The aggregation in dilute aqueous solutions of several omega-substitut
ed single-chain quaternary ammonium surfactants has been studied by Kr
afft temperature and critical aggregation/micelle concentration measur
ements and by cryo-transmission electron microscopy: (16-carboxyhexade
cyl)trimethylammonium bromide (1a); (16-methoxycarbonylhexadecyl)trime
thylammonium bromide (1b); (17,18-dihydroxyoctadecyl)trimethylammonium
bromide (1c). Octadecyltrimethylammonium bromide (2) was included for
comparison. The aggregation of 1a was also studied by Raman spectrosc
opy. Surfactant 1a at pH 6.8 forms ribbonlike fibers with lengths of u
p to 1.2 mu m and cross sections of 3-4 nm x 12-16 nm; at pH 2.2, ribb
on to rodlike fibers; and at pH 11.5, wormlike aggregates. Surfactants
1b and 1c at pH 6.8 form I-ed-shaped aggregates. The Raman spectrosco
py results indicated that 1a is not in a fully extended conformation w
ithin its fibers at pH 6.8. Tentative structural models have been prop
osed for the aggregates of surfactants 1.