 started to crumble at a small elongational strain. At our test parameters, the deformation of the PS 158K/LN3 blends was associated with an anisotropic Poisson ratio. Morphological investigations using transmission electron microscopy revealed that the PS 158K and LN3 inclusions in the LN3 and PS 158K matrix, respectively, were deformed into a filament-like shape in melt extension. Furthermore, the alignment of the lamellae of the block copolymer also increased with applied elongational strain. In relaxation after melt elongation the alignment of the lamellae persisted, whereas in recovery the alignment of the lamellae decreased.

  12. On the order-disorder transition of compressible diblock copolymer melts

    NASA Astrophysics Data System (ADS)

    Zong, Jing; Wang, Qiang

    2015-11-01

    We performed both the fast off-lattice Monte Carlo simulations of symmetric diblock copolymers (DBC) in an isothermal-isobaric ensemble and the self-consistent field calculations of asymmetric DBC to properly determine the order-disorder transition (ODT) of a model system of compressible DBC melts used in the literature when it is a first-order phase transition, and studied for the first time the co-existence of the two phases at ODT. We found that the co-existing region is quite small and decreases as the system becomes less compressible, which justifies the previous ODT results obtained by equating the Helmholtz free energy per chain of the two phases. We also found that for the most compressible system where there is no repulsion between the same type of segments, the self-consistent field theory predicts that ODT is a second-order phase transition even for asymmetric DBC melts due to its mean-field approximation.

  13. On the order-disorder transition of compressible diblock copolymer melts.

    PubMed

    Zong, Jing; Wang, Qiang

    2015-11-14

    We performed both the fast off-lattice Monte Carlo simulations of symmetric diblock copolymers (DBC) in an isothermal-isobaric ensemble and the self-consistent field calculations of asymmetric DBC to properly determine the order-disorder transition (ODT) of a model system of compressible DBC melts used in the literature when it is a first-order phase transition, and studied for the first time the co-existence of the two phases at ODT. We found that the co-existing region is quite small and decreases as the system becomes less compressible, which justifies the previous ODT results obtained by equating the Helmholtz free energy per chain of the two phases. We also found that for the most compressible system where there is no repulsion between the same type of segments, the self-consistent field theory predicts that ODT is a second-order phase transition even for asymmetric DBC melts due to its mean-field approximation. PMID:26567680

  14. On the order-disorder transition of compressible diblock copolymer melts

    SciTech Connect

    Zong, Jing; Wang, Qiang

    2015-11-14

    We performed both the fast off-lattice Monte Carlo simulations of symmetric diblock copolymers (DBC) in an isothermal-isobaric ensemble and the self-consistent field calculations of asymmetric DBC to properly determine the order-disorder transition (ODT) of a model system of compressible DBC melts used in the literature when it is a first-order phase transition, and studied for the first time the co-existence of the two phases at ODT. We found that the co-existing region is quite small and decreases as the system becomes less compressible, which justifies the previous ODT results obtained by equating the Helmholtz free energy per chain of the two phases. We also found that for the most compressible system where there is no repulsion between the same type of segments, the self-consistent field theory predicts that ODT is a second-order phase transition even for asymmetric DBC melts due to its mean-field approximation.

  15. Morphological Phase Behavior of Poly(RTIL)-Containing Diblock Copolymer Melts

    SciTech Connect

    Scalfani, Vincent F.; Wiesenauer, Erin F.; Ekblad, John R.; Edwards, Julian P.; Gin, Douglas L.; Bailey, Travis S.

    2012-10-23

    The development of nanostructured polymeric systems containing directionally continuous poly(ionic liquid) (poly(IL)) domains has considerable implications toward a range of transport-dependent, energy-based technology applications. The controlled, synthetic integration of poly(IL)s into block copolymer (BCP) architectures provides a promising means to this end, based on their inherent ability to self-assemble into a range of defined, periodic morphologies. In this work, we report the melt-state phase behavior of an imidazolium-containing alkyl-ionic BCP system, derived from the sequential ring-opening metathesis polymerization (ROMP) of imidazolium- and alkyl-substituted norbornene monomer derivatives. A series of 16 BCP samples were synthesized, varying both the relative volume fraction of the poly(norbornene dodecyl ester) block (f{sub DOD} = 0.42-0.96) and the overall molecular weights of the block copolymers (M{sub n} values from 5000-20,100 g mol{sup -1}). Through a combination of small-angle X-ray scattering (SAXS) and dynamic rheology, we were able to delineate clear compositional phase boundaries for each of the classic BCP phases, including lamellae (Lam), hexagonally packed cylinders (Hex), and spheres on a body-centered-cubic lattice (S{sub BCC}). Additionally, a liquid-like packing (LLP) of spheres was found for samples located in the extreme asymmetric region of the phase diagram, and a persistent coexistence of Lam and Hex domains was found in lieu of the bicontinuous cubic gyroid phase for samples located at the intersection of Hex and Lam regions. Thermal disordering was opposed even in very low molecular weight samples, detected only when the composition was highly asymmetric (f{sub DOD} = 0.96). Annealing experiments on samples exhibiting Lam and Hex coexistence revealed the presence of extremely slow transition kinetics, ultimately selective for one or the other but not the more complex gyroid phase. In fact, no evidence of the bicontinuous

  16. Synthesis of Polystyrene-Polylactide Bottlebrush Block Copolymers and Their Melt Self-Assembly into Large Domain Nanostructures

    SciTech Connect

    Rzayev, J.

    2009-04-07

    High molecular weight polystyrene-polylactide (PS-PLA) bottlebrush block copolymers have been shown to self-assemble into highly ordered lamellae structures with domain spacings as large as 163 nm, as identified by ultrasmall-angle X-ray scattering. Bottlebrush block copolymers were synthesized by a combination of living radical and ring-opening polymerizations. The backbone was prepared by RAFT block copolymerization of solketal methacrylate (SM) and 2-(bromoisobutyryl)ethyl methacrylate (BIEM). Polystyrene branches were grafted by ATRP from poly(BIEM) block, and PLA branches were grafted from the poly(SM) block after the removal of ketal groups. The investigation into the self-assembly of PS-PLA bottlebrush block copolymers with varying lengths of branches and backbones revealed a number of unusual trends, which were attributed to their dynamic, three-dimensional structure. The results suggest that in phase-separated melts the bottlebrush block copolymer backbone, while extended, still possesses a certain degree of flexibility to accommodate for different interfacial areas necessary to pack into lamellae microstructures.

  17. Effect of interfaces on the melting of PEO confined in triblock PS-b-PEO-b-PS copolymers.

    PubMed

    Beaudoin, E; Phan, T N T; Robinet, M; Denoyel, R; Davidson, P; Bertin, D; Bouchet, R

    2013-08-27

    Block copolymers form nanostructures that have interesting physical properties because they combine, for a single compound, the complementary features brought by each block. However, in order to fully exploit these properties, the physical state of each kind of domain must be precisely controlled. In this work, triblock PS-b-PEO-b-PS copolymers consisting of a central poly(ethylene oxide) (PEO) block covalently bonded to polystyrene (PS) blocks were synthesized by Atom Transfer Radical Polymerization. Their morphology was investigated by X-ray scattering and TEM experiments whereas their thermodynamic behavior was characterized by DSC. A strong decrease of both the melting temperature and the degree of crystallinity of PEO, due to its confinement between the PS domains, was observed and analyzed with a modified Gibbs-Thomson equation, following the approaches used for fluids confined in porous media. The existence of an amorphous bound layer, a few nanometers thick, at the PEO/PS interface, that does not undergo any phase transition in the temperature range investigated, accounts for both the melting temperature depression and the decrease of crystallinity upon confinement. This interfacial layer may significantly affect the mechanical and transport properties of these block copolymers that find applications as solid polymer electrolytes in batteries for example. Moreover, the value obtained for the solid PEO/liquid PEO surface tension is lower than those previously published but is thermodynamically consistent with the surface tensions of polymers at the solid/vapor and liquid/vapor interfaces. PMID:23865710

  18. Simulation of the gyroid phase in off-lattice models of pure diblock copolymer melts

    NASA Astrophysics Data System (ADS)

    Martínez-Veracoechea, Francisco J.; Escobedo, Fernando A.

    2006-09-01

    Particle-based molecular simulations of pure diblock copolymer (DBC) systems were performed in continuum space via dissipative particle dynamics and Monte Carlo methods for a bead-spring chain model. This model consisted of chains of soft repulsive particles often used with dissipative particle dynamics. The gyroid phase was successfully simulated in DBC melts at selected conditions provided that the simulation box size was commensurate with the gyroid lattice spacing. Simulations were concentrated at conditions where the gyroid phase is expected to be stable which allowed us to outline approximate phase boundaries. When more than one phase was observed by varying simulation box size, thermodynamic stability was discerned by comparing the Helmholtz free energy of the competing phases. For this purpose, chemical potentials were efficiently simulated via an expanded ensemble that gradually inserts/deletes a target chain to/from the system. These simulations employed a novel combination of Bennett's [J. Comput. Phys. 22, 245 (1976)] acceptance-ratio method to estimate free-energy differences and a recently proposed method to get biasing weights that maximize the number of times that the target chain is regrown. The analysis of the gyroid nodes revealed clear evidence of packing frustration in the form of an (entropically) unfavorably overstretching of chains, a phenomenon that has been suggested to provide the structural basis for the limited region of stability of the gyroid phase in the DBC phase diagram. Finally, the G phase and nodal chain stretching were also found in simulations with a completely different DBC particle-based model.

  19. Rheological Evidence of Composition Fluctuations in an Unentangled Diblock Copolymer Melt near the Order-Disorder Transition

    SciTech Connect

    Kennemur, Justin G.; Hillmyer, Marc A.; Bates, Frank S.

    2014-02-13

    Rheological and small-angle X-ray scattering (SAXS) measurements were conducted on a symmetric, low molar mass (Mn = 17.6 kg/mol), poly(tert-butylstyrene-block-methyl methacrylate) (PtBS-PMMA) diblock copolymer near the order–disorder transition temperature (TODT = 193 ± 1 °C). Evidence of composition fluctuations is apparent in the low frequency elastic (G') and loss (G") moduli and in the temperature dependence of the peak scattering intensity, I(q*), up to 50 °C above the TODT. These findings demonstrate that chain entanglements are not responsible for the well-documented fluctuation mode in the terminal viscoelastic regime of block copolymer melts.

  20. Micelles, Lamellaes and Connected Bilayer Membranes in Block Copolymer Melts, Blends and Solutions

    NASA Astrophysics Data System (ADS)

    Mortensen, Kell

    1997-03-01

    Block copolymers of poly(ethylene oxide), PEO, and poly(propylene oxide), PPO, provide a unique model system for studies of aqueous systems of amphilic macromolecules, as the amphiphilic character can be changed continuously by changing temperature(K Mortensen, W Brown, B. Nordén , Phys. Rev. Letters 13 2340 (1992)) or pressure(K Mortensen, D Schwahn S Janssen Phys. Rev. Letters 71 1728 (1993)). The structural characteristics of aqueous solutions of the PEO-PPO-PEO copolymers and their self-associated assemblies are reviewed(K Mortensen, J. Phys. Cond. Matter 8 A103 (1996)). It is shown by small-angle neutron scattering that at low temperatures and/or concentration the individual copolymers exist in solution as individual unimers. Depending on molecular design, i.e. size of the individual blocks, various aggregates are formed, including spherical, worm-like and disc-shaped micelles. The spherical micelles provide the basis for liquid-crystalline mesophases of cubic structure. The crystallization can be understood as a simple hard-sphere condensation. Worm- or rod-like micelles may form nematic or hexagonally ordered structures, whereas the discs may condense into lamellar phases. While bi-continuous microemulsions frequently appear in ternary phase diagrams of oil, water and low-molecular surfactants, there has only recently been observations of such phases in binary systems of block copolymers and solvent. The first observation was made in an aqueous solution of a low PEO-content PEO-PPO-PEO triblock copolymer(E Hecht, K Mortensen, H Hoffmann, Macromolecules 28 5465, 1995). More recently, the microemulsion sponge phase has been observed in a system of tri-block copolymers dissolved in homopolymers( JH Laurer, JC Fung, JW Sedat, DA Agard, SD Schmit, J Samseth, K Mortensen, RJ Spontak, Langmuir, submitted) and in a ternary systems of diblock copolymer and homopolymers(FS Bates, WW Maurer, PM Lipic MA Hillmyer, KA Almdal, K Mortensen, TP Lodge Science, submitted).

  1. Dual modes of self-assembly in superstrongly segregated bicomponent triblock copolymer melts

    NASA Astrophysics Data System (ADS)

    Woloszczuk, Sebastian; Mineart, Kenneth P.; Spontak, Richard J.; Banaszak, Michal

    2015-01-01

    While A B C triblock copolymers are known to form a plethora of dual-mode (i.e., order-on-order) nanostructures, bicomponent A B A triblock copolymers normally self-assemble into single morphologies at thermodynamic incompatibility levels up to the strong-segregation regime. In this study, we employ on-lattice Monte Carlo simulations to examine the phase behavior of molecularly asymmetric A1B A2 copolymers possessing chemically identical endblocks differing significantly in length. In the limit of superstrong segregation, interstitial micelles composed of the minority A2 endblock are observed to arrange into two-dimensional hexagonal arrays along the midplane of B -rich lamellae in compositionally symmetric (50 :50 A :B ) copolymers. Simulations performed here establish the coupled molecular-asymmetry and incompatibility conditions under which such micelles form, as well as the temperature dependence of their aggregation number. Beyond an optimal length of the A2 endblock, the propensity for interstitial micelles to develop decreases, and the likelihood for colocation of both endblocks in the A1-rich lamellae increases. Interestingly, the strong-segregation theory of Semenov developed to explain the formation of free micelles by diblock copolymers accurately predicts the onset of interstitial micelles confined at nanoscale dimensions between parallel lamellae.

  2. SAXS studies of the structure of a BCC-ordered block copolymer melt subjected to uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    Burghardt, Wesley; McCready, Erica

    We report in situ small-angle x-ray scattering (SAXS) investigations of a spherically-ordered block copolymer melt with a low styrene content (13%) resulting in spherical polystyrene microdomains ordered in BCC lattice. Melt annealing after clearing above the ODT produces ordered samples that have a macroscopically random orientation distribution of BCC 'grains'. Melt samples are subjected to uniaxial extensional flow in a counter-rotating drum extensional flow fixture housed in an oven with synchrotron x-ray access. During flow, initially isotropic diffraction rings in SAXS patterns become deformed, reflecting distortion of the BCC lattice. Diffracted intensity also concentrates azimuthally, indicating macroscopic alignment of the BCC lattice. There is evidence that extensional flow leads to progressive disordering of the BCC structure, with loss of higher order peaks and the emergence of a diffuse 'halo' of scattering. While the primary diffraction peak is visible in directions parallel and perpendicular to the stretching direction, the deformation of the lattice d-spacing follows affine deformation. Indications of ordering persist to higher strains in samples stretched at higher extension rates, and evidence of affine lattice deformation persists to very high strains (Hencky

  3. Phase coexistence calculations via a unit-cell Gibbs ensemble formalism for melts of reversibly bonded block copolymers

    NASA Astrophysics Data System (ADS)

    Mester, Zoltan; Lynd, Nathaniel; Fredrickson, Glenn

    2013-03-01

    Melts of block copolymer blends can exhibit coexistence between compositionally and morphologically distinct phases. We derived a unit-cell approach for a field theoretic Gibbs ensemble formalism to rapidly map out such coexistence regions. We also developed a canonical ensemble model for the reversible reaction of supramolecular polymers and integrated it into the Gibbs ensemble scheme. This creates a faster method for generating phase diagrams in complex supramolecular systems than the usual grand canonical ensemble method and allows us to specify the system in experimentally accessible volume fractions rather than chemical potentials. The integrated approach is used to calculate phase diagrams for AB diblock copolymers reversibly reacting with B homopolymers to form a new diblocks we term ``ABB.'' For our case, we use a diblock that is sixty percent A monomer and a homopolymer that is the same length as the diblock. In the limits of infinite reaction favorability (large equilibrium constant), the system approaches cases of an ABB diblock-B homopolymer blend when the AB diblock is the limiting reactant and AB diblock-ABB diblock blend when the homopolymer is the limiting reactant. As reaction favorability is decreased, the phase boundaries shift towards higher homopolymer compositions so that sufficient reaction can take place to produce the ABB diblock that has a deciding role stabilizing the observed phases.

  4. Interplay Between a Strong Memory Effect of Crystallization and Liquid-Liquid Phase Separation in Melts of Broadly Distributed Ethylene 1-Alkene Copolymers

    NASA Astrophysics Data System (ADS)

    Alamo, Rufina G.; Mamun, Al; Chen, Xuejian

    2015-03-01

    Ethylene-1-alkene copolymers with a broad, bimodal comonomer distribution display acceleration and retardation of the crystallization rate when cooling from a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. The acceleration of the rate is observed in a range of melt temperatures between 165 and 150 °C, and is due to a strong memory effect of crystallization above their equilibrium melting point. The retardation or inversion of the rate, observed in a range of 150 to 123 °C, demarcates the onset of a self-seed assisted liquid-liquid phase separation (LLPS) between comonomer-rich and comonomer poor molecules. The interplay between number of self-seeds at the initial melt temperature and chain diffusion during LLPS causes a decrease in the crystallization rate with decreasing melt temperature. When crystallites remain in the melt at temperatures <123 °C, the crystallization rate again accelerates quickly. The crystallization rates were studied by DSC, and the effect in nucleation density and in overall crystalline morphology of crystallizations from one phase or two liquid phases was followed by polarized optical microscopy and transmission electron microscopy.

  5. Effects of Polydispersity on the Order-Disorder Transition in Block Copolymer Melts

    SciTech Connect

    Lynd, Nathaniel A.; Hillmyer, Marc A.

    2008-06-30

    We prepared controlled-polydispersity poly(ethylene-alt-propylene)-b-poly(DL-lactide) (PL) and polystyrene-b-polyisoprene (SI) block copolymers to study the effects of the molecular weight distribution on the order-disorder transition at controlled composition and overall molecular weight. Small-angle X-ray scattering and rheological measurements were carried out to characterize the changes in the order-disorder transition in these self-assembled materials as a function of their composition and polydispersity index. We determined that in both asymmetric PL and SI systems increasing polydispersity in the minority component resulted in a decrease in the segregation strength at the order-disorder transition, whereas increasing polydispersity in the majority component results in an increase in the segregation strength at the order-disorder transition. We speculate that increasing PDI in the majority domain weakens the effective potential holding the phase-separated microdomains ordered on a lattice.

  6. Theory of melt polyelectrolyte blends and block copolymers: Phase behavior, surface tension, and microphase periodicity

    SciTech Connect

    Sing, Charles E.; Zwanikken, Jos W.; Olvera de la Cruz, Monica

    2015-01-21

    Polymer mixtures such as blends or block copolymers are of great interest in energy applications and functional materials, and often, one or more of these species contain charges. The traditional fashion in which such materials are studied uses Self-Consistent Field Theory (SCFT) methods that incorporate electrostatics using Poisson-Boltzmann (PB) theory. We adapt a new and rigorous approach that does not rely on the mean-field assumptions inherent in the PB theory and instead uses Liquid State (LS) integral equation theory to articulate charge correlations that are completely neglected in PB. We use this theory to calculate phase diagrams for both blends and block copolyelectrolytes using SCFT-LS and demonstrate how their phase behavior is highly dependent on chain length, charge fraction, charge size, and the strength of Coulombic interactions. Beyond providing phase behavior of blends and block copolyelectrolytes, we can use this theory to investigate the interfacial properties such as surface tension and block copolyelectrolyte lamellar spacing. Lamellar spacing provides a way to directly compare the SCFT-LS theory to the results of experiments. SCFT-LS will provide conceptual and mathematical clarification of the role of charge correlations in these systems and aid in the design of materials based on charge polymers.

  7. Microphase Separation and Shear Alignment of Gradient Copolymers: Melt Rheology and Small-Angle X-Ray Scattering Analysis

    SciTech Connect

    Mok, Michelle M.; Pujari, Saswati; Burghardt, Wesley R.; Dettmer, Christine M.; Nguyen, SonBinh T.; Ellison, Christopher J.; Torkelson, John M.

    2008-10-24

    The degree of microphase or nanophase segregation in gradient copolymers with compositions varying across the whole copolymer backbone is studied via low-amplitude oscillatory shear (LAOS) measurements and small-angle X-ray scattering (SAXS). Studies are done as a function of comonomer segregation strength, molecular weight (MW), gradient architecture and temperature. Controlled radical polymerization is used to synthesize strongly segregating styrene/4-acetoxystyrene (S/AS) and the more weakly segregating S/n-butyl acrylate (S/nBA) gradient copolymers. Results are compared to those from S/AS and S/nBA random and block copolymers. The higher MW S/AS gradient copolymer exhibits LAOS behavior similar to the highly microphase segregated S/AS block copolymer, while the lower MW S/AS gradient copolymer exhibits complex, nonterminal behavior indicative of a lower degree of microphase segregation. The S/nBA gradient copolymers demonstrate more liquidlike behavior, with the lower MW sample exhibiting near-Newtonian behavior, indicative of a weakly segregating structure, while the higher MW, steeper gradient sample shows behavior ranging from solidlike to more liquidlike with increasing temperature. With the exception of the lower MW S/nBA case, the gradient copolymers exhibit temperature-dependent LAOS behavior over a wide temperature range, reflecting their temperature-dependent nanodomain composition amplitudes. The S/AS samples have SAXS results consistent with the degree of microphase segregation observed via rheology. Shear alignment studies are done on the higher MW S/AS gradient copolymer, which is the most highly microphase segregated gradient copolymer. Rheology and SAXS provide evidence of shear alignment, despite the gradual variation in composition profile across the nanodomains of such gradient copolymers. A short review of the nomenclature and behavior of linear copolymer architectures is also provided.

  8. Microphase separation induced in the melt of Pluronic copolymers by blending with a hydrogen bonding urea-urethane end-capped supramolecular polymer.

    PubMed

    Hermida-Merino, Daniel; Newby, Gemma E; Hamley, Ian W; Hayes, Wayne; Slark, Andrew

    2015-08-01

    Blending with a hydrogen-bonding supramolecular polymer is shown to be a successful novel strategy to induce microphase-separation in the melt of a Pluronic polyether block copolymer. The supramolecular polymer is a polybutadiene derivative with urea-urethane end caps. Microphase separation is analysed using small-angle X-ray scattering and its influence on the macroscopic rheological properties is analysed. FTIR spectroscopy provides a detailed picture of the inter-molecular interactions between the polymer chains that induces conformational changes leading to microphase separation. PMID:26151722

  9. Flory-Huggins parameter χ, from binary mixtures of Lennard-Jones particles to block copolymer melts

    NASA Astrophysics Data System (ADS)

    Chremos, Alexandros; Nikoubashman, Arash; Panagiotopoulos, Athanassios Z.

    2014-02-01

    In this contribution, we develop a coarse-graining methodology for mapping specific block copolymer systems to bead-spring particle-based models. We map the constituent Kuhn segments to Lennard-Jones particles, and establish a semi-empirical correlation between the experimentally determined Flory-Huggins parameter χ and the interaction of the model potential. For these purposes, we have performed an extensive set of isobaric-isothermal Monte Carlo simulations of binary mixtures of Lennard-Jones particles with the same size but with asymmetric energetic parameters. The phase behavior of these monomeric mixtures is then extended to chains with finite sizes through theoretical considerations. Such a top-down coarse-graining approach is important from a computational point of view, since many characteristic features of block copolymer systems are on time and length scales which are still inaccessible through fully atomistic simulations. We demonstrate the applicability of our method for generating parameters by reproducing the morphology diagram of a specific diblock copolymer, namely, poly(styrene-b-methyl methacrylate), which has been extensively studied in experiments.

  10. Thermoreversible Changes in Aligned and Cross-Linked Block Copolymer Melts Studied by Two Color Depolarized Light Scattering

    SciTech Connect

    Wilbur, Jeffrey D.; Gomez, Enrique D.; Ellsworth, Mark W.; Garetz, Bruce A.; Balsara, Nitash P.

    2012-09-04

    A procedure for creating samples that can be repeatedly cycled between weakly aligned and strongly aligned states is described. Poly(styrene-b-isoprene) block copolymer samples were first shear-aligned and then cross-linked using a high energy electron beam. Samples with more than 1.0 cross-links per chain on average showed almost complete recovery of their initial alignment state even after 20 cycles of heating above the order–disorder transition temperature of the un-cross-linked block copolymer. Samples with 1.1 cross-links per chain, which showed over 90% loss of alignment on heating and almost 100% recovery of alignment on cooling, provided the best example of a reversible aligned-to-unaligned transition. Samples with lower cross-linking densities exhibited irreversible loss of alignment upon heating, while those with higher cross-linking densities exhibited less than 90% loss of alignment upon heating. Alignment was quantified by a technique that we call two color depolarized light scattering (TCDLS), an extension of the traditional depolarized light scattering experiment used to determine the state of order in block copolymers. Qualitative confirmation of our interpretation of TCDLS data was obtained by small-angle X-ray scattering and transmission electron microscopy.

  11. Flory-Huggins parameter χ, from binary mixtures of Lennard-Jones particles to block copolymer melts.

    PubMed

    Chremos, Alexandros; Nikoubashman, Arash; Panagiotopoulos, Athanassios Z

    2014-02-01

    In this contribution, we develop a coarse-graining methodology for mapping specific block copolymer systems to bead-spring particle-based models. We map the constituent Kuhn segments to Lennard-Jones particles, and establish a semi-empirical correlation between the experimentally determined Flory-Huggins parameter χ and the interaction of the model potential. For these purposes, we have performed an extensive set of isobaric-isothermal Monte Carlo simulations of binary mixtures of Lennard-Jones particles with the same size but with asymmetric energetic parameters. The phase behavior of these monomeric mixtures is then extended to chains with finite sizes through theoretical considerations. Such a top-down coarse-graining approach is important from a computational point of view, since many characteristic features of block copolymer systems are on time and length scales which are still inaccessible through fully atomistic simulations. We demonstrate the applicability of our method for generating parameters by reproducing the morphology diagram of a specific diblock copolymer, namely, poly(styrene-b-methyl methacrylate), which has been extensively studied in experiments. PMID:24511981

  12. Flory-Huggins parameter χ, from binary mixtures of Lennard-Jones particles to block copolymer melts

    SciTech Connect

    Chremos, Alexandros; Nikoubashman, Arash Panagiotopoulos, Athanassios Z.

    2014-02-07

    In this contribution, we develop a coarse-graining methodology for mapping specific block copolymer systems to bead-spring particle-based models. We map the constituent Kuhn segments to Lennard-Jones particles, and establish a semi-empirical correlation between the experimentally determined Flory-Huggins parameter χ and the interaction of the model potential. For these purposes, we have performed an extensive set of isobaric–isothermal Monte Carlo simulations of binary mixtures of Lennard-Jones particles with the same size but with asymmetric energetic parameters. The phase behavior of these monomeric mixtures is then extended to chains with finite sizes through theoretical considerations. Such a top-down coarse-graining approach is important from a computational point of view, since many characteristic features of block copolymer systems are on time and length scales which are still inaccessible through fully atomistic simulations. We demonstrate the applicability of our method for generating parameters by reproducing the morphology diagram of a specific diblock copolymer, namely, poly(styrene-b-methyl methacrylate), which has been extensively studied in experiments.

  13. X-ray scattering investigation of structural relaxation in an ordered block copolymer melt subjected to uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    Burghardt, Wesley; McCready, Erica

    2012-02-01

    The structural dynamics of an ordered styrene-ethylene butylene-styrened triblock copolymer have been studied in uniaxial extensional flow using in situ x-ray scattering. Experiments were performed in a custom instrument consisting of an SER extensional flow fixture housed in a convection oven designed to facilitate x-ray access. Use of synchrotron radiation provided sufficient time resolution to study the structural response during inception of uniaxial flow, and as a function of time following flow cessation. The sample studied here exhibits hexagonally packed cylindrical microdomains of polystyrene embedded in a poly(ethylene butylene) matrix. Application of extensional flow produces multiple structural effects, including deformation of the microphase-separated morphology, and a complex reorientation process in which elongated PS microdomains progressively orient along the stretching axis. A series of experiments was run in which samples were stretching to varying Hencky strains, allowing investigation of the nature of structural relaxation from a variety of flow-induced structural states induced during extensional flow. Significant differences in structural relaxation are found depending on the total applied extensional strain.

  14. The Effect of Filler-Polymer Interactions on Cold-Crystallization Kinetics in Crosslinked, Silica Filled PDMS/PDPS Copolymer Melts.

    SciTech Connect

    Chien, A; DeTeresa, S; Thompson, L; Cohenour, R; Balazs, B; Maxwell, R S

    2006-04-21

    Crystallization in a series of variable crosslink density poly(dimethyl-diphenyl) siloxanes random block copolymers reinforced through a mixture of precipitated and fumed silica fillers has been studied by Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and X-ray Diffraction (XRD). The silicone composite studied was composed of 94.6 mol% Dimethoylsiloxane, 5.1 mol% diphenylsiloxane, and 0.3 mol% methyl-vinyl siloxane (which formed crosslinking after a peroxide cure). The polymer was filled with a mixture of 21.6 wt. % fumed silica and 4.0 wt. % precipitated silica previously treated with 6.8 wt. % ethoxy-endblocked siloxane processing aid. The base composite was characterized by a molecular weight between crosslinks in the polymer network of {approx}24 kDa and an overall molecular weight (including the influence of the silica fillers) between crosslinks of {approx}11 kDa. Molecular weight between crosslinks and filler-polymer interaction strength were then modified by exposure to {gamma}-irradiation in either air or vacuum. The unirradiated material exhibited crystallization at -80 C as measured by DSC with a 16% crystallization as measured by XRD. Isothermal DMA experiments illustrated that crystallization at -85 C occurred over a 1.8 hour period in silica-filled systems and 2.2-2.6 hours in unfilled systems. The onset of crystallization typically occurred after a 30-minute incubation/nucleation period. The crystallization kinetics were dependent on crosslink density. Changes in molecular weight of a factor of two did not, however, change the amount of crystallization. Irradiation in vacuum resulted in faster overall crystallization rates compared to air irradiation for the same crosslink density, likely due to a reduction in the interaction between the polymer chains and the silica filler surface. Modulated differential scanning calorimetry contrasted the crystallization and melting behavior of pure PDMS versus the PDMS/PDPS base

  15. Polyether/Polyester Graft Copolymers

    NASA Technical Reports Server (NTRS)

    Bell, Vernon L., Jr.; Wakelyn, N.; Stoakley, D. M.; Proctor, K. M.

    1986-01-01

    Higher solvent resistance achieved along with lower melting temperature. New technique provides method of preparing copolymers with polypivalolactone segments grafted onto poly (2,6-dimethyl-phenylene oxide) backbone. Process makes strong materials with improved solvent resistance and crystalline, thermally-reversible crosslinks. Resulting graft copolymers easier to fabricate into useful articles, including thin films, sheets, fibers, foams, laminates, and moldings.

  16. Role of adenosine A2B receptors in inflammation

    PubMed Central

    Feoktistov, Igor; Biaggioni, Italo

    2013-01-01

    Recent progress in our understanding of the unique role of A2B receptors in the regulation of inflammation, immunity and tissue repair was considerably facilitated with the introduction of new pharmacological and genetic tools. However, it also led to seemingly conflicting conclusions on the role of A2B adenosine receptors in inflammation with some publications indicating pro-inflammatory effects and others suggesting the opposite. This chapter reviews the functions of A2B receptors in various cell types related to inflammation and integrated effects of A2B receptor modulation in several animal models of inflammation. It is argued that translation of current findings into novel therapies would require a better understanding of A2B receptors functions in diverse types of inflammatory responses in various tissues and at different points of their progression. PMID:21586358

  17. Recent developments in A2B adenosine receptor ligands.

    PubMed

    Kalla, Rao V; Zablocki, Jeff; Tabrizi, Mojgan Aghazadeh; Baraldi, Pier Giovanni

    2009-01-01

    A selective, high-affinity A(2B) adenosine receptor (AR) antagonist will be useful as a pharmacological tool to help determine the role of the A(2B)AR in inflammatory diseases and angiogenic diseases. Based on early A(2B)AR-selective ligands with nonoptimal pharmaceutical properties, such as 15 (MRS 1754: K(i)(hA(2B)) = 2 nM; K(i)(hA(1)) = 403 nM; K(i)(hA(2A)) = 503 NM, and K(i)(hA(3)) = 570 nM), several groups have discovered second-generation A(2B)AR ligands that are suitable for development. Scientists at CV Therapeutics have discovered the selective, high-affinity A(2B)AR antagonist 22, a 8-(4-pyrazolyl)-xanthine derivative, (CVT-6883, K(i)(hA(2B)) = 22 nM; K(i)(hA(1)) = 1,940 nM; K(i)(hA(2A)) = 3,280; and K(i)(hA(3)) = 1,070 nM). Compound 22 has demonstrated favorable pharmacokinetic (PK) properties (T(1/2) = 4 h and F > 35% rat), and it is a functional antagonist at the A(2B)AR(K (B) = 6 nM). In a mouse model of asthma, compound 22 demonstrated a dose-dependent efficacy supporting the role of the A(2B)AR in asthma. In two Phase I clinical trails, 22 (CVT-6883) was found to be safe, well tolerated, and suitable for once-daily dosing. Baraldi et al. have independently discovered a selective, high-affinity A(2B)AR antagonist, 30 (MRE2029F20), 8-(5-pyrazolyl)-xanthine (K(i)(hA(2B)) = 5.5 nM; K(i)(hA(1)) = 200 nM; K(i)(hA(2A), A(3)) > 1,000, that has been selected for development in conjunction with King Pharmaceuticals. Compound 30 has been demonstrated to be a functional antagonist of the A(2B)AR, and it has been radiolabeled for use in pharmacological studies. A third compound, 58 (LAS-38096), is a 2-aminopyrimidine derivative (discovered by the Almirall group) that has high A(2B)AR affinity and selectivity (K(i)(hA(2B)) = 17 nM; K(i)(hA(1)) > 1,000 nM; K(i)(hA(2A)) > 2,500; and K(i)(hA(3)) > 1,000 nM), and 58 has been moved into preclinical safety testing. A fourth selective, high-affinity A(2B)AR antagonist, 54 (OSIP339391 K(i))(hA(2B)) = 0.5 nM; K(i))(hA(1

  18. The morphology of A2B mikotoarm polymer in thin film

    NASA Astrophysics Data System (ADS)

    Kim, Hyeyoung; Kang, Beom-Goo; Sun, Zhiwei; Choi, Jaewon; Russell, Thomas

    The morphologies of A2B mikto-arm polymer consisted of poly(2-vinyl pyridine) and polystyrene ((P2VP)2PS) in thin film were examined. Solvent vapor annealing produces films with lamellae perpendicular to the substrate within a very short time. The change in the morphology for different periods of time, corresponding to different swelling ratios was observed by grazing incidence small angle x-ray scattering and scanning force microscopy. This morphology showed the smaller height difference between PS and P2VP microdomains, when compared to the corresponding diblock copolymer. We also observed the long-range ordering formed on the saw-tooth pattern. Thermal annealing, on the other hand, resulted in the lamellae being oriented parallel to the substrate, where unusual behavior was depending on the film thickness and surface energy of substrate.

  19. Crystalline Imide/Arylene Ether Copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Hergenrother, Paul M.; Bass, Robert G.

    1991-01-01

    Series of imide/arylene ether block copolymers prepared by using arylene ether blocks to impart low melt viscosity, and imide blocks to provide high strength and other desirable mechanical properties. Work represents extension of LAR-14159 on imide/arylene ether copolymers in form of films, moldings, adhesives, and composite matrices. Copolymers potentially useful in variety of high-temperature aerospace and microelectronic applications.

  20. Monitoring the melt-extrusion transesterification of ethylene-vinylacetate copolymer by self-modeling curve resolution analysis of on-line near-infrared spectra.

    PubMed

    Sasić, S; Kita, Y; Furukawa, T; Watari, M; Siesler, H W; Ozaki, Y

    2000-12-01

    The transesterification of molten ethylene-vinylacetate (EVA) copolymers by octanol with sodium methoxide as catalyst in an extruder has been monitored by on-line near infrared (NIR) spectroscopy. A total of 60 NIR spectra were acquired for 37 min with the last spectrum recorded 31 min after the addition of octanol and catalyst was stopped. The experimental spectra show strong baseline fluctuations which are corrected for by multiplicative scatter correction (MSC). The chemometric methods of the orthogonal projection approach (OPA) and multivariate curve resolution (MCR) were used to resolve the spectra and to derive concentration profiles of the species. The detailed analysis reveals the absence of completely pure variables which leads to small errors in the calculation of pure spectra. The initial estimation of a concentration that is necessary as an input parameter for MCR also presents a non-trivial task. We obtained results that were not ideal but applicable for practical concentration control. They enable a fast monitoring of the process in real-time and resolve the spectra of the EVA copolymer and the ethylene-vinyl alcohol (EVAL) copolymer to be very close to the reference spectra. The chemometric methods used and the decomposed spectra are discussed in detail. PMID:11219074

  1. Arylenesiloxane copolymers

    NASA Technical Reports Server (NTRS)

    Breed, L. W.; Elliott, R. L.

    1967-01-01

    Arylenesiloxane copolymers with regularly ordered structures were discovered during efforts to develop organosilicon polymers. Arylenesilane and siloxane monomers were both synthesized in these experiments.

  2. Summary report on the fuel performance modeling of the AFC-2A, 2B irradiation experiments

    SciTech Connect

    Pavel G. Medvedev

    2013-09-01

    The primary objective of this work at the Idaho National Laboratory (INL) is to determine the fuel and cladding temperature history during irradiation of the AFC-2A, 2B transmutation metallic fuel alloy irradiation experiments containing transuranic and rare earth elements. Addition of the rare earth elements intends to simulate potential fission product carry-over from pyro-metallurgical reprocessing. Post irradiation examination of the AFC-2A, 2B rodlets revealed breaches in the rodlets and fuel melting which was attributed to the release of the fission gas into the helium gap between the rodlet cladding and the capsule which houses six individually encapsulated rodlets. This release is not anticipated during nominal operation of the AFC irradiation vehicle that features a double encapsulated design in which sodium bonded metallic fuel is separated from the ATR coolant by the cladding and the capsule walls. The modeling effort is focused on assessing effects of this unanticipated event on the fuel and cladding temperature with an objective to compare calculated results with the temperature limits of the fuel and the cladding.

  3. Hydrogen-bonded aggregates in precise acid copolymers

    SciTech Connect

    Lueth, Christopher A.; Bolintineanu, Dan S.; Stevens, Mark J. Frischknecht, Amalie L.

    2014-02-07

    We perform atomistic molecular dynamics simulations of melts of four precise acid copolymers, two poly(ethylene-co-acrylic acid) (PEAA) copolymers, and two poly(ethylene-co-sulfonic acid) (PESA) copolymers. The acid groups are spaced by either 9 or 21 carbons along the polymer backbones. Hydrogen bonding causes the acid groups to form aggregates. These aggregates give rise to a low wavevector peak in the structure factors, in agreement with X-ray scattering data for the PEAA materials. The structure factors for the PESA copolymers are very similar to those for the PEAA copolymers, indicating a similar distance between aggregates which depends on the spacer length but not on the nature of the acid group. The PEAA copolymers are found to form more dimers and other small aggregates than do the PESA copolymers, while the PESA copolymers have both more free acid groups and more large aggregates.

  4. Morphologies of poly(cyclohexadiene) diblock copolymers

    SciTech Connect

    Kumar, Rajeev; Mays, Jimmy; Sides, Scott; Goswami, Monojoy; Sumpter, Bobby G; Hong, Kunlun; Avgeropoulos, Apostolos; Russell, Thomas P; Gido, Samuel; Tsoukatos, Thodoris; Beyer, Fredrick

    2012-01-01

    Concerted experimental and theoretical investigations have been carried out to understand the micro-phase separation in diblock copolymer melts containing poly (1,3-cyclohexadiene), PCHD, as one of the constituents. In particular, we have studied diblock copolymer melts containing polystyrene (PS), polybutadiene (PB), and polyisoprene (PI) as the second block. We have systematically varied the ratio of 1,2- /1,4-microstructures of poly (1,3-cyclohexadiene) to tune the conformational asymmetry between the two blocks and characterized the effects of these changes on the morphologies using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Our experimental investigations reveal that the melts of PCHD-b-PB, PCHD-b-PS and PCHD-b-PI containing nearly equal fractions of each component and high percentage of 1,4-microstructures in the PCHD block form cylindrical rather than lamellar morphologies as expected in symmetric diblock copolymers. In contrast, the morphologies of PCHD-b-PB, PCHD-b-PS and PCHD-b-PI containing PCHD block with higher 1,2-microstructure are found to be disordered at 110 C. The change in the morphological behavior is in good agreement with our numerical calculations using the random phase approximation and self-consistent field theory for conformationally asymmetric diblock copolymer melts. Also, the effects of composition fluctuations are studied by extending the Brazovskii-Leibler-Fredrickson-Helfand (J. Chem. Phys. 87, 697 (1987)) theory to conformationally asymmetric diblock copolymer melts. These results allow the understanding of the underlying self-assembly process that highlights the importance of the conformational asymmetry in tuning the morphologies in block copolymers.

  5. Polyether-polyester graft copolymer

    NASA Technical Reports Server (NTRS)

    Bell, Vernon L. (Inventor)

    1987-01-01

    Described is a polyether graft polymer having improved solvent resistance and crystalline thermally reversible crosslinks. The copolymer is prepared by a novel process of anionic copolymerization. These polymers exhibit good solvent resistance and are well suited for aircraft parts. Previous aromatic polyethers, also known as polyphenylene oxides, have certain deficiencies which detract from their usefulness. These commercial polymers are often soluble in common solvents including the halocarbon and aromatic hydrocarbon types of paint thinners and removers. This limitation prevents the use of these polyethers in structural articles requiring frequent painting. In addition, the most popular commercially available polyether is a very high melting plastic. This makes it considerably more difficult to fabricate finished parts from this material. These problems are solved by providing an aromatic polyether graft copolymer with improved solvent resistance and crystalline thermally reversible crosslinks. The graft copolymer is formed by converting the carboxyl groups of a carboxylated polyphenylene oxide polymer to ionic carbonyl groups in a suitable solvent, reacting pivalolactone with the dissolved polymer, and adding acid to the solution to produce the graft copolymer.

  6. A2B adenosine receptor activity is reduced in neutrophils from patients with systemic sclerosis

    PubMed Central

    Bazzichi, Laura; Trincavelli, Letizia; Rossi, Alessandra; De Feo, Francesca; Lucacchini, Antonio; Bombardieri, Stefano; Martini, Claudia

    2005-01-01

    We conducted the present study to investigate protein expression and functioning of A2A and A2B adenosine receptors (ARs) in neutrophils of patients affected by systemic sclerosis (SSc). The presence of A2A and A2B ARs was assessed by immunoblotting using specific antibodies. Equilibrium A2A and A2B ARs binding parameters were evaluated by radioligand binding assay. Functional studies were conducted to investigate coupling of the A2B AR to the adenylyl cyclase pathway. This is the first report of the use of Western blot analysis to confirm the presence of A2A and A2B ARs in human neutrophils. No significant changes in A2A AR binding parameters or expression levels were detected between SSc patients and healthy control individuals. A significant decrease (65%) in the maximum density of A2B AR binding sites occurred in SSc neutrophils, whereas no changes in the affinity constant values were found. Moreover, a decrease in A2B AR mediated adenylyl cyclase activity was observed in patients with SSc. Our findings demonstrate the occurrence of selective alterations in A2B AR density and signalling in SSc. PMID:15743465

  7. Crystallization in Ordered Polydisperse Polyolefin Diblock Copolymers

    SciTech Connect

    Li, Sheng; Register, Richard A.; Landes, Brian G.; Hustad, Phillip D.; Weinhold, Jeffrey D.

    2010-12-07

    The morphologies of polydisperse ethylene-octene diblock copolymers, synthesized via a novel coordinative chain transfer polymerization process, are examined using two-dimensional synchrotron small-angle and wide-angle X-ray scattering on flow-aligned specimens. The diblock copolymers comprise one amorphous block with high 1-octene content and one semicrystalline block with relatively low 1-octene content, and each block ideally exhibits the most-probable distribution. Near-symmetric diblocks with a sufficiently large octene differential between the amorphous and semicrystalline blocks show well-ordered lamellar domain structures with long periods exceeding 100 nm. Orientation of these domain structures persists through multiple melting/recrystallization cycles, reflecting a robust structure which self-assembles in the melt. The domain spacings are nearly 3-fold larger than those in near-monodisperse polyethylene block copolymers of similar molecular weights. Although the well-ordered lamellar domain structure established in the melt is preserved in the solid state, the crystallites are isotropic in orientation. These materials display crystallization kinetics consistent with a spreading growth habit, indicating that the lamellae do not confine or template the growing crystals. The exceptionally large domain spacings and isotropic crystal growth are attributed to interblock mixing resulting from the large polydispersity; short hard blocks dissolved in the soft-block-rich domains swell the domain spacing in the melt and allow hard block crystallization to proceed across the lamellar domain interfaces.

  8. The A2B adenosine receptor modulates pulmonary hypertension associated with interstitial lung disease.

    PubMed

    Karmouty-Quintana, Harry; Zhong, Hongyan; Acero, Luis; Weng, Tingting; Melicoff, Ernestina; West, James D; Hemnes, Anna; Grenz, Almut; Eltzschig, Holger K; Blackwell, Timothy S; Xia, Yang; Johnston, Richard A; Zeng, Dewan; Belardinelli, Luiz; Blackburn, Michael R

    2012-06-01

    Development of pulmonary hypertension is a common and deadly complication of interstitial lung disease. Little is known regarding the cellular and molecular mechanisms that lead to pulmonary hypertension in patients with interstitial lung disease, and effective treatment options are lacking. The purpose of this study was to examine the adenosine 2B receptor (A(2B)R) as a regulator of vascular remodeling and pulmonary hypertension secondary to pulmonary fibrosis. To accomplish this, cellular and molecular changes in vascular remodeling were monitored in mice exposed to bleomycin in conjunction with genetic removal of the A(2B)R or treatment with the A(2B)R antagonist GS-6201. Results demonstrated that GS-6201 treatment or genetic removal of the A(2B)R attenuated vascular remodeling and hypertension in our model. Furthermore, direct A(2B)R activation on vascular cells promoted interleukin-6 and endothelin-1 release. These studies identify a novel mechanism of disease progression to pulmonary hypertension and support the development of A(2B)R antagonists for the treatment of pulmonary hypertension secondary to interstitial lung disease. PMID:22415303

  9. Phase separations in a copolymer copolymer mixture

    NASA Astrophysics Data System (ADS)

    Zhang, Jin-Jun; Jin, Guojun; Ma, Yuqiang

    2006-01-01

    We propose a three-order-parameter model to study the phase separations in a diblock copolymer-diblock copolymer mixture. The cell dynamical simulations provide rich information about the phase evolution and structural formation, especially the appearance of onion-rings. The parametric dependence and physical reason for the domain growth of onion-rings are discussed.

  10. Crystallization and Solid State Structure of Poly(lactide) Copolymers

    NASA Astrophysics Data System (ADS)

    Baratian, S.; Runt, J.; Hall, E.; Lin, J. S.

    2000-03-01

    A series of random poly(lactide) copolymers was synthesized from L-lactide and D,L lactide using a tin (II) octanoate catalyst. The copolymers contained from 1.7 to 6.2 percent R stereochemical defects in otherwise S stereoisomer chains. Small-angle x-ray scattering experiments were used to determine the final lamellar microstructure of the copolymers. Lamellar thicknesses were strongly dependent on R co-unit concentration and it was concluded that the final structure contains significant pockets of non-crystalline material between spherulite fibrils. Equilibrium melting temperatures were estimated using the Gibbs-Thomson approach and their variation with comonomer content suggests that there is significant exclusion of R stereochemical defects from crystalline regions. Spherulite growth rates of the D-lactide copolymers were found to be larger than L-lactide/meso-lactide copolymers at equivalent optical composition.

  11. Immunodiagnosis of tumors in vivo using radiolabeled monoclonal antibody A2B5

    SciTech Connect

    Reintgen, D.S.; Shimizu, K.; Coleman, E.; Briner, W.; Kitzmiller, J.; Eisenbarth, G.; Seigler, H.F.

    1983-07-01

    Recently a murine monoclonal antibody (A2B5) has been described that reacts with a membrane associated GQ ganglioside common to peptide secreting normal cells and tumors. In vitro binding data demonstrated the presence of this ganglioside on neurons, adrenal medulla, and pancreatic islets, along with neuroendocrine tumors such as insulinomas, pheochromocytomas, melanomas and neuroblastomas. Negative binding has previously been shown for tissue sections from liver, kidney, colon, lung, stomach, and tumors not derived from the neural crest. Because of the specificity at A2B5 in vitro, this monoclonal antibody was labeled with /sup 131/I for in vivo tumor localization studies. Daily radionuclear scans were obtained in 5 KX rats bearing the radiation induced rat insulinoma with disappearance of the label from the blood pool and concentration in the tumor so that by the fourth day, the only activity present by scan was in the insulinoma. In addition A2B5 also localized to five different human melanoma cells lines grown in nude mice with high tumor/blood levels compared to normal tissues, while no localization is seen in nudes carrying osteosarcomas, colon, bladder, and renal cell carcinomas. In addition antibody A2B5 did not concentrate in any normal tissue though the antigen is present on several. The finding that A2B5 reacts across species lines (mouse, rat, man) lends itself to obvious diagnostic and therapeutic possibilities.

  12. Immunodiagnosis of tumors in vivo using radiolabeled monoclonal antibody A2B5.

    PubMed

    Reintgen, D S; Shimizu, K; Coleman, E; Briner, W; Kitzmiller, J; Eisenbarth, G; Seigler, H F

    1983-07-01

    Recently a murine monoclonal antibody (A2B5) has been described that reacts with a membrane associated GQ ganglioside common to peptide secreting normal cells and tumors. In vitro binding data demonstrated the presence of this ganglioside on neurons, adrenal medulla, and pancreatic islets, along with neuroendocrine tumors such as insulinomas, pheochromocytomas, melanomas and neuroblastomas. Negative binding has previously been shown for tissue sections from liver, kidney, colon, lung, stomach, and tumors not derived from the neural crest. Because of the specificity at A2B5 in vitro, this monoclonal antibody was labeled with 131I for in vivo tumor localization studies. Daily radionuclear scans were obtained in 5 KX rats bearing the radiation induced rat insulinoma with disappearance of the label from the blood pool and concentration in the tumor so that by the fourth day, the only activity present by scan was in the insulinoma. Tissue-counting data showed tumor/blood ratios (av +/- SE, 1.29 +/- 0.25) of A2B5 activity two to ten times the average activity found in other organs (0.28 +/- 0.05). No tumor concentration of the control nonspecific monoclonal antibody P3X63 was evident (0.27 +/- 0.04). In addition A2B5 also localized to five different human melanoma cells lines grown in nude mice with high tumor/blood levels (1.04 +/- 0.27) compared to normal tissues (0.32 +/- 0.05) (P = .0005), while no localization is seen in nudes carrying osteosarcomas, colon, bladder, and renal cell carcinomas. In addition antibody A2B5 did not concentrate in any normal tissue though the antigen is present on several. The finding that A2B5 reacts across species lines (mouse, rat, man) lends itself to obvious diagnostic and therapeutic possibilities. PMID:6306349

  13. Recent improvements in the development of A2B adenosine receptor agonists

    PubMed Central

    Tabrizi, Mojgan Aghazadeh; Fruttarolo, Francesca; Romagnoli, Romeo; Preti, Delia

    2009-01-01

    Adenosine is known to exert most of its physiological functions by acting as local modulator at four receptor subtypes named A1, A2A, A2B and A3 (ARs). Principally as a result of the difficulty in identifying potent and selective agonists, the A2B AR is the least extensively characterised of the adenosine receptors family. Despite these limitations, growing understanding of the physiological meaning of this target indicates promising therapeutic perspectives for specific ligands. As A2B AR signalling seems to be associated with pre/postconditioning cardioprotective and anti-inflammatory mechanisms, selective agonists may represent a new therapeutic group for patients suffering from coronary artery disease. Herein we present an overview of the recent advancements in identifying potent and selective A2B AR agonists reported in scientific and patent literature. These compounds can be classified into adenosine-like and nonadenosine ligands. Nucleoside-based agonists are the result of modifying adenosine by substitution at the N6-, C2-positions of the purine heterocycle and/or at the 5′-position of the ribose moiety or combinations of these substitutions. Compounds 1-deoxy-1-{6-[N′-(furan-2-carbonyl)-hydrazino]-9H-purin-9-yl}-N-ethyl-β-D-ribofuranuronamide (19, hA1Ki = 1050 nM, hA2AKi = 1550 nM, hA2B EC50 = 82 nM, hA3Ki > 5 μM) and its 2-chloro analogue 23 (hA1Ki = 3500 nM, hA2AKi = 4950 nM, hA2B EC50 = 210 nM, hA3Ki > 5 μM) were confirmed to be potent and selective full agonists in a cyclic adenosine monophosphate (cAMP) functional assay in Chinese hamster ovary (CHO) cells expressing hA2B AR. Nonribose ligands are represented by conveniently substituted dicarbonitrilepyridines, among which 2-[6-amino-3,5-dicyano-4-[4-(cyclopropylmethoxy)phenyl]pyridin-2-ylsulfanyl]acetamide (BAY-60–6583, hA1, hA2A, hA3 EC50 > 10 μM; hA2B EC50 = 3 nM) is currently under preclinical-phase investigation for treating coronary

  14. Recent improvements in the development of A2B adenosine receptor agonists

    PubMed Central

    Tabrizi, Mojgan Aghazadeh; Fruttarolo, Francesca; Romagnoli, Romeo; Preti, Delia

    2008-01-01

    Adenosine is known to exert most of its physiological functions by acting as local modulator at four receptor subtypes named A1, A2A, A2B and A3 (ARs). Principally as a result of the difficulty in identifying potent and selective agonists, the A2B AR is the least extensively characterised of the adenosine receptors family. Despite these limitations, growing understanding of the physiological meaning of this target indicates promising therapeutic perspectives for specific ligands. As A2B AR signalling seems to be associated with pre/postconditioning cardioprotective and anti-inflammatory mechanisms, selective agonists may represent a new therapeutic group for patients suffering from coronary artery disease. Herein we present an overview of the recent advancements in identifying potent and selective A2B AR agonists reported in scientific and patent literature. These compounds can be classified into adenosine-like and nonadenosine ligands. Nucleoside-based agonists are the result of modifying adenosine by substitution at the N6-, C2-positions of the purine heterocycle and/or at the 5′-position of the ribose moiety or combinations of these substitutions. Compounds 1-deoxy-1-{6-[N′-(furan-2-carbonyl)-hydrazino]-9H-purin-9-yl}-N-ethyl-β-D-ribofuranuronamide (19, hA1Ki = 1050 nM, hA2AKi = 1550 nM, hA2B EC50 = 82 nM, hA3Ki > 5 μM) and its 2-chloro analogue 23 (hA1Ki = 3500 nM, hA2AKi = 4950 nM, hA2B EC50 = 210 nM, hA3Ki > 5 μM) were confirmed to be potent and selective full agonists in a cyclic adenosine monophosphate (cAMP) functional assay in Chinese hamster ovary (CHO) cells expressing hA2B AR. Nonribose ligands are represented by conveniently substituted dicarbonitrilepyridines, among which 2-[6-amino-3,5-dicyano-4-[4-(cyclopropylmethoxy)phenyl]pyridin-2-ylsulfanyl]acetamide (BAY-60–6583, hA1, hA2A, hA3 EC50 > 10 μM; hA2B EC50 = 3 nM) is currently under preclinical-phase investigation for treating coronary

  15. Identification of A2B5-positive putative oligodendrocyte progenitor cells and A2B5-positive astrocytes in adult human white matter.

    PubMed

    Scolding, N J; Rayner, P J; Compston, D A

    1999-03-01

    Spontaneous remyelination of previously demyelinated axons is found in a substantial minority of acute and chronic lesions in multiple sclerosis. In the rodent, central remyelination restores saltatory conduction and helps restore limb function, and it seems likely that endogenous myelin repair contributes to neurological recovery in multiple sclerosis. However, the identity of the remyelinating cell remains enigmatic. Fully differentiated oligodendrocytes have very limited capacity for recapitulating their developmental activities and re-engaging myelination pathways. Proliferative oligodendrocyte progenitors--often known as O-2A cells because of their ability to differentiate in vitro into either oligodendrocytes or ("type 2") astrocytes--are, in contrast, extremely efficient at myelin repair either spontaneously, or after transplantation into the de- or dysmyelinated CNS. Oligodendrocyte progenitors are present in both developing and adult rodent CNS. We have previously demonstrated that proliferative oligodendrocyte progenitors are present in cultures prepared from the adult human CNS. Here, using fresh tissue print preparations, we report that cells with processes and the A2B5-positive immunophenotype of proliferative oligodendrocyte progenitors are present in situ in adult human white matter. This technique also reveals the occurrence of A2B5-positive astrocytes, a cell also not previously identified in the normal adult human CNS. In the light of the rodent data showing the importance of oligodendrocyte progenitors in myelin repair, our findings suggesting the presence of progenitors in the adult human brain may have significant implications for spontaneous remyelination in multiple sclerosis and other demyelinating conditions. PMID:10051212

  16. Measurements of the Urbach tail for A2B6 mixed crystals by the photothermal method

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Malinski, M.; Strzałkowski, K.; Firszt, F.; Łęgowski, S.; Męczyńska, H.

    2010-03-01

    This paper presents the influence of the composition of several mixed A2B6 crystals on the broadening of the optical absorption coefficient spectra. This broadening is observed as the change of the piezoelectric spectra associated with the change oft he Urbach tail. This effect is interpreted as a result of the increase of the compositional disorder of the crystal lattice.

  17. Expression of adenosine A2b receptor in rat type II and III taste cells.

    PubMed

    Nishida, Kentaro; Dohi, Yukari; Yamanaka, Yuri; Miyata, Ai; Tsukamoto, Katsunobu; Yabu, Miharu; Ohishi, Akihiro; Nagasawa, Kazuki

    2014-05-01

    We previously demonstrated that equilibrative nucleoside transporter 1 was expressed in taste cells, suggesting the existence of an adenosine signaling system, but whether or not the expression of an adenosine receptor occurs in rat taste buds remains unknown. Therefore, we examined the expression profiles of adenosine receptors and evaluated their functionality in rat circumvallate papillae. Among adenosine receptors, the mRNA for an adenosine A2b receptor (A2bR) was expressed by the rat circumvallate papillae, and its expression level was significantly greater in the circumvallate papillae than in the non-taste lingual epithelium. A2bR-immunoreactivity was detected primarily in type II taste cells, and partial, but significant expression was also observed in type III ones, but there was no immunoreactivity in type I ones. The cAMP generation in isolated epithelium containing taste buds treated with 500 μM adenosine or 10 μM BAY60-6583 was significantly increased compared to in the controls. These findings suggest that adenosine plays a role in signaling transmission via A2bR between taste cells in rats. PMID:24327108

  18. Protein based Block Copolymers

    PubMed Central

    Rabotyagova, Olena S.; Cebe, Peggy; Kaplan, David L.

    2011-01-01

    Advances in genetic engineering have led to the synthesis of protein-based block copolymers with control of chemistry and molecular weight, resulting in unique physical and biological properties. The benefits from incorporating peptide blocks into copolymer designs arise from the fundamental properties of proteins to adopt ordered conformations and to undergo self-assembly, providing control over structure formation at various length scales when compared to conventional block copolymers. This review covers the synthesis, structure, assembly, properties, and applications of protein-based block copolymers. PMID:21235251

  19. Thermal analytical study of polyamide copolymer/Surlyn Ionomers Blends

    SciTech Connect

    Qin, C.; Ding, Y.P.

    1993-12-31

    Thermal analytical technique was used as a screening method to study polyamide(Nylon)/ethylene-co-methacrylic acid copolymer-based ionomer(Surlyn)blends. The retardation of crystallization process from molten state of Nylon-12 by the existence of the ionomer was observed, but the crystallization of Nylon-12 can not be thwarted even at high concentration of ionomers. Zinc ionomers shows stronger effect than sodium ionomers. A Nylon copolymer, polyamide-6,6-co-polyamide-6,10, was used to blend with different ionomers and the crystallization process from molten state of Nylon copolymer could be thwarted at high concentration of zinc ionomer even at very cooling rate. Interesting cold crystallization behavior of polyamide copolymer was observed during second DSC heating cycle in the temperature range of the melting process of ionomer.

  20. Silicone/Acrylate Copolymers

    NASA Technical Reports Server (NTRS)

    Dennis, W. E.

    1982-01-01

    Two-step process forms silicone/acrylate copolymers. Resulting acrylate functional fluid is reacted with other ingredients to produce copolymer. Films of polymer were formed by simply pouring or spraying mixture and allowing solvent to evaporate. Films showed good weatherability. Durable, clear polymer films protect photovoltaic cells.

  1. Confinement of block copolymers

    SciTech Connect

    1995-12-31

    The following were studied: confinement of block copolymers, free surface confinement, effects of substrate interactions, random copolymers at homopolymer interfaces, phase separation in thin film polymer mixtures, buffing of polymer surfaces, and near edge x-ray absorption fine structure spectroscopy.

  2. Influence of Surface Preparation for Different Groups of A2B6 Mixed Crystals

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Maliński, M.; Strzałkowski, K.; Firszt, F.; Łęgowski, S.; Męczyńska, H.

    2010-01-01

    Piezoelectric photothermal spectroscopy has been used for measurements of the optical and thermal parameters of semiconductors. The investigated crystals were grown by the high-pressure Bridgman method under argon overpressure. The obtained photoacoustic (PA) spectra show the complexity of the effects observed for the different groups of selected A2B6 crystals. These effects comprise ideal samples and samples with damaged surfaces. The spectra show the influence of the surface treatment on the PA amplitude and phase spectra.

  3. Phase Behavior of Neat Triblock Copolymers and Copolymer/Homopolymer Blends Near Network Phase Windows

    SciTech Connect

    M Tureau; L Rong; B Hsiao; T Epps

    2011-12-31

    The phase behavior of poly(isoprene-b-styrene-b-methyl methacrylate) (ISM) copolymers near the styrene-rich network phase window was examined through the use of neat triblock copolymers and copolymer/homopolymer blends. Both end-block and middle-block blending protocols were employed using poly(isoprene) (PI), poly(methyl methacrylate) (PMMA), and poly(styrene) (PS) homopolymers. Blended specimens exhibited phase transformations to well-ordered nanostructures (at homopolymer loadings up to 26 vol % of the total blend volume). Morphological consistency between neat and blended specimens was established at various locations in the ISM phase space. Copolymer/homopolymer blending permitted the refinement of lamellar, hexagonally packed cylinder, and disordered melt phase boundaries as well as the identification of double gyroid (Q{sup 230}), alternating gyroid (Q{sup 214}), and orthorhombic (O{sup 70}) network regimes. Additionally, the experimental phase diagram exhibited similar trends to those found in a theoretical ABC triblock copolymer phase diagram with symmetric interactions and statistical segments lengths generated by Tyler et al.

