8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P3.38Fri 911:10-14:00Liquid crystalline order of charged colloidal plateletsRik Wensink 11 Insitute for Theoretical Physics: Soft Matter, Heinrich-Heine-University-Duesseldorf,Universitaetsstrasse 1 40225, Duesseldorf, GermanyWe present a Monte Carlo computer simulation of a model system for like-charged colloidalplatelets. The aim is to elucidate the role of electrostatic interactions on the structure of syntheticclay systems at high particle densities. Short-range repulsions between the particles are describedby a suitable hard-core model representing a discotic particle. This potential is supplemented withan electrostatic potential based on a Yukawa model for the screened Coulombic potential betweeninfinitely thin disklike macro-ions. The particle aspect-ratio and electrostatic parameters werechosen to mimic an aqueous dispersion of thin, like-charged, rigid colloidal platelets at finite saltconcentration. An examination of the fluid phase diagram reveals a marked shift in the isotropicnematictransition compared to the hard cut-sphere reference system. At low salinity and highosmotic pressure we observe anomalous hexagonal columnar structures characterized by interpenetratingcolumns with a typical intercolumnar distance corresponding to about half of that of aregular columnar phase. Increasing the ionic strength leads to the formation of glassy, disorderedstructures consisting of compact cluster of platelets stacked into finite-sized columns. These socalled‘columnar nematic’ structures have been recently observed in systems of charge-stabilizedgibbsite platelets. Our findings are corroborated by an analysis of the static structure factor from asimple density functional theory.38