Femtosecond Laser Fabrication of Wettability-Functional Surfaces: A Review of Materials, Structures, Processing, and Applications

Abstract

Wettability-functional surfaces are crucial in both theoretical investigation and engineering applications. Compared to traditional micro/nano fabrication methods (such as ion etching, sol-gel, chemical vapor deposition, template techniques, and self-assembly), femtosecond laser processing has unique advantages, such as unmatched precision, flexible controllability, and material adaptability, widely used for the fabrication of wettability-functional surfaces. This paper systematically discusses the principle and advancement of femtosecond laser micro/nano processing in regulating surface wettability and analyzes the laser modulation mechanisms and structural design strategies for wettability-functional surfaces on various materials. Additionally, this paper reviews the practical applications of femtosecond laser-based wettability-functional surfaces in environmental engineering, aerospace, and biomedical fields, while highlighting the challenges and future directions for femtosecond laser processing of wettability-functional surfaces.

Keywords: femtosecond laser; functional surface; micro/nano structures; wettability.

Figure 3

(a) Superhydrophilic stainless steel spheres with enabled droplet manipulation and self-cleaning at a magnetic field [29]; (b) square pillar and Siberian-cocklebur-like structures on PTFE, related surface morphology, contact angle at different temperatures, and ice delay time [37]; (c) micro-pit structures on PDMS with a contact angle of 150° [38]; (d) femtosecond laser-induced controllable changes in the surface morphology and wettability of shape memory polymers [49]; (e) microcone array state changes enable coverslip capture, transfer, and release [50].

Figure 4

(a) Variation in contact angle on stainless steel LIPSS surface with accumulated energy density [68]; (b) grooved structures with different periods on aluminum alloy surface by adjusting femtosecond laser spacing [53]; (c) air pockets (sealed and open) on Ni surfaces [72]; (d) periodic micro-pit arrays and self-organized complex nanostructures on quartz glass surface and the wettability [55]; (e) micro-pit arrays, non-uniform micro-clusters, and irregular nanosheet composite structures on aluminum surfaces with excellent superhydrophobic properties [73]; (f) triple-scale micro/nano structures on Cu surface [74].

Figure 6

(a) Plume shielding during femtosecond laser fabrication [85]; (b) shape modulation for processing of complex structure [80]; (c) frequency modulation for MHz/GHz burst mode [86,87]; (d) polarization modulation and processed structures with linear and radial polarization [90].

Figure 8

Applications of femtosecond laser-treated wettability-functional materials in various fields: (a) environmental engineering [97]; (b) aerospace [100]; (c) biomedical fields [103].

Figure 1

Design and application of wettability-functional surfaces via femtosecond laser processing.

Figure 2

Basic concepts related to surface wettability and several typical wettability models. (a) Young’s model for flat substrates [24]; (b) Wenzel model for rough substrates [25]; (c) Cassie–Baxter model avoiding penetration [26].

Figure 5

Femtosecond laser fabrication of non-uniform structures and the surface wettability: (a) hierarchical hydrophilic/hydrophobic/bumpy Janus membranes [77]; (b) alternative hydrophilic/hydrophobic structures for detecting the particle aggregation [78]; (c) gradient structures for droplet positioning in Raman detection [79].

Figure 7

(a) Temperature profile during Bessel femtosecond laser processing [91]; (b) temperature profile during femtosecond laser processing at GHz-burst mode [92]; (c) electronic field distribution at different polarization directions [96].