FORMATION OF CATIONIC ANIONIC MIXED SURFACTANT BILAYERS ON LAPONITE CLAY SUSPENSIONS

Adsorption of dodecyl sulfate (DS-) by an aqueous flocculated suspension of laponite-RD clay which has been cation-exchanged by cetylpyridinium (CP+) or dioctadecyldimethylammonium (DODMA+) leads to the formation of a cationic/anionic mixed surfactant bilayer at the clay-water interface which, in deionized water, redisperses the flocs. The maximum amount of DS- adsorption and the stability of the cationic/anionic surfactant bilayer in the presence of mixed micelles are strongly dependent on the ionic strength and on the structure of the cationic surfactant. The onset of pure DS- micellization causes the onset of mixed micellization and the desorption of the CP+ surfactant. In contrast, the more hydrophobic two-tailed DODMA+, which is unable to form mixed micelles with DS-, does not desorb upon DS- micellization.