83 results found
Brar NK, Brown RT, Shahbaz K, et al., 2022, Guanidinium solvents with exceptional hydrogen bond donating abilities, CHEMICAL COMMUNICATIONS, Vol: 58, Pages: 3505-3508, ISSN: 1359-7345
Seymour JM, Gousseva E, Bennett RA, et al., 2022, Resonant X-ray photoelectron spectroscopy: identification of atomic contributions to valence states, FARADAY DISCUSSIONS, Vol: 236, Pages: 389-411, ISSN: 1359-6640
Hunt P, Philippi F, Goloviznina K, et al., 2022, Charge transfer and polarisability in ionic liquids: a case study, Physical Chemistry Chemical Physics, Vol: 24, Pages: 3144-3162, ISSN: 1463-9076
The practical use of ionic liquids (ILs) is benefiting from a growing understanding of the underpinning structural and dynamic properties, facilitated through classical molecular dynamics (MD) simulations. The predictive and explanatory power of a classical MD simulation is inextricably linked to the underlying force field. A key aspect of the forcefield for ILs is the ability to recover charge based interactions. Our focus in this paper is on the description and recovery of charge transfer and polarisability effects, demonstrated through MD simulations of the widely used 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4C1im][NTf2] IL. We study the charge distributions generated by a range of ab initio methods, and present an interpolation method for determining atom-wise scaled partial charges. Two novel methods for determining the mean field (total) charge transfer from anion to cation are presented. The impact of using different charge models and different partial charge scaling (unscaled, uniformly scaled, atom-wise scaled) are compared to fully polarisable simulations. We study a range of Drude particle explicitly polarisable potentials and shed light on the performance of current approaches to counter known problems. It is demonstrated that small changes in the charge description and MD methodology can have a significant impact; biasing some properties, while leaving others unaffected within the structural and dynamic domains.
Rauber D, Philippi F, Kuttich B, et al., 2021, Curled cation structures accelerate the dynamics of ionic liquids, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 23, Pages: 21042-21064, ISSN: 1463-9076
Rowe R, Lovelock KRJ, Hunt PA, 2021, Bi(III) halometallate ionic liquids: Interactions and speciation, JOURNAL OF CHEMICAL PHYSICS, Vol: 155, ISSN: 0021-9606
Philippi F, Rauber D, Kuttich B, et al., 2020, Ether functionalisation, ion conformation and the optimisation of macroscopic properties in ionic liquids, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 22, Pages: 23038-23056, ISSN: 1463-9076
Philippi F, Pugh D, Rauber D, et al., 2020, Conformational design concepts for anions in ionic liquids, Chemical Science, Vol: 11, Pages: 6405-6422, ISSN: 2041-6520
The identification of specific design concepts for the in silico design of ionic liquids (ILs) has been accomplished using theoretical methods. Molecular building blocks, such as interchangeable functional groups, are used to design a priori new ILs which have subsequently been experimentally investigated. The conformational design concepts are developed by separately and systematically changing the central (imide), bridging (sulfonyl) and end (trifluoromethyl) group of the bis(trifluoromethanesulfonyl)imide [N(Tf)2]− anion and examining the resultant potential energy surfaces. It is shown that these design concepts can be used to tune separately the minimum energy geometry, transition state barrier height and relative stability of different conformers. The insights obtained have been used to design two novel anions for ILs, trifluoroacetyl(methylsulfonyl)imide [N(Ms)(TFA)]− and acetyl(trifluoromethanesulfonyl)imide [N(Tf)(Ac)]−. The computationally predicted structures show excellent agreement with experimental structures obtained from X-ray crystallography. [C4C1im][N(Tf)(Ac)] and [C4C1im][N(Ms)(TFA)] ILs have been synthesised and ion diffusion coefficients examined using pulsed field gradient stimulated echo NMR spectroscopy. Significantly increased diffusion was observed for the more flexible [N(Tf)(Ac)]− compared with the more rigid [N(Ms)(TFA)]− analogue. Furthermore, a pronounced impact on the fluidity was observed. The viscosity of the IL with the rigid anion was found to be twice as high as the viscosity of the IL with the flexible anion. The design concepts presented in this work will enable researchers in academia and industry to tailor anions to provide ILs with specific desired properties.
