Orientational Relaxation in Simulated Polymer Melts

The orientational relaxation of simple polymer chains was studied using second Legendre polynomial autocorrelation functions. Such functions are commonly fit with a Kohlrausch-Williams-Watts (KWW) stretched exponential form. The value of the stretching parameter, $\beta $, and the degree that it changes as the glass transition is approached are both of physical interest. In the current project, a novel approach to determining the value and variation of $\beta $ from molecular dynamics simulations is implemented. The methodology is found to produce KWW fits of high accuracy. Moreover, the stretching parameter, $\beta $, is found to collapse to a single-valued function of the decay timescale $\tau $ regardless of thermodynamic path. Connections are drawn to experimental results and theoretical implications of the research are discussed.