Molecular-dynamics simulations of thin polyisoprene films confined between amorphous silica substrates

Abstract

Constant temperature–constant pressure (NpT) molecular-dynamics computer simulations have been carried out for the united-atom model of a non-crosslinked (1,4) cis-polyisoprene (PI) melt confined between two amorphous, fully coordinated silica surfaces. The Lennard-Jones 12-6 potential was implemented to describe the polymer–silica interactions. The thickness H of the produced PI–silica film has been varied in a wide range, 1 < H/Rg < 8, where Rg is the individual PI chain radius of gyration measured under the imposed confinement. After a thorough equilibration, the PI film stratified structure and polymer segmental dynamics have been studied. The chain structure in the middle of the films resembles that in a corresponding bulk, but the polymer-density profile shows a pronounced ordering of the polymer segments in the vicinity of silica surfaces; this ordering disappears toward the film middles. Tremendous slowing down of the polymer segmental dynamics has been observed in the film surface layers, with the segmental relaxation more than 150 times slower as compared to that in a PI bulk. This effect increases with decreasing the polymer-film thickness. The segmental relaxation in the PI film middles shows additional relaxation process which is absent in a PI bulk. Even though there are fast relaxation processes in the film middle, its overall relaxation is slower as compared to that in a bulk sample. The interpretation of the results in terms of polymer glassy bridges has been discussed.

Polymer Dynamics in a Polymer-Solid Interphase: Molecular Dynamics Simulations of 1,4-Polybutadiene At a Graphite Surface

“…In fact, computer simulation of a coarse-grained model of short polymers between two equivalent attractive walls revealed an enhancement of T g (18,19); whereas, repulsive walls lead to a decrease of T g (18)(19)(20). However, several works also address structural and dynamical properties for different polymer-solid contacts using chemically realistic simulations (39)(40)(41)(42)(43). Lastly, when ξ < D/2, where the film shows bulk behavior in its center, it can be that certain experimental techniques still are dominated by this bulk behavior and do not pick up significant effects from the interfacial regions with modified physical behavior.…”

Salt concentration dependence of the mechanical properties of LiPF6/poly(propylene glycol) acrylate electrolyte at a graphitic carbon interface: A reactive molecular dynamics study

“…Furthermore, considering the small reduction of mass density at the interface (Supporting Information, Figure S4), the interface role as a preferential site of glassy region nucleation, observed in structurally similar systems, is not confirmed for the presently studied structures. Considering that the corrugated zigzag termination of GC represents an amorphous material surface, the result is found to be in a qualitative agreement with the study in terms of the reduction of interfacial polymer density at amorphous confining surfaces.…”

Molecular dynamics study of oil detachment from an amorphous silica surface in water medium

“…They investigated the adsorption on (1 1 1), (2 2 0) and (3 3 1) surface on silica. Other authors also studied the amorphous silica [23][24][25][26] that is usually obtained by annealing from 8000 to 300 K. Yang's result may help to explain the effect of amorphous silica such as fused quartz on oil detachment.…”