Fogarty R, Palgrave R, Bourne R, et al., 2019, Electron spectroscopy of ionic liquids: experimental identification of atomic orbital contributions to valence electronic structure, Physical Chemistry Chemical Physics, Vol: 21, Pages: 18893-18910, ISSN: 1463-9076
The atomic contributions to valence electronic structure for 37 ionic liquids (ILs) are identified using a combination of variable photon energy XPS, resonant Auger electron spectroscopy (RAES) and a subtraction...</p>
Turnell-Ritson RC, Sapsford JS, Cooper RT, et al., 2018, Base-induced reversible H-2 addition to a single Sn(II) centre, Chemical Science, Vol: 9, Pages: 8716-8722, ISSN: 2041-6520
A range of amines catalyse the oxidative addition (OA) of H2 to [(Me3Si)2CH]2Sn (1), forming [(Me3Si)2CH]2SnH2 (2). Experimental and computational studies point to ‘frustrated Lewis pair’ mechanisms in which 1 acts as a Lewis acid and involve unusual late transition states; this is supported by the observation of a kinetic isotope effect Image ID:c8sc03110j-t1.gif for Et3N. When DBU is used the energetics of H2 activation are altered, allowing an equilibrium between 1, 2 and adduct [1·DBU] to be established, thus demonstrating reversible oxidative addition/reductive elimination (RE) of H2 at a single main group centre.
Heller BSJ, Kolbeck C, Niedermaier I, et al., 2018, Surface enrichment in equimolar mixtures of non-functionalized and functionalized imidazolium-based ionic liquids, ChemPhysChem, Vol: 19, Pages: 1733-1745, ISSN: 1439-7641
For equimolar mixtures of ionic liquids with imidazolium‐based cations of very different electronic structure, we observe very pronounced surface enrichment effects by angle‐resolved X‐ray photoelectron spectroscopy (XPS). For a mixture with the same anion, that is, 1‐methyl‐3‐octylimidazolium hexafluorophosphate+1,3‐di(methoxy)imidazolium hexafluorophosphate ([C8C1Im][PF6]+[(MeO)2Im][PF6]), we find a strong enrichment of the octyl chain‐containing [C8C1Im]+ cation and a corresponding depletion of the [(MeO)2Im]+ cation in the topmost layer. For a mixture with different cations and anions, that is, [C8C1Im][Tf2N]+[(MeO)2Im][PF6], we find both surface enrichment of the [C8C1Im]+ cation and the [Tf2N]− (bis[(trifluoromethyl)sulfonyl]imide) anion, while [(MeO)2Im]+ and [PF6]− are depleted from the surface. We propose that the observed behavior in these mixtures is due to a lowering of the surface tension by the enriched components. Interestingly, we observe pronounced differences in the chemical shifts of the imidazolium ring signals of the [(MeO)2Im]+ cations as compared to the non‐functionalized cations. Calculations of the electronic structure and the intramolecular partial charge distribution of the cations contribute to interpreting these shifts for the two different cations.
Fogarty RM, Matthews RP, Ashworth CR, et al., 2018, Experimental validation of calculated atomic charges in ionic liquids, Journal of Chemical Physics, Vol: 148, ISSN: 0021-9606
A combination of X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy has been used to provide an experimental measure of nitrogen atomic charges in nine ionic liquids (ILs). These experimental results are used to validate charges calculated with three computational methods: charges from electrostatic potentials using a grid-based method (ChelpG), natural bond orbital population analysis, and the atoms in molecules approach. By combining these results with those from a previous study on sulfur, we find that ChelpG charges provide the best description of the charge distribution in ILs. However, we find that ChelpG charges can lead to significant conformational dependence and therefore advise that small differences in ChelpG charges (<0.3 e) should be interpreted with care. We use these validated charges to provide physical insight into nitrogen atomic charges for the ILs probed.
