A Computational Approach to the Stability of Complex Sphere Forming Phases in Block Polymer Melts

Abstract

Block polymers spontaneously self-assemble into a variety of morphologies upon cooling below their order-disorder temperature. Owing to this behavior, block polymers have various potential applications ranging from semiconductors fabrication to filtration devices. Recent discovery of the stable Frank-Kasper phases in diblock copolymer melts resulted in a shift of focus from high-symmetry morphologies to low-symmetry tetrahedrally close-packed phases. While experimentalists have been able synthesize block polymers that exhibit stable Frank-Kasper phases, they could not predictably determine the observed phases a priori. Computational tools can aid in prediction but are rooted in well-developed theories and experimental results. In this dissertation, we aim to develop theoretical understanding of the stability of Frank-Kasper phases that could aid in prediction through a computational study of block polymers guided by experimental data. To this end, we take a three-pronged approach in the dissertation. First, we examined an experimental diblock copolymer/homopolymer system which produces a variety of Frank-Kasper phases. Our computational study reproduced the salient behavior of the system and unveiled a new mechanism for the stabilization of Frank-Kasper phases. Next, we studied the disordered micelle regime, which has consequence in stabilizing metastable Frank-Kapser phases in thermal processing experiments, for conformationally asymmetric diblock copolymer melts. We uncovered a reduction in the window of stability for the disordered micelle regime with increasing conformationally asymmetric. Finally, we compared computational prediction of binary blends of high molecular weight diblock copolymer to experimental results and demonstrated their utility in accessing Frank-Kasper phases. Along with our analysis, we unveiled a potentially new mechanism that may be important in the stabilization of Frank-Kasper phases. We believe that our work in this dissertation provides additional understanding to the behavior of diblock copolymer, specifically in stabilizing Frank-Kasper phases. This work also opens up potential avenues of interest that may further our ability to tailor block polymers for specific applications.