Liquid crystal elastomers (LCEs) are shape morphing materials promising for many applications including soft robotics, actuators, and biomedical devices, but current LCE synthesis techniques lack a simple method to program new and arbitrary shape changes. Here, we demonstrate a straightforward method to directly program complex, reversible, non-planar shape changes in nematic LCEs. We show that shape-programmed LCEs are double network elastomers, and by optimizing the crosslink densities of the first and second network we can mechanically program non-planar shapes with strains between 4–100%. This enables us to directly program LCEs using mechanical deformations that impart low or high strains in the LCE including stamping, curling, stretching and embossing methods. We also demonstrate shape programming and processing through 4D printing, where the LCE is fabricated by additive manufacturing and is shape-programmed by mechanical deformation after printing. The resulting LCE transforms between the printed and mechanically deformed shape when heated and cooled, respectively, and is capable reversible strains up to 100%. We demonstrate the versatility of this method by printing a variety of LCE actuators which could not be printed using conventional 4D printing methods. This work widens the potential application of LCEs in biomedical devices, soft-robotics and micro-fluidics where arbitrary and easily programmed shapes are needed.

Optimizing the double-network structure of liquid crystal elastomers for shape programming and 4D printing

ACS Fall 2021

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