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Nanoindentation and nanoscratch testing have revealed large differences in nanomechanical behaviour on uniaxially and biaxially drawn poly(ethylene terephthalate) films. Differences can be ascribed to the processing history of the film. The biaxial material exhibited significantly higher hardness and elastic modulus than the uniaxial film, presumably due to increased crystallinity from the second...
The long standing question of how long a trans sequence in a polyethylene needs to be in order to contribute to the all-trans Raman bands at 1060 and 1130cm−1 is addressed. Various hexadecane, C16H34, conformers were studied using ab initio type calculations revealing vibrational frequencies and intensities. We found that only trans sequences longer than 10 trans bonds reveal Raman intensity primarily...
This paper addresses three important aspects, neglected in all previous literature, of the micromechanics of nanocomposites reinforced by platelet-shaped fillers. (a) A model was developed to predict the buckling of platelets in reinforced materials under compressive loading. This model predicts a critical strain above which platelet buckling, and hence a reduction in the compressive modulus relative...
Deformations in isotropic, strain-free polymer glasses are usually completely recoverable (at the test temperature or after warming to Tg), in sharp contrast with the behavior of low molecular weight glasses and crystals. The apparent ‘plastic strain’ which remains at the end of a creep or stress relaxation experiment does not recover at the test temperature, but only after the sample is heated. It...
The properties of the α- and Johari–Goldstein β-relaxations in conjunction with configurational entropy data are used to show how cooperativity of the dynamics of poly(vinylacetate) develops as temperature is decreased towards Tg from above. Such behavior is also characteristic of small molecule glass-forming liquids, demonstrating that the combined effects of configurational entropy changes and intermolecular...
We develop a coarse-grained model to investigate the influence of nanoscale particles on the phase separation and the morphology of symmetric AB diblock copolymer melts. The microphase separation is modeled by the cell dynamical systems (CDS) equations, while the particle dynamics is described by a Langevin equation. We assume that the particles have a selective affinity to the A block and thus, can...
Reaction scheme of acrylic-based superabsorbing polymers was monitored by a differential scanning calorimeter. Differential scanning calorimetry (DSC) was used to study the heat effects during the polymer synthesis in DSC pan as a micro-scale reactor. Two distinct observations, i.e. inhibition period (IP) and onset of gel formation were recorded during polymerization. The effect of reaction temperature...
The numerical determination of relaxation times or other characteristic dynamical variables is often connected with intrinsic computational problems and consequently can be legitimately criticized. We present here for finding dynamical variables a general numerical method, which allows one to avoid these problems, and which is based exclusively on numerical equilibrium values: 02.70∗∗, 05.20∗∗, 64...
We have developed a new method for the prediction of the protein secondary structure from the amino acid sequence. The method is based on the most recent version (IV) of the standard GOR (J Mol Biol 120 (1978) 97) algorithm. A significant improvement is obtained by combining multiple sequence alignments with the GOR method. Additional improvement in the predictions is obtained by a simple correction...
The cohesive properties of many engineering plastics are difficult to determine experimentally, as the polymers are frequently insoluble, have high Tgs, and are sometimes poorly characterized. For difficult polymers such as these, molecular modeling can provide useful information of higher quality than might be obtained by other methods. Ultem® is a polyether imide having a very large and relatively...
The miscibility behavior of binary mixtures of polymeric and low molecular weight molecules was studied using a combination of modified Flory–Huggins theory and molecular simulation techniques. Three different atomistic approaches were used to investigate the phase behavior and χ parameters of binary mixtures consisting of polymethyl methacrylate (PMMA) and 4-n-pentyl-4′-cyanobiphenyl (5CB). Binary...
The isothermal crystallization kinetics and morphology have been investigated for a series of dilute binary blends using six monodisperse n-alkanes as guest in C162H326 as host. Two patterns of behaviour were observed. Guest molecules shorter than the host segregate as a separate population causing growth rates to become both reduced and non-linear. Morphologies are then noticeably less spherulitic...
Tear fatigue analyzer (TFA) tests on rubber are simulated, for the first time, with a combination of a mesoscopic model of self-similar crack propagation and a complex viscoelastic rubber model (flow-enhanced linear standard solid). In this way, it is possible to establish interconnections between mechanical fracturing tests (TFA) and intrinsic material properties.
Soluble, branched (meth)acrylic copolymers have been made via facile, one-step, batch solution polymerisations taken to high conversion. Methyl methacrylate has been copolymerised with a bifunctional monomer using a chain transfer agent to inhibit gelation. Conventional chain transfer using a mercaptan has been compared to catalytic chain transfer (CCT) using a cobalt porphyrin. The polymerisations...
Chemical shift tensors (CST) for the protonated aromatic carbons in polystyrene are presented. Experimental difficulties preclude the direct measurement of these tensors. The values reported are obtained from quantum chemical calculations on 2-phenyl propane using the 6-31G basis set, after testing other basis sets against similar compounds for which the chemical shift anisotropies are known. Corrections...
Although the filler particles typically used to reinforce elastomers are at least approximately spherical, prolate (needle-shaped) or oblate (disc-shaped) particles have been used in some cases. The fact that anisotropic structures and properties can be obtained in these cases has encouraged a number of experimental and theoretical investigations. The present study extends some earlier Monte Carlo...
Polyethylene thin films are simulated using a coarse-grained on-lattice Monte Carlo technique. Properties of free-standing films, which are made up of either C50, C100 or C316 chains, are analyzed in the melt phase at 509K. As a result of increasing molecular weight, the following observations are made: (i) bulk density of the films increases; (ii) there is a higher degree of parallel orientation...
Monte Carlo simulations of linear and cyclic alkanes were performed on a coarse-grained high coordination lattice. The simulations were performed at 473K for CNH2N+2 and CNH2N where N had the values of 60, 100, and 316. The results indicated: (i) at low molecular weights, cyclic alkanes have lower diffusion coefficients than linear alkanes, and (ii) at high molecular weights, they have higher diffusion...
Fracture toughness of a semi-crystalline polyethylene naphthalate (PEN) film of thicknesses 0.050, 0.075 and 0.125mm was measured as a function of temperature and loading rate using both double edge notched tension (DENT) and single edge notched tension (SENT) specimens. The specific essential work of fracture (EWF) and the multi-specimen J-integral methods were used to evaluate fracture toughness...
In this note, we propose a mapping from the spatial coordinates of an atomistic polymer chain to its ‘primitive path’ (PP), a concept being frequently used in the framework of reptation models. For the model to be presented, the projection preserves as much structure of the atomistic chain as appropriate to replace an atomistic chain on a prescribed (parameterized) coarse-grained level. We present...
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