(517d) Mesophase Behavior of Polyhedral Particles

Anisotropic interaction fields encoded in nanoparticles of non-spherical shape can drive their assembly into many complex, ordered or partially ordered structures ("mesophases"). Some of these self-assembled 'phases' are highly desirable for their distinctive electronic, physical and optical properties and are very sensitive to the inherent interactions of their building blocks and other external driving fields. To understand the basic principles controlling formation of these assemblies, we performed systematic simulation studies to explore the effect of 'shape' or excluded volume interactions on the equilibrium mesophase behavior and on selected non-equilibrium mechanical properties of these systems. Monte Carlo simulations performed on a class of space-filling polyhedral shapes predict formation of various novel liquid-crystalline (LC) and plastic-crystalline phases. By correlating these results with particle anisotropy and rotational symmetry, guidelines for predicting phase behaviour of polyhedral particles are proposed. Moreover, detailed analysis of dynamical and static ordering in different phases across phase transitions provide further insights into the kinetics and mechanisms of these transitions. Current work focuses on studying the phase behavior of a class of polyhedral shapes, for which PbSe nanocrystals of 3-10 nm length scale can be synthesized in different stages of the 'hot-injection' process. Altogether, the body of knowledge that is emerging from these studies may prove useful in designing optimal self-assembly strategies for many desired nanostructures; e.g., as in our ongoing efforts in understanding the nanocrystal superlattice formation for solar cell applications.