Polysiloxane Inks for Multimaterial 3d Printing of High-Permittivity Dielectric Elastomers

Dielectric elastomer transducers (DET) are promising candidates for electrically-driven soft robotics. However, the high viscosity and low yield stress of DET formulations prohibit 3D printing, the most common manufacturing method for designer soft actuators. DET inks optimized for direct ink writing (DIW) produce elastomers with high stiffness and mechanical losses, diminishing the utility of DET actuators. To address the antagonistic nature of processing and performance constraints, principles of capillary suspensions are used to engineer DIW DET inks. By blending two immiscible polysiloxane liquids with a filler, a capillary ink suspension is obtained, in which the ink rheology can be tuned independently of the elastomer electromechanical properties. Rheometry is performed to measure and optimize processibility as a function of filler and secondary liquid fraction. Including polar polysiloxanes as the secondary liquid produces a printed elastomer exhibiting a four-fold permittivity increase over commercial polydimethylsiloxane. The characterization and multimaterial printing into layered DET devices demonstrates that the immiscible capillary suspension improves the processability of the inks and enhances the properties of the elastomers, enabling actuation of the devices at comparatively low voltages. It is anticipated that this formulation approach will allow soft robotics to harness the full potential of DETs.