Microstructure and Dynamics of the Water-in-Oil CTAB/<i>n</i>-Pentanol/<i>n</i>-Hexane/Water Microemulsion: A Spectroscopic and Conductivity Study

Abstract

Quaternary water-in-oil microemulsion of a cationic surfactant (cetyltrimethylammonium bromide, CTAB), n-hexane, water, and n-pentanol has been investigated using conductivity, quasi-elastic light scattering, near-infrared absorption spectroscopy, and pulsed field gradient spin-echo NMR measurements. The conductivity behavior shows features characteristic of the migration of charged droplets. Consequently, using the charge fluctuation model, the conductivity data were correlated with the droplet radius obtained from self-diffusion coefficients for different obstruction factors. Conductivity and self-diffusion measurements were found to be self-consistent for spherical droplets with hard-sphere interactions. Comparison between collective diffusion and self-diffusion coefficients fully supports this conclusion. The average head-group area of CTAB, the amount of water free in the organic bulk, and the fraction of alcohol present into the aggregates were evaluated together with the thickness of both the interfacial film and the bound water layer providing a full microscopic picture of the system.