Hard but flexible coatings

Materials Science Early coatings for display devices were based on inorganic glassy materials made from condensation reactions of alkoxysilyl groups. Although these provided scratch and wear resistance, they were brittle and not flexible—a typical trade-off seen for hard materials. Seo et al. circumvent this limitation by reacting 2-(triethoxysilyl)propyl isocyanate onto the ring part of an α-cyclodextrin–based polyrotaxane molecule. Once crosslinked using a random copolymer, the modified α-cyclodextrin rings are still able to slide along the polyrotaxane backbone, thus imparting flexibility to the hard film. In addition to providing hardness and scratch resistance, a coated surface could also be bent repeatedly without defect formation. ACS Appl. Mater. Interfaces 11 , 27306 (2019).