Association and thermal gelation in aqueous mixtures of ethyl(hydroxyethyl)cellulose and ionic surfactant: FTIR and Raman study

The first attempt to investigate polymer-surfactant interactions in gelling and nongelling aqueous mixtures of a nonionic cellulose ether and a surfac tant by means of vibrational spectroscopy is presented. A series of aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) with addition of anionic surfactant sodium dodecyl sulfate (SDS) of different concentrations was tho roughly investigated by means of Raman scattering and FTIR absorption techn iques. Our data show that even in the sol state (i.e., below the gel point) there are interactions between the polymer and the surfactant, and both bo und and free surfactant molecules were detected. This interaction, which ca nnot be characterized as a chemical one, occurs mainly between the side cha ins of the polymer and the sulfonic acid groups of SDS. Above the gel paint , a new type of interaction appears, which mainly involves the SO3- groups and water molecules. The intermolecular interactions are studied vs changes of both temperature and polymer-surfactant compositions, and a possible mo del for the gelation process is discussed.