Comparative Molecular Dynamics Study on Tri-<i>n</i>-butyl Phosphate in Organic and Aqueous Environments and Its Relevance to Nuclear Extraction Processes

Mu, Junju; Motokawa, Ryuhei; Williams, Christopher; Akutsu, Kazuhiro; Nishitsuji, Shotaro; Masters, Andrew J.

doi:10.1021/acs.jpcb.6b00781

Cited by 33 publications

(46 citation statements)

References 63 publications

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“…Numerous simulation studies have used different TBP force fields to investigate TBPwater interactions. 23,38,40 Accurate simulation of those interactions at an aqueous/organic interface or in a bulk alkane-based solution have required either a small degree of TBP charge scaling 23,24,38 or explicit polarization. 40 Accurate prediction of the interfacial tension requires careful calibration of the surfactant polarity which may be at odds with optimizations made for reproducing bulk phase properties.…”

Section: Resultsmentioning

confidence: 99%

The Role of Surfactant Force Field on the Properties of Liquid/Liquid Interfaces

Servis¹,

McCue²,

Casella³

et al. 2019

Preprint

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Surfactant-laden liquid/liquid interfaces mediate numerous chemical processes, from commercial applications of microemulsions to chemical separations. Classical molecular dynamics simulation is a prevalent method for studying microscopic and thermodynamic properties of such interfaces. However, the extent to which these features can be reliably predicted, and the variations in predicted behavior, depend upon the force field parameters employed. At present, the impact of force fields upon simulated properties is relatively understudied. Yet recent advances to sampling and analysis algorithms are increasing the interpretation of simulation data and therefore understanding force field dependence is increasingly relevant. In this study, the impact of the force field of the surfactant tri-n-butyl phosphate (TBP), as well as that of water, is investigated at a water/(n-hexane + surfactant) interface. Empirical charge scaling was employed to modulate the hydrophilicity of the surfactant. As anticipated, the relative hydrophilicity of TBP influences a number of properties, including the adsorbed concentrations of TBP at the interface, and macroscopic properties that result from hydrogen bonding interactions, such as interfacial tension and width. The dynamic properties of solvents at the interface are strongly modulated by the variation in hydrogen bond strength caused by different charge scaling of the TBP model. This includes the residence times of water at the interface, where stronger water-TBP hydrogen bonding causes long-lived residences. Interestingly, there are a number of features that are relatively insensitive to the TBP hydrophilicity. In one important case, the concentration of water-bridged TBP dimers was only impacted for the least hydrophilic model. As these dimeric species are the building block of surface protrusions that lead to water transport across the interface, this implies that collective organizational patterns and surface structures that derive from multiple driving forces (e.g. TBP hydrophilicity and organic solvent free energies of solvation) are less sensitive to individual force field parameters. Further, we note that competitive interactions can "cancel" the effects of changing TBP charge on interfacial properties. One example is the orientation and hydrogen bonding structure of interfacial water, where the direct TBP-water hydrogen bonding competes against the indirect TBP-induced interfacial roughness. In combination, these observations may assist future simulation studies in calibrating surfactant models to, or interpreting results of, a broad range of dynamic, structural and thermodynamic properties.

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Section: Resultsmentioning

confidence: 99%

The Role of Surfactant Force Field on the Properties of Liquid/Liquid Interfaces

Servis¹,

McCue²,

Casella³

et al. 2019

Preprint

View full text Add to dashboard Cite

show abstract

“…The sample solution was loaded using a peristaltic pump into a titanium cell with a thickness of 1.25 mm (path length) and quartz plate windows (6.0 mm × 2.5 mm × 0.02 mm). 51,53 All X-ray scattering data were acquired at 25 °C.…”

Section: Methodsmentioning

confidence: 99%

Globular pattern formation of hierarchical ceria nanoarchitecture

Aoyagi¹,

Motokawa²,

Okumura³

et al. 2021

Preprint

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Dissipative structures often appear as an unstable counterpart of ordered structures owing to fluctuations that do not form a homogeneous phase. Even a multiphase mixture may simultaneously undergo one chemical reaction near equilibrium and another one that is far from equilibrium. Here, we observed in real time crystal seed formation and simultaneous nanocrystal aggregation proceeding from CeIV complexes to CeO2 nanoparticles in an acidic aqueous solution, and investigated the resultant hierarchical nanoarchitecture. The formed particles exhibited two very different size ranges. The hierarchically assembled structures in solutions were CeO2 colloids, viz. primary core clusters (1–3 nm) of crystalline ceria and secondary clusters (20–30 nm) assembled through surface ions. Such self-assembly is widespread in multi-component complex fluids, paradoxically moderating hierarchical reactions. Stability and instability are not only critical but also complementary for co-optimisation around the nearby free energy landscape prior to bifurcation.

