Date of Award
Doctor of Philosophy (PhD)
Matthew A. Glaser
Noel A. Clark
Three models are examined to demonstrate novel and complex behavior stemming from simple specifications. First I explore the hard-core soft-shoulder (HCSS) system where spheres interact via isotropic, purely repulsive potentials involving a hard core repulsion of range σ and a finite step "shoulder" repulsion of range σs. This system's diverse phase morphology is illustrated by the zero-temperature phase diagram calculated via a large scale simulated annealing procedure. I explore the prospect of directed design of self-assembled structures. The system's incredibly complex behavior and numerous metastable states make it ideal as a test bed for examining the computational effectiveness of various advanced Monte Carlo techniques. I apply several existing methods as well as extend the virtual move Monte Carlo (VMMC) algorithm to models with purely repulsive interactions.
Second, I examine self assembled bundles of achiral hard rods with distributed, short-range attraction. I show that in the majority of cases the equilibrium state of the bundle is chiral. I use umbrella sampling Monte Carlo and cell theory to compute the free energy as a function of a twist order parameter, and show that the formation of spontaneously chiral bundles is driven by maximization of orientational entropy through a process called orientational escape. I map out the phase diagram of bundles in terms of the density and bundle aspect ratio (L/Db) finding transitions between untwisted, weakly twisted, and strongly twisted states.
Lastly I explore the phase behavior of tilted hard rods as a model of de Vries smectic behavior and the first order smectic C (SmC) to smectic A (SmA) phase transition. The free energy cost of azimuthal rotation of a molecule away from the local tilt direction is calculated via umbrella sampling. This calculation is used to map the hard rod system onto a lattice spin system which shows a cross-over from a continuous to first order phase transition as the tilt of the rods is increased. This analysis offers a natural explanation of the first order SmA-SmC phase transition common to de Vries smectics.
Kost-Smith, Zachary Vance, "Emergent Phenomena in Minimal Models of Soft Matter" (2014). Physics Graduate Theses & Dissertations. 3.