Transparent Omniphobic Coatings that are Flexible and Wear Resistant
Omniphobic or anti-smudge surfaces require good mechanical durability to ensure that they are suitable for practical applications. In general, the abrasion resistance of a surface depends on its hardness. However, when a coating is very hard, it is usually brittle and lacks flexibility. New coating materials that impart high degrees of hardness and flexibility without sacrificing the excellent anti-wetting properties and optical transparency would have many potential applications. However, the fabrication remained an elusive goal. Reported herein is a molecular composite that combines these desirable properties. The composite is prepared via the photo-initiated cationic ring-opening polymerization of the epoxide rings of glycidyloxypropyl polyhedral oligomeric silsesquioxane (GPOSS). While the desired hardness is rendered by the silica core of GPOSS, the flexibility is imparted by the glycidyloxypropyl network. In addition, oil and water repellency is achieved without adversely affecting the other properties by incorporating into the coating a low-surface-tension liquid lubricant polydimethylsiloxane. Various organic solvents and water readily and cleanly glide off the final coating, while complex fluids such as ink and paint facilely contract on this surface. These properties are retained after an initially flat coating sample is rolled into a U-shape 500 times or is abraded with steel wool. While the reported coatings have various applications, the insight gained from the research will also facilitate the design of other analogous materials. This thesis also reports the preparation of such a flexible hard omniphobic coating via the thermal curing of another formulation. The formulation consists of blends of poly(ethylene-alt-maleic anhydride)-graft-polydimethylsiloxane (PEMA-g-PDMS) and cycloaliphatic epoxy-functionalized oligosiloxanes (CEOS). The anti-wetting agent of polydimethylsiloxane (PDMS) was covalently attached to poly(ethylene-alt-maleic anhydride) (PEMA) via the reaction between the terminal amine group of PDMS and maleic anhydride group of PEMA. The resultant grafted polymer was further heat-cured with the chemically blending of cycloaliphatic epoxy-functionalized oligosiloxanes (CEOS). Only 2.8 wt% of polydimethylsiloxane (PDMS) existing in the coating matrix can impart the anti-smudge properties. Test liquids with various surface tension such as water, hexadecane, dodecane can easily slide off the omniphobic surface without leaving a residue. Moreover, the improvement of the coating matrix hardness can significantly increase its omniphobic durability. This coating is also transparent, foldable and has good adhesion to a flexible poly(ethylene terephthalate) (PET) substrate.