Switchable Wettability in SnO2 Nanowires and SnO2@SnO2 Heterostructures (vol 115, pg 22225, 2011)

Tin oxide nanowires and heterostructures thereof were synthesized by sequential aplication of thermal and plasma-assisted chemical vapor deposition (CVD) methods. The wetting properties of surfaces based on individual nanowires, hyperbranched SnO2@SnO2 structures, and SnO2@SnO2@SiOx core-shell heterostructures could be modulated from superhydrophilic to superhydrophobic by changing both chemical composition and the geometrical architecture of nanoheterostructures. Whereas the randomly grown SnO2 nanowires with a contact angle of 3 degrees exhibited superhydrophilicity, the contact angle of SnO2@SnO2 heterostructures synthesized by a two-step CVD process increased to 133 degrees. The corresponding contact angle of SnO2@SnO2@SiOx heterostructures was enhanced to 155.8 degrees by a hydrophobic SiOx coating. Switchable surface wettability in SnO2@SnO2@SiOx heterostructures was observed by alternation of UV irradiation, storage in dark, and O-2 annealing, indicating that geometric microstructure was the major determinant in the switchable wettability. The significant change in the surface wettability upon changing the geometrical features is of potential interest in functional coatings such as antifinger print and self-cleaning surfaces.