Shapeshifting: Reversible Shape Memory in Semicrystalline Elastomers

Abstract

We present a general strategy for enabling reversible shape transformation in semicrystalline shape memory (SM) materials, which integrates three different SM behaviors: conventional one-way SM, twoway reversible SM, and one-way reversible SM. While two-way reversible shape memory (RSM) is observed upon heating and cooling cycles, the one-way RSM occurs upon heating only. Shape reversibility is achieved through partial melting of a crystalline scaffold which secures memory of a temporary shape by leaving a latent template for recrystallization. This behavior is neither mechanically nor structurally constrained, thereby allowing for multiple switching between encoded shapes without applying any external force, which was demonstrated for different shapes including hairpin, coil, origami, and a robotic gripper. Fraction of reversible strain increases with cross-linking density, reaching a maximum of ca. 70%, and then decreases at higher cross-linking densities. This behavior has been shown to correlate with efficiency of securing the temporary shape.

Twists and Turns in Glassy, Liquid Crystalline Polymer Networks

“…A similar sensitivity to cross-link density has been reported recently in shape memory polymers. 29 The thermomechanical response of the LCN-xx.x materials is similar in that the samples flatten at an intermediate temperature before inverting handedness. The magnitude of the thermomechanical responses observed in Figure 3 are affected by the geometrical stiffness (in this case largely influenced by the modulus, Table 2) and by the inherent thermal responsivity of the material.…”

Recent progress in shape memory polymer: New behavior, enabling materials, and mechanistic understanding

“…This would quantitatively impact the 2W-SME. Along the same line, Sheiko's and coworkers [209] synthesized a poly(octylene adipate) network that also exhibited a broad melting transition. Via an identical mechanism but a different deformation mode, a surface 2W-SME was successfully demonstrated [210].…”

Ultrafast Digital Printing toward 4D Shape Changing Materials

“…[1][2][3] In numerous cases, functions of devices (e.g., biomedical) and structures (e.g., aerospace) are increasingly limited by the sophistication of accessible shapes. [4][5][6][7][8][9][10][11][12] Traditional processing techniques such as molding fail to meet the demands due to the difficulty and cost in creating complex molds and demolding. 3D printing has emerged as an attractive option given its unparalleled flexibility in producing complex shapes.…”