Different Roles of Surface Chemistry and Roughness of Laser-Induced Graphene: Implications for Tunable Wettability

Abstract

The control of surface wettability is a technological key aspect and usually poses considerable challenges connected to high cost, nanostructure, and durability, especially when aiming at surface patterning with high and extreme wettability contrast. This work shows a simple and scalable approach by using laser-induced graphene (LIG) and a locally inert atmosphere to continuously tune the wettability of a polyimide/LIG surface from hydrophilic to superhydrophobic (Φ ∼ 160°). This is related to the reduced amount of oxygen on the LIG surface, influenced by the local atmosphere. Furthermore, the influence of the roughness pattern of LIG on the wettability is investigated. Both approaches are combined, and the influence of surface chemistry and roughness is discussed. Measurements of the roll-off angle show that LIG scribed in an inert atmosphere with a low roughness has the highest droplet mobility with a roll-off angle of Φ RO = (1.7 ± 0.3)°. The superhydrophobic properties of the samples were maintained for over a year and showed no degradation after multiple uses. Applications of surfaces with extreme wettability contrast in millifluidics and fog basking are demonstrated. Overall, the proposed processing allows for the continuous tuning and patterning of the surface properties of LIG in a very accessible fashion useful for "lab-on-chip" applications.

Practical Considerations for Laser-Induced Graphene Pressure Sensors Used in Marine Applications

“…PDMS readily wets all LIG recipes used in this work, forming interconnected porous structures of LIG/PDMS composites. This is consistent with the literature focused on the wettability of high-surface-area LIG structures formed under oxygen-rich (e.g., ambient air) atmospheres or at high laser fluence (surface oxygen content > ~5%) [23,30]. Encapsulating LIG sensors with liquid elastomer precursors (e.g., PDMS, EcoFlex, or polyurethane) is commonly used to fabricate flexible sensors to form LIG/elastomer composites [23].…”