1.
Fer Dousi Begum
– Department Of Chemistry, University Of Dhaka, Dhaka, Bangladesh
2.
M. Yousuf A. Mollah
– Department Of Chemistry, University Of Dhaka, Dhaka, Bangladesh
3.
M. Muhibur Rahman And Md. Abu Bin Hasan Susan
– Department Of Chemistry, University Of Dhaka, Dhaka, Bangladesh
Abstract
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 (fW) or water to surfactant molar ratio (wo) in the reverse micelles and microemulsions. Turbidity, viscosity and surface tension plotted against fW show unusual patterns with increasing fW 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 (fC) which correlate well with viscosity, turbidity and surface tension results. The micostructural changes from water-in-oil (w/o) to bicontinuous (BC), fC1 and BC to oil-in-water (o/w), fC2 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. fW, excess refraction vs. fW and excess molar refraction vs. fW.
Keywords Microemulsion, Microstructure, Percolation, Phase transition, Physicochemical property, Reverse micelle.
