Viscoelastic properties of polybutadiene: Combination of theory and molecular dynamics simulations

In this work the description of a methodology that allows accurate calculation of viscoelastic properties of polymers using combinations of the molecular theories and computer simulations is presented. This methodology includes molecular dynamics simulations and atomic trajectory analysis of relatively short polymer oligomers, while molecular theories extend and extrapolate properties to highly entangled long chain regime, on time and length scales many orders of magnitude larger than are directly accessible to computer simulations.; In order to validate new methodology, polybutadiene was chosen as a sample material. Complex shear stress modulus, viscosity and temperature dependence of the shift factor were calculated for high molecular weight polymer utilizing three molecular models of viscoelasticity. Predicted viscoelastic properties of the polybutadiene were then compared with available experiment measurements. Very good quality of agreement for all predicted properties was demonstrated for one of the chosen models. As there is nothing special in this approach to polybutadiene, molecular dynamics simulations of similar quality for short chains of other polymers also can be expected to yield accurate viscoelastic properties using presented methodology.