Perfluorinated compounds such as perfluoroalkylsilanes (FASs) and related materials have been widely employed in a wide variety of engineering fields by taking advantages of their excellent hydrophobic/oleophobic properties. However, their chemical and physical effects on human health and the environment have been lately viewed with suspicion. In particular, the use of long-chain perfluorinated chemicals (LCPFCs) is going to phase out by the end of 2015. An alternative hydrophobic/oleophobic treatment method not requiring LCPFCs has been strongly demanded.

 In this study, we report smooth and transparent organic surfaces showing unusual dynamic dewetting behavior toward nonpolar liquids. We prepared two different surfaces on glass slides: one, organic surfaces consisting of self-assembled monolayers (SAMs) of FASs with different chain length [CF3(CF2)nCH2CH2Si(OR)3, n = 0, 3, 5, 7, R=CH3 or C2H5], and the other, organic surfaces derived from a mixture of FASs and tetramethoxysilane (TMOS). Oleophobicity on the former surfaces was markedly depended on the length of perfluoroalkyl chains, but the latter exhibited excellent dynamic oleophobicity toward various kinds of nonpolar liquids, independent of the length of the perfluoroalkyl chains. Due to the addition of TMOS, condensed silica species most likely acted as spacer moieties such that an appropriate distance now separated the perfluoroalkyl chains allowing them to rotate freely and confer liquid-like properties on the surface [1,2]. This leads to the exceptional dynamic dewetting behavior toward various nonpolar liquids.

 

[1] A. Hozumi and T. J. McCarthy, Langmuir, 26 (2010) 2567-2573.

[2] D. F. Cheng, C. Urata, M. Yagihashi and A. Hozumi, Angew. Chem. Int. Ed., 51 (2012) 2956-2959.