Facile Preparation of a Transparent and Rollable Omniphobic Coating with Exceptional Hardness and Wear Resistance

The encapsulating film for the touchscreen of a foldable smartphone consists of a flexible polymer layer covered by a hard coating and an antismudge coating, and the two coating layers are currently deposited via separate steps. This paper reports the preparation of a bilayer bifunctional coating via the deposition of a single polymer mixture. The base material for the coating is a ladder-like polysilsesquioxane (LASQ) that is derived from the sol–gel chemistry of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. Reacting a limiting amount of the liquid antismudge agent FP-COOH, which is a perfluorinated poly(propylene oxide) bearing a terminal carboxyl group, with LASQ yields m-LASQ-FP, a mixture of unreacted LASQ, and a graft copolymer LASQ-FP. m-LASQ-FP at a fluorine mass fraction of 6.0% is photocured to yield a coating with a surface energy of 12.3 ± 1.5 mJ/m2. At a thickness of 40 μm, the coating has at 500 nm a transmittance of >99% measured against its glass substrate, a remarkable nanoindentation hardness H value of 1.4 GPa, and a pencil hardness of > 9H. After being abraded for 300 strokes under a pressure of 26 kPa with steel wool, the coating exhibits no noticeable degradation in its ink contraction properties. At a thickness of 10 μm on a poly(ethylene terephthalate) film, the coating can undergo inward (on the inner surface of the bend) and outward bending to radii <1 and <2 mm, respectively, without cracking. Aside from being a superb candidate as a protective antismudge coating for foldable smartphones, this marvelous material should also have many other applications.