Laser-Architected Surface Wetting

Abstract: Technologies that require surface wetting or evaporative cooling require the ability to efficiently spread fluids across large areas, as increased wetted surface area increases evaporative flux. However, the intrinsic surfacial and bulk properties of most engineered materials substantially limit the rate and magnitude of surface wetting and lack control of flow direction, preventing them from rapidly wetting large surfaces. Here, we introduce our approach for rapid and controlled wetting of surfaces by laser-engraving channel networks that provide pathways for rapid, long-distance (cm-dm scale) capillary fluid propagation across the area, while the intrinsic material properties enable slow, short-distance (mm-cm scale) surface wetting. We investigated this approach on hardened cement paste and showed that laser engraving is a fabrication-friendly, scalable, and reproducible solution for creating channels with properties conducive to capillary fluid propagation. We demonstrate that the rate and direction of surface wetting can be controlled by tuning the channel network density, channel network anisotropy, and supplied fluid flow rate. The integration of laser-engraved channel networks demonstrated significantly greater wetting performance (up to 10-fold greater wetted area and up to 180-fold greater wetting performance when wetted area is adjusted for fluid use efficiency) and greater evaporative cooling (up to 1.8 °C cooler surfaces) compared to control (hardened cement paste without laser-engraved channel networks).