Heid E, Hunt PA, Schroeder C, 2018, Evaluating excited state atomic polarizabilities of chromophores, Physical Chemistry Chemical Physics, Vol: 20, Pages: 8554-8563, ISSN: 1463-9076
Ground and excited state dipoles and polarizabilities of the chromophores N-methyl-6-oxyquinolinium betaine (MQ) and coumarin 153 (C153) in solution have been evaluated using time-dependent density functional theory (TD-DFT). A method for determining the atomic polarizabilities has been developed; the molecular dipole has been decomposed into atomic charge transfer and polarizability terms, and variation in the presence of an electric field has been used to evaluate atomic polarizabilities. On excitation, MQ undergoes very site-specific changes in polarizability while C153 shows significantly less variation. We also conclude that MQ cannot be adequately described by standard atomic polarizabilities based on atomic number and hybridization state. Changes in the molecular polarizability of MQ (on excitation) are not representative of the local site-specific changes in atomic polarizability, thus the overall molecular polarizability ratio Image ID:c7cp08549d-t1.gif does not provide a good approximation for local atom-specific polarizability changes on excitation. Accurate excited state force fields are needed for computer simulation of solvation dynamics. The chromophores considered in this study are often used as molecular probes. The methods and data reported here can be used for the construction of polarizable ground and excited state force fields. Atomic and molecular polarizabilities (ground and excited states) have been evaluated over a range of functionals and basis sets. Different mechanisms for including solvation effects have been examined; using a polarizable continuum model, explicit solvation and via sampling of clusters extracted from a MD simulation. A range of different solvents have also been considered.
Addicoat M, Atkin R, Lopes JNC, et al., 2018, Structure and dynamics of ionic liquids: general discussion, FARADAY DISCUSSIONS, Vol: 206, Pages: 291-337, ISSN: 1359-6640
Fogarty RM, Matthews RP, Clough MT, et al., 2017, NEXAFS spectroscopy of ionic liquids: experiments versus calculations, Physical Chemistry Chemical Physics, Vol: 19, Pages: 31156-31167, ISSN: 1463-9076
Experimental near edge X-ray absorption fine structure (NEXAFS) spectra are reported for 12 ionic liquids (ILs) encompassing a range of chemical structures for both the sulfur 1s and nitrogen 1s edges and compared with time-dependent density functional theory (TD-DFT) calculations. The energy scales for the experimental data were carefully calibrated against literature data. Gas phase calculations were performed on lone ions, ion pairs and ion pair dimers, with a wide range of ion pair conformers considered. For the first time, it is demonstrated that TD-DFT is a suitable method for simulating NEXAFS spectra of ILs, although the number of ions included in the calculations and their conformations are important considerations. For most of the ILs studied, calculations on lone ions in the gas phase were sufficient to successfully reproduce the experimental NEXAFS spectra. However, for certain ILs – for example, those containing a protic ammonium cation – calculations on ion pairs were required to obtain a good agreement with experimental spectra. Furthermore, significant conformational dependence was observed for the protic ammonium ILs, providing insight into the predominant liquid phase cation–anion interactions. Among the 12 investigated ILs, we find that four have an excited state that is delocalised across both the cation and the anion, which has implications for any process that depends on the excited state, for example, radiolysis. Considering the collective experimental and theoretical data, we recommend that ion pairs should be the minimum number of ions used for the calculation of NEXAFS spectra of ILs.
