59th Annual Report on Research 2014

Environmentally responsive hydrogels hold multiple important applications. However, the functionality of these materials alone is often limited in comparison to other materials like silicon; thus there is a need to integrate soft and hard materials for the advancement of environmentally sensitive materials. In this project, we demonstrated the capability of integrating a thermoresponsive hydrogel, poly(N-isopropylacrylamide), with thin film silicon ribbons, enabling the stiff silicon ribbons to become adaptive and drivable by the soft environmentally sensitive substrate. Specifically in this period (9/1/2013-8/31/2014), we focused on controlling the thermal and mechanical properties of PNIPAAm based hydrogels by adopting different synthesis techniques. The morphological, thermal and mechanical properties of the macroporous PNIPAAm based hydrogels are quantified and compared with conventional low porosity microporous PNIPAAm hydrogels. Furthermore, to alter the transition temperature, both the macroporous and microporous hydrogels are subjected to different quality of media by introducing a co-solvent (methanol) or an anionic surfactant (sodium dodecyl sulfate). The alteration of the transition temperature along with the enthalpy change and difference in the mechanical properties due to the addition of such additives are studied. In addition, we are in the process of developing novel light responsive PNIPAAm hydrogels which are responsive to visible light. Future work will focus on integrating these visible light sensitive soft hydrogels with hard materials.