Light-Responsive Soft Materials

Stimuli-responsive materials are interesting for a variety of applications including shape-memory systems, molecular machines and delivery systems. These materials change their properties in response to one or more stimuli in their local environment, such as light, pH, magnetic fields or heat.

We are interested in stimuli-responsive materials that respond to light. Light is a very effective stimulus as it can be applied selectively at different wavelengths and intensities, at controlled times and locations. Our main focus is investigating the properties of photoresponsive surfactants, which contain a light-sensitive unit buried within an amphiphilic surfactant structure. In this way, light can be used to control the many properties of the surfactant, from interfacial tension, to spreading and foaming and self-assembly.

Photoisomerisation of the azobenzene group leads to a change in the shape and polarity of the unit.
A photorheological fluid turns from highly viscous to a Newtonian fluid under UV light (figure courtesy of Elaine Kelly)

At present we are working on photosurfactants that contain an azobenzene as the light-responsive group. Azobenzenes undergo a reversible trans-cisphotoisomerisation, which changes the shape and polarity of the molecule. This affects the interfacial properties of the photosurfactant and how they self-assemble.

Our work involves the custom design and synthesis of new surfactant structures, investigation of the physicochemical and interfacial properties and characterisation of the self-assembly of these molecules using small-angle scattering techniques. These systems are being investigated for a variety of applications including catalysis, lyotropic liquid crystal phases, photorheological fluids and emulsions.

Recent Publications

A Single-Component Photorheological Fluid with Light-Responsive Viscosity, Elaine A. Kelly, Niamh Willis-Fox, Judith E. Houston, Camille Blayo, Giorgio Divitini, Nathan Cowieson, Ronan Daly and Rachel C. Evans*, Nanoscale2020,12, 6300-6306

Multimodal Control of Liquid Crystalline Mesophases from Surfactants with Photoswitchable Tails, J. E. Houston, E. A. Kelly, M. Kruteva, K. Chrissiopoulou, N. Cowieson, R. C. Evans*, Journal of Materials Chemistry C2019, 7, 10945 – 10952.

Probing the Dynamic Self-Assembly Behaviour of Photoswitchable Wormlike Micelles in Real Time,  E. A. Kelly, J. E. Houston, R. C. Evans* Soft Matter, 2019, 15, 1253-1259.

Unlocking Structure-Self-Assembly Relationships in Cationic Azobenzene Photosurfactants, C. Blayo, J. E. Houston, S. M. King, R. C. Evans*, Langmuir2018, 34, 10123–10134.