Polymerisation of liquid crystalline phases in binary surfactant/water systems .3. Sodium 10-undecenoate

The polymerisation of a polymerisable fatty acid surfactant (sodium 10-undecenoate) has been studied in both its self-assembled and non self-assembled forms. Polymerisation in non self-assembled solution was achieved to near completion. The polymerisation produces a surface active polymer. The self-assembling behaviour of this pre-polymerised form differs markedly from that observed for the monomeric surfactant [1]. A lamellar phase only is formed in the polymeric phase diagram with no hexagonal or lamellar gel phases being observed. Polymerisation in the different self-assembled forms of sodium 10-undecenoate reached a limit of approximately 30% only, i.e., the surfactant aggregates act to inhibit the polymerisation. The nature of the hydrocarbon chain was found to play a critical role in determining the effect that polymerisation had on the underlying geometry of the surfactant molecules. When the chains are in a fluid-like state (as for the micellar and hexagonal phases) the original monomeric matrix remains largely unchanged. Whereas partial polymerisation of the lamellar gel phase results in a phase transformation. In addition the hydrolysis of the fatty acid soap at low concentrations (close to the critical micelle concentration) has been investigated. Hydrolysis was shown to produce both the parent fatty acid and an acid soap dimer. The presence of these species greatly affects the solution behaviour in this region of the phase diagram shifting the critical micelle concentration to very high concentrations of sodium 10-undecenoate (ca. 0.4 M).