Two percolation processes in microemulsions

Abstract

We present an experimental study of an AOT-decane-aqueous 0.5% NaCl microemulsion in which the oil-to-water ratio can be arbitrarily varied. This allows an investigation of the structural inversion from an water-in-oil microemulsion into an oil-in-water microemulsion which happens completely continuously without any phase separation. Conductivity, viscosity, and electrooptical Kerr effect data confirm the presence of two percolation processes. This structural inversion takes place in two stages: With increasing oil content, first a water continuous microemulsion transforms into a bicontinuous structure at roughly 20% oil (oil percolation threshold) and then at roughly 80% oil (water percolation threshold) and bicontinuous microemulsion turns into an oil continuous structure. These two percolations margin three structural regimes of a microemulsion: oil-in-water regime, water-in-oil regime, and a bicontinuous or oil and water continuous regime.

Structural properties of microheterogeneous surfactant-based catalytic systems: Multicomponent self-diffusion NMR approach

“…However, in this concentration region of up to about 0.2 of the value of the water content, the system shows the clustering of micelles detected earlier by means of conductivity measurements [23], and more rapid diffusive hopping of the surfactant molecules between micelles within micelle clusters compensates the prospective decrease in D s [24]. A similar phenomenon determines the dependence of the surfactant self-diffusion coefficient in the water-rich section, since a clustering regime is also known for O-W micelles [25].…”

New Trends on the Synthesis of Inorganic Nanoparticles Using Microemulsions as Confined Reaction Media

“…Changes on microemulsion dynamics giving rise to structural transitions can be explained in terms of percolation. Figure 5 refers to a percolation process taking place in W/O microemulsions (Borkovec et al, 1988), as the oil to water ratio  o is varied. As observed in Figure 5, at high oil concentration, the fraction of water in discrete droplets increases with water composition (decreasing oil concentration) up to a concentration, where it drastically decreases.…”

Electrical Conductivity, Near-Infrared Absorption, and Thermal Lens Spectroscopic Studies of Percolation of Microemulsions

“…The formation of random and momentary continuous water channels would therefore explain the large increase in electrical conductivity. [7][8][9][10][11][12] Clearly, electrical conductivity measurements do not provide sufficient evidence to unambiguously characterize the structures of the microemulsions. 12,13 It is important, therefore, to develop new methods that can provide structural information of microemulsions.…”