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“…The AMBER-based force field for TBP has been optimized by Ye et al 42 for the interfacial water/n-alkane system to accurately reproduce the experimentally determined extracted water concentration in the organic phase at equilibrium. 38,42 System compositions, simulation methodology and force field descriptions are given in the Supporting Information. Additional data using alternative force fields are presented in Supporting Information and validate that key results are independent of the force field employed.…”

Section: Computational Methods Simulation Systems and Force Fieldsmentioning

confidence: 99%

“…22,28,31 In this work the surfactant tri-n-butyl phosphate (TBP) is chosen because of its ubiquity in solvent extraction applications, 1,32 notably in the Plutonium Uranium Reduction EXtraction (PUREX) process, and because it has been the topic of extensive study in the MD modeling literature. 8,10,20,[33][34][35][36][37][38][39][40][41][42] Prior work 7,20,42,43 has shown that TBP adsorbs to the water/organic interface with its dipole orthogonal and alkyl tails parallel to the interface plane. While the extraction of water from the interface by TBP has been qualitatively described in the literature, 7,42 it remains to be understood -either qualitatively or quantitatively -how TBP adsorption influences the capillary wave front, including its heterogeneity, fluctuations in space, and the resulting mechanisms for water extraction into the organic phase.…”

Section: Introductionmentioning

confidence: 99%

Interfacial Heterogeneity is Essential to Water Extraction into Organic Solvents

Servis¹,

Clark²

2018

Preprint

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Liquid/liquid extraction (LLE) is one of the most industrially relevant separations methods, successfully leveraging the variable solubility of solutes (or their complexes) between two immiscible solvents. Independently from the relative solubilities of those solutes and complexes which determine their distribution between phases, the kinetics of phase transfer is impacted by the molecular interactions and structure of those species at the interface. A simple example includes the formation and extraction of water-extractant adducts observed in the ternary water/organic/tri-n-butyl phosphate (TBP) system. Despite its implications for LLE, a detailed description of the structural and dynamic mechanisms by which such adducts are formed at the interface is not established. Describing that process requires connecting the evolving interfacial molecular organization in the presence of surfactants to dynamic surface fluctuations and interfacial heterogeneity. Herein, molecular dynamics simulation is combined with state of the art network theory analysis to reveal features of interfacial structure and their relationship to the extraction of water in the water/n-hexane/TBP system. Surfactant adsorption enhances interfacial roughness which in turn causes directly interfacial water to become less connected through hydrogen bonding to subjacent layers, particularly upon formation of the water bridged TBP dimer adduct. Further, heterogeneity within the interface itself is enhanced by surfactant adsorption, and serves as the basis for the formation of protrusions of water into the organic phase at the extremes of surface fluctuations. These features disproportionately incorporate the water bridged TBP dimer and are the primary means by which water is transferred to the organic phase. This work presents for the first time a holistic understanding of how interfacial heterogeneity and spatial fluctuations become amplified in the presence of surfactants, enabling water extraction into the organic phase. It further affords the opportunity to study how solution conditions can control interfacial behavior to create more efficient solvent extraction systems.

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Comparative Molecular Dynamics Study on Tri-n-butyl Phosphate in Organic and Aqueous Environments and Its Relevance to Nuclear Extraction Processes

Cited by 33 publications

References 63 publications

The Role of Surfactant Force Field on the Properties of Liquid/Liquid Interfaces

The Role of Surfactant Force Field on the Properties of Liquid/Liquid Interfaces

Globular pattern formation of hierarchical ceria nanoarchitecture

Interfacial Heterogeneity is Essential to Water Extraction into Organic Solvents

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