Crystalline Titania Nanoplatelet Templated by Block Copolymer of PMMA-b-PEO and its Photophysical Properties
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Crystalline Titania Nanoplatelet Templated by Block Copolymer of PMMA-b-PEO and its Photophysical Properties Yajun Cheng1, Mine Memesa1, Sebastian Nett1, and Jochen Stefan Gutmann1,2 1 Max-Planck Insitute for Polymer Research, Ackermannweg 10, Mainz, 55128, Germany 2 Inst. of. Physical Chemistry, University of Mainz, Welderweg 11, Mainz, 55099, Germany
ABSTRACT A Titanium dioxide ultrathin film composed of nanoplatelet structures was prepared and characterized with AFM, SEM, and GISAXS measurement, whose photophysical properties are also studied. INTRODUCTION The last decade has seen a rapid growing interests in the studies about functional titania nanostructured thin films due to their rich intriguing physical properties and versatile applications in photovoltacis, photocatalyst, gas sensing, and Li ion batteries.1-4 The performance of the titania materials, is significantly dependent on the morphology and crystallinity of the Titania nanostrucures.5 Crystallinity is relatively easy to be controlled. For example, the anatase phase can be formed via calcination above 400°C for a certain time.6, 7 However, the precise control over the film morphology still remains a big challenge for materials scientists. One of the most important and promising recipes to solve this problem is to use organic block copolymer as a templating agent in combination with sol-gel chemistry.6-10 In this communication, we use an amphilic block copolymer of PMMA-b-PEO as a template, whose templating properties have been rarely studied, combined with a new recipe of good-poor-solvent-pair induced phase separation, which is promoted by our group. Film composed of an interesting crystalline anatase TiO2 nanoplatelet morphology has been achieved, which has not been seen reported before in this templating system. Besides the local structures studied by AFM and SEM, the lateral strcutre over large length scale is also studied by Grazing Incidence Small Angle X-ray Scattering (GISAXS). The photoluminescence spectroscopy is conducted to study the photophysical properties of the nanoplatelete structured film. EXPERIMENT An asymmetric diblock copolymer of poly (methylmethacrylate) and poly (ethylene oxide) (PMMA-b-PEO) was synthesized in the Max-Planck Institute for Polymer Research in Mainz via ATRP. The number average molecular weight is 57.7k for PMMA and 17.88k for PEO respectively and the polydispersity index for the whole block copolymer is 1.22. Titanium tetra-isopropoxide (TTIP, 97%) was purchased from Aldrich. 1,4-dioxane of analytical reagent grade was obtained from Fisher Scientific and concentrated HCl (Puriss, p.a.) (min. 37%) was purchased from Riedel-de Haën.
Sample solution of the nanoplatelet was prepared according to the following procedure: 0.0414g PMMA-b-PEO and 4.0247g 1.4-dioxane were mixed together, followed by the addition of 0.1032g 37% concentrated HCl solution and 0.4812g TTIP within 4 minutes. After complete addition the common solution was stirred for one hour. Sample solution with the transition morphology
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