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論文

Hierarchical aggregation in a complex fluid; The Role of isomeric interconversion

Massey, D.*; Williams, C. D.*; Mu, J.*; Masters, A. J.*; 元川 竜平; 青柳 登; 上田 祐生; Antonio, M. R.*

Journal of Physical Chemistry B, 127(9), p.2052 - 2065, 2023/03

 被引用回数:0 パーセンタイル:0(Chemistry, Physical)

There is an ever-increasing body of evidence that metallic complexes, involving amphiphilic ligands, do not form normal solutions in organic solvents. Instead, they form complex fluids with intricate structures. For example, the metallic complexes may aggregate into clusters and these clusters themselves may aggregate into super-clusters. In order to gain a deeper insight into the mechanisms at play, we have used an improved force field to conduct extensive molecular dynamics simulations of a system composed of zirconium nitrate, water, nitric acid, tri-$$n$$-butyl phosphate and $$n$$-octane. The important new finding is that a dynamic equilibrium between the cis and trans isomers of the metal complex is likely to play a key role in the aggregation behavior. The isolated cis and trans isomers have similar energies but simulation indicates that the clusters consist predominantly of cis isomers. With increasing metal concentration, we hypothesize that more clustering occurs and the chemical equilibrium shifts towards the cis isomer. It is possible that such isomeric effects play a role in the liquid-liquid extraction of other species and the inclusion of such effects in flowsheet modelling may lead to a better description of the process.

論文

A Telescoping view of solute architectures in a complex fluid system

元川 竜平; 小林 徹; 遠藤 仁; Mu, J.*; Williams, C. D.*; Masters, A. J.*; Antonio, M. R.*; Heller, W. T.*; 長尾 道弘*

ACS Central Science, 5(1), p.85 - 96, 2019/01

 被引用回数:43 パーセンタイル:86.39(Chemistry, Multidisciplinary)

We present a hierarchical aggregate model of an organic phase containing a coordination species that acts as a fundamental building unit of higher-order structures formed in the organic phase. We aimed to elucidate the fundamental aspects of the microscopic structure and phase separation occurring in ionic separation and recovery systems during solvent extraction. The coordination species aggregate through a hydrogen-bonding network formed by interaction between the hydrophilic part of the coordination species with extracted water and acid molecules. This reduces the hydrophilic surface area, resulting in subsequent formation of small primal clusters of 2 to 3 nm in diameter. The primal clusters further aggregate due to van der Waals interaction to form large aggregates of $$<$$ 10 nm in diameter. The size of the primal cluster does not depend on the concentration of the coordination species, whereas the size of the large aggregate increases as the aggregation number of the primal clusters increases. We conclude that hybrid interaction is a key driving force in the formation and growth of the hierarchical aggregate and the induction of phase separation of the organic phase.

論文

A Novel microemulsion phase transition; Toward the elucidation of third-phase formation in spent nuclear fuel reprocessing

Mu, J.*; 元川 竜平; 阿久津 和宏*; 西辻 祥太郎*; Masters, A. J.*

Journal of Physical Chemistry B, 122(4), p.1439 - 1452, 2018/02

 被引用回数:33 パーセンタイル:72.79(Chemistry, Physical)

We present evidence that the transition between organic and third phases, which is an unusual transition between two isotropic, bi-continuous micro-emulsion phases. This system contains quaternary; water, n-dodecane, nitric acid, tributyl phosphate (TBP). This quaternary system has been shown to exhibit, under appropriate conditions, three coexisting phases: a light organic phase, an aqueous phase, and the so-called third phase. In this work, we focused on the coexistence of the light organic phase with the third phase using methods of molecular dynamics (MD) simulation and small-angle X-ray scattering (SAXS). Snapshots from the MD simulations as well as a cluster analysis of the organic and third phases revealed structures akin to bi-continuous micro-emulsion phases, with the polar species residing within a mesh, and with the surface of the mesh formed by amphiphilic TBP molecules. The non-polar n-dodecane molecules were observed in these snapshots to be outside this mesh. The only large-scale structural differences observed between the two phases were the dimensions of the mesh. Evidence for the correctness of these structures was provided by the results of SAXS studies, where the profiles obtained for both the organic and third phases agreed well with those calculated from simulation.