  4. Role of the A2B receptor–adenosine deaminase complex in colonic dysmotility associated with bowel inflammation in rats

    PubMed Central

    Antonioli, L; Fornai, M; Awwad, O; Giustarini, G; Pellegrini, C; Tuccori, M; Caputi, V; Qesari, M; Castagliuolo, I; Brun, P; Giron, M C; Scarpignato, C; Blandizzi, C; Colucci, R

    2014-01-01

    BACKGROUND AND PURPOSE Adenosine A2B receptors regulate several physiological enteric functions. However, their role in the pathophysiology of intestinal dysmotility associated with inflammation has not been elucidated. Hence, we investigated the expression of A2B receptors in rat colon and their role in the control of cholinergic motility in the presence of bowel inflammation. EXPERIMENTAL APPROACH Colitis was induced by 2,4-dinitrobenzenesulfonic acid (DNBS). Colonic A2B receptor expression and localization were examined by RT-PCR and immunofluorescence. The interaction between A2B receptors and adenosine deaminase was assayed by immunoprecipitation. The role of A2B receptors in the control of colonic motility was examined in functional experiments on longitudinal muscle preparations (LMPs). KEY RESULTS A2B receptor mRNA was present in colon from both normal and DNBS-treated rats but levels were increased in the latter. A2B receptors were predominantly located in the neuromuscular layer, but, in the presence of colitis, were increased mainly in longitudinal muscle. Functionally, the A2B receptor antagonist MRS 1754 enhanced both electrically-evoked and carbachol-induced cholinergic contractions in normal LMPs, but was less effective in inflamed tissues. The A2B receptor agonist NECA decreased colonic cholinergic motility, with increased efficacy in inflamed LMP. Immunoprecipitation and functional tests revealed a link between A2B receptors and adenosine deaminase, which colocalize in the neuromuscular compartment. CONCLUSIONS AND IMPLICATIONS Under normal conditions, endogenous adenosine modulates colonic motility via A2B receptors located in the neuromuscular compartment. In the presence of colitis, this inhibitory control is impaired due to a link between A2B receptors and adenosine deaminase, which catabolizes adenosine, thus preventing A2B receptor activation. PMID:24286264

  5. Block and Graft Copolymers of Polyhydroxyalkanoates

    NASA Astrophysics Data System (ADS)

    Marchessault, Robert H.; Ravenelle, François; Kawada, Jumpei

    2004-03-01

    Polyhydroxyalkanoates (PHAs) were modified for diblock copolymer and graft polymer by catalyzed transesterification in the melt and by chemical synthesis to extend the side chains of the PHAs, and the polymers were studied by transmission electron microscopy (TEM) X-ray diffraction, thermal analysis and nuclear magnetic resonance (NMR). Catalyzed transesterification in the melt is used to produce diblock copolymers of poly[3-hydroxybutyrate] (PHB) and monomethoxy poly[ethylene glycol] (mPEG) in a one-step process. The resulting diblock copolymers are amphiphilic and self-assemble into sterically stabilized colloidal suspensions of PHB crystalline lamellae. Graft polymer was synthesized in a two-step chemical synthesis from biosynthesized poly[3-hydroxyoctanoate-co-3-hydroxyundecenoate] (PHOU) containing ca. 25 mol chains. 11-mercaptoundecanoic acid reacts with the side chain alkenes of PHOU by the radical addition creating thioether linkage with terminal carboxyl functionalities. The latter groups were subsequently transformed into the amide or ester linkage by tridecylamine or octadecanol, respectively, producing new graft polymers. The polymers have different physical properties than poly[3-hydroxyoctanoate] (PHO) which is the main component of the PHOU, such as non-stickiness and higher thermal stability. The combination of biosynthesis and chemical synthesis produces a hybrid thermoplastic elastomer with partial biodegradability.

  6. Processible Polyaniline Copolymers and Complexes.

    NASA Astrophysics Data System (ADS)

    Liao, Yun-Hsin

    1995-01-01

    Polyaniline (PANI) is an intractable polymer due to the difficulty of melt processing or dissolving it in common solvents. The purpose of the present investigation was to prepare a new class of conducting polyanilines with better solubility both in base and dope forms by (1) adding external salt to break aggregated chains, (2) introducing ring substituted units onto the backbone without disturbing the coplanar structure, and (3) complexing with polymeric dopants to form a soluble polymer complex. Aggregation of PANI chains in dilute solution was investigated in N-methyl-2-pyrrolidinone (NMP) by light scattering, gel permeation chromatography, and viscosity measurements. The aggregation of chains resulted in a negative second virial coefficient in light scattering measurement, a bimodal molecular weight distribution in gel permeation chromatography, and concave reduced viscosity curves. The aggregates can be broken by adding external salt, which resulting in a higher reduced viscosity. The driving force for aggregation is assumed to be a combination of hydrogen bonding between the imine and amine groups, and the rigidity of backbone. The aggregation was modeled to occur via side-on packing of PANI chains. The ring substituted PANI copolymers, poly(aniline -co-phenetidine) were synthesized by chemical oxidation copolymerization using ammonium persulfate as an oxidant. The degree of copolymerization declined with an increasing feed of o-phenetidine in the reaction mixture. The o-phenetidine had a higher reactivity than aniline in copolymerization resulting in a higher content of o-phenetidine in copolymers. The resulting copolymers can be readily dissolved in NMP up to 20% (w/w), and other common solvents, and solutions possess a longer gelation time. The highly soluble copolymer with 20 mole % o-phenetidine in the backbone has same order of conductivity as the unsubstituted PANI after it is doped by HCl. Complexation of PANI and polymeric dopant, poly

  7. A2B Adenosine Receptor Agonist Improves Erectile Function in Diabetic Rats.

    PubMed

    Wen, Jiaming; Wang, Bohan; Du, Chuanjun; Xu, Gang; Zhang, Zhewei; Li, Yi; Zhang, Nan

    2015-01-01

    Diabetes is an important risk factor for erectile dysfunction (ED). Recent studies have indicated that A2B adenosine receptor (ADORA2B) signaling is essential for penile erection. Thus, we hypothesize that diabetic ED may be attributed to impaired A2B adenosine signaling. To test this hypothesis, we generated diabetic rats by injecting streptozocin as animal model. After 12 weeks, immunohistochemistry staining was used to localize the expression of ADORA2B. Western Blot and quantitative PCR were employed to determine ADORA2B expression level. Intracavernosal pressure (ICP) measurement was used to evaluate erectile function. Diabetic rats received a single intravenous injection of BAY 60-6583, an ADORA2B agonist, or vehicle solution, at 60 min before the ICP measurement. The results showed that ADORA2B expressed in the nerve bundle, smooth muscle, and endothelium in penile tissue of control mice. Western Blot and quantitative PCR results indicated that the expression levels of ADORA2B protein and mRNA were significantly reduced in penile tissues of diabetic rats. Functional studies showed that the erectile response induced by electrical stimulation was remarkably decreased in diabetic rats, compared with age-matched control rats. However, at 60 min after BAY 60-6583 treatment, the erectile function was improved in diabetic rats, suggesting that enhancement of ADORA2B signaling may improve erectile function in diabetic ED. This preclinical study has revealed a previously unrecognized therapeutic possibility of BAY 60-6583 as an effective and mechanism-based drug to treat diabetic ED. In conclusion, we propose that impaired A2B adenosine signaling is one of the pathological mechanisms of diabetic ED. PMID:26447087

  8. Photothermal Investigation of Surface Defects of Pure Semiconducting A2B6 Materials

    NASA Astrophysics Data System (ADS)

    Zakrzewski, J.; Maliński, M.; Strzałkowski, K.; Madaj, D.; Firszt, F.; Łęgowski, S.; Męczyńska, H.

    2012-04-01

    Photoacoustic spectroscopy is a sensitive and useful method to investigate the quality of semiconducting A2B6 crystals. An imperfection of surface quality can strongly influence photoacoustic spectra but it shows the different character for the different kinds of semiconducting materials. To properly interpret the amplitude and phase spectra, the temperature distribution and its modifications, due to the surface defects, are needed. The Blonskij model of the temperature distribution was used to investigate the influence of the defect on the amplitude and phase spectra.

  9. Mixing thermodynamics of block-random copolymers

    NASA Astrophysics Data System (ADS)

    Beckingham, Bryan Scott

    microphase-separated if they were connected as a diblock. However, attachment of the A block, and consequent localization of the A-B block junction to the A-B lamellar interface, induces extensive separation between the B and C blocks. The organization of the crystallized E block was also examined and it was found that in a weakly-segregated triblock, crystallization of the E block destroys the melt lamellar structure, but for more segregated triblocks, E crystallization is effectively confined by the melt structure, leading to an orientation wherein the E crystallites stack orthogonally to the lamellar microdomains, as observed previously in E-containing diblock copolymers exhibiting confined crystallization. Addditionally, the microphase separation of the two hydrogenated derivatives of an S-I-SrhI triblock, generating A-hI-ArhI triblocks, is also probed. While the two derivatives possess nearly identical block volume fractions, differences in the magnitudes of the block interaction energies results in the formation of two disparate ordered morphologies.

  10. Antimicrobial Graft Copolymer Gels.

    PubMed

    Harvey, Amanda C; Madsen, Jeppe; Douglas, C W Ian; MacNeil, Sheila; Armes, Steven P

    2016-08-01

    In view of the growing worldwide rise in microbial resistance, there is considerable interest in designing new antimicrobial copolymers. The aim of the current study was to investigate the relationship between antimicrobial activity and copolymer composition/architecture to gain a better understanding of their mechanism of action. Specifically, the antibacterial activity of several copolymers based on 2-(methacryloyloxy)ethyl phosphorylcholine [MPC] and 2-hydroxypropyl methacrylate (HPMA) toward Staphylococcus aureus was examined. Both block and graft copolymers were synthesized using either atom transfer radical polymerization or reversible addition-fragmentation chain transfer polymerization and characterized via (1)H NMR, gel permeation chromatography, rheology, and surface tensiometry. Antimicrobial activity was assessed using a range of well-known assays, including direct contact, live/dead staining, and the release of lactate dehydrogenase (LDH), while transmission electron microscopy was used to study the morphology of the bacteria before and after the addition of various copolymers. As expected, PMPC homopolymer was biocompatible but possessed no discernible antimicrobial activity. PMPC-based graft copolymers comprising PHPMA side chains (i.e. PMPC-g-PHPMA) significantly reduced both bacterial growth and viability. In contrast, a PMPC-PHPMA diblock copolymer comprising a PMPC stabilizer block and a hydrophobic core-forming PHPMA block did not exhibit any antimicrobial activity, although it did form a biocompatible worm gel. Surface tensiometry studies and LDH release assays suggest that the PMPC-g-PHPMA graft copolymer exhibits surfactant-like activity. Thus, the observed antimicrobial activity is likely to be the result of the weakly hydrophobic PHPMA chains penetrating (and hence rupturing) the bacterial membrane. PMID:27409712

  11. Bismaleimide Copolymer Matrix Resins

    NASA Technical Reports Server (NTRS)

    Parker, John A.; Heimbuch, Alvin H.; Hsu, Ming-Ta S.; Chen, Timothy S.

    1987-01-01

    Graphite composites, prepared from 1:1 copolymer of two new bismaleimides based on N,N'-m-phenylene-bis(m-amino-benzamide) structure have mechanical properties superior to those prepared from other bismaleimide-type resins. New heat-resistant composites replace metal in some structural applications. Monomers used to form copolymers with superior mechanical properties prepared by reaction of MMAB with maleic or citraconic anhydride.

  12. Unexpected Consequences of Block Polydispersity on the Self-Assembly of ABA Triblock Copolymers

    SciTech Connect

    Widin, Joan M.; Schmitt, Adam K.; Schmitt, Andrew L.; Im, Kyuhyun; Mahanthappa, Mahesh K.

    2012-05-09

    Controlled/'living' polymerizations and tandem polymerization methodologies offer enticing opportunities to enchain a wide variety of monomers into new, functional block copolymer materials with unusual physical properties. However, the use of these synthetic methods often introduces nontrivial molecular weight polydispersities, a type of chain length heterogeneity, into one or more of the copolymer blocks. While the self-assembly behavior of monodisperse AB diblock and ABA triblock copolymers is both experimentally and theoretically well understood, the effects of broadening the copolymer molecular weight distribution on block copolymer phase behavior are less well-explored. We report the melt-phase self-assembly behavior of SBS triblock copolymers (S = poly(styrene) and B = poly(1,4-butadiene)) comprised of a broad polydispersity B block (M{sub w}/M{sub n} = 1.73-2.00) flanked by relatively narrow dispersity S blocks (M{sub w}/M{sub n} = 1.09-1.36), in order to identify the effects of chain length heterogeneity on block copolymer self-assembly. Based on synchrotron small-angle X-ray scattering and transmission electron microscopy analyses of seventeen SBS triblock copolymers with poly(1,4-butadiene) volume fractions 0.27 {le} f{sub B} {le} 0.82, we demonstrate that polydisperse SBS triblock copolymers self-assemble into periodic structures with unexpectedly enhanced stabilities that greatly exceed those of equivalent monodisperse copolymers. The unprecedented stabilities of these polydisperse microphase separated melts are discussed in the context of a complete morphology diagram for this system, which demonstrates that narrow dispersity copolymers are not required for periodic nanoscale assembly.

  13. Unexpected consequences of block polydispersity on the self-assembly of ABA triblock copolymers.

    PubMed

    Widin, Joan M; Schmitt, Adam K; Schmitt, Andrew L; Im, Kyuhyun; Mahanthappa, Mahesh K

    2012-02-29

    Controlled/"living" polymerizations and tandem polymerization methodologies offer enticing opportunities to enchain a wide variety of monomers into new, functional block copolymer materials with unusual physical properties. However, the use of these synthetic methods often introduces nontrivial molecular weight polydispersities, a type of chain length heterogeneity, into one or more of the copolymer blocks. While the self-assembly behavior of monodisperse AB diblock and ABA triblock copolymers is both experimentally and theoretically well understood, the effects of broadening the copolymer molecular weight distribution on block copolymer phase behavior are less well-explored. We report the melt-phase self-assembly behavior of SBS triblock copolymers (S = poly(styrene) and B = poly(1,4-butadiene)) comprised of a broad polydispersity B block (M(w)/M(n) = 1.73-2.00) flanked by relatively narrow dispersity S blocks (M(w)/M(n) = 1.09-1.36), in order to identify the effects of chain length heterogeneity on block copolymer self-assembly. Based on synchrotron small-angle X-ray scattering and transmission electron microscopy analyses of seventeen SBS triblock copolymers with poly(1,4-butadiene) volume fractions 0.27 ≤ f(B) ≤ 0.82, we demonstrate that polydisperse SBS triblock copolymers self-assemble into periodic structures with unexpectedly enhanced stabilities that greatly exceed those of equivalent monodisperse copolymers. The unprecedented stabilities of these polydisperse microphase separated melts are discussed in the context of a complete morphology diagram for this system, which demonstrates that narrow dispersity copolymers are not required for periodic nanoscale assembly. PMID:22280467

  14. Adenosine A2B Receptor: From Cell Biology to Human Diseases.

    PubMed

    Sun, Ying; Huang, Pingbo

    2016-01-01

    Extracellular adenosine is a ubiquitous signaling molecule that modulates a wide array of biological processes. Recently, significant advances have been made in our understanding of A2B adenosine receptor (A2BAR). In this review, we first summarize some of the general characteristics of A2BAR, and then we describe the multiple binding partners of the receptor, such as newly identified α-actinin-1 and p105, and discuss how these associated proteins could modulate A2BAR's functions, including certain seemingly paradoxical functions of the receptor. Growing evidence indicates a critical role of A2BAR in cancer, renal disease, and diabetes, in addition to its importance in the regulation of vascular diseases, and lung disease. Here, we also discuss the role of A2BAR in cancer, renal disease, and diabetes and the potential of the receptor as a target for treating these three diseases. PMID:27606311

  15. Adenosine A2B Receptor: From Cell Biology to Human Diseases

    PubMed Central

    Sun, Ying; Huang, Pingbo

    2016-01-01

    Extracellular adenosine is a ubiquitous signaling molecule that modulates a wide array of biological processes. Recently, significant advances have been made in our understanding of A2B adenosine receptor (A2BAR). In this review, we first summarize some of the general characteristics of A2BAR, and then we describe the multiple binding partners of the receptor, such as newly identified α-actinin-1 and p105, and discuss how these associated proteins could modulate A2BAR's functions, including certain seemingly paradoxical functions of the receptor. Growing evidence indicates a critical role of A2BAR in cancer, renal disease, and diabetes, in addition to its importance in the regulation of vascular diseases, and lung disease. Here, we also discuss the role of A2BAR in cancer, renal disease, and diabetes and the potential of the receptor as a target for treating these three diseases. PMID:27606311

  16. Synthesis and bioactivity of MSH4 oligomers prepared by an A2 + B2 strategy

    PubMed Central

    Dehigaspitiya, Dilani Chathurika; Navath, Suryakiran; Weber, Craig S.; Lynch, Ronald M.; Mash, Eugene A.

    2014-01-01

    Oligomers incorporating the tetrapeptide MSH4, the minimum active sequence of melanocyte stimulating hormone, were synthesized by an A2 + B2 strategy involving microwave-assisted copper-catalyzed azide-alkyne cycloaddition. A2 contained an MSH4 core while B2 contained a (Pro-Gly)3 spacer. Soluble mixtures containing compounds with up to eight MSH4 units were obtained from oligomerizations at high monomer concentrations. The avidities of several oligomeric mixtures were evaluated by means of a competitive binding assay using HEK293 cells engineered to overexpress the melanocortin 4 receptor. When based on total MSH4 concentrations, avidities were only minimally enhanced compared with a monovalent control. The lack of variation in the effect of ligands on probe binding is consistent with high off rates for MSH4 in both monovalent and oligomeric constructs relative to that of the competing probe. PMID:26120211

  17. Conical intersections between X2A1 and A2B2 electronic states of NO

    NASA Astrophysics Data System (ADS)

    Sardar, Subhankar; Mukherjee, Saikat; Paul, Amit Kumar; Adhikari, Satrajit

    2013-04-01

    We explore both the general symmetry-allowed accidental (SAA) conical intersections (CIs) and Renner-Teller (RT) interactions prevailed between the ground (X2A1) and first excited (A2B2) electronic states of NO in the configuration space of normal mode coordinates. Global ab initio potential-energy surfaces and Non Adiabatic Coupling Term (NACT) between those states are reported. For each of the three pairs of normal mode (Q1,Q2,Q3), calculated NACT show singularity at different positions, which are used to calculate Adiabatic-to-Diabatic Transformation (ADT) angles and thereby, the diagonal elements of ADT matrix display (i) sign change for odd number of SAA CI (s) and (ii) no sign change for even number of SAA CIs as well as Renner-Teller interactions. Similar to Jahn-Teller CI, the existence of SAA CIs are, further, confirmed by Longuet-Higgins' phase change.

  18. 3D-pharmacophore models for selective A2A and A2B adenosine receptor antagonists.

    PubMed

    Wei, Jing; Wang, Songqing; Gao, Shaofen; Dai, Xuedong; Gao, Qingzhi

    2007-01-01

    Three-dimensional pharmacophore models were generated for A2A and A2B adenosine receptors (ARs) based on highly selective A2A and A2B antagonists using the Catalyst program. The best pharmacophore model for selective A2A antagonists (Hypo-A2A) was obtained through a careful validation process. Four features contained in Hypo-A2A (one ring aromatic feature (R), one positively ionizable feature (P), one hydrogen bond acceptor lipid feature (L), and one hydrophobic feature (H)) seem to be essential for antagonists in terms of binding activity and A2A AR selectivity. The best pharmacophore model for selective A2B antagonists (Hypo-A2B) was elaborated by modifying the Catalyst common features (HipHop) hypotheses generated from the selective A2B antagonists training set. Hypo-A2B also consists of four features: one ring aromatic feature (R), one hydrophobic aliphatic feature (Z), and two hydrogen bond acceptor lipid features (L). All features play an important role in A2B AR binding affinity and are essential for A2B selectivity. Both A2A and A2B pharmacophore models have been validated toward a wide set of test molecules containing structurally diverse selective antagonists of all AR subtypes. They are capable of identifying correspondingly high potent antagonists and differentiating antagonists between subtypes. The results of our study will act as a valuable tool for retrieving structurally diverse compounds with desired biological activities and designing novel selective adenosine receptor ligands. PMID:17330954

  19. 19 CFR 351.214 - New shipper reviews under section 751(a)(2)(B) of the Act.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... shipper reviews under section 751(a)(2)(B) of the Act. (a) Introduction. The URAA established a new...) In an antidumping proceeding involving imports from a nonmarket economy country, a certification...

  20. Heterogeneous Nuclear Ribonucleoprotein A2/B1 as a Target Antigen in Han Chinese for BD Patients.

    PubMed

    Liang, Jinghui; Yang, Weikang; Meng, Xiangyu; Chen, Peng; Du, Hongwu

    2015-01-01

    Behcet's disease (BD) is a recurrent pathema with a typical symptom of inflammation involved in many organs. Previous report indicated that the serum of Korean patients with BD stimulates membrane expression of hnRNP A2/B1 in endothelial cells. In this study, the target 35 kDa recombinant human hnRNP A2/B1 were over-expressed and purified, then sequenced with MALDI-TOF- TOF mass spectrometry. Western blotting and ELISA were applied to detect serum reactivity against hnRNP A2/B1 respectively. The results demonstrate that hnRNP A2/B1 is an autoantigen of BD in Han Chinese population. PMID:25925770

  1. Progress in the discovery of selective, high affinity A(2B) adenosine receptor antagonists as clinical candidates.

    PubMed

    Kalla, Rao V; Zablocki, Jeff

    2009-03-01

    The selective, high affinity A(2B) adenosine receptor (AdoR) antagonists that were synthesized by several research groups should aid in determining the role of the A(2B) AdoR in inflammatory diseases like asthma or rheumatoid arthritis (RA) and angiogenic diseases like diabetic retinopathy or cancer. CV Therapeutics scientists discovered the selective, high affinity A(2B) AdoR antagonist 10, a 8-(4-pyrazolyl)-xanthine derivative [CVT-6883, K(i)(hA(2B)) = 22 nM; K(i)(hA(1)) = 1,940 nM; K(i)(hA(2A)) = 3,280; and K(i)(hA(3)) = 1,070 nM] that has favorable pharmacokinetic (PK) properties (t (1/2) = 4 h and F > 35% rat). Compound 10 demonstrated functional antagonism at the A(2B) AdoR (K(B) = 6 nM) and efficacy in a mouse model of asthma. In two phase 1 clinical trials, CVT-6883 was found to be safe, well tolerated, and suitable for once daily dosing. A second compound 20, 8-(5-pyrazolyl)-xanthine, has been nominated for development from Baraldi's group in conjunction with King Pharmaceuticals that has favorable A(2B) AdoR affinity and selectivity [K(i)(hA(2B)) = 5.5 nM; K(i)(hA(1)) > 1,000 nM; K(i)(hA(2A)) > 1,000; and K(i)(hA(3)) > 1,000 nM], and it has been demonstrated to be a functional antagonist. A third compound 32, a 2-aminopyrimidine, from the Almirall group has high A(2B) AdoR affinity and selectivity [K(i)(hA(2B)) = 17 nM; K(i)(hA(1)) > 1,000 nM; K(i)(hA(2A)) > 2,500; and K(i)(hA(3)) > 1,000 nM], and 32 has been moved into preclinical safety testing. Since three highly selective, high affinity A(2B) AdoR antagonists have been nominated for development with 10 (CVT-6883) being the furthest along in the development process, the role of the A(2B) AdoR in various disease states will soon be established. PMID:18568423

  2. Bactericidal block copolymer micelles.

    PubMed

    Vyhnalkova, Renata; Eisenberg, Adi; van de Ven, Theo

    2011-05-12

    Block copolymer micelles with bactericidal properties were designed to deactivate pathogens such as E. coli bacteria. The micelles of PS-b-PAA and PS-b-P4VP block copolymers were loaded with biocides TCMTB or TCN up to 20 or 30 wt.-%, depending on the type of antibacterial agent. Bacteria were exposed to loaded micelles and bacterial deactivation was evaluated. The micelles loaded with TCN are bactericidal; bacteria are killed in less than two minutes of exposure. The most likely interpretation of the data is that the biocide is transferred to the bacteria by repeated micelle/bacteria contacts, and not via the solution. PMID:21275041

  3. IFN-γ Prevents Adenosine Receptor (A2bR) Upregulation To Sustain the Macrophage Activation Response.

    PubMed

    Cohen, Heather B; Ward, Amanda; Hamidzadeh, Kajal; Ravid, Katya; Mosser, David M

    2015-10-15

    The priming of macrophages with IFN-γ prior to TLR stimulation results in enhanced and prolonged inflammatory cytokine production. In this study, we demonstrate that, following TLR stimulation, macrophages upregulate the adenosine 2b receptor (A2bR) to enhance their sensitivity to immunosuppressive extracellular adenosine. This upregulation of A2bR leads to the induction of macrophages with an immunoregulatory phenotype and the downregulation of inflammation. IFN-γ priming of macrophages selectively prevents the induction of the A2bR in macrophages to mitigate sensitivity to adenosine and to prevent this regulatory transition. IFN-γ-mediated A2bR blockade leads to a prolonged production of TNF-α and IL-12 in response to TLR ligation. The pharmacologic inhibition or the genetic deletion of the A2bR results in a hyperinflammatory response to TLR ligation, similar to IFN-γ treatment of macrophages. Conversely, the overexpression of A2bR on macrophages blunts the IFN-γ effects and promotes the development of immunoregulatory macrophages. Thus, we propose a novel mechanism whereby IFN-γ contributes to host defense by desensitizing macrophages to the immunoregulatory effects of adenosine. This mechanism overcomes the transient nature of TLR activation, and prolongs the antimicrobial state of the classically activated macrophage. This study may offer promising new targets to improve the clinical outcome of inflammatory diseases in which macrophage activation is dysregulated. PMID:26355158

  4. Expression of Receptors for Tetanus Toxin and Monoclonal Antibody A2B5 by Pancreatic Islet Cells

    NASA Astrophysics Data System (ADS)

    Eisenbarth, G. S.; Shimizu, K.; Bowring, M. A.; Wells, S.

    1982-08-01

    Studies of the reaction of antibody A2B5 and tetanus toxin with pancreatic islet cells, islet cell tumors, and other human amine precursor uptake and decarboxylation (APUD) tumors are described. By indirect immunofluorescence, antibody A2B5 and tetanus toxin were shown to specifically bind to the plasma membrane of human, rat, chicken, and mouse islet cells. The binding of antibody A2B5 to the cell surface of living islet cells has allowed isolation of these cells from a suspension of pancreatic cells by using a fluorescence-activated cell sorter. In studies designed to determine whether tetanus toxin and antibody A2B5 bound to the same surface antigen, A2B5 and tetanus toxin did not compete for binding to normal islet cells, a human islet cell tumor, or a rat islet cell tumor. In addition to binding to islet cell tumors, antibody A2B5 reacts with frozen sections, isolated cells, and cell lines of neural, neural crest, and APUD origin.

  5. The A2B adenosine receptor protects against inflammation and excessive vascular adhesion

    PubMed Central

    Yang, Dan; Zhang, Ying; Nguyen, Hao G.; Koupenova, Milka; Chauhan, Anil K.; Makitalo, Maria; Jones, Matthew R.; Hilaire, Cynthia St.; Seldin, David C.; Toselli, Paul; Lamperti, Edward; Schreiber, Barbara M.; Gavras, Haralambos; Wagner, Denisa D.; Ravid, Katya

    2006-01-01

    Adenosine has been described as playing a role in the control of inflammation, but it has not been certain which of its receptors mediate this effect. Here, we generated an A2B adenosine receptor–knockout/reporter gene–knock-in (A2BAR-knockout/reporter gene–knock-in) mouse model and showed receptor gene expression in the vasculature and macrophages, the ablation of which causes low-grade inflammation compared with age-, sex-, and strain-matched control mice. Augmentation of proinflammatory cytokines, such as TNF-α, and a consequent downregulation of IκB-α are the underlying mechanisms for an observed upregulation of adhesion molecules in the vasculature of these A2BAR-null mice. Intriguingly, leukocyte adhesion to the vasculature is significantly increased in the A2BAR-knockout mice. Exposure to an endotoxin results in augmented proinflammatory cytokine levels in A2BAR-null mice compared with control mice. Bone marrow transplantations indicated that bone marrow (and to a lesser extent vascular) A2BARs regulate these processes. Hence, we identify the A2BAR as a new critical regulator of inflammation and vascular adhesion primarily via signals from hematopoietic cells to the vasculature, focusing attention on the receptor as a therapeutic target. PMID:16823489

  6. A2B Adenosine Receptor–Mediated Induction of IL-6 Promotes CKD

    PubMed Central

    Dai, Yingbo; Zhang, Weiru; Wen, Jiaming; Zhang, Yujin; Kellems, Rodney E.

    2011-01-01

    Chronic elevation of adenosine, which occurs in the setting of repeated or prolonged tissue injury, can exacerbate cellular dysfunction, suggesting that it may contribute to the pathogenesis of CKD. Here, mice with chronically elevated levels of adenosine, resulting from a deficiency in adenosine deaminase (ADA), developed renal dysfunction and fibrosis. Both the administration of polyethylene glycol–modified ADA to reduce adenosine levels and the inhibition of the A2B adenosine receptor (A2BR) attenuated renal fibrosis and dysfunction. Furthermore, activation of A2BR promoted renal fibrosis in both mice infused with angiotensin II (Ang II) and mice subjected to unilateral ureteral obstruction (UUO). These three mouse models shared a similar profile of profibrotic gene expression in kidney tissue, suggesting that they share similar signaling pathways that lead to renal fibrosis. Finally, both genetic and pharmacologic approaches showed that the inflammatory cytokine IL-6 mediates adenosine-induced renal fibrosis downstream of A2BR. Taken together, these data suggest that A2BR-mediated induction of IL-6 contributes to renal fibrogenesis and shows potential therapeutic targets for CKD. PMID:21511827

  7. The A2B adenosine receptor modulates pulmonary hypertension associated with interstitial lung disease

    PubMed Central

    Karmouty-Quintana, Harry; Zhong, Hongyan; Acero, Luis; Weng, Tingting; Melicoff, Ernestina; West, James D.; Hemnes, Anna; Grenz, Almut; Eltzschig, Holger K.; Blackwell, Timothy S.; Xia, Yang; Johnston, Richard A.; Zeng, Dewan; Belardinelli, Luiz; Blackburn, Michael R.

    2012-01-01

    Development of pulmonary hypertension is a common and deadly complication of interstitial lung disease. Little is known regarding the cellular and molecular mechanisms that lead to pulmonary hypertension in patients with interstitial lung disease, and effective treatment options are lacking. The purpose of this study was to examine the adenosine 2B receptor (A2BR) as a regulator of vascular remodeling and pulmonary hypertension secondary to pulmonary fibrosis. To accomplish this, cellular and molecular changes in vascular remodeling were monitored in mice exposed to bleomycin in conjunction with genetic removal of the A2BR or treatment with the A2BR antagonist GS-6201. Results demonstrated that GS-6201 treatment or genetic removal of the A2BR attenuated vascular remodeling and hypertension in our model. Furthermore, direct A2BR activation on vascular cells promoted interleukin-6 and endothelin-1 release. These studies identify a novel mechanism of disease progression to pulmonary hypertension and support the development of A2BR antagonists for the treatment of pulmonary hypertension secondary to interstitial lung disease.—Karmouty-Quintana, H., Zhong, H., Acero, L., Weng, T., Melicoff, E., West, J. D., Hemnes, A., Grenz, A., Eltzschig, H. K., Blackwell, T. S., Xia, Y., Johnston, R. A., Zeng, D., Belardinelli, L., Blackburn, M. R. The A2B adenosine receptor modulates pulmonary hypertension associated with interstitial lung disease. PMID:22415303

  8. Morphology of Novel Semicrystalline Ethylene-α-Olefin Block Copolymers

    NASA Astrophysics Data System (ADS)

    Li, Sheng; Register, Richard; Landes, Brian

    2009-03-01

    In semicrystalline block copolymers, the solid-state structure can be set either by block incompatibility or by crystallization of one or more blocks. Depending on the block interaction strength, a wide array of solid-state morphologies may be observed, ranging from spherulitic to confined crystallization within preexisting microphase-separated domains. Dow Chemical has recently developed a novel chain shuttling polymerization process to produce olefin block copolymers with alternating amorphous and semicrystalline chain segments, where each block exhibits the most-probable distribution. We examined the melt and solid-state morphologies of these novel olefin block copolymers, having a high octene content in the amorphous block, using two- dimensional synchrotron small-angle and wide-angle x-ray scattering on specimens oriented by channel die compression. Multiblock and diblock copolymers with near-symmetric compositions showed well-ordered lamellar structures at room temperature with long periods exceeding 100 nm, with little dependence on thermal history, indicating the presence of a mesophase-separated melt which templates crystallization.

  9. Block coordination copolymers

    DOEpatents

    Koh, Kyoung Moo; Wong-Foy, Antek G.; Matzger, Adam J.; Benin, Annabelle I.; Willis, Richard R.

    2012-12-04

    The present invention provides compositions of crystalline coordination copolymers wherein multiple organic molecules are assembled to produce porous framework materials with layered or core-shell structures. These materials are synthesized by sequential growth techniques such as the seed growth technique. In addition, the invention provides a simple procedure for controlling functionality.

  10. Block coordination copolymers

    DOEpatents

    Koh, Kyoung Moo; Wong-Foy, Antek G; Matzger, Adam J; Benin, Annabelle I; Willis, Richard R

    2012-11-13

    The present invention provides compositions of crystalline coordination copolymers wherein multiple organic molecules are assembled to produce porous framework materials with layered or core-shell structures. These materials are synthesized by sequential growth techniques such as the seed growth technique. In addition, the invention provides a simple procedure for controlling functionality.

  11. Block coordination copolymers

    DOEpatents

    Koh, Kyoung Moo; Wong-Foy, Antek G; Matzger, Adam J; Benin, Annabelle I; Willis, Richard R

    2014-11-11

    The present invention provides compositions of crystalline coordination copolymers wherein multiple organic molecules are assembled to produce porous framework materials with layered or core-shell structures. These materials are synthesized by sequential growth techniques such as the seed growth technique. In addition, the invention provides a simple procedure for controlling functionality.

  12. Ultraviolet absorbing copolymers

    DOEpatents

    Gupta, Amitava; Yavrouian, Andre H.

    1982-01-01

    Photostable and weather stable absorping copolymers have been prepared from acrylic esters such as methyl methacrylate containing 0.1 to 5% of an 2-hydroxy-allyl benzophenone, preferably the 4,4' dimethoxy derivative thereof. The pendant benzophenone chromophores protect the acrylic backbone and when photoexcited do not degrade the ester side chain, nor abstract hydrogen from the backbone.

  13. Ordering stripe structures of nanoscale rods in diblock copolymer scaffolds

    NASA Astrophysics Data System (ADS)

    Chen, Kang; Ma, Yu-qiang

    2002-05-01

    We report a simulation on the formation of ordered stripe structures of nanoscale rods driven by symmetric diblock copolymer melts. Due to the preferential adsorption of one species of the diblock onto the mobile rods, the phase ordering process will couple with the movement of rods. We find that the self-assembly of rods on the copolymer scaffold produces the highly ordered nanowires of rods, and copolymer blends in turn form the well-oriented lamellar structure. This is due to the interplay among the micro-phase separating dynamics in the diblock copolymer, the wetting interaction between rods and diblock copolymer, and the nematic ordering dynamics of rods. We examine the influence of the domain size, the wetting strength, and the rod number density on the formation of such a nanoscale structure. Additionally, we indicate that the orientation of the pattern can be well controlled by external fields acting on the rods. The results suggest that our model system may provide a novel and simple way to control and design the ordering nanowire structure.

  14. Adenosine A2B receptor modulates intestinal barrier function under hypoxic and ischemia/reperfusion conditions

    PubMed Central

    Yang, Yang; Qiu, Yuan; Wang, Wensheng; Xiao, Weidong; Liang, Hongyin; Zhang, Chaojun; Yang, Hanwenbo; Teitelbaum, Daniel H; Sun, Li-Hua; Yang, Hua

    2014-01-01

    Background: Intestinal barrier function failure from ischemia/reperfusion (I/R) and acute hypoxia has been implicated as a critical determinant in the predisposition to intestinal inflammation and a number of inflammatory disorders. Here, we identified the role of Adenosine A2B receptor (A2BAR) in the regulation of intestinal barrier function under I/R and acute hypoxic conditions. Methods: C57BL/6J mice were used, and were randomized into three groups: Sham, I/R, IR+PSB1115 (a specific A2BAR antagonist) groups. After surgery, the small bowel was harvested for immunohistochemical staining, RNA and protein content, and intestinal permeability analyses. Using an epithelial cell culture model, we investigated the influence of hypoxia on the epithelial function, and the role of A2BAR in the expressions of tight junction and epithelial permeability. The expressions of Claudin-1, occludin and ZO-1 were detected by RT-PCR and Western-Blot. Epithelial barrier function was assessed with transepithelial resistance (TER). Results and conclusions: The A2BAR antagonist, PSB1115, significantly increased tight junction protein expression after intestinal I/R or acute hypoxia conditions. PSB1115 also attenuated the disrupted distribution of TJ proteins. Furthermore, inhibition of A2BAR attenuated the decrease in TER induced by I/R or acute hypoxic conditions, and maintained intestinal barrier function. Antagonism of A2BAR activity improves intestinal epithelial structure and barrier function in a mouse model of intestinal I/R and a cell model of acute hypoxia. These findings support a potentially destructive role for A2BAR under intestinal I/R and acute hypoxic conditions. PMID:24966910

  15. Signaling through the A2B Adenosine Receptor Dampens Endotoxin-Induced Acute Lung Injury

    PubMed Central

    Schingnitz, Ulrich; Hartman, Katherine; MacManus, Christopher F.; Eckle, Tobias; Zug, Stephanie; Colgan, Sean P.; Eltzschig, Holger K.

    2010-01-01

    Sepsis and septic acute lung injury are among the leading causes for morbidity and mortality of critical illness. Extracellular adenosine is a signaling molecule implicated in the cellular adaptation to hypoxia, ischemia or inflammation. Therefore, we pursued the role of the A2B adenosine receptor (A2BAR) as potential therapeutic target in endotoxin-induced acute lung injury. We gained initial insight from in vitro studies of cultured endothelia or epithelia exposed to inflammatory mediators showing time-dependent induction of the A2BAR (up to 12.9±3.4-fold, p<0.05). Similarly, murine studies of endotoxin-induced lung injury identified an almost 4.6-fold induction of A2BAR transcript and corresponding protein induction with LPS-exposure. Studies utilizing A2BAR promoter constructs and RNA-protection assays indicated that A2BAR induction involved mRNA stability. Functional studies of LPS-induced lung injury revealed that pharmacological inhibition or genetic deletion of the A2BAR was associated with dramatic increases in lung inflammation and histologic tissue injury. Studies of A2BAR-bone marrow chimeric mice suggested pulmonary A2BAR signaling in lung protection. Finally, studies with a specific A2BAR agonist (BAY 60-6583) demonstrated attenuation of lung inflammation and pulmonary edema in wild-type but not in gene-targeted mice for the A2BAR. These studies suggest the A2BAR as potential therapeutic target in the treatment of endotoxin-induced forms of acute lung injury. PMID:20348420

  16. Crystallization in Poly(ethylene)-containing Diblock Copolymers

    NASA Astrophysics Data System (ADS)

    Hamley, Ian W.; Fairclough, J. Patrick A.; Ryan, Anthony J.; Bates, Frank S.

    1997-03-01

    Crystallization in diblock copolymers containing poly(ethylene) (PE) has been studied using small-angle x-ray scattering at the Synchrotron Radiation Source, Daresbury Laboratory, U.K. For block copolymers that form ordered phases in the melt, chain folding of PE on crystallization destroys the melt morphology and the solid structure is found to be lamellar, even if the melt structure is hexagonal-packed cylinders. The orientation of the crystallized PE stems was deduced to be parallel to the lamellar interface on the basis of the orientation of peaks in the wide-angle x-ray scattering pattern with respect to those in the SAXS. For a diblock containing a glassy component, diffuse scattering parallel to the meridian in the SAXS pattern indicates lateral correlations between PE crystallites within the layers of semicrystalline PE and this was modelled using a Markov lattice. These lateral correlations are not present when the non-crystalline component is an amorphous melt. In a diblock with f_PE = 0.35, epitaxial melting of the lamellar solid structure to a hexagonal-packed cylinder structure was observed. The kinetics of crystallization were determined from the time dependence of the SAXS invariant, and found to follow Avrami kinetics with n=3, consistent with nucleation and growth of spherulites.

  17. Crystallization studies of polyethylene -poly(ethylene glycol) graft copolymers

    NASA Astrophysics Data System (ADS)

    Mark, P. R.; Hovey, G. E.; Murthy, N. S.; Breitenkamp, K.; Kade, M.; Emerick, T.

    2006-03-01

    Structure and crystallization behavior of three copolymers obtained by grafting poly (ethylene glycol) (PEG) chains to polyethylene (PE) main chain was investigated by variable temperature x-ray diffraction and thermal analysis. The results show that PEG side chains and PE main chains crystallize into separate domains. This is especially true when grafted chains are long (50 and 100 repeat units), in which the PEG domains are same as in PEG homopolymer both in structure and in melting behavior. In the copolymer with shorter chains (25 repeat units), the PEG crystals are not distinct and melting is broad. The PEG domains can be dissolved in water or ethanol without altering the mechanical integrity of the film. PE crystallites in both samples are similar to that in PE homopolymer. For instance, the thermal expansion of the basal cell plane (a- and b-axes) of the PE domains agrees well with that of PE homopolymer over the entire temperature range from ambient to melt. However, the chain-axis dimension PE-lattice in the copolymer is shorter by ˜ 0.05 å and the basal dimensions are larger by ˜ 0.05 å. The changes in these dimensions due to the changes in the length of the grafted PEG chains were investigated.

  18. 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

  19. Imide/arylene ether copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J. (Inventor); Hergenrother, Paul M. (Inventor); Bass, Robert G. (Inventor)

    1992-01-01

    Imide/arylene ether block copolymers are prepared by reacting anhydride terminated poly(amic acids) with amine terminated poly(arylene ethers) in polar aprotic solvents and by chemically or thermally cyclodehydrating the resulting intermediate poly(amic acids). The resulting block copolymers have one glass transition temperature or two, depending upon the particular structure and/or the compatibility of the block units. Most of these block copolymers form tough, solvent resistant films with high tensile properties.

  20. Block copolymer battery separator

    DOEpatents

    Wong, David; Balsara, Nitash Pervez

    2016-04-26

    The invention herein described is the use of a block copolymer/homopolymer blend for creating nanoporous materials for transport applications. Specifically, this is demonstrated by using the block copolymer poly(styrene-block-ethylene-block-styrene) (SES) and blending it with homopolymer polystyrene (PS). After blending the polymers, a film is cast, and the film is submerged in tetrahydrofuran, which removes the PS. This creates a nanoporous polymer film, whereby the holes are lined with PS. Control of morphology of the system is achieved by manipulating the amount of PS added and the relative size of the PS added. The porous nature of these films was demonstrated by measuring the ionic conductivity in a traditional battery electrolyte, 1M LiPF.sub.6 in EC/DEC (1:1 v/v) using AC impedance spectroscopy and comparing these results to commercially available battery separators.

  1. Partial Miscibility in Copolymer Blends

    NASA Astrophysics Data System (ADS)

    Clark, Elizabeth; Lipson, Jane

    2011-03-01

    Copolymers can be used to affect the miscibility of otherwise immiscible polymer blends by acting as compatibilizers. To better understand the energetics of these types of systems, we use a simple lattice model to study phase separation in binary copolymer/homopolymer blends. We focus on a copolymer that contains both A and B type monomers and a homopolymer that contains purely A type monomer. An example of a system that we are investigating is polyethylene mixed with either random or alternating poly(ethylene-co-propylene). The sequence effect on miscibility as the copolymer microstructure is varied from random to alternating is investigated as well. The support of GAANN is gratefully acknowledged.

  2. Imide/Arylene Ether Copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Hergenrother, Paul M.; Bass, Robert G.

    1991-01-01

    New imide/arylene ether copolymers prepared by reacting anhydride-terminated poly(amic acids) with amine-terminated poly(arylene ethers) in polar aprotic solvents. Each resulting copolymer may have one glass-transition temperature or two, depending on chemical structure and/or compatibility of block units. Most of copolymers form tough, solvent-resistant films with high tensile properties. Films cast from solution tough and flexible, and exhibit useful thermal and mechanical properties. Potentially useful as moldings, adhesives, or composite matrices. Because of flexible arylene ether blocks, these copolymers easier to process than polyimides.

  3. Block copolymer investigations

    NASA Astrophysics Data System (ADS)

    Yufa, Nataliya A.

    The research presented in this thesis deals with various aspects of block copolymers on the nanoscale: their behavior at a range of temperatures, their use as scaffolds, or for creation of chemically striped surfaces, as well as the behavior of metals on block copolymers under the influence of UV light, and the healing behavior of copolymers. Invented around the time of World War II, copolymers have been used for decades due to their macroscopic properties, such as their ability to be molded without vulcanization, and the fact that, unlike rubber, they can be recycled. In recent years, block copolymers (BCPs) have been used for lithography, as scaffolds for nano-objects, to create a magnetic hard drive, as well as in photonic and other applications. In this work we used primarily atomic force microscopy (AFM) and transmission electron microscopy (TEM), described in Chapter II, to conduct our studies. In Chapter III we demonstrate a new and general method for positioning nanoparticles within nanoscale grooves. This technique is suitable for nanodots, nanocrystals, as well as DNA. We use AFM and TEM to demonstrate selective decoration. In Chapters IV and V we use AFM and TEM to study the structure of polymer surfaces coated with metals and self-assembled monolayers. We describe how the surfaces were created, exhibit their structure on the nanoscale, and prove that their macroscopic wetting properties have been altered compared to the original polymer structures. Finally, Chapters VI and VII report out in-situ AFM studies of BCP at high temperatures, made possible only recently with the invention of air-tight high-temperature AFM imaging cells. We locate the transition between disordered films and cylinders during initial ordering. Fluctuations of existing domains leading to domain coarsening are also described, and are shown to be consistent with reptation and curvature minimization. Chapter VII deals with the healing of PS-b-PMMA following AFM-tip lithography or

  4. Dynamics of Block Copolymer Nanocomposites

    SciTech Connect

    Mochrie, Simon G. J.

    2014-09-09

    A detailed study of the dynamics of cadmium sulfide nanoparticles suspended in polystyrene homopolymer matrices was carried out using X-ray photon correlation spectroscopy for temperatures between 120 and 180 °C. For low molecular weight polystyrene homopolymers, the observed dynamics show a crossover from diffusive to hyper-diffusive behavior with decreasing temperatures. For higher molecular weight polystyrene, the nanoparticle dynamics appear hyper-diffusive at all temperatures studied. The relaxation time and characteristic velocity determined from the measured hyper-diffusive dynamics reveal that the activation energy and underlying forces determined are on the order of 2.14 × 10-19 J and 87 pN, respectively. We also carried out a detailed X-ray scattering study of the static and dynamic behavior of a styrene– isoprene diblock copolymer melt with a styrene volume fraction of 0.3468. At 115 and 120 °C, we observe splitting of the principal Bragg peak, which we attribute to phase coexistence of hexagonal cylindrical and cubic double- gyroid structure. In the disordered phase, above 130 °C, we have characterized the dynamics of composition fluctuations via X-ray photon correlation spectroscopy. Near the peak of the static structure factor, these fluctuations show stretched-exponential relaxations, characterized by a stretching exponent of about 0.36 for a range of temperatures immediately above the MST. The corresponding characteristic relaxation times vary exponentially with temperature, changing by a factor of 2 for each 2 °C change in temperature. At low wavevectors, the measured relaxations are diffusive with relaxation times that change by a factor of 2 for each 8 °C change in temperature.

  5. Inducing Order from Disordered Copolymers: On Demand Generation of Triblock Morphologies Including Networks

    SciTech Connect

    Tureau, Maëva S.; Kuan, Wei-Fan; Rong, Lixia; Hsiao, Benjamin S.; Epps, III, Thomas H.

    2015-10-15

    Disordered block copolymers are generally impractical in nanopatterning applications due to their inability to self-assemble into well-defined nanostructures. However, inducing order in low molecular weight disordered systems permits the design of periodic structures with smaller characteristic sizes. Here, we have induced nanoscale phase separation from disordered triblock copolymer melts to form well-ordered lamellae, hexagonally packed cylinders, and a triply periodic gyroid network structure, using a copolymer/homopolymer blending approach, which incorporates constituent homopolymers into selective block domains. This versatile blending approach allows one to precisely target multiple nanostructures from a single disordered material and can be applied to a wide variety of triblock copolymer systems for nanotemplating and nanoscale separation applications requiring nanoscale feature sizes and/or high areal feature densities.

  6. Microphase separation of short wormlike diblock copolymers with a finite interaction range.

    PubMed

    Jiang, Ying; Zhang, Xinghua; Miao, Bing; Yan, Dadong; Chen, Jeff Z Y

    2016-02-17

    We investigate several structural properties of low-molecular weight AB diblock copolymer melts, focusing on a number of features that substantially deviate from those of high-molecular weight copolymer melts. The study is based on the wormlike chain formalism aided by random phase approximation and self-consistent field theory. We examine the effects that stemmed from both the finite molecular weight and the finite interaction range between unlike AB monomers. The latter yields profound effects on systems consisting of short wormlike block copolymers. The noticeable shift of the order-disorder transition point is discussed. Attention is also paid to the strong-segregation regime, where low molecular weight polymers are subject to finite stretchability. PMID:26822622

  7. Quantitative study of temperature-dependent order in thin films of cylindrical morphology block copolymer

    NASA Astrophysics Data System (ADS)

    Mishra, Vindhya; Kramer, Edward

    2010-03-01

    Disordering and defect generation in block copolymer systems at high temperatures is of significance to get a better understanding of the physics governing these systems, which can also direct efforts to minimize them. We have studied the smectic-nematic-isotropic transition in confined monolayers and bilayers of cylindrical morphology poly (styrene-b-2vinyl pyridine) diblock copolymer. Previous studies of melting phenomena in block copolymer thin films have relied on quantitative AFM studies alone. We have supplemented AFM studies with grazing incidence small angle X-ray diffraction lineshape analysis to quantify the decay of translational and orientational order with increasing temperature. The results have been interpreted in the context of the Toner-Nelson theory of melting for layered systems.

  8. How to Place Block Copolymer Molecules at the Interface of a Binary Blend

    NASA Astrophysics Data System (ADS)

    Chen, Zhong-Ren; Xu, Yuci; Zhong, Shuo

    2015-03-01

    Block copolymers have been used to reduce the domain size of immiscible polymer blends and thus improve the mechanical and other properties. The effectiveness of this method, however, depends on the percentage of these polymeric surfactants residing at the interface of the blend. In fact, theoretical as well as experimental work indicate that a large percentage of block copolymers form micelles in the bulk of one or both of the component polymers. These micelles may serve as weak spots initiating crack propagation. Previous work have been focused on the design of molecular architecture and synthesis of new block copolymers to address this problem. In this presentation, a simple mixing strategy is applied to make each block copolymer molecule stay at the interface. As one example, when this strategy is used to mix natural rubber (NR) with butadiene rubber (BR), a small amount of low molecular weight block copolymer (LIR) improves both processing characteristics such as melt viscosity and mechanical properties of cured samples, such as crack resistance. AFM micrographs show the much smaller domain size; and an original real-time monitoring system reveals the lowest crack growth rate. Using a model A/B/A-B binary blend, we have witnessed by microscopy that all block copolymer molecules form micelles at the first mixing step, and all of these micelles are disappeared and all block copolymer molecules stay at the interface after the second mixing step.

  9. ABSORPTION OF CO2 IN HIGH ACRYLONITRILE CONTENT COPOLYMERS: DEPENDENCE ON ACRYLONITRILE CONTENT. (R829555)

    EPA Science Inventory

    In continuation of our goal to determine the ability of CO2 to plasticize acrylonitrile (AN) copolymers and facilitate melt processing at temperatures below the onset of thermal degradation, a systematic study has been performed to determine the influence of AN cont...

  10. ABSORPTION OF CO2 AND SUBSEQUENT VISCOSITY REDUCTION OF AN ACRYLONITRILE COPOLYMER. (R829555)

    EPA Science Inventory

    Acrylonitrile (AN) copolymers (AN content greater than about 85 mol%) are traditionally solution processed to avoid a cyclization and crosslinking reaction that takes place at temperatures where melt processing would be feasible. It is well known that carbon dioxide (CO

  11. Suzuki-Miyaura cross-coupling reaction on copper-trans-A(2)B corroles with excellent functional group tolerance.

    PubMed

    König, Michael; Reith, Lorenz Michael; Monkowius, Uwe; Knör, Günther; Bretterbauer, Klaus; Schoefberger, Wolfgang

    2011-06-10

    The palladium-catalyzed Suzuki-Miyaura cross-coupling reaction has been investigated on meso-substituted trans-A(2)B-corrole using tailored Pd-catalyst systems.We present the first examples of Suzuki-Miyaura cross-coupling reactions on meso-substituted trans-A(2)B-corrole derivatives with neutral, sterically hindered, inactivated and heteroaromatic boronic acids and esters, alkenylboronic acids, as well as quickly deboronating aryl boronic acids and benzo-condensated five membered heterocyclic boronic acids. In addition, we established a high-yield procedure for the Suzuki-Miyaura cross-coupling reaction of corroles with neutral boronic acids.Due to the lability of the free-base corrole macrocycles, functionalization of the corrole periphery was performed with the corresponding Cu-metallated species. meso-Substituted trans-A(2)B-corrole can hence be regarded as highly versatile platform towards more sophisticated corrole systems.X-ray structure analysis of a functionalized meso-substituted trans-A(2)B copper corrole exhibited the typical features of such a Cu-complex: short N-Cu distances and a saddled corrole configuration.Moreover, we observed a sensitivity of the formal oxidation state of the coordinated copper ions towards Suzuki-Miyaura cross-coupling reaction conditions, where the central copper(III) ion approaches the characteristic features of a copper(II) species. This redox behaviour was examined by UV/vis absorption spectra, nuclear magnetic resonance (NMR) experiments and time-dependent density functional theoretical calculations. PMID:21760646

  12. The adenosine A2B receptor is involved in anion secretion in human pancreatic duct Capan-1 epithelial cells.

    PubMed

    Hayashi, M; Inagaki, A; Novak, I; Matsuda, H

    2016-07-01

    Adenosine modulates a wide variety of biological processes via adenosine receptors. In the exocrine pancreas, adenosine regulates transepithelial anion secretion in duct cells and is considered to play a role in acini-to-duct signaling. To identify the functional adenosine receptors and Cl(-) channels important for anion secretion, we herein performed experiments on Capan-1, a human pancreatic duct cell line, using open-circuit Ussing chamber and gramicidin-perforated patch-clamp techniques. The luminal addition of adenosine increased the negative transepithelial potential difference (V te) in Capan-1 monolayers with a half-maximal effective concentration value of approximately 10 μM, which corresponded to the value obtained on whole-cell Cl(-) currents in Capan-1 single cells. The effects of adenosine on V te, an equivalent short-circuit current (I sc), and whole-cell Cl(-) currents were inhibited by CFTRinh-172, a cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel inhibitor. The adenosine A2B receptor agonist, BAY 60-6583, increased I sc and whole-cell Cl(-) currents through CFTR Cl(-) channels, whereas the A2A receptor agonist, CGS 21680, had negligible effects. The A2B receptor antagonist, PSB 603, inhibited the response of I sc to adenosine. Immunohistochemical analysis showed that the A2A and A2B receptors colocalized with Ezrin in the luminal membranes of Capan-1 monolayers and in rat pancreatic ducts. Adenosine elicited the whole-cell Cl(-) currents in guinea pig duct cells. These results demonstrate that luminal adenosine regulates anion secretion by activating CFTR Cl(-) channels via adenosine A2B receptors on the luminal membranes of Capan-1 cells. The present study endorses that purinergic signaling is important in the regulation of pancreatic secretion. PMID:26965147

  13. Confinement of elastomeric block copolymers via forced assembly coextrusion.

    PubMed

    Burt, Tiffani M; Keum, Jong; Hiltner, Anne; Baer, Eric; Korley, Lashanda T J

    2011-12-01

    Forced assembly processing provides a unique opportunity to examine the effects of confinement on block copolymers (BCPs) via conventional melt processing techniques. The microlayering process was utilized to produce novel materials with enhanced mechanical properties through selective manipulation of layer thickness. Multilayer films consisting of an elastomeric, symmetric block copolymer confined between rigid polystyrene (PS) layers were produced with layer thicknesses ranging from 100 to 600 nm. Deformation studies of the confined BCP showed an increase in ductility as the layer thickness decreased to 190 nm due to a shift in the mode of deformation from crazing to shear yielding. Postextrusion annealing was performed on the multilayer films to investigate the impact of a highly ordered morphology on the mechanical properties. The annealed multilayer films exhibited increased toughness with decreasing layer thickness and resulted in homogeneous deformation compared to the as-extruded films. Multilayer coextrusion proved to be an advantageous method for producing continuous films with tunable mechanical response. PMID:22124208

  14. A2B5+/GFAP+ Cells of Rat Spinal Cord Share a Similar Lipid Profile with Progenitor Cells: A Comparative Lipidomic Study.

    PubMed

    Itokazu, Yutaka; Tajima, Nobuyoshi; Kerosuo, Laura; Somerharju, Pentti; Sariola, Hannu; Yu, Robert K; Käkelä, Reijo

    2016-07-01

    The central nervous system (CNS) harbors multiple glial fibrillary acidic protein (GFAP) expressing cell types. In addition to the most abundant cell type of the CNS, the astrocytes, various stem cells and progenitor cells also contain GFAP+ populations. Here, in order to distinguish between two types of GFAP expressing cells with or without the expression of the A2B5 antigens, we performed lipidomic analyses on A2B5+/GFAP+ and A2B5-/GFAP+ cells from rat spinal cord. First, A2B5+/GFAP- progenitors were exposed to the leukemia inhibitory factor (LIF) or bone morphogenetic protein (BMP) to induce their differentiation to A2B5+/GFAP+ cells or A2B5-/GFAP+ astrocytes, respectively. The cells were then analyzed for changes in their phospholipid, sphingolipid or acyl chain profiles by mass spectrometry and gas chromatography. Compared to A2B5+/GFAP- progenitors, A2B5-/GFAP+ astrocytes contained higher amounts of ether phospholipids (especially the species containing arachidonic acid) and sphingomyelin, which may indicate characteristics of cellular differentiation and inability for multipotency. In comparison, principal component analyses revealed that the lipid composition of A2B5+/GFAP+ cells retained many of the characteristics of A2B5+/GFAP- progenitors, but their lipid profile was different from that of A2B5-/GFAP+ astrocytes. Thus, our study demonstrated that two GFAP+ cell populations have distinct lipid profiles with the A2B5+/GFAP+ cells sharing a phospholipid profile with progenitors rather than astrocytes. The progenitor cells may require regulated low levels of lipids known to mediate signaling functions in differentiated cells, and the precursor lipid profiles may serve as one measure of the differentiation capacity of a cell population. PMID:26915109

  15. Self-Consistent Field Approach for Cross-Linked Copolymer Materials

    NASA Astrophysics Data System (ADS)

    Schmid, Friederike

    2013-07-01

    A generalized self-consistent field approach for polymer networks with a fixed topology is developed. It is shown that the theory reproduces the localization of cross-links, which is characteristic for gels. The theory is then used to study the order-disorder transition in regular networks of end-linked diblock copolymers. Compared to diblock copolymer melts, the transition is shifted towards lower values of the incompatibility parameter χ (the Flory- Huggins parameter). Moreover, the transition becomes strongly first order already at the mean-field level. If stress is applied, the transition is further shifted and finally vanishes in a critical point.

  16. Lignin-derived thermoplastic co-polymers and methods of preparation

    DOEpatents

    Naskar, Amit K.; Saito, Tomonori; Pickel, Joseph M.; Baker, Frederick S.; Eberle, Claude Clifford; Norris, Robert E.; Mielenz, Jonathan Richard

    2014-06-10

    The present invention relates to a crosslinked lignin comprising a lignin structure having methylene or ethylene linking groups therein crosslinking between phenyl ring carbon atoms, wherein said crosslinked lignin is crosslinked to an extent that it has a number-average molecular weight of at least 10,000 g/mol, is melt-processible, and has either a glass transition temperature of at least 100.degree. C., or is substantially soluble in a polar organic solvent or aqueous alkaline solution. Thermoplastic copolymers containing the crosslinked lignin are also described. Methods for producing the crosslinked lignin and thermoplastic copolymers are also described.

