MICROSCOPIC EVALUATION OF SURFACTANT-WATER INTERACTION IN APOLAR MEDIA

Under the very limited conditions where the mole ratio of water to surfactant is about unity or so, the tightness of the interaction between various ionic surfactants and water solubilized in apolar media was evaluated using the O-H vibrational mode of water in the near infrared spectral region. Water solubilized in apolar solvents containing surfactant exhibited two absorption bands in the region. One of the two arises from water existing in bulk organic phase and appears around 1900-1910 nm. Another band arises from water bound to surfactant and appears over a range of 1920-2020 nm; it is affected primarily by the ionic head group of surfactant rather than by the counter ion. The cationic surfactants were thought to form more rigid micelles than the zwitterionic or anionic ones. The copper (H) ion cosolubilized in the system hardly altered the O-H vibrational energy of water. The dependence of the near infrared absorption band on water, the chemical shift and line width of water proton resonance in NMR, and the fluorescence intensity of terbium chloride all displayed an inflection at the point where the mole ratio of water to surfactant is about unity. This was interpreted in terms of the two step hydration mechanism. © 1980 The Chemical Society of Japan.