Controlled Swapping of Nanocomposite Surface Wettability by Multilayer Photopolymerization

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Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, via Barsanti, Arnesano, 73100 Lecce, Italy
National Nanotechnology Laboratory (NNL), CNR - Istituto Nanoscienze, via per Arnesano, 73100 Lecce, Italy
Istituto Italiano di Tecnologia (IIT), via Morego 30, 16163 Genova, Italy
Dipartimento di Ingegneria dell’Innovazione, Università del Salento, via per Arnesano, 73100 Lecce, Italy
E-mail: [email protected] (F.V.-M.); [email protected] (A.A.).
Cite this: Langmuir 2011, 27, 13, 8522–8529
Publication Date (Web):June 3, 2011
Copyright © 2011 American Chemical Society
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Single-layered photopolymerized nanocomposite films of polystyrene and TiO2 nanorods change their wetting characteristics from hydrophobic to hydrophilic when deposited on substrates with decreasing hydrophilicity. Interestingly, the addition of a second photopolymerized layer causes a swapping in the wettability, so that the final samples result converted from hydrophobic to hydrophilic or vice versa. The wettability characteristics continue to be swapped as the number of photopolymerized layers increases. In fact, odd-layered samples show the same wetting behavior as single-layered ones, while even-layered samples have the same surface characteristics as double-layered ones. Analytical surface studies demonstrate that all samples, independently of the number of layers, have similar low roughness, and that the wettability swap is due to the different concentration of the nanocomposites constituents on the samples surface. Particularly, the different interactions between the hydrophilic TiO2 nanorods and the underlying layer lead to different amounts of nanorods exposed on the nanocomposites surface. Moreover, due to the unique property of TiO2 to reversibly increase its wettability upon UV irradiation and subsequent storage, the wetting characteristics of the multilayered nanocomposites can be tuned in a reversible manner. In this way, a combination of substrate, number of photopolymerized layers, and external UV light stimulus can be used in order to precisely control the surface wettability properties of nanocomposite films, opening the way to a vast number of potential applications in microfluidics, protein assays, and cell growth.

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Figure S1, showing a TEM image of the ST/PI/TiO2 solution before photopolymerization; Figures S2 and S3, showing FT-IR spectra of photopolymerized and as-received PS/TiO2 NRs samples, respectively; Figure S4, showing a schematic representation of the light measurements; Figure S5, showing a simple model of the photopolymerization process; Figure S6, showing the WCA values of sextuple- and septuple-layered samples, both on glass and silicon substrate; and Figure S7, showing AFM images of sextuple- and septuple-layered samples on glass and silicon substrates. This material is available free of charge via the Internet at

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