Polymerization of N,N-dimethylacrylamide in Aerosol OT–water mixtures: from lamellae to segregation

The polymerizable N,N-dimethylacrylamide (DMAA) is added to the lamellar liquid crystalline system formed by the anionic surfactant Aerosol OT and water. Small angle X-ray scattering, gives the same bilayer thickness and hydrophilic group cross-sectional area as without DMAA, and an environment sensitive fluorescent probe indicates that DMAA is likely to be in the water layers between the AOT bilayers. This shows that the structure of the AOT bilayer in the lamellar phase is not affected by DMAA. However, DMAA induces instability of the lamellar phase, and a second phase, an isotropic solution, appears for larger DMAA contents. The effect of DMAA in stabilizing this phase with respect to lamellae is much larger than that expected from a simple dilution with water. Furthermore, there is a combined influence of temperature and DMAA concentration on the coexistence of the lamellar and the isotropic phases. When an initiator is added and the monomer polymerizes the tendency to phase separate increases strongly. The lamellar spacing after polymerization is below the value predicted by the global AOT/H2O ratio. This indicates that the polymer segregates from the AOT phase and that the lamellar phase is osmotically compressed by the polymer rich phase.