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/m(2). At a thickness of 40 mu m, 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 mu m 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.

Automated summary

This paper reports a new method to prepare a bilayer bifunctional coating for the touchscreen of a foldable smartphone. The coating exhibits excellent mechanical and chemical properties, and can withstand bending without cracking. Apart from its application in foldable smartphones, this material also shows promising potential for various other applications.