Effect of the addition of water-soluble polymers on the structure of aerosol OT water-in-oil microemulsions: A Fourier transform infrared spectroscopy study

Using Fourier transform infrared (FT-IR) spectroscopy and electrical conductivity measurements, the study of water-in-oil (w/o) microemulsions of Aerosol OT dissolved in toluene with different water contents, in the absence and in the presence of poly(vinylpyrrolidone) (MW 10 000), PVP K15, and poly(sodium 4-styrenesulfonate) (MW 75 000), PSS, has been carried out. Conductivity measurements show attractive interactions between droplets of w/o microemulsions without polymers containing high water contents, w(o) greater than or equal to 25. The addition of polymers prevents these interactions even at the lowest polymer concentration used in this work, 2%. From FT-IR spectra different micellar structures were detected in the absence of polymers, and vibrational modes of the surfactant molecule allow structural information to be obtained of each kind of aggregate. The structure of each kind of aggregate has a great dependence on the water content. Infrared spectra of the surfactant molecule of microemulsions containing different concentrations of PVP K15 and PSS were also recorded. The comparative analysis of these spectra with those in the absence of polymers permits, in a first place, localization of the polymer in the aqueous core and, later, study of the structural changes induced by the addition of these polymers.