Hard spheres out of equilibrium

Abstract

In this thesis, experiments and simulations are combined to investigate the nonequilibrium behaviour of hard spheres. In the first chapters we use Molecular Dynamics simulations to investigate the dynamic glass transition of polydisperse hard spheres. We show that this dynamic transition is accompanied by a thermodynamic signature. The higher-order derivatives of the pressure change abruptly at the dynamic glass transition. If a system is compressed beyond this dynamic transition, the pressure increases until it diverges when the system is completely jammed. The density at which the pressure diverges depends on the compression speed. We proceed with experiments on colloidal polymethylmethacrylate (PMMA) particles which closely resemble hard spheres. We investigate the effect of compression using gravity and electric field gradients on the nucleation and on the glass transition. The transition from glass to crystal is gradual and is strongly effected by gravity. We go back to computer simulations to investigate two different techniques to calculate the rate at which a hard-sphere system nucleates. We find that the two techniques yield similar results for the nucleation rate as well as the critical nucleus shape. From this we conclude that the simulation techniques are valid. A combination of simulations and experiments is used to study the nucleation of hard spheres on seed structures. We initiate the nucleation with a seed of particles kept in place by optical tweezers. We show that whereas the nucleation itself can be well described as an equilibrium process, the growth after nucleation can not. We demonstrate that defects play an important role in the growth of the crystal. Colloidal hard spheres can also be driven out of equilibrium using shear. We perform experiments on an equilibrium fluid phase below the coexistence density of the fluid. We show that we can induce order in an equilibrium fluid using oscillatory shear. We find five different phases for varying frequency and amplitude: four known phases and one new phase. The formation of all phases occurs via nucleation and growth and the melting, when the shear is stopped, starts on the edges and near the defects of the crystal phases. In the final chapter, we investigate the interactions between rough colloidal particles in the presence of polymers. We investigate whether surface roughness can be used to reduce the depletion attraction. We find that when the polymer is smaller than the surface roughness the attraction can be reduced significantly compared to smooth colloids.