Stimuli-responsive behavior of composites integrating thermo-responsive gels with photo-responsive fibers

Abstract

Materials that could be reconfigured multiple times into different shapes with the use of different stimuli could dramatically impact manufacturing processes. As a step toward creating such useful, adaptive materials, we use computational modeling to design a composite that integrates a thermo-responsive polymer gel and photosensitive fibers. The gel displays a lower critical solution temperature (LCST), and thus, shrinks at elevated temperatures. The elastic fibers are functionalized with spirobenzopyran (SP) chromophores, which become hydrophobic under blue light. If these chromophores are uniformly distributed in this LCST gel (without the embedded fibers), then both light and heat produce the same effect on the sample, causing the gel to undergo a uniform collapse. When the SP-functionalization is confined to fibers that are embedded in the gel, the material displays distinctly different behavior in the presence of light and heat. In particular, samples anchored to a surface bend in one direction when illuminated and in the opposite direction when heated. When the sample is detached from the surface, then the composites shrink like an accordion when heated and bend like a caterpillar when illuminated. Common to both the tethered and untethered samples, one material displays a distinct response to the different stimuli. Hence, our findings indicate how a given sample can be fashioned into different shapes through the use of separate stimuli. Overall, our results point to a robust method for controllably reconfiguring the morphology of compliant composites and amplifying the effects of external environmental cues (light or temperature) on the behavior of these systems.