  17. Counit Inclusion in Hydrogenated Polynorbornene Copolymer Crystals

    NASA Astrophysics Data System (ADS)

    Burns, Adam; Showak, Michael; Stella, Andrew; Register, Richard

    2014-03-01

    Crystallization in poly(A-co-B) random copolymers, where homopolymer A is crystalline but B is not, is dictated by the degree to which crystals of A can include B units. Typically, B units are strongly excluded from the A crystals, drastically reducing the degree of crystallinity wc and crystal thickness tc even at modest comonomer contents. However, in some cases, B units can be incorporated into the crystals as defects, significantly diminishing the counits' impact on wc and tc. The extent and consequences of counit inclusion have been investigated in hydrogenated polynorbornene (hPN) with alkylnorbornene counits, synthesized by living ring-opening metathesis polymerization followed by hydrogenation. In the case of 5-hexylnorbornene (HxN) counits, a steep decline in wc and tc with counit content is found, indicative of strong exclusion. In contrast, when the counits are 5-methylnorbornene (MeN), extensive inclusion of MeN units into the crystals is observed. hP(N-co-MeN) copolymers maintain appreciable crystallinity above 30 mol% MeN, and the dependence of the melting point Tm on tc tracks that of the hPN homopolymer. Four times as much MeN as HxN (molar basis) is required to produce a comparable drop in wc. Therefore, copolymerization with MeN can be used to tune Tm without drastically reducing wc. Additionally, hPN exhibits a polymorphic transition to a rotationally disordered (RD) crystal at temperature Tcc

  18. Skin delivery by block copolymer nanoparticles (block copolymer micelles).

    PubMed

    Laredj-Bourezg, Faiza; Bolzinger, Marie-Alexandrine; Pelletier, Jocelyne; Valour, Jean-Pierre; Rovère, Marie-Rose; Smatti, Batoule; Chevalier, Yves

    2015-12-30

    Block copolymer nanoparticles often referred to as "block copolymer micelles" have been assessed as carriers for skin delivery of hydrophobic drugs. Such carriers are based on organic biocompatible and biodegradable materials loaded with hydrophobic drugs: poly(lactide)-block-poly(ethylene glycol) copolymer (PLA-b-PEG) nanoparticles that have a solid hydrophobic core made of glassy poly(d,l-lactide), and poly(caprolactone)-block-poly(ethylene glycol) copolymer (PCL-b-PEG) nanoparticles having a liquid core of polycaprolactone. In vitro skin absorption of all-trans retinol showed a large accumulation of retinol in stratum corneum from both block copolymer nanoparticles, higher by a factor 20 than Polysorbate 80 surfactant micelles and by a factor 80 than oil solution. Additionally, skin absorption from PLA-b-PEG nanoparticles was higher by one order of magnitude than PCL-b-PEG, although their sizes (65nm) and external surface (water-swollen PEG layer) were identical as revealed by detailed structural characterizations. Fluorescence microscopy of histological skin sections provided a non-destructive picture of the storage of Nile Red inside stratum corneum, epidermis and dermis. Though particle cores had a different physical states (solid or liquid as measured by (1)H NMR), the ability of nanoparticles for solubilization of the drug assessed from their Hildebrand solubility parameters appeared the parameter of best relevance regarding skin absorption. PMID:26602293

  19. The interactions between microphase separation and crystallization in block copolymers containing polyethylene

    NASA Astrophysics Data System (ADS)

    Quiram, Daniel Jonathan

    The interactions between microphase separation and crystallization were examined in block copolymers containing polyethylene of varying chemistry, composition (fsb{E} = 0.26-0.88, where fsb{E} is weight fraction polyethylene), and molecular weight. Block copolymer compositions were altered to explore crystallization from three distinct melt morphologies: body-centered cubic spheres, hexagonally-packed cylinders, and alternating lamellae. Polymer morphology was investigated on a size-scale ranging from angstroms to microns, employing wide-angle and small-angle x-ray scattering (WAXS and SAXS), small-angle light scattering, and differential scanning calorimetry. The primary series of diblock copolymers investigated were polyethylene-b-poly(3-methyl-1-butene) (E/MB, where MB is an olefinic rubber; fsb{E} = 0.26-0.27). This composition led to a cylindrical morphology when the melt microphase separated. Molecular weights were varied to obtain differing degrees of melt incompatibility, ranging from disordered to strongly segregated. Crystallization from strongly segregated melts was confined to the cylindrical microdomains, essentially independent of thermal history. In contrast, the morphology produced by crystallization from weakly segregated melts was highly dependent upon thermal history. Several block copolymers with microphase-separated melts containing an E block and either polystyrene (glass transition temperature, Tsb{g}≈ 100sp°C) or poly(vinylcyclohexane) (Tsb{g}≈ 135sp°C) were investigated to determine the effect of a vitreous component on crystallization. SAXS experiments showed that vitrification of the amorphous material effectively confined E crystallization to its melt domain phase: cylinders in a glassy matrix, lamellae, and matrices surrounding both glassy cylinders and spheres. Crystalline chain orientation within cylinders was examined through WAXS. The chains aligned preferentially and this orientation varied depending on chain diffusion during

  20. Viscoelastic Properties of Fluorinated Ethylene-Propylene (FEP) Random Copolymers

    NASA Astrophysics Data System (ADS)

    Curtin, Megan; Wright, Benjamin; Ozisik, Rahmi

    Florinated ethylene-propylene (FEP) random copolymers contain tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) repeat units. FEP is an excellent alternative to poly(tetrafluoroethylene), PTFE, which cannot be melt processed due to its high molecular weight and extensive crystallinity. On the other hand, FEP is a melt processible polymer and offers similar if not the same properties as PTFE. Many studies have been performed on FEP over the years, however, the properties of these polymers strongly depend on the HFP concentration and molecular weight (distribution). Just like PTFE, FEP cannot be dissolved in many solvents, therefore, obtaining molecular weight distribution of these polymers is not possible with commonly used methods. In the current study, we perform rheological analysis of various FEPs and obtain their molecular weight distributions by employing the Tuminello method. This material is based upon work supported by the National Science Foundation under Grant No. CMMI-1538730.

  1. Imide/arylene ether copolymers. I

    NASA Technical Reports Server (NTRS)

    Jensen, B. J.; Hergenrother, P. M.; Bass, R. G.

    1991-01-01

    The preparation of a series of novel imide/arylene ether copolymers is described together with the results of viscosity and DSC Tg(Tm) measurements. The copolymers were synthesized from an arylene ether block and either an amorphous or semicrystalline imide block. One block copolymer was end-capped, and the molecular weight was controlled to improve compression moldability. The paper also presents results of mechanical properties tests on copolymer samples.

  2. Yield Stress Enhancement in Glassy-Polyethylene Block Copolymers

    NASA Astrophysics Data System (ADS)

    Mulhearn, William; Register, Richard

    Polyethylene (PE) has the highest annual production volume of all synthetic polymers worldwide, and is valuable across many applications due to its low cost, toughness, processability, and chemical resistance. However, PE is not well suited to certain applications due to its modest yield stress and Young's modulus (approximately 30 MPa and 1 GPa, respectively for linear, high-density PE). Irreversible deformation of PE results from dislocation of crystal stems and eventual crystal fragmentation under applied stress. The liquid-like amorphous fraction provides no useful mechanical support to the crystal fold surface in a PE homopolymer, so the only method to enhance the force required for crystal slip, and hence the yield stress, is crystal thickening via thermal treatment. An alternative route towards modifying the mechanical properties of PE involves copolymerization of a minority high-glass transition temperature block into a majority-PE block copolymer. In this work, we investigate a system of glassy/linear-PE block copolymers prepared via ring-opening metathesis polymerization of cyclopentene and substituted norbornene monomers followed by hydrogenation. We demonstrate that a large change in mechanical properties can be achieved with the addition of a short glassy block (e.g. a doubling of the yield stress and Young's modulus versus PE homopolymer with the addition of 25 percent glassy block). Furthermore, owing to the low interaction energy between PE and the substituted polynorbornene blocks employed, these high-yield PE block copolymers can exhibit single-phase melts for ease of processability.

  3. The Influence of Polydispersity on the Thermodynamics of Diblock Copolymers

    NASA Astrophysics Data System (ADS)

    Lynd, Nathaniel

    2005-03-01

    The effects of the molecular weight distribution on the thermodynamics of diblock copolymers have been predicted to affect order-disorder transitions (ODT), order-order transitions and the equilibrium morphology adopted.^1,2 We prepared several sets of Poly[(ethylene-alt-propylene)-b-(D,L-lactide)] diblock copolymers with controlled molecular weights, compositions and polydispersities (PDIs). Rheology and small angle x-ray scattering were used to evaluate the effects of PDI on the lamellar domain spacing, the ODT, and the resultant morphology. For symmetrical samples, the lamellar domain spacing increased with increasing PDI. The degree of segregation at the ODT ((χN)ODT) was dependent upon the volume fraction of the polydisperse component (fPLA). Interestingly, for fPLA = 0.33 (χN)ODT decreased with increasing PDI but for fPLA= 0.64 (χN)ODT increased with increasing PDI. We also demonstrated that an increase in PDI at constant fPLA results in a change in equilibrium morphology. Monte Carlo simulations addressing the effects of fluctuations on the ODT of polydisperse diblock copolymer melts were also performed. .(1) Sides,S.W.; Frederickson, G.H. J. Chem. Phys. 2004, 121,4974. (2) Burger,C.; Ruland, W.; Semenov, A.N. Macromolecules 1990, 23, 3339.

  4. Imidazolium-containing, hydrophobic-ionic-hydrophilic ABC triblock copolymers: synthesis, ordered phase-separation, and supported membrane fabrication

    SciTech Connect

    Wiesenauer, EF; Nguyen, PT; Newell, BS; Bailey, TS; Nobleb, RD; Gin, DL

    2013-01-01

    Novel ABC triblock copolymers containing hydrophobic, imidazolium ionic liquid (IL)-based ionic, and non-charged hydrophilic blocks were synthesized by direct sequential, ring-opening metathesis polymerization (ROMP) of three chemically immiscible norborene monomers. The resulting ABC triblock copolymers were found by small-angle X-ray scattering to phase-separate into different nanostructures in their pure melt states, depending on their block sequence and compositions. Supported composite membranes of these triblock copolymers were successfully fabricated with defect-free, <= 20 microns thick top coatings. Preliminary CO2/light gas transport studies demonstrated the potential of this new type of IL-based block copolymer material for gas separation applications.

  5. Molecular dynamics simulation of electric-field-induced self-assembly of diblock copolymers

    NASA Astrophysics Data System (ADS)

    Zhang, Qiuzhi; Xu, Rui; Kan, Di; He, Xuehao

    2016-06-01

    The self-assembly of block copolymers under an external electric field was studied with a coarse-grained polarizable model that hybridizes the conventional polymeric coarse-grained model and Drude oscillator. The polarizability of the coarse-grained polymeric segment was reflected by the Drude oscillator. Applying this model, the alignment of the lamellar phase of the block copolymer melt under an external electric field was observed and the dynamic coupling information between chain polarization and interface orientation induced by the external electric field was obtained. It is demonstrated that the alignment of the lamellar structure along the electric field direction results from the polarizability difference of the polymer components. Finally, the transitions of phase structures of the block copolymer under an external electric field, from spherical phase to cylindrical phase, from gyroid structure to cylindrical phase, and from gyroid structure to lamellae phase were simulated. The specific evolution pathways were shown.

  6. Molecular dynamics simulation of electric-field-induced self-assembly of diblock copolymers.

    PubMed

    Zhang, Qiuzhi; Xu, Rui; Kan, Di; He, Xuehao

    2016-06-21

    The self-assembly of block copolymers under an external electric field was studied with a coarse-grained polarizable model that hybridizes the conventional polymeric coarse-grained model and Drude oscillator. The polarizability of the coarse-grained polymeric segment was reflected by the Drude oscillator. Applying this model, the alignment of the lamellar phase of the block copolymer melt under an external electric field was observed and the dynamic coupling information between chain polarization and interface orientation induced by the external electric field was obtained. It is demonstrated that the alignment of the lamellar structure along the electric field direction results from the polarizability difference of the polymer components. Finally, the transitions of phase structures of the block copolymer under an external electric field, from spherical phase to cylindrical phase, from gyroid structure to cylindrical phase, and from gyroid structure to lamellae phase were simulated. The specific evolution pathways were shown. PMID:27334188

  7. Copolymers from unsaturated macrolactones: toward the design of cross-linked biodegradable polyesters.

    PubMed

    van der Meulen, Inge; Li, Yingyuan; Deumens, Ronald; Joosten, Elbert A J; Koning, Cor E; Heise, Andreas

    2011-03-14

    The enzymatic synthesis of a series of random copolyesters by ring-opening polymerization of unsaturated macrolactones like globalide and ambrettolide with 1,5-dioxepan-2-one (DXO) and 4-methyl caprolactone (4MeCL) was investigated. (13)C NMR diad analysis confirmed the randomness of all copolymers irrespective of the comonomer ratios. Thermal investigation showed that incorporating the comonomers lowered the melting points of the polymers as compared with the macrolactone homopolymers. The decrease was dependent on the comonomer ratio. The unsaturated copolymers were thermally cross-linked using dicumyl peroxide, which resulted in completely amorphous insoluble networks. It was found that 10% incorporation of the unsaturated macolactone was sufficient to obtain a gel content of 95 wt %. Preliminary degradation tests confirm that the cross-linked copolymers are enzymatically degradable and that the incorporation of hydrophilic comonomers like DXO enhances degradation. PMID:21319813

  8. Synthesis and characterization of a brush-like copolymer of polylactide grafted onto chitosan.

    PubMed

    Liu, Y; Tian, F; Hu, K A

    2004-03-15

    A brush-like poly(DL)-lactide grafted onto chitosan as the backbone was investigated. The graft copolymerization was carried out with triethylaluminum as catalyst in toluene at 70 degrees C. It was found that a greater lactide content in the feeding ratio results in a higher grafting percentage. FTIR spectrometry, (1)H NMR, DSC scanning, and wide-angle X-ray scattering, respectively, are used to characterize these branch copolymers. A copolymer has a definite melting point when the molar feeding ratio of lactide to chitosan is more than 10:1, and the deltaH of the copolymers increases with the feed ratio of lactide to chitosan in feeding. PMID:14980828

  9. Copolymers For Capillary Gel Electrophoresis

    DOEpatents

    Liu, Changsheng; Li, Qingbo

    2005-08-09

    This invention relates to an electrophoresis separation medium having a gel matrix of at least one random, linear copolymer comprising a primary comonomer and at least one secondary comonomer, wherein the comonomers are randomly distributed along the copolymer chain. The primary comonomer is an acrylamide or an acrylamide derivative that provides the primary physical, chemical, and sieving properties of the gel matrix. The at least one secondary comonomer imparts an inherent physical, chemical, or sieving property to the copolymer chain. The primary and secondary comonomers are present in a ratio sufficient to induce desired properties that optimize electrophoresis performance. The invention also relates to a method of separating a mixture of biological molecules using this gel matrix, a method of preparing the novel electrophoresis separation medium, and a capillary tube filled with the electrophoresis separation medium.

  10. Effect of chain microstructure on physical properties of olefin copolymers

    NASA Astrophysics Data System (ADS)

    Poon, Benjamin Chunman

    The effect of chain microstructure on various physical properties was studied in polyethylene and polypropylene copolymers. Adhesion of Ziegler-Natta (ZNPE) and metallocene (mPE) catalyzed ethylene-octene copolymers to polypropylene (PP) were studied by measuring the delamination toughness G of coextruded microlayers using the T-peel test. It was found that the heterogeneous ZNPE exhibited poor adhesion to polypropylene. It was proposed that the low molecular weight, highly branched ZNPE fractions migrate to the interface to form an amorphous layer. The homogeneous mPE with the same short chain branch content showed very high G. Blending ZNPE with an mPE increased G. Atomic force microscopy revealed that blending mPE into ZNPE reduced or eliminated the amorphous interfacial layer. It was hypothesized that mPE increased miscibility of low molecular weight, highly branched fractions of ZNPE and prevented their segregation at the interface. The solid state structure and properties of homogeneous propylene-octene copolymers were examined. Based on the combined observations from melting behavior, dynamic mechanical response, morphology with primarily atomic force microscopy, X-ray diffraction, and tensile deformation, a classification scheme with 4 distinct categories is proposed. The homopolymer with 60 wt% crystallinity constitutes Type IV. It is characterized by large alpha-positive spherulite. Copolymers with up to 5 mol% octene, with at least 35 wt% crystallinity, are classified as Type III. They crystallize as alpha-positive spherulites that are smaller than the homopolymer. Both Type IV and Type III materials exhibit thermoplastic behavior. Copolymers classified as Type II have between 5 and 10 mol% octene with crystallinity in the range of 20--35%. Type II materials have smaller impinging spherulites than Type III copolymers and they are negative. The materials in this category have plastomeric behavior. Type I copolymers have more than 10 mol% octene and less

  11. Self-assembly of cyclic rod-coil diblock copolymers.

    PubMed

    He, Linli; Chen, Zenglei; Zhang, Ruifen; Zhang, Linxi; Jiang, Zhouting

    2013-03-01

    The phase behavior of cyclic rod-coil diblock copolymer melts is investigated by the dissipative particle dynamics simulation. In order to understand the effect of chain topological architecture better, we also study the linear rod-coil system. The comparison of the calculated phase diagrams between the two rod-coil copolymers reveals that the order-disorder transition point (χN)ODT for cyclic rod-coil diblock copolymers is always higher than that of equivalent linear rod-coil diblocks. In addition, the phase diagram for cyclic system is more "symmetrical," due to the topological constraint. Moreover, there are significant differences in the self-assembled overall morphologies and the local molecular arrangements. For example, frod = 0.5, both lamellar structures are formed while rod packing is different greatly in cyclic and linear cases. The lamellae with rods arranged coplanarly into bilayers occurs in cyclic rod-coil diblocks, while the lamellar structure with rods arranged end by end into interdigitated bilayers appears in linear counterpart. In both the lamellar phases, the domain size ratio of cyclic to linear diblocks is ranged from 0.63 to 0.70. This is attributed to that the cyclic architecture with the additional junction increases the contacts between incompatible blocks and prevents the coil chains from expanding as much as the linear cases. As frod = 0.7, the hexagonally packed cylinder is observed for cyclic rod-coil diblocks, while liquid-crystalline smectic A lamellar phase is formed in linear system. As a result, the cyclization of a linear rod-coil block copolymer can induce remarkable differences in the self-assembly behavior and also diversify its physical properties and applications greatly. PMID:23485326

  12. Order-Disorder Transitions in Cross-Linked Block Copolymer Solids

    SciTech Connect

    Das, J.

    2005-01-12

    With a view toward creating solid block copolymers wherein the order-disorder transition can be accessed many times they investigated the nature of order-disorder transitions in cross-linked diblock copolymer melts using synergistic theory and experiment. A mean-field theory based on a coarse grained free-energy and the Random Phase Approximation (RPA) is developed for the system of interest. The quenched distribution of cross-links is averaged using the replica method. The phase behavior of a particular A-B block copolymer melt with a randomly cross-linked B-Block is determined as a function of the Florry-Huggins interaction parameter ({chi}) and the average number of cross-links per chain N{sub c}. They find for a cross-link density greater than N*{sub c} the B monomers are localized within a region of size {zeta} {approx} (N{sub c} - N*{sub c}){sup -1/2}. The cross-links strongly oppose ordering in the system as {zeta} becomes comparable to the radius of gyration of the block copolymer chain. As such the order-disorder transition temperature T{sub ODT} decreases precipitously when N{sub c} > N*{sub c}. When N{sub c} < N*{sub c}, T{sub ODT} increases weakly with N{sub c}. Experiments were conducted on cross-linked polystyrene-block-polyisoprene copolymer samples wherein the polyisoprene block was selectively cross-linked at a temperature well above the order-disorder transition temperature of the pure block copolymer. Small angle X-ray scattering (SAXS) and birefringence measurements on the cross-linked samples are consistent with the theoretical prediction. T{sub ODT} decreases rapidly when the cross-linking density exceeds the critical cross-linking density.

  13. Crystalline imide/arylene ether copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J. (Inventor); Hergenrother, Paul M. (Inventor); Bass, Robert G. (Inventor)

    1995-01-01

    Crystalline imide/arylene ether block copolymers are prepared by reacting anhydride terminated poly(amic acids) with amine terminated poly)arylene ethers) in polar aprotic solvents and chemically or thermally cyclodehydrating the resulting intermediate poly(amic acids). The block copolymers of the invention have one glass transition temperature or two, depending on the particular structure and/or the compatibility of the block units. Most of these crystalline block copolymers for tough, solvent resistant films with high tensile properties. While all of the copolymers produced by the present invention are crystalline, testing reveals that copolymers with longer imide blocks or higher imide content have increased crystallinity.

  14. Biological materials: Part A. tuning LCST of raft copolymers and gold/copolymer hybrid nanoparticles and Part B. Biobased nanomaterials

    NASA Astrophysics Data System (ADS)

    Chen, Ning

    The research described in this dissertation is comprised of two major parts. The first part studied the effects of asymmetric amphiphilic end groups on the thermo-response of diblock copolymers of (oligo/di(ethylene glycol) methyl ether (meth)acrylates, OEGA/DEGMA) and the hybrid nanoparticles of these copolymers with a gold nanoparticle core. Placing the more hydrophilic end group on the more hydrophilic block significantly increased the cloud point compared to a similar copolymer composition with the end group placement reversed. For a given composition, the cloud point was shifted by as much as 28 °C depending on the placement of end groups. This is a much stronger effect than either changing the hydrophilic/hydrophobic block ratio or replacing the hydrophilic acrylate monomer with the equivalent methacrylate monomer. The temperature range of the coil-globule transition was also altered. Binding these diblock copolymers to a gold core decreased the cloud point by 5-15 °C and narrowed the temperature range of the coil-globule transition. The effects were more pronounced when the gold core was bound to the less hydrophilic block. Given the limited numbers of monomers that are approved safe for in vivo use, employing amphiphilic end group placement is a useful tool to tune a thermo-response without otherwise changing the copolymer composition. The second part of the dissertation investigated the production of value-added nanomaterials from two biorefinery "wastes": lignin and peptidoglycan. Different solvents and spinning methods (melt-, wet-, and electro-spinning) were tested to make lignin/cellulose blended and carbonized fibers. Only electro-spinning yielded fibers having a small enough diameter for efficient carbonization (≤ 5-10 μm), but it was concluded that cellulose was not a suitable binder. Cellulose lignin fibers before carbonization showed up to 90% decrease in moisture uptake compared to pure cellulose. Peptidoglycan (a bacterial cell wall

  15. Modulated calorimetry of poly(1,4-oxybenzoate), poly(2,6-oxynaphthoate), and their copolymers

    SciTech Connect

    Ma, J; Habenschuss, A; Wunderlich, B

    2008-01-01

    Poly(1,4-oxybenzoate) (POB) and poly(2,6-oxynaphthoate) (PON) and their copolymers which have a well-established phase diagram have been studied with temperature-modulated differential scanning calorimetry (TMDSC). All the analyzed polymers have more than one disordering transition between the glass transition (from 400 to 430 K) and decomposition (starting at 700 K). Above the glass transition, the reversible heat capacity, Cp, increases beyond that calculated from the crystallinity and the known Cp of the solid and melt. This is likely due to an increase of mobility within the crystals and/or a possible rigid-amorphous fraction (mainly for the copolymers). The disordering transitions are largely irreversible, supporting the observation that semicrystalline, linear macromolecules show decreasing amounts of locally reversible melting with increasing rigidity and crystal perfection.

  16. Tensile actuators of carbon nanotube coiled yarn based on polydiacetylene–pluronic copolymers as temperature indicators

    NASA Astrophysics Data System (ADS)

    Lee, Hee Uk; Kim, Hyunsoo; Chun, Kyoung-Yong; Kwon, Cheong Hoon; Lima, Márcio D.; Baughman, Ray H.; Kim, Seon Jeong

    2016-07-01

    Most polydiacetylenes (PDAs) have been studied as chromatic sensors or temperature indicators because of their phase transition that is accompanied by a color change from blue to red. Here, we focus on the structural change based on the polydiacetylene phase transition for a temperature-responsive tensile actuator at low temperature using a copolymer composed of PDA and pluronic in a multi-walled carbon nanotube (MWCNT) coiled yarn. In this paper, we do not focus on the general color change phenomenon of PDA. We demonstrate that the volume change of PDA in the MWCNT coiled yarn provides ∼180% tensile strain at low temperature (∼53 °C). Insertion of the pluronic copolymer into the coiled yarn composed of PDA and MWCNT caused the tensile actuation temperature to decrease by ∼6 °C (with tensile actuation of ∼230%) compared to an actuator without pluronic copolymer. Furthermore, we could verify that the large tensile actuation was also predominantly affected by the melting of the nonpolymerized diacetylene (DA) monomer and the pluronic copolymer. MWCNT coiled yarn actuators with PDA-pluronic copolymer can be easily prepared, have a large tensile actuation, and are actuated at low temperature. It could be used as temperature indicators in the food, drugs, and medical fields.

  17. Multiblock copolymers prepared by patterned modification: Analytical theory and computer simulations.

    PubMed

    Govorun, E N; Gavrilov, A A; Chertovich, A V

    2015-05-28

    We describe a special type of multiblock copolymers which are synthesized by a hypothetic procedure of the modification of monomer units in a polymer melt according to a certain geometrical criterion. In particular, we explore the case of lamellar-like structures: the sequence statistics of the resulting multiblock copolymers is described and their ability to self-assemble is studied. It is found that the block-size distribution P(k) for such random copolymers contains a large fraction of short blocks with the asymptotic dependence ∼k(-3/2), where k is the block size. A characteristic feature of such multiblock copolymers is their extremely high block-size polydispersity with the polydispersity index being proportional to the space period of the modification. The morphological behavior of such copolymers is simulated by means of dissipative particle dynamics. A stable self-assembled lamellar structure is observed, but the domain size appears to be sufficiently larger than the initial pattern period. PMID:26026461

  18. Multiblock copolymers prepared by patterned modification: Analytical theory and computer simulations

    NASA Astrophysics Data System (ADS)

    Govorun, E. N.; Gavrilov, A. A.; Chertovich, A. V.

    2015-05-01

    We describe a special type of multiblock copolymers which are synthesized by a hypothetic procedure of the modification of monomer units in a polymer melt according to a certain geometrical criterion. In particular, we explore the case of lamellar-like structures: the sequence statistics of the resulting multiblock copolymers is described and their ability to self-assemble is studied. It is found that the block-size distribution P(k) for such random copolymers contains a large fraction of short blocks with the asymptotic dependence ˜k-3/2, where k is the block size. A characteristic feature of such multiblock copolymers is their extremely high block-size polydispersity with the polydispersity index being proportional to the space period of the modification. The morphological behavior of such copolymers is simulated by means of dissipative particle dynamics. A stable self-assembled lamellar structure is observed, but the domain size appears to be sufficiently larger than the initial pattern period.

  19. Synthesis, photophysical, electrochemical and electrochemiluminescence properties of A2B2 zinc porphyrins: the effect of π-extended conjugation.

    PubMed

    Galván-Miranda, Elizabeth K; Castro-Cruz, Hiram M; Arturo Arias-Orea, J; Iurlo, Matteo; Valenti, Giovanni; Marcaccio, Massimo; Macías-Ruvalcaba, Norma A

    2016-06-01

    The synthesis of two A2B2 porphyrins, {5,15-bis-[4-(octyloxy)phenyl]-porphyrinato}zinc(ii) () and {5,15-bis-(carbazol-3-yl-ethynyl)-10,20-bis-[4-(octyloxy)phenyl]-porphinato}-zinc(ii) (), is reported. Their photophysical properties were studied by steady-state absorption and emission. Substituting the carbazolylethynyl moieties at two of the meso positions results in a large bathochromic shift of all the absorption bands, a notable increase in the absorption coefficient of the Q(0,0) band, and higher fluorescence quantum yield compared to porphyrin , with two unsubstituted meso positions. Cyclic voltammetry and digital simulation show that electrogenerated radical ions of are more stable than those of . The lack of substituents at the meso positions of leads to dimerization reactions of the radical cation. Despite this, the annihilation reaction of and produces very similar electrogenerated chemiluminescence (ECL) intensity. Spectroelectrochemical experiments demonstrate that the electroreduction of leads to a strong absorption band that might quench the ECL. PMID:27194584

  20. Potential Role of A2B Adenosine Receptors on Proliferation/Migration of Fetal Endothelium Derived from Preeclamptic Pregnancies

    PubMed Central

    Acurio, Jesenia; Troncoso, Felipe; Salomon, Carlos; Aguayo, Claudio; Sobrevia, Luis

    2014-01-01

    To investigate the functionality of A2B adenosine receptor (A2BAR) and the nitric oxide (NO) and vascular endothelial growth factor (VEGF) signaling pathway in the endothelial cell proliferation/migration during preeclampsia, we used human umbilical vein endothelial cells (HUVECs) isolated from normal pregnancies (n = 15) or pregnancies with preeclampsia (n = 15). Experiments were performed in presence or absence of the nonselective adenosine receptor agonist NECA, the A2BAR selective antagonist MRS-1754, and the nitric oxide synthase (NOS) inhibitor L-NAME. Results indicated that cells from preeclampsia exhibited a significant higher protein level of A2BAR and logEC50 for NECA-mediated proliferation than normotensive pregnancies. The stimulatory effect of NECA (10 μM, 24 h) on cell proliferation was prevented by MRS-1754 (5 nM) coincubation only in cells from normotensive pregnancies. Nevertheless, L-NAME (100 μM, 24 h) reduced the NECA-induced cell proliferation/migration in HUVEC from normal pregnancy; however in preeclampsia only NECA-induced cell proliferation was reduced by L-NAME. Moreover, NECA increased protein nitration and abundance of VEGF in cells from normal pregnancy and effect prevented by MRS-1754 coincubation. Nevertheless, in preeclampsia NECA did not affect the protein level of VEGF. In conclusion HUVECs from preeclampsia exhibit elevated protein level of A2BAR and impairment of A2BAR-mediated NO/VEGF signaling pathway. PMID:24877077

  1. Excess adenosine in murine penile erectile tissues contributes to priapism via A2B adenosine receptor signaling

    PubMed Central

    Mi, Tiejuan; Abbasi, Shahrzad; Zhang, Hong; Uray, Karen; Chunn, Janci L.; Xia, Ling Wei; Molina, Jose G.; Weisbrodt, Norman W.; Kellems, Rodney E.; Blackburn, Michael R.; Xia, Yang

    2008-01-01

    Priapism, abnormally prolonged penile erection in the absence of sexual excitation, is associated with ischemia-mediated erectile tissue damage and subsequent erectile dysfunction. It is common among males with sickle cell disease (SCD), and SCD transgenic mice are an accepted model of the disorder. Current strategies to manage priapism suffer from a poor fundamental understanding of the molecular mechanisms underlying the disorder. Here we report that mice lacking adenosine deaminase (ADA), an enzyme necessary for the breakdown of adenosine, displayed unexpected priapic activity. ADA enzyme therapy successfully corrected the priapic activity both in vivo and in vitro, suggesting that it was dependent on elevated adenosine levels. Further genetic and pharmacologic evidence demonstrated that A2B adenosine receptor–mediated (A2BR-mediated) cAMP and cGMP induction was required for elevated adenosine–induced prolonged penile erection. Finally, priapic activity in SCD transgenic mice was also caused by elevated adenosine levels and A2BR activation. Thus, we have shown that excessive adenosine accumulation in the penis contributes to priapism through increased A2BR signaling in both Ada–/– and SCD transgenic mice. These findings provide insight regarding the molecular basis of priapism and suggest that strategies to either reduce adenosine or block A2BR activation may prove beneficial in the treatment of this disorder. PMID:18340377

  2. A novel mechanism of control of NFκB activation and inflammation involving A2B adenosine receptors

    PubMed Central

    Sun, Ying; Duan, Yuanyuan; Eisenstein, Anna S.; Hu, Wenbao; Quintana, Adrien; Lam, Wai Kwan; Wang, Yan; Wu, Zhenguo; Ravid, Katya; Huang, Pingbo

    2012-01-01

    Summary The nuclear factor kappa B (NFκB) pathway controls a variety of processes, including inflammation, and thus, the regulation of NFκB has been a continued focus of study. Here, we report a newly identified regulation of this pathway, involving direct binding of the transcription factor NFκB1 (the p105 subunit of NFκB) to the C-terminus of the A2B adenosine receptor (A2BAR), independent of ligand activation. Intriguingly, binding of A2BAR to specific sites on p105 prevents polyubiquitylation and degradation of p105 protein. Ectopic expression of the A2BAR increases p105 levels and inhibits NFκB activation, whereas p105 protein levels are reduced in cells from A2BAR-knockout mice. In accordance with the known regulation of expression of anti- and pro-inflammatory cytokines by p105, A2BAR-null mice generate less interleukin (IL)-10, and more IL-12 and tumor necrosis factor (TNF-α). Taken together, our results show that the A2BAR inhibits NFκB activation by physically interacting with p105, thereby blocking its polyubiquitylation and degradation. Our findings unveil a surprising function for the A2BAR, and provide a novel mechanistic insight into the control of the NFκB pathway and inflammation. PMID:22767505

  3. Molecular Simulation and Microstructure Characterization of Poly(p-phenylene/m-phenylene) Copolymers

    NASA Astrophysics Data System (ADS)

    Bubeck, Robert; Keinath, Steven

    2014-03-01

    Molecular simulation and characterization of the molecular structure and microstructure of poly(p-phenylene/m-phenylene) copolymers were carried out. Tensile modulus, yield stress, and entanglement molecular weight were modeled as amorphous polymers as a function of m-phenylene content. Significant biphasic character, however, was observed for two copolymers in the melt (environs of 300°C) using variable temperature synchrotron-based WAXS. Precise experimental determinations of entanglement molecular weights were frustrated by the occurrence of significant amounts of nematic mesophasic order in the rubbery and melt regimes of two commercial poly(p-phenylene/m-phenylene) examples. Nonetheless, entanglement molecular weights obtained by molecular modeling are useful for future experimental guidance because the level of order in the glassy phase near ambient temperature was found to be low (approx. 5%) regardless of melt processing history. The biphasic nature of the melt may also be a contributor to more difficult melt processing. Based on both the modeling and WAXS measurements, it is believed that increasing m-phenylene content might improve toughness and processibility relative to the interrogated samples. Beam time at the Cornell High Energy Synchrotron Source is gratefully acknowledged.

  4. Characterization and Molecular Simulation of Poly(p-phenylene/m-phenylene) Copolymers

    NASA Astrophysics Data System (ADS)

    Bubeck, Robert; Keinath, Steven

    Characterization and molecular simulation of the molecular structure and microstructure of poly(p-phenylene/m-phenylene) copolymers were carried out. Tensile modulus, yield stress, and entanglement molecular weight were modeled as amorphous polymers as a function of m-phenylene content. Significant biphasic character, however, was observed for two copolymers in the melt near 300ºC using variable temperature synchrotron-based WAXS. The biphasic nature of the melt may be a contributor to difficulty in melt processing. Precise experimental determinations of entanglement molecular weights were frustrated by the occurrence of significant amounts of nematic mesophasic order in the rubbery and melt regimes of two commercial poly(p-phenylene/m-phenylene) examples. Nonetheless, entanglement molecular weights obtained by molecular modeling can be useful for experimental guidance because the level of order in the glassy phase near ambient temperature was found to be low (5 %) regardless of melt processing history. Based on both the modeling and WAXS measurements, it is believed that increasing m-phenylene content reduces modulus, and improves toughness and processibility. Beamtime at the Cornell High Energy Synchrotron Source is gratefully acknowledged.

  5. In vitro degradation behavior of poly(lactide)-poly(ethylene glycol) block copolymer micelles in aqueous solution.

    PubMed

    Yang, Liu; El Ghzaoui, Abdeslam; Li, Suming

    2010-11-15

    Self-assembling micelles were prepared from polylactide-poly(ethylene glycol) (PLA-PEG) block copolymer by using two different methods: direct dissolution and dialysis. The in vitro degradation properties of the micelles were investigated at 37°C and monitored by using various techniques. During the investigated degradation time, the size of micelles by dialysis remains stable, while that of micelles by direct dissolution first increases, followed by a collapse of micellar structure. The composition of PLA-PEG copolymers greatly affects the degradation of micelles. Micelles with longer hydrophobic PLA blocks exhibit less size changes due to more compact structure. On the other hand, the structural integrity of L/D mixed micelles is preserved for longer time than that of single micelles, in agreement with the stereocomplexation effect between L-PLA and D-PLA blocks. As degradation proceeds, the average molar mass of copolymer decreases and the distribution becomes wider, especially for micelles by dialysis and L/D mixed micelles with a more compact structure. Additionally, the PEG content in the copolymer chains increases during degradation, leading to a decrease of glass transition and crystallization temperature of the copolymers. However, the residual LA fragments produced by degradation disfavors the crystallization of PEG blocks, thus resulting in the decrease of melting temperature and melting enthalpy. PMID:20816736

  6. Melt containment member

    SciTech Connect

    Rieken, Joel R.; Heidloff, Andrew J.

    2014-09-09

    A tubular melt containment member for transient containment of molten metals and alloys, especially reactive metals and alloys, includes a melt-contacting layer or region that comprises an oxygen-deficient rare earth oxide material that is less reactive as compared to the counterpart stoichiometric rare earth oxide. The oxygen-deficient (sub-stoichiometric) rare earth oxide can comprise oxygen-deficient yttria represented by Y.sub.2O.sub.3-x wherein x is from 0.01 to 0.1. Use of the oxygen-deficient rare earth oxide as the melt-contacting layer or region material reduces reaction with the melt for a given melt temperature and melt contact time.

  7. Transcriptional regulation of heat shock proteins and ascorbate peroxidase by CtHsfA2b from African bermudagrass conferring heat tolerance in Arabidopsis

    PubMed Central

    Wang, Xiuyun; Huang, Wanlu; Yang, Zhimin; Liu, Jun; Huang, Bingru

    2016-01-01

    Heat stress transcription factor A2s (HsfA2s) are key regulators in plant response to high temperature. Our objectives were to isolate an HsfA2 gene (CtHsfA2b) from a warm-season grass species, African bermudagrass (Cynodon transvaalensis Burtt-Davy), and to determine the physiological functions and transcriptional regulation of HsfA2 for improving heat tolerance. Gene expression analysis revealed that CtHsfA2b was heat-inducible and exhibited rapid response to increasing temperature. Ectopic expression of CtHsfA2b improved heat tolerance in Arabidopsis and restored heat-sensitive defects of Arabidopsis hsfa2 mutant, which was demonstrated by higher survival rate and photosynthetic parameters, and lower electrolyte leakage in transgenic plants compared to the WT or hsfa2 mutant. CtHsfA2b transgenic plants showed elevated transcriptional regulation of several downstream genes, including those encoding ascorbate peroxidase (AtApx2) and heat shock proteins [AtHsp18.1-CI, AtHsp22.0-ER, AtHsp25.3-P and AtHsp26.5-P(r), AtHsp70b and AtHsp101-3]. CtHsfA2b was found to bind to the heat shock element (HSE) on the promoter of AtApx2 and enhanced transcriptional activity of AtApx2. These results suggested that CtHsfA2b could play positive roles in heat protection by up-regulating antioxidant defense and chaperoning mechanisms. CtHsfA2b has the potential to be used as a candidate gene to genetically modify cool-season species for improving heat tolerance. PMID:27320381

  8. Transcriptional regulation of heat shock proteins and ascorbate peroxidase by CtHsfA2b from African bermudagrass conferring heat tolerance in Arabidopsis.

    PubMed

    Wang, Xiuyun; Huang, Wanlu; Yang, Zhimin; Liu, Jun; Huang, Bingru

    2016-01-01

    Heat stress transcription factor A2s (HsfA2s) are key regulators in plant response to high temperature. Our objectives were to isolate an HsfA2 gene (CtHsfA2b) from a warm-season grass species, African bermudagrass (Cynodon transvaalensis Burtt-Davy), and to determine the physiological functions and transcriptional regulation of HsfA2 for improving heat tolerance. Gene expression analysis revealed that CtHsfA2b was heat-inducible and exhibited rapid response to increasing temperature. Ectopic expression of CtHsfA2b improved heat tolerance in Arabidopsis and restored heat-sensitive defects of Arabidopsis hsfa2 mutant, which was demonstrated by higher survival rate and photosynthetic parameters, and lower electrolyte leakage in transgenic plants compared to the WT or hsfa2 mutant. CtHsfA2b transgenic plants showed elevated transcriptional regulation of several downstream genes, including those encoding ascorbate peroxidase (AtApx2) and heat shock proteins [AtHsp18.1-CI, AtHsp22.0-ER, AtHsp25.3-P and AtHsp26.5-P(r), AtHsp70b and AtHsp101-3]. CtHsfA2b was found to bind to the heat shock element (HSE) on the promoter of AtApx2 and enhanced transcriptional activity of AtApx2. These results suggested that CtHsfA2b could play positive roles in heat protection by up-regulating antioxidant defense and chaperoning mechanisms. CtHsfA2b has the potential to be used as a candidate gene to genetically modify cool-season species for improving heat tolerance. PMID:27320381

  9. Activation of A2b adenosine receptor regulates ovarian cancer cell growth: involvement of Bax/Bcl-2 and caspase-3.

    PubMed

    Hajiahmadi, Sima; Panjehpour, Mojtaba; Aghaei, Mahmoud; Shabani, Mahdi

    2015-08-01

    A2b adenosine receptor (A2bAR) acts as a potent regulator of cell growth in various cell lines. The present study was designed to understand the controlling mechanism of A2bAR agonist (NECA)-induced apoptosis in ovarian cancer cells. Real-time PCR and western blotting assays were used to evaluate the gene and protein expression profiles of A2bAR, respectively. MTT assay was used to study the cell proliferation effect of A2bAR agonist (NECA). Detection of apoptosis was conducted using annexin V-FITC/PI staining, caspase-3 activation assay, and the expression of Bax and Bcl-2 proteins analysis. The mitochondrial membrane potential (ΔΨM) was analyzed by employing JC-1 prob. The mRNA and protein expression levels of A2bAR in ovarian cancer cells were detected. NECA significantly reduced cell viability in a dose-dependent manner in OVCAR-3 and Caov-4 cell lines. The growth inhibition effect of NECA was related to the induction of cell apoptosis, which was manifested by annexin V-FITC staining, activation of caspase-3, and loss of mitochondrial membrane potentials (ΔΨm). In addition, downregulation of the regulatory protein Bcl-2 and upregulation of Bax protein by NECA were also observed. These findings demonstrated that NECA induces apoptosis via the mitochondrial signaling pathway. Thus, A2bAR agonists may be a potential agent for induction of apoptosis in ovarian cancer cells. PMID:25877700

  10. Biodegradable polymers derived from renewable resources: Highly branched copolymers of itaconic anhydride

    NASA Astrophysics Data System (ADS)

    Wallach, Joshua Andrew

    In an effort to design cyclic anhydride containing polymers that are derived from renewable resources and have biodegradable characteristics, three copolymer systems using itaconic anhydride have been studied. Two of the systems were copolymers with stearate based monomers; vinyl stearate and stearyl methacrylate, while the third was a copolymer with a methacrylate terminated poly (lactic acid) (PLA) macromonomer. For the stearate systems, stearyl methacrylate showed good copolymerization with equal conversions for both monomers. On the other hand vinyl stearate did not show as good results due to its decreased reactivity, which resulted in a copolymer highly enriched in itaconic anhydride with significant amounts of unreacted vinyl stearate under all copolymer compositions. These differing results were confirmed through analysis of reactivity ratios showing a results that are more favorable for copolymerization for the methacrylate system. Copolymers from both systems showed single melting transitions in a precarious range of 45--50°C arising from the stearyl side groups, though after quenching from the melt this shifted to below room temperature. Anhydride retention was confirmed through structural analysis. Similar to the stearyl methacrylate system, methacrylate terminated PLA macromonomers were copolymerized with itaconic anhydride. PLA's acceptance as a biodegradable material derived from renewable resources, make it a viable choice, with which to design anhydride containing copolymers. Good copolymerization was shown for all compositions studied with retention of the anhydride, though at high itaconic anhydride concentrations conversions were reduced significantly. Copolymers showed glass transition temperatures ranging from 32°C for 85 mole % PLA macromonomer to 73°C for 85 mole % itaconic anhydride. An effort to produce PLA macromonomers through a process of chemical recycling commercial PLA was also undertaken. Promising results were obtained showing

  11. A2B Adenosine Receptor Blockade Enhances Macrophage-Mediated Bacterial Phagocytosis and Improves Polymicrobial Sepsis Survival in Mice

    PubMed Central

    Belikoff, Bryan G.; Hatfield, Stephen; Georgiev, Peter; Ohta, Akio; Lukashev, Dmitriy; Buras, Jon A.; Remick, Daniel G.; Sitkovsky, Michail

    2013-01-01

    Antimicrobial treatment strategies must improve to reduce the high mortality rates in septic patients. In noninfectious models of acute inflammation, activation of A2B adenosine receptors (A2BR) in extracellular adenosine-rich microenvironments causes immunosuppression. We examined A2BR in antibacterial responses in the cecal ligation and puncture (CLP) model of sepsis. Antagonism of A2BR significantly increased survival, enhanced bacterial phagocytosis, and decreased IL-6 and MIP-2 (a CXC chemokine) levels after CLP in outbred (ICR/CD-1) mice. During the CLP-induced septic response in A2BR knockout mice, hemodynamic parameters were improved compared with wild-type mice in addition to better survival and decreased plasma IL-6 levels. A2BR deficiency resulted in a dramatic 4-log reduction in peritoneal bacteria. The mechanism of these improvements was due to enhanced macrophage phagocytic activity without augmenting neutrophil phagocytosis of bacteria. Following ex vivo LPS stimulation, septic macrophages from A2BR knockout mice had increased IL-6 and TNF-α secretion compared with wild-type mice. A therapeutic intervention with A2BR blockade was studied by using a plasma biomarker to direct therapy to those mice predicted to die. Pharmacological blockade of A2BR even 32 h after the onset of sepsis increased survival by 65% in those mice predicted to die. Thus, even the late treatment with an A2BR antagonist significantly improved survival of mice (ICR/CD-1) that were otherwise determined to die according to plasma IL-6 levels. Our findings of enhanced bacterial clearance and host survival suggest that antagonism of A2BRs offers a therapeutic target to improve macrophage function in a late treatment protocol that improves sepsis survival. PMID:21242513

  12. 21 CFR 177.1060 - n-Alkylglutarimide/acrylic copolymers.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    .../acrylic copolymers shall not be used as polymer modifiers in vinyl chloride homo- or copolymers. (e... (other than articles composed of vinyl chloride homo- or copolymers) intended for use in contact with...

  13. Crystallinity and motional dynamics study of a series of poly(arylene ether sulfone) segmented copolymer analogues.

    PubMed

    Zhang, Bin; Spano, Justin; Chen, Ying; Turner, Richard; Wi, Sungsool

    2012-07-12

    Solid-state NMR spectroscopy was utilized to study the crystallinity and its correlation to the motional dynamics of a series of biphenol based poly(arylene ether sulfone) (PAES) copolymer analogues obtained by incorporating flexible aliphatic blocks. Introduction of a series of conformationally flexible aliphatic blocks into the rigid aromatic PAES blocks in the copolymer sequence had increased the crystallinity of the polymer matrix because the copolymer system with aliphatic blocks provided a decrease in the glass transition temperature (Tg) while maintaining a nonvariant melting temperature (Tm). Modified PAES copolymer systems with aliphatic blocks had yielded shorter (1)H T1 relaxation times and longer (1)H T1ρ relaxation times relative to the neat aromatic PAES copolymer. Trends observed in (1)H T1ρ and T1 data had demonstrated direct correlations to the observed ΔT (= Tm - Tg) and thus to the amount of crystallinity in the polymer matrix. Slow segmental reorientations of PAES blocks in a few milliseconds range also became slightly faster as the size of an aliphatic, segmented block became larger. Additionally, the local electronic environments of aromatic PAES blocks were invariant to the incorporation of aliphatic segments in the copolymer sequence. PMID:22697501

  14. PAR1 inhibition suppresses the self-renewal and growth of A2B5-defined glioma progenitor cells and their derived gliomas in vivo.

    PubMed

    Auvergne, R; Wu, C; Connell, A; Au, S; Cornwell, A; Osipovitch, M; Benraiss, A; Dangelmajer, S; Guerrero-Cazares, H; Quinones-Hinojosa, A; Goldman, S A

    2016-07-21

    Glioblastoma (GBM) remains the most common and lethal intracranial tumor. In a comparison of gene expression by A2B5-defined tumor-initiating progenitor cells (TPCs) to glial progenitor cells derived from normal adult human brain, we found that the F2R gene encoding PAR1 was differentially overexpressed by A2B5-sorted TPCs isolated from gliomas at all stages of malignant development. In this study, we asked if PAR1 is causally associated with glioma progression. Lentiviral knockdown of PAR1 inhibited the expansion and self-renewal of human GBM-derived A2B5(+) TPCs in vitro, while pharmacological inhibition of PAR 1 similarly slowed both the growth and migration of A2B5(+) TPCs in culture. In addition, PAR1 silencing potently suppressed tumor expansion in vivo, and significantly prolonged the survival of mice following intracranial transplantation of human TPCs. These data strongly suggest the importance of PAR1 to the self-renewal and tumorigenicity of A2B5-defined glioma TPCs; as such, the abrogation of PAR1-dependent signaling pathways may prove a promising strategy for gliomas. PMID:26616854

  15. Terminal index: a new way for precise description of topologic structure of highly branched polymers derived from A2 + B3 stepwise polymerization.

    PubMed

    Chen, Heng; Kong, Jie

    2014-03-27

    Terminal index (TI) was presented as a new characteristic parameter for quantitative description of branched and cyclic topology of highly branched soluble polymers derived from A2 + B3 stepwise polymerization. TI is defined as the ratio of terminal units of an A2 + B3 type highly branched polymer to those in its perfect hyperbranched counterpart. TI is concisely represented as T/(D + L), which can be conveniently calculated from a quantitative NMR spectrum. The model of soluble A2 + B3 type polymers is suggested as an intermediate between multicyclic polymers and perfect hyperbranched polymers. The TI ranges between 0 and 1 where a higher TI indicates a perfect hyperbranched topology while a low TI indicates a multicyclic structure. The analysis of soluble A2 + B3 type polyesters and polycarbosilanes as model polymers demonstrates that TI as a more precise parameter, along with degree of branching, can be generally applied to understand the fine topology of highly branched polymers derived from A2 + B3 polymerization. PMID:24579792

  16. Segmented polyether-ester copolymers

    SciTech Connect

    Souffie, R.D.

    1982-08-01

    This article touches on the chemistry of manufacture and structure of thermoplastic elastomers. The physical properties and environmental resistance characteristics of these copolymers are related to their molecular makeup. Results indicate that segmented polyether esters, because of their basic chemical structure, are resistant to a wide range of oils, solvents and chemicals. They are also highly elastic, resilient polymers which can be both cost and performance effective when used in a number of industrial applications.

  17. Self-assembly of Random Copolymers

    PubMed Central

    Li, Longyu; Raghupathi, Kishore; Song, Cunfeng; Prasad, Priyaa; Thayumanavan, S.

    2014-01-01

    Self-assembly of random copolymers has attracted considerable attention recently. In this feature article, we highlight the use of random copolymers to prepare nanostructures with different morphologies and to prepare nanomaterials that are responsive to single or multiple stimuli. The synthesis of single-chain nanoparticles and their potential applications from random copolymers are also discussed in some detail. We aim to draw more attention to these easily accessible copolymers, which are likely to play an important role in translational polymer research. PMID:25036552

  18. Copolymers of fluorinated polydienes and sulfonated polystyrene

    DOEpatents

    Mays, Jimmy W.; Gido, Samuel P.; Huang, Tianzi; Hong, Kunlun

    2009-11-17

    Copolymers of fluorinated polydienes and sulfonated polystyrene and their use in fuel cell membranes, batteries, breathable chemical-biological protective materials, and templates for sol-gel polymerization.

  19. Phase Behavior of Symmetric Sulfonated Block Copolymers

    SciTech Connect

    Park, Moon Jeong; Balsara, Nitash P.

    2008-08-21

    Phase behavior of poly(styrenesulfonate-methylbutylene) (PSS-PMB) block copolymers was studied by varying molecular weight, sulfonation level, and temperature. Molecular weights of the copolymers range from 2.9 to 117 kg/mol. Ordered lamellar, gyroid, hexagonally perforated lamellae, and hexagonally packed cylinder phases were observed in spite of the fact that the copolymers are nearly symmetric with PSS volume fractions between 0.45 and 0.50. The wide variety of morphologies seen in our copolymers is inconsistent with current theories on block copolymer phase behavior such as self-consistent field theory. Low molecular weight PSS-PMB copolymers (<6.2 kg/mol) show order-order and order-disorder phase transitions as a function of temperature. In contrast, the phase behavior of high molecular weight PSS-PMB copolymers (>7.7 kg/mol) is independent of temperature. Due to the large value of Flory-Huggins interaction parameter, x, between the sulfonated and non-sulfonated blocks, PSS-PMB copolymers with PSS and PMB molecular weights of 1.8 and 1.4 kg/mol, respectively, show the presence of an ordered gyroid phase with a 2.5 nm diameter PSS network. A variety of methods are used to estimate x between PSS and PMB chains as a function of sulfonation level. Some aspects of the observed phase behavior of PSS-PMB copolymers can be rationalized using x.

  20. 21 CFR 175.210 - Acrylate ester copolymer coating.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...) The acrylate ester copolymer is a fully polymerized copolymer of ethyl acrylate, methyl methacrylate... emulsion defoamer. Disodium hydrogen phosphate Do. Formaldehyde Glyceryl monostearate Methyl...

  1. 21 CFR 175.210 - Acrylate ester copolymer coating.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...) The acrylate ester copolymer is a fully polymerized copolymer of ethyl acrylate, methyl methacrylate... emulsion defoamer. Disodium hydrogen phosphate Do. Formaldehyde Glyceryl monostearate Methyl...

  2. Interfaces between Block Copolymer Domains

    NASA Astrophysics Data System (ADS)

    Kim, Jaeup; Jeong, Seong-Jun; Kim, Sang Ouk

    2011-03-01

    Block copolymers naturally form nanometer scale structures which repeat their geometry on a larger scale. Such a small scale periodic pattern can be used for various applications such as storage media, nano-circuits and optical filters. However, perfect alignment of block copolymer domains in the macroscopic scale is still a distant dream. The nanostructure formation usually occurs with spontaneously broken symmetry; hence it is easily infected by topological defects which sneak in due to entropic fluctuation and incomplete annealing. Careful annealing can gradually reduce the number of defects, but once kinetically trapped, it is extremely difficult to remove all the defects. One of the main reasons is that the defect finds a locally metastable morphology whose potential depth is large enough to prohibit further morphology evolution. In this work, the domain boundaries between differently oriented lamellar structures in thin film are studied. For the first time, it became possible to quantitatively study the block copolymer morphology in the transitional region, and it was shown that the twisted grain boundary is energetically favorable compared to the T-junction grain boundary. [Nano Letters, 9, 2300 (2010)]. This theoretical method successfully explained the experimental results.

  3. Rheology and Structure of Molten, Olefin Multiblock Copolymers

    SciTech Connect

    Park, Heon E.; Dealy, John M.; Marchand, Gary R.; Wang, Jian; Li, Sheng; Register, Richard A.

    2010-12-07

    Several samples of a recently developed olefin multiblock copolymer were studied by means of rheology, differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). The synthesis involves a chain shuttling agent (CSA) that switches the growing chain between two catalysts, one that favors the incorporation of an {alpha}-olefin comonomer and one that suppresses incorporation. The data were used to determine the effect of octene comonomer content and CSA level on rheological behavior and the occurrence of mesophase separation transition (MST) in the melt. To distinguish between crystallization and MST, we made calorimetry scans and measured the density and rheological properties over a range of temperatures. Small angle X-ray scattering analysis of a sample that had undergone planar extensional flow revealed strong alignment of lamellar mesodomains, which maintained their alignment after annealing. This result confirmed the hypothesis based on rheological evidence that a lamellar mesophase is present in the melt at temperatures well above the melting point.

  4. Increased adenosine contributes to penile fibrosis, a dangerous feature of priapism, via A2B adenosine receptor signaling

    PubMed Central

    Wen, Jiaming; Jiang, Xianzhen; Dai, Yingbo; Zhang, Yujin; Tang, Yuxin; Sun, Hong; Mi, Tiejuan; Phatarpekar, Prasad V.; Kellems, Rodney E.; Blackburn, Michael R.; Xia, Yang

    2010-01-01

    offer a potential target for prevention and treatment of penile fibrosis, a dangerous complication seen in priapism.—Wen, J., Jiang, X., Dai, Y., Zhang, Y., Tang, Y., Sun, H., Mi, T., Phatarpekar, P. V., Kellems, R. E., Blackburn, M. R., Xia, Y. Increased adenosine contributes to penile fibrosis, a dangerous feature of priapism, via A2B adenosine receptor signaling. PMID:19858092

  5. Up regulation of A2B adenosine receptor on monocytes are crucially required for immune pathogenicity in Indian patients exposed to Leishmania donovani.

    PubMed

    Vijayamahantesh; Amit, Ajay; Kumar, Santosh; Dikhit, Manas R; Jha, Pravin K; Singh, Ashish K; Sinha, Kislay K; Pandey, Krishna; Das, V N R; Das, Pradeep; Bimal, Sanjiva

    2016-03-01

    Adenosine, an endogenous purine nucleoside is one such extracellular signalling molecule whose role in regulation of anti-inflammatory cytokines and immune pathogenicity in visceral leishmaniasis is not fully understood. Here, we investigated the relationship between Leishmania donovani infection and expression of A2B receptor on monocytes in VL patients in their pre and post treatment stage. We also investigated the molecular mechanisms influencing the interaction between immunopathogenicity and infection by exposing Leishmania donovani pulsed macrophages to Adenosine. A direct correlation of up-regulated A2B expression on monocytes with increased parasite load was also observed. Our results also suggested that A2B receptor activation is critically required for the stimulatory effect of adenosine on IL-10 production and suppression of nitric oxide release. The stimulatory effect of adenosine on Leishmania donovani induced IL-10 production required ERK1/2 activation and is p-38 MAPK independent. PMID:26748211

  6. Deletion of the distal COOH-terminus of the A2B adenosine receptor switches internalization to an arrestin- and clathrin-independent pathway and inhibits recycling

    PubMed Central

    Mundell, SJ; Matharu, A-L; Nisar, S; Palmer, TM; Benovic, JL; Kelly, E

    2010-01-01

    Background and purpose: We have investigated the effect of deletions of a postsynaptic density, disc large and zo-1 protein (PDZ) motif at the end of the COOH-terminus of the rat A2B adenosine receptor on intracellular trafficking following long-term exposure to the agonist 5′-(N-ethylcarboxamido)-adenosine. Experimental approach: The trafficking of the wild type A2B adenosine receptor and deletion mutants expressed in Chinese hamster ovary cells was studied using an enzyme-linked immunosorbent assay in combination with immunofluorescence microscopy. Key results: The wild type A2B adenosine receptor and deletion mutants were all extensively internalized following prolonged treatment with NECA. The intracellular compartment through which the Gln325-stop receptor mutant, which lacks the Type II PDZ motif found in the wild type receptor initially trafficked was not the same as the wild type receptor. Expression of dominant negative mutants of arrestin-2, dynamin or Eps-15 inhibited internalization of wild type and Leu330-stop receptors, whereas only dominant negative mutant dynamin inhibited agonist-induced internalization of Gln325-stop, Ser326-stop and Phe328-stop receptors. Following internalization, the wild type A2B adenosine receptor recycled rapidly to the cell surface, whereas the Gln325-stop receptor did not recycle. Conclusions and implications: Deletion of the COOH-terminus of the A2B adenosine receptor beyond Leu330 switches internalization from an arrestin- and clathrin-dependent pathway to one that is dynamin dependent but arrestin and clathrin independent. The presence of a Type II PDZ motif appears to be essential for arrestin- and clathrin-dependent internalization, as well as recycling of the A2B adenosine receptor following prolonged agonist addition. PMID:20128803

  7. Melt inclusions: Chapter 6

    USGS Publications Warehouse

    Audétat A.; Lowenstern, J. B.

    2014-01-01

    Melt inclusions are small droplets of silicate melt that are trapped in minerals during their growth in a magma. Once formed, they commonly retain much of their initial composition (with some exceptions) unless they are re-opened at some later stage. Melt inclusions thus offer several key advantages over whole rock samples: (i) they record pristine concentrations of volatiles and metals that are usually lost during magma solidification and degassing, (ii) they are snapshots in time whereas whole rocks are the time-integrated end products, thus allowing a more detailed, time-resolved view into magmatic processes (iii) they are largely unaffected by subsolidus alteration. Due to these characteristics, melt inclusions are an ideal tool to study the evolution of mineralized magma systems. This chapter first discusses general aspects of melt inclusions formation and methods for their investigation, before reviewing studies performed on mineralized magma systems.

  8. Glass Melt Stability

    NASA Astrophysics Data System (ADS)

    Schaeffer, Helmut A.; Müller-Simon, Hayo

    The employment of sensors during glass melting represents a major prerequisite for an improved process control leading to higher production yields. In situ sensoring techniques can be divided into two groups: on the one hand, techniques which extract information of glass melt properties, e.g., oxidation state and concentrations of relevant polyvalent species (such as iron, sulfur, chromium) and on the other hand, techniques which monitor the furnace atmosphere with respect to toxic emissions (e.g., SO2, NO x ) and combustion species (e.g., CO, CO2, H2O). Nowadays it is feasible not only to install early warning systems indicating deviations from target glass properties, but also to implement process control systems which enforce a stable and reproducible glass melting. Examples are given for the redox control of green glass melting utilizing high portions of recycled cullet and the redox control of amber glass melting.

  9. Thermodynamics of Glass Melting

    NASA Astrophysics Data System (ADS)

    Conradt, Reinhard

    First, a model based on linear algebra is described by which the thermodynamic properties of industrial multi-component glasses and glass melts can be accurately predicted from their chemical composition. The model is applied to calculate the heat content of glass melts at high temperatures, the standard heat of formation of glasses from the elements, and the vapor pressures of individual oxides above the melt. An E-fiber glass composition is depicted as an example. Second, the role of individual raw materials in the melting process of E-glass is addressed, with a special focus on the decomposition kinetics and energetic situation of alkaline earth carriers. Finally, the heat of the batch-to-melt conversion is calculated. A simplified reaction path model comprising heat turnover, content of residual solid matter, and an approach to batch viscosity is outlined.

