(604j) Tailoring Liquid Crystal Elastomer Networks for Shape Programming and Additive Manufacturing

Liquid crystal elastomers (LCEs) are shape morphing materials promising for many applications including soft robotics, actuators, and biomedical devices, but LCE synthesis techniques lack a simple method to program new and arbitrary shape changes. Furthermore, current approaches to additive manufacturing of LCEs rely on alignment during printing and limits the range of actuation responses possible. In this work, we demonstrate how optimizing the LCE network structure leads to a straightforward method to directly program complex, reversible, non-planar shape changes in nematic LCEs. We furthermore tailor our network preparation method to produce printable and shape-programmable LCEs. We utilize a double network thiol-ene synthesis process that results in a competitive double network LCE. 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. Our approach to additive manufacturing LCEs involves first printing LCE precursor solution into a catalyst bath, producing complex architectures defined by printing. Shape changes are then programmed through mechanical deformation and UV irradiation. Finally, we demonstrate that systematic variations of the network liquid crystal content enable us to reduce the nematic-to-isotropic transition temperature near room temperature. This work widens the potential application of LCEs in biomedical devices, soft-robotics and micro-fluidics where arbitrary and easily programmed shapes are needed.