Conductive Behavior of High TiO 2 Nanoparticle Content of Inorganic/Organic Nanostructured Composites Junkal Gutierrez, Agnieszka Tercjak,* and In ˜ aki Mondragon* “Materials + Technologies” Group, Departamento de Ingenierı ´a Quı ´mica y Medio Ambiente, Escuela Politecnica, UniVersidad Pais Vasco/Euskal Herriko Unibertsitatea, Pza. Europa 1, 20018 Donostia-San Sebastian, Spain Received October 1, 2009; E-mail: agnieszka.tercjaks@ehu.es; inaki.mondragon@ehu.es Abstract: Amphiphilic polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymers with different block ratios were used as templates for the incorporation of a high content of titanium dioxide nanoparticles using the sol-gel method. Confinement of the inorganic part in the PEO block of the block copolymer allows the generation of nanostructured systems with a high nanoparticle content. As successfully demonstrated using tunneling atomic force microscopy, the investigated systems maintained the conductive properties of the TiO 2 nanoparticles. The obtained results confirmed that with increasing TiO 2 nanoparticle content, the local current value increased up to 15 pA, and this conductivity value strongly depended on the amount of the PEO block in the block copolymer template. Moreover, the results indicated that control of the ratio between the sol-gel and the PEO block allows the design of well-dispersed, conductive inorganic/ organic hybrids with high inorganic content. These materials can provide attractive strategies in the field of dye-sensitized solar cells. Introduction At the present time, block-copolymer-based materials have attracted much attention in view of their potential applications, since the self-assembly capacity of this kind of material with nanoscale periodicity allows the creation of nanopatterned materials. 1-4 Several studies have reported the use of block copolymers as templates for the synthesis of nanostructured materials because of their ability to control both the size and the spatial organization by varying their composition and molecular weight. 5,6 On the other hand, nanostructures of semiconductors and metals have been extensively studied in recent years because of their unique magnetic, optical, electrical, and catalytic properties and their potential applications in the field of nanotechnology. 7-10 It is well-known that the properties of such nanostructured materials depend strongly on the size, shape, and composition. 11,12 In particular, titanium dioxide nanoparticles have received considerable interest because of their large surface areas and wide application in the fields of dye-sensitized solar cells (DSSC) 13-17 and electric and photocatalytic systems. 18,19 Extensive work involving methods for obtaining metal nano- particles selectively incorporated within one of the micro- domains of block copolymers has been reported. 7,8,20 The sol-gel method is a simple fabrication protocol for synthesizing nanoparticles with well-defined sizes. However, all of the parameters must be strictly controlled, since a small change in one of the parameters, such as temperature, reaction time, or concentration, can significantly influence the results. 21 In this study, the sol-gel method has been used for the synthesis of inorganic/organic nanostructured composites based on titanium dioxide nanoparticles. Two different molecular weight poly- styrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymers have been used as templating agents. These amphiphilic block copolymers allow the synthesis to be performed without using any type of surfactant since the generated sol-gel solution (1) Hamley, I. W. Prog. Polym. Sci. 2009, in press. (2) Li, M.; Ober, C. K. Mater. Today 2006, 9, 30–39. (3) Olson, D. A.; Chen, L.; Hillmyer, M. A. Chem. Mater. 2008, 20, 869– 890. (4) Darling, S. B. Surf. Sci. 2007, 601, 2555–2561. (5) Grosso, D.; Cagnool, F.; Soler-Illia, G. J. D. A.; Crepaldi, E. L.; Amenitsch, H.; Bruneau, A.; Bourgeois, A.; Sanchez, C. 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