Preparation and physical properties of a macroscopically aligned lyotropic hexagonal phase templated hydrogel

Lyotropic liquid crystal (LLC) materials, such as lyotropic liquid single crystal hydrogels (LLSCHs) and LLC templated hydrogels, have the potential for a wide range of applications from nanomaterials to drug delivery. Most of the applications are dependent on transport processes through the gels. While powder distribution LLC hydrogels and elastomers have been shown to be alignable by uniaxial stress/strain, LLSCH that are macroscopically aligned can be made by photopolymerisation after alignment of suitable polymerisable surfactants. Cross-linked polyethylene glycol diacrylate (PEG-DA) hydrogels, have previously been templated using powder distribution LLC phases of non-polymerisable surfactants. In this work, a macroscopically aligned LLC hexagonal phase templated PEG-DA hydrogel was made. The alignment was monitored with 2H NMR quadrupole splitting which showed that the hydrogel retained the macroscopic alignment after photopolymerisation. The effects of compression/deswelling were recorded using optical and polarised optical microscopy (POM). However, the focus of this work was on studying the self-diffusion of water in the hydrogel, which is pertinent not only for the typical applications of these materials but for potentially new applications. Pulsed gradient spin-echo nuclear magnetic resonance (PGSE NMR) provides a way of investigating the self-diffusion easily and non-invasively. Interestingly the measured self-diffusion of water, at least for the sample in this study, was relatively independent of the diffusion time used (i.e., 70 ms to 3 s).