High Energy Density Shape Memory Polymers Using Strain-Induced Supramolecular Nanostructures

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/m 3 ). 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/m 3 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.

A Shift from Efficiency to Adaptability: Recent Progress in Biomimetic Interactive Soft Robotics in Wet Environments

“…A typical actuator, also known as artificial muscle, is the work horse of soft robots. [ 34 ] It typically needs external stimuli, such as water, [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ] pH, [ 46 , 47 , 48 , 49 , 50 ] heat, [ 47 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ] light, [ 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 ] electricity, [ 53 , 66 , 67 , 68 , 69 , 70 , 71 ] and magnetic field to perform. [ 27 , 72 , 73 , 74 , 75 ] In recent years, soft actuators can be classified based on materials as elastomeric pneumatic actuator (PA), hydrogel actuator (HA), bio‐hybrid actuator (BHA), actuators made of DE, twisted and coiled yarns (TCY), SMA, liquid crystal elastomers (LCE), and ionic polymer‐metal composites (IPMC).…”

Shape-Memory Polymers Designed in View of Thermomechanical Energy Storage and Conversion Systems

“…In this respect, Bao and coworkers designed an amorphous one-way shape-memory polymer optimized in its recoverable mechanical stress level when programmed at 300% deformation. 1 …”

“…Bao and coworkers demonstrate the potential of their SMP as a thermomechanical energy storage system by lifting weights; 1 the principle is presented in Figure 1 a. The polymer sample is stretched at an ambient temperature.…”

“… Comparison of the chemical structure of (a) shape-memory polyetherurethane with (b) the polyetherurea PPG-MPU introduced in ref ( 1 ). Red dots indicate hydrogen bond interactions between urethane or urea groups on neighboring chains.…”

“…This symmetry has important consequences. Under uniaxial strain (see Figure 4 of ref ( 1 )), the polymer chains align into stable supramolecular nanostructures consisting of long, fibril shaped regions (length >10 μm, width ∼100 nm) that are parallel to the strain. These long fibrils comprise stacked layers of nanofibers (diameter 8 nm) oriented perpendicular to the strain and are separated by an amorphous material.…”