Shape Morphing Polymer Networks Based on Ion Gels

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NON-TECHNICAL SUMMARY:Polymer-based materials that can undergo rapid programmed changes in three-dimensional (3D) shape, surface texture, and properties have seen major progress in recent years, offering promise for the development of soft robots, tactile interfaces, and adaptive materials that respond to changes in their environment or user needs. However, critical limitations exist on the performance of current-generation materials, motivating the development of new paradigms for responsive polymer networks, alongside efforts to improve our understanding of these materials on both molecular and macroscopic scales. The current project seeks to take advantage of the unique benefits offered by polymer networks based on ionic liquids (ILs), which are salts with low melting points (often below room temperature) that have useful properties including low volatility and good electrical conductivity and stability. The proposed networks of polymers and ILs could enable transformative advances in the design of shape-morphing materials that can operate under a wide range of environmental conditions and in response to low-voltage electrical control signals. The fundamental understanding developed through the work will also hold relevance for IL-based polymer materials in other contexts including soft, flexible, and responsive electronic devices, or as membranes for batteries or fuel cells. The project will engage, mentor, and train a diverse group of participants at a variety of levels ranging from K-12 students and the general public, to graduate students and post-doctoral fellows, with a particular emphasis on expanding a partnership with high-school students in nearby Springfield, MA. TECHNICAL SUMMARY:While shape-morphing polymer networks have seen rapid recent advances, state-of-the-art materials suffer from key limitations. For example, stimuli-responsive polymer hydrogels typically rely on exchange of water with their surroundings, limiting operation to aqueous environments, while dielectric elastomer actuators require very high triggering voltages of ca. 10 kV to function. The current effort seeks to take advantage of the special properties of ionic liquid (IL)-based polymer materials, in particular their very low volatility, high ionic conductivity, and good electrochemical stability, to enable new classes of responsive and shape-morphing polymer networks. Motivated by these goals, the PI will conduct fundamental studies of the thermodynamics, response kinetics, mechanics, and electrical characteristics of IL-based polymers and networks, and demonstrate new types of responsive materials that are capable of functioning in non-hydrated environments and in response to low voltage electrical signals. Alongside the new capabilities for the design of soft actuators and shape morphing materials, the fundamental understanding gained will have broad relevance for IL-based polymer networks in stimuli-responsive materials, membranes, and iontronic devices.