Two-way shape-memory polymer design based on periodic dynamic crosslinks inducing supramolecular nanostructures

Stanford University, Stanford CA

Investigators

Abstract

PART 1: NON-TECHNICAL SUMMARY Shape memory polymers (SMPs) have many potential applications, including aerospace, biomedical, soft robotics, and others. Current limitations of SMPs including low energy density, which means the material cannot be subjected to a large load. Furthermore, they do not have high robustness and have poor reversibility. The PI's work addresses limitations of SMPs through a new mechanism of strain-induced long-range ordered nanostructures formed from supramolecular assembly. The PI and her group will advance the state of knowledge in materials chemistry and polymer science through understanding novel materials design and structure-property relationships specific to two-way SMP (2WSMP) design. By integrating synthesis, processing, and advanced characterization, they will aim to enable a new generation of 2WSMPs with unprecedented energy densities synthesized from low-cost and scalable commercial starting chemicals. Compared to current widely used liquid-crystal elastomer shape-actuation materials, these 2WSMPs would actuate under much larger loads at a much lower material cost. This should allow more widespread testing and adoption, and help advance research on soft actuators. The collection of curated, high-quality experimental datasets produced from this project can potentially be used to benchmark theory and simulation models. With the potential applications and visual effects of 2WSMP behaviors, this work also offers appealing opportunities for recruiting and training students as next-generation workforce and research leaders. PART 2: TECHNICAL SUMMARY Polymer networks formed through dynamic noncovalent or covalent bonds exhibit a range of interesting and tunable mechanical properties (e.g., tough, elastic, self-healable, stimuli-responsive, and reconfigurable). In nature, hierarchically ordered structures are formed through weak but cooperative interactions to perform precise functions. This work will investigate a new molecular design concept of high energy-density shape memory polymers through strain-induced large range order of supramolecular nanostructure formation. The hypothesis is that the ability to form strain-induced supramolecular structures in periodic dynamic polymers (PDPs) may stabilize polymer chain alignment under large strains through non-covalent and covalent crosslinks and as a result crystallite alignment in the prepared two-way shape memory polymers (2WSMPs). The planned work will focus on addressing fundamental questions related to molecular design, polymer thin film and fiber morphology control and crystalline domain orientation, and ultimately their impact on the new designs of SMP behaviors. This study will lead to high energy density 2WSMPs synthesized from low cost and scalable reagents. The resulting 2WSMPs are aimed to have high stroke, actuation under large loads, and minimal cycling hysteresis. . 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.