| Abstract
| - Molecular dynamics simulations have been used to delineate the pressure dependence ofconformational dynamics in polyethylene. Chain dynamics have been studied as a function of pressure(0−25 kbar) at 400 K and as a function of temperature (280−450 K) at an elevated pressure of 10 kbar.The volumetric glass transition is found isobarically (10 kbar) at ∼315 K and is considerably elevatedfrom the ∼220 K atmospheric pressure value. On increasing pressure at constant temperature, the systemdisplays several signatures indicative of the vitrification process that are complementary to thosepreviously found to be associated with lowering of temperature. These include a large increase inautocorrelation function relaxation times, divergence of the relaxation times from conformational transitionrates, an increase in spatial heterogeneity of the distribution of conformational transition rates over thevarious bonds, and an increase in self-correlation of the conformational transitions. Isobarically at highpressure (10 kbar), the variation with temperature of the relaxation times associated with the decay ofthe dipolar autocorrelation function is in accord with dielectric relaxation experiments. Upon loweringthe temperature, the relaxation times diverge from the conformation transition rates, an effect alsoobserved at low pressure.
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