Controllable impact spreading behavior is critical for effective thermal management of spray cooling. However, splash and retraction are common problems on hydrophobic (HPB) and hydrophilic (HPL) surfaces. Herein, by regulation of surface wettability, we report a controllable ultrafast impact superspreading behavior (superspreading time of ∼3.0 ms) without splash and retraction on superamphiphilic (SAPL) silicon surfaces. Analysis of dynamic wetting processes combined with observation of lateral force microscopy images on SAPL surfaces reveals the existence of a precursor film at the spreading edge induced by heterogeneous surface wettability at nanoscale. Further study indicates that the inhibition of splash results from the high liquid flux in precursor film, which suppresses the interposition of air at the spreading edge. The reduction of Laplace forces owing to the presence of precursor film inhibits retraction at the spreading frontier. Taking advantage of this impact superspreading behavior on SAPL surfaces, effective heat dissipation is demonstrated, offering uniform and high heat flux for the spray cooling process.
Cai Long,Yongquan Qing,Kai An,Xiao Long,Chen Liu,Shuo Shang,Chuanning Yang,Changsheng Liu
Extreme wettability coatings with repellent-liquids have attracted considerable attention due to their various advantages. Such coatings are not only restricted by poor robustness, but it is difficult to achieve for controlled liquid transport and inhibiting liquid splash due to allowing the droplet to roll-off and bounce, limiting functional applications. Here, we developed two opposite extreme wettability coaitngs with a superhydrophobic-oleophilic coating (SC) and coexisting superoleophobic-superhydrophilic coating (CSC), by changing only the type of fluorination agent. These coatings have shown strong mechanical robustness under sandpaper abrasion, washing, finger-wipe, knife-scratch, and tape-peel due to the synergistic enhancement between native rosin and grafted nanoparticles. Surprisingly, the perfluorinated liquid-infused SC surface could achieve a smart interface for inhibiting splash and recovery of water droplets along with the five-pointed star/branch pattern. Besides, oil droplets could be transported controllable along the desired sinusoidal shape and letter “YOU” wetted path on the water-infused CSC surface by dynamic control. Undoubtedly, these can have a broad applicability spectrum in the micro-fluidics and precision industry.
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