Tuning a surface super-repellent to liquid metal by a femtosecond laser.

Eutectic gallium-indium (EGaIn) liquid metal (LM) attracts increasing interest because of its broad applications in flexible circuits and soft devices. However, LM can easily adhere to a solid substrate due to the existence of a high-adhesive oxide outside layer, which greatly limits the real application of LM materials. Current methods to reduce the LM adhesion are mostly based on chemical treatment rather than surface microstructure, which are not suitable for most practical applications. In this paper, microstructure was simply created on various substrates by femtosecond laser ablation. The resultant surfaces show excellent repellence to EGaIn LM and the LM is difficult to adhere to the structured surface. Such a surface is defined as a "super-metal-phobic" surface. For example, the laser-ablated silica glass surface shows a contact angle of 157° ± 3°, sliding angle of 10°, and adhesive force of 1.2 μN to a LM droplet. The LM repellence is very stable even if the LM droplet is heavily pressed towards the sample surfaces. It is demonstrated that the adhesion of LM can be significantly reduced by the laser-induced surface microstructures. The method of controlling the wettability of LM has important potential applications in manipulating LM and preparing flexible circuits.