| Very recently experimental proof of the theoretically predicted Critical Casimir Effect has been published. This effect is thought to play an important role in wetting and aggregation phenomena in biophysical systems and materials science; however, it is far from being understood. The Critical Casimir effect manifests itself as an attractive force in a system of charge stabilized colloidal particles suspended in a binary liquid mixture. This offers a novel route to the formation of colloidal phases and structures that have important applications e.g. for photonic devices. We observed that when density matching of particles and suspending fluid reduced the effect of gravity, the attraction induced gas-liquid and liquid-solid transitions in the colloidal system. Two length scales determine the particle interactions: the correlation length of the Critical Casimir attraction and the Debye screening length of the repulsive Coulomb potential. Variation of the correlation length with temperature offers a unique temperature control over the particle interactions, which should ultimately result in a fine control over colloidal structures. An accurate characterization of the phase behaviour is, however, impeded by gravity. Our aim is investigate the Critical Casimir effect in the formation of colloidal phases in the absence of gravity, where the Critical Casimir attraction and the Coulomb repulsion alone determine phase behavior. Temperature will serve as a continuous control parameter to tune particle interactions and manipulate colloidal structures with external control. |
