Composite gels of poly(acrylamide) with incorporated bentonite. Interaction with cationic surfactants, ESR and SAXS study

The swelling behavior and the structure of composite gels of poly(acrylamide) with incorporated bentonite clay and the products of their reactions with a cationic surfactant, cetylpyridinium chloride, were studied by SAXS and ESR (spin-probe) methods. The ESR data show that the adsorption of CPC on the clay platelets already leads to the formation of the ordered surfactant aggregates with low molecular mobility in the region of surfactant concentrations much below the cmc. A SAXS study demonstrates that further adsorption of the surfactant results in the formation of lamellas, including alternating layers of clay platelets and double layers of CPC. These two steps of the adsorption are accompanied by the strong shrinking of the gel composite. At high concentrations of the surfactant, total overcharging of the surface of the clay particles occurs, resulting in a change in the direction of the electroosmotic transport of water through the gel and in the reswelling of the gel composite. The models of the clay/surfactant complexes in the gel phase are discussed.