Inkjet material deposition is a promising approach to print multiple functional components for dielectric elastomer (DE) devices. The automatic fabrication process promotes reliable and repeatable results, and allows scaling to a few millimetres, which is advantageous in areas such as microfluidics and optics. We present here the printing and evaluation of novel ink formulae comprising silicone and a conductive filler. Carbon black, the conductive filler, is a popular electrode material. Although it has a relatively high resistance, it has been shown to produce compliant electrodes of good performance for dielectric elastomer actuators (DEA). Carbon black is added to liquid silicone rubber and solvents in order to obtain a solution that can be inkjet-printed. The silicone provides binding of the carbon particles into a soft matrix as well as bonding to the elastomer membrane on which it is printed. Each ink has unique electromechanical properties, e.g. sheet resistances ranging from a few kΩ/sq to MΩ/sq. We can apply different inks to provide conductive electrodes for DEA or piezoresistive components such as the dielectric elastomer switch (DES) - able to locally control charge over DEA - or simple resistor and electrode tracks. We discuss ink behaviours and printed sample components for networks of DEA and combined driving circuitry, all with soft, flexible materials.
We present a method for the patterning of compliant electrodes for dielectric elastomer actuators (DEA) using drop-on-demand (DoD) printing and a lift-off process. DoD is a very appealing method for the patterning of electrodes, due to its high resolution, and the design versatility brought by printing from computer files. However, it has very narrow requirements regarding the viscosity, surface tension, and agglomeration size of the solution to be printed, and a new jetting waveform must be developed for each ink. This makes experimenting with new compliant electrode formulations difficult and time-consuming. Our approach consists in printing a watersoluble sacrificial layer on the elastomer, which serves as a mask selectively protecting portions of the membrane. Compliant electrodes can then be applied on the mask by different means (brush, spray coating, stamping etc.), and the mask can subsequently be dissolved to wash away the excess of ink and reveal the pattern, similar to a lift-off process. The inkjet printing process must only be developed and optimized for a single solution (the sacrificial layer), whereas many different electrodes formulations can then rapidly be patterned and tested, without having to meet the requirements of the printer regarding viscosity, surface tension or agglomeration size. We demonstrate the method by patterning an Polyvinylpyrrolidone (PVP) mask. We then use an airbrush to apply a carbon black/silicone mixture over the whole membrane. Finally, we wash away the mask to reveal the compliant electrodes.