MEASUREMENT OF INTER-PARTICLE FORCES FROM THE OSMOTIC-PRESSURE OF PARTIALLY FROZEN DISPERSIONS

When an oil-continuous dispersion is frozen two microdomains are forme d: one, the pure oil solvent which is selectively solidified (I), the other, a concentrated 'liquid' dispersion of particles in oil (II). Th ese two domains are intimately mixed within the frozen colloid and exi st in a state of equilibrium determined by the system pressure and tem perature. The position of equilibrium controls the proportion of the s olvent which is solidified, and thereby the concentration of particles within the fluid microdomains (II). Combined with SANS measurements, to determine the inter-particle separation in these microdomains, an a nalysis based on osmotic pressure provides a measure of the inter-part icle repulsion forces presented by the surfactant layers.