AQUEOUS HEXADECYLTRIMETHYLAMMONIUM ACETATE SOLUTIONS - PH AND CRITICAL MICELLE CONCENTRATION EVIDENCE FOR DEPENDENCE OF THE DEGREE OF MICELLE IONIC DISSOCIATION ON ACETATE ION CONCENTRATION

The counterion binding parameters (beta) of aqueous hexadecyltrimethyl ammonium acetate (C(16)TAOAc) are estimated from pH data at various C( 16)TAOAc-AcOH concentrations with or without added sodium acetate buff er. In contrast to what is usually reported for ionic amphiphiles asso ciated with less hydrophilic counterions, beta varies from ca. 0.4 to ca. 0.7 and depends upon the acetate ion concentration in the aqueous phase. The critical micelle concentrations (cmc) for C(16)TAOAc, C(16) TAOAc-NaOAc, C(16)TAOAc-AcOH, and C(16)TAOAc-NaOAc-AcOH solutions, mea sured from extinction data for fluorescence of acridine, are also exam ined in terms of AcO- concentration dependence. The plot of the logari thm of the amphiphile activity at cmc vs the logarithm of acetate ion activity is markedly curved, as expected for significant variations in beta.