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Professor Fernando Escobedo
School of Chemical and Biomolecular Engineering
Cornell University
Thursday, February 21, 2008
102 Chemistry Building
10:00 a.m. - 11:00 a.m.
Abstract
Both colloidal particles and polymers often form ordered liquid phases that posses unique optical, rheological, and mechanical properties, making them attractive components in the preparation of novel fibers, coatings, nanocomposites, and electronic materials.
Consistent with the recent advances in synthetic techniques that are realizing novel mesogenic building blocks with unprecedented degree of control, our goal is to use molecular simulations to map out the still uncharted phase behavior of systems containing such building blocks.
In this talk, I will discuss both the methodology employed (which includes optimized approaches for the simulation of free-energies and transition states) and the simulation results on suspensions of cuboids and peanut-shaped particles, and on melts of diblock copolymers.
In the system of cuboids, our results show the presence of novel liquid-crystalline phases (yet to be realized experimentally), which arise from a competition between orientational entropy and packing entropy. A rich phase behavior is predicted upon varying the aspect ratio of the cuboid (going from a square tile to a long rod). The peanut system serves to illustrate how novel transition-path sampling methods can be used to understand the kinetic mechanism of order-disorder phase transitions.
In the diblock copolymer we focus on how to design additives (like selective nanoparticles and homopolymer) that can target the formation of the often elusive bi-continuous phases (like the gyroid, double-diamond, and plumber's nightmare phases). Our results elucidate the origins of the packing frustration that limits the viability of such phases and provide insights as to how overcome it.