Principles, construction and application of liquid-like surfaces

Liquid-like surfaces are smooth, omniphobic surfaces that are modified with highly flexible polymers. The most typical feature of liquid-like surfaces is their extremely low contact angle hysteresis for both polar and nonpolar liquids. Droplets can slide effortlessly on liquid-like surfaces without leaving any residues. Compared to conventional superhydrophobic and superoleophobic surfaces, liquid-like surfaces are not reliant on micro/nanostructures, resulting in improved wear resistance and generalizability. In addition, liquid-like surfaces exhibit superior dynamic anti-wettability compared to conventional superhydrophobic surfaces. The excellent dynamic anti-wettability properties of liquid-like surfaces stem from the high flexibility of the employed polymer molecular chains. These molecules have an extremely low glass transition temperature and exhibit very low rotational barriers in their chemical bonds. Upon covalently grafting one end of the molecular chain to a solid surface, the other end can still rotate freely. The dynamic behavior of flexible molecular chains helps to overcome the energy barriers associated with the movement of droplet contact lines, leading to a reduction in the contact angle hysteresis and enhanced droplet sliding on surfaces. In addition, organic liquids induce a swelling effect on liquid-like molecules, suppressing the terminal relaxation time and enhancing the chain mobility. Consequently, the contact angle hysteresis and sliding angle of organic liquids on liquid-like surfaces are smaller than those of water. Additionally, the grafted molecules conceal structural defects on the solid surface, resulting in a smooth and chemically homogeneous surface that allows easier droplet slide. The methods of constructing liquid-like surfaces can be categorized into two groups. The first involves the direct covalent grafting of liquid-like molecules onto the substrate to obtain a liquid-like molecular brush surface. The second method involves incorporating liquid-like molecules into polyurethane or acrylic resins, followed by curing through heat or light, to construct transparent and wear-resistant coatings of a certain thickness on diverse substrates. The simple preparation process, stable performance and low cost of liquid-like coatings have facilitated their practical applications in various fields. Liquid-like surfaces offer advantages in practical applications due to their simplicity in preparation, stable performance and low cost. As a result, they hold promising application potential in various fields. For instance, self-transporting surfaces modified with liquid-like PFPE molecules can effectively inhibit microscopic liquid residues. Surfaces modified with liquid-like PDMS brushes demonstrate superior anti-scale and anti-icing properties compared to conventional superhydrophobic surfaces. Filtration membranes modified with PDMS brushes can resist the adhesion of high viscosity crude oil, thereby enhancing the efficiency of oil-water separation. Liquid-like coating can effectively resist the residue of fingerprint liquid, preventing contamination and corrosion of the material surface caused by the fingerprint liquid. Liquid-like surfaces exhibit resistance against the adhesion of cells, proteins, bacteria and other microorganisms, ensuring the cleanliness of medical equipment. This paper reviews the fundamental principles and fabrication methods employed in the development of liquid-like surfaces. Additionally, it presents the latest research applications of liquid-like surfaces, and provides prospects on potential directions for future research.