Unusual self-assembly of bicephalous surfactants: Nanomorphology and nanostructure from SANS

A novel class of surfactants have been synthesized – which we term bicephalous surfactants, with two quaternary ammonium headgroups linked by a C2 linker and 1 or 2 Cn-acyl tails connected to one of the headgroups. These bicephalous surfactants exhibit remarkable thermoresponsive and rheological behavior. For instance, the single-tailed C18-DQA undergoes reversible thermally-induced gelation-fluidization at ~ the body temperature. It is particularly unusual and perplexing that gelation would occur upon heating, in contrast to other small-molecule gels. Both trial SANS and cryo-TEM results indicated formation elongated aggregates. The zero-shear viscosity of the 800 mM C18-DQA solution would increase from 0.02 Pa s to 100,000 Pa s, by 7-8 orders of magnitude upon gelation. These striking observations from low molecular weight molecules are completely new and could open up significant potential applications. Here, we propose a first SANS study of the nanostructure and nanomorphology of self-assembled bicephalous surfactants, systematically varying the molecular architecture (sing tail and double tail of different lengths) and temperature.