Seed Assisted Phase Control of TiOPc: Application of Microfluidic Mixing
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Seed assisted phase control of TiOPc: Application of microfluidic mixing Enkhtuvshin Dorjpalam1, Hiroyuki Nakamura1, Kenichi Yamashita1, Masato Uehara1, and Hideaki Maeda1,2,3 1
Micro-&Nano Space Chemistry Group, Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) , Tosu, Saga, Japan. 2 Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga ,Fukuoka, Japan 3 CREST, Japan Science and Technology Agency, Hon-cho, Kawaguchi, Japan
Abstract Microfluidic mixing was applied to conventional acid pasting process to re-crystallize organic nanocrystals of Titanyl phthalocyanine (TiOPc). TiOPc nanocrystals were re-crystallized in a two step process. Seed particles were prepared by mixing TiOPc, dissolved in concentrated sulfuric acid with deionized water using high speed microchannel mixers. Seed particles were then subjected to post-precipitation treatment to achieve final crystalline product. Effects of seed preparation conditions, such as mixing efficiency (mixer type) and mixing temperature on the structure of final product were studied. Time evolution of optical absorption spectra was examined with a view to elucidate structure evolution during early stages of seed formation process. Introduction Recently, photo- and electroactive organic materials have received much research attention [1-3]. In order to realize efficient organic optoelectronic material a precise control over its crystalline structure is essential. In contrast to inorganic materials, which is built of covalent or ionic bonds evenly distributed over the entire structure, organic materials are composed of individual molecules bound together with a weak intermolecular force. Due to this reason, crystal structure tuning of organic materials is very delicate process. In most cases, previously prepared seed material is treated with a various solvents [4-7] to optimize the crystalline structure by means of adjusting the surface energy. In case of this process, reproducibility is most commonly experienced problem. In the present study, we tried to trace effects of seed structure on the structure of final product. The target material is TiOPc, Y-phase of which is recognized as an efficient photoreceptor material [8-9]. Due to the lack of suitable ‘good’ solvent, solution based preparation techniques except for acid-paste process are not practical for the production of TiOPc. In acid pasting, concentrated sulfuric acid and deionized water are used as the ‘good’ and ‘poor’ solvents, respectively. The excessive heat released during initial mixing and the large difference in viscosity of sulfuric acid and water (26.7cP vs. 1.0cP at 20°C) cause inevitable polydispersity from the very beginning of particle nucleation, resulting in non-uniform crystallization. Thus, it is difficult to control the acid pasting process both thermodynamically and kinetically. With a view to overcome this problem, we have adopted microfluidic mixing for seed preparation. Compared to a conventio
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