STUDY OF THE 2,6-O-DIMETHYL-BETA-CYCLODEXTRIN PLUS HEXADECYLTRIMETHYLAMMONIUM BROMIDE PLUS WATER-SYSTEM FROM SPEED OF SOUND MEASUREMENTS

The effect of the presence of 2,6-o-dimethyl-β-cyclodextrin (DIMEB) on aqueous solutions of hexadecyltrimethylammonium bromide (CTAB), due to the formation of inclusion complexes, has been analyzed by measuring the speed of sound, u, in two complementary studies: (1) as a function of [CTAB] in the presence of different constant concentrations of DIMEB, and (II) as a function of [DIMEB] for various nonmicellar and micellar solutions of CTAB. Two kinds of inclusion complexes between DIMEB and CTAB have been detected: a 1:1 complex (DIMEB:CTAB) in excess of CTAB with respect to DIMEB, and a 2:1 complex (DIMEB2:CTAB) in excess of DIMEB with respect to CTAB, not usually found in this type of system. On the other band, the presence of the cyclodextrin causes the apparent critical micellar concentration, CMC*, to increase upon the addition of cyclodextrin, while the concentration of free surfactant available for the micellization process in the postmicellar region, [CTAB]r, remains basically constant. © 1993 Academic Press, Inc.