Estudo sobre a Influência da topografia na transição dos estados de molhabilidade de filmes finos nanoestruturados

Abstract

In the last years, wetting has receive increasing attention due to the superhydropho- bic properties of surfaces that leds to anticorrosive, anticontamination and selfcleaning behaviors.This work reports the study of wetting states transition through functionalized surfaces of metallic oxides with tailored roughness. Were performed sol-gel synthesis for three different oxides (silica, alumina and titania), thin films deposition on glass, using the dip-coating method, etching texturing, in order to obtain tailored nanostructures and surfaces functionalization with different surfactants to ensure low surface energy, aiming super-hydrophobicity. Alumina was texturized in boiling water, fluoridric acid was used for the titania and sodium carbonate was used for the silica, with etching times of t = 2 n in order to obtain tailored structures. The topography of the samples were characterized by scanning electron microscopy, White light interferometry and atomic force microscopy. The chemical properties were characterized by X-ray photoelectron spectroscopy. The wetting properties were characterized by sessil drop analises through the contact angle measurement. The desired structures were observed in the alumina samples, as well as superhydrophobicity, considering the static criteria. The silica etched with sodium car- bonate was not enough to provide high water repellency and for titania was obtained promising surface structures, but without the desired wettability. With this study it was proved the theoretical approach of the Wenzel roughness parameter as a function of the declivity, since experimental data fit the curve for the gaussian height distribution sur- faces. It was possible to observe the deviation of the experimental data of the measured contact angle in relation to the Wenzel model, keeping the chemical behavior constant, for the hydrophobic and the hydrophilic cases. This indicates the transition of the wetting states for the hydrophobic case and the usefulless of the Wenzel model for the hydrophilic case. Due to the monotonic relation between the Wenzel roughness parameter and the rms declivity, it was possible to set a declivity range responsable for rise up the water among the urface structures as consequence of capillarity forces.