論文

Comparative molecular dynamics study on tri-$$n$$-butyl phosphate in organic and aqueous environments and its relevance to nuclear extraction processes

Mu, J.*; 元川 竜平; Williams, C. D.*; 阿久津 和宏*; 西辻 祥太郎*; Masters, A. J.*

Journal of Physical Chemistry B, 120(23), p.5183 - 5193, 2016/06

 被引用回数:27 パーセンタイル:60.57(Chemistry, Physical)

A refined model for tri-$$n$$-butyl phosphate (TBP), which uses a new set of partial charges generated from our ab initio density functional theory calculations, has been proposed in this study. Molecular dynamics simulations are conducted to determine the thermodynamic properties, transport properties, and the microscopic structures of liquid TBP, TBP/water mixtures, and TBP/$$n$$-alkane mixtures. These results are compared with those obtained from four other TBP models, previously described in the literature. We conclude that our refined TBP model appears to be the only TBP model from this set that, with reasonable accuracy, can simultaneously predict the properties of TBP in bulk TBP, in organic diluents, and in aqueous solution. This new TBP model is thus appropriate for the simulation of liquid-liquid extraction systems in the nuclear extraction process, where one needs to simultaneously model TBP in both aqueous and organic phases. It is also promising for the investigation of the microscopic structure of the organic phase in these processes and for the characterization of third-phase formation, where TBP again interacts simultaneously with both polar and nonpolar molecules. Because the proposed TBP model uses OPLS-2005 Lennard-Jones parameters, it may be used with confidence to model mixtures of TBP with other species whose parameters are given by the OPLS-2005 force field.

口頭

ジルコニウム錯体のクラスター形成を考慮した溶媒抽出平衡解析

岡村 浩之; 上田 祐生; 元川 竜平; Mu, J.*; Masters, A. J.*; Antonio, M. R.*

no journal, , 

近年、有機溶媒中での金属-抽出剤錯体クラスターの形成が液-液抽出において重要な役割を果たすことが示された。液-液抽出に関しては、多数の反応機構が提案されているが、溶質濃度が高い条件においては、金属-抽出剤の化学量論を評価するスロープ解析法の適用が困難になる。そこで本研究では、抽出過程における有機相中でのクラスター凝集体形成を考慮した、実用的な液-液系のための溶媒抽出平衡解析を行った。分子動力学(MD)シミュレーションを行ったところ、${it n}$-オクタン中で1から9個のZr(NO$$_{3}$$)$$_{4}$$(TBP)$$_{2}$$錯体が凝集したクラスターを形成していることが見出され、各クラスターの組成とモル分率を算出できた。さらに、抽出平衡反応を検討することで、MD解析で得られたパラメータから各クラスターの抽出平衡定数K$$_{ex, j}$$(${it j}$ = 1-9)を求めることができ、K$$_{ex, j}$$から計算した分配比の曲線は、実験値とよく一致した。したがって、1回のMDシミュレーションからクラスター化/凝集液-液抽出系における分配比曲線を正確に再現でき、スロープ解析法の限界を克服することに成功した。

口頭

金属錯体によるナノクラスター化現象の精密構造解析に基づいた古典的平衡論解析の拡張

岡村 浩之; 上田 祐生; 元川 竜平; Mu, J.*; Masters, A. J.*; Antonio, M. R.*

no journal, , 

溶質濃度が高い実用的な液-液抽出条件下では、有機相中で金属-抽出剤錯体クラスターが生成することがある。このような条件においては、金属-抽出剤の化学量論を決定するスロープ解析法の適用が困難になり、理想からのずれは、非線形や非整数の傾きとして現れる。そこで本研究では、クラスター形成を考慮した、実用的な液-液系のための新たな抽出平衡解析法を開発し、古典的平衡論解析の拡張に挑戦した。分子動力学(MD)シミュレーションのスナップショットを解析したところ、${it n}$-オクタン中で1から9個のZr(NO$$_{3}$$)$$_{4}$$(TBP)$$_{2}$$錯体が凝集したクラスターを形成していることが明らかになり、各クラスターの組成とモル分率を算出できた。${it j}$個のZr(NO$$_{3}$$)$$_{4}$$(TBP)$$_{2}$$錯体から構成されるクラスターの抽出平衡を考慮し、MD解析で得られた各クラスターのモル分率と分配比から、抽出平衡定数K$$_{ex, j}$$ (${it j}$ = 1-9)を算出した。得られたK$$_{ex, j}$$から計算した分配比の曲線は、実験値とよく一致することが明らかになった。したがって、MDシミュレーションにより、クラスター化/凝集液-液抽出系における実験値を正確に再現できることが明らかになり、古典的平衡論解析の拡張に成功した。

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