Fast and reversible photo-responsive wettability on TiO 2 based hybrid surfaces (original) (raw)
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International Journal of Nanomanufacturing, 2010
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 TiO 2 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 TiO 2 , 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.
Reversible wettability control of TiO2 surface by light irradiation
Surface Science, 2002
Titanium dioxide (TiO 2 ) thin films with various surface morphologies were prepared on the substrates of (1 0 0) plane of strontium titanate by a metalorganic chemical vapor deposition process. These TiO 2 thin films became highly hydrophilic by ultraviolet (UV) irradiation, and returned to the initial relatively hydrophobic state by visible-light (VIS) irradiation. The hydrophobic-hydrophilic conversion induced by UV irradiation, is due to the increase in dissociated water adsorption on the film surface. In contrast, the conversion from hydrophilic to hydrophobic by VIS irradiation is caused by the elimination of water adsorbed on the surface due to the heat generated. Changes of water contact angle between hydrophilic states and hydrophobic ones strongly depended on the roughness of the film surface. The wettability of the TiO 2 surface was enabled to convert between hydrophilic and hydrophobic reversibly by alternative UV and VIS irradiation. Ó 2002 Published by Elsevier Science B.V.
Surface chemical analysis of photocatalytic wettability conversion of TiO2 nanoparticle coating
Surface and Coatings Technology, 2012
Surface chemical analysis of photocatalytic wettability conversion of the TiO 2 nanoparticle coating is performed by the water contact angle measurement and X-ray photoelectron spectroscopy (XPS). It is observed that the UVA irradiation and heat treatment strongly affect on the water contact angle. Initially superhydrophobic TiO 2 nanoparticle coated paperboard surfaces can undergo several transition loops between hydrophobic and hydrophilic states: the surface hydrophilicity can be induced by ultraviolet A (UVA) radiation whereas high temperature oven treatment results in superhydrophobic surface. The XPS spectra shows that UVA irradiation induces photocatalytic oxidation of the TiO 2 nanocoated surface whereas the oven treatment decreases the amount of oxygen related to the hydroxyl groups. The wettability changes are related to the degree of hydroxyl groups or aliphatic chains present on the TiO 2 surface.
Controlling wettability by light: illuminating the molecular mechanism
European Physical Journal E, 2003
The functionalisation of a surface with an organic monolayer containing photoactive moieties such as the azobenzene chromophore opens an elegant route for controlling its wettability by light. In this paper we investigate the microscopic origin of the macroscopic change in wettability upon photoinduced cis-trans isomerization of a copolymeric diphenyl-diazene Langmuir-Blodgett monolayer. Polarised UV-Vis and FTIR spectroscopy have been used to monitor the orientational order of various functional groups, Atomic Force Microscopy and Imaging Ellipsometry is employed for the quantification of the surface roughness and morphology, contact angle and surface potential measurements are carried out for a characterisation of the polar ordering. The data analysis is further supported by semi-empirical and ab-initio calculations of the molecular dipole moments and the normal IR-modes of the fluorinated chromophore. The combination of all these techniques provides a detailed molecular picture. The data suggest that changes in the projection of the dipole moment onto the surface normal caused by isomerization of the azobenzene are responsible for the observed changes in the surface energy. This knowledge allowed us to predict guidelines for the synthesis of molecules in order to maximize the wetting contrast upon photo-irradiation.
Molecular design of photoswitchable surfaces with controllable wettability
Journal of Materials …, 2011
In this work, we developed a photocontrollable substrate which was prepared using an azobenzenecontaining self-assembled monolayer (SAM) on the silicon surface via the chemisorption of 3glycidoxypropyltrimethoxysilane (GPTS) and 4-(4 0 -aminophenylazo) benzoic acid (APABA). The prepared surfaces were chemically characterized by X-ray photoelectron spectroscopy (XPS). The reversible photoswitching performance of APABA molecules were investigated by UV spectroscopy in dimethylsulfoxide (DMSO) solution. To understand and control this reversible photoswitchable mechanism and wettability properties, contact angle measurements were performed by using a variety of liquids after UV and visible light irradiation. These contact angle results are used to approximate the components of the APABA-modified surface energy under UV and visible light using the Lifshitz-van der Waals/acid-base approach. The total surface energy (g s ) after visible light irradiation (for trans formation) was calculated to be 37.28 mJ m À2 , whereas the value after UV light exposure (for cis formation) was also calculated to be 36.95 mJ m À2 . All the results demonstrate the great potential to control molecular events within and on the surfaces of molecular constructs using light.
ATOMIC LAYER DEPOSITION OF TIO2 FOR REVERSIBLY SWITCHABLE HYDROPHOBIC/HYDROPHILIC SURFACES
Control of surface wetting properties is of interest in many different applications ranging from microfluidics, biomicroarrays, printing, green energy technologies to self-cleaning surfaces. We propose to program surfaces with full wetting re-versibility by micro-nano patterning of titanium dioxide (TiO2) thin films. Our TiO2 is deposited by Atomic Layer Deposition (ALD). We study the effects of surface preparation, film thickness, deposi-tion temperature and micro and nanopatterns on UV photoswitchability and recovery. We show superhy-drophilic (SHL) to hydrophobic (HB) reversible transitions by UV exposure and dark storage. With fixed TiO2 thickness, temperature variation in ALD film quality has been investigated by water contact angle (CA) measurements. We conform to control the TiO2 thin films switchability by controlling the ALD effective factors.