Volume 46, Number 6 (November - December 2001)

Key words: SDS mixed micelles, LLS, alcohols, fatty acids, fatty acid methyl  esters, effect of NaCl and temperature

The size and shape of sodium dodecyl sulfate (SDS) micelles containing the solubilized normal alcohols, fatty acids, and fatty acid methyl esters were investgated using laser light scattering spectroscopy. In the presence of NaCl (0.4-0.6 mol l^-1) the mean hydrodynamic radius (R_h) of the mixed micelles strongly increased in function of the solute concentration. R_h also increased upon addition of NaCl and decreased with increasing temperature. As the number of the carbon atoms in the solute hydrocarbon chain was increased from 6 to 16, R_h increased to a maximum at ten carbon atoms, and then decreased. With the compound studied, the micellar size change was essentially independent of the nature of the solute added. The solute chain length dependence of R_h was thought to be caused by combination of stabilizing effects of hydrophobic and van der Waals forces and steric destabilization of the cylindrical structure as the length of the solute chain became similar to that of SDS.