Elastic properties, structures and phase transitions in model colloids

Abstract

The nature of the melting transition for a system of hard discs with translational degrees offreedom in two spatial dimensions has been analysed by a combination of computersimulation methods and a finite size scaling technique. The behaviour of the system isconsistent with the predictions of the Kosterlitz–Thouless–Halperin–Nelson–Young(KTHNY) theory.The structural and elastic properties of binary colloidal mixtures in two and three spatialdimensions are discussed as well as those of colloidal systems with quenched pointimpurities.Hard and soft discs in external periodic (light-) fields show rich phase diagrams includingfreezing and melting transitions when the density of the system is varied. Monte Carlosimulations for detailed finite size scaling analysis of various thermodynamic quantities likethe order parameter, its cumulants, etc, have been used in order to map the phasediagram of the system for various values of the density and the amplitude of theexternal potential. For hard discs we find clear indication of a reentrant liquid phaseover a significant region of the parameter space. The simulations therefore showthat the system of hard discs behaves in a fashion similar to charge stabilizedcolloids which are known to undergo an initial freezing, followed by a remeltingtransition as the amplitude of the imposed modulating field produced by crossed laserbeams is steadily increased. Detailed analysis of the simulation data shows severalfeatures consistent with a recent dislocation unbinding theory of laser inducedmelting. The differences and similarities of systems with soft potentials (DLVO,1/r12,1/r6) and the relation to experimental data is analysed.