Objectif
The origin and the mechanism of molecular motions, as well as the effect of the packing environment on these motions in the mesomorphic state of polymers, are fundamental problems in polymer science. One of the most interesting problems is the nature of the non-Arrhenius temperature dependence of the dielectric relaxation times observed experimentally in poly-p-hydroxybenzoic acid (PHBA) copolyester systems.
In this project two characteristic types of motion of PHBA will be investigated by means of different simulation techniques. The disorder of crankshaft-like fragments in layers of phenyl rings will be investigated by Monte Carlo simulations. The structures obtained from these simulations will be used to start molecular dynamics simulations to obtain information on vibrational motions and the reorientational motions of chain fragments. The latter will be analyzed using umbrella sampling. This technique allows for the investigation of the free-energy barrier for that kind of motion.
Additionally, analytical approaches to the problem will be developed, and Langevin dynamics will be applied to obtain correlation functions for the torsional angles.
Thème(s)
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64287 Darmstadt
Allemagne