STUDY OF BETAINE SOLUTIONS BY FLUORESCENT-PROBES OF PYRENE AND PYRENE-3-CARBOXALDEHYDE

The steady-state fluorescence characteristics, I-5, I-5/I-1 and I-3/I- 1, of pyrene and lambda(max) of pyrene-3-carboxaldehyde, which are sen sitive to the probes' environment, and the dynamic quenching of pyrene molecules by the excimer formation in micelles have been used to stud y the critical micelle concentration (CMC) and aggregation number (N) of N-alkylbetaine systems, respectively. The variations in CMC and N o f N-dodecylbetaine and N-tetradecylbetaine aqueous solutions with pH, NaCl concentration, and addition of anionic and cationic surfactants w ere studied. The effect of salt on the CMC and N values of the N-alkyl betaines at pH values below the isoelectric point were more pronounced than above the isoelectric point. The surface activity and N values o f binary systems of N-alkylbetaine with the commonly used anionic and cationic surfactants were higher than that of N-alkylbetaine solutions . The results obtained also showed that I-5/I-1 of pyrene is a more re liable parameter than I-3/I-1 for the CMC determination. Pyrene-3-carb oxaldehyde was not suitable for the CMC determination of acidic surfac tant solutions.