Abstract
Using molecular dynamics simulation of a polymer glass model we investigate free-standing polymer films focusing on the in-plane shear modulus , defined by means of the stress-fluctuation formula, as a function of temperature , film thickness (tuned by means of the lateral box size ), and sampling time . Various observables are seen to vary linearly with , demonstrating thus the (to leading order) linear superposition of bulk and surface properties. Confirming the time-translational invariance of our systems, is shown to be numerically equivalent to a second integral over the shear-stress relaxation modulus . It is thus a natural smoothing function statistically better behaved as . As shown from the standard deviations and , this is especially important for large times and for temperatures around the glass transition. and are found to decrease continuously with and a jump-singularity is not observed. Using the Einstein-Helfand relation for and the successful time-temperature superposition scaling of and , the shear viscosity can be estimated for a broad range of temperatures.
7 More- Received 7 September 2018
- Revised 25 October 2018
DOI:https://doi.org/10.1103/PhysRevE.98.062502
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