The reversible liquid-to-solid transition of the alkane-continuous phase of a dilute colloidal dispersion (w/o microemulsion or surfactant-stabilised nanoparticles) can be induced by pressure and temperature changes, without destabilising the colloid. The structural changes have been studied by Small-Angle Neutron Scattering (SANS) at high pressure (P = 1–600 bar) and over a range of temperature (T = 3–20°C). In the freezing process two microdomains are formed within the frozen dispersion; one, the pure oil solvent which is selectively solidified (I), the other, a concentrated “liquid” dispersion of particles (II) which separates when the solvent freezes. These two microdomains are intimately mixed and bi-continuous within the frozen colloid and exist in a state of equilibrium at fixed pressure and temperature. The position of equilibrium, represented by the proportion of the solvent which is solidified, and thereby the concentration of particles within the ejected microdomains (II), depends on both temperature and pressure. At constant temperature, increasing pressure results in an increase in the particle concentration such that at high pressure the surfactant layers on adjacent particles become compressed or interdigitated. ombined with SANS measurements, to determine the interparticle separation, an analysis in terms of the osmotic pressure (π) provides a “unification” of the effects of both temperature and pressure on the system. The results provide a measure of the interparticle repulsion forces between the adsorbed monolayers on a 3D configuration of particles as a function of particle separation.

Similar results have now been obtained for certain L₁ self-assembly systems undergoing the water-ice transition. Distinct from this behaviour is that occurring when the aqueous phase is solidified by hydrate formation above the normal freezing point. In this case the slowly propagating clathrate structure “engulfs” the dispersed phase which is not ejected into microdomains i.e. the inter-particle structure is here completely “frozen–in”.