EFFECT OF COUNTERION SIZE ON THE VISCOSITY BEHAVIOR OF SODIUM DODECYL-SULFATE MICELLAR SOLUTIONS

The present studies were performed to see the influence of counterion size on the viscosity behaviour of 0.3M sodium dodecyl sulphate micell ar solutions at 30 degrees C. Some symmetrical quaternary ammonium sal ts (R4NBr where R=H, CH3, C2H5, n-C3H7 or n-C4H9) and two organic salt s (thiamine hydrochloride and guanidine hydrochloride, THCl and GuHCl) ) were used for deriving the counterions. The viscosity decreased, inc reased and again decreased as the concentration of R4NBr was progressi vely increased (no initial fall was detected with (n-C4H9)(4)NBr). The \eta(r)\ was always higher with the combination SDS-(C2H5)(4)NBr than with SDS-(n-C3H7)(4)NBr. The results are interpreted in the light of adsorption/intercalation of the counterions or their electrostrictive/ hydrophobic nature. Similar reasoning is invoked for THCl addition. Th e viscosity results of GuHCl addition are discussed with reference to its water structure breaking nature. (C) 1998 Elsevier Science B.V.