Computational Study of Molecular Structure and Self-Association of Tri-<i>n</i>-butyl Phosphates in <i>n</i>-Dodecane

Vo, Quynh N.; Hawkins, Cory A.; Dang, Liem X.; Nilsson, Mikael; Nguyen, Hung D.

doi:10.1021/jp510365c

Cited by 45 publications

(75 citation statements)

References 46 publications

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“…These results are in good agreement with the experimental results published by Motokawa et al . Previous MD simulations reported in the literature describe either TBP dimers in alkane‐diluted organic phases,,, or TBP trimers or even tetramers in more concentrated solutions . However, all of these MD simulations were performed for “dry” organic phases (i.e., without any water molecules), although TBP is known to be very hydrophilic.…”

Section: Resultssupporting

confidence: 90%

Determination of the Structures of Uranyl–Tri‐n‐butyl‐Phosphate Aggregates by Coupling Experimental Results with Molecular Dynamic Simulations

Guilbaud

Berthon

Louisfrema

et al. 2017

Chemistry A European J

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The complex structure of a plutonium uranium refining by extraction (PUREX) process organic phase was characterized by combining results from experiments and molecular dynamics simulations. For the first time, the molecular interactions between tri-n-butyl phosphate (TBP) and the extracted solutes, as well as TBP aggregation after the extraction of water and/or uranyl nitrate, were described and analyzed concomitantly. Coupling molecular dynamics simulations with small- and wide-angle X-ray scattering (SWAXS) experiments can lead to simulated organic solutions that are representative of the experimental ones, even for high extractant and solute concentrations. Furthermore, this coupling is well adapted for the interpretation of SWAXS experiments without preliminary hypothesis on the size or shape of aggregates. The results link together previous literature studies obtained for each level of depiction separately (complexation or aggregation). Without uranium, or at low metal concentration, almost no aggregation was observed. At high uranium concentration, organic phases contain small [UO (NO ) (TBP) ] polymetallic aggregates (with n=2 to 4), in which the 1:2 U/TBP stoichiometry is preserved.

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Section: Resultssupporting

confidence: 90%

Determination of the Structures of Uranyl–Tri‐n‐butyl‐Phosphate Aggregates by Coupling Experimental Results with Molecular Dynamic Simulations

Guilbaud

Berthon

Louisfrema

et al. 2017

Chemistry A European J

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“…20, to fit experimental values for pure TBP density, molecular dipole and enthlapy of vaporization. This approach to fitting bulk phase properties of GAFF TBP without charge scaling is similar to the TBP model described in ref 21. Charge-scaled TBP models based on the AMBER force fields are referred to by the scaling percent used to reduce their charges, "A-90" and "A-70."…”

Section: Force Fields and Systemsmentioning

confidence: 99%

“…26 n-Hexane was modeled with the GAFF force field with some reparameterization to the match experimental density and enthalpy of vaporization. 21 In the ternary water/(TBP + n-hexane) system, TIP4P water was used with three different TBP force fields. Lorenz-Berthelot mixing rules were applied for all Lennard-Jones cross terms for all force fields.…”

Section: Force Fields and Systemsmentioning

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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“…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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Computational Study of Molecular Structure and Self-Association of Tri-n-butyl Phosphates in n-Dodecane

Cited by 45 publications

References 46 publications

Determination of the Structures of Uranyl–Tri‐n‐butyl‐Phosphate Aggregates by Coupling Experimental Results with Molecular Dynamic Simulations

Determination of the Structures of Uranyl–Tri‐n‐butyl‐Phosphate Aggregates by Coupling Experimental Results with Molecular Dynamic Simulations

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

Interfacial Heterogeneity is Essential to Water Extraction into Organic Solvents

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