Molecular simulation of liquid crystal polymer flow : a wavelet-finite element analysis
Name
42249612-MIT.pdf
Description
Full printable version
Size
27.35 MB
Format
Adobe PDF
Checksum (MD5)
6efe4df9db9af3737c9e2116b714e23d
Author(s)
Nayak, Radha, 1969-
Advisor(s)
Robert C. Armstrong and Robert A. Brown.
Alternative Title
Wavelet-finite element analysis
Date Issued
1998
Publisher
Massachusetts Institute of Technology
Abstract
The focus of this thesis was twofold. First, efficient numerical methods were developed for the modeling of the molecular orientation distribution function, f, of rigid rod polymers in flow. These methods were used to investigate the liquid crystal polymer (LCP) system. Second, the distribution function calculations were incorporated into a discontinuous Galerkin finite element framework for the modeling of complex LCP flows. Due to the localized nature of f under flow, the Daubechies D6 wavelets were used as basis functions for the approximation of f, and resulted in an efficient numerical technique to model LCPs. Bifurcation analysis of the Doi LCP model in shear flow showed that steady state solutions are lost due to the formation of a limit point in the plot of structure parameter S vs. concentration parameter N, beyond which time-periodic solutions are the only stable solutions. At low De, the time-periodic solutions onset as tumbling states at a global bifurcation. At high De, they onset as wagging states at a Hopf bifurcation, with a subsequent second transition to tumbling as N is increased. The period of oscillation of all tumbling states follows the experimentally observed scaling with strain. However, the wagging states do not follow this scaling, indicating that tumbling and wagging states belong to different solution. families. Computation of f in pressure-driven channel flow of LCPs using the waveletfinite element method showed that the range of tumbling periods, combined with the existence of an infinite period tumbling streamline at the centerline, provides a mechanism for texture generation and refinement. The analysis also demonstrated the possibility of predicting biphasic solutions to LCP problems. Simulations of LCP flow in a tapering contraction geometry showed that the Doi model predicts intermediate concentrations to be most effective in producing flow-alignment of molecular distributions. At higher concentrations, tumbling is found to be widespread in the tapering section despite the presence of an elongational component in the strain rate. Taken together, these calculations demonstrate the feasibility of performing complex flow calculations with molecular models, which will lead to a better physical understanding of the effect of molecular configuration in polymer flows.
Description
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1998.
Includes bibliographical references (v. 2, leaves 358-374).
Subjects
Chemical Engineering
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
Terms of Use
M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.
Persistent DSpace Link
