The influences of hydroxyl functional group (-OH) on the thermodynamic and structural properties of ionic liquids (ILs) composed of 1-(2-Hydroxyethyl)-3-methyl imidazolium ([C2OHmim](+)) cation and the six different conventional anions, including [Cl](-), [NO3](-), [BF4](-), [PF6](-), [TfO](-), and [Tf2N](-) have been extensively investigated using classical molecular dynamics (MD) simulations combined with ab initio calculations over a wide range of temperature (298-550 K). The volumetric thermodynamic properties, enthalpy of vaporization, cohesive energy density, Hildebrand solubility parameter, and heat capacity at constant pressure were estimated at desired temperature. The simulated densities were in good agreement with the experimental data with a slight overestimation. The interionic interaction of selected ILs was also computed using both the MD simulations and ab initio calculations. It was found that the highest association of cation and anion is attributed to [C2OHmim][Cl] followed by [C2OHmim][NO3], and [C2OHmim][Tf2N] with the bulkiest anion has the weakest interionic interaction among chosen ILs. The similar trend of interactions energies was nearly observed from cohesive energy density results. Additional structural details were comprehensively yielded by calculating radial distribution functions (RDFs) and spatial distribution function (SDFs) at 358 K. The most stable configurations of isolated and dimer ion pairs of these ILs were in excellent consistency with RDFs and SDFs results. Significant changes in arrangement of anions around the [C2OHmim](+) cation in comparison with conventional imidazolium-based ILs can be inferred from the MD simulations and ab initio results. Also, microscopic structural properties disclosed that the most strong cation-cation interaction is ascribed to the hydroxyl-functionalized ILs composed of bulkier anions, whereas ILs incorporating [Cl](-) and [NO3](-) anions are mainly involved in cation-anion interactions. The formation of the intramolecular hydrogen bonding in the [C2OHmim](+) cation is another interesting result of the present study.

Molecular dynamics simulations of four ionic liquids (ILs) based on the [Tf 2 N] − , bis(trifluoromethanesulfonyl)imide anion, and imidazolium cations with different alkyl side chains have been performed. These simulations investigate the influence of butyl side chain elimination, tail amine functional addition, and C2 methylation on the dynamics and transport properties of this family of ionic liquids at 400 K. In our earlier work (J. Chem. Eng. Data, 2014, 59, 2834−2849), a suite of thermodynamic quantities and microscopic structures of these ILs were studied by classical molecular dynamics simulations and ab initio calculations. In this work, the dynamics of the ILs are studied by calculating the mean-square displacement (MSD) and the velocity autocorrelation function (VACF) for selected atomic sites and the centers of mass of the ions. These results are used to calculate the self-diffusion and the ionic conductivity from both the Einstein and Green−Kubo formulas. The calculated ionic self-diffusion coefficients are used to estimate the cationic transference number and the Stokes−Einstein viscosity for the four ILs. In agreement with experiments, the general simulated trends in the MSD, self-diffusion, and ionic conductivity are [bmim][Tf 2 N] > [apmim][Tf 2 N] > [bmmim][Tf 2 N] > [mim][Tf 2 N]. These trends are the reverse of the trend in the viscosity of four selected ILs. As expected by applying a nonpolarizable force field, the simulation results tend to underestimate the self-diffusivity and conductivity, and overestimate the shear viscosity. The highest and the lowest degrees of ionic association are detected for [mim][Tf 2 N] and [bmim][Tf 2 N], respectively.

