FIBERS AND OTHER AGGREGATES OF OMEGA-SUBSTITUTED SURFACTANTS

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.