In situ determination of the water condensation mechanisms on superhydrophobic and superhydrophilic titanium dioxide nanotubes
Macias-Montero, Manuel (Instituo de Ciencias de los Materiales de Sevilla)
Lopez-Santos, Carmen (Instituo de Ciencias de los Materiales de Sevilla)
Filippin, A. Nicolas (Instituo de Ciencias de los Materiales de Sevilla)
Rico, Victor J. (Instituo de Ciencias de los Materiales de Sevilla)
Espinos, Juan Pedro (Instituo de Ciencias de los Materiales de Sevilla)
Fraxedas, Jordi (Institut Català de Nanociència i Nanotecnologia)
Pérez-Dieste, Virginia (ALBA Laboratori de Llum de Sincrotró)
Escudero, Carlos (ALBA Laboratori de Llum de Sincrotró)
Gonzalez-Elipe, Agustín (Instituo de Ciencias de los Materiales de Sevilla)
Borras, Ana (Instituo de Ciencias de los Materiales de Sevilla)

Data:	2017
Resum:	One-dimensional (1D) nanostructured surfaces based on high-density arrays of nanowires and nanotubes of photoactive titanium dioxide (TiO) present a tunable wetting behavior from superhydrophobic to superhydrophilic states. These situations are depicted in a reversible way by simply irradiating with ultraviolet light (superhydrophobic to superhydrophilic) and storage in dark. In this article, we combine in situ environmental scanning electron microscopy (ESEM) and near ambient pressure photoemission analysis (NAPP) to understand this transition. These experiments reveal complementary information at microscopic and atomic level reflecting the surface wettability and chemical state modifications experienced by these 1D surfaces upon irradiation. We pay special attention to the role of the water condensation mechanisms and try to elucidate the relationship between apparent water contact angles of sessile drops under ambient conditions at the macroscale with the formation of droplets by water condensation at low temperature and increasing humidity on the nanotubes' surfaces. Thus, for the as-grown nanotubes, we reveal a metastable and superhydrophobic Cassie state for sessile drops that tunes toward water dropwise condensation at the microscale compatible with a partial hydrophobic Wenzel state. For the UV-irradiated surfaces, a filmwise wetting behavior is observed for both condensed water and sessile droplets. NAPP analyses show a hydroxyl accumulation on the as-grown nanotubes surfaces during the exposure to water condensation conditions, whereas the water filmwise condensation on a previously hydroxyl enriched surface is proved for the superhydrophilic counterpart.
Ajuts:	Ministerio de Economía y Competitividad MAT2013-40852-R Ministerio de Economía y Competitividad MAT2013-42900-P Ministerio de Economía y Competitividad MAT2016-79866-R Ministerio de Economía y Competitividad 201560E055
Drets:	Tots els drets reservats.
Llengua:	Anglès
Document:	Article ; recerca ; Versió acceptada per publicar
Matèria:	Dropwise condensation ; Environmental scanning electron microscopies (ESEM) ; Filmwise condensation ; Nanostructured surface ; Photoemission analysis ; Titanium dioxide nanotubes ; Titanium dioxides (TiO2) ; Water contact angle
Publicat a:	Langmuir, Vol. 33, issue 26 (July 2017) , p. 6449-6456, ISSN 1520-5827

DOI: 10.1021/acs.langmuir.7b00156

Postprint 25 p, 1.3 MB

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