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The evolution of order in liquid crystals and polymer crystals

This dissertation describes computer simulations and theoretical analyses of ordering processes in liquid crystals and polymers. One ordering process in liquid crystals occurs during the isotropic to nematic transition in which point and line defects form and annihilate. Monte Carlo simulations support the newly-derived scaling of the defect density, which was found to scale with time as $-$6/7 in both two and three dimensions, contrary to the mean-field result of $-$1. Frustration was determined to be a key factor in this difference. Another ordering process in liquid crystals is the evolution of inversion walls and loops. Analogous to the model of a shrinking elastic loop in a viscous medium which has been theoretically investigated by deGennes and Brochard, our lattice Monte Carlo simulations of inversion walls and loops show the same scaling behavior with time and the same predicted dependence of shrinkage rate on the orientational diffusion coefficient. Polymer crystallization constitutes the other major topic of this dissertation. The initial stages of crystallization are difficult to study experimentally but by using the united-atom Langevin dynamics method, single and multi-chain crystallization can be simulated. The simulations show that random fluctuations nucleate regions of higher order which in turn can induce further crystallization. Lamellar thicknesses obtained from simulations at various undercoolings showed the same scaling behavior as experimental data from literature. Besides homogeneous nucleation, secondary nucleation was also observed, with the newly-attached chains continuing to undergo conformational changes on the crystal surface. Finally, the phenomenon of lamellar thickening was investigated. Lamellar thickening was observed to occur cooperatively in a stepwise, quantized manner.
Date01 January 1998
CreatorsLiu, Chester
PublisherScholarWorks@UMass Amherst
Source SetsUniversity of Massachusetts, Amherst
Detected LanguageEnglish
SourceDoctoral Dissertations Available from Proquest

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