Polarity dependent electrowetting for directional transport of water through patterned superhydrophobic laser induced graphene fibers

The possibilities of the precise control of wetting properties of a series of laser-induced graphene (LIG) films consisting of microscale air pockets on top of nano-scale surface roughness using electrowetting are demonstrated. By application of a marginal DC bias (-2 V), water can efficiently wet as well as can be pumped through the superhydrophobic LIG substrates. Interestingly, the electrowetting phenomenon is strongly dependent on the applied voltage polarity and it causes an abrupt wetting transition from superhydrophobic (contact angle-152 degrees) Cassie state to superhydrophilic (contact angle -7 degrees) Wenzel state on the LIG films. By analyzing the voltage polarity dependent electrowetting results with an equivalent electrical circuit model at the solid-liquid interface, and considering the hierarchical dual surface roughness (micro-nano scale), the transition between the slippy Cassie state and the sticky Wenzel states is explained. Furthermore, we demonstrate that the unique structural characteristics of the custom-designed micropatterned LIGs, with precisely tailored surface energy by simple post-annealing treatment, enable easy preparation of superhydrophobic LIG films. The approach to prepare stable superhydrophobic LIG with voltage polarity dependent wetting mode transition is used here to controllably transport of water through 3D porous LIG surfaces. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study demonstrates the precise control of wetting properties of laser-induced graphene films through electrowetting, showing a transition from superhydrophobic to superhydrophilic states. The unique structural characteristics of custom-designed micropatterned LIGs enable the preparation of stable superhydrophobic films with voltage polarity dependent wetting mode transition for controllable water transport.