  10. The morphological behavior of miktoarm star and multiple-graft block copolymers

    NASA Astrophysics Data System (ADS)

    Beyer, Frederick Louis, III

    The effects of molecular architecture on block copolymer morphological behavior for two distinct types of architectures have been investigated. The first, AnBm-type stars, have a single, centrally located junction point from which blocks of two polymer species radiate, and are referred to as miktoarm stars. The extremes of a model proposed by Milner were investigated using three miktoarm systems, A2B2 stars, A8B 8 "Vergina" stars, and A5B stars. Samples having a low molecular asymmetry agreed in general with the predictions of this model, although bicontinuous morphologies were not observed. The A5B miktoarm samples, which have a high level of molecular asymmetry, exhibited behavior not predicted by the model, but which was consistent with a trend of discrepancies observed in prior studies. The effect of the junction point on chain stretching behavior in miktoarm stars was noted by comparing the lamellar period of several A2B2 and A8B8 stars to comparable AB diblocks. These materials were found to have significantly increased lamellar periods, thought to result from the increased chain stretching at and near the junction point. The second type of molecular architecture investigated was the multiple-graft architecture. Three series of multigrafts, were characterized: regular multigrafts with tetrafunctional branch points, random multigrafts with trifunctional branch points, and random multigrafts; with tetrafunctional branch points. Using the constituting block copolymer hypothesis, the behavior of these molecules was predicted using existing theories for block copolymers with simpler architectures. Use of this hypothesis is justified herein, and illustrates that the behavior of block copolymers with complex architectures is dictated by the preferred behavior of smaller architectural subunits from which the multigraft is comprised. The morphological behavior of multiple-graft block copolymers was shown to be influenced by branch point functionality, branch point

  11. Effect of chain topology of block copolymer on micellization: ring vs linear block copolymer

    NASA Astrophysics Data System (ADS)

    Kim, Kwang Hee; Huh, June; Jo, Won Ho

    2003-03-01

    The aggregation of amphiphilic block copolymers in solution to form micelles has attracted great interest in recent years because of its importance in industrial applications. Many studies on these systems have mainly focused on a di- or triblock copolymer and much less attention was given to other architectures such as ring block copolymer. Recent experimental work has extended those works to include ring block copolymer, made by end-linking the triblock copolymer. Although the micellization of the ring block copolymer seemed to be favored over that of the linear triblock copolymer, two block copolymers showed similar values of cmc in experiments. In the present work, micellization of ring block copolymer (ring-B9A8) was simulated by Brownian dyanmics and micellar behavior is compared with triblock copolymer (A4B9A4) to investigate more systematically the effect of molecular architecture. Critical micelle concentration (cmc), average aggregation number and micellar distribution are compared with corresponding quantities measured for linear triblock copolymers having the same chain length and composition. Simulation results show that the cmc of ring-B9A8 is smaller than that of A4B9A4. The difference is explained by simple mean-field type theory.

  12. Fluctuations in Symmetric Diblock Copolymers: Testing Theories Old and New

    NASA Astrophysics Data System (ADS)

    Qin, Jian; Morse, David C.

    2012-06-01

    Computer simulations are used to study composition fluctuations in disordered diblock copolymer melts over a range of values of the chain length N, and test several theories for the structure factor S(q). Specifically, we test the random-phase approximation (RPA), which is based on a self-consistent field treatment of fluctuations, the Fredrickson-Helfand theory, which was designed to describe fluctuations near the order-disorder transition, and the relatively new renormalized one-loop (ROL) theory. The results confirm claims that the RPA is exact in the limit N→∞ and that the ROL theory yields the dominant corrections to the RPA within a systematic expansion in powers of N-1/2, and show that the ROL theory is much more accurate than either older theory.

  13. Diblock copolymers in bulk and in thin films: Morphology and kinetics

    NASA Astrophysics Data System (ADS)

    Podariu, Iulia Anca

    In this thesis I numerically study the phase diagram and kinetics of a diblock copolymers melt in both bulk and thin films in the strong segregation limit. I probe various values of the volume fraction, f, of the shorter block of the copolymer chains, spanning the bulk phase diagram for the diblock copolymers from a spherical body-centered cubic (BCC) phase to a hexagonally packed cylindrical (HCP) phase, to a bicontinuous gyroid phase (G), to finally a lamellar phase(L). Finite size and wetting properties of the substrate modify the film morphology by shifting the effective value of the composition in the film. For neutral substrates, the film morphology is shifted toward a smaller relative composition f, while for substrates which prefer the longer blocks of the copolymers, the film morphology is shifted toward a large value of f. A dramatic change in thin film morphology takes place for a small change in external parameters if one chooses the composition f to be at the borderline between two different bulk phases. The next question addressed is that of the control over the thin film structure in the case of a symmetric diblock copolymer films with a thickness smaller than the bulk equilibrium period. These films are cast on either flat or corrugated substrates. The results show that the formation of uniformly sized lateral domains that appear randomly on a flat surface can be controlled by using topographically patterned substrates. Control of lateral pattern fails if the distance between steps is smaller than the lamellar wavelength or the lateral size of the corrugation is larger than the bulk lamellar wavelength. For thin block copolymer (BCP) films on a homogeneous substrate, a fast domain growth exponent has recently been observed in experiments. I have carried out numerical simulations of ordering and domain growth in a two-dimensional system of BCP melts. The model calculations explicitly include viscous, hydrodynamic flow and provide a scaling

  14. 21 CFR 180.22 - Acrylonitrile copolymers.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... ADDITIVES PERMITTED IN FOOD OR IN CONTACT WITH FOOD ON AN INTERIM BASIS PENDING ADDITIONAL STUDY Specific Requirements for Certain Food Additives § 180.22 Acrylonitrile copolymers. Acrylonitrile copolymers may be... uses subject to the denial are thereafter unapproved food additives and consequently unlawful. (3)...

  15. Dimensionally Stable Ether-Containing Polyimide Copolymers

    NASA Technical Reports Server (NTRS)

    Fay, Catharine C. (Inventor); St.Clair, Anne K. (Inventor)

    1999-01-01

    Novel polyimide copolymers containing ether linkages were prepared by the reaction of an equimolar amount of dianhydride and a combination of diamines. The polyimide copolymers described herein possess the unique features of low moisture uptake, dimensional stability, good mechanical properties, and moderate glass transition temperatures. These materials have potential application as encapsulants and interlayer dielectrics.

  16. Imide/arylene ether block copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, B. J.; Hergenrother, P. M.; Bass, R. G.

    1991-01-01

    Two series of imide/arylene either block copolymers were prepared using an arylene ether block and either an amorphous or semi-crystalline imide block. The resulting copolymers were characterized and selected physical and mechanical properties were determined. These results, as well as comparisons to the homopolymer properties, are discussed.

  17. Thermochemical characteristics of chitosan-polylactide copolymers

    NASA Astrophysics Data System (ADS)

    Goruynova, P. E.; Larina, V. N.; Smirnova, N. N.; Tsverova, N. E.; Smirnova, L. A.

    2016-05-01

    The energies of combustion of chitosan and its block-copolymers with different polylactide contents are determined in a static bomb calorimeter. Standard enthalpies of combustion and formation are calculated for these substances. The dependences of the thermochemical characteristics on block-copolymer composition are determined and discussed.

  18. 21 CFR 173.65 - Divinylbenzene copolymer.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... Adjuvants for Food Treatment § 173.65 Divinylbenzene copolymer. Divinylbenzene copolymer may be used for the... extraction with a water soluble alcohol until the level of divinylbenzene in the extract is less than 50... is then treated with water according to the manufacturer's recommendation to remove the...

  19. Signatures of nonthermal melting.

    PubMed

    Zier, Tobias; Zijlstra, Eeuwe S; Kalitsov, Alan; Theodonis, Ioannis; Garcia, Martin E

    2015-09-01

    Intense ultrashort laser pulses can melt crystals in less than a picosecond but, in spite of over thirty years of active research, for many materials it is not known to what extent thermal and nonthermal microscopic processes cause this ultrafast phenomenon. Here, we perform ab-initio molecular-dynamics simulations of silicon on a laser-excited potential-energy surface, exclusively revealing nonthermal signatures of laser-induced melting. From our simulated atomic trajectories, we compute the decay of five structure factors and the time-dependent structure function. We demonstrate how these quantities provide criteria to distinguish predominantly nonthermal from thermal melting. PMID:26798822

  20. Signatures of nonthermal melting

    PubMed Central

    Zier, Tobias; Zijlstra, Eeuwe S.; Kalitsov, Alan; Theodonis, Ioannis; Garcia, Martin E.

    2015-01-01

    Intense ultrashort laser pulses can melt crystals in less than a picosecond but, in spite of over thirty years of active research, for many materials it is not known to what extent thermal and nonthermal microscopic processes cause this ultrafast phenomenon. Here, we perform ab-initio molecular-dynamics simulations of silicon on a laser-excited potential-energy surface, exclusively revealing nonthermal signatures of laser-induced melting. From our simulated atomic trajectories, we compute the decay of five structure factors and the time-dependent structure function. We demonstrate how these quantities provide criteria to distinguish predominantly nonthermal from thermal melting. PMID:26798822

  1. Preparation and characterization of amorphous solid dispersions of nimesulide in cyclodextrin copolymers.

    PubMed

    Skiba, M; Skiba, M; Milon, N; Bounoure, F; Fessi, H

    2014-04-01

    A study to enhance the dissolution rate of nimesulide (NIM), a poorly water-soluble, non-steroidal anti-inflammatory drug, was carried out through developing new amorphous solid dispersions (ASD) based on soluble or insoluble water cyclodextrin copolymers (alpha-cyclodextrin, beta-cyclodextrin and y-cyclodextrin polymers) synthesized by direct melt polycondensation. Amorphous solid dispersions of NIM in cyclodextrin copolymers, obtained by solvent evaporation, were characterized by thermogravimetric analyzer (TGA), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and fourier transform-infrared spectroscopy (FT-IR). These analyses provided the existence of interactions between amorphous drug and its carrier. A burst release of more than 80% NIM within approximately 70 minutes was seen with soluble alpha-cyclodextrin polymers (poly-alpha-sol) and insoluble gamma-cyclodextrin polymers (poly-gamma-insol) where no significant differences were observed with the other copolymers. Mathematical kinetic models such as zero order, Higuchi and Korsmeyer-Peppas were used to evaluate the kinetic and mechanism of release of NIM from the different ASD compared to lactose reference matrix. The kinetic of release of NIM from different ASD followed a Higuchi model and the mechanism of release was explained by Korsmeyer-Peppas model in which a fickian diffusion for lactose and soluble beta-cyclodextrin polymers (poly-beta-sol) was observed. However, an anomalous non-Fickian transport was found for the other copolymers. PMID:24734689

  2. Reversible Micro- and Nano- Phase Programming of Anthraquinone Thermochromism Using Blended Block Copolymers.

    PubMed

    Zhang, Yumiao; Lovell, Jonathan F

    2015-12-22

    Here, we present an approach to generate materials with programmable thermochromic transition temperatures (TTTs), based on the reversible microcrystallization of anthraquinone dyes with the assistance of blended Pluronic block copolymers. At temperatures above block copolymer critical micellization temperature (CMT), hydrophobic anthraquinone dyes, including Sudan blue II, were dispersed in copolymer micelles, whereas at lower temperature, the dyes formed microcrystals driven by dye-dye and dye-Pluronic molecular interactions. The crystallization process altered the optical properties of the dye with bathochromatic shifts detectable by eye and the thermochromic process was fully reversible. Not only could Pluronic reversibly incorporate the anthraquinone dyes into micelles at elevated temperatures, but it also modulated the crystallization process and resulting morphology of microcrystals via tuning the molecular interactions when the temperature was lowered. Crystal melting transition points (and TTTs) were in agreement with the CMTs, demonstrating that the thermochromism was dependent on block copolymer micellization. Thermochromism could be readily programmed over a broad range of temperatures by changing the CMT by using different types and concentrations of Pluronics and combinations thereof. PMID:26626998

  3. Self-assembly of rod-coil-rod ABA-type triblock copolymers.

    PubMed

    Chen, Ji-Zhong; Sun, Zhao-Yan; Zhang, Cheng-Xiang; An, Li-Jia; Tong, Zhen

    2008-02-21

    Self-assembled behavior of symmetric ABA rod-coil-rod triblock copolymer melts is studied by applying self-consistent-field lattice techniques in three-dimensional space. The phase diagram is constructed to understand the effects of the chain architecture on the self-assembled behavior. Four stable structures are observed for the ABA rod-coil-rod triblock, i.e., spherelike, lamellar, gyroidlike, and cylindrical structures. Different from AB rod-coil diblock and BAB coil-rod-coil triblock copolymers, the lamellar structure observed in ABA rod-coil-rod triblock copolymer melts is not stable for high volume fraction of the rod component (f(rod)=0.8), which is attributed to the intramolecular interactions between the two rod blocks of the polymer chain. When 0.3

  4. Pattern transfer using block copolymers.

    PubMed

    Gu, Xiaodan; Gunkel, Ilja; Russell, Thomas P

    2013-10-13

    To meet the increasing demand for patterning smaller feature sizes, a lithography technique is required with the ability to pattern sub-20 nm features. While top-down photolithography is approaching its limit in the continued drive to meet Moore's law, the use of directed self-assembly (DSA) of block copolymers (BCPs) offers a promising route to meet this challenge in achieving nanometre feature sizes. Recent developments in BCP lithography and in the DSA of BCPs are reviewed. While tremendous advances have been made in this field, there are still hurdles that need to be overcome to realize the full potential of BCPs and their actual use. PMID:24000358

  5. Melt fracture revisited

    SciTech Connect

    Greenberg, J. M.

    2003-07-16

    In a previous paper the author and Demay advanced a model to explain the melt fracture instability observed when molten linear polymer melts are extruded in a capillary rheometer operating under the controlled condition that the inlet flow rate was held constant. The model postulated that the melts were a slightly compressible viscous fluid and allowed for slipping of the melt at the wall. The novel feature of that model was the use of an empirical switch law which governed the amount of wall slip. The model successfully accounted for the oscillatory behavior of the exit flow rate, typically referred to as the melt fracture instability, but did not simultaneously yield the fine scale spatial oscillations in the melt typically referred to as shark skin. In this note a new model is advanced which simultaneously explains the melt fracture instability and shark skin phenomena. The model postulates that the polymer is a slightly compressible linearly viscous fluid but assumes no slip boundary conditions at the capillary wall. In simple shear the shear stress {tau}and strain rate d are assumed to be related by d = F{tau} where F ranges between F{sub 2} and F{sub 1} > F{sub 2}. A strain rate dependent yield function is introduced and this function governs whether F evolves towards F{sub 2} or F{sub 1}. This model accounts for the empirical observation that at high shears polymers align and slide more easily than at low shears and explains both the melt fracture and shark skin phenomena.

  6. Rapid self-assembly of block copolymers to photonic crystals

    DOEpatents

    Xia, Yan; Sveinbjornsson, Benjamin R; Grubbs, Robert H; Weitekamp, Raymond; Miyake, Garret M; Atwater, Harry A; Piunova, Victoria; Daeffler, Christopher Scot; Hong, Sung Woo; Gu, Weiyin; Russell, Thomas P.

    2016-07-05

    The invention provides a class of copolymers having useful properties, including brush block copolymers, wedge-type block copolymers and hybrid wedge and polymer block copolymers. In an embodiment, for example, block copolymers of the invention incorporate chemically different blocks comprising polymer size chain groups and/or wedge groups that significantly inhibit chain entanglement, thereby enhancing molecular self-assembly processes for generating a range of supramolecular structures, such as periodic nanostructures and microstructures. The present invention also provides useful methods of making and using copolymers, including block copolymers.

  7. Structure and Interactions in Concentrated Diblock Copolymer Solutions

    NASA Astrophysics Data System (ADS)

    McConnell, Glen A.

    We report on investigations of polystyrene/polyisoprene (PS/PI) diblock copolymers suspended in decane using small angle scattering techniques. The primary objective of this research is the understanding of the bulk properties and structure in concentrated diblock copolymers in a solvent selective for one block. In this case, decane is a good solvent for polyisoprene. Suspending PS/PI diblocks in decane at low concentrations produces monodisperse, spherical micelles comprising a dense core of polystyrene and a diffuse corona of polyisoprene. These micelles are well idealized as spherical cores with a fixed number of polyisoprene chains tethered to the surface. Since the local curvature plays an important role in determining the coronal density profile, the core radius and aggregation number are experimentally calculated. This experimental characterization lends each polymeric micelle to a description of the micellar architecture and pair-interaction potential through use of self-consistent mean field equations for tethered-chain systems. We use these pair-potentials to describe the liquid-like interference and disorder-order transition observed experimentally. Gillan's method, subject to a Rogers-Young closure, provides a description of the liquid-state. Density functional theory, specifically the modified weighted density approximation of Denton and Ashcroft, is used to estimate the solid-state. We supplement these calculations with a semi-quantitative phase diagram demonstrating the diversity in phase behavior resulting from tuning the range of the repulsions by varying block asymmetry; the phase diagram includes regions of face-centered cubic (FCC) and body-centered cubic (BCC) crystals depending on the range of the coronal layer thickness relative to the core dimension. In addition to these studies, we conclude with a discussion of the phase behavior of diblock copolymers at concentrations intermediate to those witnessing cubic micellar crystals and the ordered

  8. Tetragonal Ordering in Block Copolymer-Homopolymer Blend Films Laterally Confined in a Square Well

    NASA Astrophysics Data System (ADS)

    Hur, Su-Mi; García-Cervera, Carlos; Kramer, Ed; Fredrickson, Glenn

    2009-03-01

    Self-consistent field theory (SCFT) simulations are presented for a melt blend of AB diblock copolymers and A homopolymers in a thin film confined to a square well. The work aims to guide self-assembly towards tetragonal ordering, which is a pattern of technological interest in block copolymer lithography. By using suitable A homopolymer additives, we have succeeded in achieving square lattices of cylinders not observed in the confined or bulk pure diblock system. A phase diagram is presented that shows the region of stability of the tetragonal phase as a function of chain length and volume fraction of the homopolymer additive, in addition to several other interesting phases that result from a competition between surface and bulk contributions to the free energy. Results are also presented on the effect of line edge roughness in the square confinement well on the achievement of robust and defect free tetragonal order.

  9. Diamino Telechelic Polybutadienes for Solventless Styrene-butadiene-styrene (SBS) Triblock Copolymer Formation.

    PubMed

    Ji, Shengxiang; Hoye, Thomas R; Macosko, Christopher W

    2008-11-10

    High molecular weight, high functionality diamino telechelic polybutadienes (TPBs) were synthesized by ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene (COD) in the presence of a chain transfer agent, 1,8-dicyano-4-octene, followed by lithium aluminum hydride reduction. Melt coupling of diamino TPB with anhydride-terminated polystyrene (PS-anh) resulted in the formation of styrene-butadiene-styrene (SBS) triblock copolymers; ca. 80% maximum conversion of PS-anh was achieved within 30 seconds. The results from SAXS, TEM, and rheological measurements of the coupling products confirmed the formation of SBS triblock copolymers having lamellar morphology. A fluororesent-labeled PS-anh was used to study the coupling kinetics by diluting the reactants by the addition of non-functional PS. PMID:19907636

  10. Impact property enhancement of poly (lactic acid) with different flexible copolymers

    NASA Astrophysics Data System (ADS)

    Likittanaprasong, N.; Seadan, M.; Suttiruengwong, S.

    2015-07-01

    The objective of this work was to improve the impact property of Poly (lactic acid) (PLA) by blending with different copolymers. Six flexible copolymers, namely, acrylonitrile butadiene styrene (ABS) powder, Biomax, polybutyrate adipate co-terephthalate (PBAT), polyether block amide (PEBAX), ethylene-vinyl acetate (EVA) and ethylene acrylic elastomer (EAE), with loading less than 20wt% were used and compared. The rheological, mechanical and morphological properties of samples were investigated by melt flow index, tensile testing, impact testing and scanning electron microscope (SEM), respectively. It was found that PLA added 20wt% EAE showed the highest impact strength (59.5 kJ/m2), which was 22 times higher than neat PLA. The elongation at break was also increased by 12 folds compared to neat PLA. The SEM images showed good interface and distribution for PLA containing 20wt% EAE, 15 phr Biomax and 20 wt% PEBAX.

  11. Quasi-Block Copolymers Based on a General Polymeric Chain Stopper.

    PubMed

    Sanguramath, Rajashekharayya A; Nealey, Paul F; Shenhar, Roy

    2016-07-11

    Quasi-block copolymers (q-BCPs) are block copolymers consisting of conventional and supramolecular blocks, in which the conventional block is end-terminated by a functionality that interacts with the supramolecular monomer (a "chain stopper" functionality). A new design of q-BCPs based on a general polymeric chain stopper, which consists of polystyrene end-terminated with a sulfonate group (PS-SO3 Li), is described. Through viscosity measurements and a detailed diffusion-ordered NMR spectroscopy study, it is shown that PS-SO3 Li can effectively cap two types of model supramolecular monomers to form q-BCPs in solution. Furthermore, differential scanning calorimetry data and structural characterization of thin films by scanning force microscopy suggests the existence of the q-BCP architecture in the melt. The new design considerably simplifies the synthesis of polymeric chain stoppers; thus promoting the utilization of q-BCPs as smart, nanostructured materials. PMID:27276387

  12. Diamino Telechelic Polybutadienes for Solventless Styrene-butadiene-styrene (SBS) Triblock Copolymer Formation

    PubMed Central

    Ji, Shengxiang; Hoye, Thomas R.; Macosko, Christopher W.

    2008-01-01

    High molecular weight, high functionality diamino telechelic polybutadienes (TPBs) were synthesized by ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene (COD) in the presence of a chain transfer agent, 1,8-dicyano-4-octene, followed by lithium aluminum hydride reduction. Melt coupling of diamino TPB with anhydride-terminated polystyrene (PS-anh) resulted in the formation of styrene-butadiene-styrene (SBS) triblock copolymers; ca. 80% maximum conversion of PS-anh was achieved within 30 seconds. The results from SAXS, TEM, and rheological measurements of the coupling products confirmed the formation of SBS triblock copolymers having lamellar morphology. A fluororesent-labeled PS-anh was used to study the coupling kinetics by diluting the reactants by the addition of non-functional PS. PMID:19907636

  13. Hydrolytic degradation study of biodegradable polyesteramide copolymers based on epsilon-caprolactone and 11-aminoundecanoic acid.

    PubMed

    Qian, Zhiyong; Li, Sai; He, Yi; Zhang, Hailian; Liu, Xiaobo

    2004-05-01

    In this paper, a new kind of aliphatic biodegradable polyesteramide copolymers P(CL/AU)x/y based on epsilon-caprolactone and 11-aminoundecanoic acid were synthesized by the melt polycondensation method. Hydrolytic degradation behavior of P(CL/AU) copolymers were studied by using FTIR, 1H-NMR and DSC. Chemical compositions, macromolecular weight, thickness of the test sample, and pH of the degradation medium have great effect on degradation rate. The degradation rate decreased with increase in aminoundecanoic acid content, macromolecular weight, and thickness of the test samples, but increased with incubation temperature and pH of the degradation medium. The degradation mechanism was studied according to the mathematical model developed by professor Göpferich. PMID:14741611

  14. Injectible bodily prosthetics employing methacrylic copolymer gels

    DOEpatents

    Mallapragada, Surya K.; Anderson, Brian C.

    2007-02-27

    The present invention provides novel block copolymers as structural supplements for injectible bodily prosthetics employed in medical or cosmetic procedures. The invention also includes the use of such block copolymers as nucleus pulposus replacement materials for the treatment of degenerative disc disorders and spinal injuries. The copolymers are constructed by polymerization of a tertiary amine methacrylate with either a (poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) polymer, such as the commercially available Pluronic.RTM. polymers, or a poly(ethylene glycol) methyl ether polymer.

  15. Block Copolymer Membranes for Biofuel Purification

    NASA Astrophysics Data System (ADS)

    Evren Ozcam, Ali; Balsara, Nitash

    2012-02-01

    Purification of biofuels such as ethanol is a matter of considerable concern as they are produced in complex multicomponent fermentation broths. Our objective is to design pervaporation membranes for concentrating ethanol from dilute aqueous mixtures. Polystyrene-b-polydimethylsiloxane-b-polystyrene block copolymers were synthesized by anionic polymerization. The polydimethylsiloxane domains provide ethanol-transporting pathways, while the polystyrene domains provide structural integrity for the membrane. The morphology of the membranes is governed by the composition of the block copolymer while the size of the domains is governed by the molecular weight of the block copolymer. Pervaporation data as a function of these two parameters will be presented.

  16. LaRC-ITPI/arylene ether copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Working, Dennis C.

    1991-01-01

    As part of an effort to develop high performance structural resins for aerospace applications, work has continued on block copolymers containing imide and arylene ether segments. The arylene ether block used in this study contains a bulky fluorene group in the polymer backbone while the imide block contains an arylene ketone segment similar to that in the arylene ether block and has been named LaRC-ITPI. A series of imide/arylene ether block and segmented copolymers were prepared and characterized. Films were prepared from these copolymers and mechanical properties were measured.

  17. Confinement effects on the miscibility of block copolymer blends.

    PubMed

    Spencer, Russell K W; Matsen, Mark W

    2016-04-01

    Thin films of long and short symmetric AB diblock copolymers are examined using self-consistent field theory (SCFT). We focus on hard confining walls with a preference for the A component, such that the lamellar domains orient parallel to the film with an even number ν of monolayers. For neat melts, confinement causes the lamellar period, D, to deviate from its bulk value, Db, in order to be commensurate with the film thickness, i.e., L = νD/2. For blends, however, the melt also has the option of macrophase separating into ν(l) large and ν((s)) small monolayers so as to provide a better fit, where L = ν(l)D(l)/2 + ν(s)D((s))/2. In addition to performing full SCFT calculations of the entire film, we develop a semi-analytical calculation for the coexistence of thick and thin monolayers that helps explain the complicated interplay between miscibility and commensurability. PMID:27106106

  18. Simulation of polymer crystallization: Application to specific homopolymers and copolymers

    SciTech Connect

    Goldbeck-Wood, G.; Barham, P.J.

    1995-12-01

    The growth of polymer single crystals has been simulated on the basis of a simple two-dimensional {open_quote}entropic barrier{close_quote} model. The chain is described by a sequence of growth units. Their additions and removals are determined by rate constants obeying detailed balance. The crystallization is then simulated by a kinetic Monte Carlo algorithm. A simulation of the lamellar thickness and growth rates of specific crystallizable homopolymers (polyethylene, isotactic polystyrene, isotactic polypropylene poly-hydroxybuterate and polypivalolactone) as well as the cocrystalization of copolymers like PHB/HV is presented. The model input parameters are calculated from surface free energies, bulk enthalpies, melting points and crystallographic repeat lengths. The only {open_quote}free{close_quote} parameter, the length of a model growth unit, is shown to be related to the lamellar crystal thickness at large undercooling. Good agreement with experimental evidence is found. An analysis of the unit lengths of the different polymers indicates a scaling with the chain persistence length in the melt.

  19. Dual A1/A2B Receptor Blockade Improves Cardiac and Renal Outcomes in a Rat Model of Heart Failure with Preserved Ejection Fraction.

    PubMed

    Tofovic, Stevan P; Salah, Eman M; Smits, Glenn J; Whalley, Eric T; Ticho, Barry; Deykin, Aaron; Jackson, Edwin K

    2016-02-01

    Heart failure with preserved ejection fraction (HFpEF) is prevalent and often accompanied by metabolic syndrome. Current treatment options are limited. Here, we test the hypothesis that combined A1/A2B adenosine receptor blockade is beneficial in obese ZSF1 rats, an animal model of HFpEF with metabolic syndrome. The combined A1/A2B receptor antagonist 3-[4-(2,6-dioxo-1,3-dipropyl-7H-purin-8-yl)-1-bicyclo[2.2.2]octanyl]propanoic acid (BG9928) was administered orally (10 mg/kg/day) to obese ZSF1 rats (n = 10) for 24 weeks (from 20 to 44 weeks of age). Untreated ZSF1 rats (n = 9) served as controls. After 24 weeks of administration, BG9928 significantly lowered plasma triglycerides (in mg/dl: control group, 4351 ± 550; BG9928 group, 2900 ± 551) without adversely affecting plasma cholesterol or activating renin release. BG9928 significantly decreased 24-hour urinary glucose excretion (in mg/kg/day: control group, 823 ± 179; BG9928 group, 196 ± 80) and improved oral glucose tolerance, polydipsia, and polyuria. BG9928 significantly augmented left ventricular diastolic function in association with a reduction in cardiac vasculitis and cardiac necrosis. BG9928 significantly reduced 24-hour urinary protein excretion (in mg/kg/day: control group, 1702 ± 263; BG9928 group, 1076 ± 238), and this was associated with a reduction in focal segmental glomerulosclerosis, tubular atrophy, tubular dilation, and deposition of proteinaceous material in the tubules. These findings show that, in a model of HFpEF with metabolic syndrome, A1/A2B receptor inhibition improves hyperlipidemia, exerts antidiabetic actions, reduces HFpEF, improves cardiac histopathology, and affords renal protection. We conclude that chronic administration of combined A1/A2B receptor antagonists could be beneficial in patients with HFpEF, in particular those with comorbidities such as obesity, diabetes, and dyslipidemias. PMID:26585572

  20. The Quintiles Prize Lecture 2004. The identification of the adenosine A2B receptor as a novel therapeutic target in asthma.

    PubMed

    Holgate, Stephen T

    2005-08-01

    Adenosine is a powerful bronchoconstrictor of asthmatic, but not normal, airways. In vitro studies on isolated human mast cells and basophils revealed that adenosine and selective analogues augmented inflammatory mediator release from mast cells by stimulating A(2) receptors. Pharmacological blockade of mast cell mediator release in vivo also attenuated adenosine-induced bronchoconstriction, as did theophylline, by adenosine A(2) receptor antagonism. Further in vitro studies revealed that the asthmatic response to adenosine is likely to be mediated via the A(2B) subtype which is selectively antagonised by enprofylline. Studies in animal models, especially mice, have shown a close synergistic interaction between adenosine, Th2 and airway remodelling responses. The recent description of A(2B) receptors on human airway smooth muscle cells that mediate cytokine and chemokine release and induce differentiation of fibroblasts into myofibroblasts strengthens the view that adenosine maybe more than an inflammatory mediator in asthma but also participates in airway wall remodelling in this disease. These data have provided a firm basis for developing adenosine A(2B) receptor antagonists as a new therapeutic approach to this disease. PMID:15980878

  1. The Quintiles Prize Lecture 2004: The identification of the adenosine A2B receptor as a novel therapeutic target in asthma

    PubMed Central

    Holgate, Stephen T

    2005-01-01

    Adenosine is a powerful bronchoconstrictor of asthmatic, but not normal, airways. In vitro studies on isolated human mast cells and basophils revealed that adenosine and selective analogues augmented inflammatory mediator release from mast cells by stimulating A2 receptors. Pharmacological blockade of mast cell mediator release in vivo also attenuated adenosine-induced bronchoconstriction, as did theophylline, by adenosine A2 receptor antagonism. Further in vitro studies revealed that the asthmatic response to adenosine is likely to be mediated via the A2B subtype which is selectively antagonised by enprofylline. Studies in animal models, especially mice, have shown a close synergistic interaction between adenosine, Th2 and airway remodelling responses. The recent description of A2B receptors on human airway smooth muscle cells that mediate cytokine and chemokine release and induce differentiation of fibroblasts into myofibroblasts strengthens the view that adenosine maybe more than an inflammatory mediator in asthma but also participates in airway wall remodelling in this disease. These data have provided a firm basis for developing adenosine A2B receptor antagonists as a new therapeutic approach to this disease. PMID:15980878

  2. Synthesis of biocompatible poly(ɛ-caprolactone)- block-poly(propylene adipate) copolymers appropriate for drug nanoencapsulation in the form of core-shell nanoparticles

    PubMed Central

    Nanaki, Stavroula G; Pantopoulos, Kostas; Bikiaris, Dimitrios N

    2011-01-01

    Poly(propylene adipate)-block-poly(ɛ-caprolactone) copolymers were synthesized using a combination of polycondensation and ring-opening polymerization of ɛ-caprolactone in the presence of poly(propylene adipate). Gel permeation chromatography was used for molecular weight determination, whereas hydrogen-1 nuclear magnetic resonance and carbon-13 nuclear magnetic resonance spectroscopy were employed for copolymer characterization and composition evaluation. The copolymers were found to be block while their composition was similar to the feeding ratio. They formed semicrystalline structures, while only poly(ɛ-caprolactone) formed crystals, as shown by wide angle X-ray diffraction. Differential scanning calorimetry data suggest that the melting point and heat of fusion of copolymers decreased by increasing the poly(propylene adipate) amount. The synthesized polymers exhibited low cytotoxicity and were used to encapsulate desferrioxamine, an iron-chelating drug. The desferrioxamine nanoparticles were self-assembled into core shell structures, had mean particle size <250 nm, and the drug remained in crystalline form. Further studies revealed that the dissolution rate was mainly related to the melting temperature, as well as to the degree of crystallinity of copolymers. PMID:22162656

  3. Block Copolymers with a Twist

    SciTech Connect

    Ho, R.; Chiang, Y; Chen, C; Wang, H; Hasegawa, H; Akasaka, S; Thomas, E; Burger, C; Hsiao, B

    2009-01-01

    Chiral block copolymers (BCPs*) comprising chiral entities were designed to fabricate helical architectures (i.e., twisted morphologies) from self-assembly. A new helical phase (H*) with P622 symmetry was discovered in the self-assembly of poly(styrene)-b-poly(l-lactide) (PS-PLLA) BCPs*. Hexagonally packed, interdigitated PLLA helical microdomains in a PS matrix were directly visualized by electron tomography. The phase diagram of the PS-PLLA BCPs* was also established. Phase transitions from the H* phase to the stable cylinder and gyroid phases were found after long-time annealing, suggesting that the H* is a long-lived metastable phase. In contrast to racemic poly(styrene)-b-poly(d,l-lactide) BCPs, chiral interaction significantly enhances the incompatibility between achiral PS and chiral PLLA blocks in the PS-PLLA BCPs* and can be estimated through the determination of the interaction parameter.

  4. Arbitrary lattice symmetries via block copolymer nanomeshes

    PubMed Central

    Majewski, Pawel W.; Rahman, Atikur; Black, Charles T.; Yager, Kevin G.

    2015-01-01

    Self-assembly of block copolymers is a powerful motif for spontaneously forming well-defined nanostructures over macroscopic areas. Yet, the inherent energy minimization criteria of self-assembly give rise to a limited library of structures; diblock copolymers naturally form spheres on a cubic lattice, hexagonally packed cylinders and alternating lamellae. Here, we demonstrate multicomponent nanomeshes with any desired lattice symmetry. We exploit photothermal annealing to rapidly order and align block copolymer phases over macroscopic areas, combined with conversion of the self-assembled organic phase into inorganic replicas. Repeated photothermal processing independently aligns successive layers, providing full control of the size, symmetry and composition of the nanoscale unit cell. We construct a variety of symmetries, most of which are not natively formed by block copolymers, including squares, rhombuses, rectangles and triangles. In fact, we demonstrate all possible two-dimensional Bravais lattices. Finally, we elucidate the influence of nanostructure on the electrical and optical properties of nanomeshes. PMID:26100566

  5. Block copolymer structures in nano-pores

    NASA Astrophysics Data System (ADS)

    Pinna, Marco; Guo, Xiaohu; Zvelindovsky, Andrei

    2010-03-01

    We present results of coarse-grained computer modelling of block copolymer systems in cylindrical and spherical nanopores on Cell Dynamics Simulation. We study both cylindrical and spherical pores and systematically investigate structures formed by lamellar, cylinders and spherical block copolymer systems for various pore radii and affinity of block copolymer blocks to the pore walls. The obtained structures include: standing lamellae and cylinders, ``onions,'' cylinder ``knitting balls,'' ``golf-ball,'' layered spherical, ``virus''-like and mixed morphologies with T-junctions and U-type defects [1]. Kinetics of the structure formation and the differences with planar films are discussed. Our simulations suggest that novel porous nano-containers can be formed by confining block copolymers in pores of different geometries [1,2]. [4pt] [1] M. Pinna, X. Guo, A.V. Zvelindovsky, Polymer 49, 2797 (2008).[0pt] [2] M. Pinna, X. Guo, A.V. Zvelindovsky, J. Chem. Phys. 131, 214902 (2009).

  6. Phase behaviors of cyclic diblock copolymers.

    PubMed

    Zhang, Guojie; Fan, Zhongyong; Yang, Yuliang; Qiu, Feng

    2011-11-01

    A spectral method of self-consistent field theory has been applied to AB cyclic block copolymers. Phase behaviors of cyclic diblock copolymers, such as order-disorder transition, order-order transition, and domain spacing size, have been studied, showing good consistency with previous experimental and theoretical results. Compared to linear diblocks, cyclic diblocks are harder to phase separate due to the topological constraint of the ring structure. A direct disorder-to-cylinder transition window is observed in the phase diagram, which is significantly different from the mean field phase diagram of linear diblock copolymers. The domain spacing size ratio between cyclic and linear diblock copolymers is typically close to 0.707, indicating in segregation that the cyclic polymer can be considered to be made up of linear diblocks with half of the original chain length. PMID:22070321

  7. Electrostatic control of block copolymer morphology

    NASA Astrophysics Data System (ADS)

    Sing, Charles E.; Zwanikken, Jos W.; Olvera de La Cruz, Monica

    2014-07-01

    Energy storage is at present one of the foremost issues society faces. However, material challenges now serve as bottlenecks in technological progress. Lithium-ion batteries are the current gold standard to meet energy storage needs; however, they are limited owing to the inherent instability of liquid electrolytes. Block copolymers can self-assemble into nanostructures that simultaneously facilitate ion transport and provide mechanical stability. The ions themselves have a profound, yet previously unpredictable, effect on how these nanostructures assemble and thus the efficiency of ion transport. Here we demonstrate that varying the charge of a block copolymer is a powerful mechanism to predictably tune nanostructures. In particular, we demonstrate that highly asymmetric charge cohesion effects can induce the formation of nanostructures that are inaccessible to conventional uncharged block copolymers, including percolated phases desired for ion transport. This vastly expands the design space for block copolymer materials and is informative for the versatile design of battery electrolyte materials.

  8. Method for making block siloxane copolymers

    DOEpatents

    Butler, Nora; Jessop, Edward S.; Kolb, John R.

    1982-01-01

    A method for synthesizing block polysiloxane copolymers. Diorganoscyclosiloxanes and an end-blocking compound are interacted in the presence of a ring opening polymerization catalyst, producing a blocked prepolymer. The prepolymer is then interacted with a silanediol, resulting in condensation polymerization of the prepolymers. A second end-blocking compound is subsequently introduced to end-cap the polymers and copolymers formed from the condensation polymerization.

  9. Method for making block siloxane copolymers

    DOEpatents

    Butler, N.L.; Jessop, E.S.; Kolb, J.R.

    1981-02-25

    A method for synthesizing block polysiloxane copolymers is disclosed. Diorganoscyclosiloxanes and an end-blocking compound are interacted in the presence of a ring opening polymerization catalyst, producing a blocked prepolymer. The prepolymer is then interacted with a silanediol, resulting in condensation polymerization of the prepolymers. A second end-blocking compound is subsequently introduced to end-cap the polymers and copolymers formed from the condensation polymerization.

  10. Responsive Copolymers for Enhanced Petroleum Recovery

    SciTech Connect

    McCormick, C.; Hester, R.

    2001-02-27

    The objectives of this work was to: synthesize responsive copolymer systems; characterize molecular structure and solution behavior; measure rheological properties of aqueous fluids in fixed geometry flow profiles; and to tailor final polymer compositions for in situ rheology control under simulated conditions. This report focuses on the synthesis and characterization of novel stimuli responsive copolymers, the investigation of dilute polymer solutions in extensional flow and the design of a rheometer capable of measuring very dilute aqueous polymer solutions at low torque.

  11. Phase behavior of ABC-type triple-hydrophilic block copolymers in aqueous solutions.

    PubMed

    Zheng, Lingfei; Wu, Jianqi; Wang, Zheng; Yin, Yuhua; Jiang, Run; Li, Baohui

    2016-07-01

    The phase behavior of symmetric ABC triple-hydrophilic triblock copolymers in concentrated aqueous solutions is investigated using a simulated annealing technique. Two typical cases, in which the hydrophilicity of the middle B-block is either stronger or weaker than that of the end A- and C-blocks, are studied. In these two cases, a variety of phase diagrams are constructed as a function of the volume fraction of the B-block and the copolymer concentration ([Formula: see text] for both non-frustrated and frustrated copolymers. Structures, such as two-color alternatingly packed cylinders or gyroid, and lamellae-in-lamellae etc. that do not occur in the melt system, are obtained in solutions. Rich phase transition sequences, especially re-entrant phase transitions involving complex continuous networks of alternating gyroid and alternating diamond are observed for a given copolymer with decreasing [Formula: see text] . The difference in hydrophilicity among different blocks can result in inhomogeneous distribution of solvent molecules in the morphology, and with the decrease of [Formula: see text] , the distribution of solvent molecules presents a non-monotonic variation. This results in a non-monotonic variation of the effective volume fraction of each domain with the decrease of [Formula: see text] , which induces the re-entrant phase transitions. The presence of a good solvent for all the blocks can cause changes in the effective segregation strengths between different blocks and also in chain conformations, hence can alter the bulk phases and results in the occurrence of new structures and phase transitions. Especially, structures having A-C interfaces or A-C mixed domains can be obtained even in the non-frustrated copolymer systems, and structures obtained in the frustrated systems may be similar to those obtained in the non-frustrated systems. The window of the alternating gyroid structures may occupy a large part of the phase diagram for non

  12. Effects of Process Parameters on Replication Accuracy of Microinjection Molded Cyclic Olefins Copolymers Parts

    NASA Astrophysics Data System (ADS)

    Lin, Hsuan-Liang; Chen, Chun-Sheng; Lee, Ruey-Tsung; Chen, Shia-Chung; Chien, Rean-Der; Jeng, Ming-Chang; Hwang, Jiun-Ren

    2013-04-01

    In this study, the effects of various processing parameters of microinjection molding on the replication accuracy of the micro featured fluidic platform used for DNA/RNA tests are investigated. LIGA-like processes were utilized to prepare a silicon-based SU-8 photoresist, followed by electroforming to make a Ni-Co-based stamp. A cyclic olefin copolymer (COC) was used as the injection molding material. The molding parameters associated with the replication accuracy of micro channel parts were investigated. It was found that for microinjection molded devices, the replication accuracies of the imprint width and depth increase with increasing of mold temperature, melt temperature, injection velocity, and packing pressure.

  13. Viscosity Measurement for Tellurium Melt

    NASA Technical Reports Server (NTRS)

    Lin, Bochuan; Li, Chao; Ban, Heng; Scripa, Rosalia N.; Su, Ching-Hua; Lehoczky, Sandor L.

    2006-01-01

    The viscosity of high temperature Te melt was measured using a new technique in which a rotating magnetic field was applied to the melt sealed in a suspended ampoule, and the torque exerted by rotating melt flow on the ampoule wall was measured. Governing equations for the coupled melt flow and ampoule torsional oscillation were solved, and the viscosity was extracted from the experimental data by numerical fitting. The computational result showed good agreement with experimental data. The melt velocity transient initiated by the rotating magnetic field reached a stable condition quickly, allowing the viscosity and electrical conductivity of the melt to be determined in a short period.

  14. hnRNP A2/B1 interacts with influenza A viral protein NS1 and inhibits virus replication potentially through suppressing NS1 RNA/protein levels and NS1 mRNA nuclear export

    SciTech Connect

    Wang, Yimeng; Zhou, Jianhong; Du, Yuchun

    2014-01-20

    The NS1 protein of influenza viruses is a major virulence factor and exerts its function through interacting with viral/cellular RNAs and proteins. In this study, we identified heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) as an interacting partner of NS1 proteins by a proteomic method. Knockdown of hnRNP A2/B1 by small interfering RNA (siRNA) resulted in higher levels of NS vRNA, NS1 mRNA, and NS1 protein in the virus-infected cells. In addition, we demonstrated that hnRNP A2/B1 proteins are associated with NS1 and NS2 mRNAs and that knockdown of hnRNP A2/B1 promotes transport of NS1 mRNA from the nucleus to the cytoplasm in the infected cells. Lastly, we showed that knockdown of hnRNP A2/B1 leads to enhanced virus replication. Our results suggest that hnRNP A2/B1 plays an inhibitory role in the replication of influenza A virus in host cells potentially through suppressing NS1 RNA/protein levels and NS1 mRNA nucleocytoplasmic translocation. - Highlights: • Cellular protein hnRNP A2/B1 interacts with influenza viral protein NS1. • hnRNP A2/B1 suppresses the levels of NS1 protein, vRNA and mRNA in infected cells. • hnRNP A2/B1 protein is associated with NS1 and NS2 mRNAs. • hnRNP A2/B1 inhibits the nuclear export of NS1 mRNAs. • hnRNP A2/B1 inhibits influenza virus replication.

  15. Thermoacoustic Streaming and Ultrasonic Processing of Low Melting Melts

    NASA Technical Reports Server (NTRS)

    Trinh, E. H.

    1997-01-01

    Ultrasonic levitation allows the processing of low melting materials both in 1 G as well as in microgravity. The free suspension of the melts also facilitates undercooling, permitting the measurements of the physical properties of the metastable liquids.

  16. Processing Effects on Block-Copolymer Based Pressure-Sensitive Adhesives

    NASA Astrophysics Data System (ADS)

    O'Connor, A. E.; Macosko, C. W.

    2000-03-01

    The goal of this work is to investigate how the variables in the hot-melt coating process affect the microstructure and properties of pressure-sensitive adhesives based on a styrene isoprene styrene triblock copolymer. This polymer is a thermoplastic elastomer, able to be coated at high temperatures and physically crosslinked at lower temperatures. Adhesive tape samples have been made through hot-melt and solvent coating methods. Hot-melt coatings are prepared at speeds up to 110 feet/minute. Materials with the same thermal history have been coated using both methods and then tested for comparison of properties. PSA properties are strongly dependent on the time scale of application and debonding, as revealed by shear rheology data, and three types of performance tests (tack, peel, and shear holding power) are used to capture the various responses. Solvent-coated tape has superior shear strength, while hot-melt-coated tape performs better in peel tests. It is expected that the varying flow and deformation histories of the samples will lead to distinct chain orientations, while the rate of cooling of hot-melt-coated samples may influence the degree of phase separation achieved. These factors will cause the adhesive coatings to have different microstructures and therefore different properties.

  17. Ion and temperature sensitive polypeptide block copolymer.

    PubMed

    Joo, Jae Hee; Ko, Du Young; Moon, Hyo Jung; Shinde, Usha Pramod; Park, Min Hee; Jeong, Byeongmoon

    2014-10-13

    A poly(ethylene glycol)/poly(L-alanine) multiblock copolymer incorporating ethylene diamine tetraacetic acid ([PA-PEG-PA-EDTA(m)) was synthesized as an ion/temperature dual stimuli-sensitive polymer, where the effect of different metal ions (Cu(2+), Zn(2+), and Ca(2+)) on the thermogelation of the polymer aqueous solution was investigated. The dissociation constants between the metal ions and the multiblock copolymer were calculated to be 1.2 × 10(-7), 6.6 × 10(-6), and 1.2 × 10(-4) M for Cu(2+), Zn(2+), and Ca(2+), respectively, implying that the binding affinity of the multiblock copolymer for Cu(2+) is much greater than that for Zn(2+) or Ca(2+). Atomic force microscopy and dynamic light scattering of the multiblock copolymer containing metal ions suggested micelle formation at low temperature, which aggregated as the temperature increased. Circular dichroism spectra suggested that changes in the α-helical secondary structure of the multiblock copolymer were more pronounced by adding Cu(2+) than other metal ions. The thermogelation of the multiblock copolymer aqueous solution containing Cu(2+) was observed at a lower temperature, and the modulus of the gel was significantly higher than that of the system containing Ca(2+) or Zn(2+), in spite of the same concentration of the metal ions and their same ionic valence of +2. The above results suggested that strong ionic complexes between Cu(2+) and the multiblock copolymer not only affected the secondary structure of the polymer but also facilitated the thermogelation of the polymer aqueous solution through effective salt-bridge formation even in a millimolar range of the metal ion concentration. Therefore, binding affinity of metal ions for polymers should be considered first in designing an effective ion/temperature dual stimuli-sensitive polymer. PMID:25178662

  18. Remifentanil-induced preconditioning has cross-talk with A1 and A2B adenosine receptors in ischemic-reperfused rat heart

    PubMed Central

    Lee, Yong-Cheol; Jung, Jiyoon; Park, Sang-Jin

    2016-01-01

    The purpose of this study was to determine whether there is a cross-talk between opioid receptors (OPRs) and adenosine receptors (ADRs) in remifentanil preconditioning (R-Pre) and, if so, to investigate the types of ADRs involved in the cross-talk. Isolated rat hearts received 30 min of regional ischemia followed by 2 hr of reperfusion. OPR and ADR antagonists were perfused from 10 min before R-Pre until the end of R-Pre. The heart rate, left ventricular developed pressure (LVDP), velocity of contraction (+dP/dtmax), and coronary flow (CF) were recorded. The area at risk and area of necrosis were measured. After reperfusion, the LVDP, +dP/dtmax, and CF showed a significant increase in the R-Pre group compared with the control group (no intervention before or after regional ischemia). These increases in the R-Pre group were blocked by naloxone, a nonspecific ADR antagonist, an A1 ADR antagonist, and an A2B ADR antagonist. The infarct size was reduced significantly in the R-Pre group compared with the control group. The infarct-reducing effect in the R-Pre group was blocked by naloxone, the nonspecific ADR antagonist, the A1 ADR antagonist, and the A2B ADR antagonist. The results of this study demonstrate that there is cross-talk between ADRs and OPRs in R-Pre and that A1 ADR and A2B ADR appear to be involved in the cross-talk. PMID:26773185

  19. Remifentanil-induced preconditioning has cross-talk with A1 and A2B adenosine receptors in ischemic-reperfused rat heart.

    PubMed

    Lee, Yong-Cheol; Jung, Jiyoon; Park, Sang-Jin

    2016-01-01

    The purpose of this study was to determine whether there is a cross-talk between opioid receptors (OPRs) and adenosine receptors (ADRs) in remifentanil preconditioning (R-Pre) and, if so, to investigate the types of ADRs involved in the cross-talk. Isolated rat hearts received 30 min of regional ischemia followed by 2 hr of reperfusion. OPR and ADR antagonists were perfused from 10 min before R-Pre until the end of R-Pre. The heart rate, left ventricular developed pressure (LVDP),velocity of contraction (+dP/dtmax), and coronary flow (CF) were recorded. The area at risk and area of necrosis were measured. After reperfusion, the LVDP, +dP/dtmax,and CF showed a significant increase in the R-Pre group compared with the control group (no intervention before or after regional ischemia). These increases in the R-Pre group were blocked by naloxone, a nonspecific ADR antagonist, an A1 ADR antagonist, and an A2B ADR antagonist. The infarct size was reduced significantly in the R-Pre group compared with the control group. The infarct-reducing effect in the R-Pre group was blocked by naloxone, the nonspecific ADR antagonist, the A1 ADR antagonist, and the A2B ADR antagonist. The results of this study demonstrate that there is cross-talk between ADRs and OPRs in R-Pre and that A1 ADR and A2B ADR appear to be involved in the cross-talk. PMID:26773185

  20. Precise sequence control in linear and cyclic copolymers of 2,5-bis(2-thienyl)pyrrole and aniline by DNA-programmed assembly.

    PubMed

    Chen, Wen; Schuster, Gary B

    2013-03-20

    A series of linear and cyclic, sequence controlled, DNA-conjoined copolymers of aniline (ANi) and 2,5-bis(2-thienyl)pyrrole (SNS) were synthesized. In one approach, linear copolymers were prepared from complementary DNA oligomers containing covalently attached SNS and ANi monomers. Hybridization of the oligomers aligns the monomers in the major groove of the DNA. Treatment of the SNS- and ANi-containing duplexes with horseradish peroxidase (HRP) and H2O2 causes rapid and efficient polymerization. In this way, linear copolymers (SNS)4(ANi)6 and (ANi)2(SNS)2(ANi)2(SNS)2(ANi)2 were prepared and analyzed. A second approach to the preparation of linear and cyclic copolymers of ANi and SNS employed a DNA encoded module strategy. In this approach, single-stranded DNA oligomers composed of a central region containing (SNS)6 or (ANi)5 covalently attached monomer blocks and flanking 5'- and 3'-single-strand DNA recognition sequences were combined in buffer solution. Self-assembly of these oligomers by Watson-Crick base pairing of the recognition sequences creates linear or cyclic arrays of SNS and ANi monomer blocks. Treatment of these arrays with HRP/H2O2 causes rapid and efficient polymerization to form copolymers having patterns such as cyclic BBA and linear ABA, where B stands for an (SNS)6 block and A stands for an (ANi)5 block. These DNA-conjoined copolymers were characterized by melting temperature analysis, circular dichroism spectroscopy, native and denaturing polyacrylamide gel electrophoresis, and UV-visible-near-IR optical spectroscopy. The optical spectra of these copolymers are typical of those of conducting polymers and are uniquely dependent on the specific order of monomers in the copolymer. PMID:23448549

  1. Novel functional conjugative hyperbranched polymers with aggregation-induced emission: synthesis through one-pot "A2+B4" polymerization and application as explosive chemsensors and PLEDs.

    PubMed

    Wu, Wenbo; Ye, Shanghui; Yu, Gui; Liu, Yunqi; Qin, Jingui; Li, Zhen

    2012-01-01

    With the aim to develop new tetraphenylethylene (TPE)-based conjugated hyperbranched polymer, TPE units, one famous aggregation-induced emission (AIE) active group, are utilized to construct hyperbranched polymers with three other aromatic blocks, through an "A2+B4" approach by using one-pot Suzuki polycondensation reaction. These three hyperbranched polymers exhibit interesting AIEE behavior and act as explosive chemsensors with high sensitivity both in the nanoparticles and solid states. This is the first report of the AIE activity of the TPE-based conjugated hyperbranched polymers. Their corresponding PLED devices also demonstrate good performance. PMID:22134953

  2. 21 CFR 177.1060 - n-Alkylglutarimide/acrylic copolymers.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... vinyl chloride homo- or copolymers. (e) Conditions of use. The n-alkylglutarimide/acrylic copolymers are used as articles or components of articles (other than articles composed of vinyl chloride homo-...

  3. 21 CFR 177.1060 - n-Alkylglutarimide/acrylic copolymers.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... vinyl chloride homo- or copolymers. (e) Conditions of use. The n-alkylglutarimide/acrylic copolymers are used as articles or components of articles (other than articles composed of vinyl chloride homo-...

  4. 21 CFR 177.1060 - n-Alkylglutarimide/acrylic copolymers.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... vinyl chloride homo- or copolymers. (e) Conditions of use. The n-alkylglutarimide/acrylic copolymers are used as articles or components of articles (other than articles composed of vinyl chloride homo-...

  5. 21 CFR 177.1060 - n-Alkylglutarimide/acrylic copolymers.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... vinyl chloride homo- or copolymers. (e) Conditions of use. The n-alkylglutarimide/acrylic copolymers are used as articles or components of articles (other than articles composed of vinyl chloride homo-...

  6. Initiator Effects in Reactive Extrusion of Starch Graft Copolymers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Graft copolymers of starch with water-soluble polymers such as polyacrylamide have potential applications including hydrogels, superabsorbents, and thickening agents. Reactive extrusion is a rapid, continuous method for production of starch graft copolymers with high reaction and grafting efficienc...

  7. Thermodynamics of Oligonucleotide Duplex Melting

    ERIC Educational Resources Information Center

    Schreiber-Gosche, Sherrie; Edwards, Robert A.

    2009-01-01

    Melting temperatures of oligonucleotides are useful for a number of molecular biology applications, such as the polymerase chain reaction (PCR). Although melting temperatures are often calculated with simplistic empirical equations, application of thermodynamics provides more accurate melting temperatures and an opportunity for students to apply…

  8. Diblock Copolymers for Nanoscale Patterning

    NASA Astrophysics Data System (ADS)

    Russell, Thomas

    2006-03-01

    As the size scale of device features becomes increasingly smaller, conventional lithographic processes become increasingly more difficult and expensive, especially at a minimum feature size of less than 50 nm. Consequently, to achieve higher density circuits, storage devices or displays, it is evident that alternative routes need to be developed to circumvent both cost and manufacturing issues. An ideal process would be compatible with existing technological processes/manufacturing techniques and these strategies, together with novel materials, could allow significant advances to be made in meeting both short-term and long-term demands for higher density and faster devices. The self-assembly of block copolymers (BCP), two polymer chains covalently linked together at one end, provides a robust solution to these challenges. As thin films, immiscible BCP self-assemble into a range of highly-ordered morphologies where with size scale of the features is limited to the size of the polymers chains and are, therefore, nanoscopic in size. While self-assembly alone is sufficient for a number of applications in fabricating advanced microelectronics, directed self-orienting self-assembly processes are also required to produce complex devices with the required density and addressability of elements to meet future demands. By combining tailored self-assembly processes, a bottom-up approach, with micro-fabrication processes, a top-down approach, the ever-present thirst of the consumer for faster, better and cheaper devices can be met in very simple, yet robust, ways.

  9. Random Copolymer: Gaussian Variational Approach

    NASA Astrophysics Data System (ADS)

    Moskalenko, A.; Kuznetsov, Yu. A.; Dawson, K. A.

    1997-03-01

    We study the phase transitions of a random copolymer chain with quenched disorder. We calculate the average over the quenched disorder in replica space and apply a Gaussian variational approach based on a generic quadratic trial Hamiltonian in terms of the correlation functions of monomer Fourier coordinates. This has the advantage that it allows us to incorporate fluctuations of the density, determined self-consistently, and to study collapse, phase separation transitions and the onset of the freezing transition within the same mean field theory. The effective free energy of the system is derived analytically and analyzed numerically in the one-step Parisi scheme. Such quantities as the radius of gyration, end-to-end distance or the average value of the overlap between different replicas are treated as observables and evaluated by introducing appropriate external fields to the Hamiltonian. As a result we obtain the phase diagram in terms of model parameters, scaling for the freezing transition and the dependence of correlation functions on the chain index.

  10. Synthesis and Characterization of a Poly(ethylene glycol)-Poly(simvastatin) Diblock Copolymer

    PubMed Central

    Asafo-Adjei, Theodora A.; Dziubla, Thomas D.; Puleo, David A.

    2014-01-01

    Biodegradable polyesters are commonly used as drug delivery vehicles, but their role is typically passive, and encapsulation approaches have limited drug payload. An alternative drug delivery method is to polymerize the active agent or its precursor into a degradable polymer. The prodrug simvastatin contains a lactone ring that lends itself to ring-opening polymerization (ROP). Consequently, simvastatin polymerization was initiated with 5 kDa monomethyl ether poly(ethylene glycol) (mPEG) and catalyzed via stannous octoate. Melt condensation reactions produced a 9.5 kDa copolymer with a polydispersity index of 1.1 at 150 °C up to a 75 kDa copolymer with an index of 6.9 at 250 °C. Kinetic analysis revealed first-order propagation rates. Infrared spectroscopy of the copolymer showed carboxylic and methyl ether stretches unique to simvastatin and mPEG, respectively. Slow degradation was demonstrated in neutral and alkaline conditions. Lastly, simvastatin, simvastatin-incorporated molecules, and mPEG were identified as the degradation products released. The present results show the potential of using ROP to polymerize lactone-containing drugs such as simvastatin. PMID:25431653

  11. Poly(lactide)-block-poly([epsilon]-caprolactone-co-[epsilon]-decalactone)-block-poly(lactide) copolymer elastomers

    SciTech Connect

    Schneiderman, Deborah K.; Hill, Erin M.; Martello, Mark T.; Hillmyer, Marc A.

    2015-08-28

    Batch ring opening transesterification copolymerization of ε-caprolactone and ε-decalactone was used to generate statistical copolymers over a wide range of compositions and molar masses. Reactivity ratios determined for this monomer pair, rCL = 5.9 and rDL = 0.03, reveal ε-caprolactone is added preferentially regardless of the propagating chain end. Relative to poly(ε-caprolactone) the crystallinity and melting point of these statistical copolymers were depressed by the addition of ε-decalactone; copolymers containing greater than 31 mol% (46 wt%) ε-decalactone were amorphous. Poly(lactide)-block-poly(ε-caprolactone-co-ε-decalactone)-block-poly(lactide) triblock polymers were also prepared and used to explore the influence of midblock composition on the temperature dependent Flory-Huggins interaction parameter (χ). In addition, uniaxial extension tests were used to determine the effects of midblock composition, poly(lactide) content, and molar mass on the mechanical properties of these new elastomeric triblocks.

  12. Solution assembly behaviors of 3-hexylthiophene polymer based rod-coil graft copolymer

    NASA Astrophysics Data System (ADS)

    Kim, Youngkwon; Kim, Jin-Sung; Kim, Hyeong Jun; Kim, Bumjoon

    Solution assembly of conjugated polymer based block copolymers (BCPs) is an attractive approach for achieving conducting nanowires (NWs) with nanometer-scale cross-sectional dimensions. In particular, conjugated block offers one-dimensional self-growth of crystalline NWs, and secondary block gives rise to stable dispersion of NWs and additional tuning parameter for the structures of NWs. Herein, we developed a series of poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) (P3HT-g-P2VP) rod-coil copolymers with systematically controlled crystallinity by modifying both grafting density and molecular weight (Mn) of coil block, and their solution assembly behaviors were carefully examined. As increasing the volume fraction and grafting density of the secondary blocks, melting temperatures, crystallization temperatures, and the crystallinity were gradually decreased by hindering rod-rod interaction between P3HT backbones, resulting in the formation of short NWs. Furthermore, the length of NMs was relatively shorter for the densely grafted copolymer despite same volume fraction of secondary block. These results suggested that controlling Mn and the number of branched coil block was critical to regulate the crystalline properties and new approach for determining the NWs growth.

  13. Controlling Miscibility in Polyethylene-Polynorbornene Block Copolymers via Side-Group Chemistry

    NASA Astrophysics Data System (ADS)

    Mulhearn, William; Register, Richard

    Block copolymers containing a crystallizable block, such as polyethylene (PE), and an amorphous block with high glass transition temperature (Tg) are an interesting class of materials since the rigid glassy block can improve the mechanical response of the article under strain by reinforcing the crystal fold surface. However, to prepare an easily processable PE-containing block copolymer it is necessary to avoid microphase separation in the melt by selection of amorphous blocks with weak repulsive interactions against PE (low Flory interaction parameter χ or interaction energy density X) . Most such low- χ polymers are chemically similar to PE, such as copolymers of ethylene and a small amount of an α-olefin, and therefore exhibit similarly low glass transition temperatures. This work investigates a series of low- and high-Tg polymers based on substituted norbornene monomers, polymerized via ring-opening metathesis polymerization (ROMP). Hydrogenated polynorbornene derivatives possess a wide range of glass transition temperatures, and miscibility with PE can be readily tuned by the choice of substituents on the monomers (e.g. aromatic vs. aliphatic groups). Two species investigated, hydrogenated poly(cyclohexyl norbornene) and hydrogenated poly(norbornyl norbornene), have high Tg and also remain miscible with polyethylene to high molecular weight. Furthermore, we develop a set of mixing rules to qualitatively predict the solubility behavior of substituted ROMP polynorbornenes as a function of their side-groups.

