22G05
Chemical Kinetic Simulation in Aqueous Solution for Plasma-Induced
Chemical Processing
プラズマ誘起液中化学プロセスにおける液中化学反応シミュレーション
Naofumi Ohnishi1 , Katsuhisa Kitano2 , Satoshi Ikawa3 , and Atsushi Tani4
大西直文, 北野勝久, 井川聡, 谷篤史
1

Department of Aerospace Engineering, Tohoku University
6-6-01 Aramaki-Aza-Aoba, Aoba-ku, Sendai 980-8579, Japan
2
Center for Atomic and Molecular Technologies, Osaka University
3
Technology Research Institute of Osaka Prefecture
4
Department of Earth and Space Science, Osaka University
1
東北大学大学院工学研究科航空宇宙工学専攻 〒 980-8579 仙台市青葉区荒巻字青葉 6-6-012
大阪大学大学院工学研究科原子分子イオン制御理工学センター
3
大阪府立産業技術総合研究所
4
大阪大学大学院理学研究科宇宙地球科学専攻

Chemical kinetic simulations for more than twenty chemical species inside aqueous solution incontact with plasma source were performed with simple diﬀusion process to examine anomalous
penetration of bactericidal radicals observed in past experiments. Penetration lengths of the radicals are signiﬁcantly limited to sub-mm or less due to their theoretical short lifetimes while amm-order penetration was suggested by the experiments. Some eﬀects by external electric ﬁeld,
such as electrophoresis or electro-osmosis ﬂow, should be considered in the assessment of theanomalous penetration because source of ions and radicals is a plasma jet in the atmospheric air
attached with the solution, which can supply a large potential ﬂuctuation in the realistic situation.
1.

Introduction

such deep solution.
In the present work, we have numerically modeleda system of chemical kinetics in aqueous solution withsome other physical processes in order to estimate apenetration depth of the radicals and clarify important chemical species or exposure conditions for the
anomalous penetration.

Low-temperature plasmas in an atmospheric air have apossibility of new medical technology with less physical stress for a livig body and have vigorously been investigated by many authors to develop an application
for soft-materials[1]. In particular, a low-frequency(LF) plasma jet proposed by Kitano et al.[2] is expected to be widely used for plasma process in aque2. Numerical Modelingous solutions from nano-particle synthesis[3] to medical application in a wet-condition because the plasma As a ﬁrst step of our computational work, we have
jet is formed in a quite low temperature and then does developed a chemical kinetic code with 25 chemical
not heat nor break the irradiated materials while its species and selected 66 reactions. A linear diﬀusion
chemical reactivity is high enough[4].
process with species-depended but constant diﬀusion
In their in-vitro experiments, E. coli in low pH- coeﬃcients was installed in the code for a simplicity.
controlled solution was drastically inactivated by a ir- The system of stiﬀ diﬀerential equations is solved byradiated plasma jet in a short duration less than one the well-known matrix solver, LSODE which was deminute[5]. This reduced pH method has been applied veloped and distributed by Lawrence Livermore Nato dental therapy[6]. After the careful assessment based tional Laboratory[8]. Simulations were conducted withon an acid dissociation constant (pKa = 4.7), they con- several boundary conditions of the input ﬂux of thecluded that superoxide (O•−2 ) and its conjugate acid, chemical species, which mimic the conditions of thehydroperoxide radical (HOO• ) should play an impor- interface between the air and the solution as the ﬁnaltant role to inactivate[7] and penetrate the container of reactants are reasonably created at the end of the simthe solution whose depth is 10 mm in the exposure du- ulations.
ration though their lifetimes are too short to survive in3.

Result and Discussion

Unfortunately, the key radicals (e.g., HOO• ) for inactivation hardly penetrate in the order of mm while
the sub-mm penetration is found in a speciﬁc condition. Some eﬀects by an external electric ﬁeld, such as
electrophoresis or electro-osmosis ﬂow, should be installed in the assessment of the anomalous penetration
because source of ions and radicals is the plasma jet in
the atmospheric air attached with the solution, which
can supply a large potential ﬂuctuation in the realisticsituation. So we are upgrading our code with electric
mobility of the species in the solution to include theeﬀects of the ﬂuctuating external electric ﬁeld.
References[1] 北野勝久, 浜口智志, 現代化学, 東京化学同人, 7月号, pp. 25–31 (2009).
[2] 北野勝久, 浜口智志, 応用物理学会誌, 4 月号 (2008); 北野勝久, 浜口智志, 日本国特許第4408957 号.
[3] H. Furusho, K. Kitano, S. Hamaguchi, and Y. Nagasaki, Chem. Mater., 21, pp. 3526–3535 (2009).
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[6] H. Yamazaki, Dental Mat. Journal, 30, p. 384(2011).
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43, p. 95 (2002).
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