Spatio-Temporal Emergence of Morphological Patterns in Liquid Crystalline Polymer and Rigid-Rod Polymer Systems during Solidification

University Of Akron, Akron OH

Investigators

Abstract

The present proposal entails experimental and theoretical elucidation of (i) dynamics of hollow fiber (or nano-tube) formation during solidification of main chain liquid crystalline polymers (MCLCP) and/or rigid-rod polymer solution, (ii) dynamics of nano-porous membranes of monomeric mesognes during pattern polymerization, (iii) dynamics of microfibril formation during dry-jet spinning, and (iv) hybrid-composites. The well-established time-dependent Ginzburg-Landau TDGL (Model C) will be applied in conjunction with the advection term for the tracking of solvent evaporation and flow. The physical significanace of all parameters pertaining to the governing non-linear reaction-diffusion equations will be clarified, and their predictive capabilitieis will be demonstrated. The dynamics of pattern formation will be investigated by comparison with the recent experimental observations made in dry-jet and/or electro-spinning. Recognizing the possible control of domain morphology and improved understanding of mesogenic interactions, the proposed study will be extended to microporous membranes and nano-composites. The theoretical scheme proposed here demonstrates the spation-temporal evolution of the order parameters (such as density, concentration and orientation fluctuations) based on the local free energy and non-local gradient (diffusive) terms. The numerical simulation further illustrates the emergence of the local internal structures during solidification. Moreover, this methodology can applied to elucidating the microfibrillation dynamics in spinning of semicrystalline polymers and hydrogen bonding systems. It is encouraging to discern unique morphological features encompassing (i) nano-tube formation, (ii) concentric rings/spiral-breakup leading to microfibrillation and (iii) viscous fingering patterns. The observed phenomenon of spiral breakup is one of the most debated topics in the no-linear dynamics of excitable media and biological systems. Furthermore, it clearly demonstrates a new approach to the decades-old problem of predicting morphology development in solution-spun fibers such as rough skin/core structures, collapsed kidney shape morphology, and microfibrils. This methodology has potential for modern technological applications including electro-spinning of nano-fibers/tubes, microporous membranes through pattern photopolymerization induced phase separation, and nano-hybrid composites. It is anticipated that these microporous membranes have widespread applications usch as fuel cell membranes, filtration, and drug delivery. Furthermore, some of the simutaion programs have been written in C++ and can be shown on live-mode with the aid of an LCD projector. Such interactive programs are proven to be useful for classroom teaching and demonstration to the public.