Effects of nonionic, cationic, and mixed nonionic-cationic surfactants on the acid-base behavior of phenyl salicylate

The effects of Brij 35 micelles, CTABr micelles, and mixed Brij 35-CTABr mi celles on the acid-base behavior of phenyl salicylate (PST) have been studi ed in aqueous solution containing 2% v/v acetonitrile, The apparent pK(b) ( pK(b)(app)) of PST is decreased by 1.5 pK units with the increase in [Brij 35] from 0 to 0.02 M which is attributed to micellar medium effect. The val ues of pK(b)(app) remain almost independent of [CTABr] within its range 0.0 1-0.03 M. The increase in [CTABr] from 0 to 0.03 M in aqueous solution cont aining 0.02 M Brij 35 has not resulted in a change in pK(b)(app). This show s that the characeristic structural features of nonionic Brij 35 micelles r emain essentially unchanged on addition of CTABr under the present experime ntal conditions. (C) 1999 Academic Press.