Berlin 2012 – scientific programme
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O: Fachverband Oberflächenphysik
O 57: Solid / liquid interfaces II
O 57.1: Talk
Wednesday, March 28, 2012, 16:45–17:00, A 060
Two-Dimensional Colloidal Alloys — •Adam Law1, Martin Buzza2, and Tommy Horozov3 — 1Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany — 2Surfactant and Colloid Group, Department of Physics, The University of Hull, England, HU6 7RX — 3Surfactant and Colloid Group, Department of Chemistry, The University of Hull, England, HU6 7RX
We study both experimentally and theoretically the structure of mixed monolayers of large (3 μm) and small (1μm) very hydrophobic silica particles at an octane/water interface as a function of the number fraction of small particles. We find that a rich variety of two-dimensional hexagonal superlattices of large and small particles can be obtained in this system experimentally due to strong and long-range electrostatic repulsions through the nonpolar oil phase. These represent the first experimental results for long-range order in a 2D binary colloid system. The structures obtained for the different compositions are in good agreement with zero temperature lattice sum calculations and finite temperature Monte Carlo simulations. Our theoretical analysis also reveals that the melting behaviour of the superlattice structures is very rich, proceeding via a multi-stage process, with melting temperatures that have a very strong and non-monotonic dependence on composition.