Aqueous lyotropic liquid crystals (LLCs) arise from the water-driven supramolecular self-assembly of small molecule amphiphiles into spatially periodic assemblies with distinct hydrophilic and hydrophobic domains. Commonly observed LLC phases include 3D sphere packings, hexagonally-packed cylinders, lamellae (bilayers), and polycontinuous 3D network phases. In applications including therapeutic delivery vehicles, membranes for water purification, structured ion transporting media, and as templates for mesoporous inorganic electrodes and catalysts, 3D network phases are often the most desirable morphology due to their interpenetrating hydrophobic and hydrophilic domains. These phases are unfortunately difficult to access, because their negative Gaussian curvature hydrophobic/hydrophilic domain interfaces exhibit substantially deviations from a constant mean curvature. Consequently, few amphipihiles allow robust access to LLC network phases.
Using a combination of organic synthesis and advanced materials characterization techniques (e.g., scattering, rheology, and microscopy), we are studying structure/self-assembly relationships in ionic small molecule surfactants to discover new surfactant molecular architectures that form LLC network phases. Our studies focus not only on the phase behaviors of these molecules in water, but also in the presence of additives such as salts, hydrophobic oils, and co-surfactants (e.g., alcohols). Thus, these studies seek to advance our fundamental understanding of how LLC network phases form while potentially addressing real world problems related to bicontinuous microemulsion stabilization for applications spanning enhanced oil recovery to food texturing and nutritional supplement stabilization and delivery.
Toward the development of efficient H+ and HO- transporting polymer electrolyte membranes (PEMs) for fuel cells and solar fuels production, we are using LLC phases to elucidate reliable molecular design criteria to guide syntheses of superior ion transporting media. We are addressing this fundamental yet technologically important challenge by using aqueous LLCs as a platform for fundamental studies to identify how pore functionality )––CO2H, –SO3H, etc.), diameter (0.6–5 nm), and tortuosity impact ion transport in water-filled nanochannels. Using a combination of X-ray and neutron scattering tehcniques, we have developed new insights into next-generation ion transporting materials design.
In order to transform the above self-assembly insights into actual membranes with real applications, we are currently developing new strategies for covalently crosslinking LLC phases using a variety of different polymerization techniques. A key goal in this new and growing project area is to understand how crosslinking chemistry and reaction kinetics impact LLC structure retention or transformation, with the ultimate goal of devloping robust strategies for the fabrication of defect-free thin film composite membranes for size- and chemo- selective separations applications.