Structure of concentrated nonionic surfactant microemulsions studied by small angle neutron scattering

Abstract

The structure of the microemulsion system consisting of 40% in volume of the nonionic surfactant pentaethyleneglycol-4-octylphenyl ether and equal volumes of decane and of the aqueous phase, has been studied by means of Small Angle Neutron Scattering (SANS) and electrical conductivity experiments. The influence of several kinds of additives present in the aqueous phase (KCl, sodium dodecyl sulphate, and n-butanol) on the microstructure of the system at different temperatures has also been studied. SANS experiments revealed the existence of a water-in-oil structure with droplet sizes of the order of 2.6 nm and polydispersity around 20% in mostly all the cases. A slight increase in the distance between droplets with the addition of KCl can be observed, while the addition of SDS or n-butanol results in smaller size and polydispersity. High electrical conductivity values have been obtained for the samples with salts, which can be due to interactions induced by the applied electrical field.