AbstmcL The three-component ionic microemulsion system consisting o f ~o~/water/decane shows an U~USUBI phase behaviour in the vicinity of room temperature The phase diagram in the temperaturevolume-fra~tio" (of the dispened phase) plane exhibits a lower coiisolute critical point at about 40 'C and 10% t'olume fraction. A percolorion line, stmtmg from the vicinity of the critical point. cuts across the plane. extending to the high-volume-fraction side at progrecsively lower temperatures. This phase behaviour can be understood in t e r m o f a system o f polydispersed spherical water droplets, each coated by a monolayer of AOT, dispersed in a continuum of oil. These droplets interact with each other via n hard-core plus a shon-range attractive interaction. the strength of which increases with temperature. We rhow thal Baxter's sticky-sphere model CM account for the phase behaviour, including the percolation line, quantitatively provided th3t the stickiness pmmeter is a suitable function of temperature. We use the structure factors measured by small-angle neutron scattering (SANS) below the critical temperature to determine this functional dependence. We 3150 invstigate the dynamics of droplets. below and approaching the critical and pcrcolalion points, by dynamic light scattering. The first cumulant and time evoluuon of the droplet density correlation function can be quantitatively calculared by assuming the existence o f polydispersed fractal clusters formed by the microemulsion droplets due to attraction. The relaxation phenomena obselved in an extensive set of measurements o f electrical conductivity and permittivity close to percolalion can also be inrerpreted through the same cluster-forming mechanism, which reproduces the most relevant features o f the frequency-dependent complex dielectric constant o f this system.

We have made an extensive investigation of the phase diagrams and the associated mierastructure of a pseudo-temary system AOT/water (0.6 wt% NaCl)/ decane. This micro-emulsion system shows, for a surfactant concentration in excess of 6 wt%, acharacterkticphase progressionfrom a water-in-oil(w/o) micro-emulsion in coexistence with excess water at low temperatures to an oil-in-water (OlW) microemulsion in coexistence with excess oil at high temperatures through a onephase micro-emulsion in the intermediate temperatures. Thus, one expects a StNcturd invusion to occur somewhere in the one-phase &d.We haw performed extensive small angle neutron scattering (SANS) measurements to study the pathway of such a structural inversion in this micro-emulsionsystem when there are comparable a m o u t s of oil and water in the system, and when the volume fraction of water is much higher than that of oil. In the former ease, we observed the inversion of the w/o to the olw micro-emulsions tlmugh an intermediate bicontinuous one-phase mi-emulsion.In the latter case, we show that the inversion takes pkce through a pathway of L3-Lo-L1 as temperature increaser. Particular emphasis is put on analyses of the interfacial structure in different mic-emulsion p h a s .