Distribution of Chloride and Bromide Counterions of Cetyltrimethylammonium Micelles in Water. A Fluorescence Study

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Relative fluorescence intensities of anthracene, fluorene, and 9,10‐dimethylanthracene in aqueous solutions of cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC) have been measured as functions of surfactant concentrations. Fluorescence was found to be quenched by bromide but not by chloride ions. At low total concentrations (cs < 0.01 M) of CTAB/CTAC‐mixtures quenching efficiencies depend linearly on the CTAB‐mole fraction. Deviations from linearity are observed for higher cs‐values and attributed to preferential binding of bromide ions to the micelles. Additional deviations at cs > 0.3 M are connected with changes in micelle shape (rod formation).