Laser Fabrication of Bioinspired Gradient Surfaces for Wettability Applications

Abstract

materials with gradients inspired by biological surfaces has therefore attracted much interest. Strategies for preparing gradient surfaces include vapor-phase diffusion, gradual immersion, electrochemical oxidation, and photolithography that have broadly adopted. [20-26] However, their material constraints, tedious and time-consuming processes, and their single-pattern limit their widespread use. Developing a substrate-independent, facile and efficient, pattern-diverse method for preparing gradient surfaces would aid fundamental science and practical application. Among various techniques, laser processing has recently emerged as a powerful tool in integratedoptics and biomimetic micro-nanodevices. This technology can be used to precisely control the preparation of micro/nanoscale structures on various substrates such as metals, glass, ceramics, and polymers. [27-33] Besides, the high energy density of lasers allows the machining process to be completed quickly and efficiently. Combining laser machining with computer-aided control allows laser ablation parameters to be precisely controlled, including the processing position, scanning speed, scanning interval, and scanning track. Laser processing can therefore be used to produce flexible and diverse patterns in complex workpieces. And laser micro/nano fabrication has been applied to regulate surface wettability. [34-43] Therefore, laser processing has great potential for developing samples with different wettability and geometries on various materials. This review discusses laser fabrication of bioinspired gradient surfaces for wettability applications, whose overview is shown in Figure 1. The related backgrounds including gradient surfaces in natural creatures, the theoretical basis of wettability, and the distinct characteristics of laser processing are introduced. Gradient surfaces can be classified into wettability gradients and geometric gradients, and they are discussed in terms of various laser fabrication approaches and wettability applications. It is worth mentioning the definition of wettability gradient and geometric gradient in this review. Wettability gradient is defined as a surface with no obvious geometric change in the shape, and there is a difference of contact angles on the macro level resulting from the roughness gradient on the micro level. Geometric gradient is defined as a surface possessing significant geometric changes in the shape, but not much difference in the roughness of the entire surface at the microscopic level. Specially, a wettability gradient surface generates a water driving force as a result of its varying surface roughness. Wettability gradient surfaces can be applied in water droplet control, Inspired by nature, gradient surfaces have attracted broad research interest because of their potential in microfluidics, fog/water collection, and water electrolysis. Among the various techniques for preparing gradient surfaces, laser processing is substrate-independent, facile and efficient, patterndiverse, which can be used to prepare...

Modulation and Control of Wettability and Hardness of Zr-Based Metallic Glass via Facile Laser Surface Texturing

“…In recent years, laser-based surface texturing has been proved to be one of the most efficient techniques to modify and control important surface functionalities, including surface wettability [18][19][20][21][22], reflectivity [23,24], anti-icing property [25,26], corrosion resistance [27], etc. For example, wettability transition from superhydrophilicity to superhydrophobicity has been achieved on various materials including aluminum [28], copper [29], stainless steel [30,31], and titanium [32][33][34][35][36] by combining laser surface texturing and lowtemperature annealing.…”

Design of Hybrid Superwetting Surfaces with Self‐Driven Droplet Transport Feature for Enhanced Condensation

“…Nature can always find an alternate to solve the survival issues owing to evolution from harsh living environment. [ 31 ] A beetle in Namib Desert uses its hydrophobic back for achieving drop‐wise condensation while taking advantage of hydrophilic bump patched on its back to realize synchronized film‐wise condensation. This hybrid drop‐film‐wise condensation mode is beneficial for promoting the removal of drop‐wise condensate as it would be transferred into the film‐wise condensate immediately when contacting the film‐wise region due to the Laplace pressure gradient.…”

Rapid construct superhydrophobic microcracks on the open-surface platform for droplet manipulations

“…In addition, open surface microfluidics offers several advantages over the conventional counterpart, including simple monolithic construction, direct environmental accessibility, no cavitation/interfacial obstruction, clear optical path, and compatibility with biological experiments 9 . In recent years, open-surface microfluidics has attracted much attention due to several advantages, such as reduced consumption of reagents and samples 10 ; a simplified integration processes and controlled system (i.e., no bonding is required); and most importantly, no channels exist, thereby avoiding trapped bubbles and eliminating the risk of the microchannel clogging 11 – 13 . Thus, open-surface microfluidics has great potential in point-of-care (POC) diagnostics and lab-on-a-chip (LOC) applications 14 , 15 .…”