Title: Reversible wettability of hybrid organic/inorganic surfaces of systems upon light irradiation/storage cycles

Authors: Athanassia Athanassiou, Roberto Cingolani, Gianvito Caputo, Barbara Cortese, Giuseppe Gigli, Concetta Nobile, P. Davide Cozzoli

Addresses: NNL – National Nanotechnology Laboratory of CNR-INFM, Via per Arnesano, 73100 Lecce, Italy; IIT – Italian Institute of Technology, Via Morego 30, 16152 Genova, Italy. ' NNL – National Nanotechnology Laboratory of CNR-INFM, Via per Arnesano, 73100 Lecce, Italy; IIT – Italian Institute of Technology, Via Morego 30, 16152 Genova, Italy. ' NNL – National Nanotechnology Laboratory of CNR-INFM, Via per Arnesano, 73100 Lecce, Italy. ' NNL – National Nanotechnology Laboratory of CNR-INFM, Via per Arnesano, 73100 Lecce, Italy. ' NNL – National Nanotechnology Laboratory of CNR-INFM, Via per Arnesano, 73100 Lecce, Italy. ' NNL – National Nanotechnology Laboratory of CNR-INFM, Via per Arnesano, 73100 Lecce, Italy. ' NNL – National Nanotechnology Laboratory of CNR-INFM, Via per Arnesano, 73100 Lecce, Italy; Scuola Superiore ISUFI, Universita del Salento, Distretto Tecnologico ISUFI, Via per Arnesano, 73100 Lecce, Italy

Abstract: In this work we present hybrid organic/inorganic structures that can exhibit reversible surface wettability, altered in a controllable manner. In particular, we use the method of photo-patterning to produce polymeric SU-8 pillars of specific geometries, onto which we subsequently deposit colloidal TiO₂ nanorods. In this way, we combine the microroughness of the polymeric pillars with the nanoroughness of the nanorod-coating to create highly hydrophobic surfaces. The hydrophobicity of these systems can be changed reversibly into hydrophilicity upon irradiation of the hybrid structures with pulsed UV laser light. This behaviour is due to the well-known property of TiO₂, that becomes superhydrophilic upon UV light irradiation. This property is reversible and we monitor the recovery of our hybrid polymeric/inorganic-nanorods structures to their initial hydrophobic character upon dark storage and heating. The wetting behaviour has been modelled and analysed according to the surface geometry. The direct implementation of such structures into microfluidics devices is demonstrated.

Keywords: reversible wettability; hydrophobicity; hydrophilicity; TiO2 nanorods; SU-8 polymer; photopatterning; UV laser light; titanium dioxide; nanotechnology; microroughness; nanoroughness; microfluidic devices; microfluidics; surface wettability.

DOI: 10.1504/IJNM.2010.034793

International Journal of Nanomanufacturing, 2010 Vol.6 No.1/2/3/4, pp.312 - 323

Published online: 22 Aug 2010 *

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