Influence of Polyethylene Glycols on the Percolation Behavior of Anionic and Nonionic Water-in-Oil Microemulsions

Abstract

Replacing a proportion of water by oligo- and polyethylene glycols (PEGs) in water-in-oil (w/o) microemulsions strongly affects the phase boundaries and the percolation behavior of these systems. The influence of ethylene glycol (EG) and PEG on systems stabilized by ionic Aerosol OT (AOT) and nonionic Igepal CO-520 (IG) surfactants is examined using electric conductivity and time-resolved electric birefringence (Kerr-effect) measurements. Addition of ethylene glycol induces percolation in AOT microemulsions but stabilizes droplets in IG systems. This effect of EG is contrary to almost all other solutes, stabilizing the same structure in ionic and nonionic systems. It can be understood by the different interaction of EG with the solvated polar headgroups of AOT and IG respectively. Regarding the molecular weight dependence one can distinguish three regimes in the AOT system: Small oligoethylene glycols induce percolation, medium size polymers increasingly stabilize droplets, and for a degree of polymeriza...