Quantitative analysis and applications of laser-induced superhydrophobic metal surfaces
Creators: name: Huang, Wuji
Publisher: name: University of Iowa
Year: 2024
Subjects: Laser Processing
Superhydrophobic Surface
Machine Learning

description: The wettability of a metal surface can have a critical impact in ubiquitous engineering applications, including anti-corrosion, microfluidic systems, liquid transportation, etc., and therefore has aroused intense interest in both academia and industrial community. Two major factors, viz. surface topography and surface chemical composition, codetermine the wetting behavior of textured solids. In recent years, many engineering methods have been explored to fabricate surfaces with various wetting behaviors by modification of surface micro- and nanostructures and of surface chemistry. However, the effect of surface topography and chemistry on surface wettability has not been systematically investigated.A novel nanosecond laser-based high-throughput surface nanostructuring (nHSN) process has been developed by the author’s group that can simultaneously create random nanostructures and attain desirable surface chemistry over large-area metal alloy surfaces. In the present work, nHSN process is implemented and modified to fabricate a variety of metallic surfaces with special wettability. A series of descriptors, including fractal dimension, 2D entropy, and periodicity are developed to quantify the surface topography, while the surface chemistry is quantitatively analyzed by measuring the amount of fluorinated (-CF2-, -CF3) or polar nitrile (-CN) functional groups. By controlling the surface topography and surface chemistry, their effects on wettability are quantitatively evaluated.
description: Leveraging the insights from the quantitative analysis of superhydrophobic surfaces, a laser-assisted functionalization (LAF) method is developed to pattern large-area metal surfaces with varying functionalities, including i. Surface wetting, ranging from superhydrophilicity to superhydrophobicity; ii. Surface topography, ranging from a low-roughness, isotropic, random nanostructured texture to a microscale, highly structured texture; iii. Anti-reflection, ranging from moderately reduced reflectivity to ultralow reflectivity of less than 10%. Two sets of engineering parameters can be adjusted in the LAF process to accurately control these functionalities. The laser surface processing parameters, i.e., laser power intensity, scanning speed and overlap ratio, etc. are controlled to primarily modify surface topography; and the chemical immersion treatment parameters are selected to modify surface chemistry. The treated surfaces have been applied to enhance water collection from fog, employing bio-inspired, venation-like wettability patterns, resulting in a doubling of the water collection rate compared to untreated surfaces. Furthermore, the mechanisms behind fog harvesting have been explored experimentally.
description: Additionally, the LAF technique has been extended to 3D-printed metal alloys, demonstrating the potential for achieving consistent superhydrophobicity and specific wettability patterns by manipulating both surface topography and chemistry. This exploration encompasses a broad spectrum of superhydrophobicity, from low to high surface adhesion, considering both physical and chemical surface properties. The successful application of the lotus-rose petal patterns on 3D-printed surfaces highlights the method's adaptability for advanced surface engineering applications.