The effects of incorporating the ester functional group (COO) into the side chain of the 1-alkyl-3methylimidazolium cation ([C 1 COOC n C 1 im] + , n = 1, 2, 4) paired with [Br] − , [NO 3 ] − , [BF 4 ] − , [PF 6 ] − , [TfO] − , and [Tf 2 N] − anions on the various thermodynamic properties and interaction energies of these biodegradable ionic liquids (ILs) were investigated by means of molecular dynamics (MD) simulations combined with ab initio calculations in the temperature range of 298−550 K. Excluding the simulated density, the highest values of the volumetric properties such as molar volume, isobaric expansion coefficient, and isothermal compressibility coefficient can be attributed to the largest cation incorporated with the weakest coordinating anion, [Tf 2 N] − , and the minimum of the corresponding properties correspond to the smallest cation, especially when combined with the smaller anions, including [NO 3 ] − and [Br] − . In addition, ion-pair, cationic, and anionic volumes were computed using MD simulations as well as ab initio calculations. The results revelaed an increasing trend in the molar enthalpy of vaporization. The reverse trends of the volumetric properties were observed for the cohesive energy density, Hildebrand solubility parameter, surface tension, surface excess enthalpy, lattice energy, thermal pressure, internal pressure, binding energy, and interaction energy. On the basis of the optimized structures, we believed that a reduction in the strength of the hydrogen bonds due to the larger charge distribution and steric hindrance of bulkier ions is responsible for the observed trends. These results were also confirmed by calculating the critical and boiling temperatures (by two different empirical equation), surface excess enthalpies, parachors, and standard molar entropies. The other derivatives of the thermodynamic properties such as the isobaric and isochoric heat capacities, isothermal bulk moduli, and speeds of sound in the ILs were computed as functions of temperature. Interestingly, a direct relationship was found between the simulated results for the surface tension and the computed values of the bulk modulus. Furthermore, it was found that sound waves are transmitted faster in a compact IL than in a compressible IL. In addition, for each IL, the molar refraction, refractive index, dielectric constant, and mean static polarizability were approximated at room temperature. The smallest values of these properties were observed for ILs composed of the spherically symmetric anions [PF 6 ] − and [BF 4 ] − . In addition, the formation of multiple intramolecular hydrogen bonds between the O atoms of the ester functional group and the hydrogen atoms of the cation was also observed for all optimized conformations. Finally, the obtained results demonstrate that the introduction of an ester group significantly increases the interionic interactions and, subsequently, the packing efficiency of these ILs in comparison with those of conventional imidazolium-based ILs.

The effects of ester addition on nanostructural properties of biodegradable ILs composed of 1-alkoxycarbonyl-3-alkyl-imidazolium cations ([C1COOCnC1im](+), n = 1, 2, 4) combined with [Br](-), [NO3](-), [BF4](-), [PF6](-), [TfO](-), and [Tf2N](-) were explored by using the molecular dynamics (MD) simulations and quantum theory of atoms in molecules (QTAIM) analysis at 400 K. Various thermodynamic properties of these ILs were extensively computed in our earlier work (Ind. Eng. Chem. Res., 2015, 54, 11678-11700). Nano-scale segregation analysis demonstrates the formation of a small spherical island-like hydrocarbon within the continuous ionic domain for ILs with short alkyl side chain ([C1COOC1C1im]), and a sponge-like nanostructure for the compound with long alkyl side chain ([C1COOC4C1im]). Ester-functionalized ILs with ethyl side chain ([C1COOC2C1im]) are the turning point between two different morphologies. Non-polar channels were observed for [C1COOC4C1im] ILs composed of smaller anions such as [Br] and [NO3], whereas clustering organization was found for the other anions. Formation of the spherical micelle-like nanostructure was seen for lengthened cations. Finally, the incorporation of an ester group into the alkyl side chain of the cation leads to stronger segregation between charged and uncharged networks, which consequently increased the possibility of self-assembly and micelle formation.

All-atom molecular dynamics simulations combined with ab initio calculations are used to study the thermodynamic properties and microscopic structure of four ionic liquids (ILs) based on the imidazolium cation with different alkyl side branches, ([bmmim] + , 1-butyl-2,3-dimethylimidazolium; [bmim] + , 1-butyl-3-methylimidazolium; [apmim] + , 1-(3-aminopropyl)-3-methylimidazolium; [mim] + , 1-methylimidazolium), paired with the [(CF 3 SO 2 ) 2 N] − , bis-(trifluoromethanesulfonyl)imide anion, in the temperature range of (298 to 600) K. We observed the highest value of the molar internal energy, enthalpy of vaporization, and cohesive energy density for the amine-functionalized [apmim][Tf 2 N] ionic liquid. Structural analysis shows that the amine functionalization of the end of the alkyl side chain of imidazolium cation does not significantly affect the organization of [Tf 2 N] − around [apmim] + , but additional NH 2 groups lead to short-range cation−cation structural correlations between neighboring [apmim] + . The C2 methylation extensively affects preferential out-of-plane face-toface locations of [Tf 2 N] − around [bmmim] + and also the cation−cation distributions. [mim][Tf 2 N] has the highest simulated density and better packing efficiency of liquid phase in comparison with other studied ILs. The strongest first shell probability density region of [mim] + neighbors above and below the imidazolium ring of the reference cation represents better π−π stacking in the liquid phase of this ionic liquid. The presented results determine the role of the cation structure on the properties of this family of ILs. Good agreement was achieved between simulation results of the bulk phase and quantum calculations which are performed to determine the optimized structure of isolated ion pairs in chosen configurations and the strength of cation−anion interactions.

