Reactive Jetting of High Viscosity Nanocomposites for Dielectric Elastomer Actuation

The layer-by-layer nature of additive manufacturing is well matched to the layer construction of stacked dielectric actuators, with inkjet printing offering a unique opportunity due to its droplet-on-demand capability, suitable for multi-material processing at high resolution. This paper demonstrates the use of high viscosity, multi-material jetting to deposit two-part reactive inks with functionalized nanofillers to digitally manufacture dielectric elastomers for soft robots with high precision, and shape manipulation. Graphene-based fillers, including graphene oxide (GO) and thermally reduced graphene oxides (TRGOs), have been incorporated into a polydimethylsiloxane (PDMS) matrix at low loading (below the percolation threshold). Consequently, the dielectric constant of the elastomer dramatically increases (by 97%) compared to neat PDMS, yielding a more than 20-fold increase in the electric-field induced electromechanical contraction (from 0.3 to 6.7%). This study shows that the oxygen-functionalities present in GO and TRGOs, which possess a moderate conductivity, improve the dispersion of those fillers in polymer matrices, thus significantly improving the dielectric constant of the polymer composites. Inkjet printing of high-performance, soft electroactive composites enables high-speed, reliable fabrication of monolithic artificial muscles (leading to stronger, cheaper, and more capable soft robotic devices) and provides a vital stepping stone towards fully additively manufactured soft robots.