Kuzmina O, Hassan NH, Patel L, et al., 2017, The impact of ionic liquids on the coordination of anions with solvatochromic copper complexes, Dalton Transactions, Vol: 46, Pages: 12185-12200, ISSN: 1477-9234
Solvatochromic transition metal (TM)-complexes with weakly associating counter-anions are often used to evaluate traditional neutral solvent and anion coordination ability. However, when employed in ionic liquids (IL) many of the common assumptions made are no longer reliable. This study investigates the coordinating ability of weakly coordinating IL anions in traditional solvents and within IL solvents employing a range of solvatochromic copper complexes. Complexes of the form [Cu(acac)(tmen)][X] (acac = acetylacetonate, tmen = tetramethylethylenediamine) where [X]− = [ClO4]−, Cl−, [NO3]−, [SCN]−, [OTf]−, [NTf2]− and [PF6]− have been synthesised and characterised both experimentally and computationally. ILs based on these anions and imidazolium and pyrrolidinium cations, some of which are functionalised with hydroxyl and nitrile groups, have been examined. IL-anion coordination has been investigated and compared to typical weakly coordinating anions. We have found there is potential for competition at the Cu-centre and cases of anions traditionally assigned as weakly associating that demonstrate a stronger than expected level of coordinating ability within ILs. [Cu(acac)(tmen)][PF6] is shown to contain the least coordinating anion and is established as the most sensitive probe studied here. Using this probe, the donor numbers (DNs) of ILs have been determined. Relative donor ability is further confirmed based on the UV-Vis of a neutral complex, [Cu(sacsac)2] (sacsac = dithioacetylacetone), and DNs evaluated via23Na NMR spectroscopy. We demonstrate that ILs can span a wide donor range, similar in breadth to conventional solvents.
Brooks NJ, Castiglione F, Doherty CM, et al., 2017, Linking the structures, free volumes, and properties of ionic liquid mixtures, Chemical Science, Vol: 8, Pages: 6359-6374, ISSN: 2041-6520
The formation of ionic liquid (IL) mixtures has been proposed as an approach to rationally fine-tune the physicochemical properties of ILs for a variety of applications. However, the effects of forming such mixtures on the resultant properties of the liquids are only beginning to be understood. Towards a more complete understanding of both the thermodynamics of mixing ILs and the effect of mixing these liquids on their structures and physicochemical properties, the spatial arrangement and free volume of IL mixtures containing the common [C4C1im]+ cation and different anions have been systematically explored using small angle X-ray scattering (SAXS), positron annihilation lifetime spectroscopy (PALS) and 129Xe NMR techniques. Anion size has the greatest effect on the spatial arrangement of the ILs and their mixtures in terms of the size of the non-polar domains and inter-ion distances. It was found that differences in coulombic attraction between oppositely charged ions arising from the distribution of charge density amongst the atoms of the anion also significantly influences these inter-ion distances. PALS and 129Xe NMR results pertaining to the free volume of these mixtures were found to strongly correlate with each other despite the vastly different timescales of these techniques. Furthermore, the excess free volumes calculated from each of these measurements were in excellent agreement with the excess volumes of mixing measured for the IL mixtures investigated. The correspondence of these techniques indicates that the static and dynamic free volume of these liquid mixtures are strongly linked. Consequently, fluxional processes such as hydrogen bonding do not significantly contribute to the free volumes of these liquids compared to the spatial arrangement of ions arising from their size, shape and coulombic attraction. Given the relationship between free volume and transport properties such as viscosity and conductivity, these results provide a link between the s
Fogarty RM, Rowe R, Matthews RP, et al., 2017, Atomic charges of sulfur in ionic liquids: experiments and calculations, Faraday Discussions, Vol: 206, Pages: 183-201, ISSN: 1359-6640
Experimental near edge X-ray absorption fine structure (NEXAFS) spectra, X-ray photoelectron (XP) spectra and Auger electron spectra are reported for sulfur in ionic liquids (ILs) with a range of chemical structures. These values provide experimental measures of the atomic charge in each IL and enable the evaluation of the suitability of NEXAFS spectroscopy and XPS for probing the relative atomic charge of sulfur. In addition, we use Auger electron spectroscopy to show that when XPS binding energies differ by less than 0.5 eV, conclusions on atomic charge should be treated with caution. Our experimental data provides a benchmark for calculations of the atomic charge of sulfur obtained using different methods. Atomic charges were computed for lone ions and ion pairs, both in the gas phase (GP) and in a solvation model (SMD), with a wide range of ion pair conformers considered. Three methods were used to compute the atomic charges: charges from the electrostatic potential using a grid based method (ChelpG), natural bond orbital (NBO) population analysis and Bader’s atoms in molecules (AIM) approach. By comparing the experimental and calculated measures of the atomic charge of sulfur, we provide an order for the sulfur atoms, ranging from the most negative to the most positive atomic charge. Furthermore, we show that both ChelpG and NBO are reasonable methods for calculating the atomic charge of sulfur in ILs, based on the agreement with both the XPS and NEXAFS spectroscopy results. However, the atomic charges of sulfur derived from ChelpG are found to display significant, non-physical conformational dependence. Only small differences in individual atomic charge of sulfur were observed between lone ion (GP) and ion pair IL(SMD) model systems, indicating that ion–ion interactions do not strongly influence individual atomic charges.
