Analysis of uncertainties in polymer viscoelastic properties obtained from equilibrium computer simulations

The Journal of Chemical Physics
Suchira SenPawel Keblinski

Abstract

We critically evaluate the uncertainties in the stress autocorrelation function obtained from equilibrium molecular dynamics simulation of model polymer melts. This quantity is central to evaluating transport properties, e.g., the complex modulus and the viscosity. In contrast to the intuitive expectation that simulations have to be run five to six orders of magnitude longer than the chain relaxation time to reduce uncertainties to acceptable levels, our analysis shows that the majority of the uncertainty is associated with rapidly oscillating bonded interactions. These fluctuations occur on time scales which are approximately 10(4) times shorter than the relaxation time of a chain of length 80. Consequently, the effects of these oscillations on the stress autocorrelation function can be dramatically reduced by (i) conducting long simulations (typically 10(6) times longer than the bond relaxation times or only 10(2) chain relaxation times) and (ii) by performing running averages with time windows whose time scales are much longer than these oscillations. Conducting such long simulations also allows for the accurate determination of the melt viscosity and the low-frequency complex modulus, but performing running averages do not ...Continue Reading

Citations

Dec 3, 2008·The Journal of Chemical Physics·Teena GoelCharusita Chakravarty
Dec 3, 2008·The Journal of Chemical Physics·Jun LiuLiqun Zhang
Oct 19, 2010·The Journal of Chemical Physics·R M PuscasuJ S Hansen

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