Superhydrophobic Hierarchically Assembled Films of Diblock Copolymer Hollow Nanospheres and Nanotubes

Abstract

Reported are the formation of rough particulate films from cross-linked diblock copolymer vesicles and nanotubes and the wetting properties of the resultant films. The diblock copolymers used were F₆₆M₂₀₀ and F₉₅A₁₃₅, where the subscripts denote the repeat unit numbers, whereas M, A, and F denote poly­(2-cinnamoyloxyethyl methacrylate), poly­(2-cinnamoyloxyethyl acrylate), and poly­(2,2,2-trifluoroethyl methacrylate), respectively. The precursory polymers to F₆₆M₂₀₀ and F₉₅A₁₃₅ were prepared by atom transfer radical polymerization. In 2,2,2-trifluoroethyl methacrylate (FEMA), a selective solvent for F, vesicles and tubular micelles were prepared from F₆₆M₂₀₀ and F₉₅A₁₃₅, respectively. Photo-cross-linking the M and A blocks of these aggregates yielded hollow nanospheres and nanotubes bearing F coronal chains. These particles were dispersed into CH₂Cl₂/methanol, where CH₂Cl₂ was a good solvent for both blocks and methanol was a poor solvent for F. Casting CH₂Cl₂/methanol dispersions of these particles yielded films consisting of hierarchically assembled diblock copolymer nanoparticles. For example, the hollow nanospheres fused into microspheres bearing nanobumps after being cast from CH₂Cl₂/methanol at methanol volume fractions of 30 and 50%. The roughness of these films increased as the methanol volume fraction increased. The films that were cast at high methanol contents were superhydrophobic, possessing water contact angles of ∼160° and water sliding angles of ∼3°