R. Ranganathan et al., Growth of cetyltrimethylammonium chloride and acetate micelles with counterion concentration, J COLL I SC, 214(2), 1999, pp. 238-242
Time resolved fluorescence quenching measurements with pyrene as probe are
employed to determine aggregation numbers for hexadecyltrimethylammonium ac
etate (CTAOAc) and chloride (CTACl) micelles as a function of the concentra
tion of detergent and added common-counterion salt. The aggregation numbers
, N-A, of CTACl are roughly twice those of CTAOAc micelles at equivalent co
ncentrations of detergent and salt, consistent with the known relative coun
terion binding affinity (chloride much greater than acetate). For both dete
rgents, the increase of N-A with the net concentration of counterions in th
e intermicellar aqueous phase ([Y-aq]) follows the relationship found previ
ously for anionic micelles: log N-A = log N-o + gamma log[Y-aq], where gamm
a and N-o are constants. However, compared to anionic micelles, for which g
amma = 0.2-0.25, spherical micelles of both CTAOAc and CTACl exhibit less p
ronounced growth, with gamma = 0.1. (C) 1999 Academic Press.