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

P5.166Wed 711:10-14:00A phase diagram for colloidal suspensions aggregatedby critical Casimir forcesMinh Triet Dang, 1 Van Duc Nguyen, 1 Peter Bolhuis, 2 and Peter Schall 11 Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098 XH,Amsterdam, Netherlands2 Van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Amsterdam,NetherlandsColloidal particles provide a novel way for investigating phase behavior directly controlled by theCritical Casimir effect. This effect produces attractive forces between particle surfaces induced bytemperature-tunable critical solvent fluctuations. These forces allow us to directly manipulate theaggregation process to investigate equilibrium transitions from gas to liquid and solid state. Here,we use molecular simulation to construct a phase diagram, which yields a unified view of colloidalphase behavior induced by Critical Casimir effect. We experimentally measure the temperaturedependentparticle pair potential from the distribution of particles in dilute suspensions, and extrapolatethese potentials in a wider range of temperature based on universal scaling theory. We usethese data as input parameters for our Monte Carlo calculations in the Gibbs ensemble to map thegas-liquid coexistence region, and estimate the critical temperature of gas-liquid phase transition.The simulated gas-liquid coexistence curve exhibits 3D Ising scaling, and the estimated criticalpoint agrees with experimental observations. We then use Gibbs-Duhem integration to trace alongthe solid-fluid coexistence boundaries and determine the triple point. Remarkably, the whole gasliquid-solidphase diagram obtained from Monte Carlo simulation is in very good agreement withwhat we observe in experiments. This unified phase diagram may open a new opportunity forprecisely controlling the self-assembly of micro- and nano-devices.166