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The flow-induced coil-stretch transition of high molecular weight polymers has generally been held to be of first order. But evidence of significant slowing down in the rate at which the polymers relax to equilibrium in the vicinity of the transition suggests that the thermodynamic character of the transition may be less clear-cut. The above slowing down effect is actually characteristic of a second-order transition, and it points to the existence of a broad spectrum of conformational states in the transition region, analogous to the existence of fluctuations of all length scales at a critical point. In this paper, using a path integral approach based on a free-draining finitely extensible chain model, we calculate various polymer properties as a function of elongational flow as a way of exploring different statistical mechanical details of the coil-stretch transition. These properties include the molecular weight dependence of the flow-extension curve of the polymer, the distribution of its steady-state end-to-end distances, and the characteristic relaxation time τR of these distances. Among other findings, our calculations indicate that the coil-stretch transition is discontinuous in the N → ∞ limit, that the effective free energy of the chain is unimodal at all values of the flow, becoming broad and flat in the immediate vicinity of the transition, and that the ratio of τR to the Rouse relaxation time increases abruptly at the transition before eventually reaching a plateau value at large flow strengths. These aspects of the coil-stretch transition place it among a larger class of unconventional nominally first-order single chain transitions that include the adsorption transition of surface-tethered polymers and the escape transition of compressed polymers. [ABSTRACT FROM AUTHOR]

The effective diffusivity in a polymer matrix modified with inclusions is usually calculated based on Kalnin-Kotomin's model [J. R. Kalnin, E. A. Kotomin, and J. Maier, J. Phys. Chem. Solids 63, 449-456 (2002)], which extends the well known Maxwell-Garnett formula. Kalnin-Kotomin's model correctly predicts effective diffusivity for stationary diffusion or for infinite media. In the present paper diffusion in composite media is studied for finite systems under transient conditions. The process of diffusion is modeled numerically and effective diffusion coefficient in the transient state is estimated, which, under certain conditions, is different from the predictions of the Kalnin-Kotomin's model. An analytical model is proposed to explain deviations of the transient effective coefficient of diffusion from the stationary case. [ABSTRACT FROM AUTHOR]

In a recent paper [V. N. Novikov, K. S. Schweizer, and A. P. Sokolov, J. Chem. Phys. 138, 164508 (2013)] a simple analytical ansatz has been proposed to describe the momentum transfer (Q) dependence of the collective relaxation time of glass-forming systems in a wide Q-range covering the region of the first maximum of the static structure factor S(Q) and the so-called intermediate length scale regime. In this work we have generalized this model in order to deal with glass-forming systems where the atomic diffusive processes are sub-linear in nature. This is for instance the case of glass-forming polymers. The generalized expression considers a sub-linear jump-diffusion model and reduces to the expression previously proposed for normal diffusion. The generalized ansatz has been applied to the experimental results of the Q- and temperature-dependence of polyisobutylene (PIB), which were previously published. To reduce the number of free parameters of the model to only one, we have taken advantage of atomistic molecular dynamics simulations of PIB properly validated by neutron scattering results. The model perfectly describes the experimental results capturing both, Q- and temperature-dependences. Moreover, the model also reproduces the experimental Q-dependence of the effective activation energy of the collective relaxation time in the temperature range of observation. This non-trivial result gives additional support to the way the crossover between two different relaxation mechanisms of density fluctuations is formulated in the model. [ABSTRACT FROM AUTHOR]

Prior experiments of membrane inflation (biaxial extension) on ultrathin polymer films have evidenced a dramatic stiffening in the rubbery regime whose origins remain unclear. Here, we describe results from bubble inflation measurements on ultrathin films of a previously unexamined material [poly (n-butyl methacrylate) (PBMA)] and show that the observed rubbery stiffening behavior can be attributed to a mixture of “molecular or confinement-induced stiffening” and surface tension effects. The results suggest that the molecular stiffening contribution is significant, with the macroscopic surface tension being unchanged even for films as thin as 20 nm. It is also found that PBMA exhibits a significantly different behavior from both poly(vinyl acetate) and polystyrene, illustrating that the magnitude of the molecular or confinement-induced stiffening in ultrathin films depends on the polymer repeat unit structure. [ABSTRACT FROM AUTHOR]

By employing the Massieu formalism presented in the preceding paper, Monte Carlo methods and extrapolation techniques are combined to simulate polymers with chain-length polydispersity. Semigrand canonical and grand canonical ensembles supplemented by identity exchange moves and expanded-ensemble moves have been tailored to simulate both thermodynamic properties and the structure of various coarse-grained model systems. It is demonstrated that the proposed methods can be used to simulate systems with arbitrary molecular weight distribution (e.g., to match experimental data), bulk-pore partitioning of polymer solutions, and liquid–liquid equilibrium of polydisperse polymer melts. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper studies the geometry of a semiflexible polymer at finite temperatures. The writhe correlation functions can be calculated from the properties of Gaussian random walks on the sphere. The writhe of a polymer is analogous to geometric or Berry phases studied in optics and wave mechanics. These results can be applied to confocal microscopy studies of stiff filaments and to simulations of short DNA loops. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a correction to a paper about renormalization of polymers.

Presents corrections to expressions used in a paper on the cubic susceptibility dispersion of alkoxy-nitro-stilbene and di-alkyl-amino-nitro-stilbene side chain substituted polymers.