EFFECTS OF SHORT-CHAINED ALCOHOLS ON THE INTRAMICELLAR FLUORESCENCE QUENCHING OF 2,3-DIMETHYLNAPHTHALENE BY THE COUNTERION IN MIXED MICELLES OF ALCOHOL AND DECYLTRIMETHYLAMMONIUM BROMIDE

Time-resolved fluorescence intensity measurements of 2,3-dimethylnaphthalene (2,3-DMN) in decyltrimethylammonium bromide (C10TAB) micellar systems in the absence and presence of 1-propanol, 1-butanol, 1-pentanol, and 2-(n-butoxy)ethanol have been carried out at 25-degrees-C. Fluorescence quenching of the fluorophore by both cetylpyridinium bromide (CpyB) and the bromide (Br-) counterions of the micelles has been observed. The quenching kinetics of the Br- counterion were estimated by first studying the fluorescence quenching of 2,3-DMN by CpyB in sodium dodecyl sulfate micellar systems where it is assumed that there is little or no quenching by the counterion. In the absence of alcohols, the fluorescence quenching of 2,3-DMN by Br- shows that 2,3-DMN becomes more accessible to Br- as the hydrocarbon chain length increases in the surfactant series C10TAB, C12TAB, and C16TAB. This is possibly due to a decrease in the thickness of the Stern layer with increasing surfactant hydrocarbon chain length. The addition of alcohols to the micellar phase of C10TAB increases the accessibility of Br- to 2,3-DMN, and this accessibility increases with increasing hydrocarbon chain length of the alcohol. This result may be due to decreased solvation of the head groups of the micellized surfactants as the alcohol chain length increases.