Engineering surface-grafted polymers for adhesion and friction control

The last few decades have witnessed the great progress in surface modification through the use of functional polymer coatings. Surface-grafted polymers with thickness ranging from several nanometers to micrometers have been proven to significantly improve the surface properties of materials, thus enabling diverse, customizable, and controllable performances. Consequently, surface-grafting has become a key tool in scientific research on surface/interface and in surface engineering applications. The interface adhesion and friction between materials and their environments can be precisely controlled by grafting specially designed polymer coatings on material surfaces. As a result, the use of surface-grafted polymers to control the adhesion and friction of materials has attracted extensive attention across various disciplines, from polymer chemistry, physics, and materials science to biology and medical science. This review starts with a discussion of functional surfaces in nature that exhibit unique adhesion and friction phenomena. It then introduces the fundamental principles of tribology and the adhesion and friction behaviors of polymer surfaces. It covers different methods for producing polymer coatings and the corresponding strategies for controlling adhesion and friction. Finally, the challenges and barriers that prevent broader application of surface-grafted polymers are discussed and an outlook of future opportunities is presented.