Cross-Linking of Reactive Lyotropic Liquid Crystals for Nanostructure Retention

In applications requiring nanoscale order, control over the structure formation is critical for appropriate function. Reactive surfactants forming reactive lyotropic liquid crystals (LLC) enable the formation of nanotructured polymers that exhibit enhanced physical properties when the original order is retained after polymerization. In this work, the use of a cross-linker to retain the LLC order for a monomethacrylate quaternary ammonium surfactant monomer in water during polymerization was explored. The cross-linker segregates to the polar regions of the surfactant assembly, likely near the quaternary ammonium group of the reactive surfactant. The use of a cross-linker enables the retention of the original LLC order after polymerization for hexagonal LLC phases that are not retained by other means. Increased polymerization rates are observed at low cross-linker concentrations. At higher cross-linker concentrations, the polymerization rates decrease because of a decrease in LLC order. More regular ordered morphologies are observed for systems that retain the hexagonal LLC order during polymerization. The resulting LLC order is also present after drying and swelling the polymer in water, therefore producing a polymer with robust LLC order. Enhancements in water uptake were also observed for polymers that retain the original order through cross-linking compared to systems that exhibit change in order. This behavior is directly related to the retention of the original LLC order.