Z. (2020) Nonlinear rheology and dynamics of supramolecular polymer networks formed by associative telechelic chains under shear and extensional flows.

The dynamics of an entangled polymer melt confined in a channel by parallel plates is investigated by Molecular Dynamics (MD) simulations of a detailed, multi-chain model. A primitive path analysis predicts that the density of entanglements remains approximately constant throughout the gap and drops to lower values only in the immediate vicinity of the surface. Based on these observations, we propose a coarse-grained, single-chain slip-spring model with a uniform density of slip-spring anchors and slip-links. The slip-spring model is compared to the Kremer-Grest MD bead-spring model via equilibrium correlation functions of chain orientations. Reasonably good agreement between the single-chain model and the detailed multi-chain model is obtained for chain relaxation dynamics, both away from the surface and for chains whose center of mass positions are at a distance from the surface that is less than the bulk chain radius of gyration, without introducing any additional model parameters. Our results suggest that there is no considerable drop in topological interactions for chains in the vicinity of a single flat surface. We infer from the slip-spring model that the experimental plateau modulus of a confined polymer melt may be different to a corresponding unconfined system even if there is no drop in topological interactions for the confined case.

This study examined linear viscoelasticity (LVE) of stereo-regular poly(1-butene) (PB) and its random copolymer with polyethylene (PBE), with number fraction of ethylene comonomer ≤ 10%, using a conventional shear rheometer combined with a quartz resonator.This combination resulted in the detection of LVE in a broad frequency range from Rouse region to terminal relaxation. LVE thus determined was fit to the double reptation model through utilizing inputting molecular weights determined by gel permeation chromatography equipped with refractive index and two-angle laser light scattering monitors, and the segmental time and entanglement molecular weight as the two fitting parameters.Quantitative prediction was finally achieved when the two fitting parameters changed systematically by the increase of ethylene content; a decrease of segmental time quantified a plasticizing effect and a decrease of entanglement molecular weight reflected enhanced chain flexibility. The entanglement molecular weight of the PB samples was found to be lower than those reported for stereo-irregular PB, suggesting the important effect of stereo-regularity on chain flexibility.

We show experimentally that chemical and mechanical self-oscillations in Belousov–Zhabotinsky hydrogels are inherently asynchronous, that is, there is a detectable delay in swelling–deswelling response after a change in the chemical redox state. This phenomenon is observable in many previous experimental studies and potentially has far-reaching implications for the functionality and response time of the material in future applications; however, so far, it has not been quantified or reported systematically. Here, we provide a comprehensive qualitative and quantitative description of the chemical-to-mechanical delay, and we propose to explain it as a consequence of the slow nonequilibrium swelling–deswelling dynamics of the polymer material. Specifically, standard hydrogel pieces are large enough that transport processes, for example, counterion migration and water diffusion, cannot occur instantaneously throughout the entire gel piece, as opposed to previous theoretical considerations. As a result, the volume response of the polymer to a chemical change may be governed by a characteristic response time, which leads to the emergence of delay in mechanical oscillation. This is supported by our theoretical calculations.

Selfassembled micellar structures of Lipopeptides with variable number of attached lipid chains revealed by atomistic molecular dynamics simulations.