(580d) Ultrafast Thin Liquid Film Spreading on Hierarchical Nanowire Superhydrophilic Surface

The spreading of thin liquid film is a key controlling feature of many processes, including falling film heat and mass transfer, falling film reaction, micro-reactor, microfluidics, pesticide spraying and so on. The capillary wicking at solid surfaces has potential effect in thin liquid film spreading process. The geometrical size of micro/nanostructured surfaces could provide strong capillary force to enhance and regulate the thin liquid film wicking, spreading. However, the viscous forces resulted from the micro/nanostructure would. In this paper, the spreading dynamics of copper nanowire arrays with V-shaped microgroove are investigated experimentally and theoretically. The 3D hierarchical structures were composed of a vast array of copper nanowire structure and V-shaped microgroove structure. The different V-shaped microgrooves were formed due to the agglomeration of nanowires. Synergy reaction of two structures with different scales is the principal affect to rapid spreading of thin liquid film. The highly uniform copper nanowires provide prominent capillary force to drive liquid spreading. At the same time, the micro-V-groove provides an outstanding liquid film transport channel. Based on the balance between the driving capillary forces and viscous dissipation forces, a theoretical model on the dynamics of spreading on hierarchical micro/nanostructures was presented. Good agreement between theoretical model and experimental results was obtained. The result potentially provides guidelines of design and optimization of hierarchical structured superhydrophilic surface to manipulate thin liquid film and achieve ultra-fast spreading.