Polymerisation in lyotropic liquid-crystalline phases of dioctadecyldimethylammonium bromide

Abstract

The polymerisation of styrene in lyotropic liquid-crystalline (LC) phases of dioctadecyldimethylammonium bromide (DODAB) in water is explored. Amphiphile concentrations between 20 and 50 wt % are employed. The study is set out as a model study for polymerisation reactions in nonstabilised, nonfunctional bilayer systems. X-ray characterisation was used to assess the phase behaviour of the lyotropic mesophases before, during and after polymerisation. The DODAB/water system forms the lamellar phase within the concentration range considered. Addition of styrene to the lamellar phase of DODAB at an equimolar ratio induces a phase shift to a bicontinuous cubic phase at elevated temperatures near the phase-transition temperature. Upon polymerisation within this cubic phase, the phase structure is maintained if the system is kept at constant temperature; however, if the polymer/amphiphile phase is cooled, the lamellar phase, being typical of the DODAB/water system, is restored. It is concluded that, as a result of phase separation between the polymer and the amphiphile phase, the polymerisation in lyotropic LC phases does not provide a stable copy of the templating amphiphile phase. This is in analogy to the observations for polymerisations in other lyotropic phases.