Hunt PA, 2017, Quantum chemical modeling of hydrogen bonding in ionic liquids, Topics in Current Chemistry, Vol: 375, ISSN: 0340-1022
Hydrogen bonding (H-bonding) is an important and very general phenomenon. H-bonding is part of the basis of life in DNA, key in controlling the properties of water and ice, and critical to modern applications such as crystal engineering, catalysis applications, pharmaceutical and agrochemical development. H-bonding also plays a significant role for many ionic liquids (IL), determining the secondary structuring and affecting key physical parameters. ILs exhibit a particularly diverse and wide range of traditional as well as non-standard forms of H-bonding, in particular the doubly ionic H-bond is important. Understanding the fundamental nature of the H-bonds that form within ILs is critical, and one way of accessing this information, that cannot be recovered by any other computational method, is through quantum chemical electronic structure calculations. However, an appropriate method and basis set must be employed, and a robust procedure for determining key structures is essential. Modern generalised solvation models have recently been extended to ILs, bringing both advantages and disadvantages. QC can provide a range of information on geometry, IR and Raman spectra, NMR spectra and at a more fundamental level through analysis of the electronic structure.
Ward B, Hunt PA, 2016, Hydrophosphination of styrene and polymerization of vinylpyridine: a computational investigation of calcium-catalyzed reactions and the role of fluxional noncovalent interactions, ACS Catalysis, Vol: 7, Pages: 459-468, ISSN: 2155-5435
A computational investigation of the intermolecular hydrophosphination of styrene and 2-vinylpyridine, catalyzed by the heteroleptic β-diketiminato-stabilized calcium complex [(PhNC(Me)CHC(Me)NPh)CaPPh2], is presented. Alkene insertion does not proceed via the traditional route as proposed by experimental and theoretical research related to intermolecular hydroamination catalyzed by alkaline earth or lanthanide complexes. In contrast, for the hydrophosphination mechanism, insertion proceeds via outer sphere, conjugative addition where there is no direct interaction of Ca with the vinyl functionality. Following the initial rate-determining alkene insertion, two distinct mechanisms emerge, protonolysis or polymerization. Polymerization of styrene is energetically less favorable than protonolysis, whereas the reverse is determined for 2-vinylpyridine, thereby providing strong evidence of outcomes observed experimentally. The vinylarene ring is important as it allows for preferential coordination of the unsaturated substrate through numerous noncovalent Ca···π, CH···π, and Ca ← E (E = P or N) interactions; moreover, the vinylarene ring counteracts unfavorable charge localization within the activated transition state. The additional stability of the Ca ← N over Ca ← P dative interaction in vinylpyridine provides a rationalization for the experimentally observed enhanced reactivity of vinylpyridine, particularly in the context of the almost identical local alkene insertion barriers. Previously, little emphasis has been placed on the involvement of noncovalent interactions; however, our calculations reveal that Ca···π, CH···π, and Ca ← donor interactions are critical, stabilizing key intermediates and transition states, while also introducing numerous competitive pathways.