  14. Dynamic Processes in Diblock Copolymer Micelles

    NASA Astrophysics Data System (ADS)

    Robertson, Megan; Singh, Avantika

    2013-03-01

    Diblock copolymers, which form micelle structures in selective solvents, offer advantages of robustness and tunability of micelle characteristics as compared to small molecule surfactants. Diblock copolymer micelles in water have been a subject of great interest in drug delivery applications based on their high loading capacity and targeted drug delivery. The aim of this work is to understand the dynamic processes which underlie the self-assembly of diblock copolymer micelle systems which have a semi-crystalline core. Due to the large size of the molecules, the self-assembly of block copolymer micelles occurs on significantly longer time scales than small molecule analogues. The present work focuses on amphiphilic diblock copolymers containing blocks of poly(ethylene oxide) (a hydrophilic polymer) and polycaprolactone (a hydrophobic, semi-crystalline polymer), which spontaneously self-assemble into spherical micelles in water. A variety of experimental techniques are used to probe the kinetic processes relevant to micelle self-assembly, including time-resolved neutron scattering, dynamic light scattering, pulsed field gradient nuclear magnetic resonance, and fluorescence resonance energy transfer experiments.

  15. A widespread sequence-specific mRNA decay pathway mediated by hnRNPs A1 and A2/B1

    PubMed Central

    Geissler, Rene; Simkin, Alfred; Floss, Doreen; Patel, Ravi; Fogarty, Elizabeth A.; Scheller, Jürgen; Grimson, Andrew

    2016-01-01

    3′-untranslated regions (UTRs) specify post-transcriptional fates of mammalian messenger RNAs (mRNAs), yet knowledge of the underlying sequences and mechanisms is largely incomplete. Here, we identify two related novel 3′ UTR motifs in mammals that specify transcript degradation. These motifs are interchangeable and active only within 3′ UTRs, where they are often preferentially conserved; furthermore, they are found in hundreds of transcripts, many encoding regulatory proteins. We found that degradation occurs via mRNA deadenylation, mediated by the CCR4–NOT complex. We purified trans factors that recognize the motifs and identified heterogeneous nuclear ribonucleoproteins (hnRNPs) A1 and A2/B1, which are required for transcript degradation, acting in a previously unknown manner. We used RNA sequencing (RNA-seq) to confirm hnRNP A1 and A2/B1 motif-dependent roles genome-wide, profiling cells depleted of these factors singly and in combination. Interestingly, the motifs are most active within the distal portion of 3′ UTRs, suggesting that their role in gene regulation can be modulated by alternative processing, resulting in shorter 3′ UTRs. PMID:27151978

  16. Identification of hnRNPs K, L and A2/B1 as candidate proteins involved in the nutritional regulation of mRNA splicing

    PubMed Central

    Griffith, Brian N.; Walsh, Callee M.; Szeszel-Fedorowicz, Wioletta; Timperman, Aaron T.; Salati, Lisa M.

    2007-01-01

    Summary Nutrient regulation of glucose-6-phosphate dehydrogenase (G6PD) expression occurs through changes in the rate of splicing of G6PD pre-mRNA. This posttranscriptional mechanism accounts for the 12- to 15-fold increase in G6PD expression in livers of mice that were starved and then refed a high-carbohydrate diet. Regulation of G6PD pre-mRNA splicing requires a cis-acting element in exon 12 of the pre-mRNA. Using RNA probes to exon 12 and nuclear extracts from livers of mice that were starved or refed, proteins of 60 kDa and 37 kDa were detected bound to nucleotides 65–79 of exon 12 and this binding was decreased by 50% with nuclear extracts from refed mice. The proteins were identified as hnRNP K, and L, and hnRNP A2/B1 by LC-MS/MS. The decrease in binding of these proteins to exon 12 during refeeding was not accompanied by a decrease in the total amount of these proteins in total nuclear extract. HnRNPs K, L and A2/B1 have known roles in the regulation of mRNA splicing. The decrease in binding of these proteins during treatments that increase G6PD expression is consistent with a role for these proteins in the inhibition of G6PD mRNA splicing. PMID:17095106

  17. Adenosine A(1), A(2a), A(2b), and A(3) receptors in hematopoiesis. 1. Expression of receptor mRNA in four mouse hematopoietic precursor cells.

    PubMed

    Streitová, D; Sefc, L; Savvulidi, F; Pospísil, M; Holá, J; Hofer, M

    2010-01-01

    Four mouse bone marrow or thymus cell populations, namely granulopoietic/monocytopoietic, erythropoietic, B-lymphopoietic, and T-lymphopoietic precursor cells have been assayed by RT-PCR technique for the presence and relative amounts of adenosine A(1), A(2a), A(2b), and A(3) receptor mRNA. It has been found that (i) all four populations studied express all four adenosine receptor subtypes, (ii) the A(1), receptor is the least expressed in all populations studied, (iii) the A(3) receptor is markedly expressed in the populations of granulopoietic/monocytopoietic and erythropoietic cells, (iv) the A(2a) receptor is markedly expressed in the populations of B-lymphopoietic and T-lymphopoietic cells, and v) the A(2b) receptor does not predominate in any of the precursor cells studied. Our data offer a new possibility for the assessment of the readiness of these cells to respond, by receptor-mediated mechanisms, to adenosine or its analogs present in the tissues as a result of endogenous processes and/or following their administration. PMID:19249907

  18. Excess adenosine A2B receptor signaling contributes to priapism through HIF-1α mediated reduction of PDE5 gene expression

    PubMed Central

    Ning, Chen; Wen, Jiaming; Zhang, Yujin; Dai, Yingbo; Wang, Wei; Zhang, Weiru; Qi, Lin; Grenz, Almut; Eltzschig, Holger K.; Blackburn, Michael R.; Kellems, Rodney E.; Xia, Yang

    2014-01-01

    Priapism is featured with prolonged and painful penile erection and is prevalent among males with sickle cell disease (SCD). The disorder is a dangerous urological and hematological emergency since it is associated with ischemic tissue damage and erectile disability. Here we report that phosphodiesterase-5 (PDE5) gene expression and PDE activity is significantly reduced in penile tissues of two independent priapic models: SCD mice and adenosine deaminase (ADA)-deficient mice. Moreover, using ADA enzyme therapy to reduce adenosine or a specific antagonist to block A2B adenosine receptor (ADORA2B) signaling, we successfully attenuated priapism in both ADA−/− and SCD mice by restoring penile PDE5 gene expression to normal levels. This finding led us to further discover that excess adenosine signaling via ADORA2B activation directly reduces PDE5 gene expression in a hypoxia-inducible factor-1α (HIF-1α)-dependent manner. Overall, we reveal that excess adenosine-mediated ADORA2B signaling underlies reduced penile PDE activity by decreasing PDE5 gene expression in a HIF-1α-dependent manner and provide new insight for the pathogenesis of priapism and novel therapies for the disease.—Ning, C., Wen, J., Zhang, Y., Dai, Y., Wang, W., Zhang, W., Qi, L., Grenz, A., Eltzschig, H. K., Blackburn, M. R., Kellems, R. E., Xia, Y. Excess adenosine A2B receptor signaling contributes to priapism through HIF-1α mediated reduction of PDE5 gene expression. PMID:24614760

  19. 21 CFR 175.210 - Acrylate ester copolymer coating.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Acrylate ester copolymer coating. 175.210 Section... COATINGS Substances for Use as Components of Coatings § 175.210 Acrylate ester copolymer coating. Acrylate ester copolymer coating may safely be used as a food-contact surface of articles intended for...

  20. pH-sensitive methacrylic copolymers and the production thereof

    DOEpatents

    Mallapragada, Surya K.; Anderson, Brian C.; Bloom, Paul D.; Sheares Ashby, Valerie V.

    2006-02-14

    The present invention provides novel multi-functional methacrylic copolymers that exhibit cationic pH-sensitive behavior as well as good water solubility under acidic conditions. The copolymers are constructed from tertiary amine methacrylates and poly(ethylene glycol) containing methacrylates. The copolymers are useful as gene vectors, pharmaceutical carriers, and in protein separation applications.

  1. 21 CFR 177.1820 - Styrene-maleic anhydride copolymers.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... sieve No. 20. 2. Styrene-maleic anhydride copolymer modified with butadiene, (CAS Reg. No. 27288-99-9... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Styrene-maleic anhydride copolymers. 177.1820... Use Food Contact Surfaces § 177.1820 Styrene-maleic anhydride copolymers. Styrene-maleic...

  2. 21 CFR 177.1820 - Styrene-maleic anhydride copolymers.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... units by weight and not more than 20 percent styrene-butadiene and/or butadiene rubber units by weight... 21 Food and Drugs 3 2013-04-01 2013-04-01 false Styrene-maleic anhydride copolymers. 177.1820... copolymers. Styrene-maleic anhydride copolymers identified in paragraph (a) of this section may be...

  3. 21 CFR 177.1820 - Styrene-maleic anhydride copolymers.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... units by weight and not more than 20 percent styrene-butadiene and/or butadiene rubber units by weight... 21 Food and Drugs 3 2012-04-01 2012-04-01 false Styrene-maleic anhydride copolymers. 177.1820... copolymers. Styrene-maleic anhydride copolymers identified in paragraph (a) of this section may be...

  4. pH-sensitive methacrylic copolymers and the production thereof

    DOEpatents

    Mallapragada, Surya K.; Anderson, Brian C.; Bloom, Paul D.; Sheares Ashby, Valerie V.

    2007-01-09

    The present invention provides novel multi-functional methacrylic copolymers that exhibit cationic pH-sensitive behavior as well as good water solubility under acidic conditions. The copolymers are constructed from tertiary amine methacrylates and poly(ethylene glycol) containing methacrylates. The copolymers are useful as gene vectors, pharmaceutical carriers, and in protein separation applications.

  5. 40 CFR 721.484 - Fluorinated acrylic copolymer (generic name).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Fluorinated acrylic copolymer (generic... Specific Chemical Substances § 721.484 Fluorinated acrylic copolymer (generic name). (a) Chemical substance... fluorinated acrylic copolymer (PMN P-95-1208) is subject to reporting under this section for the...

  6. 40 CFR 721.484 - Fluorinated acrylic copolymer (generic name).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Fluorinated acrylic copolymer (generic... Specific Chemical Substances § 721.484 Fluorinated acrylic copolymer (generic name). (a) Chemical substance... fluorinated acrylic copolymer (PMN P-95-1208) is subject to reporting under this section for the...

  7. 21 CFR 172.775 - Methacrylic acid-divinylbenzene copolymer.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 3 2011-04-01 2011-04-01 false Methacrylic acid-divinylbenzene copolymer. 172.775... HUMAN CONSUMPTION Other Specific Usage Additives § 172.775 Methacrylic acid-divinylbenzene copolymer. Methacrylic acid-divinylbenzene copolymer may be safely used in food in accordance with the...

  8. 21 CFR 172.775 - Methacrylic acid-divinylbenzene copolymer.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Methacrylic acid-divinylbenzene copolymer. 172.775... Additives § 172.775 Methacrylic acid-divinylbenzene copolymer. Methacrylic acid-divinylbenzene copolymer may... produced by the polymerization of methacrylic acid and divinylbenzene. The divinylbenzene functions as...

  9. 21 CFR 172.775 - Methacrylic acid-divinylbenzene copolymer.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 3 2012-04-01 2012-04-01 false Methacrylic acid-divinylbenzene copolymer. 172.775... HUMAN CONSUMPTION Other Specific Usage Additives § 172.775 Methacrylic acid-divinylbenzene copolymer. Methacrylic acid-divinylbenzene copolymer may be safely used in food in accordance with the...

  10. 21 CFR 177.1310 - Ethylene-acrylic acid copolymers.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 3 2011-04-01 2011-04-01 false Ethylene-acrylic acid copolymers. 177.1310 Section... Basic Components of Single and Repeated Use Food Contact Surfaces § 177.1310 Ethylene-acrylic acid copolymers. The ethylene-acrylic acid copolymers identified in paragraph (a) of this section may be...

  11. 21 CFR 177.1310 - Ethylene-acrylic acid copolymers.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 3 2012-04-01 2012-04-01 false Ethylene-acrylic acid copolymers. 177.1310 Section... Basic Components of Single and Repeated Use Food Contact Surfaces § 177.1310 Ethylene-acrylic acid copolymers. The ethylene-acrylic acid copolymers identified in paragraph (a) of this section may be...

  12. 21 CFR 172.775 - Methacrylic acid-divinylbenzene copolymer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Methacrylic acid-divinylbenzene copolymer. 172.775... HUMAN CONSUMPTION Other Specific Usage Additives § 172.775 Methacrylic acid-divinylbenzene copolymer. Methacrylic acid-divinylbenzene copolymer may be safely used in food in accordance with the...

  13. 21 CFR 177.1310 - Ethylene-acrylic acid copolymers.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Ethylene-acrylic acid copolymers. 177.1310 Section... Basic Components of Single and Repeated Use Food Contact Surfaces § 177.1310 Ethylene-acrylic acid copolymers. The ethylene-acrylic acid copolymers identified in paragraph (a) of this section may be...

  14. 21 CFR 177.1310 - Ethylene-acrylic acid copolymers.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 3 2013-04-01 2013-04-01 false Ethylene-acrylic acid copolymers. 177.1310 Section... Basic Components of Single and Repeated Use Food Contact Surfaces § 177.1310 Ethylene-acrylic acid copolymers. The ethylene-acrylic acid copolymers identified in paragraph (a) of this section may be...

  15. 21 CFR 173.60 - Dimethylamine-epichlorohydrin copolymer.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 3 2011-04-01 2011-04-01 false Dimethylamine-epichlorohydrin copolymer. 173.60... HUMAN CONSUMPTION Polymer Substances and Polymer Adjuvants for Food Treatment § 173.60 Dimethylamine-epichlorohydrin copolymer. Dimethylamine-epichlorohydrin copolymer (CAS Reg. No. 25988-97-0) may be safely used...

  16. 21 CFR 173.60 - Dimethylamine-epichlorohydrin copolymer.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 3 2013-04-01 2013-04-01 false Dimethylamine-epichlorohydrin copolymer. 173.60... HUMAN CONSUMPTION Polymer Substances and Polymer Adjuvants for Food Treatment § 173.60 Dimethylamine-epichlorohydrin copolymer. Dimethylamine-epichlorohydrin copolymer (CAS Reg. No. 25988-97-0) may be safely used...

  17. 21 CFR 173.60 - Dimethylamine-epichlorohydrin copolymer.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 3 2012-04-01 2012-04-01 false Dimethylamine-epichlorohydrin copolymer. 173.60... HUMAN CONSUMPTION Polymer Substances and Polymer Adjuvants for Food Treatment § 173.60 Dimethylamine-epichlorohydrin copolymer. Dimethylamine-epichlorohydrin copolymer (CAS Reg. No. 25988-97-0) may be safely used...

  18. Melt spinning study

    NASA Astrophysics Data System (ADS)

    Workman, Gary L.; Rathz, Thomas

    1993-04-01

    Containerless processing of materials provides an excellent opportunity to study nucleation phenomena and produce unique materials, primarily through the formation of metastable phases and deep undercoolings. Deep undercoolings can be readily achieved in falling drops of molten material. Extended solute solubilities and greatly refined microstructures can also be obtained in containerless processing experiments. The Drop Tube Facility at Marshall Space Flight Center has played an important role in enhancing that area of research. Previous experiments performed in the Drop Tube with refractory metals has shown very interesting microstructural changes associated with deep undercoolings. It is apparent also that the microstructure of the deep undercooled species may be changing due to the release of the latent heat of fusion during recalescence. For scientific purposes, it is important to be able to differentiate between the microstructures of the two types of metallic species. A review of the literature shows that although significant advances have been made with respect to the engineering aspects of rapid solidification phenomena, there is still much to be learned in terms of understanding the basic phenomena. The two major ways in which rapid solidification processing provides improved structures and hence improved properties are: (1) production of refined structures such as fine dendrites and eutectics, and (2) production of new alloy compositions, microstructures, and phases through extended solid solubility, new phase reaction sequences, and the formation of metallic-glass microstructures. The objective of this work has been to determine the optimal methodology required to extract this excess energy without affecting the thermo-physical parameters of the under-cooled melt. In normal containerless processing experiments recalescence occurs as the melt returns toward the melting point in order to solidify. A new type of experiment is sought in which the resultant

  19. Melt spinning study

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.; Rathz, Thomas

    1993-01-01

    Containerless processing of materials provides an excellent opportunity to study nucleation phenomena and produce unique materials, primarily through the formation of metastable phases and deep undercoolings. Deep undercoolings can be readily achieved in falling drops of molten material. Extended solute solubilities and greatly refined microstructures can also be obtained in containerless processing experiments. The Drop Tube Facility at Marshall Space Flight Center has played an important role in enhancing that area of research. Previous experiments performed in the Drop Tube with refractory metals has shown very interesting microstructural changes associated with deep undercoolings. It is apparent also that the microstructure of the deep undercooled species may be changing due to the release of the latent heat of fusion during recalescence. For scientific purposes, it is important to be able to differentiate between the microstructures of the two types of metallic species. A review of the literature shows that although significant advances have been made with respect to the engineering aspects of rapid solidification phenomena, there is still much to be learned in terms of understanding the basic phenomena. The two major ways in which rapid solidification processing provides improved structures and hence improved properties are: (1) production of refined structures such as fine dendrites and eutectics, and (2) production of new alloy compositions, microstructures, and phases through extended solid solubility, new phase reaction sequences, and the formation of metallic-glass microstructures. The objective of this work has been to determine the optimal methodology required to extract this excess energy without affecting the thermo-physical parameters of the under-cooled melt. In normal containerless processing experiments recalescence occurs as the melt returns toward the melting point in order to solidify. A new type of experiment is sought in which the resultant

  20. Block copolymer blend phase behavior: Binary diblock blends and amphiphilic block copolymer/epoxy mixtures

    NASA Astrophysics Data System (ADS)

    Lipic, Paul Martin

    The phase behavior of block copolymers and block copolymer blends has provided an extensive amount of exciting research and industrial applications for over thirty years. However, the unique nanoscale morphologies of microphase separated block copolymer systems is still not completely understood. This thesis examines the phase behavior of diblock copolymers and binary diblock copolymer blends in the strong segregation limit (SSL), and blends of an amphiphilic diblock copolymer with an epoxy resin. Studies of high molecular weight (˜84,000 g/mole) poly(ethylene)-poly(ethyl ethylene) (PE-PEE) diblock copolymers probed the ability of block copolymers to reach equilibrium in the SSL. Samples of pure diblocks or binary diblock blends prepared using different preparation techniques (solvent casting or precipitation) had different phase behaviors, as identified with transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS), confirming non-equilibrium phase behavior. This non-equilibrium behavior was metastable, and these results identify the caution that should be used when claiming equilibrium phase behavior in the SSL. Blends of an amphiphilic diblock copolymer, poly(ethylene oxide)-poly(ethylene-alt-propylene) (PEO-PEP) with a polymerizable epoxy resin selectively miscible with PEO, poly(Bisphenol-A-co-epichlorohydrin), supported theoretical calculations and increased the understanding of block copolymer/homopolymer blends. These blends formed different ordered structures (lamellae, bicontinuous cubic gyroid, hexagonally packed cylinders, cubic and hexagonally packed spheres) as well as a disordered spherical micellar structure, identified with SAXS and rheological measurements. Addition of hardener, methylene dianiline, to the system resulted in cross-linking of the epoxy resin and formation of a thermoset material. Macrophase separation between the epoxy and block copolymer did not occur, but local expulsion of the PEO from the epoxy was

  1. Thermodynamic Interactions in Organometallic Block Copolymers

    SciTech Connect

    Pople, John A

    2002-08-06

    The thermodynamic interactions in anionically synthesized poly(styrene-block-ferrocenyldimethylsilane) (SF) copolymers were examined using birefringence, small angle X-ray and neutron scattering (SAXS and SANS). We show that birefringence detection of the order-disorder transition is possible in colored samples provided the wavelength of the incident beam is in the tail of the absorption spectrum. The location of the order-disorder transition was confirmed by SAXS. The temperature-dependence of the Flory-Huggins parameter, {chi}, of SF copolymers, determined by SAXS, is similar in magnitude to that between polystyrene and polyisoprene chains. We find that {chi} is independent of block copolymer composition (within experimental error). We also demonstrate that the neutron scattering length densities of styrene and ferrocenyldimethylsilane moieties are identical due to a surprising cancellation of factors related to density and atomic composition.

  2. Rod-Coil Block Polyimide Copolymers

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B. (Inventor); Kinder, James D. (Inventor)

    2005-01-01

    This invention is a series of rod-coil block polyimide copolymers that are easy to fabricate into mechanically resilient films with acceptable ionic or protonic conductivity at a variety of temperatures. The copolymers consist of short-rigid polyimide rod segments alternating with polyether coil segments. The rods and coil segments can be linear, branched or mixtures of linear and branched segments. The highly incompatible rods and coil segments phase separate, providing nanoscale channels for ion conduction. The polyimide segments provide dimensional and mechanical stability and can be functionalized in a number of ways to provide specialized functions for a given application. These rod-coil black polyimide copolymers are particularly useful in the preparation of ion conductive membranes for use in the manufacture of fuel cells and lithium based polymer batteries.

  3. Graft copolymer separators — development and use

    NASA Astrophysics Data System (ADS)

    Lovell, K. V.; Adams, L. B.

    Graft copolymer membranes have been used for a number of years as interelectrode separators in alkaline batteries either singly, laminated to cellophane, or in conjunction with other materials such as felts. The preparation details of some of the Royal Military College of Science's copolymers are summarised with emphasis on the production of commercial quantities having a high degree of uniformity and reproducibility. Important properties in a battery environment are discussed and, where possible, compared with other separator materials; notably cellophane. The use of graft copolymers in a number of primary and secondary alkaline battery systems is reported and test data given. Conclusions are drawn relating the properties of these separators to their performance in cells.

  4. Polyimide nanofoams from aliphatic polyester based copolymers

    SciTech Connect

    Hedrick, J.L.; Carter, K.R.; Richter, R.; Russell, T.P.

    1996-10-01

    High temperature polymer foams were prepared using microphase separated block copolymers where the major component is thermally stable block and the minor component is thermally labile. Upon thermal treatment, the dispersed minor component undergoes thermolysis leaving pores the size and shape of which are dictated by the initial copolymer morphology. The driving force behind the survey of aliphatic polyesters as possible labile blocks stems from their quantitative degradation into low boiling, polar degradation products via a backbiting process. Block copolymers were prepared using either a monofunctional caprolactone or a valerolactone oligomer and a high T. polyimide. Microphase morphologies were observed in each case. Thermal decomposition of the polyester blocks was accomplished by a thermal treatment at 370{degrees}C for 5 h. Significant density reductions were measured, and the resulting foams showed pore sizes in the 60-70 {Angstrom} range.

  5. Lyotropic Phase Behavior of Poly(ethylene oxide)-Poly(butadiene) Diblock Copolymers: Evolution of the Random Network Morphology

    SciTech Connect

    Jain, Sumeet; Dyrdahl, Mitchell H.E.; Gong, Xiaobo; Scriven, L.E.; Bates, Frank S.

    2008-10-24

    The phase behavior of poly(ethylene oxide)-poly(butadiene) (PEO-PB) diblock copolymers mixed with water was studied using small-angle X-ray scattering (SAXS), cryogenic scanning electron microscopy (cryo-SEM), cryogenic transmission electron microscopy (cryo-TEM), and dynamic mechanical spectroscopy. Two sets of diblocks were synthesized by adding different lengths of PEO to hydroxy terminated PB with degrees of polymerization N{sub PB} = 46 and 170. Two-component mixtures were investigated as a function of block composition and copolymer molecular weight, between 1 and 100 wt % polymer content. Melt phase behavior is consistent with established theory and known experimental behavior for diblock copolymers. Various lyotropic liquid crystalline structures, notably lamellae (L), hexagonally packed cylinders (H), and spheres (S) arranged on cubic (body-centered cubic, face-centered cubic) lattices, were documented as a function of water content. At the higher molecular weights (N{sub PB} = 170), a random network phase (N) was identified over a sizable portion of the phase portrait, located between hexagonally ordered cylinders and ordered lamellae. This new structure, along with branching of cylindrical micelles in the dilute limit, bear a striking similarity to experimentally observed and theoretically predicted phase behavior in certain ternary water/oil/surfactant systems. These findings demonstrate that block copolymer surfactants are characterized by at least four structural building blocks -- spheres, cylinders, bilayers, and branched cylinders -- above a threshold molecular weight.

  6. [Hydrodynamic properties of exopolysaccharide-acrylamide copolymer].

    PubMed

    Votselko, S K

    2000-01-01

    The method for producing copolymer EPAA of exopolysaccharide (EPS)--polyacrylamide (PAA) has been presented which was based on microbial exopolysaccharides (enposane, xampane), their mixture and model EPS (xanthane sigma, rodopol P-23). The copolymer was produced by acrylamide polymerization in 1-2% water solutions of polysaccharides, the concentration of acrylamide in the reaction mixture being 4.7-2% and that of polysaccharides 0.1-1% of the weight. Hydrodynamic parameters of the studied polymers have been determined, their heterogenity as to molecular-weight characteristics has been demonstrated. Molecular-weight distribution of copolymers showed that the content of low-molecular fractions decreased, thus the Mw values were (0.08-0.2) x 10(6) Da in contrast to that of exopolysaccharides possessing Mw (1.2-0.4) x 10(6) Da and of polyacrylamide possessing Mw within (2-30) x 10(6) Da. The value of efficient viscosity of copolymers ranged from 120 to 131 mPa.s that was lower than that of polyacrylamide (500 mPa.s), and higher than that of exopolysaccharides (42 mPa.s), and it depended on the sample, raw material, production conditions. A possibility has been shown to produce a new copolymer based on microbial polysaccharides enposane and xampane in the process of acrylamide polymerization. It has been found out that the studied copolymers EPAA differ from initial ones as to their hydrodynamical properties, which determines their preference: better solubility, good glueing properties, prolonged term of preservation, resistance to bacterial pollution. PMID:11300081

  7. Biodegradable blends of poly (lactic acid) (PLA) / polyhydroxybutrate (PHB) copolymer and its effects on rheological, thermal and mechanical properties

    NASA Astrophysics Data System (ADS)

    Sood, Nitin K.

    Poly (Lactic acid) is the most important plastic derived from the renewable resources. PLA based products have extensively been used in the medical industry. However, PLA has a few disadvantages such as inherent brittleness and low toughness despite a high modulus. A focus of this experiment was to study the improvement in toughness of PLA and to study the changes in thermal and rheological properties by blending PLA with a PHB copolymer. Where, PLA and PHB copolymer were melt blended using a twin screw Brabender extruder in the ratios of 100/0, 70/30, 50/50, 30/70, 0/100. Further, the blends were injection molded into tensile bar and impact bars for mechanical testing. Rheological properties were studied using a Galaxy capillary rheometer for melt viscosities and temperature dependence indicated a shear-thinning behavior along with power law model and consistency index. Blends were characterized to study the phase model using a differential scanning calorimetric (DSC), showed two separate phases. Mechanical properties were analyzed using a Tensile and Izod impact test indicating decrease in elastic modulus with increase in toughness and elongation as the PHB copolymer content was increased in the blend.

  8. Structure of Poly(3-(2'-ethyl)hexylthiophene) (P3EHT) Containing Diblock Copolymers Controlled via Thermal Processing

    NASA Astrophysics Data System (ADS)

    Davidson, Emily; Segalman, Rachel

    Poly(3-alkylthiophene)s with modified alkyl side chains crystallize confined within block copolymer microphases, serving as a good model system for the confined crystallization of semiflexible polymers. We hypothesize that the diblock structure may impose an equilibrium degree of crystalline conjugated chain folding which here is only accessible for small degrees of undercooling. Crystallization of these P3ATs in soft confinement drives microdomain expansion; here, we show that this expansion is minimized for crystallization at small degrees of undercooling. Upon heating, domains return to their melt structure over three distinct regimes. These regimes directly correspond to thermal features we assign to the relaxation of a rigid-amorphous fraction at the diblock interface, melt-recrystallization which reorganizes the degree of chain folding, and a final complete melting transition.

  9. Phase diagram of selectively cross-linked block copolymers shows chemically microstructured gel

    NASA Astrophysics Data System (ADS)

    von der Heydt, Alice; Zippelius, Annette

    2015-02-01

    We study analytically the intricate phase behavior of cross-linked AB diblock copolymer melts, which can undergo two main phase transitions due to quenched random constraints. Gelation, i.e., spatially random localisation of polymers forming a system-spanning cluster, is driven by increasing the number parameter μ of irreversible, type-selective cross-links between random pairs of A blocks. Self-assembly into a periodic pattern of A/B-rich microdomains (microphase separation) is controlled by the AB incompatibility χ inversely proportional to temperature. Our model aims to capture the system's essential microscopic features, including an ensemble of random networks that reflects spatial correlations at the instant of cross-linking. We identify suitable order parameters and derive a free-energy functional in the spirit of Landau theory that allows us to trace a phase diagram in the plane of μ and χ. Selective cross-links promote microphase separation at higher critical temperatures than in uncross-linked diblock copolymer melts. Microphase separation in the liquid state facilitates gelation, giving rise to a novel gel state whose chemical composition density mirrors the periodic AB pattern.

  10. Towards biomimetic scaffolds: anhydrous scaffold fabrication from biodegradable amine-reactive diblock copolymers.

    PubMed

    Hacker, Michael; Tessmar, Jörg; Neubauer, Markus; Blaimer, Andrea; Blunk, Torsten; Göpferich, Achim; Schulz, Michaela B

    2003-11-01

    The development of biomimetic materials and their processing into three-dimensional cell carrying scaffolds is one promising tissue engineering strategy to improve cell adhesion, growth and differentiation on polymeric constructs developing mature and viable tissue. This study was concerned with the fabrication of scaffolds made from amine-reactive diblock copolymers, N-succinimidyl tartrate monoamine poly(ethylene glycol)-block-poly(D,L-lactic acid), which are able to suppress unspecific protein adsorption and to covalently bind proteins or peptides. An appropriate technique for their processing had to be both anhydrous, to avoid hydrolysis of the active ester, and suitable for the generation of interconnected porous structures. Attempts to fabricate scaffolds utilizing hard paraffin microparticles as hexane-extractable porogens failed. Consequently, a technique was developed involving lipid microparticles, which served as biocompatible porogens on which the scaffold forming polymer was precipitated in the porogen extraction media (n-hexane). Porogen melting during the extraction and polymer precipitation step led to an interconnected network of pores. Suitable lipid mixtures and their melting points, extraction conditions (temperature and time) and a low-toxic polymer solvent system were determined for their use in processing diblock copolymers of different molecular weights (22 and 42 kDa) into highly porous off-the-shelf cell carriers ready for easy surface modification towards biomimetic scaffolds. Insulin was employed to demonstrate the principal of instant protein coupling to a prefabricated scaffold. PMID:12922156

  11. Phase diagram of selectively cross-linked block copolymers shows chemically microstructured gel.

    PubMed

    von der Heydt, Alice; Zippelius, Annette

    2015-02-01

    We study analytically the intricate phase behavior of cross-linked AB diblock copolymer melts, which can undergo two main phase transitions due to quenched random constraints. Gelation, i.e., spatially random localisation of polymers forming a system-spanning cluster, is driven by increasing the number parameter μ of irreversible, type-selective cross-links between random pairs of A blocks. Self-assembly into a periodic pattern of A/B-rich microdomains (microphase separation) is controlled by the AB incompatibility χ inversely proportional to temperature. Our model aims to capture the system's essential microscopic features, including an ensemble of random networks that reflects spatial correlations at the instant of cross-linking. We identify suitable order parameters and derive a free-energy functional in the spirit of Landau theory that allows us to trace a phase diagram in the plane of μ and χ. Selective cross-links promote microphase separation at higher critical temperatures than in uncross-linked diblock copolymer melts. Microphase separation in the liquid state facilitates gelation, giving rise to a novel gel state whose chemical composition density mirrors the periodic AB pattern. PMID:25662662

  12. Simulations on a swollen gyroid nanostructure in thin films relevant to systems of ionic block copolymers.

    PubMed

    Knychała, P; Banaszak, M

    2014-07-01

    Self-assembly of symmetric A/S-B copolymer melt to gyroid nanostructure, partitioning space into interpenetrating nano-labyrinths (channels), in thin films, is investigated using a minimal lattice model with short-range interactions. This model is relevant to poly(styrenesulfonate)-b -polymethylbutylene melt consisting of three types of segments, A, B and S, corresponding to styrene, methylbutylene and styrenesulfonate, respectively. A single sequence of A, B, and S is used in simulations and the fraction of S segments is fixed at p = 0.647 which corresponds to experimental data. The film thickness, L(z), is restricted to nine values (L(z) = 17 , 22, 26, 30, 34, 42, 51, 60, and 68 in units of the underlying lattice constant). The gyroid nanostructure is found to be stable if the film thickness is equal to or greater than the bulk period of the nanophase. The observed gyroid is referred to as swollen since the volume fraction of two continuous networks made of the B segments is anomalous with respect to that of conventional diblock copolymers. In contrast to bulk state, we do not directly observe the order-disorder transition to the gyroid nanophase for thin films. In this case, however, simulations indicate a direct order-disorder transition to a lamellar phase and the order-disorder transition temperature is higher than that in the bulk state, varying strongly with the film thickness. PMID:25080175

  13. Synthesis of comb-like copolymers from renewable resources: Itaconic anhydride, stearyl methacrylate and lactic acid

    NASA Astrophysics Data System (ADS)

    Shang, Shurui

    The synthesis and properties of comb-like copolymers and ionomers derived from renewable resources: itaconic anhydride (ITA), stearyl methacrylate (SM) and lactic acid (LA) are described. The copolymers based on ITA and SM (ITA-SM) were nearly random with a slight alternating tendency. The copolymers exhibited a nanophase-separated morphology, with the stearate side-chains forming a bilayer, semi-crystalline structure. The crystalline side-chains suppressed molecular motion of the main-chain, so that a glass transition temperature (Tg) was not resolved unless the ITA concentration was sufficiently high so that Tg > the melting point (Tm). The softening point and modulus of the copolymers increased with the increasing ITA concentration, but the thermal stability decreased. The ITA moiety along the main chain of the copolymers was neutralized with metal acetates to produce Na-, Ca- and Zn- random ionomers with comb-like architectures. In general, the incorporation of the ionic groups increased the Tg and suppressed the crystallinity of the side-chain packing. Ionomers with high SM side-chain density had two competing driving forces for self-assembled nano-phase separation: ionic aggregation and side-chain crystalline packing. Upon neutralization, a morphological transition from semi-crystalline lamella to spherical ionic aggregation was observed by small angle X-ray scattering (SAXS) analysis and transmission electron microscopy (TEM). Thermomechanical analysis revealed an increasing resistance to penetration deformation with an increasing degree of neutralization and an apparent rubbery plateau was observed above Tg. A controlled transesterification of PLA in glassware was an effective way to prepare a methacrylate functionalized PLA macromonomer with controlled molecular weight, which was used to synthesize a variety of copolymers. The copolymerization of this functionalized PLA macromonomer with ITA totally suppressed the side-chain crystallinity for the PLA chain

  14. Microphase separation in a model graft copolymer

    SciTech Connect

    Dozier, W.D.; Thiyagarajan, P.; Peiffer, D.G.

    1993-10-01

    We present a preliminary overview of our work on a series of graft copolymers having poly(ethyl acrylate) backbones with pendant chains of polystyrene (PS). The copolymer system appeared to be in the strong segregation limit and exhibited evidence of ordered structures. The morphology of these structures can apparently be very different from what would be expected. For instance, we observed a lamellar structure in a material containing 28 wt.% PS grafts. Samples under uniaxial strain showed either conventional (i.e., affine deformation) and anomalous ({open_quotes}butterfly{close_quotes} isointensity patterns) behavior in small-angle neutron scattering.

  15. Substrate tolerant direct block copolymer nanolithography.

    PubMed

    Li, Tao; Wang, Zhongli; Schulte, Lars; Ndoni, Sokol

    2016-01-01

    Block copolymer (BC) self-assembly constitutes a powerful platform for nanolithography. However, there is a need for a general approach to BC lithography that critically considers all the steps from substrate preparation to the final pattern transfer. We present a procedure that significantly simplifies the main stream BC lithography process, showing a broad substrate tolerance and allowing for efficient pattern transfer over wafer scale. PDMS-rich poly(styrene-b-dimethylsiloxane) (PS-b-PDMS) copolymers are directly applied on substrates including polymers, silicon and graphene. A single oxygen plasma treatment enables formation of the oxidized PDMS hard mask, PS block removal and polymer or graphene substrate patterning. PMID:26606904

  16. Co-polymer Films for Sensors

    NASA Technical Reports Server (NTRS)

    Ryan, Margaret A. (Inventor); Homer, Margie L. (Inventor); Yen, Shiao-Pin S. (Inventor); Kisor, Adam (Inventor); Jewell, April D. (Inventor); Shevade, Abhijit V. (Inventor); Manatt, Kenneth S. (Inventor); Taylor, Charles (Inventor); Blanco, Mario (Inventor); Goddard, William A. (Inventor)

    2012-01-01

    Embodiments include a sensor comprising a co-polymer, the co-polymer comprising a first monomer and a second monomer. For some embodiments, the first monomer is poly-4-vinyl pyridine, and the second monomer is poly-4-vinyl pyridinium propylamine chloride. For some embodiments, the first monomer is polystyrene and the second monomer is poly-2-vinyl pyridinium propylamine chloride. For some embodiments, the first monomer is poly-4-vinyl pyridine, and the second monomer is poly-4-vinyl pyridinium benzylamine chloride. Other embodiments are described and claimed.

  17. Co-polymer films for sensors

    NASA Technical Reports Server (NTRS)

    Ryan, Margaret A. (Inventor); Homer, Margie L. (Inventor); Yen, Shiao-Pin S. (Inventor); Kisor, Adam (Inventor); Jewell, April D. (Inventor); Shevade, Abhijit V. (Inventor); Manatt, Kenneth S. (Inventor); Taylor, Charles (Inventor); Blanco, Mario (Inventor); Goddard, William A. (Inventor)

    2010-01-01

    Embodiments include a sensor comprising a co-polymer, the co-polymer comprising a first monomer and a second monomer. For some embodiments, the first monomer is poly-4-vinyl pyridine, and the second monomer is poly-4-vinyl pyridinium propylamine chloride. For some embodiments, the first monomer is polystyrene and the second monomer is poly-2-vinyl pyridinium propylamine chloride. For some embodiments, the first monomer is poly-4-vinyl pyridine, and the second monomer is poly-4-vinyl pyridinium benzylamine chloride. Other embodiments are described and claimed.

  18. The versatility in morphology and physical properties offered by chain shuttled olefin block copolymers

    NASA Astrophysics Data System (ADS)

    Weinhold, Jeffrey

    2014-03-01

    Chain shuttling catalysis enables the production of olefin block copolymers (OBCs) with a wide range of block compositions. Unique morphology and property combinations can be achieved with highly crystalline hard blocks and low crystallinity or fully amorphous soft blocks. The effect of the amount of comonomer in the soft blocks on phase behavior, morphology and properties will be the focus of this presentation. In one class of materials, the soft blocks contain just enough octene comonomer to give elastic behavior but, unlike a random copolymer-based olefin elastomer, the soft segments are held together by thick crystals formed by the hard blocks. In addition to strengthening the network, these crystals provide temperature resistance and, by solidifying at higher temperature, they allow faster product fabrication. Increasing the soft block's octene content yields the next class of materials which have improved compatibility with polypropylene. This property allows the formation of fine, uniformly-dispersed OBC elastomer particles in PP. Since the impact strength of toughened PP increases as the particle size is reduced, a lower amount of elastomer is required to achieve an application's target for toughness. The direct benefit of lower elastomer loading is an increase in modulus, which enables lightweighting in applications. With further increases in the soft block's octene content, the incompatibility between the hard and soft blocks becomes large enough to cause the OBCs to form ordered melt morphologies. In the solid state, the alternating crystalline and amorphous regions have surprisingly large domain spacings and, due to the difference in refractive index between the domains, the periodicity results in a partial photonic band gap for frequencies in the visible spectrum. Comparisons to the morphology of monodisperse block copolymers and the predictions of theories will be presented. Also, the results of an extension to strong segregation theory will be shown

  19. Melting the Divide

    NASA Astrophysics Data System (ADS)

    Gibson, S. M.

    2014-12-01

    Presenting Quaternary Environmental Change to students who fall into Widening Participation criteria at the University of Cambridge, gives a unique opportunity to present academic debate in an approachable and entertaining way. Literally by discussing the melting of our ice caps, melts the divide Cambridge has between its reputation and the reality for the brightest, underprivileged, students. There is a balance between presenting cutting edge research with the need to come across as accessible (and importantly valuable to "learning"). Climate change over the Quaternary lends itself well to this aim. By lecturing groups of potential students through the entire Quaternary in an hour, stopping to discuss how our ancestors interacted with past Interglacials and what are the mechanisms driving change (in generalized terms), you are able to introduce cutting edge research (such as the latest NEEM ice core) to the students. This shows the evolution and importance of higher education and academic research. The lecture leads well onto group discussions (termed "supervisions" in Cambridge), to explore their opinions on the concern for present Anthropogenic Climate Change in relation to Past Climate Change after being presented with images that our ancestors "made it". Here discussion thrives off students saying obvious things (or sarcastic comments!) which quickly can lead into a deep technical discussion on their terms. Such discussions give the students a zest for higher education, simply throwing Ruddiman's (2003) "The Anthroprocene Started Several Thousand Years Ago" at them, questions in a second their concept of Anthropogenic Climate Change. Supervisions lend themselves well to bright, articulate, students and by offering these experiences to students of Widening Participation criteria we quickly melt the divide between the reputation of Cambridge ( and higher education as a whole) and the day to day practice. Higher education is not for the privileged, but a free and

  20. Synthesis of amphiphilic diblock copolymer for surface modification of Ethylene-Norbornene Copolymers

    NASA Astrophysics Data System (ADS)

    Levinsen, Simon; Svendsen, Winnie Edith; Horsewell, Andy; Almdal, Kristoffer

    2014-03-01

    The aim of this work is to produce polymer modifiers in order to develop hydrophilic polymeric surfaces for use in microfluidics. The use of hydrophilic polymers in microfluidics will have many advantages e.g. preventing protein absorbance. Here we present an amphiphilic diblock copolymer consisting of a bulk material compatible block and a hydrophilic block. To utilize the possibility of incorporating diblock copolymers into ethylene-norbornene copolymers, we have in this work developed a model poly(ethylene-1-butene) polymer compatible with the commercial available ethylene-norbornene copolymer TOPAS. Through matching of the radius of gyration for the model polymer and TOPAS the miscibility was achieved. The poly(ethylene-1-butene) polymer was synthesized from a hydrogenated anionic polymerized polybutadiene polymer. As hydrophilic block poly(ethylene oxide) was subsequently added also with anionic polymerization. Recent miscibility results between the model polymer and TOPAS will be presented, as well ongoing efforts to study the hydrophilic surface.

  1. Molecular Interaction Control in Diblock Copolymer Blends and Multiblock Copolymers with Opposite Phase Behaviors

    NASA Astrophysics Data System (ADS)

    Cho, Junhan

    2014-03-01

    Here we show how to control molecular interactions via mixing AB and AC diblock copolymers, where one copolymer exhibits upper order-disorder transition and the other does lower disorder-order transition. Linear ABC triblock copolymers possessing both barotropic and baroplastic pairs are also taken into account. A recently developed random-phase approximation (RPA) theory and the self-consistent field theory (SCFT) for general compressible mixtures are used to analyze stability criteria and morphologies for the given systems. It is demonstrated that the copolymer systems can yield a variety of phase behaviors in their temperature and pressure dependence upon proper mixing conditions and compositions, which is caused by the delicate force fields generated in the systems. We acknowledge the financial support from National Research Foundation of Korea and Center for Photofunctional Energy Materials.

  2. Water-soluble copolymers. IV. Random copolymers of acrylamide with sulfonated comonomers

    SciTech Connect

    McCormick, C.L.; Chen, G.S.

    1982-03-01

    Random copolymers of acrylamide with sodium-2-sulfoethyl methacrylate and with sodium-2-acrylamido-2-methylpropane sulfonate were synthesized in aqueous solutions utilizing persulfate initiators. Copolymer compositions were determined by elemental analysis and by infrared spectroscopic methods. Monomer reactivity ratios were calculated using Fineman-Ross, Kelen-Tuedos, and/or Mayo-Lewis techniques at appropriate conversions. The copolymer microstructure, including mean sequence length distributions, was calculated from reactivity ratios. Membrane osmometry and viscometry measurements were utilized to estimate molecular weight and size. The large dimensions of these polyelectrolytes in aqueous solutions, as well as their inherent hydrogen bonding capacity and pseudoplasticity, make these copolymers excellent candidates for application as mobility control agents in enhanced oil recovery.

  3. MicroRNA signatures predict dysregulated vitamin D receptor and calcium pathways status in limb girdle muscle dystrophies (LGMD) 2A/2B.

    PubMed

    Aguennouz, M; Lo Giudice, C; Licata, N; Rodolico, C; Musumeci, O; Fanin, M; Migliorato, A; Ragusa, M; Macaione, V; Di Giorgio, R M; Angelini, C; Toscano, A

    2016-08-01

    miRNA expression profile and predicted pathways involved in selected limb-girdle muscular dystrophy (LGMD)2A/2B patients were investigated. A total of 187 miRNAs were dysregulated in all patients, with six miRNAs showing opposite regulation in LGMD2A versus LGMD2B patients. Silico analysis evidence: (1) a cluster of the dysregulated miRNAs resulted primarily involved in inflammation and calcium metabolism, and (2) two genes predicted as controlled by calcium-assigned miRNAs (Vitamin D Receptor gene and Guanine Nucleotide Binding protein beta polypeptide 1gene) showed an evident upregulation in LGMD2B patients, in accordance with miRNA levels. Our data support alterations in calcium pathway status in LGMD 2A/B, suggesting myofibre calcium imbalance as a potential therapeutic target. Copyright © 2016 John Wiley & Sons, Ltd. PMID:27558075

  4. Correlation of A2bAR and KLF4/KLF15 with Obesity-Dyslipidemia Induced Inflammation in Uygur Population

    PubMed Central

    Wang, Cuizhe; Ha, Xiaodan; Li, Wei; Xu, Peng; Gu, Yajuan; Wang, Tingting; Wang, Yan; Xie, Jianxin; Zhang, Jun

    2016-01-01

    In this paper, the researchers collected visceral adipose tissue from the Uygur population, which were divided into two groups: the normal control group (NC, n = 50, 18.0 kg/m2 ≤ BMI ≤ 23.9 kg/m2) and the obese group (OB, n = 45, BMI ≥ 28 kg/m2), and then use real-time PCR to detect the mRNA expression level of key genes involved in inflammation signaling pathway. The findings suggest that, in obese status, the lower expression level of A2bAR, KLF4, and KLF15 of visceral adipose tissue may correlate with obese-dyslipidemia induced inflammation in Uygur population. PMID:27199507

  5. Block copolymer nanolithography for the fabrication of patterned media.

    SciTech Connect

    Warke, Vishal V; Bakker, Martin G; Hong, Kunlun; Mays, Jimmy; Britt, Phillip F; Li, Xuefa; Wang, Jin

    2008-01-01

    Abstract Bit patterned perpendicular media has the potential to increase the density of magnetic recording beyond what can be achieved by granular media. Self assembling diblock copolymers are of interest as templates for patterned media, as they potentially provide a low cost fabrication route. A method to fabricate the desired pattern using cylinder forming diblock copolymers of (PS-b-PMMA) as template is reported. Upon phase separation hexagonally packed cylinders of the minority phase (PMMA) surrounded by the continuous majority phase (PS) are obtained. The processing sequence began with spin coating the block copolymer on a suitable substrate, followed by annealing the block copolymer thin film in vacuum to orient it perpendicular to the substrate. Block copolymer templates were obtained by glacial acetic acid treatment which opened the pores in the block copolymer thin film. Ni was electrodeposited in the block copolymer templates and this pattern was then transferred onto the underlying substrate by ion milling

  6. Vavilosides A1/A2-B1/B2, new furostane glycosides from the bulbs of Allium vavilovii with cytotoxic activity.

    PubMed

    Zolfaghari, Behzad; Sadeghi, Masoud; Troiano, Raffaele; Lanzotti, Virginia

    2013-04-01

    A phytochemical analysis of the bulbs of Allium vavilovii M. Pop. & Vved. was attained for the first time extensively, affording to the isolation of four new furostanol saponins, named vavilosides A1/A2-B1/B2 (1a/b-2a/2b), as two couple of isomers in equilibrium, together with ascalonicoside A1/A2 (3a/3b) and 22-O-methyl ascalonicoside A1/A2 (4a/4b), previously isolated from shallot, Allium ascalonicum. High concentrations of kaempferol, kaempferide, and kaempferol 4(I)-glucoside were also isolated. The chemical structures of the new compounds, established through a combination of extensive nuclear magnetic resonance, mass spectrometry and chemical analyses, were identified as (25R)-furost-5(6)-en-1β,3β,22α,26-tetraol 1-O-α-L-rhamnopyranosyl-(1→2)-O-β-D-galactopyranosyl 26-O-α-L-rhamnopyranoside (vaviloside A1), (25R)-furost-5(6)-en-1β,3β,22β,26-tetraol 1-O-α-L-rhamnopyranosyl-(1→2)-O-β-D-galactopyranosyl 26-O-α-L-rhamnopyranoside (vaviloside A2), (25R)-furost-5(6)-en-1β,3β,22α,26-tetraol 1-O-α-L-rhamnopyranosyl-(1→2)-O-β-D-xylopyranosyl 26-O-α-L-rhamnopyranoside (vaviloside B1), (25R)-furost-5(6)-en-1β,3β,22β,26-tetraol 1-O-α-L-rhamnopyranosyl-(1→2)-O-β-d-xylopyranosyl 26-O-α-L-rhamnopyranoside (vaviloside B2). The isolated saponins showed cytotoxic activity on J-774, murine monocyte/macrophage, and WEHI-164, murine fibrosarcoma, cell lines with the following rank: vaviloside B1/B2>ascalonicoside A1/A2>vaviloside A1/A2. PMID:23415085

  7. Melting in Martian Snowbanks

    NASA Technical Reports Server (NTRS)

    Zent, A. P.; Sutter, B.

    2005-01-01

    Precipitation as snow is an emerging paradigm for understanding water flow on Mars, which gracefully resolves many outstanding uncertainties in climatic and geomorphic interpretation. Snowfall does not require a powerful global greenhouse to effect global precipitation. It has long been assumed that global average temperatures greater than 273K are required to sustain liquid water at the surface via rainfall and runoff. Unfortunately, the best greenhouse models to date predict global mean surface temperatures early in Mars' history that differ little from today's, unless exceptional conditions are invoked. Snowfall however, can occur at temperatures less than 273K; all that is required is saturation of the atmosphere. At global temperatures lower than 273K, H2O would have been injected into the atmosphere by impacts and volcanic eruptions during the Noachian, and by obliquity-driven climate oscillations more recently. Snow cover can accumulate for a considerable period, and be available for melting during local spring and summer, unless sublimation rates are sufficient to remove the entire snowpack. We decided to explore the physics that controls the melting of snow in the high-latitude regions of Mars to understand the frequency and drainage of snowmelt in the high martian latitudes.

  8. Thermal Conductivity of Ethylene Vinyl Acetate Copolymer/Nanofiller Blends

    NASA Technical Reports Server (NTRS)

    Ghose, S.; Watson, K. A.; Working, D. C.; Connell, J. W.; Smith, J. G., Jr.; Lin, Y.; Sun, Y. P.

    2007-01-01

    To reduce weight and increase the mobility, comfort, and performance of future spacesuits, flexible, thermally conductive fabrics and plastic tubes are needed for the Liquid Cooling and Ventilation Garment. Such improvements would allow astronauts to operate more efficiently and safely for extended extravehicular activities. As an approach to raise the thermal conductivity (TC) of an ethylene vinyl acetate copolymer (Elvax 260), it was compounded with three types of carbon based nanofillers: multi-walled carbon nanotubes (MWCNTs), vapor grown carbon nanofibers (CNFs), and expanded graphite (EG). In addition, other nanofillers including metallized CNFs, nickel nanostrands, boron nitride, and powdered aluminum were also compounded with Elvax 260 in the melt at various loading levels. In an attempt to improve compatibility between Elvax 260 and the nanofillers, MWCNTs and EG were modified by surface coating and through noncovalent and covalent attachment of organic molecules containing alkyl groups. Ribbons of the nanocomposites were extruded to form samples in which the nanofillers were aligned in the direction of flow. Samples were also fabricated by compression molding to yield nanocomposites in which the nanofillers were randomly oriented. Mechanical properties of the aligned samples were determined by tensile testing while the degree of dispersion and alignment of nanoparticles were investigated using high-resolution scanning electron microscopy. TC measurements were performed using a laser flash (Nanoflash ) technique. TC of the samples was measured in the direction of, and perpendicular to, the alignment direction. Additionally, tubing was also extruded from select nanocomposite compositions and the TC and mechanical flexibility measured.

  9. Melting processes under microgravity conditions

    NASA Astrophysics Data System (ADS)

    Glicksman, M. E.; Lupulescu, A.; Koss, M. B.

    2003-07-01

    The kinetics of melting pivalic acid (PVA) dendrites was observed under convection-free conditions on STS-87 as part of the United States Microgravity Payload Mission (USMP-4) flown on Columbia in 1997. Analysis of video data show that PVA dendrites melt without relative motion with respect to the quiescent melt phase. Dendritic fragments display shrinking to extinction, with fragmentation occurring at higher initial supercoblings. Individual fragments follow a characteristic time-dependence derived elsewhere. The microgravity melting kinetics against which the experimental observations are compared is based on conduction-limited quasi-static melting under shape-preserving conditions. Agreement between analytic theory and our experiments is found when the melting process occurs under shape-preserving conditions as measured using the C/A ratio of individual needle-like crystal fragments.

  10. Melting of ice under pressure

    PubMed Central

    Schwegler, Eric; Sharma, Manu; Gygi, François; Galli, Giulia

    2008-01-01

    The melting of ice under pressure is investigated with a series of first-principles molecular dynamics simulations. In particular, a two-phase approach is used to determine the melting temperature of the ice-VII phase in the range of 10–50 GPa. Our computed melting temperatures are consistent with existing diamond anvil cell experiments. We find that for pressures between 10 and 40 GPa, ice melts as a molecular solid. For pressures above ≈45 Gpa, there is a sharp increase in the slope of the melting curve because of the presence of molecular dissociation and proton diffusion in the solid before melting. The onset of significant proton diffusion in ice-VII as a function of increasing temperature is found to be gradual and bears many similarities to that of a type-II superionic solid. PMID:18809909

  11. Melting of Ice under Pressure

    SciTech Connect

    Schwegler, E; Sharma, M; Gygi, F; Galli, G

    2008-07-31

    The melting of ice under pressure is investigated with a series of first principles molecular dynamics simulations. In particular, a two-phase approach is used to determine the melting temperature of the ice-VII phase in the range of 10 to 50 GPa. Our computed melting temperatures are consistent with existing diamond anvil cell experiments. We find that for pressures between 10 to 40 GPa, ice melts as a molecular solid. For pressures above {approx}45 GPa there is a sharp increase in the slope of the melting curve due to the presence of molecular dissociation and proton diffusion in the solid, prior to melting. The onset of significant proton diffusion in ice-VII as a function of increasing temperature is found to be gradual and bears many similarities to that of a type-II superionic solid.

  12. Copolymer sealant compositions and method for making

    NASA Technical Reports Server (NTRS)

    Singh, Navjot (Inventor); Leman, John Thomas (Inventor); Whitney, John M. (Inventor); Krabbenhoft, Herman Otto (Inventor)

    2002-01-01

    Condensation curable poly(fluoroorgano)siloxane-poly(silarylene)siloxane block copolymer compositions having a glass transition temperature not exceeding about -54.degree. C. and excellent solvent resistance have been found useful as sealants. Polyalkoxysilylorgano compounds, such as 1,4-bis[trimethoxysilyl(ethyl)]benzene have been found to be effective as cross-linkers.

  13. Copolymer sealant compositions and method for making

    NASA Technical Reports Server (NTRS)

    Singh, Navjot (Inventor); Leman, John Thomas (Inventor); Whitney, John M. (Inventor); Krabbenhoft, Herman Otto (Inventor)

    2004-01-01

    Condensation curable poly(fluoroorgano)siloxane-poly(silarylene)siloxane block copolymer compositions having a glass transition temperature not exceeding about -54.degree. C. and excellent solvent resistance have been found useful as sealants. Polyalkoxysilylorgano compounds, such as 1,4-bis[trimethoxysilyl(ethyl)]benzene have been found to be effective as cross-linkers.

  14. Copolymer sealant compositions and method for making

    NASA Technical Reports Server (NTRS)

    Singh, Navjot (Inventor); Leman, John Thomas (Inventor); Whitney, John M. (Inventor); Krabbenhoft, Herman Otto (Inventor)

    2003-01-01

    Condensation curable poly(fluoroorgano)siloxane-poly(silarylene)siloxane block copolymer compositions having a glass transition temperature not exceeding about -54.degree. C. and excellent solvent resistance have been found useful as sealants. Polyalkoxysilylorgano compounds, such as 1,4-bis[trimethoxysilyl(ethyl)]benzene have been found to be effective as cross-linkers.

  15. 21 CFR 173.65 - Divinylbenzene copolymer.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 3 2013-04-01 2013-04-01 false Divinylbenzene copolymer. 173.65 Section 173.65 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) SECONDARY DIRECT FOOD ADDITIVES PERMITTED IN FOOD FOR HUMAN CONSUMPTION Polymer Substances and Polymer Adjuvants...

  16. 21 CFR 173.65 - Divinylbenzene copolymer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Divinylbenzene copolymer. 173.65 Section 173.65 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) SECONDARY DIRECT FOOD ADDITIVES PERMITTED IN FOOD FOR HUMAN CONSUMPTION Polymer Substances and Polymer Adjuvants...

  17. 21 CFR 173.65 - Divinylbenzene copolymer.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 3 2011-04-01 2011-04-01 false Divinylbenzene copolymer. 173.65 Section 173.65 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) SECONDARY DIRECT FOOD ADDITIVES PERMITTED IN FOOD FOR HUMAN CONSUMPTION Polymer Substances and Polymer Adjuvants...

  18. Fungal biodegradation of lignopolystyrene graft copolymers.

    PubMed Central

    Milstein, O; Gersonde, R; Huttermann, A; Chen, M J; Meister, J J

    1992-01-01

    White rot basidiomycetes were able to biodegrade styrene (1-phenylethene) graft copolymers of lignin containing different proportions of lignin and polystyrene [poly(1-phenylethylene)]. The biodegradation tests were run on lignin-styrene copolymerization products which contained 10.3, 32.2, and 50.4% (wt/wt) lignin. The polymer samples were incubated with the white rot fungi Pleurotus ostreatus, Phanerochaete chrysosporium, and Trametes versicolor and the brown rot fungus Gloeophyllum trabeum. White rot fungi degraded the plastic samples at a rate which increased with increasing lignin content in the copolymer sample. Both polystyrene and lignin components of the copolymer were readily degraded. Polystyrene pellets were not degradable in these tests. Degradation was verified for both incubated and control samples by weight loss, quantitative UV spectrophotometric analysis of both lignin and styrene residues, scanning electron microscopy of the plastic surface, and the presence of enzymes active in degradation during incubation. Brown rot fungus did not affect any of the plastics. White rot fungi produced and secreted oxidative enzymes associated with lignin degradation in liquid media during incubation with lignin-polystyrene copolymer. Images PMID:1444360

  19. 21 CFR 177.2470 - Polyoxymethylene copolymer.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ....2470 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) INDIRECT FOOD ADDITIVES: POLYMERS Substances for Use Only as... copolymer identified in this section may be safely used as an article or component of articles intended...

  20. 21 CFR 177.2470 - Polyoxymethylene copolymer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ....2470 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION (CONTINUED) INDIRECT FOOD ADDITIVES: POLYMERS Substances for Use Only as... copolymer identified in this section may be safely used as an article or component of articles intended...

  1. Block copolymers for enhanced oil recovery

    SciTech Connect

    Wu, M.M.; Ball, L.E.

    1987-05-19

    A water soluble block copolymer is described comprising two or more water soluble polymer blocks, wherein the water soluble polymer blocks comprise polymerized monomers. The monomers are selected from the group consisting of acrylamide, methacrylamide, vinyl methyl ether, acrylic and methacrylic acid and their water soluble salts and N-substituted acrylamides.

  2. Molecular transfer printing using block copolymers.

    PubMed

    Ji, Shengxiang; Liu, Chi-Chun; Liu, Guoliang; Nealey, Paul F

    2010-02-23

    Soft lithographic techniques augment or enhance the capabilities of traditional patterning processes and expand the diversity of materials that can be patterned. Realization of robust parallel techniques for creating chemical patterns at the nanoscale has been challenging. Here we present a method for creating and replicating chemical patterns that uses functionalized homopolymer inks that are preferentially segregated into the nanodomains of phase-separated diblock copolymer films. The inks are transferred by reaction to substrates that are brought into contact with block copolymer films, creating chemical patterns on the substrate that mirror the domain structure present at the film surface with high fidelity and resolution. In addition to printing from self-assembled domain structures, we can also direct the assembly of the block copolymer films from which transfer occurs using lithographically defined masters so as to replicate and transfer patterns of inks with controlled and well-defined geometries. The transferred patterns may be at higher resolution than the lithographically defined master, and the process can be repeated to create multiple copies of identical replicas. Transfer of one ink from one block of the copolymer is also possible, and filling the interspatial regions of the pattern with a second ink provides a pathway toward creating patterns with diverse chemical functionalities. PMID:20041629

  3. Amphiphilic block copolymer nanocontainers as bioreactors

    NASA Astrophysics Data System (ADS)

    Nardin, C.; Widmer, J.; Winterhalter, M.; Meier, W.

    2001-04-01

    Self-assembly of an amphiphilic triblock copolymer carrying polymerizable end-groups is used to prepare nanometer-sized vesicular structures in aqueous solution. The triblock copolymer shells of the vesicles can be regarded as a mimetic of biological membranes although they are 2 to 3 times thicker than a conventional lipid bilayer. Nevertheless, they can serve as a matrix for membrane-spanning proteins. Surprisingly, the proteins remain functional despite the extreme thickness of the membranes and that even after polymerization of the reactive triblock copolymers. This opens a new field to create mechanically stable protein/polymer hybrid membranes. As a representative example we functionalize (polymerized) triblock copolymer vesicles by reconstituting a channel-forming protein from the outer cell wall of Gram-negative bacteria. The protein used (OmpF) acts as a size-selective filter, which allows only for passage of molecules with a molecular weight below 400 g mol^{-1}. Therefore substrates may still have access to enzymes encapsulated in such protein/polymer hybrid nanocontainers. We demonstrate this using the enzyme β -lactamase which is able to hydrolyze the antibiotic ampicillin. In addition, a transmembrane voltage above a given threshold causes a reversible gating transition of OmpF. This can be used to reversibly activate or deactivate the resulting nanoreactors.

