Morphology transitions in multilayer polymer melts due to hole growth and layer interactions

The central focus of this study was the importance of hole formation and growth in thin melt layers and their effect on subsequent morphology changes in the melt. Most prior studies related to this work focused on a single fluid layer dewetting on a solid substrate. The present work is a more generalized case where holes form in multiple fluid layers without any solid substrate present. The physical problem consisted of two different fluids (fluid 1 and fluid 2) arranged in multiple layers. A hole in fluid 1 was filled by fluid 2 and connected adjacent fluid 2 layers. This initial arrangement of holes was motivated by examining experimental micrographs. Hole formation due to layer instabilities was not considered and the focus was on what happened after holes formed. Both ordered and random hole arrangements that have been documented experimentally were considered.; A relatively new CFD tool, the lattice Boltzmann method (LBM), has been used for studying the interactive growth of various hole patterns in film layers in a periodic, three-dimensional domain. The LBM was particularly suitable for two-component viscous flow with interfacial tension. The method was also very amenable to parallel implementation. Having gained some confidence in the LBM, it was then applied to the actual problem of in-situ morphology transitions in layers. The model results were broadly divided in two parts. The first part was morphology changes in quiescent flow. This corresponded to conditions where interface tension and viscous forces were the only dominant agents. The second set of results included the effect of external shear. In this case, both imposed shear force and interfacial forces influenced morphology changes. Within these two broad classifications, the influence of various types of hole patterns (ordered and random), geometric parameters relating to hole size and spacing, volume composition and viscosity ratio were examined. It was demonstrated computationally that hole growth can lead to fine droplet distributions, oriented and numerous thin fibers and co-continuous morphologies.; The advantages of obtaining such structures via controllable multi-layer formation and breakup are discussed. Experiments were carried out separately, but in tandem with modeling work so that cross-fertilization of ideas could occur. Experimental micrographs were analyzed and often provided inputs for initial structures in the LBM model. (Abstract shortened by UMI.)...