Hunt PA, Ashworth C, Matthews R, et al., 2016, Doubly Ionic Hydrogen Bond Interactions Within the Choline Chloride - Urea Deep Eutectic Solvent, Physical Chemistry Chemical Physics, Vol: 18, Pages: 18145-18160, ISSN: 1463-9084
Deep eutectic solvents (DESs) are exemplars of systems with the ability to form neutral, ionic and doubly ionic H-bonds. Herein, the pairwise interactions of the constituent components of the choline chloride–urea DES are examined. Evidence is found for a tripodal CH⋯Cl doubly ionic H-bond motif. Moreover it is found that the covalency of doubly ionic H-bonds can be greater than, or comparable with, neutral and ionic examples. In contrast to many traditional solvents, an “alphabet soup” of many different types of H-bond (OH⋯O[double bond, length as m-dash]C, NH⋯O[double bond, length as m-dash]C, OH⋯Cl, NH⋯Cl, OH⋯NH, CH⋯Cl, CH⋯O[double bond, length as m-dash]C, NH⋯OH and NH⋯NH) can form. These H-bonds exhibit substantial flexibility in terms of number and strength. It is anticipated that H-bonding will have a significant impact on the entropy of the system and thus could play an important role in the formation of the eutectic. The 2 : 1 urea : choline–chloride eutectic point of this DES is often associated with the formation of a [Cl(urea)2]− complexed anion. However, urea is found to form a H-bonded urea[choline]+ complexed cation that is energetically competitive with [Cl(urea)2]−. The negative charge on [Cl(urea)2]− is found to remain localised on the chloride, moreover, the urea[choline]+ complexed cation forms the strongest H-bond studied here. Thus, there is potential to consider a urea[choline]+·urea[Cl]− interaction.
Hunt PA, Welton T, Hallett J, et al., 2016, Solubility of Alkali Metal Halides in the Ionic Liquid [C4C1im][OTf], Physical Chemistry Chemical Physics, Vol: 18, Pages: 16161-16168, ISSN: 1463-9084
The solubilities of the metal halides LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbCl, CsCl,CsI, were measured at temperatures ranging from 298.15 to 378.15 K in the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4C1im][OTf]). Li+, Na+and K+salts with anionsmatching the ionic liquid have been also investigated to determine how well these cations dissolve in[C4C1im][OTf]. This study compares the influence of metal cation and halide anion on the solubility ofsalts within this ionic liquid. The highest solubility found was for iodide salts and the lowestsolubility, for the three fluoride salts. There is no outstanding difference in the solubility of salts withmatching anions in comparison to halide salts. The experimental data were correlated employingseveral phase equilibria models, including ideal mixtures, van’t Hoff, the λh (Buchowski) equation,the modified Apelblat equation, and the non-random two-liquid model (NRTL). It was found that thevan’t Hoff model gave the best correlation results. On the basis of the experimental data thethermodynamic dissolution parameters (ΔH, ΔS, and ΔG) were determined for the studied systemstogether with computed gas phase metathesis parameters. Dissolution depends on the energydifference between enthalpies of fusion and dissolution of the solute salt. This demonstrates thatovercoming the lattice energy of the solid matrix is the key to the solubility of inorganic salts in ionicliquids.
Clough MT, Geyer K, Hunt PA, et al., 2016, Azoniaspiro salts: towards bridging the gap between room-temperature ionic liquids and molten salts., Physical Chemistry Chemical Physics, Vol: 18, Pages: 3339-3351, ISSN: 1463-9084
In a continued effort to improve the suitability of ionic liquids in applications operating at raised temperatures, novel spirocyclic 'azoniaspiro' salts (with cations derived from five-, six-, seven- and eight-membered rings) are prepared and characterised. The structural and thermal properties of these salts are compared against those of established analogues. The stable geometries and ion pairing behaviour of these species are investigated via a combined experimental/computational approach, employing X-ray crystallography and Density Functional Theory (DFT) methods. Subsequently, the thermal stabilities of these organic salts are characterised and compared using a broad range of techniques. Hyphenated Thermogravimetry-Mass Spectrometry investigations enable complex mechanisms underlying thermal decomposition to be elucidated. Lastly, transition state structures are optimised, corresponding to plausible decomposition mechanisms of the azoniaspiro salt, 6-azoniaspiro[6.5]dodecanium chloride, and one prototypical monocyclic species 1-butyl-1-methylpiperidinium chloride, using DFT. The observed improved thermal stabilities of the azoniaspiro salts, and their potential higher-temperature stable-liquid ranges, render them promising candidates for future ionic liquid applications.
