INFLUENCE OF ALCOHOL ON THE BEHAVIOR OF SODIUM DODECYL-SULFATE MICELLES

The effect of medium chain alcohol molecules on the size and shape of sodium dodecylsulfate micelles, and on the self-diffusion coefficient of the surfactant and alcohol, has been investigated by means of small angle neutron scattering (SANS), and Fourier transform pulsed field g radient spin echo (FT-PGSE) nuclear magnetic resonance measurements. A ll measurements were done in D2O containing a sodium chloride concentr ation of 0.4 mol/kg, and a surfactant concentration of 0,04 mol/kg, Th e alcohols used were 1-propanol, 1-butanol, and 1-pentanol. The data o btained from the different techniques agrees qualitatively. The result s show that propanol successively breaks down the micelles while penta nol brings about a structural change toward large wormlike aggregates. Butanol shows a highly complex behavior on the structure of the micel les and can decrease and increase the size of the aggregates, dependin g on the added alcohol concentration range. All analyzed solutions sho w a distribution of the alcohol between the aqueous bulk solution and the palisade layer of the micelles, resulting in an increased ''hydrat ion'' of D2O in the micellar surface. Moreover, the structural changes of the micelles indicate that butanol and pentanol solubilize in the micellar core in the high molality range, near the end of the solubili ty limit. Propanol is apparently too hydrophilic to do so. (C) 1998 Ac ademic Press.