Nanostructure Dependent Surface Energy of Silica Nanorod Arrays through Block Copolymer Templating Processes
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Nanostructure Dependent Surface Energy of Silica Nanorod Arrays through Block Copolymer Templating Processes Yongbin Zhao, Aihua Chen, Tomokazu Iyoda* Division of Integrated Molecular Engineering, Chemical Resources Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan. ABSTRACT The self-assembled block copolymer films with poly (ethylene oxide) (PEO) and hydrophobic polymetharylate (PMA) with azobenzene mesogen in the side chain, denoted as PEOm-b-PMA(Az)n, were used as the template to prepare hexagonally ordered silica nanorod arrays by immersing the template films in the silicate precursor containing tetraetoxysilane (TEOS). The diameter and the center-to-center distance of the SiO2 nanorod arrays were controlled by selecting the block copolymer with different PEO volume fraction.In addition, the contact angles of different kinds’ solvents for the SiO2 nanorod arrays were characterized. We further found, the diameter and the period distance of silica nanorods are very important factors for controlling the contact angle of different kind’s solvents on the surface of the SiO2 nanorod arrays. INTRODUCTION Self-organization,as a powerful route to the ‘bottom-up’ fabrication of nanostructures for use in optical, optoelectronic, and magnetic storage devices,has been attracted in the world[1-2]. Recently, the self-assembly of block-copolymeric system into aligned, highly ordered arrays that cover the range between approximately 10 and 100nm, makes them ideal candidates as template and scaffolds for the fabrication of nanostructured materials. For example, by using perpendicular PS-b-PMMA cylinder nanopatterns as template, the ferromagnetic Co nanowires with high-density vertical arrays has been fabricated through subsequent direct current electrodeposition[4]. In addition, using the similar process, it also has been demonstrated the replication of nanoscale feature into a variety of materials [5-6], including the formation of metal nanorods, nanoporous metal films, nanoelectrode arrays, etc. Recently, our group has developed a new series of amphiphilic liquid crystalline diblock copolymers consisting of poly(ethylene oxide) (PEO) and poly(methacrylate) bearing an azobenzene mesogen in the side chain as template to prepare high ordered nanoarrays, such as Ag nanodot arrays on the flexible and rigid substrated[7], mesoporous silica nanorods arrays with tunable aspect ratios[8], etc. In this work, the self-assembled block copolymer, denoted as PEOm-b-PMA(Az)n films with normal PEO cylindrical domains was used as the template to prepare hexagonally ordered silica nanorod array by immersing the template films in the silicate precursor containing tetraetoxysilane (TEOS). The diameter and the center-to-center distance of the SiO2 nanorod
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arrays were further controlled by selecting the block copolymer thin films with different PEO volume fraction.In addition, the contact angles of different kinds’ solvents for the SiO2 nanorod arrays were characterized. We found, the diameter and the period di
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