Collaborative Research: Micromechanics, Damage and Healing of Self-Actuated, Entangled Networks

This research will study the fundamental relationships that control the assembly of solid materials from many small, shape changing ribbon-like particles using combined and integrated experiments and numerical modeling and simulation. Made of liquid crystal elastomers, these particles can reversibly change from flat, ribbon-like shapes to 3D curved shapes in response to changes in temperature. If many of these particles change shape in proximity to one another, the individual particles are linked through entanglement, thus creating a porous solid with controlled mechanical properties. This porous solid exists only until the temperature is reverted and the individual particles return to their flat state, breaking the entanglement. Typical porous materials are notoriously fragile and difficult to recycle. The use of reversible physical entanglement will enable new ways to extend the lifetime of porous materials through healing and new ways to recycle porous structures. The structural approach to material assembly is applicable to a wide range of other shape-changing materials, like hydrogels. The fundamental principles in this work could be used to design injectable biomaterials. These entangled materials will also serve as powerful tools to demonstrate basic scientific concepts to the next generation of scientists and engineers. This research will elucidate the fundamental stimulus-structure-property relationships that govern a new class of responsive materials, which is derived from the reversible physical entanglement of many shape-changing polymer ribbons. This work will enable porous synthetic materials that self-assemble via macroscopic entanglement on command and have widely tunable mechanical properties and porosity. In this class of materials, changes in temperature will induce a fluid dispersion to assemble into an open-celled porous material with controlled viscoelastic properties. Furthermore, these dynamic, transient solids will have self-healing capability without needing chemical reactions or diffusion. This research includes closely integrated experiments and computational models and will provide fundamental understanding of structure-property-assembly relationships of these materials as a function of the shape change and mechanical properties of the individual polymer ribbons. This research is comprised of three tasks: assemble dynamic aggregates from liquid crystal elastomer ribbons and characterize microstructure and thermomechanical properties of aggregates; construct a theoretical model to fundamentally understand the link between the network statistics and the emerging behavior of the material; and fabricate and characterize aggregates of ribbons that can combine bending and twist deformation. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.