title: Wetting studies of hydrophilic-hydrophobic TiO2@SiO2 nanopatterns prepared by photocatalytic decomposition.
abstract: TiO(2)@SiO(2) nanopatterns were prepared with the evaporation-induced self-assembly (EISA) technique. The material consists of an ultrathin (approximately 2 nm) layer of titania with hexagonally ordered craters of roughly 30 nm in diameter, on a silica substrate. The open pore structure and high homogeneity of the pattern makes these materials ideal for detailed wetting studies. The nanopatterns were functionalized with a fluoroalkylsilane (FAS), which attached on both titania and silica, resulting in a hydrophobic surface. By irradiating the composite material with UV light for different lengths of time, the hydrophilic/hydrophobic contrast in the nanopattern could be tuned. This is a result of the very different photocatalytic properties of titania and silica. The area fraction covered with FAS, f(FAS), as a function of UV irradiation time was calculated from water contact angle measurements of the composite film and corresponding reference samples, by using existing wetting models for heterogeneous surfaces. The results were compared to area fractions derived from X-ray photoelectron spectroscopy (XPS). f(FAS)-values determined from static water contact angles gave the best agreement with XPS, while advancing and receding contact angles overestimated and underestimated the f(FAS)-values, respectively. The Cassie model gave a slightly better fit to the XPS data than the Israelachivili model.
authors.affiliation: Center for Functional Materials, Laboratory of Physical Chemistry, Department of Natural Sciences, Abo Akademi University, Porthansgatan 3-5, FI-20500 Finland.
authors.forename: Mikael
authors.initials: M
authors.lastname: Järn
authors.forename: Qian
authors.initials: Q
authors.lastname: Xu
authors.forename: Mika
authors.initials: M
authors.lastname: Lindén