Solvatochromic UV−vis shifts of three probes 4-nitroaniline, 4-nitroanisol, and Reichardt's dye in binary mixtures of polyethylene glycol p-(1,1,3,3tetramethylbutyl)-phenyl ether (Triton X-100 or TX-100) with methanol, ethanol, 1propanol, and water have been investigated at 298 K. Structural and intermolecular interactions of solvatochromic probes were determined in these systems. Solvatochromic parameters, including normalized polarity (E T N ), dipolarity-polarizability (π*), hydrogenbond donor (α), and hydrogen-bond acceptor (β) abilities, were measured at a wide range of mole fraction (0 ≤ X ≤ 1) with 0.1 increment. Interestingly, a similar behavior of E T N and α is observed in alcohols/TX-100 mixtures. The E T N parameters obtained from absorbance of Reichardt's dye within various mixtures of surfactant were observed to be lower than predicted values from ideal additive behavior. A negative deviation from ideality is shown by E T N parameter in all alcohols/TX-100 mixtures, while a fluctuated behavior for other probes can be seen. The optimized geometries exhibit that the hydroxyl (−OH) group on the side chain of TX-100 significantly affects the arrangement of the selected solvents around TX-100. All binary systems show complex behavior for chosen probes. The results demonstrate that 4-nitroanisole and Reichardt's dye have stronger interactions with binary mixtures of alcohols/TX-100 systems. Synergistic solvation behavior for water/TX-100 was observed. Preferential solvation model was applied for the first time in the surfactant binary mixtures and from this model information solute−solvent and solvent−solvent interactions were interpreted. Preferential solvation (specific solute−solvent interactions) or the solvent−solvent interaction is the reason for deviation from ideal behavior of probes. As a main result, alkyl chain length of alcoholic solvents does not have impressive effects on predicted trends of solvatochromic parameters. Ab initio calculations of solvents/TX-100 mixtures demonstrate the following trend for magnitude order of interactions: water > methanol > ethanol >1-propanol. Electrostatic potential map is another confident evidence for predicted order.

The effects of ester addition on structural and dynamic properties of biodegradable ILs composed of the 1-(alkoxycarbonyl)-3-alkylimidazolium cation ([CCOOCCim], n = 1, 2, 4) coupled with [Br], [NO], [BF], [PF], [TfO], and [TfN] are explored using the molecular dynamics (MD) simulations and quantum theory of atoms in molecules (QTAIM) at 400 K. Formation of the intramolecular H bonds between O atoms of the ester group and H atoms of the imidazolium ring as well as the nearest H atom of the alkyl chain to the ester group are disclosed from reduced density gradient (RDG) results. Nanoscale organization that leads to aggregation of the alkyl chain into the uncharged domains and formation of different morphologies can be clearly found by the results of site-site static partial structure factors of cations. Despite the fact that H atoms of the imidazolium ring are more acidic than the nearest H atoms of the alkyl side chain to the ester group, the cation-cation spatial distribution functions (SDFs) and the velocity SDFs demonstrate a reverse trend. This corresponds to the long-range organization of cations and nanoscale arrangement. Transport properties were calculated using the Green-Kubo and Einstein relations. Cations totally diffuse faster than anions and their discrepancies gradually vanish with elongation of the alkyl side chain. The translational motion of the terminal carbon atoms of the ester-functionalized cations decrease when the alkyl group is elongated, whereas the reverse trend is reported for common imidazolium-based ILs. The dynamic heterogeneity of selected ILs is comprehensively investigated by the computing vibrational density of states, van Hove function, and non-Gaussian parameter. Non-Gaussian parameters are finite over the entire time scale for ILs composed of bulkier cations and diverge from zero, verifying the long-lived cage effect. Nanoscale ordering is believed to be responsible for these observations. Finally, the simulated viscosity and ionic conductivity are in good agreement with the experimental data.

The reverse osmosis (RO) desalination capability of hydrogenated and hydroxylated graphene nanomesh membranes (GNMs) inspired by the morphology of carbon nitride (C 2 N) has been studied by using molecular dynamics simulation. As an advantage, water permeance of the GNMs is found to be several orders of magnitude higher than that of the available RO filters and comparable with highly strained C 2 N (S-C 2 N) as follows: 6,6-H,OH > 12-H > S-C 2 N > 5,5-H,OH > 10-H. The reverse order is found for salt rejection, regardless of S-C 2 N. The hydrophilic character of the incorporated −OH functional group is believed to be responsible for linking the water molecules in feed and permeate sides via the formation of strong hydrogen bonds. This leads to a remarkable reduction in resistance of water molecules during penetration across GNMs. In fact, water permeance and salt rejection of the GNMs are controllable by adjusting the effective size and chemistry of their nanopores, while these kinds of adjustments are principally impossible for C 2 N, resulting in limiting the water permeance. More importantly, the C 2 N nanofilter works efficiently only under high tensile strain, which is not so straightforward in practice. These observations are also verified by computing electrostatic potential map interaction and barrier energies for transportation of water molecules/ions through GNMs based on quantum chemistry aspects.