Harnessing Light-Responsive Structural Control in Lyotropic Liquid Crystals

Materials that change their nanoscale structure in response to external stimuli are of interest as smart materials for a wide range of applications, including targeted drug or catalyst release, soft bio-robotics and energy-storage systems. We have recently demonstrated the first example of light-responsive cubic lyotropic liquid crystal (LLC) lipid dispersions, or cubosomes, in which photoswitchable azobenzene photosurfactants (AzoPS) were used to enable external control over the LLC structure and subsequent on-demand release of entrapped guest molecules. Upon irradiation with light, the AzoPS within the cubosomes undergo trans-cis photoisomerization, which in turn leads to squeezing of the cubic lattice and release of entrapped cargo. However, the mechanism for photoisomerisation of azobenzene, especially in condensed, self-assembled states, and the knock-on effect this has on the long-range structural order, are still poorly understood. This knowledge is essential to inform the targeted, bottom-up design of next-generation systems where the light-response is harnessed for optimal control. The aim of this study is to use selective deuteration in small-angle neutron scattering (SANS) to understand where the photosurfactant resides in mixed LLC structures of different symmetries. We will use this to explore how photoisomerisation affects the long-range structural order.