SURFACTANTS AND COSURFACTANTS IN LAMELLAR LIQUID-CRYSTALS AND ADSORBED ON SOLID-SURFACES .1. THE MODEL SYSTEM SODIUM DODECYL-SULFATE BUTANOL OR SODIUM DODECYL-SULFATE BENZYL ALCOHOL AND ALPHA-ALUMINA

Phase diagrams of the model systems sodium dodecyl sulfate (SDS)/1-butanol/water and SDS/benzyl alcohol/water have been determined. In both model systems we have found a lamellar lyotropic liquid crystalline phase D with regular molecular packing of the surfactant/cosurfactant. The model systems have also been used for adsorption studies on solid A12O3 in 0.3 M NaCl. At the adsorption plateau SDS is found to cover an area of 0.40 nm2, 1-butanol an area of 0.30 nm2, and benzyl alcohol an area of 0.24 nm2. Corresponding values in the lamellar D phase (without NaCl) are 0.40 (average value), 0.14, and 0.20 nm2. The good agreement between the area requirements of SDS under these conditions reveals a close connection of an ion-condensation model for the lamellar phase and the surface charge distribution on the solid alumina surface. The discrepancy in the areas for the butanol is attributed to differing water solubilities, which affect the structuring in the monolayer at the solid surface more than in the bilayer in the D phase and/or longitudinal translation of the alcohol molecules in molecular bilayers. For long-chain alcohols a value of around 0.20 nm2 is obtained in both cases. © 1990.