EFFECTS OF SOLIDIFICATION OF THE OIL PHASE ON THE STRUCTURE OF COLLOIDAL DISPERSIONS IN CYCLOHEXANE

The liquid-to-solid transition of the alkane-continuous phase of a dil ute surfactant-stabilized particle or droplet dispersion can be induce d in a reversible manner without destabilizing the colloid by pressure and/or temperature changes. The structural changes have been studied by small-angle neutron scattering (SANS) over a range of pressure (1-6 00 bar) and temperatures (3-20-degrees-C). The SANS results indicate t hat there are different levels of structure in the solidified system i n which a solid alkane coexists with fluid cluster domains. The cluste rs show large-scale structural correlations of order 5-50 mum; within these clusters the particles are in close contact, so that under certa in conditions, e.g. high pressure, the stabilizing surfactant layers o f adjacent particles are interdigitated. The distance between particle centers, and therefore the degree of surfactant interdigitation, can be readily varied by the application of pressure. An interpretation of the SANS results is given in terms of the effects of temperature and pressure upon the osmotic pressure of the concentrated solution of par ticles/droplets. The analysis provides an estimate of the interparticl e pair potential energy between adjacent particles in a cluster as a f unction of separation.