(511c) Photopolymerization Kinetics, Crosslinking, and the Resulting Properties of Polymerizable Lyotropic Liquid Crystals

Recently, lyotropic liquid crystals (LLC) systems have generated significant interest for the creation of new organic nanomaterials because of the nanometer size scale structures that they form. Applications ranging from catalysis to chemical protection suits and nonocomposite synthesis have been proposed and investigated. The primary reason that these materials have not been used more often is due to entropic limitations during the polymerization process. Before materials with controlled lyotropic structure can be created in a controllable way, the polymerization process needs to be understood. Polymerizable versions of these systems could enable the creation of new nanostructured materials by fixing the original structure using covalent bonds. In this study the effect of the polymerization kinetics and crosslinking used in the photopolymerization process on the resulting polymer structure is examined.

The order/stability of the polymerized system is an important factor to consider when studying structure evolution for polymerizable surfactants. The polymerization kinetics is dependent on the order of the system, being the fastest in the more ordered phase. At the same time, the stability of the phase when adding a crosslinkable mesogen has an effect in the reaction kinetics. For binary systems (polymerizable surfactant and water) the structure retention is dependent on the order while for tertiary systems (polymerizable surfactant, crosslinker, and water) the structure retention is mostly dependent on the crosslinking effect. An enhancement in the physical properties were observed for the resulting polymer, some directly related to the retention of the hexagonal structure. SEM pictures show a decrease in the voids when adding the crosslinker to the system. This behavior suggest the use of these materials for tuning pore sizes in separation applications.

Finally, the structures and pore sizes of the obtained polymers do not appear to be a direct template of the original LLC phase. Possible causes for this are demixing processes due to thermodynamic factors during polymerization and sample preparation. These results indicate that the kinetics of the polymerization process is a very important variable to take into account when studying structure evolution of polymerizable surfactants.