  4. Synthesis of Diblock copolymer poly-3-hydroxybutyrate -block-poly-3-hydroxyhexanoate [PHB-b-PHHx] by a β-oxidation weakened Pseudomonas putida KT2442

    PubMed Central

    2012-01-01

    Background Block polyhydroxyalkanoates (PHA) were reported to be resistant against polymer aging that negatively affects polymer properties. Recently, more and more attempts have been directed to make PHA block copolymers. Diblock copolymers PHB-b-PHHx consisting of poly-3-hydroxybutyrate (PHB) block covalently bonded with poly-3-hydroxyhexanoate (PHHx) block were for the first time produced successfully by a recombinant Pseudomonas putida KT2442 with its β-oxidation cycle deleted to its maximum. Results The chloroform extracted polymers were characterized by nuclear magnetic resonance (NMR), thermo- and mechanical analysis. NMR confirmed the existence of diblock copolymers consisting of 58 mol% PHB as the short chain length block with 42 mol% PHHx as the medium chain length block. The block copolymers had two glass transition temperatures (Tg) at 2.7°C and −16.4°C, one melting temperature (Tm) at 172.1°C and one cool crystallization temperature (Tc) at 69.1°C as revealed by differential scanning calorimetry (DSC), respectively. This is the first microbial short-chain-length (scl) and medium-chain-length (mcl) PHA block copolymer reported. Conclusions It is possible to produce PHA block copolymers of various kinds using the recombinant Pseudomonas putida KT2442 with its β-oxidation cycle deleted to its maximum. In comparison to a random copolymer poly-3-hydroxybutyrate-co-3-hydroxyhexanoate (P(HB-co-HHx)) and a blend sample of PHB and PHHx, the PHB-b-PHHx showed improved structural related mechanical properties. PMID:22480145

  5. Block copolymer/ferroelectric nanoparticle nanocomposites

    NASA Astrophysics Data System (ADS)

    Pang, Xinchang; He, Yanjie; Jiang, Beibei; Iocozzia, James; Zhao, Lei; Guo, Hanzheng; Liu, Jin; Akinc, Mufit; Bowler, Nicola; Tan, Xiaoli; Lin, Zhiqun

    2013-08-01

    Nanocomposites composed of diblock copolymer/ferroelectric nanoparticles were formed by selectively constraining ferroelectric nanoparticles (NPs) within diblock copolymer nanodomains via judicious surface modification of ferroelectric NPs. Ferroelectric barium titanate (BaTiO3) NPs with different sizes that are permanently capped with polystyrene chains (i.e., PS-functionalized BaTiO3NPs) were first synthesized by exploiting amphiphilic unimolecular star-like poly(acrylic acid)-block-polystyrene (PAA-b-PS) diblock copolymers as nanoreactors. Subsequently, PS-functionalized BaTiO3 NPs were preferentially sequestered within PS nanocylinders in the linear cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer upon mixing the BaTiO3 NPs with PS-b-PMMA. The use of PS-b-PMMA diblock copolymers, rather than traditional homopolymers, offers the opportunity for controlling the spatial organization of PS-functionalized BaTiO3 NPs in the PS-b-PMMA/BaTiO3 NP nanocomposites. Selective solvent vapor annealing was utilized to control the nanodomain orientation in the nanocomposites. Vertically oriented PS nanocylinders containing PS-functionalized BaTiO3 NPs were yielded after exposing the PS-b-PMMA/BaTiO3 NP nanocomposite thin film to acetone vapor, which is a selective solvent for PMMA block. The dielectric properties of nanocomposites in the microwave frequency range were investigated. The molecular weight of PS-b-PMMA and the size of BaTiO3 NPs were found to exert an apparent influence on the dielectric properties of the resulting nanocomposites.Nanocomposites composed of diblock copolymer/ferroelectric nanoparticles were formed by selectively constraining ferroelectric nanoparticles (NPs) within diblock copolymer nanodomains via judicious surface modification of ferroelectric NPs. Ferroelectric barium titanate (BaTiO3) NPs with different sizes that are permanently capped with polystyrene chains (i.e., PS-functionalized BaTiO3NPs) were

  6. Melting line of polymeric nitrogen

    NASA Astrophysics Data System (ADS)

    Yakub, L. N.

    2013-05-01

    We made an attempt to predict location of the melting line of polymeric nitrogen using two equations for Helmholtz free energy: proposed earlier for cubic gauche-structure and developed recently for liquid polymerized nitrogen. The P-T relation, orthobaric densities and latent heat of melting were determined using a standard double tangent construction. The estimated melting temperature decreases with increasing pressure, alike the temperature of molecular-nonmolecular transition in solid. We discuss the possibility of a triple point (solid-molecular fluid-polymeric fluid) at ˜80 GPa and observed maximum of melting temperature of nitrogen.

  7. Melting processes under microgravity conditions

    NASA Astrophysics Data System (ADS)

    Glicksman, M.; Lupulescu, A.; Koss, M.

    The Rensselaer Isothermal Dendritic Growth Experiment (RIDGE) uses the large data archive amassed through a series of three NASA-supported microgravity experiments (IDGE/USMP-2, -3, and -4), all of which flew aboard the space shuttle Columbia. The IDGE instruments aboard USMP-2 and -3 provided in-flight CCD images, and 35-mm films (postflight). USMP-4 also allowed streaming of near-real-time video. Using 30 fps video data, it became possible for the first time to study both freezing and melting sequences for high-purity pivalic acid (PVA). We report on the melting process observed for PVA crystal fragments, observed under nearly ideal convection-free conditions. Conduction-limited melting processes are of importance in orbital melting of materials, meteoritic genesis, mushy-zone evolution, and in fusion weld pools where length scales for thermal buoyancy are restricted. Microgravity video show clearly that PVA dendrites melt into fragments that shrink at accelerating rates to extinction. The melting paths of individual fragments follow characteristic time dependences derived from theory. The theoretical melting kinetics against which the experimental observations are carefully compared is based on conduction-limited quasi-static melting under shape-preserving conditions. Good agreement between theory and experiment is found for the stable melting of needle-shaped prolate spheroidal PVA crystal fragments with aspect ratios near C /A = 12.

  8. Viscosity of Hydrous Rhyolitic Melts

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Xu, Z.; Liu, Y.

    2002-12-01

    It is critical to understand and to be able to predict viscosity of hydrous silicate melts for understanding magma transport, bubble growth, volcanic eruptions, and magma fragmentation. We report new viscosity data for hydrous rhyolitic melt in the viscosity range of 109 to 1015 Pa s based on the kinetics of hydrous species reaction in the melt upon cooling (i.e., based on the equivalence between the glass transition temperature and the apparent equilibrium temperature). We also report viscosity data obtained from bubble growth experiments. Our data show that the viscosity model of Hess and Dingwell (1996) systematically overestimates the viscosity of hydrous rhyolitic melt at the high viscosity range by a factor of 2 to 4 (still within their stated 2σ uncertainty). Another problem with the model of Hess and Dingwell is that the functional dependence of viscosity on total H2O content cannot be extended to dry melt: as total H2O content decreases to zero, the viscosity would first increase, and then decrease to zero. A zero viscosity for a dry melt makes no sense. Hence we need a mixing law for hydrous melt viscosity that is extendible to dry melts. By examining the viscosity of rhyolitic melts containing 6 ppm to about 8.0 wt% total H2O (both our own data and literature data), we propose the following relation for the dependence of viscosity on total H2O content: 1/η = 1/η 1+(1/η 2-1/η 1)xn ≈ 1/η 1+xn/η 2 where η is viscosity and 1/η is fluidity, η 1 is the viscosity of the dry melt, x is the mole fraction of total dissolved H2O, n and η 2 are two fitting parameters, and η 2 can be identified to be the viscosity of the hypothetical melt consisting of pure H2O (η 2 cannot be directly measured since such a melt does not exist). The above equation appears to work well for the viscosity of hydrous rhyolitic melts. By fitting hydrous rhyolitic melt viscosity with the above equation, we find that rhyolitic melt viscosity vary by 1.2 orders of magnitude

  9. Melt pool dynamics during selective electron beam melting

    NASA Astrophysics Data System (ADS)

    Scharowsky, T.; Osmanlic, F.; Singer, R. F.; Körner, C.

    2014-03-01

    Electron beam melting is a promising additive manufacturing technique for metal parts. Nevertheless, the process is still poorly understood making further investigations indispensable to allow a prediction of the part's quality. To improve the understanding of the process especially the beam powder interaction, process observation at the relevant time scale is necessary. Due to the difficult accessibility of the building area, the high temperatures, radiation and the very high scanning speeds during the melting process the observation requires an augmented effort in the observation equipment. A high speed camera in combination with an illumination laser, band pass filter and mirror system is suitable for the observation of the electron beam melting process. The equipment allows to observe the melting process with a high spatial and temporal resolution. In this paper the adjustment of the equipment and results of the lifetime and the oscillation frequencies of the melt pool for a simple geometry are presented.

  10. Conduction-limited crystallite melting

    NASA Astrophysics Data System (ADS)

    Lupulescu, A.; Glicksman, M. E.; Koss, M. B.

    2005-04-01

    High-purity pivalic acid (PVA) dendrites were observed growing under convection-free conditions during the isothermal dendritic growth experiment (IDGE) flown on NASA's space shuttle Columbia on STS-87. The IDGE was part of the complement of primary scientific experiments designated as the United States Microgravity Payload Mission (USMP4) launched late in 1997. The IDGE video data show that PVA dendrites may be melted without exhibiting any detectable relative motion with respect to the surrounding quiescent melt phase. Thus, melting occurs by heat conduction alone. When a small fixed superheating is imposed on pre-existing dendritic fragments, they melt steadily toward extinction. Individual fragments steadily decrease in size according to a square-root of time dependence predicted using quasi-static conduction-limited theory. Agreement between analytic melting theory and microgravity experiments was found originally if the melting process occurs under the restriction of shape-preserving conditions, where needle-like crystal fragments may be approximated as ellipsoids with a constant axial ratio. Among the new results reported here is the influence of capillarity effects on melting in needle-like crystallites, observed as a dramatic change in their axial ratio, when the size scale of a crystallite decreases below a critical value. In microgravity melting experiments, the axial ratio of individual crystallites does not remain constant, because of interactions with neighboring fragments within the mushy zone. The kinetic data were then "sectorized" to divide the total melting process into a series of short intervals. Each melting sector for a crystallite could then be approximated by a constant average value of the axial ratio. Sectorization also allows accurate prediction of melting kinetics by applying quasi-static heat conduction theory, despite the suspected presence of capillarity and the occurrence of fragmentation. These additional processes that accompany

  11. Microphase separation in copolymers of hydrophilic PEG blocks and hydrophobic tyrosine-derived segments using simultaneous SAXS/WAXS/DSC.

    PubMed

    Murthy, N S; Wang, W; Kohn, J

    2010-08-01

    Hydration- and temperature-induced microphase separations were investigated by simultaneous small- and wide-angle X-ray scattering (SAXS and WAXS) and differential scanning calorimetry (DSC) in a family of copolymers in which hydrophilic poly(ethylene glycol) (PEG) blocks are inserted randomly into a hydrophobic polymer made of either desaminotyrosyl-tyrosine ethyl ester (DTE) or iodinated I(2)DTE segments. Iodination of the tyrosine rings in I(2)DTE increased the X-ray contrast between the hydrophobic and hydrophilic segments in addition to facilitating the study of the effect of iodination on microphase separation. The formation of phase-separated, hydrated PEG domains is of considerable significance as it profoundly affects the polymer properties. The copolymers of DTE (or I(2)DTE) and PEG are a useful model system and the findings presented here may be applicable to other PEG-containing random copolymers as well. In copolymers of PEG and DTE and I(2)DTE, the presence of PEG depressed the glass transition temperature (T(g)) of the copolymer relative to the homopolymer, poly(DTE carbonate), and the DTE/ I(2)DTE segments hindered the crystallization of the PEG segments. In the dry state, at large PEG fractions (> 70 vol%), the PEG domains self-assembled into an ordered structure with 14-18 nm distance between the domains. These domains gave rise to a SAXS peak at all temperatures in the iodinated polymers, but only above the T(g) in non-iodinated polymers, due to the unexpected contrast- match between the crystalline PEG domains and the glassy DTE segments. Irrespective of whether PEG was crystalline or not, immersion of these copolymers in water resulted in the formation of hydrated PEG domains that were 10-20 nm apart. Since both water and the polymer chains must be mobile for the phase separation to occur, the PEG domains disappeared when the water froze, and reappeared as the ice began to melt. This transformation was reversible, and showed hysteresis as did

  12. Microphase separation in copolymers of hydrophilic PEG blocks and hydrophobic tyrosine-derived segments using simultaneous SAXS/WAXS/DSC

    SciTech Connect

    Murthy, N.S.; Wang, W.; Kohn, J.

    2010-10-22

    Hydration- and temperature-induced microphase separations were investigated by simultaneous small- and wide-angle X-ray scattering (SAXS and WAXS) and differential scanning calorimetry (DSC) in a family of copolymers in which hydrophilic poly(ethylene glycol) (PEG) blocks are inserted randomly into a hydrophobic polymer made of either desaminotyrosyl-tyrosine ethyl ester (DTE) or iodinated I{sub 2}DTE segments. Iodination of the tyrosine rings in I{sub 2}DTE increased the X-ray contrast between the hydrophobic and hydrophilic segments in addition to facilitating the study of the effect of iodination on microphase separation. The formation of phase-separated, hydrated PEG domains is of considerable significance as it profoundly affects the polymer properties. The copolymers of DTE (or I{sub 2}DTE) and PEG are a useful model system, and the findings presented here may be applicable to other PEG-containing random copolymers. In copolymers of PEG and DTE and I{sub 2}DTE, the presence of PEG depressed the glass transition temperature (T{sub g}) of the copolymer relative to the homopolymer, poly(DTE carbonate), and the DTE/I{sub 2}DTE segments hindered the crystallization of the PEG segments. In the dry state, at large PEG fractions (>70 vol%), the PEG domains self-assembled into an ordered structure with 14-18 nm distance between the domains. These domains gave rise to a SAXS peak at all temperatures in the iodinated polymers, but only above the T{sub g} in non-iodinated polymers, due to the unexpected contrast-match between the crystalline PEG domains and the glassy DTE segments. Irrespective of whether PEG was crystalline or not, immersion of these copolymers in water resulted in the formation of hydrated PEG domains that were 10-20 nm apart. Since both water and the polymer chains must be mobile for the phase separation to occur, the PEG domains disappeared when the water froze, and reappeared as the ice began to melt. This transformation was reversible, and showed

  13. A2B adenosine receptor contributes to penile erection via PI3K/AKT signaling cascade-mediated eNOS activation

    PubMed Central

    Wen, Jiaming; Grenz, Almut; Zhang, Yujin; Dai, Yingbo; Kellems, Rodney E.; Blackburn, Michael R.; Eltzschig, Holger K.; Xia, Yang

    2011-01-01

    Normal penile erection is under the control of multiple factors and signaling pathways. Although adenosine signaling is implicated in normal and abnormal penile erection, the exact role and the underlying mechanism for adenosine signaling in penile physiology remain elusive. Here we report that shear stress leads to increased adenosine release from endothelial cells. Subsequently, we determined that ecto-5′-nucleotidase (CD73) is a key enzyme required for the production of elevated adenosine from ATP released by shear-stressed endothelial cells. Mechanistically, we demonstrate that shear stress-mediated elevated adenosine functions through the adenosine A2B receptor (A2BR) to activate the PI3K/AKT signaling cascade and subsequent increased endothelial nitric oxide synthase (eNOS) phosphorylation. These in vitro studies led us to discover further that adenosine was induced during sustained penile erection and contributes to PI3K/AKT activation and subsequent eNOS phosphorylation via A2BR signaling in intact animal. Finally, we demonstrate that lowering adenosine in wild-type mice or genetic deletion of A2BR in mutant mice significantly attenuated PI3K/AKT activation, eNOS phosphorylation, and subsequent impaired penile erection featured with the reduction of ratio of maximal intracavernosal pressure to systemic arterial pressure from 0.49 ± 0.03 to 0.41 ± 0.05 and 0.38 ± 0.04, respectively (both P<0.05). Overall, using biochemical, cellular, genetic, and physiological approaches, our findings reveal that adenosine is a novel molecule signaling via A2BR activation, contributing to penile erection via PI3K/AKT-dependent eNOS activation. These studies suggest that this signaling pathway may be a novel therapeutic target for erectile disorders.—Wen, J., Grenz, A., Zhang, Y., Dai, Y., Kellems, R. E., Blackburn, M. R., Eltzschig, H. K., Xia, Y. A2B adenosine receptor contributes to penile erection via PI3K/AKT signaling cascade-mediated eNOS activation. PMID

  14. Beyond the Melting Pot Reconsidered.

    ERIC Educational Resources Information Center

    Anderson, Elijah

    2000-01-01

    Discusses the 1963 book, "Beyond the Melting Pot," which suggested that eventually the problem of different ethnicities in the U.S. would be resolved and society would become one melting pot. Examines how changes in immigration and economic structures have affected the issue, noting the devastating effect of the dominant culture's denigration of…

  15. Solid-state structure and dynamics of lactide copolymers and blends

    NASA Astrophysics Data System (ADS)

    Kanchanasopa, Mantana

    This dissertation focuses on polymers synthesized from L-lactide and its stereoisomers, i.e., poly L-lactide (L-PLA), L-lactide/meso-lactide random copolymers and L-PLA/D-PLA blends. Height and phase images from tapping mode AFM experiments, acquired at various tapping forces, reveal that the morphology and lamellar thickness of the L-lactide/meso-lactide copolymers are strongly influenced by meso-lactide content and crystallization conditions. Good agreement was observed between mean lamellar thicknesses derived from AFM and previous small-angle X-ray scattering experiments. The considerable decrease in lamellar thickness with increasing comonomer content suggests that meso-lactide units are substantially excluded from the L-lactide crystal lattice, at least under the isothermal crystallization conditions used here. A dielectric study of amorphous and crystalline samples of the L-lactide/meso-lactide copolymers demonstrates that the relaxation strength and mean relaxation time (and its distribution) of the segmental process are modified by the presence of the crystalline phase. The mean segmental relaxation time is longer and its distribution is broader in the samples with higher degrees of crystallinity. The significant difference in the fraction of mobile segments (determined from the relaxation strength) and the amorphous fraction derived from DSC) indicates the existence of the so-called "rigid amorphous phase". This conclusion is also supported by the observation of a difference in temperature dependent behavior of the relaxation strength of amorphous and crystalline samples. Differences in the details of the relaxation processes, as well as the fraction of rigid amorphous phase of these copolymers, suggest that the chain dynamics of amorphous segments are influence by both degree of crystallinity and lamellar organization. For D-PLA/L-PLAs blends, stereocomplex crystallites are observed along with homopolymer crystals. The content of each crystal type is

  16. Solvent enhanced block copolymer ordering in thin films

    NASA Astrophysics Data System (ADS)

    Misner, Matthew J.

    Diblock copolymer self-assembly of materials is emerging as a key element in the fabrication of functional nanostructured materials. By solvent casting or solvent annealing block copolymer thin films, we have demonstrated methods to produce diblock copolymer films with highly oriented, close-packed arrays of nanoscopic cylindrical domains with a high degree of long-range lateral order with few defects. The solvent imparts a high degree of mobility in the microphase-separated copolymer that enables a rapid removal of defects and a high degree of lateral order. Though the use of a selective cosolvent during solvent casting, it was found that the microdomain size and spacing could be increased, leading to a size-tunable system. Additionally, the presence of water also led to the ability to control the microdomain orientation during solvent annealing. Ionic complexation within cylinder-forming PS- b-EO block copolymer thin films was also investigated, where added salts bind PEO block as the minor component. Small amounts of added salts, on the order a few ions per chain, show large effects on the ordering of the copolymer films during solvent annealing. By using gold or cobalt salts, well-organized patterns of nanoparticles can be generated in the copolymer microdomains. Topographically and chemically patterned surfaces were used as a route to sectorizing and controlling the lattice orientation of copolymer films. Topographically patterned surfaces allow well-defined boundaries to confine the copolymer microdomains on a surface and effectively direct the ordering and grain orientation of the copolymer microdomains. Chemically patterned surfaces provide a route to direct the block copolymer ordering on completely flat surface, which may have advantages in applications where adding additional topography may be undesirable. To generate nanoporous templates from PS-b-PEO bases materials several routs were followed. The first route was through the addition and selective

  17. Structure property relations in glassy-semicrystalline block copolymers

    NASA Astrophysics Data System (ADS)

    Khanna, Vikram

    The ability of block copolymers to segregate into nanoscale morphologies makes them a versatile class of engineering materials. This work investigates the relation between the block copolymer structure and its mechanical properties, film dynamics and diffusion kinetics. The first part investigates the influence of structure on the mechanical properties of poly(cyclohexylethylene)-poly(ethylene) (PCHE-PE) block copolymer films. For lamellar block copolymers the mechanical properties depend significantly on the chain architecture (diblock, triblock and pentablock). Diblock copolymer films show complete failure at small strains and pentablock copolymer films show the toughest, response. Moreover, the orientation of the cylinders in a cylinder forming pentablock copolymer affects the toughness of the block copolymer films. In the second part, the effect of surface energy and chain architecture on the orientation of microdomains in the same block copolymer films is investigated. Cylindrical and lamellar triblock copolymers with a PE midblock orient their microdomains normal to the surface. However, a lamellar diblock copolymer prefers a parallel orientation of the sheets with an E surface. Moreover, a cylindrical triblock copolymer with a reduced surface energy poly(ethylene-butylene) midblock orders with the cylinder domains oriented parallel to the surface. Self-consistent field theory calculations suggest that the entropic cost of forming a wetting layer comprised entirely of looping blocks for the triblock architecture, a constraint absent in diblock copolymers, stabilizes the perpendicular orientation. Thus in triblock copolymers, parallel orientations are only stabilized when the surface energy of the midblock is small enough to compensate for this conformational penalty. Finally, a study of the diffusion kinetics of cylinder forming poly(styrene)-poly(ethylene) triblock (SES) and pentablock (SESES) copolymers suggests that for similar molecular weights SESES

  18. Phase behavior of model ABC triblock copolymers

    NASA Astrophysics Data System (ADS)

    Chatterjee, Joon

    The phase behavior of poly(isoprene-b-styrene- b-ethylene oxide) (ISO), a model ABC triblock copolymer has been studied. This class of materials exhibit self-assembly, forming a large array of ordered morphologies at length scales of 5-100 nm. The formation of stable three-dimensionally continuous network morphologies is of special interest in this study. Since these nanostructures considerably impact the material properties, fundamental knowledge for designing ABC systems have high technological importance for realizing applications in the areas of nanofabrication, nanoporous media, separation membranes, drug delivery and high surface area catalysts. A comprehensive framework was developed to describe the phase behavior of the ISO triblock copolymers at weak to intermediate segregation strengths spanning a wide range of composition. Phases were characterized through a combination of characterization techniques, including small angle x-ray scattering, dynamic mechanical spectroscopy, transmission electron microscopy, and birefringence measurements. Combined with previous investigations on ISO, six different stable ordered state symmetries have been identified: lamellae (LAM), Fddd orthorhombic network (O70), double gyroid (Q230), alternating gyroid (Q214), hexagonal (HEX), and body-centered cubic (BCC). The phase map was found to be somewhat asymmetric around the fI = fO isopleth. This work provides a guide for theoretical studies and gives insight into the intricate effects of various parameters on the self-assembly of ABC triblock copolymers. Experimental SAXS data evaluated with a simple scattering intensity model show that local mixing varies continuously across the phase map between states of two- and three-domain segregation. Strategies of blending homopolymers with ISO triblock copolymer were employed for studying the swelling properties of a lamellar state. Results demonstrate that lamellar domains swell or shrink depending upon the type of homopolymer that

  19. Switching dynamics of ferroelectric Langmuir-Blodgett copolymer films

    NASA Astrophysics Data System (ADS)

    Othon, Christina M.

    Ferroelectric switching dynamics in ferroelectric copolymer films of poly(vinylidene fluoride-trifluoroethylene) can vary over nine orders of magnitude; 100 seconds for the slowest ultrathin (1-50 nm) Langmuir-Blodgett films to 100 ns for the fastest polymorphous spin-coat films (˜50 mum thick). These ultra-thin films share many of the same ferroelectric properties of bulk films such as polarization, phase transition temperatures, crystalline structure, and high electrical resistance (>10 MO). The slow nature of switching in ultrathin films is believed to be caused by the intrinsic nature of the switching. The polarization is no longer switching by nucleation and domain wall growth enabled by defects and nanostructures in the polymorphous samples. We investigate this hypothesis by the introduction of defects in the form of nucleation sites and/or grain boundaries by electron irradiation, production of individual ferroelectric nano-crystals, and the introduction of domain wall boundaries through Direct Laser Interference Patterning (DLIP). Electron-irradiation was performed for a large range of doses from 16 to 110 Mrad, on ultra thin films 36 nm thick. It was thought that the defects introduced by electron irradiation could act as nucleation sites, promoting faster switching. However, the primary effect of electron irradiation was the decrease in crystallinity and therefore the fraction of ferroelectric material. Even for lower doses the increase in switching speed was negligible in comparison to the loss of ferroelectricity. The introduction of false domain walls through laser annealing was used to produce more complex and controlled shapes than given by the nanomesas. We investigated patterning by continuous-wave direct write, and by pulsed laser irradiation DLIP. We have demonstrated the ability to pattern films reversibly into films of ferroelectric regions surrounded by paraelectric phase, as well as irreversibly ferroelectric regions surrounded by melted

  20. Fault rheology beyond frictional melting.

    PubMed

    Lavallée, Yan; Hirose, Takehiro; Kendrick, Jackie E; Hess, Kai-Uwe; Dingwell, Donald B

    2015-07-28

    During earthquakes, comminution and frictional heating both contribute to the dissipation of stored energy. With sufficient dissipative heating, melting processes can ensue, yielding the production of frictional melts or "pseudotachylytes." It is commonly assumed that the Newtonian viscosities of such melts control subsequent fault slip resistance. Rock melts, however, are viscoelastic bodies, and, at high strain rates, they exhibit evidence of a glass transition. Here, we present the results of high-velocity friction experiments on a well-characterized melt that demonstrate how slip in melt-bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition. Slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt, slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state. Where a rock is present next to the melt, we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes. We conclude that in the case of pseudotachylyte generation during an earthquake, slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition, which involves a response in the brittle/solid regime of these rock melts. We warn of the inadequacy of simple Newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte-bearing fault systems in the evaluation and prediction of their slip dynamics. PMID:26124123

  1. Fault rheology beyond frictional melting

    PubMed Central

    Lavallée, Yan; Hirose, Takehiro; Kendrick, Jackie E.; Hess, Kai-Uwe; Dingwell, Donald B.

    2015-01-01

    During earthquakes, comminution and frictional heating both contribute to the dissipation of stored energy. With sufficient dissipative heating, melting processes can ensue, yielding the production of frictional melts or “pseudotachylytes.” It is commonly assumed that the Newtonian viscosities of such melts control subsequent fault slip resistance. Rock melts, however, are viscoelastic bodies, and, at high strain rates, they exhibit evidence of a glass transition. Here, we present the results of high-velocity friction experiments on a well-characterized melt that demonstrate how slip in melt-bearing faults can be governed by brittle fragmentation phenomena encountered at the glass transition. Slip analysis using models that incorporate viscoelastic responses indicates that even in the presence of melt, slip persists in the solid state until sufficient heat is generated to reduce the viscosity and allow remobilization in the liquid state. Where a rock is present next to the melt, we note that wear of the crystalline wall rock by liquid fragmentation and agglutination also contributes to the brittle component of these experimentally generated pseudotachylytes. We conclude that in the case of pseudotachylyte generation during an earthquake, slip even beyond the onset of frictional melting is not controlled merely by viscosity but rather by an interplay of viscoelastic forces around the glass transition, which involves a response in the brittle/solid regime of these rock melts. We warn of the inadequacy of simple Newtonian viscous analyses and call for the application of more realistic rheological interpretation of pseudotachylyte-bearing fault systems in the evaluation and prediction of their slip dynamics. PMID:26124123

  2. Rich Phase Behavior of Sphere-Forming Asymmetric ABA'C Block Copolymer Melts

    NASA Astrophysics Data System (ADS)

    Chanpuriya, Sid; Arora, Akash; Kim, Kyungtae; Dorfman, Kevin; Bates, Frank

    Motivated by self-consistent field theory simulations, the effect of ABA' corona block length asymmetry on the phase behavior of ABA'C-type tetrablock terpolymers has been examined. The chosen model system, poly(styrene)- b-poly(isoprene)- b-poly(styrene)- b-poly(ethylene oxide) (SIS'O), has been characterized using a combination of small-angle X-ray scattering, transmission electron microscopy, and dynamic mechanical spectroscopy. Asymmetric SIS'O tetrablocks reveal a rich variety of sphere-forming phases over compositions and molecular weights where symmetric SISO polymers formed only hexagonally oriented cylinders. These include FCC, HCP, and complex symmetries such as the Frank-Kasper σ and A15 phases. NSF Award 1333669.

  3. 40 CFR 721.10523 - Perfluoroalkylethyl methacrylate copolymer with hydroxymethyl acrylamide, vinyl chloride and long...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... copolymer with hydroxymethyl acrylamide, vinyl chloride and long chain fatty alkyl acrylate (generic). 721... methacrylate copolymer with hydroxymethyl acrylamide, vinyl chloride and long chain fatty alkyl acrylate (PMN P... Substances § 721.10523 Perfluoroalkylethyl methacrylate copolymer with hydroxymethyl acrylamide,...

  4. 40 CFR 721.10523 - Perfluoroalkylethyl methacrylate copolymer with hydroxymethyl acrylamide, vinyl chloride and long...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... copolymer with hydroxymethyl acrylamide, vinyl chloride and long chain fatty alkyl acrylate (generic). 721... methacrylate copolymer with hydroxymethyl acrylamide, vinyl chloride and long chain fatty alkyl acrylate (PMN P... Substances § 721.10523 Perfluoroalkylethyl methacrylate copolymer with hydroxymethyl acrylamide,...

  5. 21 CFR 872.3500 - Polyvinylmethylether maleic anhydride (PVM-MA), acid copolymer, and carboxymethylcellulose sodium...

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    .... Polyvinylmethylether maleic anhydride (PVM-MA), acid copolymer, and carboxymethylcellulose sodium (NACMC) denture adhesive is a device composed of polyvinylmethylether maleic anhydride, acid copolymer, and... maleic anhydride (PVM-MA), acid copolymer, and carboxymethylcellulose sodium (NACMC) denture...

  6. 21 CFR 872.3500 - Polyvinylmethylether maleic anhydride (PVM-MA), acid copolymer, and carboxymethylcellulose sodium...

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    .... Polyvinylmethylether maleic anhydride (PVM-MA), acid copolymer, and carboxymethylcellulose sodium (NACMC) denture adhesive is a device composed of polyvinylmethylether maleic anhydride, acid copolymer, and... maleic anhydride (PVM-MA), acid copolymer, and carboxymethylcellulose sodium (NACMC) denture...

  7. 21 CFR 872.3500 - Polyvinylmethylether maleic anhydride (PVM-MA), acid copolymer, and carboxymethylcellulose sodium...

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    .... Polyvinylmethylether maleic anhydride (PVM-MA), acid copolymer, and carboxymethylcellulose sodium (NACMC) denture adhesive is a device composed of polyvinylmethylether maleic anhydride, acid copolymer, and... maleic anhydride (PVM-MA), acid copolymer, and carboxymethylcellulose sodium (NACMC) denture...

  8. Synthesis, spectroscopic, and cellular properties of α-pegylated cis-A2B2- and A3B-types ZnPcs

    PubMed Central

    Ongarora, Benson G.; Zhou, Zehua; Okoth, Elizabeth A.; Kolesnichenko, Igor; Smith, Kevin M.; Vicente, M. Graça H.

    2015-01-01

    A series of pegylated cis-A2B2- or A3B-type ZnPcs, substituted on the α-positions with tri(ethylene glycol) and hydroxyl groups, were synthesized from a new bis-phthalonitrile. A clamshell-type bis-phthalocyanine was also obtained as a byproduct. The hydroxyl group of one ZnPc was alkylated with 3-dimethylaminopropyl chloride to afford a pegylated ZnPc functionalized with an amine group. All mononuclear ZnPcs were soluble in polar organic solvents, showed intense Q absorptions in DMF, and had fluorescence quantum yields in the range 0.10–0.23. The clamshell-type bis-phthalocyanine adopts mainly open shell conformations in DMF, and closed clamshell conformations in chloroform. All ZnPcs were highly phototoxic to human carcinoma HEp2 cells, particularly the amino-ZnPc mainly protonated under physiological conditions, which showed the highest phototoxicity (IC50 = 0.5 μM at 1.5 J/cm2) and dark cytotoxicity (IC50 = 22 μM), in part due to its high cellular uptake. The ZnPcs localized in multiple organelles, including mitochondria, lysosomes, Golgi and ER. PMID:26064037

  9. Actinin-1 binds to the C-terminus of A2B adenosine receptor (A2BAR) and enhances A2BAR cell-surface expression.

    PubMed

    Sun, Ying; Hu, Wenbao; Yu, Xiaojie; Liu, Zhengzhao; Tarran, Robert; Ravid, Katya; Huang, Pingbo

    2016-07-15

    A2BAR (A2B adenosine receptor) has been implicated in several physiological conditions, such as allergic or inflammatory disorders, vasodilation, cell growth and epithelial electrolyte secretion. For mediating the protein-protein interactions of A2BAR, the receptor's C-terminus is recognized to be crucial. In the present study, we unexpectedly found that two point mutations in the A2BAR C-terminus (F297A and R298A) drastically impaired the expression of A2BAR protein by accelerating its degradation. Thus we tested the hypothesis that these two point mutations disrupt A2BAR's interaction with a protein essential for A2BAR stability. Our results show that both mutations disrupted the interaction of A2BAR with actinin-1, an actin-associated protein. Furthermore, actinin-1 binding stabilized the global and cell-surface expression of A2BAR. By contrast, actinin-4, another non-muscle actinin isoform, did not bind to A2BAR. Thus our findings reveal a previously unidentified regulatory mechanism of A2BAR abundance. PMID:27208173

  10. Structure and expression of the gene (HNRPA2B1) encoding the human hnRNP protein A2/B1

    SciTech Connect

    Kozu, Tomoko; Henrich, B.; Schaefer, K.P.

    1995-01-20

    Heterogeneous nuclear ribonucleoprotein (hnRNP) A2 is a major nuclear protein and one of the major components of the hnRNP core complex in mammalian cells. We first determined the complete sequence of the human gene for hnRNP protein A2 (HNRPA2B1). The human HNRPA2B1 gene exists in a single copy over 9 kb in length. The gene was split into 12 exons, including a 36-nucleotide mini-exon, which was specific to the hnRNP protein B1, providing genetic evidence that the B1 mRNA was generated from the primary HNRPA2B1 transcript by alternative splicing. The 5{prime} region of HNRPA2B1 was GC-rich and contained several DNA motifs for the binding of several transcription factors, which included 2 CCAAT boxes and no TATA sequences. The 5{prime} ends of the mRNA were mapped to multiple positions. These structural features are characteristic of promoter regions of housekeeping genes. Northern blot and RT-PCR analyses of the HNRPA2B1 transcripts revealed levels of B1 mRNA from 2 to 5% of total A2/B1 transcripts and showed that both A2 and B1 mRNAs were transcribed in all human cell lines and mouse tissues studied. The structural and evolutionary characteristics of the A2 and A1 proteins as they relate to each other are discussed. 38 refs., 5 figs.

  11. Nonlinear absorption properties of 5,10-A2B2 porphyrins--correlation of molecular structure with the nonlinear responses.

    PubMed

    Zawadzka, Monika; Wang, Jun; Blau, Werner J; Senge, Mathias O

    2013-06-01

    The nonlinear absorption properties of two series of novel free base and metalated meso 5,10-A2B2 substituted porphyrins, both bearing p-tolyl as an A substituent and TMS-ethynyl or bromine as a B substituent, were investigated with the open Z-scan technique at 532 nm in the ns time regime. Most of the compounds exhibited a transmission drop with increasing input fluence. This behavior is desirable for their applications in optical limiting. More complex responses: a drop in transmission followed by an increase in transmission or an increase in transmission followed by a transmission drop, with increasing input fluence, were detected for certain compounds. All of the recorded responses were successfully fitted with a four-level model with simultaneous two-photon absorption arising from the higher excited states (consecutive one- + one- + two-photon absorption). The TMS-ethynyl group was found to be a more efficient meso substituent in optical limiting than the bromine atom. Indium, lead and zinc complexes with TMS-ethynyl substituents were the strongest positive nonlinear absorbers amongst compounds studied which makes them the most interesting candidates for optical limiting application. PMID:23503655

  12. Promoter-associated small double-stranded RNA interacts with heterogeneous nuclear ribonucleoprotein A2/B1 to induce transcriptional activation.

    PubMed

    Hu, Jia; Chen, Zhong; Xia, Ding; Wu, Jia; Xu, Hua; Ye, Zhang-Qun

    2012-11-01

    Several recent reports have demonstrated that small activating dsRNA [double-stranded RNA; saRNA (small activating dsRNA)] complementary to promoter regions can up-regulate gene expression in mammalian cells, a phenomenon termed RNAa (RNA activation). However, the mechanism of RNAa remains obscure with regard to what is the target molecule for promoter-targeted saRNA and what are the proteins involved in this process. p21Waf1/Cip1 (p21) [CDKN1A (cyclin-dependent kinase inhibitor 1A)], an important tumour suppressor gene, is among the genes that can be activated by RNAa in tumour cells. In the present study, we provide direct evidence that p21 promoter-targeted saRNA interact with its intended target on the p21 promoter to activate p21 expression. This process is associated with recruitment of RNA polymerase II and AGO2 (argonaute 2) protein to the saRNA-target site. Additionally, we found that several hnRNPs (heterogeneous nuclear ribonucleoproteins) (A1, A2/B1 and C1/C2) are associated with saRNA. Further studies show that hnRNPA2/B1 interacts with the saRNA in vivo and in vitro and is required for RNAa activity. These findings indicate that RNAa results from specific targeting of promoters and reveals additional mechanistic details of RNAa. PMID:23035981

  13. Bulk and mechanical properties of the Paintbrush tuff recovered from boreholes UE25 NRG-2, 2A, 2B, and 3: Data report

    SciTech Connect

    Boyd, P.J.; Martin, R.J.; Noel, J.S.; Price, R.H.

    1996-09-01

    An integral part of the licensing procedure for the potential nuclear waste repository at Yucca Mountain, Nevada, involves characterization of the in situ rheology for the design and construction of the facility and the emplacement of canisters containing radioactive waste. The data used to model the thermal and mechanical behavior of the repository and surrounding lithologies include dry and saturated bulk densities, average grain density, porosity, compressional and shear wave velocities, elastic moduli, and compressional and tensional fracture strengths. In this study, a suite of experiments was performed on cores recovered from boreholes UE25 NRG-2, 2A, 2B, and 3 drilled in support of the Exploratory Studies Facility (ESF) at Yucca Mountain. The holes penetrated the Timber Mountain tuff and two thermal/mechanical units of the Paintbrush tuff. The thermal/mechanical stratigraphy was defined by Ortiz to group rock horizons of similar properties for the purpose of simplifying modeling efforts. The relationship between the geologic stratigraphy and the thermal/mechanical stratigraphy for each borehole is presented. The tuff samples in this study have a wide range of welding characteristics (usually reflected in sample porosity), and a smaller range of mineralogy and petrology characteristics. Generally, the samples are silicic, ash-fall tuffs that exhibit large variability in their elastic and strength properties.

  14. DFT+ U study of electronic structure and Curie temperature of A2 B ReO6 (A=Sr, Ca and B=Cr, Fe)

    NASA Astrophysics Data System (ADS)

    Lee, Alex; Marianetti, Chris

    Re-based double perovskites (DPs) have attracted much attention due to their high Curie temperature (TC) and colossal magneto resistance with large potential for spintronic applications. Here we investigate the electronic and magnetic properties of the Re-based DPs A2 B ReO6 (A=Sr, Ca and B=Cr, Fe) using density functional theory + U (DFT+ U) calculations. While monoclinic Ca2CrReO6 and Ca2FeReO6 (monoclinic) are insulating within GGA+ U, tetragonal Sr2CrReO6 (a0a0c0) and Sr2FeReO6 (a0a0c-) remain metallic. We show that both on-site interaction U and octahedral tilting are critical to obtain the insulating phases. The a0a0c- -phase of Sr2CrReO6 is most stable and insulating with nonzero U, suggesting that the high quality Sr2CrReO6 film on STO substrate can be a semiconductor as reported in recent experiments. We explain that the insulator-to-metal transition (MIT) of Ca2FeReO6 at 140K is predominantly due to a structural phase transition which drives the insulating state. Curie temperatures of Re-based DPs are calculated using the classical Monte Carlo simulations based on the Heisenberg model.

  15. Synthesis and Characterization of New Poly(silole-fluorene) Copolymers.

    PubMed

    Lee, Yun-Ji; Park, Jeong Cheol; Yun, Hui-Jun; Park, Jong-Man; Kim, Yun-Hi

    2015-02-01

    New poly(silole-fluorene) copolymers were designed and synthesized. Copolymers were obtained by Suzuki coupling reaction with different ratio of fluorene and silole. The obtained copolymers were characterized by the spectroscopic methods such as FT-IR and 1H-NMR spectroscopies. The resulting copolymers were soluble in common organic solvents such as toluene, tetrahydrofurane, chloroform, chlorobenzene, etc. The obtained copolymers showed thermal stabilities, which were characterized by TGA and DSC. PLEDs with device configurations of ITO/PEDOT:PSS/Copolymer I~VI/LiF/AI. The best device performances, with maximum brightness of 231.5 cd/m2 at a current density (J) of 408.3 mA/cm2, and a maximum luminance efficiency of 0.115 cd/A, were achieved in the composition of fluorene and silole moiety (0.9:0.1). PMID:26353724

  16. Oxygen plasma resistant phosphine oxide containing imide/arylene copolymers

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.

    1993-01-01

    A series of oxygen plasma resistant imide/arylene ether copolymers were prepared by reacting anhydride-terminated poly(amide acids) and amine-terminated polyarylene ethers containing phosphine oxide units. Inherent viscosities for these copolymers ranged from 0.42 to 0.80 dL/g. After curing, the resulting copolymers had glass transition temperatures ranging from 224 C to 228 C. Solution cast films of the block copolymers were tough and flexible with tensile strength, tensile moduli, and elongation at break up to 16.1 ksi, 439 ksi, and 23 percent, respectively at 25 C and 9.1 ksi, 308 ksi and 97 percent, respectively at 150 C. The copolymers show a significant improvement in resistance to oxygen plasma when compared to the commercial polyimide Kapton. The imide/arylene ether copolymers containing phosphine oxide units are suitable as coatings, films, adhesives, and composite matrices.

  17. Bulk nanostructured alloys prepared by flux melting and melt solidification

    SciTech Connect

    Shen, T.D.; Schwarz, R.B.; Zhang, X.

    2005-10-03

    We have prepared bulk nanostructured Ag{sub 60}Cu{sub 40} alloys by a flux-melting and melt-solidification technique. The flux purifies the melts, leading to a large undercooling and nanometer-sized microstructure. The as-prepared alloys are composed of nanolayered Ag and Cu within micrometer-sized grains. The bulk nanostructured alloys have an ultimate tensile strength of approximately 560 MPa, similar yield strength in tension and compression, elongation of 7% in tension, strain hardening exponent of 0.1, and relatively high mechanical and thermal stability up to 400 deg. C.

  18. On the birefringence of multilayered symmetric diblock copolymer films

    SciTech Connect

    Kim, J.; Chin, I.; Smith, B.A.; Russell, T.P. ); Mays, J.W. . Dept. of Chemistry)

    1993-09-27

    The chain extension at lamellar interfaces was studied in thin films of symmetric diblock copolymers on gold substrates. The first copolymer consisted of blocks of polystyrene (PS) and poly(2-vinylpyridine) (P2VP), denoted P(S-b-2VP). The second was a diblock copolymer of PS and poly(methyl methacrylate) (PMMA), denoted P(S-b-MMA), on a gold substrate. Using attenuated total reflectance spectroscopy, the refractive indices parallel, n[sub [parallel

  19. Reversible geling co-polymer and method of making

    DOEpatents

    Gutowska, Anna

    2005-12-27

    The present invention is a thereapeutic agent carrier having a thermally reversible gel or geling copolymer that is a linear random copolymer of an [meth-]acrylamide derivative and a hydrophilic comonomer, wherein the linear random copolymer is in the form of a plurality of linear chains having a plurality of molecular weights greater than or equal to a minimum geling molecular weight cutoff and a therapeutic agent.

  20. Commercial Zone Melting Ingots

    NASA Astrophysics Data System (ADS)

    Zheng, Yun; Xie, Hongyao; Shu, Shengcheng; Yan, Yonggao; Li, Han; Tang, Xinfeng

    2014-06-01

    Bismuth telluride-based compounds have been extensively utilized for commercial application. However, thermoelectric materials must suffer numerous mechanical vibrations and thermal stresses while in service, making it equally important to discuss the mechanical properties, especially at high temperature. In this study, the compressive and bending strengths of Bi0.5Sb1.5Te3 commercial zone melting (ZM) ingots were investigated at 25, 100, and 200 °C, respectively. Due to the obvious anisotropy of materials prepared by ZM method, the effect of anisotropy on the strengths was also explored. Two-parameter Weibull distribution was employed to fit a series of values acquired by a universal testing machine. And digital speckle photography was applied to record the strain field evolution, providing visual observation of surface strain. The compressive and bending strengths along ZM direction were approximately three times as large as those perpendicular to the ZM direction independent of the temperature, indicating a weak van der Waals bond along the c axis.

  1. Structure-property relationships in multilayered polymeric system and olefinic block copolymers

    NASA Astrophysics Data System (ADS)

    Khariwala, Devang

    diffusion. Subsequently, the oxygen permeability was directly related to the composition profile in each layer and changed as the interdiffusion proceeded. This methodology enabled the extraction of the mutual diffusion co-efficient, D, for the Nylon-6/EVOH system. The effect of comonomer content in EVOH on the mutual diffusion coefficient was also studied by comparing the kinetics of interdiffusion of Nylon-6 with two EVOHs containing 24 and 44 mole % ethylene. Chapter 3. Exciting new developments in polyolefin synthesis give rise to olefinic block copolymers with properties typical of thermoplastic elastomers. The block copolymers synthesized by chain shuttling technology consist of crystallizable ethylene-octene blocks with low comonomer content and high melting temperature (hard blocks), alternating with amorphous ethylene-octene blocks with high comonomer content and low glass transition temperature (soft blocks). This study describes the material science of these unique polymers as characterized by thermal analysis, X-ray diffraction, microscopy, and tensile deformation. The crystallizable blocks are long enough to form well-organized lamellar crystals with the orthorhombic unit cell and high melting temperature. The lamellae are organized into space-filling spherulites in all compositions even in copolymers with only 18 wt% hard block. The morphology is consistent with crystallization from a miscible melt. Crystallization of the hard blocks forces segregation of the noncrystallizable soft blocks into the interlamellar regions. Good separation of hard and soft blocks in the solid state is confirmed by distinct and separate beta- and alpha-relaxations in all the block copolymers. Compared to statistical ethylene-octene copolymers, the blocky architecture imparts a substantially higher crystallization temperature, a higher melting temperature and a better organized crystalline morphology, while maintaining a lower glass transition temperature. The differences between

  2. Diblock Copolymers under Nano-Confinement

    NASA Astrophysics Data System (ADS)

    Meng, Dong; Yin, Yuhua; Wang, Qiang

    2009-03-01

    Nano-confinement strongly affects and can thus be used to control the self-assembled morphology of block copolymers. Understanding such effects is of both fundamental and practical interest. In this work, we use real-space self-consistent field calculations with high accuracy to study the self-assembled morphology of diblock copolymers (DBC) under nano-confinement for several systems, including 1D lamellae-forming DBC confined between two homogeneous and parallel surfaces, in nano-pores, and on topologically patterned substrates; 2D cylinder-forming DBC on chemically strip-patterned substrates; and 3D gyroid- forming DBC confined between two homogeneous and parallel surfaces. The stable phases are identified through free-energy comparison, and our SCF results are compared with available experiments and Monte Carlo simulations in each case.

  3. Photothermal degradation of ethylene/vinylacetate copolymer

    NASA Technical Reports Server (NTRS)

    Liang, R. H.; Chung, S.; Clayton, A.; Di Stefano, S.; Oda, K.; Hong, S. D.; Gupta, A.

    1983-01-01

    Photothermal degradation studies were conducted on a 'stabilized' formulation of ethylene/vinyl acetate copolymer (EVA) in the temperature range 25-105 C under three different oxygen environments (in open air, with limited access to O2, and in a dark closed stagnant oven). These studies were performed in order to evaluate the utility of EVA as an encapsulation material for photovoltaic modules. Results showed that at low temperature (25 C), slow photooxidation of the polymer occurred via electronic energy transfer involving the UV absorber incorporated in the polymer. However, no changes in the physical properties of the bulk polymer were detected up to 1500 hours of irradiation. At elevated temperatures, leaching and evaporation of the additives occurred, which ultimately resulted in the chemical crosslinking of the copolymer and the formation of volatile photoproducts such as acetic acid.

  4. Rapid ordering of block copolymer thin films.

    PubMed

    Majewski, Pawel W; Yager, Kevin G

    2016-10-12

    Block-copolymers self-assemble into diverse morphologies, where nanoscale order can be finely tuned via block architecture and processing conditions. However, the ultimate usage of these materials in real-world applications may be hampered by the extremely long thermal annealing times-hours or days-required to achieve good order. Here, we provide an overview of the fundamentals of block-copolymer self-assembly kinetics, and review the techniques that have been demonstrated to influence, and enhance, these ordering kinetics. We discuss the inherent tradeoffs between oven annealing, solvent annealing, microwave annealing, zone annealing, and other directed self-assembly methods; including an assessment of spatial and temporal characteristics. We also review both real-space and reciprocal-space analysis techniques for quantifying order in these systems. PMID:27537062

  5. Hierarchical porous polymer scaffolds from block copolymers.

    PubMed

    Sai, Hiroaki; Tan, Kwan Wee; Hur, Kahyun; Asenath-Smith, Emily; Hovden, Robert; Jiang, Yi; Riccio, Mark; Muller, David A; Elser, Veit; Estroff, Lara A; Gruner, Sol M; Wiesner, Ulrich

    2013-08-01

    Hierarchical porous polymer materials are of increasing importance because of their potential application in catalysis, separation technology, or bioengineering. Examples for their synthesis exist, but there is a need for a facile yet versatile conceptual approach to such hierarchical scaffolds and quantitative characterization of their nonperiodic pore systems. Here, we introduce a synthesis method combining well-established concepts of macroscale spinodal decomposition and nanoscale block copolymer self-assembly with porosity formation on both length scales via rinsing with protic solvents. We used scanning electron microscopy, small-angle x-ray scattering, transmission electron tomography, and nanoscale x-ray computed tomography for quantitative pore-structure characterization. The method was demonstrated for AB- and ABC-type block copolymers, and resulting materials were used as scaffolds for calcite crystal growth. PMID:23908232

  6. Phase Behavior of Gradient Copolymer Solution

    NASA Astrophysics Data System (ADS)

    Pandav, Gunja; Gallow, Keith; Loo, Yueh-Lin; Ganesan, Venkat

    2012-02-01

    We study the behavior of amphiphilic linear gradient copolymer chains under poor solvent conditions. Using Bond Fluctuation model and parallel tempering algorithm, we explore qualitative behavior of this class of polymers with varying gradient strength; which is the largest difference in the instantaneous composition along the polymer chain. Under poor solvent conditions, the chains collapse to form micelles. We find a linear dependence of hydrophilic to hydrophobic transition temperature on gradient strength. Systematic analysis of these clusters reveals a strong dependence of micelle properties on gradient strength. Also, we discuss our results with reference to recent experiments on synthesis and cloud point depression in gradient copolymers confirming gradient strength as key parameter in tuning micelle properties.

  7. Multigraft Copolymer Superelastomers: Synthesis Morphology, and Properties

    SciTech Connect

    Uhrig, David; Schlegel, Ralf; Weidisch, Roland; Mays, Jimmy

    2011-01-01

    The synthesis of well-defined multigraft copolymers having a polydiene backbone with polystyrene side chains is briefly reviewed, with particular focus on controlling branch point spacing and branch point functionality. Use of living anionic polymerization and chlorosilane linking chemistry has led to the synthesis of series of materials having regularly spaced trifunctional (comb), tetrafunctional (centipede), and hexafunctional (barbwire) branch points. The morphologies of these materials were characterized by transmission electron microscopy and small-angle X-ray scattering, and it was found that the morphologies were controlled by the local architectural asymmetry associated with each branch point. Mechanical properties studies revealed that such multigraft copolymers represent a new class of thermoplastic elastomers (TPEs) with superior elongation at break and low residual strains as compared to conventional TPEs.

  8. Structure Formation of Block Copolymer Membranes

    NASA Astrophysics Data System (ADS)

    Abetz, Volker

    2013-03-01

    Isoporous membranes have received increasing attention during the last couple of years. The advantage of these materials is to give access to membranes with a very high number density of pores with controlled diameters, thus leading to ultrafiltration membranes with a very high permeability, and simultaneously also with a very high selectivity in terms of size exclusion. Different approaches have been reported, which typically involve the transfer of a thin block copolymer film from a solid to a porous support, eventually followed by an edging step. An alternative strategy is to form integral asymmetric membranes, where the thin top layer is continuously changing into a spongy support layer, thus avoiding the build-up of mechanical stresses. This happens by subjecting the cast polymer solution film into a precipitant, inducing the so-called phase inversion by exchange of solvent with the non-solvent. Here it is important to have a system where solvent and nonsolvent are fully miscible. This strategy also enables the direct formation of open pores without a subsequent edging step, if the solvents and nonsolvents are appropriately chosen. Different types of amphiphilic block copolymers based on styrene, 2- or 4-vinyl pyridine, and ethylene oxide with various compositions and molecular weights will be discussed. These block copolymers were dissolved at different concentrations in various solvent mixtures, and then cast on a non-woven support, which was either pretreated with a liquid, or not. Varying the time before the cast solution was subjected to phase inversion, as well as choosing the temperature of the precipitation bath, are further parameters having strong influence on the obtained membrane film structure. Membranes with pore forming blocks showing pH or temperature sensitive behaviour can be reversibly switched from an open state to a closed state. The size of the pores can be controlled by both molecular weight and composition of the block copolymers.

  9. Critical adsorption of copolymer tethered on selective surfaces

    NASA Astrophysics Data System (ADS)

    Li, Hong; Qian, Chang-Ji; Luo, Meng-Bo

    2016-04-01

    Critical adsorption behaviors of flexible copolymer chains tethered to a flat homogeneous surface are studied by using Monte Carlo simulations. We have compared the critical adsorption temperature Tc, estimated by a finite-size scaling method, for different AB copolymer sequences with A the attractive monomer and B the inert monomer. We find that Tc increases with an increase in the fraction of monomers A, fA, in copolymers, and it increases with an increase in the length of block A for the same fA. In particular, Tc of copolymer (AnBn)r can be expressed as a function of the block length, n, and Tc of copolymer (AnB)r and (ABm)r can be expressed as a linear function of fA. Tc of random copolymer chains also can be expressed as a linear function of fA and it can be estimated by using weight-average of Tc of different diblocks in the random copolymer. However, the crossover exponent is roughly independent of AB sequence distributions either for block copolymers or for random copolymers.

  10. 21 CFR 175.210 - Acrylate ester copolymer coating.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... polymerized copolymer of ethyl acrylate, methyl methacrylate, and methacrylic acid applied in emulsion form to... Glyceryl monostearate Methyl cellulose Mineral oil Paraffin wax Potassium hydroxide Potassium...

  11. The Human Genomic Melting Map

    PubMed Central

    Liu, Fang; Tøstesen, Eivind; Sundet, Jostein K; Jenssen, Tor-Kristian; Bock, Christoph; Jerstad, Geir Ivar; Thilly, William G; Hovig, Eivind

    2007-01-01

    In a living cell, the antiparallel double-stranded helix of DNA is a dynamically changing structure. The structure relates to interactions between and within the DNA strands, and the array of other macromolecules that constitutes functional chromatin. It is only through its changing conformations that DNA can organize and structure a large number of cellular functions. In particular, DNA must locally uncoil, or melt, and become single-stranded for DNA replication, repair, recombination, and transcription to occur. It has previously been shown that this melting occurs cooperatively, whereby several base pairs act in concert to generate melting bubbles, and in this way constitute a domain that behaves as a unit with respect to local DNA single-strandedness. We have applied a melting map calculation to the complete human genome, which provides information about the propensities of forming local bubbles determined from the whole sequence, and present a first report on its basic features, the extent of cooperativity, and correlations to various physical and biological features of the human genome. Globally, the melting map covaries very strongly with GC content. Most importantly, however, cooperativity of DNA denaturation causes this correlation to be weaker at resolutions fewer than 500 bps. This is also the resolution level at which most structural and biological processes occur, signifying the importance of the informational content inherent in the genomic melting map. The human DNA melting map may be further explored at http://meltmap.uio.no. PMID:17511513

  12. Gyroid nickel nanostructures from diblock copolymer supramolecules.

    PubMed

    Vukovic, Ivana; Punzhin, Sergey; Voet, Vincent S D; Vukovic, Zorica; de Hosson, Jeff Th M; ten Brinke, Gerrit; Loos, Katja

    2014-01-01

    Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template's channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology. PMID:24797367

  13. Sulfonated Polymerized Ionic Liquid Block Copolymers.

    PubMed

    Meek, Kelly M; Elabd, Yossef A

    2016-07-01

    The successful synthesis of a new diblock copolymer, referred to as sulfonated polymerized ionic liquid (PIL) block copolymer, poly(SS-Li-b-AEBIm-TFSI), is reported, which contains both sulfonated blocks (sulfonated styrene: SS) and PIL blocks (1-[(2-acryloyloxy)ethyl]-3-butylimidazolium: AEBIm) with both mobile cations (lithium: Li(+) ) and mobile anions (bis(trifluoromethylsulfonyl)imide: TFSI(-) ). Synthesis consists of polymerization via reversible addition-fragmentation chain transfer, followed by post-functionalization reactions to covalently attach the imidazolium cations and sulfonic acid anions to their respective blocks, followed by ion exchange metathesis resulting in mobile Li(+) cations and mobile TFSI(-) anions. Solid-state films containing 1 m Li-TFSI salt dissolved in ionic liquid result in an ion conductivity of >1.5 mS cm(-1) at 70 °C, where small-angle X-ray scattering data indicate a weakly ordered microphase-separated morphology. These results demonstrate a new ion-conducting block copolymer containing both mobile cations and mobile anions. PMID:27125600

  14. Regulating block copolymer phases via selective homopolymers.

    PubMed

    Yang, Shuang; Lei, Zhen; Hu, Nan; Chen, Er-Qiang; Shi, An-Chang

    2015-03-28

    The phase behavior of strongly segregated AB diblock copolymer and selective C homopolymer blends is examined theoretically using a combination of strong stretching theory (SST) and self-consistent field theory (SCFT). The C-homopolymer is immiscible with the B-blocks but strongly attractive with the A-blocks. The effect of homopolymer content on the order-order phase transitions is analyzed. It is observed that, for AB diblock copolymers with majority A-blocks, the addition of the C-homopolymers results in lamellar to cylindrical to spherical phase transitions because of the A/C complexation. For diblock copolymers with minor A-blocks, adding C-homopolymers leads to transitions from spherical or cylindrical morphology with A-rich core to lamellae to inverted cylindrical and spherical morphologies with B-rich core. The results from analytical SST and numerical SCFT are in good agreement within most regions of the phase diagram. But the deviation becomes more obvious when the composition of A-blocks is too small and the content of added C-homopolymers is large enough, where the SCFT predicts a narrow co-existence region between different ordered phases. Furthermore, it is found that the phase behavior of the system is insensitive to the molecular weight of C-homopolymer. PMID:25833605

  15. Gyroid Nickel Nanostructures from Diblock Copolymer Supramolecules

    PubMed Central

    Vukovic, Ivana; Punzhin, Sergey; Voet, Vincent S. D.; Vukovic, Zorica; de Hosson, Jeff Th. M.; ten Brinke, Gerrit; Loos, Katja

    2014-01-01

    Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template's channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology. PMID:24797367

  16. Regulating block copolymer phases via selective homopolymers

    SciTech Connect

    Yang, Shuang E-mail: eqchen@pku.edu.cn; Lei, Zhen; Hu, Nan; Chen, Er-Qiang E-mail: eqchen@pku.edu.cn; Shi, An-Chang

    2015-03-28

    The phase behavior of strongly segregated AB diblock copolymer and selective C homopolymer blends is examined theoretically using a combination of strong stretching theory (SST) and self-consistent field theory (SCFT). The C-homopolymer is immiscible with the B-blocks but strongly attractive with the A-blocks. The effect of homopolymer content on the order-order phase transitions is analyzed. It is observed that, for AB diblock copolymers with majority A-blocks, the addition of the C-homopolymers results in lamellar to cylindrical to spherical phase transitions because of the A/C complexation. For diblock copolymers with minor A-blocks, adding C-homopolymers leads to transitions from spherical or cylindrical morphology with A-rich core to lamellae to inverted cylindrical and spherical morphologies with B-rich core. The results from analytical SST and numerical SCFT are in good agreement within most regions of the phase diagram. But the deviation becomes more obvious when the composition of A-blocks is too small and the content of added C-homopolymers is large enough, where the SCFT predicts a narrow co-existence region between different ordered phases. Furthermore, it is found that the phase behavior of the system is insensitive to the molecular weight of C-homopolymer.

  17. Comparing Fluid and Elastic Block Copolymer Shells

    NASA Astrophysics Data System (ADS)

    Rozairo, Damith; Croll, Andrew B.

    2014-03-01

    Emulsions can be stabilized with the addition of an amphiphilic diblock copolymer, resulting in droplets surrounded and protected by a polymer monolayer. Such droplets show considerable promise as advanced cargo carriers in pharmaceuticals or cosmetics due to their strength and responsiveness. Diblock copolymer interfaces remain mostly fluid and may not be able to attain the mechanical performance desired by industry. To strengthen block copolymer emulsion droplets we have developed a novel method for creating thin elastic shells using polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-PAA-PS). Characterization of the fluid filled elastic shells is difficult with traditional means which lead us to develop a new and general method of mechanical measurement. Specifically, we use laser scanning confocal microscopy to achieve a high resolution measure of the deformation of soft spheres under the influence of gravity. To prove the resilience of the technique we examine both a polystyrene-b-poly(ethylene oxide) (PS-PEO) stabilized emulsion and the PS-PAA-PS emulsion. The mechanical measurement allows the physics of the polymer at the interface to be examined, which will ultimately lead to the rational development of these technologies.

