@article {2460,
	title = {Hydrophobicity/Hydrophilicity of 1-Butyl-2,3-dimethyl and 1-Ethyl-3-methylimodazolium Ions: Toward Characterization of Room Temperature Ionic Liquids},
	journal = {Journal of Physical Chemistry B},
	volume = {113},
	number = {44},
	year = {2009},
	note = {ISI Document Delivery No.: 510QMTimes Cited: 2Cited Reference Count: 52Kato, Hitoshi Miki, Kumiko Mukai, Tomohiro Nishikawa, Keiko Koga, Yoshikata},
	month = {Nov},
	pages = {14754-14760},
	type = {Article},
	abstract = {We continue to experimentally characterize the constituent ions of room temperature ionic liquids in terms of their interactions with H2O. By using the so-called 1-propanol probing methodology, we experimentally index the relative hydrophobicity/hydrophilicity of a test ion. In this paper, we examine 1-butyl-2,3 dimethylimidazolium (abbreviated as [C(4)C(1)mim](+)) and 1-ethyl-3-methylimidazolium ([C(2)mim](+)). We found that [C(4)C(1)mim](+) dissociates completely in dilute aqueous solution less than 0.006 mol fraction, and hence, its hydrophobicity/hydrophilicity could be determined. The results indicate that [C(4)C(1)mim](+) is highly amphiphilic with much stronger hydrophobicity and hydrophilicity than normal ions. Our earlier similar studies indicated the same conclusion for such typical constituent ions as 1-butyl-3-methylimidazolium ([C(4)mim](+)) PF6-, CF3SO3-, and N(SO2CF3)(2)(-). Hence, we suggest that the constituent ions of room temperature ionic liquids that we have studied so far are all amphiphiles with much stronger hydrophobicity and hydrophilicity than normal ions. We found, furthermore, that the hydrophobicity and hydrophilicity of [C(4)C(1)mim](+) are stronger than those for [C(4)mim](+). A possible reason for higher hydrpohilicity is discussed in terms of strong acidic character of H on the C(2) of the imidazolium ring, which tends to attract the delocalized positive charge toward itself oil forming a hydrogen bond to H2O. On replacing it with CH3 in [C(4)C(1)mim](+), the lack of acidic H enhances the positive charge in the vicinity of N-C-N in the ring that interacts with the surrounding H2O strongly to an induced dipole of O of the H2O. For [C(2)mim](+), we found it does not dissociate completely, even in dilute aqueous solution, and hence, we could not characterize it within the present methodology.},
	keywords = {1-BUTYL-3-METHYLIMIDAZOLIUM BROMIDE, AGGREGATION BEHAVIOR, ALKYL CHAIN-LENGTH, APPROACH, AQUEOUS-SOLUTIONS, HOFMEISTER SERIES, MIXING SCHEMES, MOLECULAR-ORGANIZATION, partial molar enthalpy, PHYSICOCHEMICAL PROPERTIES, THERMODYNAMIC},
	isbn = {1520-6106},
	url = {<Go to ISI>://000271105600027},
	author = {Kato, H. and Miki, K. and Mukai, T. and Nishikawa, K. and Koga,Yoshikata}
}
@article {2620,
	title = {Structural and dynamical properties of ionic liquids: The influence of charge location},
	journal = {Journal of Chemical Physics},
	volume = {130},
	number = {10},
	year = {2009},
	note = {ISI Document Delivery No.: 420IFTimes Cited: 8Cited Reference Count: 31Spohr, H. V. Patey, G. N.},
	month = {Mar},
	pages = {11},
	type = {Article},
	abstract = {The properties of ionic liquids depend on the chemical structure of the constituent ions. An important difference between molten inorganic salts and room temperature ionic liquids (RTILs) is that in RTILs the charge is frequently not located at the center of mass. This paper describes a molecular dynamics investigation of the influence of charge location on the structure and transport properties of ionic liquids. The model considered consists of univalent spherical ions with the cation charge moved away from its center of mass. It is shown that the charge location has an important influence on the liquid properties. As the charge is moved off center, the electrical conductivity initially increases, and the shear viscosity decreases. However, when the charge exceeds a certain displacement, this behavior is reversed. With