Fabrication of "roll-off" and "sticky" superhydrophobic cellulose surfaces via plasma processing

Most of the artificial superhydrophobic surfaces that have been fabricated to date are not biodegradable, renewable, or mechanically flexible and are often expensive, which limits their potential applications. In contrast, cellulose, a biodegradable, renewable, flexible, inexpensive, biopolymer which is abundantly present in nature, satisfies all the above requirements, but it is not superhydrophobic. Superhydrophobicity on cellulose paper was obtained by domain-selective etching of amorphous portions of the cellulose in an oxygen plasma and subsequently coating the etched surface with a thin fluorocarbon film deposited via plasma-enhanced chemical vapor deposition using pentafluoroethane as a precursor. Variation of plasma treatment yielded two types of superhydrophobicity : "roll-off' (contact angle (CA), 166.7 degrees +/- 0.9 degrees; CA hysteresis, 3.4 degrees +/- 0.1 degrees) and "sticky" (CA, 144.8 degrees +/- 5.7 degrees; CA hysteresis, 79.1 degrees +/- 15.8 degrees) near superhydrophobicity. The nanometer scale roughness obtained by delineating the internal roughness of each fiber and the micrometer scale roughness which is inherent to a cellulose paper surface are robust when compared to roughened structures created by traditional polymer grafting, nanoparticle deposition, or other artificial means.