Polyhedral nanoparticles (NPs) can be assembled into super-lattice materials that has the potential to form phases exhibiting vastly different optical, electronic, physical, and chemical properties. This proposal, building on past successes, will focus on understanding the kinetics of the transitions between phases, mesophases, and crystals. Such kinetics play a crucial role in the experimental realization of these structures and the insights gained would allow ways to catalyze the self-assembly process, or design ways to steer the systems into desirable phases. In the long term, such results could have an impact on the ceramic, plastics, and semiconductor industries by helping broaden the approaches available to develop stable nanocomposites, liquid armors, colloid-based mesocrystals for photonic materials, and nanocrystal arrays for photovoltaics.
Advanced Monte Carlo (e.g., Gibbs-Duhem integration with semi-grand canonical ensembles) and Molecular Dynamics simulations will be used to study how hard (or square-well attraction) shapes organize at different volume fractions. For such systems, it's easy to become kinetically trapped experimentally (either as a desired or undesired structure), so it's very important to understand, not just the equilibrium state, but the kinetics, which is the focus here. In this context, the mesophases that are formed may provide intermediate states that lower the otherwise high energy barrier between disordered and crystalline states. The investigations will include not just pure systems (containing one type of polyhedral particles), but also the thermodynamics and kinetics of phase transitions in binary mixtures. Particles to be investigated include polyhedra that can be produced in experiments (cubes, cuboctahedra, truncated octahedra, and octahedra), and mixtures of those (including also spherical particles). The simulations will model the thermodynamic behavior of the mixtures, and new order parameters and variants of the forward flux sampling method will be used to simulate the kinetics of phase transitions.
