Rotator-to-Lamellar Phase Transition in Janus Colloids Driven by Pressure Anisotropy.

We demonstrate through Brownian dynamics simulations a phase transition in plastic crystalline assemblies of Janus spheres through controlled pressure anisotropy. When the pressure in plane with hexagonally ordered layers is increased relative to that normal to the layers, a rapid first-order rotator-to-lamellar transition of Janus sphere orientation occurs at constant temperature. We show that the underlying mechanism closely follows the Maier-Saupe theory, originally developed for isotropic-to-nematic transition in positionally disordered materials but here applied to positionally ordered ones. Since the transition involves almost no translational diffusion or volume change, and occurs rapidly by particle rotation, the results should help guide the design of rapidly switchable colloidal crystals. [ABSTRACT FROM AUTHOR]