Laser-Assisted Tailoring of Surface Wettability - Fundamentals and Applications: A Critical Review

Abstract

The control of ubiquitous wetting behavior that is determined by the surface free energy of the solid and the surface tension of the interacting liquid is an area of intense research, largely due to its applications in various sectors, ranging from healthcare to automotive industry. The failure and/or toxic nature of the conventionally employed chemical methods to engineer the surface free energy of solids paved the way for utilizing alternative techniques such as laser-based physical texturing of the surface to achieve the desired wettability behavior. This review provides insight into the implementation of lasers to engineer the surfaces of various kinds of materials and how the surface engineering manipulates their wetting characteristics based on the state of the art knowledge of the field. Various theories that explain the wetting behavior of droplets on the surfaces of homogeneous, heterogeneous, and complex structures are discussed with a special emphasis on the role of surface roughness. Further, the article focuses on the lasermatter interaction at different time scales and modification of the surfaces with different kinds of lasers (nano, pico, and femtosecond laser) and their applications. A critical analysis of the effects of experimental parameters such as laser fluence, repetition rate, laser wavelength, inter-pattern spacing on the experimentally observed wetting behavior in the recent literature is also presented. Emerging applications of laser structured surfaces in various fields, including biomedical, water harvesting, anti-bacterial, spectroscopic analysis, oil/water separation, etc. are discussed in detail.

Expedited Transition in the Wettability Response of Metal Meshes Structured by Femtosecond Laser Pulses for Oil-Water Separation

“…Although these techniques can separate oil-water mixtures, they consume harmful complex chemicals, and they lack durability and longevity since they are prone to mechanical damaging of the coated layers, which deteriorates their performance. On the other hand, laser surface structuring has proven to be an effective and durable technique for controlling the wettability of superhydrophobic and superhydrophilic wetting states (Peethan et al, 2019 ; Boltaev et al, 2020 ). Femtosecond laser surface structuring has lately emerged as a robust, environmentally friendly, non-contact, and mask-less process that is capable of producing features with very fine resolution over large areas, which makes it suitable for a wide range of applications (Vorobyev and Guo, 2013 ).…”

Oil-Grafted Track-Assisted Directional Transport of Water Droplets and Submerged Air Bubbles on Solid Surfaces

“…Tailoring of the surface wettability properties via physical as well as chemical methods is a subject of intense research as it finds applications in diverse areas, ranging from superhydrophobic textiles to therapeutic delivery. − The majority of these surfaces are fabricated by biomimicking naturally occurring animals or plants. For example, the surface of lotus leaves is mimicked to achieve superhydrophobic surfaces whereas desert beetle and pitcher plant surfaces are imitated to obtain wettability contrast and slippery surfaces, respectively. − Advances in the fabrication of hierarchical micro and nanoscale structures facilitated the creation of surfaces with extreme wettability, ranging from superhydrophobic to superhydrophilic surfaces. − Inspired by the fog-basking nature of the desert beetle, research has been carried out to create a wettability contrast surface that can harvest water from fog and humidity.…”

Non-adhesive contrast substrate for single-cell trapping and Raman spectroscopic analysis

“…17–19 A lotus-leaf-inspired hierarchically structured superhydrophobic surface is normally characterized by the beading up of a water droplet and subsequent rolling off due to low adhesion and friction, and this is normally explained based on an entrapped air plastron and the Cassie–Baxter model. 20 Meanwhile, hydrogen bonds mediate efficient adhesive interaction with the substrate and are used to explain superhydrophilic surfaces (SHL). A few previous publications already exploited the SHB/SHL contrast to create a microliter droplet assay and to trap single cells.…”