Study on the Aggregation Number of Betaine and its Mixed Micelles by the Time-Resolved Fluorescence Method

The dynamic quenching of pyrene molecule by the excimer formation in micelles has been used to study the aggregation number(N) of aqueous micellar systems of dodecylbetaine (C₁₂Be),C₁₂Be/sodium dodeyl sulfonate(As)and C₁₂Be/centyltrimethylammonium bromide (CTAB).It is observed that at pH=2.0 and 8.0 the N of C₁₂Be increased from 178 to 241 and from 151 to 210 respectively when the concentration of NaCl increased from 0.1mol·L^-1 to 0.8mol·L^-1. The N of C₁₂Be/As system at pH=2.0 varied with the variation of the molar ratio of As(x_AS). The N increased from 406 to 622 when x_AS increased from 0.05 to 0.1, and decreased from 931 to 339 when x_AS increased from 0.8 to 0.95. Precipitation occured when 0.1<x_AS<0.8. At pH=8. 0 the N of C₁₂Be/CTAB system increased form 280 to 607 when the molar ratio of CFAB increased from 0.1 to 0.7.