Ordering effects on the photopolymerization of a lyotropic liquid crystal

Abstract

The synthesis of polymers bearing the highly ordered nanostructure of lyotropic liquid crystal (LLC) phases has recently been of great interest. This work describes the polymerization behavior and structural evolution of a cationic amphiphile in various LLC phases. The type and degree of LLC phases formed from this monomer depend strongly on the composition and temperature. By adding a nonpolymerizable surfactant a variety of LLC phases are formed including hexagonal, bicontinuous cubic, and lamellar morphologies while maintaining a constant monomer concentration. The highly ordered lamellar LLC phase exhibits the fastest polymerization rate with the slowest occurring in the hexagonal phase. The polymerization rates of the bicontinuous morphology were intermediate to the lamellar and hexagonal phases. The faster polymerization kinetics is due to diffusional limitations imposed on the propagating polymer by the highly ordered lamellar LLC phase. Also, the order of this LLC system has a strong dependence on temperature. At higher temperatures, the degree of LLC order and correspondingly the polymerization rate decrease. The original LLC phase morphology appears to be retained to the greatest extent in the faster polymerizing lamellar phase. The original nanostructure is also retained in the hexagonal and cubic LLC phases but with some slight changes in structure. This LLC structure is preserved at temperatures well exceeding the thermal phase transitions of the unpolymerized LLC samples.