Vibrational mode behavior of SDS aqueous solutions studied by Raman scattering

Aqueous solutions of sodium dodecyl sulfate with concentrations between 12.6 and 100% of SDS are studied by Raman scattering. Raman spectrum behavior is followed vs. temperature, and a phase transition is observed for all samples. The authors focus their study mainly on the intensity variations of both the symmetrical and antisymmetrical vibrational modes of CH/sub 2/ groups situated in the region 2800-3000 cm/sup -1/ and on skeletal vibrations (C-C binding) in the region 1050-1150 cm/sup -1/. The study of the high-frequency part of the spectrum showed the characteristics of an order-disorder transition already studied on other materials. Apparently, the skeletal vibrational spectrum shows an unusual behavior, but polarization experiments help us to solve this difficulty. The authors show that the C-C antisymmetrical stretching mode is perturbed by a SO/sub 3/ symmetrical stretching mode appearing in the micellar phase. Concentrations of SDS between cmc and 62% can have two low-temperature phases, depending on the cooling procedure. One of these phases could be the so-called gel phase. 34 references, 15 figures, 1 table.