Salt effect on self-aggregation of sodium dodecylsulfate (SDS) and tetradecyltrimethylammonium bromide (TTAB): Physicochemical correlation and assessment in the light of Hofmeister (lyotropic) effect

Amphiphile micellization is a well explored physicochemical process that can be affected by environmental conditions (temperature, pressure and additives). Salts have power to appreciably influence the water activity and self-association of ionic micelles; their effects on physicochemical processes are often examined in terms of Hofmeister or lyotropic series. In this work, physicochemical investigations on the self-association of sodium dodecylsulfate (SDS) and tetradecyltrimethylammonium bromide (TTAB) in aqueous medium in presence of a number of monovalent, bivalent and trivalent inorganic and organic salts at μ = 0.01 at 303 K has been undertaken. Their critical micellar concentration (CMC), counter ion binding of micelles, and energetics of micellization have been estimated by the methods of conductometry and microcalorimetry. The ion effects on the physicochemical parameters have been found to poorly or loosely obey Hofmeister or lyotropic series; for a correlation, the lyotropic number (Ln) has been found to be better than both the effective hydrodynamic radius (Rh) and the polarizability (α) of the counter ions (cations for anionic SDS micelles, and anions for cationic TTAB micelles).