《Advances in Engineering》 专题报道课题组论文“Nature-Inspired Superwettability Achieved by Femtosecond Lasers”

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Nature-Inspired Superwettability Achieved by Femtosecond Lasers

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Significance 

Wettability is one of the main intrinsic chemical and physical properties of solid surfaces. Thanks to many years of evolution, many organisms in nature have exhibited exceptional surface wettability. For example, oil spillage cannot contaminate fish underwater, lotus leaves display self-cleaning capabilities, and rain does not prevent butterflies from flying. With the advances in microscopy and microanalysis techniques, the microstructure and chemical composition of solid surfaces have been found to be responsible for the wettability of material surfaces. As a result, nature-inspired superwettability has become a hot research area in materials science engineering owing to its fundamental role in solving numerous problems related to the environment, energy, public health and many more.

Inspired by these exceptional wettability occurrences in nature, a series of superwettabilities have been accomplished based on various available micro/nanomachining techniques like chemical etching and electrochemical deposition methods. The developed superwettability has been widely applied in a wide range of applications. Although superwettability can be achieved via conventional micro/nano processing methods, these methods suffer from some intrinsic limitations such as lack of flexibility, complex preparing steps and limitations to specific materials. To date, the production of a versatile, feasible and efficient method or tool for engineering superwetting microstructures on different solid substrates remains a big challenge.

The laser technique, one of the greatest 20^th-century inventions, is a vital tool for modern ultra-precision manufacturing. In particular, femtosecond laser characterized by small heat-affected zones, high spatial resolution and non-contact processing can ablate nearly all materials to produce microstructures on the material’s surface. The femtosecond laser is also beneficial in the fine design of micro/nanostructures. Moreover, it can create various superwettabilities on substrate surfaces by forming special micro/nanostructures due to the significant impact of the surface microstructure on the wettability of solid substrates. Thus, femtosecond laser processing has many advantages over traditional manufacturing and is a promising technique for designing and modifying the wettability of materials.

Recently, Professor Jiale Yong, Professor Qing Yang, Professor Xun Hou and Professor Feng Chen from Xi’an Jiaotong University systematically summarized the recent research progress and applications of superwettability accomplished by femtosecond laser microfabrication. The authors commenced by discussing the concepts and wetting models commonly used in superwettability field as well as the characteristics of the femtosecond lasers used. The rich applications of the developed and emerging superwetting surfaces were also discussed. Finally, they commented on the challenges and prospects of femtosecond laser-induced superwettabilities. Their review is currently published in the, Ultrafast Science: A science Partner Journal.

Numerous superwettabilities inspired by nature have been successfully obtained on different substrates by combining the femtosecond laser-induced micro/nanostructures with suitable chemical compositions. Forming a hierarchical microstructure on a hydrophilic substrate produces superhydrophilicity that causes water to fully wet material surfaces. Superhydrophobicity is achieved by directly forming hierarchical microstructures on hydrophobic substrates or when hierarchical microstructures constructed on hydrophilic substrates by femtosecond laser are modified by low-surface energy. Superhydrophobic surfaces have robust repulsive effects on aqueous solutions. The reentrant microstructure is vital to achieving superamphiphobic surfaces that exhibit both superoleophobic and superhydrophobic properties. In contrast to the preparation of superamphiphobic materials, underwater superoleophobic surfaces can be prepared effortlessly by constructing microstructure on a hydrophilic substrate. Although both types of superoleophobic surfaces exhibit strong repellence to oily liquids and oils, underwater superoleophobic materials are more effective in water, while superamphiphobic materials are more effective in the air.

Superhydrophilic microstructures and superhydrophobic microstructures fabricated by femtosecond laser usually display superaerophobicity and superaerophilicity in a water medium, respectively. Whereas underwater superaerophobic surfaces can repel bubbles to prevent them from sticking to the material surface in water, underwater superaerophilic surfaces effectively absorb bubbles. Additionally, the laser-induced pores can be filled with lubricating fluid to create a thin lubricating layer on the substrate surface. The as-prepared slippery surfaces have excellent liquid repellence against many composite liquids. The femtosecond laser-functionalized surfaces have many possibilities in practical applications owing to the special wettability of solid materials, including self-cleaning, cell engineering, oil/water separation, water harvesting, manipulation of liquid droplets, among others.

Compared to traditional methods, femtosecond laser microfabrication has numerous advantages in achieving superwettability. For example, it is not limited to specific substrates and can process a wide range of materials. Additionally, this technology is feasible, flexible and precise for complex design of surface wettability. Moreover, it is relatively environmentally friendly as it does not rely on toxic reagents, hazardous operations and chemical reactions. Although femtosecond laser manufacturing still experiences problems related to the regulation of surface wettability, its robustness and ability to process nearly all materials are unmatched.

In a nutshell, a critical review discussing the recent developments in the field of femtosecond laser-induced superwettability was reported. With the engineering of more superwetting surfaces for new applications, femtosecond laser-induced superwettability is certainly an important field. In a statement to Advances in Engineering, Professor Jiale Yong, first author expressed his confidence that femtosecond laser microfabrication will enable large-scale production and commercial application of different nature-inspired superwetting materials.

Reference

Yong, J., Yang, Q., Hou, X., & Chen, F. (2022). Nature-Inspired Superwettability Achieved by Femtosecond Lasers. Ultrafast Science, 2022, 9895418.