Physical properties of hydrogels synthesized from lyotropic liquid crystalline templates

Abstract

Recently, a considerable amount of research has centered on the synthesis of nanostructured hydrogels via the polymerization of monomers in lyotropic liquid crystal (LLC) phases. Because of the potential for controllable nanostructures, these materials have exhibited tremendous potential for a variety of applications. This work describes the impact of photopolymerization kinetics and polymer nanostructure on the physical properties of hydrogels synthesized from LLC templates. Both acrylamide and 2-hydroxyethyl methacrylate (HEMA) photopolymerize more rapidly in the highly ordered LLC phases, resulting in higher molecular weight polymers. The photopolymerization of these monomers in organized surfactant/water assemblies allow formation of highly ordered polymeric hydrogels. The ultimate physical properties appear to be a function of the different polymerization kinetics and polymer nanostructure. Nanostructured polyacrylamide hydrogels swell faster and to a greater extent than isotropic hydrogels. Compressive moduli are also higher for nanostructured polyacrylamide hydrogels when compared to isotropic analogues. The photopolymerization of HEMA results in nanostructured hydrogels, although some structural changes are evident. As a result of the different nanostructures, vastly different physical properties are observed. The isotropic polyHEMA hydrogels swell to a greater extent and considerably faster than any of the organized hydrogels. Additionally, the isotropic polyHEMA hydrogels exhibit higher compressive modulus than the hydrogels synthesized in the organized LLC phases. For both polyHEMA and polyacrylamide gels, different nanostructures produce different physical properties, implying that characteristics such as swelling and mechanical strength can be optimized simply by changing the parent LLC phase.