Laser-assisted tailoring of surface wettability - Fundamentals and applications: A critical review

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 laser-matter 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.