Embedding Azobenzene-Functionalized Carbon Nanotubes into a Polymer Matrix for Stretchable, Composite Solar Thermal Devices

Solar thermal batteries allow for on-demand heat release of stored chemical energy. Azobenzene (AB) is a photoactive molecule of particular interest for thermal storage applications due to its ability to absorb ultraviolet light, isomerize to the cis isomer, and release heat upon discharging to the trans isomer. In a functioning device, AB requires a substrate matrix to not only stabilize the "charged" cis state but also provide enough free volume for AB charging and discharging. In this work, we integrate multiwalled carbon nanotubes (MWCNTs) with carboxylic acid patterning and an AB derivative into a stretchable matrix of a styrene-ethylene-butylene-styrene (SEBS) triblock copolymer to create a stretchable, lightweight solar thermal battery. We demonstrate tunable charge and discharge properties based on controlling the SEBS styrene content and the covalent linkage of AB to MWCNTs. Our results illustrate that embedding AB into SEBS sufficiently stabilizes the AB cis state for energy storage and that the linkage of AB to MWCNTs could provide enhanced absorption for use in ambient solar light.