Digitally Driven Mesoscopic Self-Assembly of Functional Materials by Selective Plasma Induced Super-Hydrophilicity

Digitally driven bottom-up manufacturing approaches promise new devices with unprecedented functionality by enabling the realisation of complex heterogeneous multi-material structures. However, the next generation of devices demands substantial progression beyond the capabilities of current manufacturing technologies. Presently, there are shortcomings associated with digital techniques concerning process resolution, compatible materials, production time, and unit cost. Presented here is progress on a novel manufacturing technology, whereby water-based inks containing functional materials self-assemble into user-defined patterns. The self-assembly is driven by selective surface functionalisation resulting from a localised plasma discharge created by a computer-controlled micro atmospheric plasma jet. This functionalisation corresponds to a replacement of the hydrophobic methyl groups of a polydimethylsiloxane substrate with hydrophilic silanol groups. Subsequently, inks are attracted to the regions of high silanol concentration. Through control of the voltage and frequency used to ignite the plasma, in combination with its motion, the ability to continuously vary the spatial distribution of the functionalisation to create self-assembled structures between 10^-1m and 10^-5m is demonstrated. Moreover, digital control over the ignition parameters enables efficient fabrication across these dimensional scales. Inks loaded with silver nanoparticles, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), and hard magnetic cobalt ferrite are demonstrated to be compatible. This range of mechanical, electrical, and magnetic properties already offers the opportunity to create functional devices across a diverse range of fields. Furthermore, we present a rapid characterisation technique to accelerate the future expansion of material libraries for both substrates and inks. We demonstrate the potential of this technique through the fabrication of demonstration devices within the fields of flexible electronics and magnetically actuated robotics. This fabrication technology addresses the shortcomings of current bottom-up fabrication approaches, offering a high-resolution, accurate, flexible, sustainable, and economically scalable manufacturing solution for the next generation of devices.