further charge displacement, the conductivity decreases sharply and the viscosity increases rapidly. This behavior reversal can be traced to the formation of directional ion pairs that are present in sufficient numbers, and have lifetimes sufficiently long to strongly influence the liquid properties. We suggest that the influence of directional ion pairing can explain what appear to be anomalously low conductivities and high viscosities observed for some RTILs. The rotational and reorientational motions of the cations are examined, and shown to be strongly influenced by ion-pair formation when the charge is far off center. The temperature dependence of the transport properties is considered for selected systems, and deviations from Arrhenius behavior are found to be most important for the conductivity. Based on our results, this possibly indicates that directional ion pairs create an additional "barrier" to charge transport in some ionic liquids.},
	keywords = {ANION, DIFFUSION, electrical conductivity, HYDROGEN-BONDS, liquid metals, liquid structure, liquid theory, molecular dynamics method, MOLECULAR-DYNAMICS, PHYSICOCHEMICAL PROPERTIES, pressure, TEMPERATURE, TRANSPORT-PROPERTIES, VISCOSITIES, VISCOSITY},
	isbn = {0021-9606},
	url = {<Go to ISI>://000264281800024},
	author = {Spohr, H. V. and Patey, G. N.}
}
@article {2258,
	title = {Structural and dynamical properties of ionic liquids: The influence of ion size disparity},
	journal = {Journal of Chemical Physics},
	volume = {129},
	number = {6},
	year = {2008},
	note = {ISI Document Delivery No.: 338FDTimes Cited: 10Cited Reference Count: 28Spohr, H. V. Patey, G. N.},
	month = {Aug},
	pages = {8},
	type = {Article},
	abstract = {The influence of ion size disparity on structural and dynamical properties of ionic liquids is systematically investigated employing molecular dynamics simulations. Ion size ratios are varied over a realistic range (from 1:1 to 5:1) while holding other important molecular and system parameters fixed. In this way we isolate and identify effects that stem from size disparity alone. In strongly size disparate systems the larger species (cations in our model) tend to dominate the structure; the anion-anion distribution is largely determined by anion-cation correlations. The diffusion coefficients of both species increase, and the shear viscosity decreases with increasing size disparity. The influence of size disparity is strongest up to a size ratio of 3:1, then decreases, and by 5:1 both the diffusion coefficients and viscosity appear to be approaching limiting values. The conventional Stokes-Einstein expression for diffusion coefficients holds reasonably well for the cations but fails for the smaller anions as size disparity increases likely due to the neglect of strong anion-cation correlations. The electrical conductivity is not a simple monotonic function of size disparity; it first increases up to size ratios of 2:1, remains nearly constant until 3:1, then decreases such that the conductivities of the 1:1 and 5:1 systems are similar. This behavior is traced to the competing influences of ion diffusion (enhancing) and ion densities (reducing) on conductivities at constant packing fraction. The temperature dependence of the transport properties is examined for the 1:1 and 3:1 systems. In accord with experiment, the temperature dependence of all transport properties is well represented by the Vogel-Fulcher-Tammann equation. The dependence of the diffusion coefficients on the temperature/viscosity ratio is well described by the fractional Stokes-Einstein relation D proportional to(T/eta)(beta) with beta approximate to 0.8, consistent with the exponent observed for many molten inorganic salts.},
	keywords = {MOLECULAR-DYNAMICS, PHYSICOCHEMICAL PROPERTIES, pressure, SIMULATION, TRANSPORT-PROPERTIES},
	isbn = {0021-9606},
	url = {<Go to ISI>://000258490600052},
	author = {Spohr, H. V. and Patey, G. N.}
}
