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The backbone dynamics of barnase has been studied by a recently developed off-lattice Monte Carlo (MC)/Metropolis simulation technique, where a low-resolution model (virtual-bond model) is used together with knowledge-based potentials, with the main emphasis on its cooperative motions at different time windows. The conformations generated around the native state are analysed by time-dependent auto-...
Atomistic (atom-scale) and coarse-grained (meso-scale) simulations of the structure and dynamics of poly-isoprene melts are compared. The local structure and chain packing is mainly determined by the atomistic details of the polymer architecture. The large-time dynamics encountered in NMR experiments can be explained by meso-scale simulations including stiffness. The connecting link between the two...
Molecular modeling techniques were applied to predicting binding energies for nanocomposites comprising exfoliated clay layers treated with ammonium salts (usually quaternary) and dispersed in nylon 6,6 resin. For each of 12 selected ammonium ions (quats), a molecular dynamics simulation was performed at 600K for 100–300ps with a time step of 0.001ps on a computer model built from 20 repeating units...
Poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) are structurally related polyesters. In each polymer, the ethylene glycol diesters are separated by rigid rings and are attached to the 1,4-positions of the phenyl and the 2,6-positions of the naphthyl rings in PET and PEN, respectively. Because neighboring ethylene glycol units of each polyester are separated by phenyl or...
Dynamic heterogeneity, where it is noticed in molecular dynamics (MD) simulations that, for example, conformational transition rates vary greatly from bond to bond, is characteristic of polymeric glasses. The phenomenon can be attributed to the fact that certain local bond sequences are more capable of conformational rearrangement than others. These local sequences become fixed sites when the overall...
This paper reports Monte Carlo simulation results of a polymer melt of short, non-entangled chains which are embedded between two impenetrable walls. The melt is simulated by the bond-fluctuation lattice model under athermal conditions, i.e. only excluded volume interactions between the monomers and between the monomers and the walls are taken into account. In the simulations, the wall separation...
Computational models of protein folding and ligand docking are large and complex. Few systematic methods have yet been developed to optimize the parameters in such models. We describe here an iterative parameter optimization strategy that is based on minimizing a structural error measure by descent in parameter space. At the start, we know the ‘correct’ native structure that we want the model to produce,...
The self-excited oscillation of neck propagation during cold drawing of polymer films has been examined experimentally. On the basis of Barenblatt's model considering a thermo-mechanical coupling at the neck, the temperature rise at the neck has been studied with an infrared camera. The temperature began to rise in a range showing a negative velocity dependence of the applied load. The behavior is...
Photocrosslinkable chalcone-epoxy compound comprising 1,3-bis-(4-hydroxy-phenyl)-propenone was synthesized for studying the optically induced anisotropy of the thin films. Chalcone group was introduced into the main chain unit of the epoxy oligomer. We observed a photodimerization behavior and an optical anisotropy of this material by irradiation of linearly polarized UV light (LPL). With a trace...
The effect of several compatibilizers on mechanical property and morphology of ethylene-propylene diene monomer rubber (EPDM)/nylon copolymer (PA) blends was investigated. A significant reduction of dispersed phase dimension was observed when chlorinated polyethylene (CPE) was added to EPDM/PA blend, due to interaction that exists between CPE and PA. Based on differential thermal analysis, dynamic...
Three triblock copolymers of poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) of different molecular weights and one diblock copolymer of poly[styrene-b-(ethylene-co-butylene)] (SEB) were used to compatibilize high density polyethylene/syndiotactic polystyrene (HDPE/sPS, 80/20) blend. Morphology observation showed that phase size of the dispersed sPS particles was significantly reduced on addition...
The emulsification efficiency of three different block copolymers consisting of hydrogenated polybutadiene (HPB) and polystyrene (PS), i.e. a pure diblock , a tapered diblock and a triblock copolymer has been compared in low density polyethylene/polystyrene (LDPE/PS) blends rich in polyethylene. The comparison relies upon the ability of these potential interfacial agents to stabilize fine phase dispersion...
The effect of coreacting diglycidyl ether of bisphenol F (DGEBP-F) with diglycidyl ether of 4,4'-dihydroxybiphenol (DGE-DHBP) on mechanical properties is investigated. DGE-DHBP shows a liquid crystal (LC) transition upon curing. Tensile, impact and fracture toughness test results are evaluated. Dynamic mechanical analysis is conducted to determine the effect of the DGE-DHBP component. Scanning electron...
The enthalpy of dilution of chitosan and alkylchitosan solutions in aqueous 0.3M acetic acid was experimentally studied over the entire concentration range at 298K, and the values of Flory-Huggins interaction parameter were determined with the help of a new scaling approach which took into account the electrostatic contribution to the enthalpy of dilution of polyelectrolyte solutions. That made it...
Organically modified montmorrillonite clay, containing a long chain aliphatic quarternary ammonium cation, was used to prepare polyimide/organoclay hybrids. Several approaches were examined in an attempt to achieve fully exfoliated nanocomposites. These included simple mixing of the clay in a pre-made high molecular weight poly(amide acid) solution; simple mixing followed by sonication of the organoclay/poly(amide...
The miscibility of atactic poly(epichlorohydrin) (aPECH) with poly(vinyl acetate) (PVAc) was examined under two different conditions: (i) in dilute solution, using vicometeric measurements and (ii) as cast films, using differential scanning calorimetric (DSC) and FT-infrared spectroscopy. Phase separation on heating, i.e. lower critical solution temperature (LCST) behavior of the aPECH/PVAc blends...
All commercially available (as-received) perfluorinated ion-exchange polymers are in the form of hydrolyzed polymers and are semi-crystalline and may contain ionic clusters. The membrane form of these polymers has a typical thickness in the range of approximately 100-300μm. Such a thin thickness of commercially available membranes permits fast mass transfer for use in various chemical processes. Although...
Dissolution and reprocessing of exfoliated montmorillonite-nylon 6 (NLS) nanocomposite is demonstrated, illustrating the potential of using polymer nanocomposites as the foundation for fabricating nano- and mesoscopic structures, nanofibers in this case, and thus exerting hierarchical control of morphology and form through the combination of a nanostructured material and a nanoscale fabrication technique...
In order to give a toughness and improve adhesion properties of the cured epoxy system, modified epoxy resins, which have pre-reacted urethane microspheres formed using dynamic vulcanization method in liquid diglycidylether of bisphenol A, were prepared. It was found that the size of the particles decreased to sub-micro order with increase in solubility of urethane oligomers in epoxy resin, and coefficient...
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