Shapes of Micelles and Molecular Geometry Synthesis and Studies on the Phase Behaviour, Surface Tension and Rheology of Rigid Rod-Like Surfactants in Aqueous Solutions

Amphiphiles with rigid rod-like hydrophobic moieties have been synthesized in order to investigate the effect of the packing restraints of such moieties on the micellar association behaviour of amphiphiles in aqueous solution. Investigations of the phase behaviour of amphiphile/water mixtures reveal that liquid-crystalline phases exist in defined temperature and concentration regimes and that they are all lamellar, regardless of the hydrophilic-hydrophobic balance of the amphiphile. For these lyotropic liquid-crystalline phases a polymorphism is observed which is similar to the polymorphism of thermotropic smectic liquid crystals. Surface tension measurements indicate critical micelle concentrations of the amphiphiles in dilute solutions which are similar to those of conventional surfactants. From rheological measurements it can be assumed that the variation of temperature and/or concentration of the solution does not influence the micellar shape. This is in contrast to the behaviour of non-ionic surfactants having a flexible hydrophobic group.