Lt. Okano et al., Fluorescence and light-scattering studies of the aggregation of cationic surfactants in aqueous solution: Effects of headgroup structure, LANGMUIR, 16(7), 2000, pp. 3119-3123
Aggregation of the following cationic surfactants has been studied in aqueo
us solution: cetyltrimethylammonium chloride, CMe(3)ACl; cetyldimethylpheny
lammonium chloride, CMe(2)PhACl; cetyldimethylbenzylammonium chloride, CMe(
2)BzACl; cetyldimethyl-2-phenylethylammonium chloride, CMe(2)PhEtACl; and c
etyldimethyl-3-phenylpropylammonium chloride, CMe(2)PhPrACl. Critical micel
le concentrations, cmc's, were obtained from surface tension and conductanc
e measurements; data of the latter were also employed to determine the degr
ee of the surfactant counterion dissociation, alpha. Static and quasi-elast
ic light-scattering measurements were employed to obtain micellar weight-av
erage molecular weights, aggregation numbers, N-agg, micellar hydrodynamic
radii, R-h, and interfacial area/surfactant headgroup. The latter area was
also obtained from surface tension measurements. Finally, time-resolved flu
orescence decay measurements with pyrene as probe were employed to obtain N
-agg. The structure of micelles of CMe(2)PhACl is different from that of th
e other phenyl-group-bearing surfactants because its aromatic ring cannot f
old back on the micellar interface. Increasing the number of the methylene
segments in the headgroup results in an increase in a and interfacial surfa
ce area/headgroup and a decrease in the cmc, N-agg and R-h. There is good a
greement between micellar properties obtained by the different techniques e
mployed.