  18. Sulfur copolymers for infrared optical imaging

    NASA Astrophysics Data System (ADS)

    Namnabat, S.; Gabriel, J. J.; Pyun, J.; Norwood, R. A.; Dereniak, E. L.; van der Laan, J.

    2014-06-01

    The development of organic polymers with low infrared absorption has been investigated as a possible alternative to inorganic metal oxide, semiconductor, or chalcogenide-based materials for a variety of optical devices and components, such as lenses, goggles, thermal imaging cameras and optical fibers. In principle, organic-based polymers are attractive for these applications because of their low weight, ease of processing, mechanical toughness, and facile chemical variation using commercially available precursors. Herein we report on the optical characterization of a new class of sulfur copolymers that are readily moldable, transparent above 500 nm, possess high refractive index (n > 1.8) and take advantage of the low infrared absorption of S-S bonds for potential use in the mid-infrared at 3-5 microns. These materials are largely made from elemental sulfur by an inverse vulcanization process; in the current study we focus on the properties of a chemically stable, branched copolymer of poly(sulfur-random-1,3-diisopropenylbenzene) (poly(S-r- DIB). Copolymers with elemental sulfur content ranging from 50% to 80% by weight were studied by UV-VIS spectroscopy, FTIR, and prism coupling for refractive index measurement. Clear correlation between material composition and the optical properties was established, confirming that the high polarizability of the sulfur atom leads to high refractive index while also maintaining low optical loss in the infrared.

  19. High-performance dual-action polymer-TiO2 nanocomposite films via melting processing.

    PubMed

    Kubacka, Anna; Serrano, Cristina; Ferrer, Manuel; Lünsdorf, Heinrich; Bielecki, Piotr; Cerrada, María Luisa; Fernández-García, Marta; Fernández-García, Marcos

    2007-08-01

    The incorporation of TiO2 nanoparticles into (ethylene-vinyl alcohol)-based food packaging copolymers affords an opportunity to synthesize polymer-based nanocomposite materials with novel and powerful biocidal and photodegradability properties, resulting in the production of an advanced, environmentally friendly system prepared using a cost-effective synthesis method via a simple melt compounding without the need of a coupling agent incorporation. The presented materials display an unprecedented performance in the killing of both Gram positive and negative bacteria without the necessity of being release to the media and an easy degradation under sunlight which favorably competes with biodegradation procedures. PMID:17625905

  20. Are block copolymer worms more effective Pickering emulsifiers than block copolymer spheres?

    PubMed

    Thompson, K L; Mable, C J; Cockram, A; Warren, N J; Cunningham, V J; Jones, E R; Verber, R; Armes, S P

    2014-11-21

    RAFT-mediated polymerisation-induced self-assembly (PISA) is used to prepare six types of amphiphilic block copolymer nanoparticles which were subsequently evaluated as putative Pickering emulsifiers for the stabilisation of n-dodecane-in-water emulsions. It was found that linear poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer spheres and worms do not survive the high shear homogenisation conditions used for emulsification. Stable emulsions are obtained, but the copolymer acts as a polymeric surfactant; individual chains rather than particles are adsorbed at the oil-water interface. Particle dissociation during emulsification is attributed to the weakly hydrophobic character of the PHPMA block. Covalent stabilisation of these copolymer spheres or worms can be readily achieved by addition of ethylene glycol dimethacrylate (EGDMA) during the PISA synthesis. TEM studies confirm that the resulting cross-linked spherical or worm-like nanoparticles survive emulsification and produce genuine Pickering emulsions. Alternatively, stabilisation can be achieved by either replacing or supplementing the PHPMA block with the more hydrophobic poly(benzyl methacrylate) (PBzMA). The resulting linear spheres or worms also survive emulsification and produce stable n-dodecane-in-water Pickering emulsions. The intrinsic advantages of anisotropic worms over isotropic spheres for the preparation of Pickering emulsions are highlighted. The former particles are more strongly adsorbed at similar efficiencies compared to spheres and also enable smaller oil droplets to be produced for a given copolymer concentration. The scalable nature of PISA formulations augurs well for potential applications of anisotropic block copolymer nanoparticles as Pickering emulsifiers. PMID:25254485

  1. Melting granites to make granites

    NASA Astrophysics Data System (ADS)

    Carvalho, Bruna B.; Sawyer, Edward W.; Janasi, Valdecir de A.

    2014-05-01

    Large-scale partial melting in the continental crust is widely attributed to fluid-absent incongruent breakdown of hydrous minerals in the case of pelites, greywackes and meta-mafic rocks. Granite is a far more common rock in the continental crust, but fluid-absent hydrate-breakdown melting is unlikely to result in significant melting in granites because of their low modal abundance of mica or amphibole. Experiments show that fluid-present melting can produce ~30% melt at low temperatures (690°C). Thus, granites and leucogranites can be very fertile if H2O-present melting occurs via reactions such as plagioclase + quartz + K-feldspar + H2O = melt, because of their high modal proportions of the reactant phases. Our study investigates the Kinawa Migmatite in the São Francisco Craton, southeastern Brazil. This migmatite is derived from an Archaean TTG sequence and can be divided into; 1) pink diatexites, 2) leucosomes, 3) grey gneisses and 4) amphibolites. The migmatite records upper-amphibolite to beginning of granulite facies metamorphism in a P-T range from 5.1-6.6 kbar and ~650-780°C. Pink diatexites are the most abundant rocks, and their appearance varies depending on the amount of melt they contained. Three types are recognised: residual diatexites (low melt fraction (Mf)), schlieren diatexites (moderate Mf) and homogeneous diatexites (high Mf). They are very closely related spatially in the field, with mostly transitional contacts. There is a sequence with progressive loss of ferromagnesian minerals, schollen and schlieren through the sequence to the most melt-rich parts of the diatexites as magmatic flow became more intense. There are fewer ferromagnesian minerals, thus the melt becomes cleaner (more leucocratic) and, because the schlieren have disaggregated the aspect is more homogeneous. These parts are texturally similar to leucogranites in which the biotite is randomly distributed and pre-melting structures are completely destroyed. The likely protolith

  2. Elevated Ecto-5’-nucleotidase-Mediated Increased Renal Adenosine Signaling Via A2B Adenosine Receptor Contributes to Chronic Hypertension

    PubMed Central

    Zhang, Weiru; Zhang, Yujin; Wang, Wei; Dai, Yingbo; Ning, Chen; Luo, Renna; Sun, Kaiqi; Glover, Louise; Grenz, Almut; Sun, Hong; Tao, Lijian; Zhang, Wenzheng; Colgan, Sean P.; Blackburn, Michael R.; Eltzschig, Holger K.; Kellems, Rodney E.; Xia, Yang

    2013-01-01

    Rationale Hypertension is the most prevalent life-threatening disease worldwide and is frequently associated with chronic kidney disease (CKD). However, the molecular basis underlying hypertensive CKD is not fully understood. Objective We sought to identify specific factors and signaling pathways that contribute to hypertensive CKD and thereby exacerbate disease progression. Methods and Results Using high-throughput quantitative reverse-transcription polymerase chain reaction profiling, we discovered that the expression level of 5′-ectonucleotidase (CD73), a key enzyme that produces extracellular adenosine, was significantly increased in the kidneys of angiotensin II–infused mice, an animal model of hypertensive nephropathy. Genetic and pharmacological studies in mice revealed that elevated CD73-mediated excess renal adenosine preferentially induced A2B adenosine receptor (ADORA2B) production and that enhanced kidney ADORA2B signaling contributes to angiotensin II–induced hypertension. Similarly, in humans, we found that CD73 and ADORA2B levels were significantly elevated in the kidneys of CKD patients compared with normal individuals and were further elevated in hypertensive CKD patients. These findings led us to further discover that elevated renal CD73 contributes to excess adenosine signaling via ADORA2B activation that directly stimulates endothelin-1 production in a hypoxia-inducible factor-α–dependent manner and underlies the pathogenesis of the disease. Finally, we revealed that hypoxia-inducible factor-α is an important factor responsible for angiotensin II–induced CD73 and ADORA2B expression at the transcriptional level. Conclusions Overall, our studies reveal that angiotensin II–induced renal CD73 promotes the production of renal adenosine that is a prominent driver of hypertensive CKD by enhanced ADORA2B signaling–mediated endothelin-1 induction in a hypoxia-inducible factor-α–dependent manner. The inhibition of excess adenosine

  3. Melting of iron-aluminide alloys

    SciTech Connect

    Sikka, V.K.

    1990-01-01

    The melting of Fe{sub 3}Al-based alloys at the Oak Ridge National Laboratory (ORNL) and commercial vendors is described. The melting processes evaluated includes are melting, air-induction melting (AIM), vacuum-induction melting (VIM), and electroslag remelting (ESR). The quality of the ingots studied are base on internal soundness and the surface finish obtained. The ingots were analyzed for recovery of various elements during melting. The impurity levels observed in the alloys by various melting processes were compared. Recommendations are made for viable processes for commercial melting of these alloys. 1 ref., 5 figs., 3 tabs.

  4. Synthesis and Self-Assembly of Rod2Coil Miktoarm Star Copolymers of Poly(3-dodecxylthiophene) and Poly(methyl methacrylate) with high rod fractions

    NASA Astrophysics Data System (ADS)

    Park, Jicheol; Moon, Hong Chul; Choi, Chung-Royng; Kim, Jin Kon

    2015-03-01

    Poly(3-dodecylthiophene)-b-poly(methyl methacrylate) diblock copolymer (P3DDT- b-PMMA) can self-assembled into various microdomains such as spheres, cylinders, and lamellae depending on weight fraction of P3DDT. However, only filbril morphology was formed when weight fraction of P3DDT (wP 3 DDT) was major (wP 3 DDT ~ 0.76). Here, we introduce a new approach to obtain microdomain structures even at high wP 3 DDT by using well-defined A2B miktoarm star copolymer composed of P3DDT and PMMA ((P3DDT)2PMMA. We found via small angle X-ray scattering and transmission electron microscopy that (P3DDT)2PMMA showed PMMA cylinder packed hexagonally in the matrix of P3DDT and body-centered-cubic spheres of PMMA for wP 3 DDT of 0.66 and 0.75, respectively. This because of much reduction of the rod-rod interaction in (P3DDT)2PMMA compared with P3DDT- b-PMMA diblock copolymers.

  5. Scaleable Clean Aluminum Melting Systems

    SciTech Connect

    Han, Q.; Das, S.K.

    2008-02-15

    The project entitled 'Scaleable Clean Aluminum Melting Systems' was a Cooperative Research and Development Agreements (CRADAs) between Oak Ridge National Laboratory (ORNL) and Secat Inc. The three-year project was initially funded for the first year and was then canceled due to funding cuts at the DOE headquarters. The limited funds allowed the research team to visit industrial sites and investigate the status of using immersion heaters for aluminum melting applications. Primary concepts were proposed on the design of furnaces using immersion heaters for melting. The proposed project can continue if the funding agency resumes the funds to this research. The objective of this project was to develop and demonstrate integrated, retrofitable technologies for clean melting systems for aluminum in both the Metal Casting and integrated aluminum processing industries. The scope focused on immersion heating coupled with metal circulation systems that provide significant opportunity for energy savings as well as reduction of melt loss in the form of dross. The project aimed at the development and integration of technologies that would enable significant reduction in the energy consumption and environmental impacts of melting aluminum through substitution of immersion heating for the conventional radiant burner methods used in reverberatory furnaces. Specifically, the program would couple heater improvements with furnace modeling that would enable cost-effective retrofits to a range of existing furnace sizes, reducing the economic barrier to application.

  6. Thermal Conductivity of Ethylene Vinyl Acetate Copolymer/Nanofiller Blends

    NASA Technical Reports Server (NTRS)

    Ghose, Sayata; Watson, Kent A.; Working, Dennis C.; Connell, John W.; Smith, Joseph G., Jr.; Lin, Y.; Sun, Y. P.

    2007-01-01

    To reduce weight and increase the mobility, comfort, and performance of future spacesuits, flexible, thermally conductive fabrics and plastic tubes are needed for the Liquid Cooling and Ventilation Garment. Such improvements would allow astronauts to operate more efficiently and safely for extended extravehicular activities. As an approach to raise the thermal conductivity (TC) of an ethylene vinyl acetate copolymer (Elvax(TM)260), it was compounded with three types of carbon based nanofillers: multi-walled carbon nanotubes (MWCNTs), vapor grown carbon nanofibers (CNFs), and expanded graphite (EG). In addition, other nanofillers including metallized CNFs, nickel nanostrands, boron nitride, and powdered aluminum were also compounded with Elvax(TM) 260 in the melt at various loading levels. In an attempt to improve compatibility between Elvax 260 and the nanofillers, MWCNTs and EG were modified by surface coating and through noncovalent and covalent attachment of organic molecules containing alkyl groups. Ribbons of the nanocomposites were extruded to form samples in which the nanofillers were aligned in the direction of flow. Samples were also fabricated by compression molding to yield nanocomposites in which the nanofillers were randomly oriented. Mechanical properties of the aligned samples were determined by tensile testing while the degree of dispersion and alignment of nanoparticles were investigated using high-resolution scanning electron microscopy. TC measurements were performed using a laser flash (Nanoflash(TM)) technique. TC of the samples was measured in the direction of, and perpendicular to, the alignment direction. Additionally, tubing was also extruded from select nanocomposite compositions and the TC and mechanical flexibility measured.

  7. Mode-coupling theory of self-diffusion in diblock copolymers I. General derivation and qualitative predictions

    SciTech Connect

    Guenza, M.; Tang, H.; Schweizer, K.S.

    1998-01-01

    A microscopic theory of self-diffusion in diblock copolymer melts and solutions has been developed based on polymeric mode-coupling methods formulated at the level of the time and space correlated interchain excluded volume and chi-parameter forces. Equilibrium structural correlations are determined via microscopic liquid state integral equation or coarse-grained field theoretic methods. The specific dynamical consequences of self-assembly are predicted to depend rather sensitively on temperature, degree of polymerization, copolymer composition and concentration, and local block friction coefficients. The dominant physical effect for entangled diblocks is the retardation of the relaxation time of the interchain excluded volume forces due to the thermodynamically-driven segregation of blocks into microdomains, resulting in suppression of translational motion. Analytic analysis in the long chain limit allows the derivation of new scaling laws relating the self-diffusion constant and chain degree of polymerization and solution concentration. Potential limitations for real copolymer materials associated with the structurally and dynamically isotropic description adopted by the theory are discussed. {copyright} {ital 1998 American Institute of Physics.}

  8. Anomalous Pressure Dependence of the Critical Fluctuations in binary blends and diblock copolymers of PDMS and PEE.

    NASA Astrophysics Data System (ADS)

    Mortensen, Kell; Schwahn, Dietmar; Frielinghaus, Henrich; Almdal, Kristoffer

    2000-03-01

    The structure factor of binary blends of PDMS and PEE, and the corresponding diblock copolymer PDMS-PEE have been measured by small-angle neutron scattering as a function of both temperature and pressure. The study includes as well dependencies of the polymer molar masses. The phase behavior of both the blend and the diblock copolymer systems shows the similar anomalous trend: with increasing pressure the critical temperature decreases, but upon further increase in pressure the critical temperature also increases. In the block copolymer system this leads with monotonously increasing pressure to first a melting and subsequently an ordering, while the blend goes from two-phase to one-phase and back to two-phase. Based on analysis of the Flory-Huggins type, the origin of this behavior can be associated with changes in the entropic and the enthalpic parts of the interaction parameter. The abnormal behavior seems to be closely related to the characteristics of the PDMS part of the system. An additional result of the pressure dependent structural data is the conformational compressibility. In contrast to theoretical expectations, analysis of the peak position of the experimental structure factor results in a pronounced peak in the conformational compressibility at the order-to-disorder transition temperature.

  9. Actuator based on sulfonated comb copolymer of poly (ethylene-co-vinyl alcohol) grafted by poly (ethylene glycol)

    NASA Astrophysics Data System (ADS)

    Gong, Guifen; Li, Lei; Zhang, Yujun

    2007-07-01

    Comb copolymer consisting of poly (ethylene-co-vinyl alcohol) (EVAL) as backbone and poly (ethylene glycol) (PEG) as side chains (EVAL-g-PEG) has been synthesized, then it was sulfonated by 1,3-propane sultone to get the final ionomer (EVAL-g-SPEG), and ionic polymer-metal composite (IPMC) based on EVAL-g-SPEG was prepared through electroless deposition of platinum onto the surfaces of EVAL-g-SPEG membrane. The graft copolymers were characterized with respect to molecular weight using gel permeation chromatography (GPC) and composition using 1H-NMR. The results showed that the No. of PEG graft of the side chains is n=1, 2 and others. Thermal properties were examined by DSC and TG. The melt temperature (T m) and glass transition temperature (T g) of the comb copolymer increase with the increasing length and the number of the side chains. Moreover, the deformation performance of IPMC material was tested and its results show that the starting response voltage of IPMC actuator decreases with the increasing IEC value. On the other hand, the starting response voltage increases with the decreased side chain length. The IPMC with n=2 side chain length of PEG has the maximum tip displacement, and the maximum tip displacement of IPMC membrane generally decreases with the side chain length of EVAL-g-SPEG. This feature may be the reflection of two opposite effects, namely the decreasing ion densities and increasing water sorption of the membrane.

  10. Unexpected Temperature Behavior of Polyethylene Glycol Spacers in Copolymer Dendrimers in Chloroform

    NASA Astrophysics Data System (ADS)

    Markelov, Denis A.; Matveev, Vladimir V.; Ingman, Petri; Nikolaeva, Marianna N.; Penkova, Anastasia V.; Lahderanta, Erkki; Boiko, Natalia I.; Chizhik, Vladimir I.

    2016-04-01

    We have studied copolymer dendrimer structure: carbosilane dendrimers with terminal phenylbenzoate mesogenic groups attached by poly(ethylene) glycol (PEG) spacers. In this system PEG spacers are additional tuning to usual copolymer structure: dendrimer with terminal mesogenic groups. The dendrimer macromolecules were investigated in a dilute chloroform solution by 1H NMR methods (spectra and relaxations). It was found that the PEG layer in G = 5 generations dendrimer is “frozen” at high temperatures (above 260 K), but it unexpectedly becomes “unfrozen” at temperatures below 250 K (i.e., melting when cooling). The transition between these two states occurs within a small temperature range (~10 K). Such a behavior is not observed for smaller dendrimer generations (G = 1 and 3). This effect is likely related to the low critical solution temperature (LCST) of PEG and is caused by dendrimer conformations, in which the PEG group concentration in the layer increases with growing G. We suppose that the unusual behavior of PEG fragments in dendrimers will be interesting for practical applications such as nanocontainers or nanoreactors.

  11. Comprehensive Phase Behavior of Poly(isoprene-b-styrene-b-ethylene oxide) Triblock Copolymers

    SciTech Connect

    Chatterjee, Joon; Jain, Sumeet; Bates, Frank S.

    2010-03-05

    The phase behavior of 44 poly(isoprene-b-styrene-b-ethylene oxide) (ISO) linear triblock copolymer melts was investigated at weak to intermediate segregation strengths and spanning a comprehensive range of compositions. Phases were characterized by a combination of experimental techniques, including small-angle X-ray scattering, dynamic mechanical spectroscopy, transmission electron microscopy, and birefringence measurements. Combined with our previous results, six different stable ordered state symmetries have been identified: lamellae (LAM), Fddd orthorhombic network (O{sup 70}), double gyroid (Q{sup 230}), alternating gyroid (Q{sup 214}), hexagonal (HEX), and body-centered cubic (BCC). The phase map of ISO specimens was found to be somewhat asymmetric around the f{sub I} = f{sub O} isopleth. This work provides a guide for theoretical studies and gives insight into the intricate effects of various parameters on the self-assembly of ABC triblock copolymers. Experimental SAXS data evaluated with a simple scattering intensity model show that local mixing varies continuously across the phase map between states of two- and three-domain segregation.

  12. Fluorine effects on morphology and surface energy of diblock copolymer thin films

    NASA Astrophysics Data System (ADS)

    Shrestha, Umesh; Perahia, Dvora; Clarson, Stephen

    2015-03-01

    The interfacial composition and structure formed by the segregation between the incompatible blocks in a diblock copolymer thin film influence the stability and response of the film to external stimuli. Introduction of fluorine enhances the interfacial energy as well as chemical and thermal stability of the polymer film. Here we follow the interfacial structure and response of Si containing diblock co-polymer polytrifluoro propyl methyl siloxane-polystyrene (PTEPMS-PS) with the SiF fraction ranging from 0.03 to 0.5 in surface of the films as a function of temperature and solvent, using atomic force microscopy and contact angle measurement. We found that the tendency of the fluorine to migrate towards surface affects the surface energy while Si in backbone enhances the flexibility of the chains. Thin films prepared from selective good solvent for one of the blocks and good solvent for both blocks formed different structures compared to their melts. Correlation between morphology and volume fraction is dominant above the Tg of the polystyrene whereas below Tg limited effect is observed. NSF DMR 0907390.

  13. Polarization switching characteristics of vinylidene fluoride/tefrafluoroethylene copolymer thin films

    NASA Astrophysics Data System (ADS)

    Nakagawa, Yuuta; Hashizume, Yoichiro; Nakajima, Takashi; Okamura, Soichiro

    2015-10-01

    The polarization switching characteristics of vinylidene fluoride/tetrafluoroethylene (VDF/TeFE) copolymer thin film obtained from a melt-crystallization process were investigated over a wide electric field range from 80 to 180 MV/m. It was found that full polarization reversal occurred in 210-, 270-, and 320-nm-thick films; such reversal is independent of film thickness. The analysis of the switching kinetics based on the Avrami equation indicated a one- or two-dimensional domain growth process. The switching time obeyed the exponential law as evidence of the linear relationship between log τs and 1/E, which is consistent with the results for the vinylidene fluoride/trifluoroethylene (VDF/TrFE) copolymer. The switching time for VDF/TeFE was shorter than that for VDF/TrFE. For instance, switching times at 120 MV/m were 1.8 and 3.3 µs for VDF/TeFE and VDF/TrFE, respectively. It was revealed that the polarization switching of the VDF/TeFE can be achieved in a shorter time than that of the VDF/TrFE.

  14. Block copolymers confined in a nanopore: Pathfinding in a curving and frustrating flatland

    NASA Astrophysics Data System (ADS)

    Sevink, G. J. A.; Zvelindovsky, A. V.

    2008-02-01

    We have studied structure formation in a confined block copolymer melt by means of dynamic density functional theory. The confinement is two dimensional, and the confined geometry is that of a cylindrical nanopore. Although the results of this study are general, our coarse-grained molecular model is inspired by an experimental lamella-forming polysterene-polybutadiene diblock copolymer system [K. Shin et al., Science 306, 76 (2004)], in which an exotic toroidal structure was observed upon confinement in alumina nanopores. Our computational study shows that a zoo of exotic structures can be formed, although the majority, including the catenoid, helix, and double helix that were also found in Monte Carlo nanopore studies, are metastable states. We introduce a general classification scheme and consider the role of kinetics and elongational pressure on stability and formation pathway of both equilibrium and metastable structures in detail. We find that helicity and threefold connections mediate structural transitions on a larger scale. Moreover, by matching the remaining parameter in our mesoscopic method, the Flory-Huggins parameter χ, to the experimental system, we obtain a structure that resembles the experimental toroidal structure in great detail. Here, the most important factor seems to be the roughness of the pore, i.e., small variations of the pore radius on a scale that is larger than the characteristic size in the system.

  15. Bentonite-based organoclays as innovative flame retardants agents for SBS copolymer.

    PubMed

    Franchini, M Comes; Fabbri, P; Frache, A; Ori, G; Messori, M; Siligardi, C; Ricci, A

    2008-12-01

    Two organophilic bentonites, based on nitrogen-containing compounds, have been synthesised via ion exchange starting from pristine bentonite with octadecyltrimethylammonium bromide (OTAB) and with synthetic melamine-derived N2,N4-dihexadecyl-1,3,5-triazine-2,4,6-triamine (DEDMEL). The chemical and morphological characterization of the organoclays was based on XRD, TEM, Laser Granulometry, X-Ray Fluorescence and CEC capacity. Copoly(styrene-butadiene-styrene)-nanocomposites (SBS-nanocomposites) were obtained by intercalation of the SBS-copolymer into these new organoclays by melt intercalation method. XRD and TEM analysis of the organoclays and of the micro/nano-composites obtained are presented. The effect of the organoclays on the SBS-nanocomposite's flammability properties was investigated using cone calorimeter. An encouraging decrease of 20% in the peak heat released rate (PHRR) has been obtained confirming the important role of melamine's based skeleton and its derived organoclays to act as effective fire retardants and for the improvement of this important functional property in SBS copolymers. PMID:19205200

  16. Controlled hydrophobic functionalization of natural fibers through self-assembly of amphiphilic diblock copolymer micelles.

    PubMed

    Aarne, Niko; Laine, Janne; Hänninen, Tuomas; Rantanen, Ville; Seitsonen, Jani; Ruokolainen, Janne; Kontturi, Eero

    2013-07-01

    The functionalization of natural fibers is an important task that has recently received considerable attention. We investigated the formation of a hydrophobic layer from amphiphilic diblock copolymer micelles [polystyrene-block-poly(N-methyl-4-vinyl pyridinium iodide)] on natural fibers and on a model surface (mica). A series of micelles were prepared. The micelles were characterized by using cryoscopic TEM and light scattering, and their hydrophobization capability was studied through contact angle measurements, water adsorption, and Raman imaging. Mild heat treatment (130 °C) was used to increase the hydrophobization capability of the micelles. The results showed that the micelles could not hydrophobize a model surface, but could render the natural fibers water repellent both with and without heat treatment. This effect was systematically studied by varying the composition of the constituent blocks. The results showed that the micelle size (and the molecular weight of the constituent diblock copolymers) was the most important parameter, whereas the cationic (hydrophilic) part played only a minor role. We hypothesized that the hydrophobization effect could be attributed to a combination of the micelle size and the shrinkage of the natural fibers upon drying. The shrinking caused the roughness to increase on the fiber surface, which resulted in a rearrangement of the self- assembled layer in the wet state. Consequently, the fibers became hydrophobic through the roughness effects at multiple length scales. Mild heat treatment melted the micelle core and decreased the minimum size necessary for hydrophobization. PMID:23687082

  17. Unexpected Temperature Behavior of Polyethylene Glycol Spacers in Copolymer Dendrimers in Chloroform.

    PubMed

    Markelov, Denis A; Matveev, Vladimir V; Ingman, Petri; Nikolaeva, Marianna N; Penkova, Anastasia V; Lahderanta, Erkki; Boiko, Natalia I; Chizhik, Vladimir I

    2016-01-01

    We have studied copolymer dendrimer structure: carbosilane dendrimers with terminal phenylbenzoate mesogenic groups attached by poly(ethylene) glycol (PEG) spacers. In this system PEG spacers are additional tuning to usual copolymer structure: dendrimer with terminal mesogenic groups. The dendrimer macromolecules were investigated in a dilute chloroform solution by (1)H NMR methods (spectra and relaxations). It was found that the PEG layer in G = 5 generations dendrimer is "frozen" at high temperatures (above 260 K), but it unexpectedly becomes "unfrozen" at temperatures below 250 K (i.e., melting when cooling). The transition between these two states occurs within a small temperature range (~10 K). Such a behavior is not observed for smaller dendrimer generations (G = 1 and 3). This effect is likely related to the low critical solution temperature (LCST) of PEG and is caused by dendrimer conformations, in which the PEG group concentration in the layer increases with growing G. We suppose that the unusual behavior of PEG fragments in dendrimers will be interesting for practical applications such as nanocontainers or nanoreactors. PMID:27052599

  18. Basic physical properties/structure of polystyrene-polyisobutylene-polystyrene triblock copolymers

    SciTech Connect

    Kaszas, G.

    1993-12-31

    Polystyrene-b-polyisobutylene-b-polystyrene (PSt-PIB-PSt) triblock copolymers, with various molecular architectures, have been synthesized to establish basic physical properties/structure correlations for this novel thermoplastics elastomer (TPE). The test results have confirmed that these triblock copolymers have a unique combination of physical properties which is currently unavailable on the TPE market. The fully saturated character of the PIB backbone provides excellent ozone resistance. Barrier, electrical, and low-temperature properties, were measured, and found to be equivalent to those of conventional butyl vulcanizates. The low initial modules of PIB, and the fact that the PSt content can be kept low without significant loss in tensile properties, renders the material soft. The high incompatibility of PIB and PSt allows the overall chain length and, therefore, the melt viscosity, to be kept low. This could bring an important advantage, in processing, over other TPE`s. The combination of the above properties, and the inherent properties of PIB, makes this material in excellent candidate for wire and cable coating, seal and gasket, adhesive and vibration damping applications.

  19. Influence of Homopolymers on the Microdomain Behavior of Block Copolymers in 2D Confinement

    NASA Astrophysics Data System (ADS)

    Kim, Youngkeol; Hwang, Sungyoul; Yu, Guiduk; Char, Kookheon

    Constraints imposed by nanometer scale confinement lead to changes in bulk equilibrium behavior of block copolymers (BCPs). Cylindrical pores with diameters corresponding to the length equivalent of several copolymer chains have been employed to investigate the influence of two-dimensional confinement on the behavior of BCPs. In this study, we expand the scope to homopolymer-BCP binary blends. Given fraction of homopolymers, the phase behavior of blends is dependent on molecular weight (Mw) of homopolymers. Lamella- and cylinder-forming poly(styrene-b-butadiene) (PS-b-PBD) and PS homopolymers (hPS) were drawn into the pores of anodized aluminum oxide (AAO) membranes in the melt by capillary forces. Based on the detailed observation of the morphologies within porous columns, we analyzed the structural transition of BCPs induced by the presence of hPS and confinement. The effect of hPS on the micro-domain of BCPs is greatly accentuated in nanoscale confinement compared to the bulk state due to the entropic loss of polymer chains. Pore diameters of AAO and Mw of the PS-b-PBD are also controlled so as to examine the effects of confinement on the phase transition of PS-b-PBD/hPS blends.

  20. Unexpected Temperature Behavior of Polyethylene Glycol Spacers in Copolymer Dendrimers in Chloroform

    PubMed Central

    Markelov, Denis A.; Matveev, Vladimir V.; Ingman, Petri; Nikolaeva, Marianna N.; Penkova, Anastasia V.; Lahderanta, Erkki; Boiko, Natalia I.; Chizhik, Vladimir I.

    2016-01-01

    We have studied copolymer dendrimer structure: carbosilane dendrimers with terminal phenylbenzoate mesogenic groups attached by poly(ethylene) glycol (PEG) spacers. In this system PEG spacers are additional tuning to usual copolymer structure: dendrimer with terminal mesogenic groups. The dendrimer macromolecules were investigated in a dilute chloroform solution by 1H NMR methods (spectra and relaxations). It was found that the PEG layer in G = 5 generations dendrimer is “frozen” at high temperatures (above 260 K), but it unexpectedly becomes “unfrozen” at temperatures below 250 K (i.e., melting when cooling). The transition between these two states occurs within a small temperature range (~10 K). Such a behavior is not observed for smaller dendrimer generations (G = 1 and 3). This effect is likely related to the low critical solution temperature (LCST) of PEG and is caused by dendrimer conformations, in which the PEG group concentration in the layer increases with growing G. We suppose that the unusual behavior of PEG fragments in dendrimers will be interesting for practical applications such as nanocontainers or nanoreactors. PMID:27052599

  1. Block-copolymer healing of simple defects in a chemoepitaxial template

    NASA Astrophysics Data System (ADS)

    Patrone, Paul N.; Gallatin, Gregg M.

    2013-03-01

    Using the Leibler-Ohta-Kawasaki (LOK) phase-field model of block copolymers (BCPs), we characterize how a chemoepitaxial template with parallel lines of arbitrary width affects the BCP microdomain shape. We apply boundary conditions that account for the interactions of the polymers with the templated substrate and a neutral top-coat. We derive formulas for the monomer density and the microdomain interface profile of periodic, lamellar BCP melts whose template lines are wider or narrower than the bulk microdomain width. For such systems, our analysis (i) shows that mass conservation causes the microdomain interfaces to oscillate about their bulk positions and (ii) determines the length scale λ over which these oscillations decay away from the substrate.

  2. Piezoelectric Properties of Non-Polar Block Copolymers

    SciTech Connect

    Pester, Christian; Ruppel, Markus A; Schoberth, Heiko; Schmidt, K.; Liedel, Clemens; Van Rijn, Patrick; Littrell, Ken; Schindler, Kerstin; Hiltl, Stephanie; Czubak, Thomas; Mays, Jimmy; Urban, Volker S; Boker, Alexander

    2011-01-01

    Piezoelectric properties in non-polar block copolymers are a novelty in the field of electroactive polymers. The piezoelectric susceptibility of poly(styrene-b-isoprene) block copolymer lamellae is found to be up to an order of magnitude higher when compared to classic piezoelectric materials. The electroactive response increases with temperature and is found to be strongest in the disordered phase.

  3. Morphological studies on block copolymer modified PA 6 blends

    SciTech Connect

    Poindl, M. E-mail: christian.bonten@ikt.uni-stuttgart.de; Bonten, C. E-mail: christian.bonten@ikt.uni-stuttgart.de

    2014-05-15

    Recent studies show that compounding polyamide 6 (PA 6) with a PA 6 polyether block copolymers made by reaction injection molding (RIM) or continuous anionic polymerization in a reactive extrusion process (REX) result in blends with high impact strength and high stiffness compared to conventional rubber blends. In this paper, different high impact PA 6 blends were prepared using a twin screw extruder. The different impact modifiers were an ethylene propylene copolymer, a PA PA 6 polyether block copolymer made by reaction injection molding and one made by reactive extrusion. To ensure good particle matrix bonding, the ethylene propylene copolymer was grafted with maleic anhydride (EPR-g-MA). Due to the molecular structure of the two block copolymers, a coupling agent was not necessary. The block copolymers are semi-crystalline and partially cross-linked in contrast to commonly used amorphous rubbers which are usually uncured. The combination of different analysis methods like atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) gave a detailed view in the structure of the blends. Due to the partial cross-linking, the particles of the block copolymers in the blends are not spherical like the ones of ethylene propylene copolymer. The differences in molecular structure, miscibility and grafting of the impact modifiers result in different mechanical properties and different blend morphologies.

  4. 40 CFR 721.10213 - Polyether polyester copolymer phosphate (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... phosphate (generic). 721.10213 Section 721.10213 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.10213 Polyether polyester copolymer phosphate (generic). (a) Chemical... as polyether polyester copolymer phosphate (PMN P-09-253) is subject to reporting under this...

  5. Morphological studies on block copolymer modified PA 6 blends

    NASA Astrophysics Data System (ADS)

    Poindl, M.; Bonten, C.

    2014-05-01

    Recent studies show that compounding polyamide 6 (PA 6) with a PA 6 polyether block copolymers made by reaction injection molding (RIM) or continuous anionic polymerization in a reactive extrusion process (REX) result in blends with high impact strength and high stiffness compared to conventional rubber blends. In this paper, different high impact PA 6 blends were prepared using a twin screw extruder. The different impact modifiers were an ethylene propylene copolymer, a PA PA 6 polyether block copolymer made by reaction injection molding and one made by reactive extrusion. To ensure good particle matrix bonding, the ethylene propylene copolymer was grafted with maleic anhydride (EPR-g-MA). Due to the molecular structure of the two block copolymers, a coupling agent was not necessary. The block copolymers are semi-crystalline and partially cross-linked in contrast to commonly used amorphous rubbers which are usually uncured. The combination of different analysis methods like atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) gave a detailed view in the structure of the blends. Due to the partial cross-linking, the particles of the block copolymers in the blends are not spherical like the ones of ethylene propylene copolymer. The differences in molecular structure, miscibility and grafting of the impact modifiers result in different mechanical properties and different blend morphologies.

  6. 40 CFR 721.484 - Fluorinated acrylic copolymer (generic name).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Fluorinated acrylic copolymer (generic name). 721.484 Section 721.484 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED... Specific Chemical Substances § 721.484 Fluorinated acrylic copolymer (generic name). (a) Chemical...

  7. 40 CFR 721.4700 - Metalated alkylphenol copolymer (generic name).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Metalated alkylphenol copolymer (generic name). 721.4700 Section 721.4700 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.4700 Metalated alkylphenol copolymer (generic name). (a)...

  8. 40 CFR 721.4700 - Metalated alkylphenol copolymer (generic name).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Metalated alkylphenol copolymer (generic name). 721.4700 Section 721.4700 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.4700 Metalated alkylphenol copolymer (generic name). (a)...

  9. 40 CFR 721.336 - Perfluoroalkylethyl acrylate copolymer (generic name).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Perfluoroalkylethyl acrylate copolymer (generic name). 721.336 Section 721.336 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.336 Perfluoroalkylethyl acrylate copolymer (generic name). (a)...

  10. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  11. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  12. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  13. 21 CFR 177.1211 - Cross-linked polyacrylate copolymers.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... weight of aqueous sodium chloride solution at 20 °C for 24 hours. The low molecular weight extractives... applied mass). The solvent used shall be at least 60 milliliters aqueous sodium chloride solution per gram... polyacrylate copolymers consist of: (1) The grafted copolymer of cross-linked sodium polyacrylate identified...

  14. 21 CFR 181.32 - Acrylonitrile copolymers and resins.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Acrylonitrile copolymers and resins. 181.32 Section 181.32 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES (CONTINUED) PRIOR-SANCTIONED FOOD INGREDIENTS Specific Prior-Sanctioned Food Ingredients § 181.32 Acrylonitrile copolymers and resins. (a)...

  15. 21 CFR 177.1310 - Ethylene-acrylic acid copolymers.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Ethylene-acrylic acid copolymers. 177.1310 Section... Use Food Contact Surfaces § 177.1310 Ethylene-acrylic acid copolymers. The ethylene-acrylic acid... for use in contact with food subject to the provisions of this section. (a) The ethylene-acrylic...

  16. Computer simulations of block copolymer tethered nanoparticle self-assembly

    NASA Astrophysics Data System (ADS)

    Chan, Elaine R.; Ho, Lin C.; Glotzer, Sharon C.

    2006-08-01

    We perform molecular simulations to study the self-assembly of block copolymer tethered cubic nanoparticles. Minimal models of the tethered nanoscale building blocks (NBBs) are utilized to explore the structures arising from self-assembly. We demonstrate that attaching a rigid nanocube to a diblock copolymer affects the typical equilibrium morphologies exhibited by the pure copolymer. Lamellar and cylindrical phases are observed in both systems but not at the corresponding relative copolymer tether block fractions. The effect of nanoparticle geometry on phase behavior is investigated by comparing the self-assembled structures formed by the tethered NBBs with those of their linear ABC triblock copolymer counterparts. The tethered nanocubes exhibit the conventional triblock copolymer lamellar and cylindrical phases when the repulsive interactions between different blocks are symmetric. The rigid and bulky nature of the cube induces interfacial curvature in the tethered NBB phases compared to their linear ABC triblock copolymer counterparts. We compare our results with those structures obtained from ABC diblock copolymer tethered nanospheres to further elucidate the role of cubic nanoparticle geometry on self-assembly.

  17. 21 CFR 177.1312 - Ethylene-carbon monoxide copolymers.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from the American Society for... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Ethylene-carbon monoxide copolymers. 177.1312... Use Food Contact Surfaces § 177.1312 Ethylene-carbon monoxide copolymers. The ethylene-carbon...

  18. 21 CFR 173.60 - Dimethylamine-epichlorohydrin copolymer.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... Polymer Adjuvants for Food Treatment § 173.60 Dimethylamine-epichlorohydrin copolymer. Dimethylamine... 21 Food and Drugs 3 2014-04-01 2014-04-01 false Dimethylamine-epichlorohydrin copolymer. 173.60... epichlorohydrin in which not more than 5 mole-percent of dimethylamine may be replaced by an equimolar amount...

  19. Imide/arylene ether copolymers with pendent trifluoromethyl groups

    NASA Technical Reports Server (NTRS)

    Jensen, Brian J.; Havens, Stephen J.

    1992-01-01

    A series of imide/arylene ether block copolymers were prepared using an arylene ether block containing a hexafluoroisopropylidene group and an imide block containing a hexafluoroisopropylidene and a trifluoromethyl group in the polymer backbone. The copolymers were characterized and mechanical properties were determined and compared to the homopolymers.

  20. 40 CFR 721.10213 - Polyether polyester copolymer phosphate (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... phosphate (generic). 721.10213 Section 721.10213 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.10213 Polyether polyester copolymer phosphate (generic). (a) Chemical... as polyether polyester copolymer phosphate (PMN P-09-253) is subject to reporting under this...

  1. 40 CFR 721.10213 - Polyether polyester copolymer phosphate (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... phosphate (generic). 721.10213 Section 721.10213 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.10213 Polyether polyester copolymer phosphate (generic). (a) Chemical... as polyether polyester copolymer phosphate (PMN P-09-253) is subject to reporting under this...

  2. 40 CFR 721.10213 - Polyether polyester copolymer phosphate (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... phosphate (generic). 721.10213 Section 721.10213 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.10213 Polyether polyester copolymer phosphate (generic). (a) Chemical... as polyether polyester copolymer phosphate (PMN P-09-253) is subject to reporting under this...

  3. Breadth of neutralization and synergy of clinically relevant human monoclonal antibodies against HCV genotypes 1a, 1b, 2a, 2b, 2c, and 3a

    PubMed Central

    Carlsen, Thomas H.R.; Pedersen, Jannie; Prentoe, Jannick C.; Giang, Erick; Keck, Zhen-Yong; Mikkelsen, Lotte S.; Law, Mansun; Foung, Steven K. H.; Bukh, Jens

    2015-01-01

    Human monoclonal antibodies (HMAbs) with neutralizing capabilities constitute potential immune-based treatments or prophylaxis against hepatitis C virus (HCV). However, lack of cell culture-derived HCV (HCVcc) harboring authentic envelope proteins (E1/E2) has hindered neutralization investigations across genotypes, subtypes, and isolates. We investigated the breadth of neutralization of 10 HMAbs with therapeutic potential against a panel of 16 JFH1-based HCVcc expressing patient-derived Core-NS2 from genotypes 1a (strains H77, TN, and DH6), 1b (J4, DH1, and DH5), 2a (J6, JFH1, and T9), 2b (J8, DH8, and DH10), 2c (S83), and 3a (S52, DBN, and DH11). Virus stocks used for in vitro neutralization analysis contained authentic E1/E2, with the exception of full-length JFH1 that acquired the N417S substitution in E2. The 50% inhibition concentration (IC50) for each HMAb against the HCVcc panel was determined by dose-response neutralization assays in Huh7.5 cells with antibody concentrations ranging from 0.0012 to 100 μg/ml. Interestingly, IC50-values against the different HCVcc’s exhibited large variations among the HMAbs, and only three HMAbs (HC-1AM, HC84.24, and AR4A) neutralized all 16 HCVcc recombinants. Furthermore, the IC50-values for a given HMAb varied greatly with the HCVcc strain, which supports the use of a diverse virus panel. In cooperation analyses, HMAbs HC84.24, AR3A, and, especially HC84.26, demonstrated synergistic effects towards the majority of the HCVcc’s when combined individually with AR4A. Conclusion: Through a neutralization analysis of 10 clinically relevant HMAbs against 16 JFH1-based Core-NS2 recombinants from genotypes 1a, 1b, 2a, 2b, 2c, and 3a, we identified at least 3 HMAbs with potent and broad neutralization potential. The neutralization synergism obtained when pooling the most potent HMAbs could have significant implications for developing novel strategies to treat and control HCV. PMID:25043937

  4. In adenosine A2B knockouts acute treatment with inorganic nitrate improves glucose disposal, oxidative stress, and AMPK signaling in the liver

    PubMed Central

    Peleli, Maria; Hezel, Michael; Zollbrecht, Christa; Persson, A. Erik G.; Lundberg, Jon O.; Weitzberg, Eddie; Fredholm, Bertil B.; Carlström, Mattias

    2015-01-01

    Rationale: Accumulating studies suggest that nitric oxide (NO) deficiency and oxidative stress are central pathological mechanisms in type 2 diabetes (T2D). Recent findings demonstrate therapeutic effects by boosting the nitrate-nitrite-NO pathway, which is an alternative pathway for NO formation. This study aimed at investigating the acute effects of inorganic nitrate on glucose and insulin signaling in adenosine A2B receptor knockout mice (A−/−2B), a genetic mouse model of impaired metabolic regulation. Methods: Acute effects of nitrate treatment were investigated in aged wild-type (WT) and A−/−2B mice. One hour after injection with nitrate (0.1 mmol/kg, i.p.) or placebo, metabolic regulation was evaluated by intraperitoneal glucose and insulin tolerance tests. NADPH oxidase-mediated superoxide production and AMPK phosphorylation were measured in livers obtained from non-treated or glucose-treated mice, with or without prior nitrate injection. Plasma was used to determine insulin resistance (HOMA-IR) and NO signaling. Results: A−/−2B displayed increased body weight, reduced glucose clearance, and attenuated overall insulin responses compared with age-matched WT mice. Nitrate treatment increased circulating levels of nitrate, nitrite and cGMP in the A−/−2B, and improved glucose clearance. In WT mice, however, nitrate treatment did not influence glucose clearance. HOMA-IR increased following glucose injection in the A−/−2B, but remained at basal levels in mice pretreated with nitrate. NADPH oxidase activity in livers from A−/−2B, but not WT mice, was reduced by nitrate treatment. Livers from A−/−2B displayed reduced AMPK phosphorylation compared with WT mice, and this was increased by nitrate treatment. Finally, injection with the anti-diabetic agent metformin induced similar therapeutic effects in the A−/−2B as observed with nitrate. Conclusion: The A−/−2B mouse is a genetic mouse model of metabolic syndrome. Acute treatment

  5. A2B adenosine receptors mediate relaxation of the pig intravesical ureter: adenosine modulation of non adrenergic non cholinergic excitatory neurotransmission

    PubMed Central

    Hernández, Medardo; Barahona, María Victoria; Bustamante, Salvador; García-Sacristán, Albino; Orensanz, Luis M

    1999-01-01

    or NO, through activation of A2B-receptors located in the smooth muscle. This relaxation may modulate the ureteral NANC excitatory neurotransmission through a postsynaptic mechanism. PMID:10193777

  6. Particle-Tracking Velocimetric Investigation of Large Amplitude Oscillatory Shear of Entangled Polymer Melts

    NASA Astrophysics Data System (ADS)

    Zartman, Gregory; Wang, Yangyang; Wang, Shi-Qing

    2009-03-01

    Large amplitude oscillatory shear (LAOS) experiments were carried out on a series of entangled monodisperse styrene-butadiene random copolymers (SBR). The deformation field during the measurements was monitored with a particle-tracking velocimetric technique. It was found that when the applied frequency was higher than the overall relaxation rate of the sample, the entangled melt would undergo uniform deformation at small strains, but exhibit shear banding at large strains. The inhomogeneity of the deformation field suggests that yielding through chain disentanglement cannot take place uniformly. This is the first report of shear banding in LAOS for melts and consequently rules out any speculation that shear banding could originate from concentration variation (due to shear induced phase separation) in entangled solutions.

  7. New modified hydrocarbon resins; An alternative to styrenated terpene resins in hot melts

    SciTech Connect

    Carper, J.D. )

    1990-06-01

    This paper reports on the development of two hydrocarbon-based resin formulations that could be used with different thermoplastic block copolymers to formulate pressure-sensitive adhesives. Results are examined with one of these resins in formulations with styrene-isoprene-styrene (SIS) and styrene-butadiene (SB) compounds. The new modified hydrocarbon resin, with a softening point of 98{degrees} C, matches the adhesive performance of a terpene resin with a softening point of 105{degrees} C. The resin performs as well as the modified terpene in SIS-, SB-, and EVA-based adhesives. The new hydrocarbon resin is especially well suited for hot-melt adhesives. It exhibits low volatility, good color stability, and excellent melt viscosity stability. Since the new resin is based on petroleum hydrocarbon feedstocks, it should be available at moderate, stable prices. The other hydrocarbon resin, with a softening point of 85{degrees} C, produced comparable results.

  8. Quantifying melting and mobilistaion of interstitial melts in crystal mushes

    NASA Astrophysics Data System (ADS)

    Veksler, Ilya; Dobson, Katherine; Hess, Kai-Uwe; Ertel-Ingrisch, Werner; Humphreys, Madeleine

    2015-04-01

    The deformation of crystals mushes and separation of melts and crystals in is critical to understanding the development of physical and chemical heterogeneity in magma chambers and has been invoked as an eruption trigger mechanism. Here we investigate the behaviour of the melt in the well characterised, classic crystal mush system of the Skaergaard intrusion by combining experimental petrology and the non-destructive 3D imaging methods. Starting materials for partial melting experiments were four samples from the upper Middle Zone of the Layered Series. Cylinders, 15 mm in diameter and 20 mm in length, were drilled out of the rock samples, placed in alumina crucibles and held for 5 days in electric furnaces at atmospheric pressure and 1050-1100 °C. Redox conditions set by the CO-CO2 gas mixture were kept close to those of the FMQ buffer. We then use spatially registered 3D x-ray computed tomography images, collected before and after the experiment, to determine the volume and distribution of the crystal framework and interstitial phases, and the volume, distribution and connectivity the interstitial phases that undergo melting and extraction while at elevated temperature. Image analysis has allowed us to quantify these physical changes with high spatial resolution. Our work is a first step towards quantitative understanding of the melt mobilisation and migration processes operating in notionally locked crystal rich magmatic systems.

  9. Methods for Melting Temperature Calculation

    NASA Astrophysics Data System (ADS)

    Hong, Qi-Jun

    Melting temperature calculation has important applications in the theoretical study of phase diagrams and computational materials screenings. In this thesis, we present two new methods, i.e., the improved Widom's particle insertion method and the small-cell coexistence method, which we developed in order to capture melting temperatures both accurately and quickly. We propose a scheme that drastically improves the efficiency of Widom's particle insertion method by efficiently sampling cavities while calculating the integrals providing the chemical potentials of a physical system. This idea enables us to calculate chemical potentials of liquids directly from first-principles without the help of any reference system, which is necessary in the commonly used thermodynamic integration method. As an example, we apply our scheme, combined with the density functional formalism, to the calculation of the chemical potential of liquid copper. The calculated chemical potential is further used to locate the melting temperature. The calculated results closely agree with experiments. We propose the small-cell coexistence method based on the statistical analysis of small-size coexistence MD simulations. It eliminates the risk of a metastable superheated solid in the fast-heating method, while also significantly reducing the computer cost relative to the traditional large-scale coexistence method. Using empirical potentials, we validate the method and systematically study the finite-size effect on the calculated melting points. The method converges to the exact result in the limit of a large system size. An accuracy within 100 K in melting temperature is usually achieved when the simulation contains more than 100 atoms. DFT examples of Tantalum, high-pressure Sodium, and ionic material NaCl are shown to demonstrate the accuracy and flexibility of the method in its practical applications. The method serves as a promising approach for large-scale automated material screening in which

  10. Block Copolymer Templates for Optical Materials and Devices

    NASA Astrophysics Data System (ADS)

    Urbas, Augustine; Martin, Maldovan; Carter, W. C.; Thomas, E. L.; Fasolka, Michael; Fraser, Cassandra

    2002-03-01

    Block copolymers can act as super-lattices for creating novel optical structures. We have fabricated block copolymer photonic crystals from one, two and three dimensionally periodic systems and have enhanced their dielectric properties towards creating complete 3D band gaps. By using carefully selected blends of linear and star block copolymers, we are able to create hierarchical blends which exhibit precise molecular positioning of fluorescent molecules. We are exploring these unique patterning capabilities of block copolymer systems for the formation of ordered arrays of optically active components within a photonic crystal. Precise location of both fluorescent and nonlinear components within block copolymer photonic crystals affords new opportunities for creating low threshold, upconverting and array lasers as well as optical modulators and other photonic devices.

  11. Light-emitting block copolymers composition, process and use

    DOEpatents

    Ferraris, John P.; Gutierrez, Jose J.

    2006-11-14

    Generally, and in one form, the present invention is a composition of light-emitting block copolymer. In another form, the present invention is a process producing a light-emitting block copolymers that intends polymerizing a first di(halo-methyl) aromatic monomer compound in the presence of an anionic initiator and a base to form a polymer and contacting a second di(halo-methyl) aromatic monomer compound with the polymer to form a homopolymer or block copolymer wherein the block copolymer is a diblock, triblock, or star polymer. In yet another form, the present invention is an electroluminescent device comprising a light-emitting block copolymer, wherein the electroluminescent device is to be used in the manufacturing of optical and electrical devices.

  12. Preparation and Morphology of ABn Mictoarm Block Copolymers

    NASA Astrophysics Data System (ADS)

    Takano, Atsushi; Watanabe, Momoka; Asai, Yusuke; Suzuki, Jiro; Matsushita, Yushu

    A series of ABn mictoarm block copolymers (bottle brush copolymers) consisting of polystyrene (S) as a backbone and polyisoprenes (I) as grafts were precisely synthesized by an anionic polymerization, and their microphase-separated structures were investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering(SAXS). A copolymer with composition of φS =0.57 and number of grafts(n) of 10 shows characteristic cylindrical structure, where microdomains of S reveals hexagonal cross section with non-constant mean curvature interface. While a sample with composition of φS =0.37 and number of grafts(n) of 40 shows spherical structure with rather large S isolated domains and characteristic domain packing manner was found. Furthermore composition dependence of microphase-separated structures for SIn mictoarm block copolymers were investigated and compared to SI diblock copolymer system.

  13. Materials Design for Block Copolymer Lithography

    NASA Astrophysics Data System (ADS)

    Sweat, Daniel Patrick

    Block copolymers (BCPs) have attracted a great deal of scientific and technological interest due to their ability to spontaneously self-assemble into dense periodic nanostructures with a typical length scale of 5 to 50 nm. The use of self-assembled BCP thin-films as templates to form nanopatterns over large-area is referred to as BCP lithography. Directed self-assembly of BCPs is now viewed as a viable candidate for sub-20 nm lithography by the semiconductor industry. However, there are multiple aspects of assembly and materials design that need to be addressed in order for BCP lithography to be successful. These include substrate modification with polymer brushes or mats, tailoring of the block copolymer chemistry, understanding thin-film assembly and developing epitaxial like methods to control long range alignment. The rational design, synthesis and self-assembly of block copolymers with large interaction parameters (chi) is described in the first part of this dissertation. Two main blocks were chosen for introducing polarity into the BCP system, namely poly(4-hydroxystyrene) and poly(2-vinylpyridine). Each of these blocks are capable of ligating Lewis acids which can increase the etch contrast between the blocks allowing for facile pattern transfer to the underlying substrate. These BCPs were synthesized by living anionic polymerization and showed excellent control over molecular weight and dispersity, providing access to sub 5-nm domain sizes. Polymer brushes consist of a polymer chain with one end tethered to the surface and have wide applicability in tuning surface energy, forming responsive surfaces and increasing biocompatibility. In the second part of the dissertation, we present a universal method to grow dense polymer brushes on a wide range of substrates and combine this chemistry with BCP assembly to fabricate nanopatterned polymer brushes. This is the first demonstration of introducing additional functionality into a BCP directing layer and opens up

  14. Melting chocolate and melting snowmen: analogical reasoning and causal relations.

    PubMed

    Goswami, U; Brown, A L

    1990-04-01

    Children's performance in the classical a:b::c:d analogy task is traditionally very poor prior to the Piagetian stage of formal operations. The interpretation has been that the ability to reason about higher-order relations (the relations between the a:b and c:d parts of the analogy) is late-developing. However, an alternative possibility is that the relations used to date in the analogies are too difficult for younger children. Two experiments presented children aged 3, 4 and 6 years with a:b::c:d analogies which were based on relations of physical causality such as melting and cutting, for example chocolate bar:melted chocolate::snowman:melted snowman. Understanding of these particular causal relations is known to develop between the ages of 3 and 4 years. It was found that even 3-year-olds could solve the classical analogies if they understood the causal relations on which they were based. PMID:2340713

  15. Fluctuation Dynamics of Block Copolymer Vesicles

    SciTech Connect

    Falus, P.; Borthwick, M.A.; Mochrie, S.G.J.

    2010-07-13

    X-ray photon correlation spectroscopy was used to characterize the wave-vector- and temperature-dependent dynamics of spontaneous thermal fluctuations in a vesicle (L4) phase that occurs in a blend of a symmetric poly(styrene-ethylene/butylene-styrene) triblock copolymer with a polystyrene homopolymer. Measurements of the intermediate scattering function reveal stretched-exponential behavior versus time, with a stretching exponent slightly larger than 2/3. The corresponding relaxation rates show an approximate q{sup 3} dependence versus wave vector. Overall, the experimental measurements are well described by theories that treat the dynamics of independent membrane plaquettes.

  16. Oriented Protein Nanoarrays on Block Copolymer Template.

    PubMed

    Shen, Lei; Zhu, Jintao

    2016-03-01

    Here, a simple yet robust method is developed to fabricate oriented protein nanoarrays by employing a block copolymer (BCP) template, which presents nano-scaled spot areas at high-density arrays. Unlike the conventional BCP nanolithography, the BCP platform described here resists nonspecific protein adsorption and prevents the denaturation of immobilized proteins in aqueous solution. The orderly arranged array areas are functionalized by linking chemistry which allows for the precise control of protein orientation. This approach allows us to generate potentially oriented protein nanoarrays at high-density array spots, which is useful for miniaturized nanoarrays within high-throughput proteomic applications. PMID:26785818

  17. A amphoteric copolymer profile modification agent

    SciTech Connect

    Wang HongGuan; Yu LianCheng; Tian HongKun

    1995-11-01

    This report provides a new gel profile modification agent prepared by an amphoteric copolymer (FT-213) and a novel crosslinking agent (BY), and introduces the preparations of the amphoteric polymer, the crosslinking agent and the profile modification agent, the action mechanism, the test conditions and the evaluations of the performance of the agent. The 45 well treatments in oilfields demonstrate that the agent can be prepared conveniently, the agent has better compatibility and application performances, and the treatment life is longer with the use of the agent. 80,000 tons incremental oil and 60,000 m{sup 3} decreasing water production have been achieved.

  18. 21 CFR 175.365 - Vinylidene chloride copolymer coatings for polycarbonate film.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 3 2013-04-01 2013-04-01 false Vinylidene chloride copolymer coatings for... chloride copolymer coatings for polycarbonate film. Vinylidene chloride copolymer coatings identified in... chapter. (b) The coatings are prepared from vinylidene chloride copolymers produced by...

  19. 21 CFR 175.365 - Vinylidene chloride copolymer coatings for polycarbonate film.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 3 2011-04-01 2011-04-01 false Vinylidene chloride copolymer coatings for... chloride copolymer coatings for polycarbonate film. Vinylidene chloride copolymer coatings identified in... chapter. (b) The coatings are prepared from vinylidene chloride copolymers produced by...

  20. 21 CFR 175.365 - Vinylidene chloride copolymer coatings for polycarbonate film.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 3 2012-04-01 2012-04-01 false Vinylidene chloride copolymer coatings for... chloride copolymer coatings for polycarbonate film. Vinylidene chloride copolymer coatings identified in... chapter. (b) The coatings are prepared from vinylidene chloride copolymers produced by...

  1. Impact melt generation and transport

    NASA Technical Reports Server (NTRS)

    Orphal, D. L.; Borden, W. F.; Larson, S. A.; Schultz, P. H.

    1980-01-01

    The results from the first two calculations in a series of continuum mechanics computer code calculations, investigating the effects of variations in impactor mass and velocity on the generation and transport of impact melt, are reported. In the present calculations, the impactor is modeled as a spherical iron projectile with a mass of one trillion grams, and the target as a gabbroic anorthosite (GA) half-space, where the cases calculated have impact velocities of 5 and 15.8 km/sec. Early-time ejection velocities are 1-2 km/sec in both cases. The first calculation results in 0.07 projectile masses of GA being partly or completely melted, with all the melted GA being ejected from the crater, and a maximum impact range for the ejected melted material of 30 km. The second calculation yields 10.4 projectile masses of melted GA, 50% of which is ejected from the crater to ranges of up to about 130 km. Peak shock pressure attenuation with depth is reported for both cases, and transient cavity dynamics are described and compared to that for surface and near-surface explosions.

  2. Melting in temperature sensitive suspensions

    NASA Astrophysics Data System (ADS)

    Alsayed, Ahmed M.

    We describe two experimental studies about melting in colloidal systems. In particular we studied melting of 1-dimensional lamellar phases and 3-dimensional colloidal crystals. In the first set of experiments we prepared suspensions composed of rodlike fd virus and the thermosensitive polymer, poly(N-isopropylacrylamide). The phase diagram of this systems is temperature and concentration dependent. Using video microscopy, we directly observed melting of lamellar phases and single lamellae into nematic phase. We found that lamellar phases swell with increasing temperature before melting into the nematic phase. The highly swollen lamellae can be superheated as a result of topological nucleation barriers that slow the formation of the nematic phase. In another set of experiments we prepared colloidal crystals from thermally responsive microgel spheres. The crystals are equilibrium close-packed three-dimensional structures. Upon increasing the temperature slightly above room temperature, particle volume fraction decreased from 0.74 to less than 0.5. Using video microscopy, we observed premelting at grain boundaries and dislocations within bulk colloidal crystals. Premelting is the localized loss of crystalline order at surfaces and defects at sample volume fractions above the bulk melting transition. Particle tracking revealed increased disorder in crystalline regions bordering defects, the amount of which depends on the type of defect, distance from the defect, and particle volume fraction. In total these observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and in atomic scale crystals.

  3. Thermodynamics of freezing and melting

    PubMed Central

    Pedersen, Ulf R.; Costigliola, Lorenzo; Bailey, Nicholas P.; Schrøder, Thomas B.; Dyre, Jeppe C.

    2016-01-01

    Although the freezing of liquids and melting of crystals are fundamental for many areas of the sciences, even simple properties like the temperature–pressure relation along the melting line cannot be predicted today. Here we present a theory in which properties of the coexisting crystal and liquid phases at a single thermodynamic state point provide the basis for calculating the pressure, density and entropy of fusion as functions of temperature along the melting line, as well as the variation along this line of the reduced crystalline vibrational mean-square displacement (the Lindemann ratio), and the liquid's diffusion constant and viscosity. The framework developed, which applies for the sizable class of systems characterized by hidden scale invariance, is validated by computer simulations of the standard 12-6 Lennard-Jones system. PMID:27530064

  4. Generalized melting criterion for amorphization

    SciTech Connect

    Devanathan, R. |; Lam, N.Q.; Okamoto, P.R.; Meshii, M.

