(489e) Electric-Field Assembly of Two-Dimensional Colloidal Quasicrystals

Quasicrystals are a type of aperiodic material with long-range orientational order. Lacking periodic unit cells, colloidal quasicrystals are predicted to exhibit distinctive optical, electrical, and mechanical properties that differ from those of traditional crystals. However, most quasicrystals are formed from atomic constituents, as in metal alloys, and there are only a few examples of quasicrystals formed from micron scale constituents, making the formation and dynamics of quasicrystals difficult to directly observe in experiments. To address these challenges, we report simulation and theory of electric-field directed assembly of colloidal quasicrystals confined to a surface.

In previous experimental work, we found that polystyrene colloids in deionized water spontaneously organized into two layers near an electrode surface when subjected to an external electric-field, forming a variety of intricate ordered phases, including hexagonal bilayer and sigma phases. These structures were found to be in quantitative agreement with Monte Carlo simulations in which isotropic colloids confined to two layers interact via Lennard-Jones and dipolar interactions. By tuning the concentration, dipolar strength, and number ratio of particles in the upper layer to particles in the lower layer, we observe several unique structures previously found in experiments. We find that by equilibrating at high temperature, followed by gradual annealing, quasicrystals can be assembled over a range of parameters. We characterize the quasicrystals by several means, including the scattering patterns, global orientational order, local coordination, and phason strain. We find excellent agreement between the parameters obtained from our simulations compared to those of an ideal Schlottmann dodecagonal quasicrystal. The theoretical energy landscapes of ideal quasicrystals, sigma, and hexagonal phases are determined, and the resulting phase diagrams compare favorably with our simulation results. Our simulation results allow observation of quasicrystal assembly while providing a framework to assembling micron-scale quasicrystals in the laboratory.