Enabling Superhydrophobicity-Guided Superwicking in Metal Alloys via a Nanosecond Laser-Based Surface Treatment Method

Abstract

Enabling capillary wicking on bulk metal alloys is challenging due to processing complexity at different size scales. This work presents a laser-chemical surface treatment to fabricate superwicking patterns guided by a superhydrophobic region over a large-area metal alloy surface. The laser-chemical surface treatment generates surface micro/nanostructures and desirable surface chemistry simultaneously. The superhydrophobic surface was first fabricated over the whole surface by laser treatment under water confinement and fluorosilane treatment; subsequently, superwicking stripes were processed by a second laser treatment in air and cyanosilane treatment. The resultant surface shows superwicking regions surrounded by superhydrophobic regions. During the process, superwicking regions possess dual-scale structures and polar nitrile surface chemistry. In contrast, random nanoscale structures and fluorocarbon chemistry are generated on the superhydrophobic region of the aluminum alloy 6061 substrates. The resultant superwicking region demonstrates self-propelling anti-gravity liquid transport for methanol and water. The combination of the capillary effect of the dual-scale surface microgrooves and the water affinitive nitrile group contributes toward the self-propelling movement of water and methanol at the superwicking region. The initial phase of wicking followed Washburn dynamics, whereas it entered a non-linear regime in the later phase. The wicking height and rate are regulated by microgroove geometry and spacing.