Temperature and pressure effects on local structure and chain packing in cis-1,4-polybutadiene from detailed molecular dynamics simulations

摘要

We present results for the temperature and pressure dependence of local structure and chain packing in cis-1,4-polybutadiene (cis-1,4-PB) from detailed detailed molecular dynamics (MD) simulations with a united-atom model. The simulations have been executed in the NPT statistical ensemble with a parallel, multiple time step MD algorithm, which allowed us to access simulation times up to 1 mu s. Because of this, a 32 chain C-128 cis-1,4-PB system was successfully simulated over a wide range of temperature (from 430 to 195 K) and pressure (from 1 atm to kbar) conditions. Simulation predictions are reported for the temperature and pressure dependence of the: (a) density; (b) chain character ratio, C-n; (c) intermolecular pair distribution function, g(r), static structure factor, S(q), and first peak position, Q(max), in the S(q) vs. q findings of this work is that the component of the S(q) vs. q plot representing cis-1,4-PB sample exhibits a monotonic decrease with q which remains completely unaffected by the pressure. In contrast, the intermolecular contribution exhibits a distinct peak (at around 1.4 angstrom(-1)) whose position shifts towards higher q values as the pressure is raised, accompanied by a decrease in its intensity.