Characterization and polymerization behavior of polymerizable lyotropic liquid crystalline systems
The development and application of nanostructured polymers have recently become a significant area of research. Nanomaterials show significant promise in applications such as drug delivery, catalysis, nanocomposite synthesis, and any other application requiring a well-defined nanostructure. One promising route to the synthesis of materials with controllable nanostructures utilizes lyotropic liquid crystal (LLC) phases. LLC phases however, are not useful as materials. Therefore, synthesizing polymeric materials with the unique nanostructure of LLC phases has generated considerable interest. There are two methods for synthesizing polymers bearing LLC phase morphologies. One route is through the polymerization of amphiphilic monomers that form LLC phases. Another method for synthesizing these nanostructured materials is by polymerizing nonmesogenic monomers in common LLC phase forming systems, which would act as a structure inducing template. This work focuses on understanding the processes involved in the development of polymers bearing LLC nanomorphologies. Through this understanding the ability to reliably and controllably synthesize materials with LLC nanostructures will be enhanced. The fundamental aspect in the synthesis of nanostructured polymers from LLC phases lies in the polymerization itself. The effects of the type and degree of LLC order on the polymerization were primarily investigated by following the polymerization in real-time with photo-differential scanning calorimetry. The reaction kinetics and mechanisms were studied for various monomers polymerized in the various LLC phases. Interestingly, as the type and degree of LLC order changed, dramatic increases in polymerization rates are observed. Increases in polymerization rate occur with amphiphilic monomers and for nonmesogenic monomers polymerized in common LLC phases. Through the use of small angle X-ray scattering (SAXS) and various NMR spectroscopic techniques, the role of monomer segregation and orientation in the LLC phases were determined. For amphiphilic monomers these techniques correlated the degree of orientational order to the rate enhancements observed. For LLC systems with solvated monomers, hydrophobic monomers segregated into the hydrophobic domains of the LLC phases, whereas hydrophilic monomers reside to a greater extent in the aqueous domains. Additionally in the case of the hydrophilic monomers the LLC phase actually imposes orientational order. SAXS and polarizing light microscopy were utilized to determine if the original LLC structures were retained and correlated to the polymerization kinetics. In some cases the LLC systems with enhanced polymerization rates exhibit greater degrees of structure retention. Additionally, the physical properties of polymeric materials synthesized in the various LLC phases were characterized. Specifically, the swelling dynamics and compressive modulus of hydrophilic polymers were determined. Both swelling kinetics and compressive modulus of these polymers depend heavily on the LLC morphology in which they were polymerized.