Orientation of Rod-Like Surfactant Aggregates in a Non-Aqueous Physical Gel

Physical gels obtained by aggregation of a steroid derivative in cyclohexane are constituted with very long rod-like fibres. We present here some preliminary results concerning rod orientation effects in this system. on the one hand without any external forces and on the other hand, with magnetic fields.

Long range orientation order is observed in concentrated gel samples as a consequence of excluded volume effects. Typical Schlieren optical textures characterize nematic-like domains in the samples.

The use of strong magnetic fields during the steroid aggregation kinetics can give strikingly more ordered samples. The initial state of these experiments is a fluid sol phase which allows the reorientational motion of the rod-like aggregates. An oriented xerogel can be obtained from a phase separation process of the unstable gel phase. Polarizing optical microscopy, magnetically induced optical birefringence and two dimensional small angle neutron scattering patterns are used to detect the anisotropic states.