Microstructural Phase Transfer Analysis in Microemulsions and Reverse Micelles of Cetyltrimethylammonium Bromide/1-Butanol/Cyclohexane/Water

Reverse micelles and microemulsions of cetyltrymethylammonium bromide (CTAB) have been prepared over a wide range of compositions and the physicochemical properties have been studied in detail. Conductivity and density increase, while the refractive index decreases with increasing volume fraction of water (ϕW) or water to surfactant molar ratio (wo) in the reverse micelles and microemulsions. Turbidity, viscosity and surface tension plotted against ϕW show unusual patterns with increasing ϕW indicating different microstructures in microemulsions and reverse micelles. Percolation theory was applied on conductivity results to identify microstructures of microemulsions and reverse micelles. The conductivity values show percolation thresholds (ϕC) which correlate well with viscosity, turbidity and surface tension results. The micostructural changes from water-in-oil (w/o) to bicontinuous (BC), ϕC₁ and BC to oil-in-water (o/w), ϕC₂ give rise to phase transitions in percolation thresholds in the microemulsions. Phase transitions at these percolation thresholds were also observed from volumetric and refraction properties. The structural phase transitions from w/o-BC -o/w microemulsions could be inferred from the profiles of excess volume vs. ϕW, excess refraction vs. ϕW and excess molar refraction vs. ϕW.