(171h) 3D Printing of Poly-Dimethyl Siloxane (PDMS)/Liquid Metal Composites for Micro-Patterning Applications

Micropatterning has broad applications in bio-sensing, cell culture, anti-bacterial anti-slip packaging, and microfluidic devices. Previously used methods, such as the photolithographic approach, selective positive and negative etching after laser irradiation, laser ablation, and ion reaction etching through masks, have demonstrated successful patterning. However, these conventional processes are more energy consuming, delicate in parameter design, and involve large footprint instruments. Here reported is a method for the fabrication of micropatterned polydimethylsiloxane (PDMS) structures in a one-step procedure enabled by a new 3D printing technique, the Multiphase Direct Ink Writing (MDIW). Our method uses a customized nozzle capable of incorporating two material feedstocks that were divided, multiplied, and reorientated into alternating layers. The microlayered structures consist of (i) one layer containing eutectic gallium indium, a high surface tension liquid metal with a critical yield stress of ~0.5 mN/m, and (ii) the alternating layer PDMS. Though attractive in using 3D printing for patterning purposes, many challenges exist in controlling the flow of liquid metals, as they tend to agglomerate and oxidize. First, the substrate needs to be prepared specifically to enhance the liquid metal wetting tendency. Apart from that, forming a thin passivating oxide layer almost instantly allows for non-diffusive interaction with PDMS. Besides, the elastomer’s high permeability to oxygen favors surface oxidation, allowing the formation of alternating layers. Our liquid metal/elastomer composites have broad applications in stretchable electronics, directional conductors, and anisotropic heat exchangers, among many others.