THE EFFECT OF MEDIUM-CHAIN LENGTH ALCOHOLS ON THE MICELLAR PROPERTIESOF SODIUM DODECYL-SULFATE IN SODIUM-CHLORIDE SOLUTIONS

The effect of medium chain length alcohols on the micellar size and sh ape of sodium dodecyl sulfate in electrolyte solutions has been invest igated by means of small angle neutron scattering (SANS), dynamic ligh t scattering (DLS), and viscosity measurements. The surfactant content was kept constant throughout, at 0.04 m, and the alcohols used were 1 -butanol, 1-pentanol, and 1-hexanol. The data from the various techniq ues are qualitatively in agreement. The SANS data generally fit a mode l for prolate ellipsoids with varying ratios of the major to minor axi s. Addition of butanol first leads to a decrease in micellar size, the major to minor axis ratio decreases from about 6 to less than 2. Howe ver, as the butanol concentration exceeds 0.5 m, the micelles starts t o grow again. The same can be seen from the diffusion coefficient as m easured by DLS. Addition of pentanol or hexanol do not bring about thi s minimum in micellar size. The minor axis decreases and the major axi s increases as these alcohols are added. Thus these alcohols make the prolate ellipsoidal micelles grow continuously towards large rod-like structures. The viscosity data are less detailed, but confirm the gene ral trend upon alcohol addition. (C) 1994 Academic Press, Inc.