Transparent organic/silica nanocomposite coating that is flexible, omniphobic, and harder than a 9H pencil

Abstract

Coatings that are transparent, wear resistant, flexible, and anti-smudge may be used on foldable touchscreens, for example. However, there have been only few reports on such coatings. This paper reports such a coating. The coating is prepared from the thermal curing of cycloaliphatic epoxy-functionalized oligosiloxanes (CEOS) with PEMA-g-PDMS, poly[ethylene-alternating-(maleic anhydride)] (PEMA) grafted with PDMS side chains. Here CEOS is prepared via sol–gel reactions involving [2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane, an inexpensive coupling agent. Meanwhile PEMA-g-PDMS is prepared from commercially available PEMA and monoamine-terminated PDMS. The coating is cured via heat-induced ring opening of the epoxide groups of CEOS by maleic anhydride groups of PEMA. With a final PDMS weight fraction of 2.8 wt% and a thickness of 40 µm, the cured coating has a transmittance of 94.9% at 500 nm. On such a coating, test liquids with surface tensions exceeding ~22 mN/m readily and cleanly slide, while ink traces and graffiti paint readily contract. These properties are retained after the coating is abraded with cheesecloth under a pressure of 15.5 kPa for 10,000 cycles. Additionally, this coating exhibits exceptional flexibility. On either side of a PET film, the bilayer film can be bent into a shape with a U cross section without coating damage. While this coating may have practical applications, the chemistry used may be used for the development of other coatings.