Microphase-separated block copolymer film anchored on ITO substrate with newly designed self-assembled monolayer
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Microphase-separated block copolymer film anchored on ITO substrate with newly designed self-assembled monolayer Takenori Goda1, 2, Shingo Hadano2 and Tomokazu Iyoda2* 1
TOPPAN PRINTING CO., LTD. 4-2-3 Takanodaiminami, Sugito-machi, Saitama 345-8508, Japan 2 Chemical Resources Laboratory, Tokyo Institute of Technology, R1-25 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503, Japan ABSTRACT The surface of Indium-tin-oxide (ITO) substrate was modified with a newly designed silane coupling molecule bearing azobenzene moiety. The silane coupling molecules formed self-assembled monolayer (SAM) on pretreated ITO surface. The SAM growth and coverage were quantified by contact angle measurement and X-ray photoelectron spectroscopy (XPS). The silane coupling molecules improved the adhesion between the ITO surface and an amphiphilic block copolymer (BC) thin film, which consists of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) with azobenzene mesogens, because the azobenzene moieties of the SAM anchor the liquid crystalline PMA azobenzene domains of BC. INTRODUCTION The functionalization of the surface of indium-tin-oxide (ITO) using self-assembled monolayer (SAM) has been studied due to the potential applications in linking molecular-level structures to macroscopic interfacial effect such as wetting, adhesion and friction. [1] Most of researches for SAM have been interested in alkyl-silanes and alkyl phosphonic acid, with which can be modified on hydroxyl-terminated surface. [2] [3] However, the SAM structure should be optimized to the molecular structure of attached surface for effective interactions with the interface. Herein, we report the newly designed silane-coupling molecule which was optimized to increase the adhesion between substrate and functional thin films. We have developed highly ordered microphase separation with hydrophilic polyethylene oxide (PEO) cylindrical nanodomains perpendicularly oriented to thin films of a series of amphiphilic liquid crystalline block copolymer consisting of PEO and hydrophobic polymethacrylate bearing azobenzene mesogen (PMA(Az)) in side-chain. [4] This block copolymer thin film has been applied as a highly ordered template to fabricate high density nanodot arrays by dip-doping, or nanorod arrays by wet-etching. [5] [6] [7] In this report, a silane-coupling molecule which structure is identical to the azobenzene-containing side chain of the block copolymer so as to anchor the liquid crystalline PMA(Az) domains of block copolymer template was synthesized . The effect of SAM for adhesion between ITO surface and the template was observed by demonstrating a peeling test. EXPERIMENTAL SECTION Materials
11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate(Azo-MA) was obtained from Kanto Chem. Co. (Japan) and purified by recrystallizaion. 3-triethoxysilylpropyl isocyanate was obtained from Tokyo Chemical Industry Co., Ltd., Japan and used without further purification. All other solvents and reagents were analytical grade quality.
Figure 1. Synthetic scheme of {11-[
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