Respiratory mucosa-inspired “sticky-slippery coating” with transparency and structure adaptation based on comb-polymer nanogel

Liquid-repellent surfaces are materials or coatings that exhibit the ability to repel liquids. These surfaces are designed to reduce the amount of liquid that comes into contact with the surface, causing the liquid to roll off or sliding off effortlessly. Existing liquid-repellent surfaces rely on supporting liquids with topographic characteristics and immiscible media, such as super-liquid-repellent surfaces and slippery liquid-infused porous surfaces. However, due to external disturbances and delicate architectures, these surfaces frequently lack pressure resistance. Another method is to graft flexible macromolecular chains of liquid polymers, such as perfluorinated polyether or poly, onto substrate surfaces to create liquid-like lubricating coatings. Even though they are covalently linked to the surface, these molecular structures can lose their liquid-repellent capabilities with minor wear. Another current idea is to generate slippery surfaces by grafting macromolecular chains onto polymers such as polyurethane or epoxy. However, most present liquid-repellent coatings rely largely on organic solvents, which are hazardous to human health and the environment. Furthermore, typical polymer coatings are dense and continuous, obstructing the inherent pore structure of porous materials. The use of comb-polymer nanogels to create liquid-repellent surfaces with multilayer topologies offers a viable option to overcome the limitations of existing techniques. These surfaces have numerous applications, including marine facility maintenance, biomedicine, environmental protection, and optical devices.

In a new study published in the peer-reviewed Chemical Engineering Journal, Dr. Mengnan Yu, Dr. Jichao Zhang, Dr. Yilin Wu and Dr. Shaohai Fu from Jiangnan University proposed a new multilayer sticky-slippery liquid-like coating based on comb-polymer nanogel synthesized by miniemulsion polymerization. This coating is inspired by the respiratory mucosa from the human body, which has unique multilayer structures that remove foreign bodies to keep the mucosal surface clean.

The research team employed miniemulsion polymerization to synthesize a comb-polymer nanogel. In their method, monomers were mixed with a surfactant in water, and polymerization was started to make tiny particles. The authors used vinyl-terminated polydimethylsiloxane monomers to dissolve bulyl acrylate, glycidyl methacrylate, and hexa-fluorobutyl methacrylate. They put sodium dodecyl sulfonate and hexadecane in deionized water and added it to the solution. The solution was then mixed with a magnet to make a pre-emulsion. To get regular dispersions, the pre-emulsion was further mixed with a cell pulverizer. These dispersions were put into a three-port flask and heated at 70°C under nitrogen protection.  A potassium peroxodisulfate solution in water was slowly added to the mixture to start the polymerization process. Due to the unique viscous flow nature and comb-polymer structure, the nanogel spontaneously forms a sticky-slippery coating via microphase separation during the film-forming process. The acrylate segments migrated to the substrate and Vi-PDMS segments with low surface energy quickly migrated toward the surface, forming a multilayer coating that was sticky and slippery, like a liquid, and had good surface adhesion and water resistance.

The research team used various characterization techniques to assess the properties of the multilayer sticky-slippery liquid-like coating. Using contact angle measurements, the liquid repellency of the coating was determined. The low sliding angles of 4◦ were reported, indicating that the coating has a strong ability to repel liquids. The substrate adhesion of the polymer was evaluated via a 90◦ peel

strength test, which revealed a strong interfacial adhesion with a high adhesion force value of 9.0 MPa. The superior transparency (87.5 %) of the liquid-repellent coating is quite essential in special fields, such as optical devices, buildings, and automotive glasses. Encouragingly, the biomimetic sticky-slippery coatings from comb-polymer nanogel possessed prominent substrate adaptation,

Tribological experiments were conducted to assess the friction and wear properties of the coating. The results indicated a low coefficient of friction, indicating that the lubrication properties were favorable. When subjected to sliding against a metal surface, the static friction coefficient and kinetic friction coefficient of coated fiber were 0.015 and 0.001, and suggesting that the coating appropriate for applications involving sliding or rubbing surfaces. Meanwhile, the resultant coating exhibited excellent flexibility, fascinating transparency, good antifouling performance, and long-term structure stability under harsh conditions.In conclusion, the authors developed a multilayer sticky-slippery liquid-like coating by synthesizing an innovative comb-polymer nanogel through miniemulsion polymerization. The research contributed to the advancement of novel materials with unique properties inspired by biological systems. In a statement to Advances in Engineering, the corresponding author, Dr. Jichao Zhang said that these new findings in comb-polymer nanogels can be used in the obtained multilayer transparent coating showed a strong interfacial adhesion. .

Different from the traditional slippery coatings, the biomimetic sticky-slippery coating could fully cover various substrates without changing the original morphology of the substrates. Moreover, this simple and universal method is useful for designing advanced slippery surfaces with broad application potential in a range of industry, military equipment, and aquaculture. These are just a few examples of the potential applications of comb-polymer nanogels. As research in the field progresses, more innovative applications are likely to emerge, further expanding their utility in various domains.