Shear-stress fluctuations in free-standing polymer films

Abstract

Using molecular dynamics simulation of a polymer glass model we investigate free-standing polymer films focusing on the in-plane shear modulus $μ$ and the corresponding shear-stress relaxation modulus $G(t)$ as functions of temperature $T$, film thickness $H$ (tuned by means of the lateral box size $L$) and sampling time $Δt$. Various observables are seen to vary linearly with $1/H$ demonstrating thus the (to leading order) linear superposition of bulk and surface properties. In agreement with recent studies on three-dimensional polymer glass-formers, $μ$ and $G(t)$ are found to decrease continuously with $T$. A jump-singularity is not observed. Confirming the time-translational invariance of our systems, the $Δt$-dependence of $μ$ is traced back to $G(t)$.

15 pages, 14 figures, accepted to Phys. Rev. E (Nov 2018) https://journals.aps.org/pre/accepted/b9077R77J041fb19b5843389c816aa554b5d02468