Abstract
Shape memory polymers are promising materials in many emerging applications due to their large extensibility and excellent shape recovery. However, practical application of these polymers is limited by their poor energy densities (up to ∼1 MJ/m3). Here, we report an approach to achieve a high energy density, one-way shape memory polymer based on the formation of strain-induced supramolecular nanostructures. As polymer chains align during strain, strong directional dynamic bonds form, creating stable supramolecular nanostructures and trapping stretched chains in a highly elongated state. Upon heating, the dynamic bonds break, and stretched chains contract to their initial disordered state. This mechanism stores large amounts of entropic energy (as high as 19.6 MJ/m3 or 17.9 J/g), almost six times higher than the best previously reported shape memory polymers while maintaining near 100% shape recovery and fixity. The reported phenomenon of strain-induced supramolecular structures offers a new approach toward achieving high energy density shape memory polymers.
Highlights
Many emerging applications, such as soft robotics, deployable hinges or space structures, sealants, and smart biomedical sutures and devices require high energy density, one-way shape memory materials capable of large-strain and hysteresis-free shape recovery.[1−5] Shape memory polymers (SMPs) are a promising choice due to their excellent shape recovery and fixity, large extensibility, low density, and ease of processing.[6]
SMPs can be integrated with 3D or 4D printing, can be patterned or programmed into complex shapes, and exhibit locally controlled actuation, which greatly enhances their potential for broader application.[7−9] SMPs ubiquitously suffer from poor energy density (
The recovery stress generated by an SMP as it returns to its initial state is determined by the stored entropic energy in the network, which is controlled by the density and strength of network
Summary
Many emerging applications, such as soft robotics, deployable hinges or space structures, sealants, and smart biomedical sutures and devices require high energy density, one-way shape memory materials capable of large-strain and hysteresis-free shape recovery.[1−5] Shape memory polymers (SMPs) are a promising choice due to their excellent shape recovery and fixity, large extensibility, low density, and ease of processing.[6]. SMPs reversibly alternate between a temporary deformed state and an initial undeformed state through application of a stimulus, such as heat or light. SMPs return to their original undeformed state, driven by the relaxation of deformed chains between network junctions (e.g., topological entanglements, chemical cross-links, or secondary interpenetrating networks) that preserve the material’s memory of its initial state via stored entropic energy.[29]. Achieving high energy density SMPs that simultaneously possess high recovery stress and large recoverable strain poses a significant challenge.[6] In general, the recovery stress generated by an SMP as it returns to its initial state is determined by the stored entropic energy in the network, which is controlled by the density and strength of network
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