(603e) 3D Printing of Interdigitated Dielectric Elastomer Actuators

Among soft actuators, dielectric elastomer actuators exhibit excellent energy density and strain rate. However, typical fabrication methods are based on sequential planar processing, which results in planar devices with low fabrication rate. 3D printing provides the potential to rapidly fabricate versatile designs of actuators with high throughput. Interdigitated DEAs were fabricated by 3D printing vertical arrays of electrodes followed by casting a dielectric. Minimizing print defects such as end beads in the vertical electrodes is important for eliminating premature breakdown. Print defects are reduced by optimizing the ink rheology; the electrode ink is composed of a vinyl-terminated poly(ethylene glycol ethylene sulfide) oligomers with carbon black as the rheological modifier and conductive filler. The print fidelity is optimized by reducing the molecular weight of the oligomer. However, in order to achieve a low elastic modulus in the cured state, a high molecular weight between crosslinks is required. We implemented a strategy of simultaneous chain extension and crosslinking to achieve low-modulus, highly extensible elastomers using low-molecular weight precursors.

The dielectric is a chemically crosslinked oil gel with a dielectric constant of 6. The acrylate crosslinking mechanism allows chemical bonding with the electrodes, providing structural integrity in the device. The oil component in the dielectric fulfills several purposes, including reducing the uncured viscosity to improve infilling in the electrodes, reducing the tangent delta in the cured state, and providing self-healing characteristics. Self-healing occurs because oil molecules damaged by charge leakage can diffuse away from the damaged site, allowing the actuator to be actuated again.

Multinozzle 3D printing enables rapid fabrication of contractile actuators with actuation strains up to 9%. The electrodes can be fabricated at a rate of 0.73 cm³/min; a device with an area of 7.5x3.9 cm² can be fabricated in ~6 min. The use of 3D printing enables versatile designs, including actuators with orthogonal pixels and prestrain-free rotational actuators.