In order to reliably produce soft-matter technologies and validate our theories and designs, we continue to develop new methods of fabrication. These methods are based on existing techniques in rapid prototyping and soft lithography and allow for test samples to be produced in minutes or hours.
Integrated Soft Electronics with Laser Patterning
We have introduced a novel method to simultaneously pattern conductive polymers and thin films of Ga-based liquid metal (LM) alloy using a CO2 laser. Conductive polymers include PEDOT:PSS and soft poly(dimethylsiloxane) elastomer filled with conductive microparticles of acetylene carbon black (cPDMS) or silver (AgPDMS). Whereas these materials may be patterned through photothermal ablation, liquid GaIn alloy is instead patterned through a unique mechanism that exploits the “moldability” of the liquid enabled by its surface oxide and the vapor recoil force of the PDMS substrate.
M. Weigel, T. Lu, G. Bailly, A. Oulasvirta, C. Majidi, J. Steimle, “iSkin: Flexible, Stretchable and Visually Customizable On-Body Touch Sensors for Mobile Computing,” ACM Conference on Human Factors in Computing Systems (CHI), Seoul, Korea (2015).
Z-Axis Conductive Film for Soft Electronics Interfacing
In order to form electrical connections with surface-mounted electronics or human skin, embedded LM circuits must be sealed with z-axis conductive elastomer. The z-axis film is composed of vertically aligned columns of magnetic microparticles and conducts electricity only through the thickness. This enables the formation of electrical vias to surface contacts without causing shorting between circuit features within the plane.
T. Lu, J. Wissman, Ruthika, C. Majidi, “Soft Anisotropic Conductors as Electric Vias for Ga-Based Liquid Metal Circuits,” ACS Applied Materials & Interfaces 7 26923–26929 (2015). [link]