(417c) Tunable Hygromorphism: Structural Implications of Molecular Gels and Electrospun Nanofibers in Bilayer Composites

Seed pods with layered structures that have variations in properties such as elastic modulus and water absorption have given rise to a dynamic response known as hygromorphism. Hygromorphism is the ability of a material to change shape in response to water absorption from either humidity or submersion. The key to obtaining hygromorphic response lies in a bilayer structure composed of an active layer and a passive layer. In this work, pinecones served as bio-inspiration to design tunable hygromorphic bilayers utilizing molecular gels and electrospun fibers embedded in an elastomeric matrix. Molecular gels, typically used in solution-state applications, were utilized in the solid-state by using the self-assembled nanofiber network to reinforce the passive layer and increase hydrophobicity. Electrospun nanofibers served as my active component – their water absorption increases the hygroscopic expansion coefficient of the active layer while decreasing the layer modulus. By utilizing random and aligned electrospun nanofibers, we are able to tune hygromorphic properties, such as curvature shape, and decrease the response rate from 20 minutes to 2 minutes. The two fiber networks were interfaced in a single elastomer, forming a durable, seamless interface. With this body of work, we hope to expand the application of molecular gels by employing them in solid-state biomimicry, while also introducing facile alternatives to achieve tunable and reproducible hygromorphic actuating platforms.