G. Liu, M. Rabnawaz, H. Hu
Keywords: coatings, amphiphobic coatings, anti-fingerprint, anti-smudge
Summary:Fluorine-free anti-smudge coatings that are transparent, wear-tolerant, and adherent to different substrates are very useful. For example, on the windows of skyscrapers, they should inhibit stain formation and reduce window cleaning costs. On historic buildings and statues, they can provide protection against graffiti. On kitchen hoods and fans, they should make these appliances self-cleaning. In addition, on the touchscreens of hand-held electronic devices, they should reduce fingerprint deposition and facilitate smudge removal. Dream coatings that are practical and possess all of the above-mentioned properties have been developed by us recently.[1-2] We report in this talk our nano-design for this type of coatings and discuss example systems developed using this design principle. The coating matrices that we have used so far include polyurethane and epoxy. These matrices were utilized because polyurethane and epoxy coatings are widely used and mature formulations and established industrial application protocols exist for them. In addition, the coatings adhere well to many substrates. To render anti-smudge properties, we grafted liquid polymers such as poly(dimethyl siloxane) (PDMS) unto the surfaces of the traditional polyurethane or epoxy coatings. The grafted liquid polymers turned the original solid coating surfaces into a slippery liquid surface. Since a liquid cannot grab foreign objects as well as a solid surface, liquids with surface tension above 22 mN/m, which is 2 mN/m above that of PDMS, all cleanly slid down such coatings without leaving a trace behind, when the substrate was slightly tilted. The repelled liquids included water, cooking oil, paints, ink, and artificial fingerprint liquids. PDMS was also embedded as nano-reservoirs throughout the coating matrices. The nanosize of the reservoirs minimized light scattering and the coatings were thus optically clear. Upon coating wearing, the embedded PDMS chains initially underneath were released, replenishing the surface with new PDMS chains. Therefore, these coatings retained their anti-smudge properties after extensive wear or damage.  M. Rabnawaz, G. Liu, Angew. Chem. Int. Ed. 2015, 54, 6516-6520.  M. Rabnawaz, G. J. Liu, H. Hu, Angew. Chem. Int. Ed. 2015, 54, 12722-12727.