Microstructural impact of sodium dodecyl sulfate/1-butanol/cyclohexane/water microemulsions on hydrolysis of crystal violet

Abstract

Microemulsions are superior to micellar systems for solubilization potential and thermodynamic stability and offer advantages over unstable dispersions. They have unique features associated with different textures: oil in water (o/w), water in oil (w/o), bicontinuous (BC). In this work, sodium dodecyl sulfate (SDS)/1-butanol/cyclohexane/water microemulsions have been used as media for kinetic studies of hydrolysis of crystal violet (CV). Kinetics of the reaction was followed spectrophotometrically under pseudo first order conditions. Three microstructures in w/o, BC and o/w microemulsions were determined by applying percolation theory and percolation scaling law on conductivity results. Change in viscosity with variation in the volume fraction of water (ϕW) has also provided evidence for percolation behavior. Percolation thresholds (ϕC) obtained from conductivity results were in accordance with viscosity results. At these two percolation thresholds, microstructural phase changes from w/o to BC (ϕC1) and BC to o/w (ϕC2) microemulsions. Microstructural transitions of microemulsions were also confirmed by excess volume or excess molar refraction – ϕW profiles. Furthermore, the hydrolysis of CV is greatly affected by microstructures and microstructural transitions of microemulsions. Pseudo first order rate constants – ϕW profiles show that rates are higher in w/o, almost constant in BC and lower in o/w microemulsions with increasing ϕW. Transition of hydrolysis rates could also be marked at microstructural transitions from w/o to BC and BC to o/w obtained from percolation theory. Thus, kinetic results of any reaction have excellent correlation and can be controlled with microstructures of SDS/1-butanol/cyclohexane/water microemulsions.