POLARIZED FLUORESCENCE EMISSION MEASUREMENTS IN MIXTURES OF 2-BUTOXYETHANOL, CETYLTRIMETHYLAMMONIUM BROMIDE, AND WATER

Polarized fluorescence emission and fluorescence lifetime measurements are reported for two fluorescent probes, diphenylbutadiene (DPB) and 2-(p-toluidino)naphthalene-6-sulfonate, potassium salt (2,6-TNS), dissolved in binary water-surfactant systems for several different surfactants. As well, data for the probe DPB in ternary solutions of 2-butoxyethanol (BE)-cetyltrimethylammonium bromide (CTAB)-water are presented. The use of the probe 2,6-TNS to investigate alkyltrimethylammonium bromide surfactants was found to be impractical because of the occurrence of a strong complexation reaction with the surfactant. Estimates of the local microviscosity (eta) around the probe were calculated, and, because of the solvent-dependent emission properties of DPB, it was possible to infer the relative polarity and solubilization site of the probe. For ternary solutions containing <5 mol % BE, the microviscosity was found to increase with increasing CTAB concentration. However, for those solutions containing >5 mol % BE, the addition of CTAB has no effect on the microviscosity around DPB. This result is interpreted as arising from the breakdown of the CTAB micelles which occurs from the swelling of the micelle upon solubilization of BE. Water-rich regions of these systems also were studied by using the fluorescent probe dimethylaminonaphthalene sulfonate (1,8-DNS), sodium salt. The emission wavelength maximum for 1,8-DNS is sensitive to the polarity of the surrounding solvent, and its negative charge makes it a suitable probe to investigate the surface of cationic micelles. Studies of these systems show that initial solubilization of BE occurs at the micelle surface with concomitant swelling of the micelle. Further addition of BE leads to micelle breakdown. These results are in agreement with previously reported ultrasonic absorption and light-scattering studies of these systems.