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Material preparation in ionic liquids and environmental pollution control by ionic liquids are often closely dependent on the aggregation behavior of ionic liquids in solution. In the present work, conductivity, fluorescence probe, and dynamic light scattering techniques have been used to study the effect of organic solvents on the aggregation behavior of 1-dodecyl-3-methylimidazolium bromide in water. It was shown that the critical aggregation concentration (CAC), the ionization degree of the aggregates (α), and the standard Gibbs energy of aggregation (ΔGm°) of the ionic liquid increase, while its aggregation number (Nagg) and aggregates’ size decrease with increasing concentration of organic additives in water. These results have been discussed from the favorable interactions of alkyl chain of the ionic liquid with the mixed solvents. It is suggested that the solvophobic parameter, characterized quantitatively by Gibbs energy of transfer of hydrocarbon from gas into a given solvent, can be used to account for the effect of organic additives on the formation and growth of the ionic liquid aggregates in water. Aggregation behavior of ionic liquids in aqueous organic solutions can be modulated simply by the solvophobic parameters of hydrocarbon in the mixed solvents. [ABSTRACT FROM AUTHOR]

Thermodynamicdissociation constants of the Brønsted acidicionic liquids (ILs) are important for their catalytic and separationapplications. In this work, a series of imidazolium bromides withone carboxylic acid substitute group in their alkyl chain ([{(CH2)nCOOH}mim]Br, n= 1,3,5,7) have been synthesized, and their dissociation constants(pKa) at different ionic strengths havebeen determined in aqueous and aqueous organic solvents at 0.1 molefraction (x) of ethanol, glycol, iso-propanol, anddimethyl sulfoxide by potentiometric titrations at 298.2 K. The standardthermodynamic dissociation constants (pKaT) of the ILs in these solvents were calculated from theextended Debye–Hückel equation. It was found that thepKavalues increased with the increaseof ionic strength of the media and of the addition of organic solventin water. The pKaTvalues alsoincreased with the increase of the alkyl chain length of cations ofthe ILs. In addition, the effect of solvent nature on pKaTvalues is interpreted from solvation ofthe dissociation components and their Gibbs energy of transfer fromwater to aqueous organic solutions. [ABSTRACT FROM AUTHOR]

Recently,it has been reported that addition of a cosolvent significantlyinfluences solubility of cellulose in ionic liquids (ILs), but littleis known about the influence mechanism of the cosolvent on the molecularlevel. In this work, four kinds of typical molecular solvents (dimethylsulfoxide (DMSO), N,N-dimethylformamide(DMF), CH3OH, and H2O) were used to investigatethe effect of cosolvents on cellulose dissolution in [C4mim][CH3COO] by molecular dynamics simulations and quantumchemistry calculations. It was found that dissolution of cellulosein IL/cosolvent systems is mainly determined by the hydrogen bondinteractions between [CH3COO]−anionsand the hydroxyl protons of cellulose. The effect of cosolvents onthe solubility of cellulose is indirectly achieved by influencingsuch hydrogen bond interactions. The strong preferential solvationof [CH3COO]−by the protic solvents (CH3OH and H2O) can compete with the cellulose–[CH3COO]−interaction in the dissolution process,resulting in decreased cellulose solubility. On the other hand, theaprotic solvents (DMSO and DMF) can partially break down the ionicassociation of [C4mim][CH3COO] by solvationof the cation and anion, but no preferential solvation was observed.The dissociated [CH3COO]−would readilyinteract with cellulose to improve the dissolution of cellulose. Furthermore,the effect of the aprotic solvent-to-IL molar ratio on the dissolutionof cellulose in [C4mim][CH3COO]/DMSO systemswas investigated, and a possible mechanism is proposed. These simulationresults provide insight into how a cosolvent affects the dissolutionof cellulose in ILs and may motivate further experimental studiesin related fields. [ABSTRACT FROM AUTHOR]

Dilution enthalpies and mixing enthalpies of sodium halideandsome saccharides (glucose, galactose, xylose, arabinose, fructose,and sucrose) in aqueous solution were determined by calorimetric measurementsat 298.15 K. The values were used to determine enthalpic pair interactionparameters. Combined with Gibbs energy pair parameters, entropic pairinteraction parameters were also obtained. Theoretical calculationsat the B3LYP/6-311(d,p) level were carried out to provide the informationof structures and thermodynamic functions. The information revealsthe thermodynamic essence of the interactions between sodium halideand saccharides in aqueous solutions. The experimental results andtheoretical calculations show that the sign of enthalpic pair interactionparameter 2υhESis determined bythe direct interaction between saccharides and ions, whereas the differencein value of 2υhESfor differentsaccharides or electrolytes depends on the partial dehydration ofsaccharides or anions in aqueous solution. The difference in valueof entropic pair interaction parameters depends partly on the differentdominant interactions in the process of partial dehydration of saccharidesor ions. An enthalpy–entropy compensation relationship wasobserved for the sodium bromide–aldopyranose–water systems.Remarkably, it can be conjectured that the hydration entropy of glucoseis lower than for other monosaccharides. Perhaps it is one of thereasons why glucose plays an important role in living organisms ratherthan other monosaccharides. [ABSTRACT FROM AUTHOR]