    1992-12-01

    We present a thermodynamic model of solid-state amorphization based on a generalization of the well-known Lindemann criterion. The original Lindemann criterion proposes that melting occurs when the root-mean-square amplitude of thermal displacement exceeds a critical value. This criterion can be generalized to include solid-state amorphization by taking into account the static displacements. In an effort to verify the generalized melting criterion, we have performed molecular dynamics simulations of radiation-induced amorphization in NiZr, NiZr{sub 2}, NiTi and FeTi using embedded-atom potentials. The average shear elastic constant G was calculated as a function of the total mean-square atomic displacement following random atom-exchanges and introduction of Frenkel pairs. Results provide strong support for the generalized melting criterion.

  5. Thermodynamics of freezing and melting.

    PubMed

    Pedersen, Ulf R; Costigliola, Lorenzo; Bailey, Nicholas P; Schrøder, Thomas B; Dyre, Jeppe C

    2016-01-01

    Although the freezing of liquids and melting of crystals are fundamental for many areas of the sciences, even simple properties like the temperature-pressure relation along the melting line cannot be predicted today. Here we present a theory in which properties of the coexisting crystal and liquid phases at a single thermodynamic state point provide the basis for calculating the pressure, density and entropy of fusion as functions of temperature along the melting line, as well as the variation along this line of the reduced crystalline vibrational mean-square displacement (the Lindemann ratio), and the liquid's diffusion constant and viscosity. The framework developed, which applies for the sizable class of systems characterized by hidden scale invariance, is validated by computer simulations of the standard 12-6 Lennard-Jones system. PMID:27530064

  6. Partial Melting of the Indarch (EH4) Meteorite : A Textural, Chemical and Phase Relations View of Melting and Melt Migration

    NASA Technical Reports Server (NTRS)

    McCoy, Timothy J.; Dickinson, Tamara L.; Lofgren, Gary E.

    2000-01-01

    To Test whether Aubrites can be formed by melting of enstatite Chondrites and to understand igneous processes at very low oxygen fugacities, we have conducted partial melting experiments on the Indarch (EH4) chondrite at 1000-1500 C. Silicate melting begins at 1000 C. Substantial melt migration occurs at 1300-1400 C and metal migrates out of the silicate change at 1450 C and approx. 50% silicate partial melting. As a group, our experiments contain three immiscible metallic melts 9Si-, and C-rich), two immiscible sulfide melts(Fe-and FeMgMnCa-rich) and Silicate melt. Our partial melting experiments on the Indarch (EH4) enstatite Chondrite suggest that igneous processes at low fO2 exhibit serveral unique features. The complete melting of sulfides at 1000 C suggest that aubritic sulfides are not relicts. Aubritic oldhamite may have crystallized from Ca and S complexed in the silicate melt. Significant metal-sulfide melt migration might occur at relatively low degrees of silicate partial melting. Substantial elemental exchange occurred between different melts (e.g., between sulfide and silicate, Si between silicate and metal), a feature not observed during experiments at higher fO2. This exchange may help explain the formation of aubrites from known enstatite chondrites.

  7. Anomalous Micellization of Pluronic Block Copolymers

    NASA Astrophysics Data System (ADS)

    Leonardi, Amanda; Ryu, Chang Y.

    2014-03-01

    Poly(ethylene oxide) - poly(propylene oxide) - poly(ethylene oxide) (PEO-PPO-PEO) block copolymers, commercially known as Pluronics, are a unique family of amphiphilic triblock polymers, which self-assemble into micelles in aqueous solution. These copolymers have shown promise in therapeutic, biomedical, cosmetic, and nanotech applications. As-received samples of Pluronics contain low molecular weight impurities (introduced during the manufacturing and processing), that are ignored in most applications. It has been observed, however, that in semi-dilute aqueous solutions, at concentrations above 1 wt%, the temperature dependent micellization behavior of the Pluronics is altered. Anomalous behavior includes a shift of the critical micellization temperature and formation of large aggregates at intermediate temperatures before stable sized micelles form. We attribute this behavior to the low molecular weight impurities that are inherent to the Pluronics which interfere with the micellization process. Through the use of Dynamic Light Scattering and HPLC, we compared the anomalous behavior of different Pluronics of different impurity levels to their purified counterparts.

  8. Block copolymer ion gels for gas separation

    NASA Astrophysics Data System (ADS)

    Gu, Yuanyan; Lodge, Timothy

    2012-02-01

    Carbon dioxide removal from light gases (eg. N2, CH4, and H2) is a very important technology for industrial applications such as natural gas sweetening, CO2 capture from coal-fire power plant exhausts and hydrogen production. Current CO2 separation method uses amine-absorption, which is energy-intensive and requires frequent maintenance. Membrane separation is a cost-effective solution to this problem, especially in small-scale applications. Ionic liquids have recently received increasing interest in this area because of their selective solubility for CO2 and non-volatility. However, ionic liquid itself lacks the persistent structure and mechanical integrity to withstand the high pressure for gas separation. Here, we report the development and gas separation performances of physically crosslinked ion gels based on self-assembly of ABA-triblock copolymers in ionic liquids. Three different types of polymers was used to achieve gelation in ionic liquids. Specifically, a triblock copolymer ion gel with a polymerized ionic liquid mid-block shows performances higher than the upper bound of well-known ``Robeson Plot'' for CO2/N2.

  9. Chain exchange in triblock copolymer micelles

    NASA Astrophysics Data System (ADS)

    Lu, Jie; Lodge, Timothy; Bates, Frank

    2015-03-01

    Block polymer micelles offer a host of technological applications including drug delivery, viscosity modification, toughening of plastics, and colloidal stabilization. Molecular exchange between micelles directly influences the stability, structure and access to an equilibrium state in such systems and this property recently has been shown to be extraordinarily sensitive to the core block molecular weight in diblock copolymers. The dependence of micelle chain exchange dynamics on molecular architecture has not been reported. The present work conclusively addresses this issue using time-resolved small-angle neutron scattering (TR-SANS) applied to complimentary S-EP-S and EP-S-EP triblock copolymers dissolved in squalane, a selective solvent for the EP blocks, where S and EP refer to poly(styrene) and poly(ethylenepropylene), respectively. Following the overall SANS intensity as a function of time from judiciously deuterium labelled polymer and solvent mixtures directly probes the rate of molecular exchange. Remarkably, the two triblocks display exchange rates that differ by approximately ten orders of magnitude, even though the solvophobic S blocks are of comparable size. This discovery is considered in the context of a model that successfully explains S-EP diblock exchange dynamics.

  10. Interface-enforced complexation between copolymer blocks.

    PubMed

    Steinschulte, Alexander A; Xu, Weinan; Draber, Fabian; Hebbeker, Pascal; Jung, Andre; Bogdanovski, Dimitri; Schneider, Stefanie; Tsukruk, Vladimir V; Plamper, Felix A

    2015-05-14

    Binary diblock copolymers and corresponding ternary miktoarm stars are studied at oil-water interfaces. All polymers contain oil-soluble poly(propylene oxide) PPO, water-soluble poly(dimethylaminoethyl methacrylate) PDMAEMA and/or poly(ethylene oxide) PEO. The features of their Langmuir compression isotherms are well related to the ones of the corresponding homopolymers. Within the Langmuir-trough, PEO-b-PPO acts as the most effective amphiphile compared to the other PPO-containing copolymers. In contrast, the compression isotherms show a complexation of PPO and PDMAEMA for PPO-b-PDMAEMA and the star, reducing their overall amphiphilicity. Such complex formation between the blocks of PPO-b-PDMAEMA is prevented in bulk water but facilitated at the interface. The weakly-interacting blocks of PPO-b-PDMAEMA form a complex due to their enhanced proximity in such confined environments. Scanning force microscopy and Monte Carlo simulations with varying confinement support our results, which are regarded as compliant with the mathematical random walk theorem by Pólya. Finally, the results are expected to be of relevance for e.g. emulsion formulation and macromolecular engineering. PMID:25807174

  11. Controlling Structure in Sulfonated Block Copolymer Membranes

    NASA Astrophysics Data System (ADS)

    Truong, Phuc; Stein, Gila; Strzalka, Joe

    2015-03-01

    In many ionic block copolymer systems, the strong incompatibility between ionic and non-ionic segments will trap non-equilibrium structures in the film, making it difficult to engineer the optimal domain sizes and transport pathways. The goal of this work is to establish a framework for controlling the solid-state structure of sulfonated pentablock copolymer membranes. They have ABCBA block sequence, where A is poly(t-butyl styrene), B is poly(hydrogenated isoprene), and C is poly(styrene sulfonate). To process into films, the polymer is dissolved in toluene/n-propanol solvent mixtures, where the solvent proportions and the polymer loading were both varied. Solution-state structure was measured with small angle X-ray scattering (SAXS). We detected micelles with radii that depend on the solvent composition and polymer loading. Film structure was measured with grazing-incidence SAXS, which shows (i) domain periodicity is constant throughout film thickness; (ii) domain periodicity depends on solvent composition and polymer loading, and approximately matches the micelle radii in solutions. The solid-state packing is consistent with a hard sphere structure factor. Results suggest that solid-state structure can be tuned by manipulating the solution-state self-assembly.

  12. Challenges in Melt Furnace Tests

    NASA Astrophysics Data System (ADS)

    Belt, Cynthia

    2014-09-01

    Measurement is a critical part of running a cast house. Key performance indicators such as energy intensity, production (or melt rate), downtime (or OEE), and melt loss must all be understood and monitored on a weekly or monthly basis. Continuous process variables such as bath temperature, flue temperature, and furnace pressure should be used to control the furnace systems along with storing the values in databases for later analysis. While using measurement to track furnace performance over time is important, there is also a time and place for short-term tests.

  13. Sequence-Specific Copolymer Compatibilizers designed via a Genetic Algorithm

    NASA Astrophysics Data System (ADS)

    Meenakshisundaram, Venkatesh; Patra, Tarak; Hung, Jui-Hsiang; Simmons, David

    For several decades, block copolymers have been employed as surfactants to reduce interfacial energy for applications from emulsification to surface adhesion. While the simplest approach employs symmetric diblocks, studies have examined asymmetric diblocks, multiblock copolymers, gradient copolymers, and copolymer-grafted nanoparticles. However, there exists no established approach to determining the optimal copolymer compatibilizer sequence for a given application. Here we employ molecular dynamics simulations within a genetic algorithm to identify copolymer surfactant sequences yielding maximum reductions the interfacial energy of model immiscible polymers. The optimal copolymer sequence depends significantly on surfactant concentration. Most surprisingly, at high surface concentrations, where the surfactant achieves the greatest interfacial energy reduction, specific non-periodic sequences are found to significantly outperform any regularly blocky sequence. This emergence of polymer sequence-specificity within a non-sequenced environment adds to a recent body of work suggesting that specific sequence may have the potential to play a greater role in polymer properties than previously understood. We acknowledge the W. M. Keck Foundation for financial support of this research.

  14. Using Tapered Block Copolymers to Create Conducting Nanomaterials

    NASA Astrophysics Data System (ADS)

    Epps, Thomas, III

    2014-03-01

    Soft materials, such as polymers, colloids, surfactants, and liquid crystals, are a technologically important class of matter employed in a variety of applications. One sub-class of soft material, block copolymers, provides the opportunity to design materials with attractive chemical and mechanical properties based on the ability to assemble into periodic structures with nanoscale domain spacings. Several applications for block copolymers currently under investigation in my group include battery and fuel cell membranes, analytical separations membranes, nano-tool templates, precursors to electronic arrays, and drug delivery vehicles. One area of recent progress in the group focuses on the behavior of conventional block copolymer and tapered block copolymer systems for lithium battery membrane applications. We find that we can tune poly(styrene- b-ethylene oxide) diblock copolymer nanostructures by adjusting the lithium counterion and lithium salt concentration, as well as the taper volume fraction and composition. Additionally, we can estimate the effective interaction parameters (χeff) for the salt-doped copolymers to determine the overall influence of tapering on the energetics of copolymer assembly. These tapered materials allow us to design nanostructured membrane systems with increased conductivity and improved mechanical properties in ion transport devices. We gratefully acknowledge AFOSR-PECASE (FA9550-09-1-0706) and NSF-CAREER (DMR-0645586) for financial support.

  15. Effects of Blockiness on the phase behavior of random copolymers

    NASA Astrophysics Data System (ADS)

    Vanderwoude, Gordon; Shi, An-Chang

    Theoretical study of random block copolymers remains a challenging topic due in part to the sheer enormity of their phase space. In this study we use the self-consistent field theory to investigate the phase behaviour of linear (AB)n-type and (AB)n-C-type multiblock copolymers with randomly distributed A and B blocks. In particular, we examine the effect of ``blockiness'' of the random copolymers on the formation of ordered phases. The blockiness can be quantified by the average length of individual A or B blocks, which can be taken as a measure of the heterogeneity of the random copolymers. We observed that the critical value of the χ parameter, at which the order-disorder transition occurs, decreases with increasing blockiness in the (AB)n copolymers. We also observed that the phase behaviour of the (AB)n-C copolymers depends strongly on the blockiness of the random chain. In particular, the blockiness governs whether or not the A/B blocks can phase separate within the A/B domains, thus dictating whether the (AB)n-C behaves as A/B-C diblock copolymers or as ABC terpolymers. The theoretical phase diagrams will be compared with available experiments.

  16. Tribological Behavior of Aqueous Copolymer Lubricant in Mixed Lubrication Regime.

    PubMed

    Ta, Thi D; Tieu, A Kiet; Zhu, Hongtao; Zhu, Qiang; Kosasih, Prabouno B; Zhang, Jie; Deng, Guanyu

    2016-03-01

    Although a number of experiments have been attempted to investigate the lubrication of aqueous copolymer lubricant, which is applied widely in metalworking operations, a comprehensive theoretical investigation at atomistic level is still lacking. This study addresses the influence of loading pressure and copolymer concentration on the structural properties and tribological performance of aqueous copolymer solution of poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO) at mixed lubrication using a molecular dynamic (MD) simulation. An effective interfacial potential, which has been derived from density functional theory (DFT) calculations, was employed for the interactions between the fluid's molecules and iron surface. The simulation results have indicated that the triblock copolymer is physisorption on iron surface. Under confinement by iron surfaces, the copolymer molecules form lamellar structure in aqueous solution and behave differently from its bulk state. The lubrication performance of aqueous copolymer lubricant increases with concentration, but the friction reduction is insignificant at high loading pressure. Additionally, the plastic deformation of asperity is dependent on both copolymer concentration and loading pressure, and the wear behavior shows a linear dependence of friction force on the number of transferred atoms between contacting asperities. PMID:26828119

  17. Manipulating Ordering Transitions in Interfacially Modified Block Copolymers

    SciTech Connect

    Singh, N.; Tureau, M; Epps, T

    2009-01-01

    We report a synthetic strategy that allows us to manipulate the interfacial region between blocks and control ordering transitions in poly(isoprene-b-styrene) [P(I-S)] block copolymers. This interfacial modification is accomplished by combining a semi-batch feed with anionic polymerization techniques. Using this approach, we are able to control the segmental composition and molecular interactions in our phase-separated block copolymers, independent of molecular weight and block constituents. A library of copolymers is prepared with various interfacial modifications to examine the effect of interfacial composition on copolymer self-assembly. The morphological characteristics of the self-assembled structures are investigated using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and dynamic mechanical analysis (DMA). Normal and inverse tapered block copolymers, containing approximately 15-35 vol% tapered material, show a measurable decrease in the order-disorder transition temperature (TODT) relative to the corresponding non-tapered diblock copolymers, with the inverse tapered materials showing the greatest deviation in TODT. Additionally, TODT was inversely related to the volume fraction of the tapered region in both normal and inverse tapered copolymer materials.

  18. A comparison of two different methods for formation of the beta phase in nanocomposites based on vinylidene fluoride-hexafluoropropylene copolymer

    NASA Astrophysics Data System (ADS)

    Borisova, Lyudmila; Kiryakova, Dimitrina; Atanassov, Atanas

    2014-06-01

    Nanocomposite materials based on vinylidene fluoride-hexafluoropropylene copolymer and organically modified montmorillonite Cloisite®15A were prepared by two different methods: melt mixing and co-precipitation. The changes taking place in crystalline structure, tensile strength, thermal behavior and the formation of piezoelectric b-phase as a result of the polymer system dissolution in dimethyl sulfoxide were studied. The technological specificity of each method has certain effect on the properties of the obtained nanocomposites. The highest content of b-phase — 95 % was achieved by co-precipitation from the solution of vinylidene fluoride-hexafluoropropylene copolymer in dimethyl sulfoxide and 6 mass % content of Cloisite®15A. Despite the common view that the use of solvents and prolonged technological procedure lead to overall higher expenses, the obtained nanocomposites could be promising for the preparation of new piezo-materials.

  19. Nanopatterning of recombinant proteins and viruses using block copolymer templates

    NASA Astrophysics Data System (ADS)

    Cresce, Arthur Von Wald

    The study of interfaces is important in understanding biological interactions, including cellular signaling and virus infection. This thesis is an original effort to examine the interaction between a block copolymer and both a protein and a virus. Block copolymers intrinsically form nanometer-scale structures over large areas without expensive processing, making them ideal for the synthesis of the nanopatterned surfaces used in this study. The geometry of these nanostructures can be easily tuned for different applications by altering the block ratio and composition of the block copolymer. Block copolymers can be used for controlled uptake of metal ions, where one block selectively binds metal ions while the other does not. 5-norbornene-2,3-dicarboxylic acid is synthesized through ring-opening metathesis polymerization. It formed spherical domains with spheres approximately 30 nm in diameter, and these spheres were then subsequently loaded with nickel ion. This norbornene block copolymer was tested for its ability to bind histidine-tagged green fluorescent protein (hisGFP), and it was found that the nickel-loaded copolymer was able to retain hisGFP through chelation between the histidine tag and the metal-containing portions of the copolymer surface. Poly(styrene-b-4-vinylpyridine) (PS/P4VP) was also loaded with nickel, forming a cylindrical microstructure. The binding of Tobacco mosaic virus and Tobacco necrosis virus was tested through Tween 20 detergent washes. Electron microscopy allowed for observation of both block copolymer nanostructures and virus particles. Results showed that Tween washes could not remove bound Tobacco mosaic virus from the surface of PS/P4VP. It was also seen that the size and tunability of block copolymers and the lack of processing needed to attain different structures makes them attractive for many applications, including microfluidic devices, surfaces to influence cellular signaling and growth, and as a nanopatterning surface for

  20. Stabilization of fenofibrate in low molecular weight hydroxypropylcellulose matrices produced by hot-melt extrusion.

    PubMed

    Deng, Weibin; Majumdar, Soumyajit; Singh, Abhilasha; Shah, Sejal; Mohammed, Noorullah Naqvi; Jo, Seongbong; Pinto, Elanor; Tewari, Divya; Durig, Thomas; Repka, Michael A

    2013-02-01

    The objective of this study was to improve the dissolution rate and to enhance the stability of a poorly water-soluble and low glass-trasition temperature (T(g)) model drug, fenofibrate, in low molecular weight grades of hydroxypropylcellulose matrices produced by hot-melt extrusion (HME). Percent drug loading had a significant effect on the extrudability of the formulations. Dissolution rate of fenofibrate from melt extruded pellets was faster than that of the pure drug (p < 0.05). Incorporation of sugars within the formulation further increased the fenofibrate release rates. Differential scanning calorimetry results revealed that the crystalline drug was converted into an amorphous form during the HME process. Fenofibrate is prone to recrystallization due to its low T(g). Various polymers were evaluated as stabilizing agents among which polyvinylpyrrolidone 17PF and amino methacrylate copolymer exhibited a significant inhibitory effect on fenofibrate recrystallization in the hot-melt extrudates. Subsequently immediate-release fenofibrate tablets were successfully developed and complete drug release was achieved within 5 min. The dissolution profile was comparable to that of a currently marketed formulation. The hot-melt extruded fenofibrate tablets were stable, and exhibited an unchanged drug release profile after 3-month storage at 40°C/75% RH. PMID:22524504

  1. Universality of elasticity on PAAM-NIPA copolymer gels

    NASA Astrophysics Data System (ADS)

    Akin Evingür, Gülşen; Pekcan, Önder

    2015-01-01

    Polyacrylamide (PAAm)-N-isopropylacrylamide (NIPA) copolymers were prepared via free radical crosslinking copolymerization with different molar of NIPA varying in the range between 0 and 2 M. The mechanical properties of swollen PAAm-NIPA copolymers were characterized by the compressive testing technique. It is understood that the compressive elastic modulus was found to increase by increasing NIPA contents, keeping temperature constant at 30 °C. The critical exponent of elasticity, y above the critical NIPA concentration is found to be as 0.74, which is consistent with the suggestions of percolation for superelastic percolation network (SEPN) and the critical theory for PAAm-NIPA copolymers.

  2. Transparent zero-birefringence copolymer and its optical properties.

    PubMed

    Iwata, S; Tsukahara, H; Nihei, E; Koike, Y

    1997-07-01

    Birefringence is caused by both orientation of polymer chains and photoelasticity. These birefringences were compensated by random copolymerization of negative birefringent methyl methacrylate and positive birefringent benzyl methacrylate, but orientational and photoelastic zero birefringences were achieved with quite different compositions of the copolymers. Note that the birefringence of the copolymer that occurred in the process of injection molding was almost completely eliminated with a composition for orientational zero birefringence. The orientational and photoelastic zero-birefringence copolymers possessed enough transparency as optical materials that the total scattering losses were 30.4 and 19.5 dB/km, respectively, competing with the transparency of homopolymers. PMID:18259249

  3. Macroscopic phase decomposition in block copolymers driven by thermooxidative reactions

    NASA Astrophysics Data System (ADS)

    Fan, Shaobin

    Macroscopic phase separations have been observed in a commercial styrene- block-butadiene-block-styrene (SBS) triblock copolymer (Kraton 1102), an as-synthesized SBS triblock copolymer, an as-synthesized styrene-block-butadiene (SB) diblock copolymer and a commercial styrene-block-isoprene-block-styrene (SIS) triblock copolymer (Kraton 1107) at elevated temperatures. To the best of our knowledge, this is the first report on macroscopic phase separations in neat copolymers, including block copolymers. The temporal evolution of the structure, growth dynamics, origin and mechanism of the macroscopic phase separations have been investigated. A theoretical model has been established to describe such phase separation in SB diblock copolymer and numerical simulations have been undertaken to predict the structure evolution and growth dynamics. For styrene-butadiene block copolymers, the phase transition process consists of the first and second phase separations. The origin of such phase separations is attributed to chain scission and crosslinking reactions due to thermooxidative degradation. The formation of phase separated domains is the result of separation of polystyrene-rich domains from polybutadiene-rich domains. A mechanism, termed secondary spinodal decomposition, has been proposed to explain second phase separation. It has also demonstrated that the theoretical model and numerical simulations capture the essential features of the experimental observations. Growth rate was seen to depend on phase separation as well as reaction kinetics. The universal scaling laws have been shown to be invalid in macroscopic phase separations of styrene-butadiene block copolymers. The macroscopic phase separation process is more complex in the SIS triblock copolymer. It consists of a first phase separation, phase dissolution and a second phase separation. The origin of such phase decompositions has been shown to be a progressive chain scission reaction during thermal oxidative

  4. Thin membranes of new hard/soft segment copolymers

    SciTech Connect

    Ho, W.S.; Sartori, G.; Thaler, W.A.

    1996-12-31

    Thin membranes of new hard/soft segment copolymers have been synthesized for the separation of aromatics from saturates through high temperature pervaporation. In the membranes, hard segments provide temperature stability and solvent resistance, while soft segments govern aromatic/saturate selectivity and flux. We have synthesized new chlorinated polyurethane/polyester and polyimide/polyester copolymers. Based on a polyimide copolymer membrane, a new technology has been developed recently to separate heavy catalytically cracked naphtha into an aromatics-rich permeate and an aromatics-lean retentate.

  5. Electrically conductive doped block copolymer of polyacetylene and polyisoprene

    DOEpatents

    Aldissi, Mahmoud

    1985-01-01

    An electrically conductive block copolymer of polyisoprene and polyacetyl and a method of making the same are disclosed. The polymer is prepared by first polymerizing isoprene with n-butyllithium in a toluene solution to form an active isoprenyllithium polymer. The active polymer is reacted with an equimolar amount of titanium butoxide and subsequently exposed to gaseous acetylene. A block copolymer of polyisoprene and polyacetylene is formed. The copolymer is soluble in common solvents and may be doped with I.sub.2 to give it an electrical conductivity in the metallic regime.

  6. Photocrosslinkable copolymers for non-linear optical applications

    SciTech Connect

    Kawatsuki, N.; Pakbaz, K.; Schmidt, H.W.

    1993-12-31

    New photocrosslinkable copolymers have been synthesized and applied as non-linear optical materials. The copolymers are based on methyl methacrylate, a photo-excitable benzophenone monomer, a non-linear optical active 4`-[(2-hydroxyethyl)ethylamino]-4-nitro-azobenzene (disperse red 1) side chain monomer and a crosslinkable 2-butenyl monomer. These copolymers can be crosslinked by UV light at 366 nm in the poled state and show a stable alignment of NLO chromophore by monitoring the adsorption spectra. The crosslinked and poled film did not change its alignment after storing 4 weeks at room temperature.

  7. Thermal properties of defect melting

    NASA Astrophysics Data System (ADS)

    Ami, S.; Hofsäss, T.; Horsley, R.

    1984-03-01

    Using mean field theory and high temperature expansions the transition temperature, entropy jump and heat capacity are calculated in the recent microscopic model of defect melting proposed by Kleinert. The results are compared with the experimental data for almost isotropic substances.

  8. Elongational rheology of polyethylene melts

    NASA Astrophysics Data System (ADS)

    Seyfzadeh, Bijan

    Elongational melt flow behavior is an important and fundamental concept underlying many industrial plastics operations which involve a rapid change of shape as for example fiber spinning and stretching, bottle blow molding, and film blowing and stretching. Under high process loads polymeric materials experience enormous stresses causing the molecular structure to gain considerable orientation. This event has significant effects on the melt flow behavior and can be measured in terms of elongational viscosity and changes in enthalpy and entropy. Different polymeric materials with unique molecular characteristics are expected to respond uniquely to the elongational deformation; hence, molecular parameters such as molecular weight and degree of branching were related to the measurable elongational flow variables. Elongational viscosities were measured for high and low density polyethylenes using an advanced capillary extrusion rheometer fitted with semi-hyperbolic dies. Said dies establish a purely elongational. flow field at constant elongational strain rate. The elongational viscosities were evaluated under influence of process strain rate, Hencky strain (natural logarithm of area reduction of the extrusion die), and temperature. Enthalpy and entropy changes associated with the orientation development of semi-hyperbolic processed melts were also determined. Results showed that elongational viscosities were primarily affected by differences in weight average molecular weight rather than degree of branching. This effect was process strain rate as well as temperature dependent. An investigation of melt relaxation and the associated first decay time constants revealed that with increasing strain rate the molecular field of the melt asymptotically gained orientation in approaching a limit. As a result of this behavior molecular uniqueness vanished at high process strain rates, yielding to orientation development and the associated restructuring of the melt's molecular

  9. The infidelity of melt inclusions?

    NASA Astrophysics Data System (ADS)

    Kent, A. J.

    2008-12-01

    Melt inclusions provide important information about magmatic systems and represent unique records of magma composition and evolution. However, it is also clear that melt inclusions do not necessarily constitute a petrological 'magic bullet', and potential exists for trapped melt compositions to be modified by a range of inclusion-specific processes. These include trapping of diffusional boundary layers, crystallization of the host mineral after trapping and dissolution of co-trapped minerals during homogenization, diffusional exchange between trapped liquid and the host mineral and external melt, and cryptic alteration of trapped material during weathering or hydrothermal alteration. It clearly important to identify when melt inclusions are unmodified, and which compositional indices represent the most robust sources of petrogenetic information. In this presentation I review and discuss various approaches for evaluating compositions and compositional variations in inclusion suites. An overriding principle is that the variations evident in melt inclusions should be able to be understood in terms of petrological processes that are known, or can be reasonably inferred to also effect bulk magma compositions. One common approach is to base petrological conclusions on species that should be more robust, and many workers use variations in incompatible trace elements for this purpose. However important information may also be obtained from a comparison of variations in melt inclusions and the lavas that host them, and in most cases this comparison is the key to identifying inclusions and suites that are potentially suspect. Comparisons can be made between individual inclusions and lavas, although comparison of average inclusion composition and the host lava, after correction for differences in crystal fractionation, may also be valuable. An important extension of this is the comparison of the variability of different species in inclusions and host lavas. This also provides

  10. Patchy micelles based on coassembly of block copolymer chains and block copolymer brushes on silica particles.

    PubMed

    Zhu, Shuzhe; Li, Zhan-Wei; Zhao, Hanying

    2015-04-14

    Patchy particles are a type of colloidal particles with one or more well-defined patches on the surfaces. The patchy particles with multiple compositions and functionalities have found wide applications from the fundamental studies to practical uses. In this research patchy micelles with thiol groups in the patches were prepared based on coassembly of free block copolymer chains and block copolymer brushes on silica particles. Thiol-terminated and cyanoisopropyl-capped polystyrene-block-poly(N-isopropylacrylamide) block copolymers (PS-b-PNIPAM-SH and PS-b-PNIPAM-CIP) were synthesized by reversible addition-fragmentation chain transfer polymerization and chemical modifications. Pyridyl disulfide-functionalized silica particles (SiO2-SS-Py) were prepared by four-step surface chemical reactions. PS-b-PNIPAM brushes on silica particles were prepared by thiol-disulfide exchange reaction between PS-b-PNIPAM-SH and SiO2-SS-Py. Surface micelles on silica particles were prepared by coassembly of PS-b-PNIPAM-CIP and block copolymer brushes. Upon cleavage of the surface micelles from silica particles, patchy micelles with thiol groups in the patches were obtained. Dynamic light scattering, transmission electron microscopy, and zeta-potential measurements demonstrate the preparation of patchy micelles. Gold nanoparticles can be anchored onto the patchy micelles through S-Au bonds, and asymmetric hybrid structures are formed. The thiol groups can be oxidized to disulfides, which results in directional assembly of the patchy micelles. The self-assembly behavior of the patchy micelles was studied experimentally and by computer simulation. PMID:25811763

  11. Solid state solubility of miconazole in poly[(ethylene glycol)-g-vinyl alcohol] using hot-melt extrusion.

    PubMed

    Litvinov, V M; Guns, S; Adriaensens, P; Scholtens, B J R; Quaedflieg, M P; Carleer, R; Van den Mooter, G

    2012-10-01

    The use of hot-melt extrusion for preparing homogeneous API-excipient mixtures is studied for miconazole-PEG-g-PVA [poly(ethylene glycol)-poly(vinyl alcohol) graft copolymer] solid dispersions with a 5 cm(3) table-top, twin-screw corotating microcompounder (DSM Xplore). Phase behavior of PEG-g-PVA, miscibility of miconazole in PEG-g-PVA and the partitioning of miconazole between PEG and PVA amorphous phases are characterized using a combination of modulated DSC, XRPD, and solid-state (1)H and (13)C NMR methods. The (1)H NMR transverse magnetization relaxation (T(2) relaxation) method is used to analyze the phase composition and molecular mobility of the copolymer. The T(2) relaxation decay of pure PEG-g-PVA can be described by four T(2) relaxation components in the temperature range studied. PVA crystallinity is not largely affected by hot-melt extrusion and the presence of the drug. Miconazole preferably resides in the PEG amorphous phase, and its molecules are well dispersed in the PEG-g-PVA matrix using hot-melt extrusion mixing. Miconazole forms amorphous nanoclusters whose average size equals approximately 1.6 nm, indicating solid solution formation (molecular level dispersion) of the drug in the polymer. PMID:22905779

  12. [FTIR study on the synthesis of poly(propylene fumarate) and its copolymer].

    PubMed

    Zhang, Na; Cai, Zhong-yu; Chang, Jun-biao

    2010-01-01

    Poly(propylene fumarate) (PPF) is one kind of linear biodegradable polyester and the unsaturated double bonds along its main chain can be crosslinked with other olefinic monomers to form three-dimensional networks, and the networks can support tissues. In the present paper, firstly, the intermediate oligomer-bis (2-hydroxypropyl) fumarate (PFP) was synthesized, and then the unsaturated linear polyester PPF was synthesized with the oligomer PFP through melting condensation process. Additionally, on the base of the process, the oligomer bis(2-hydroxypropyl) sebacate (PSP) was synthesized by similar method and then a kind of new copolymer named poly(propylene fumarate-co-propylene sebacate) [P(PF-co-PS)] that comprised bis(2-hydroxypropyl) sebacate segments was synthesized with PFP and PSP by melting condensation. During the synthesis process, the structures of bis(2-hdroxypropyl) fumarate, bis(2-hydroxypropyl) sebacate, PPF and P(PF-co-PS) were characterized by FTIR The results shows that with the polymerization going along, oligomer bis (2-hydroxypropyl) fumarate and bis(2-hydroxypropyl) sebacate converted to PPF or P(PF-co-PS) gradually. PMID:20302075

  13. Selective Stabilization of the Fddd Diblock Copolymer Microphase in an Applied Electric Field

    NASA Astrophysics Data System (ADS)

    Martin, Jonathan; Li, Wei; Delaney, Kris; Fredrickson, Glenn

    Using self-consistent field theory, we explore the phase behavior of AB diblock copolymer melts in a uniform applied electric field. We assign an isotropic polarizability to each monomer type, such that the electric field selectively destabilizes AB interfaces that are perpendicular to the applied field. Under the mean-field approximation of the present model, lamellar and cylindrical structures align such that their AB interfaces are parallel to the electric field, and their relative stability with respect to the disordered phase is unchanged. Sphere and network phases do not have an axis of uniformity, so the preferred orientation for each of these phases must be identified by simulation. Small distortions in morphology are induced by the electric field for these phases, such that the free energy response includes non-harmonic terms. We compute the phase diagram for a melt in an applied electric field by comparing free energies of each morphology at its preferred orientation. We find that the stability regions for the sphere and network phases shrink with increasing electric field strength. Moreover, the double gyroid phase is relatively destabilized against the Fddd phase, extending the stability region for the Fddd phase to larger segregation strengths.

  14. Frictional melt and seismic slip

    NASA Astrophysics Data System (ADS)

    Nielsen, S.; di Toro, G.; Hirose, T.; Shimamoto, T.

    2008-01-01

    Frictional melt is implied in a variety of processes such as seismic slip, ice skating, and meteorite combustion. A steady state can be reached when melt is continuously produced and extruded from the sliding interface, as shown recently in a number of laboratory rock friction experiments. A thin, low-viscosity, high-temperature melt layer is formed resulting in low shear resistance. A theoretical solution describing the coupling of shear heating, thermal diffusion, and extrusion is obtained, without imposing a priori the melt thickness. The steady state shear traction can be approximated at high slip rates by the theoretical form τss = σn1/4 (A/?) ? under a normal stress σn, slip rate V, radius of contact area R (A is a dimensional normalizing factor and W is a characteristic rate). Although the model offers a rather simplified view of a complex process, the predictions are compatible with experimental observations. In particular, we consider laboratory simulations of seismic slip on earthquake faults. A series of high-velocity rotary shear experiments on rocks, performed for σn in the range 1-20 MPa and slip rates in the range 0.5-2 m s-1, is confronted to the theoretical model. The behavior is reasonably well reproduced, though the effect of radiation loss taking place in the experiment somewhat alters the data. The scaling of friction with σn, R, and V in the presence of melt suggests that extrapolation of laboratory measures to real Earth is a highly nonlinear, nontrivial exercise.

  15. Characterization of copolymer latexes by capillary electrophoresis.

    PubMed

    Anik, Nadia; Airiau, Marc; Labeau, Marie-Pierre; Bzducha, Wojciech; Cottet, Hervé

    2010-02-01

    Latexes are widely used for industrial applications, including decorative paints, binders for the papermaking industry, and drilling fluids for oil-field applications. In this work, the interest of capillary zone electrophoresis (CE) for the characterization of hydrophobic block copolymer latexes obtained by the conventional emulsion polymerization technique consisting of a core of polystyrene (PS) surrounded by a layer of poly(ethyl acrylate) (PEA) has been investigated. The PEA part of the copolymer can be partially hydrolyzed in poly(acrylic acid) (PAA) leading to PS-PEA-AA water-soluble amphiphilic copolymer having high viscosifying properties. The main purpose of this work was to evaluate the potential of CE for the characterization of the latexes at the different stages of the synthesis (PS core, PS-PEA diblock latex, and hydrolyzed PS-PEA-AA gel). The main analytical issues were to state (i) if there was free PS or PEA homopolymer latexes in the PS-PEA latex sample and (ii) if there was free PS, PEA, PS-PEA latexes, or free PAA chains in the PS-PEA-AA gel. Within this scope, this work describes the optimization of the selectivity of the separation between the different species (PS, PEA particles in the not hydrolyzed diblock latex and PS, PEA, PS-PEA particles as well as the polymer PAA chains in the PS-PEA-AA diblock gel sample obtained by latter latex hydrolysis). For that purpose, several experimental parameters were investigated such as pH and ionic strength of the background electrolyte (BGE) or the concentration of neutral surfactant added in the BGE. A challenging issue was to overcome the high viscosity of the PS-PEA-AA gel. This was resolved by the addition of 10 mM neutral surfactant in the gel sample and in the BGE. Finally, it is demonstrated that, within the detection limits, CE is a suitable analytical tool for controlling and monitoring the syntheses of these latexes and for intrinsically characterizing the distribution in charge density of

  16. On the Viability of Slab Melting

    NASA Astrophysics Data System (ADS)

    Van Hunen, J.; Bouilhol, P.; Magni, V.; Maunder, B. L.

    2014-12-01

    Melting subducted mafic crust is commonly assumed to be the main process leading to silicic melts with an adakitic signature, which may form Archaean granitoids and generate early continental crust. Alternatively, melting of the overriding lower mafic crust and near-Moho depth fractional crystallisation of mantle melts can form differentiated magmas with an adakitic signature. Previous work shows how only very young slabs melt through dehydration melting, or depict melting of dry eclogites via water addition from deeper slab dehydration. Alternatively, underplated subducted material via delamination and diapirism may be important in the generation of felsic continental crust. We quantify subduction dehydration and melting reactions in a warm subduction system using a thermo-mechanical subduction model with a thermodynamic database. We find that even young (hot) slabs dehydrate before reaching their solidus, which suppresses any slab dehydration melting and creates significant amounts of mantle wedge melting irrespective of slab age. Significant slab crust melting is only achieved in young slabs via water present melting if metamorphic fluids from the subducted mantle flux through the dry eclogites. These slab melts, however, interfere with massive mantle wedge melting and unlikely to participate in the overriding plate felsic magmatism, unlike the shallower, primitive mantle wedge melts. We also explore the conditions for delaminating the mafic subducted crust. For a wide range of ages, the uppermost part of the subducted slab might delaminate to form compositionally buoyant plumes that rise through the mantle wedge. Thick crust on young slabs (as perhaps representative for a hotter, early Earth) may delaminate entirely and reside in the mantle wedge. Under such conditions, this ponded crust might melts subsequently, forming "adakitic" felsic melts contributing to a significant amount of the overriding plate crustal volumes.

  17. Equilibrium and Kinetics of Block Copolymers Micelles

    NASA Astrophysics Data System (ADS)

    Mysona, Joshua; Morse, David

    Both equilibrium properties of micelles, such as the critical micelle concentration (CMC), and dynamical properties such as the micelle lifetime are difficult to study in simulations because of the slow dynamics of the processes by which micelles are created and destroyed. We first discuss a method of precisely identifying the CMC in a simple model of block copolymer micelles in a homopolymer matrix, which makes use of thermodynamic integration to compute the free energy of formation. We then examine the free energy barriers to competing mechanisms for creating and destroying micelles, which could occur predominantly either by a step-wise process involving insertion and extraction of single molecules or by fission and fusion of entire micelles.

  18. Cationic vinyl pyridine copolymers and products thereof

    NASA Technical Reports Server (NTRS)

    Rembaum, Alan (Inventor)

    1978-01-01

    Quaternized, cross-linked, insoluble copolymers of unsubstituted and substituted vinyl pyridines and a dihalo organic compound are spontaneously formed at ambient temperature on mixing the two monomers in bulk, in solution or in suspension. The amount of cross-linking may be varied according to the composition and reaction conditions. The polymer product exhibits ion exchange capacity and undergoes a reversible color change from black at a pH above 7 to yellow at a pH below 7. The polymer may be formed in the presence of preformed polymers, substrates such as porous or impervious particles or films to deposit an ion exchange film in situ or on the surface of the substrate. The coated or resin impregnated substrate may be utilized for separation of anionic species from aqueous solution.

  19. Surface photodegradation of a polyolefin copolymer

    NASA Astrophysics Data System (ADS)

    Brandon, J. Ph.; Cabala, R.; Chambaudet, A.; Jaffiol, F.

    1988-05-01

    Methods and data concerning the morphological and microstructural characterizations of the surface of a polypropylene copolymer (PP-PE) are presented: samples of this polymer were moulded under different temperature conditions; some were subjected to UV irradiation in conditioning chambers such as the Xenotest apparatus. Scanning electron microscopy (SEM) gives pictures of a surface morphologies before and after irradiation and shows the emergence of microcracks resulting from polymer photodegradation. Methods such as mercury microporosimetry provide quantitative analyses of these cracks. Selective surface etching of samples reveals crystalline areas in the microstructure of the polymer. Infrared (attenuated total reflection) spectroscopy and X-ray diffraction permit determining the crystallinity ratios of the samples before and after degradation.

  20. Log-rolling block copolymers cylinders

    NASA Astrophysics Data System (ADS)

    Kim, So Youn; Kim, Ye Chan; Kim, Dong Hyup; Kwon, Na Kyung; Register, Richard A.

    Shear has been the most effective method to create long range order of micro- or nano- structures in soft materials. When shear is applied, soft particles or polymers tend to align along the shear direction to minimize the viscous dissipation, thus transverse (so-called ``log-rolling'') alignment is unfavored. In this study, for the first time we report the transverse alignment of cylinder-forming block copolymers. Poly(styrene-b-methyl methacrylate), PS-PMMA, can form a metastable hemicylinder structure when confined in a thin film, and this hemicylinder structure can align either along the shear direction, or transverse to the shear direction (``log-rolling''), depending on the shearing temperature. This unusual ``log-rolling'' behavior is explained by the different chain mobility of the two blocks in PS-PMMA; the rigidity of core cylinder is the critical parameter determining the direction of shear alignment.

  1. Orientation Distribution for Thin Film Block Copolymers

    NASA Astrophysics Data System (ADS)

    Jones, Ronald; Zhang, Xiaohua; Kim, Sangcheol; Karim, Alamgir; Briber, Robert; Kim, Ho-Cheol

    2008-03-01

    The directed self-assembly of nanostructured films with vertically oriented morphologies is a potential solution for manufacture of next generation data storage platforms, microelectronic devices, and nanoporous membranes. In many of these applications, the distribution of orientation must be tightly controlled to enable pattern transfer. This parameter is expected to depend on factors such as the Flory-Huggins chi parameter, but little data has been reported to date. We present results from tomographic small angle scattering on a series of block copolymer films whose assembly has been directed through solvent annealing. Films of poly(styrene-b-ethylene oxide) are cast as a function of annealing time and their orientation distribution reported. The results provide significant insight into the fundamental limits of line edge roughness and defect control possible using this fabrication technique.

  2. Computational engineering of low bandgap copolymers

    PubMed Central

    Wykes, Michael; Milián-Medina, Begoña; Gierschner, Johannes

    2013-01-01

    We present a conceptual approach to low bandgap copolymers, in which we clarify the physical parameters which control the optical bandgap, develop a fundamental understanding of bandgap tuning, unify the terminology, and outline the minimum requirements for accurate prediction of polymer bandgaps from those of finite length oligomers via extrapolation. We then test the predictive power of several popular hybrid and long-range corrected (LC) DFT functionals when applied to this task by careful comparison to experimental studies of homo- and co-oligomer series. These tests identify offset-corrected M06HF, with 100% HF exchange, as a useful alternative to the poor performance of tested hybrid and LC functionals with lower fractions of HF exchange (B3LYP, CAM-B3LYP, optimally-tuned LC-BLYP, BHLYP), which all significantly overestimate changes in bandgap as a function of system size. PMID:24790963

  3. Synthesis of Amylose-b-P2 VP Block Copolymers.

    PubMed

    Kumar, Kamlesh; Woortman, Albert J J; Loos, Katja

    2015-12-01

    A new class of rod-coil block copolymers is synthesized by chemoenzymatic polymerization. In the first step, maltoheptaose, which acts as a primer for the synthesis of amylose, is attached to poly(2-vinyl pyridine) (P2 VP). The enzymatic polymerization of maltoheptaose is carried out by phosphorylase to obtain amylose-b-P2 VP block copolymers. The block copolymer is characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, and wide-angle X-ray scattering techniques. The designed molecules combine the inclusion complexation ability of amylose with the supramolecular complexation ability of P2 VP and therefore this kind of rod-coil block copolymers can be used to generate well-organized novel self-assembled structures. PMID:26437256

  4. Deformation studies of near single-crystal triblock copolymers

    SciTech Connect

    Honeker, C.; Villar, M.A.; Thomas, E.L.

    1993-12-31

    The mechanical behavior of block copolymers is being studied in order to determine the evolution of the microphase-separation morphologies with deformation. To facilitate analysis a novel processing technique termed {open_quotes}roll-casting{close_quotes} is used to orient the copolymers. Large, near single-crystal macroscopically oriented films are produced by applying a shear field on a homogeneous solution and allowing the solvent to evaporate until the copolymer has microphase separated. Deformation behavior is studied with in situ small angle x-ray diffraction and TEM studies of films deformed up to 700% extension. Initial studies on poly(styrene-butadiene-styrene) triblock copolymers with a cylindrical morphology indicate a break-up of the morphology at low deformations and a development of a characteristic 4 point pattern at high deformations. Hysteresis is observed in deformation directions of 0 and 90 degrees.

  5. Insensitive explosive composition of halogenated copolymer and triaminotrinitrobenzene

    DOEpatents

    Benziger, Theodore M.

    1976-01-01

    A highly insensitive and heat resistant plastic-bonded explosive containing 90 wt % triaminotrinitrobenzene and 10 wt % of a fully saturated copolymer of chlorotrifluoroethylene and vinylidene fluoride is readily manufactured by the slurry process.

  6. HPMA copolymers: Origins, early developments, present, and future☆

    PubMed Central

    Kopeček, Jindřich; Kopečková, Pavla

    2010-01-01

    The overview covers the discovery of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers, initial studies on their synthesis, evaluation of biological properties, and explorations of their potential as carriers of biologically active compounds in general and anticancer drugs in particular. The focus is on the research in the authors’ laboratory – the development of macromolecular therapeutics for the treatment of cancer and musculoskeletal diseases. In addition, the evaluation of HPMA (co)polymers as building blocks of mod and new biomaterials is presented: the utilization of semitelechelic poly(HPMA) and HPMA copolymers for the modification of biomaterial and protein surfaces and the design of hybrid block and graft HPMA copolymers that self-assemble into smart hydrogels. Finally, suggestions for the design of second-generation macromolecular therapeutics are portrayed. PMID:19919846

  7. Stimuli-Responsive Peptide-based Triblock and Star Copolymers

    NASA Astrophysics Data System (ADS)

    Ray, Jacob; Naik, Sandeep; Johnson, Ashley; Ly, Jack; Savin, Daniel

    2011-03-01

    Stimuli-responsive copolymers demonstrate diverse aggregation behavior in aqueous solution. In general, the molecular architecture and the balance of hydrophilic and hydrophobic volumes influence morphology. This study involves polypeptide-based ABA linear triblock and AB2 star copolymer (which structurally resemble phospholipids) amphiphiles. Model systems for this study are poly(L-lysine)-b-poly(propylene oxide)-b-poly(L-lysine) (KPK) triblocks and poly(L-glutamate) (PE) based star copolymers. Extensive studies with KPK systems have resulted in morphological transitions by modifying pH, and we hypothesize that a change in individual chain conformation is the driving force for these transitions. Preliminary results for PE-based star copolymers with various hydrophobic moieties suggest polymersome (vesicle) formation. Light scattering (dynamic and static) and TEM were used to determine aggregate size and morphology as a function of pH; furthermore, circular dichroism (CD) spectroscopy was used to measure helix-to-coil transitions of the polypeptide blocks.

  8. Syntheses of Gradient pi-Conjugated Copolymers of Thiophene

    SciTech Connect

    Locke, Jonas R.; McNeil, Anne J.

    2010-11-09

    we prepared the first gradient π-conjugated copolymers via Ni-catalyzed chain-growth copolymerization of 3-hexylthiophene and 3-((hexyloxy)methyl)thiophene. Because rate studies indicated little difference in monomer reactivities, one monomer was gradually added to the polymerization over time to form gradient copolymers. Now that controlled sequence π-conjugated copolymers can be synthesized, the next goal is to identify their unique properties, including phase-compatibilizing abilities in homopolymer blends. Preliminary data reported herein suggest that the solid-state optical and physical properties are influenced by the copolymer sequence. Finally, although the Ni-catalyzed copolymerizations are chain growth under the conditions reported herein, our preliminary attempts to expand the substrate scope by examining the copolymerization of monomers with varying steric and electronic properties has highlighted a need for developing improved catalysts.

  9. Nanopatterned articles produced using surface-reconstructed block copolymer films

    DOEpatents

    Russell, Thomas P.; Park, Soojin; Wang, Jia-Yu; Kim, Bokyung

    2016-06-07

    Nanopatterned surfaces are prepared by a method that includes forming a block copolymer film on a substrate, annealing and surface reconstructing the block copolymer film to create an array of cylindrical voids, depositing a metal on the surface-reconstructed block copolymer film, and heating the metal-coated block copolymer film to redistribute at least some of the metal into the cylindrical voids. When very thin metal layers and low heating temperatures are used, metal nanodots can be formed. When thicker metal layers and higher heating temperatures are used, the resulting metal structure includes nanoring-shaped voids. The nanopatterned surfaces can be transferred to the underlying substrates via etching, or used to prepare nanodot- or nanoring-decorated substrate surfaces.

  10. Multicompartmental Microcapsules from Star Copolymer Micelles

    SciTech Connect

    Choi, Ikjun; Malak, Sidney T.; Xu, Weinan; Heller, William T.; Tsitsilianis, Constantinos; Tsukruk, Vladimir V.

    2013-02-26

    We present the layer-by-layer (LbL) assembly of amphiphilic heteroarm pH-sensitive star-shaped polystyrene-poly(2-pyridine) (PSnP2VPn) block copolymers to fabricate porous and multicompartmental microcapsules. Pyridine-containing star molecules forming a hydrophobic core/hydrophilic corona unimolecular micelle in acidic solution (pH 3) were alternately deposited with oppositely charged linear sulfonated polystyrene (PSS), yielding microcapsules with LbL shells containing hydrophobic micelles. The surface morphology and internal nanopore structure of the hollow microcapsules were comparatively investigated for shells formed from star polymers with a different numbers of arms (9 versus 22) and varied shell thickness (5, 8, and 11 bilayers). The successful integration of star unimers into the LbL shells was demonstrated by probing their buildup, surface segregation behavior, and porosity. The larger arm star copolymer (22 arms) with stretched conformation showed a higher increment in shell thickness due to the effective ionic complexation whereas a compact, uniform grainy morphology was observed regardless of the number of deposition cycles and arm numbers. Small-angle neutron scattering (SANS) revealed that microcapsules with hydrophobic domains showed different fractal properties depending upon the number of bilayers with a surface fractal morphology observed for the thinnest shells and a mass fractal morphology for the completed shells formed with the larger number of bilayers. Moreover, SANS provides support for the presence of relatively large pores (about 25 nm across) for the thinnest shells as suggested from permeability experiments. The formation of robust microcapsules with nanoporous shells composed of a hydrophilic polyelectrolyte with a densely packed hydrophobic core based on star amphiphiles represents an intriguing and novel case of compartmentalized microcapsules with an ability to simultaneously store different hydrophilic, charged, and hydrophobic

  11. Fluid/Melt Partition Coefficients Of Halogens In Basaltic Melt

    NASA Astrophysics Data System (ADS)

    Alletti, M.; Baker, D.; Scaillet, B.; Aiuppa, A.; Moretti, R.; Ottolini, L.

    2007-12-01

    Despite the importance of halogens (F, Cl) in volcanic degassing, solubility and fluid/melt partitioning of these elements have not been comprehensively studied in natural basaltic melts. Experimental determinations of halogen solubility in Mount Etna melts are lacking, despite this volcano being one of the most active and intensively monitored on Earth with an estimated output of thousands tonnes of halogens per day. In order to better understand halogen degassing, we present the results of a series of halogen partitioning experiments performed at different pressures (1-200 MPa), redox conditions (from Δ NNO = + 2 to Δ NNO = - 0.3) and fluid compositions. Experiments used a hawaiitic, glassy, alkaline basalt with Mg# = 0.59, sampled during the July 2001 eruption of Mount Etna. A series of experiments were conducted using H2O-NaCl or H2O-NaF solutions. The effect of CO2 in multi-component fluid H2O-CO2-NaCl or H2O-CO2-NaF was also investigated. The experimental run products were mostly glasses, but a few run products contained less than 10% crystals. The concentration of halogens in the fluid phase after the experiment was calculated from mass balance, and the partition coefficients for both Cl and F at the studied conditions determined. Using these measurements and thermodynamical models, the dependence of these partition coefficients on the fugacities of various gaseous species was investigated.

  12. Searching for Nectaris Basin Impact Melt Rocks

    NASA Astrophysics Data System (ADS)

    Cohen, B. A.

    2015-07-01

    Because Nectaris Basin is a key stratigraphic marker for lunar bombardment, we are conducting an effort to identify Nectaris basin impact-melt rocks, to model their emplacement, and to examine sites where Nectaris impact melt is abundant.

  13. Double-Gyroid Network Morphology in Tapered Diblock Copolymers

    SciTech Connect

    R Roy; J Park; W Young; S Mastroianni; M Tureau; T Epps III

    2011-12-31

    We report the formation of a double-gyroid network morphology in normal-tapered poly(isoprene-b-isoprene/styrene-b-styrene) [P(I-IS-S)] and inverse-tapered poly(isoprene-b-styrene/isoprene-b-styrene) [P(I-SI-S)] diblock copolymers. Our tapered diblock copolymers with overall poly(styrene) volume fractions of 0.65 (normal-tapered) and 0.67 (inverse-tapered), and tapered regions comprising 30 vol % of the total polymer, were shown to self-assemble into the double-gyroid network morphology through a combination of small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The block copolymers were synthesized by anionic polymerization, where the tapered region between the pure poly(isoprene) and poly(styrene) blocks was generated using a semibatch feed with programmed syringe pumps. The overall composition of these tapered copolymers lies within the expected network-forming region for conventional poly(isoprene-b-styrene) [P(I-S)] diblock copolymers. Dynamic mechanical analysis (DMA) clearly demonstrated that the order-disorder transition temperatures (T{sub ODT}'s) of the network-forming tapered block copolymers were depressed when compared to the T{sub ODT} of their nontapered counterpart, with the P(I-SI-S) showing the greater drop in T{sub ODT}. These results indicate that it is possible to manipulate the copolymer composition profile between blocks in a diblock copolymer, allowing significant control over the T{sub ODT}, while maintaining the ability to form complex network structures.

  14. Double-Gyroid Network Morphology in Tapered Diblock Copolymers

    SciTech Connect

    Roy, Raghunath; Park, Jong Keun; Young, Wen-Shiue; Mastroianni, Sarah E.; Tureau, Maeva S.; Epps, III, Thomas H.

    2012-11-14

    We report the formation of a double-gyroid network morphology in normal-tapered poly(isoprene-b-isoprene/styrene-b-styrene) [P(I-IS-S)] and inverse-tapered poly(isoprene-b-styrene/isoprene-b-styrene) [P(I-SI-S)] diblock copolymers. Our tapered diblock copolymers with overall poly(styrene) volume fractions of 0.65 (normal-tapered) and 0.67 (inverse-tapered), and tapered regions comprising 30 vol % of the total polymer, were shown to self-assemble into the double-gyroid network morphology through a combination of small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The block copolymers were synthesized by anionic polymerization, where the tapered region between the pure poly(isoprene) and poly(styrene) blocks was generated using a semibatch feed with programmed syringe pumps. The overall composition of these tapered copolymers lies within the expected network-forming region for conventional poly(isoprene-b-styrene) [P(I-S)] diblock copolymers. Dynamic mechanical analysis (DMA) clearly demonstrated that the order-disorder transition temperatures (T{sub ODT}'s) of the network-forming tapered block copolymers were depressed when compared to the T{sub ODT} of their nontapered counterpart, with the P(I-SI-S) showing the greater drop in T{sub ODT}. These results indicate that it is possible to manipulate the copolymer composition profile between blocks in a diblock copolymer, allowing significant control over the T{sub ODT}, while maintaining the ability to form complex network structures.

  15. Orientation of Microdomains of Block Copolymers by Zone casting

    NASA Astrophysics Data System (ADS)

    Tang, Chuanbing; Matyjaszewski, Krzysztof; Kowalewski, Tomasz

    2007-03-01

    As a ``bottom up'' method, the self-assembly of block copolymers plays a vital role in the development of soft lithography for the fabrication of microelectronic devices. A variety of methods have been developed toward better and more precise controlled patterns on solid substrates. This presentation will describe a novel solution casting technique, ``zone casting'', to induce orientation of cylindrical and lamellar microphase-separated domains of various block copolymers.

  16. Photooxidative degradation of clear ultraviolet absorbing acrylic copolymer surfaces

    NASA Technical Reports Server (NTRS)

    Gupta, A.; Liang, R. H.; Vogl, O.; Pradellok, W.; Huston, A. L.; Scott, G. W.

    1983-01-01

    Photodegradation of copolymer of methyl methacrylate and 2(2'-hydroxy 5'vinyl-phenyl) 2H-benzotriazole has been investigated in order to determine the changes in the chemical composition of the surface of the copolymer on photooxidation. An electronic energy transfer mechanism has been postulated in order to interpret the observed photochemical changes in the polymer. Preliminary examination of the photophysical properties of the chromophore provides support for such a mechanism.

  17. Immobilization of enzymes on alginic acid-polyacrylamide copolymers

    SciTech Connect

    Kumaraswamy, M.D.K.; Panduranga R.K.; Thomas J.K.; Santappa, M.

    1981-08-01

    In this report, the authors present initial results and limitations of a polymeric system for the immobilization of enzymes. Enzymes attached to insoluble polymers of natural and synthetic origin are gaining importance in many industrial and biomedical applications. Graft copolymers are used as enzyme supports and in this study a novel polymeric system of alginic acid-polyacrylamide graft copolymer is described which was used for immobilizing enzymes. (Refs. 4).

  18. Biodegradable copolymers carrying cell-adhesion peptide sequences.

    PubMed

    Proks, Vladimír; Machová, Lud'ka; Popelka, Stepán; Rypácek, Frantisek

    2003-01-01

    Amphiphilic block copolymers are used to create bioactive surfaces on biodegradable polymer scaffolds for tissue engineering. Cell-selective biomaterials can be prepared using copolymers containing peptide sequences derived from extracellular-matrix proteins (ECM). Here we discuss alternative ways for preparation of amphiphilic block copolymers composed of hydrophobic polylactide (PLA) and hydrophilic poly(ethylene oxide) (PEO) blocks with cell-adhesion peptide sequences. Copolymers PLA-b-PEO were prepared by a living polymerisation of lactide in dioxane with tin(II)2-ethylhexanoate as a catalyst. The following approaches for incorporation of peptides into copolymers were elaborated. (a) First, a side-chain protected Gly-Arg-Gly-Asp-Ser-Gly (GRGDSG) peptide was prepared by solid-phase peptide synthesis (SPPS) and then coupled with delta-hydroxy-Z-amino-PEO in solution. In the second step, the PLA block was grafted to it via a controlled polymerisation of lactide initiated by the hydroxy end-groups of PEO in the side-chain-protected GRGDSG-PEO. Deprotection of the peptide yielded a GRGDSG-b-PEO-b-PLA copolymer, with the peptide attached through its C-end. (b) A protected GRGDSG peptide was built up on a polymer resin and coupled with Z-carboxy-PEO using a solid-phase approach. After cleavage of the delta-hydroxy-PEO-GRGDSG copolymer from the resin, polymerisation of lactide followed by deprotection of the peptide yielded a PLA-b-PEO-b-GRGDSG block copolymer, in which the peptide is linked through its N-terminus. PMID:12903721

  19. Block copolymer adhesion promoters via ring-opening metathesis polymerization

    DOEpatents

    Kent, Michael S.; Saunders, Randall

    1997-01-01

    Coupling agents based on functionalized block copolymers for bonding thermoset polymers to solid materials. These are polymers which possess at least two types of functional groups, one which is able to attach to and react with solid surfaces, and another which can react with a thermoset resin, which are incorporated as pendant groups in monomers distributed in blocks (typically two) along the backbone of the chain. The block copolymers in this invention are synthesized by living ring-opening metathesis polymerization.

  20. Oligoaniline-containing supramolecular block copolymer nanodielectric materials.

    PubMed

    Hardy, Christopher G; Islam, Md Sayful; Gonzalez-Delozier, Dioni; Ploehn, Harry J; Tang, Chuanbing

    2012-05-14

    We report a new generation of nanodielectric energy storage materials based on supramolecular block copolymers. In our approach, highly polarizable, conducting nanodomains are embedded within an insulating matrix through block copolymer microphase separation. An applied electric field leads to electronic polarization of the conducting domains. The high interfacial area of microphase-separated domains amplifies the polarization, leading to high dielectric permittivity. Specifically, reversible addition fragmentation transfer (RAFT) polymerization was used to prepare block copolymers with poly(methyl acrylate) (PMA) as the insulating segment and a strongly acidic dopant moiety, poly-(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), as the basis for the conducting segment. The PAMPSA block was complexed with an oligoaniline trimer to form a dopant-conjugated moiety complex that is electronically conductive after oxidation. For the undoped neat block copolymers, the increase of the PMA block length leads to a transition in dielectric properties from ionic conductor to dielectric capacitor with polarization resulting from migration of protons within the isolated PAMPSA domains. The oligoaniline-doped copolymers show remarkably different dielectric properties. At frequencies above 200 kHz, they exhibit characteristics of dielectric capacitors with much higher permittivity and lower dielectric loss than the corresponding undoped copolymers. PMID:22331602