MOLECULAR PACKING OF SURFACTANTS AND CO-SURFACTANTS ON SILICA AND IN LIQUID-CRYSTALS

The adsorption of sodium dodecyl sulfate, hexadecylpyridinium chloride and hexaethylene nonylphenol ether onto silica has been studied at pH 6.5. The adsorption of the anionic surfactant is strongly dependent on the preparation of the silica surface and the density of surface silanol groups. The cationic surfactant shows a high affinity for the silica surface. In the presence of benzyl alcohol, the competitive adsorption results in the replacement on the surface of the ionic surfactant by alcohol molecules. The close-packing array of the surfactant/co-surfactant layer formed, and of the non-ionic surfactant at saturation, is similar to that in the lamellar liquid crystalline D phase.