Temporal and spatial analysis of glass transition phenomena using a molecular dynamics study of Lennard-Jones chains
Abstract
Molecular dynamics simulations have been performed with freely-rotating chains of Lennard-Jones spheres in order to study the local PVT behavior of a model polymer during its solidification process. Twenty chains, each containing twenty monomer units, have been quenched from an equilibrated liquid reduced density of 1.0 at 120K with quench rates including 3 $\times$ 10$\sp{13}$K/s, 3 $\times$ 10$\sp{12}$ K/s, and 3 $\times$ 10$\sp{11}$ K/s. During each quench, sample configurations were taken every 10K and annealed for 200 picoseconds. Each of these annealing runs was analyzed in terms of single particle potential energy, kinetic energy, Voronoi volume, temperature, and pressure. All local variables were pursued to test the hypothesis that a single variable acts as an ordering parameter. An ordering parameter would be very sensitive to the glass transition and would be used to characterize the PVT behavior of the material in terms of a fourth variable. Analysis showed that all variables sensitive to local packing slow down upon entering the glass, if these variables are normalized with respect to their ensemble average. Normalization allows for the determination of the time frame required for each variable to explore all available phase space. This "ergodicity" measure shows that the glass transition is characterized by all local-packing variables losing ergodicity at a more drastic rate. Non-ergodic behavior remains homogeneous in space for the system size studied. Non-ergodic behavior is compared with the predictions of molecular hydrodynamics.
Degree
Ph.D.
Advisors
Wiest, Purdue University.
Subject Area
Chemical engineering
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