Jackson G, Lau GV, Muller EA, et al., 2015, Water droplet excess free energy determined by cluster mitosis using guidedmolecular dynamics, Journal of Chemical Physics, Vol: 143, ISSN: 1089-7690
Atmospheric aerosols play a vital role in affecting climate by influencing the properties and lifetimes of clouds and precipitation. Understanding the underlying microscopic mechanisms involved in the nucleation of aerosol droplets from the vapour phase is therefore of great interest. One key thermodynamic quantity in nucleation is the excess free energy of cluster formation relative to that of the saturated vapour. In our current study, the excess free energy is extracted for clusters of pure water modelled with the TIP4P/2005 intermolecular potential using a method based on nonequilibrium molecular dynamics and the Jarzynski relation. The change in free energy associated with the “mitosis” or division of a cluster of N water molecules into two N/2 sub-clusters is evaluated. This methodology is an extension of the disassembly procedure used recently to calculate the excess free energy of argon clusters [H. Y. Tang and I. J. Ford, Phys. Rev. E 91, 023308 (2015)]. Our findings are compared to the corresponding excess free energies obtained from classical nucleation theory (CNT) as well as internally consistent classical theory (ICCT). The values of the excess free energy that we obtain with the mitosis method are consistent with CNT for large cluster sizes but for the smallest clusters, the results tend towards ICCT; for intermediate sized clusters, we obtain values between the ICCT and CNT predictions. Furthermore, the curvature-dependent surface tension which can be obtained by regarding the clusters as spherical droplets of bulk density is found to be a monotonically increasing function of cluster size for the studied range. The data are compared to other values reported in the literature, agreeing qualitatively with some but disagreeing with the values determined by Joswiak et al. [J. Phys. Chem. Lett. 4, 4267 (2013)] using a biased mitosis approach; an assessment of the differences is the main motivation for our current study.
Clough M, Geyer K, Hunt P, et al., 2015, Ionic liquids: Not always innocent solvents for cellulose, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Clough M, Grasvik J, Hunt P, et al., 2015, Physicochemical investigation of ionic liquid mixtures, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Lau GV, Ford IJ, Hunt PA, et al., 2015, Surface thermodynamics of planar, cylindrical, and spherical vapour-liquid interfaces of water, Journal of Chemical Physics, Vol: 142, ISSN: 1089-7690
Hunt PA, Ashworth CR, Matthews RP, 2015, Hydrogen bonding in ionic liquids, CHEMICAL SOCIETY REVIEWS, Vol: 44, Pages: 1257-1288, ISSN: 0306-0012
Xue L, Tamas G, Matthews RP, et al., 2015, An OHD-RIKES and simulation study comparing a benzylmethylimidazolium ionic liquid with an equimolar mixture of dimethylimidazolium and benzene, Physical Chemistry Chemical Physics, Vol: 17, Pages: 9973-9983, ISSN: 1463-9084
The principal difference between 1-benzyl-3-methyl-imidazolium triflimide [BzC1im][NTf2] and an equimolar mixture of benzene and dimethylimidazolium triflimide [C1C1im][NTf2] is that in the former the benzene moieties are tied to the imidazolium ring, while in the latter they move independently. We use femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) and molecular simulations to explore some properties of these two systems. The Kerr spectra show small differences in the spectral densities; the simulations also show very similar environments for both the imidazolium rings and the phenyl or benzene parts of the molecules. The low frequency vibrational densities of states are also similar in the model systems. In order to perform the simulations we developed a model for the [BzC1im]+ cation and found that the barriers to rotation of the two parts of the molecule are low.
Scarbath-Evers LK, Hunt PA, Kirchner B, et al., 2015, Molecular features contributing to the lower viscosity of phosphonium ionic liquids compared to their ammonium analogues, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 20205-20216, ISSN: 1463-9076
Matthews RP, Welton T, Hunt PA, 2015, Hydrogen bonding and pi-pi interactions in imidazolium-chloride ionic liquid clusters, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 14437-14453, ISSN: 1463-9076
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