OPTICAL MICROSCOPY OF LYOTROPIC MESOPHASES IN DILUTE-SOLUTIONS OF SODIUM LAURYL SULFATE-LAURYL ALCOHOL (OR CETYL ALCOHOL)-WATER SYSTEMS

The dilute gel phases formed from sodium lauryl sulfate (SLS)-lauryl alcohol(LOH)-water and sodium lauryl sulfate-cetyl alcohol (CA)-water systems were prepared at water concentrations greater than 97 wt %. Compositions were examined at a fixed SLS concentration of 20 mM with varying alcohol concentrations by using a polarizing microscope. Once the compositions were sonicated, patterns of the phase behavior were similar to the schlieren textures of the nematic liquid crystalline phase. The effect of flow-induced ordering was also noted for these solutions. The compositions outside the gel phase consisted of a two-phase mixture comprised of a clear micellar solution and sedimented alcohol. The crystalline shapes of the sediment consisted of needle-like and short thread-like particles which appeared to be the basic structures for the gel phase. When heated, the birefringent textures and rod-like particles disappeared at temperatures near the melting point of the alcohol, denoting the transition from an ordered to an isotropic phase.