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Atomistic insight into tetraalkylphosphonium-bis(oxalato)borate ionic liquid/water mixtures. I. Local microscopic structure
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
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2015 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 16, 5251-5264 p.Article in journal (Refereed) Published
Abstract [en]

Atomistic simulations have been performed to investigate the microscopic structural organization of aqueous solutions of trihexyltetradecylphosphonium bis(oxalato)borate ([P<inf>6,6,6,14</inf>][BOB]) ionic liquid (IL). The evolution of the microscopic liquid structure and the local ionic organization of IL/water mixtures as a function of the water concentration is visualized and systematically analyzed via radial and spatial distribution functions, coordination numbers, hydrogen bond network, and water clustering analysis. The microscopic liquid structure in neat IL is characterized by a connected apolar network composed of the alkyl chains of [P<inf>6,6,6,14</inf>] cations and isolated polar domains consisting of the central segments of [P<inf>6,6,6,14</inf>] cations and [BOB] anions, and the corresponding local ionic environment is described by direct contact ion pairs. In IL/water mixtures with lower water mole fractions, the added water molecules are dispersed and embedded in cavities between neighboring ionic species and the local ionic structure is characterized by solvent-shared ion pairs through cation-water-anion triple complexes. With a gradual increase in the water concentration in IL/water mixtures, the added water molecules tend to aggregate and form small clusters, intermediate chain-like structures, large aggregates, and eventually a water network in water concentrated simulation systems. A further progressive dilution of IL/water mixtures leads to the formation of self-organized micelle-like aggregates characterized by a hydrophobic core and hydrophilic shell consisting of the central polar segments in [P<inf>6,6,6,14</inf>] cations and [BOB] anions in a highly branched water network. The striking structural evolution of the [P<inf>6,6,6,14</inf>][BOB] IL/water mixtures is rationalized by the competition between favorable hydrogen bonded interactions and strong electrostatic interactions between the polar segments in ionic species and the dispersion interactions between the hydrophobic alkyl chains in [P<inf>6,6,6,14</inf>] cations. © 2015 American Chemical Society.

Place, publisher, year, edition, pages
2015. Vol. 119, no 16, 5251-5264 p.
Keyword [en]
Aggregates, Complex networks, Distribution functions, Hydrogen bonds, Hydrophobicity, Ionic liquids, Ions, Mixtures, Molecules, Negative ions, Positive ions, Atomistic simulations, Dispersion interaction, Hydrogen bond networks, Hydrophobic alkyl chain, Microscopic structures, Structural evolution, Structural organization, Trihexyltetradecylphosphonium, Liquids
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-167743DOI: 10.1021/acs.jpcb.5b00667ISI: 000353604800015ScopusID: 2-s2.0-84928485335OAI: diva2:815605
Swedish Research CouncilKnut and Alice Wallenberg Foundation

QC 20150601

Available from: 2015-06-01 Created: 2015-05-22 Last updated: 2015-10-20Bibliographically approved

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Glavatskih, Sergei B.
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Machine Design (Dept.)
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