Development of a Coating-Less Aluminum Superhydrophobic Gradient for Spontaneous Water Droplet Motion Using One-Step Laser-Ablation

Abstract

Nature shows various approaches to create superhydrophobicity, such as the lotus leaf, where the superhydrophobic (SHPB) surface arising from its hierarchical surface consists of random microscale bumps with superimposed nanoscale hairs. Some natural systems, such as the hydrophilic silk of some spider's webs, even allow the passive transport of water droplets from one part of a surface to another by creating gradients in surface tension and Laplace pressure. We look to combine both ideas and replicate the superb water repellence of the lotus leaf and the surface tension gradient-driven motion of the spider silk to form an all-metal, coating-less surface that promotes spontaneous droplet motion. We present the design, fabrication, and investigation of such superhydrophobic gradient surfaces on aluminum, which are aimed at spontaneous water droplet movement for improved surface water management. One surface demonstrates a droplet travel distance of almost 2 mm for a 11 μL droplet volume. We also present surfaces that map the theoretical ranges of the surface tension gradient surfaces tested here.

Patterning Wettability for Open-Surface Fluidic Manipulation: Fundamentals and Applications

“…In a condensing environment, the condensate droplets moved at a microscale from a HPB line to a HPL channel; at the 10, pattern viii, using laser etching, which promoted a nanoscale line-edge roughness supporting a SHPB wetting state at one end of the gradient. 129 As first reported in ref 105, this style of gradient also displayed bimodal transport of liquid droplet depending upon the surface contamination. When the surface was cleaned, the Wenzel wetting state was promoted, resulting in spontaneous spreading.…”

“…Misiiuk et al prepared a gradient type, as shown in Figure , pattern viii, using laser etching, which promoted a nanoscale line-edge roughness supporting a SHPB wetting state at one end of the gradient . As first reported in ref , this style of gradient also displayed bimodal transport of liquid droplet depending upon the surface contamination.…”

“…When the surface was cleaned, the Wenzel wetting state was promoted, resulting in spontaneous spreading. Once a hydrocarbon overlayer had naturally formed on the surface, the CB state was promoted, resulting in spontaneous slip movement …”

“…Once a hydrocarbon overlayer had naturally formed on the surface, the CB state was promoted, resulting in spontaneous slip movement. 129 Whereas the previous gradients were generally linear by design, other researchers have focused on radial gradients. A topographic radial gradient presented by Khoo et al (similar to Figure 11, pattern i) consisted of topographic wedges pointed radially outward.…”

3D gradient printing based on digital light processing

“…, all proved to be suitable for multiple wettability materials, whether they themselves are hydrophobic or not. 29,39–43 Analogously, gradient topography also affects microbial adhesion to the matrix, which provides an easy-to-manipulate way to guide cell behaviours, such as cell adhesion, cell migration, cell proliferation, and stem cell differentiation. As indicated in Fig.…”