Enthalpic interactions in aqueous strong electrolytes upon addition of ionic liquids

The present study deals with the inter-ionic interactions between strong electrolytes and ionic liquids based on the thermodynamic properties such as excess partial molar enthalpy, HEIL, relative apparent molar enthalpy, ϕL, and the enthalpic interaction parameters.

Thermodynamic properties of water in the water-poor region of binary water + alcohol mixtures

In our previous thermodynamic studies, we suggested that alcohol molecules in water-poor water + alcohol mixtures exist as alcohol clusters in a form similar to the pure alcohols. Here, we use calorimetry and densitometry to investigate how H2O interacts with alcohol clusters in water-poor binary aqueous mixtures of 12 different alcohols. The composition dependence of the measured excess partial molar enthalpy and volume of water (HEW and VEW), along with entropy data calculated from HEW and literature data for excess chemical potentials, showed that in water-poor solutions of small alcohols such as methanol, ethanol, and 1-propanol, mutual water–water interactions are endothermic, but entropically favorable. Conversely, in long-chain solvents such as 1-octanol and 1-decanol, the interaction is exothermic and entropically unfavorable. We suggest that these observations reflect water–alcohol hydrogen bonding in short-chain solvents and water clustering with more hydrogen bonding than in pure water or "dewetting" in mixtures of the longer alcohols, respectively. The composition dependence of HEW was also used to locate anomalies that specify the boundary between the mixing schemes characterizing the intermediate and the water-poor regions of alcohol + water mixtures.Key words: aqueous alkane-mono-ols, excess partial molar enthalpy, entropy and volume, mixing schemes.

Fluctuations in aqueous methanol, ethanol, and propan-1-ol: amplitude and wavelength of fluctuation

Density, heat capacity, and isentropic compressibility data for aqueous methanol, ethanol, and propan-1-ol by Benson's group were used to evaluate two kinds of fluctuations; mean-square fluctuation densities; and (mean-square) normalized fluctuations, respectively, in volume, entropy, and cross (entropy/volume) effect. The mean-square fluctuation densitiesprovide measures for the amplitude (intensity) of the fluctuation, while the normalized fluctuations contain information regarding the wavelength (extensity) of the fluctuation. Furthermore, their composition derivatives, the partial molar fluctuationsof alcohols were calculated. These quantities signify the effect of additional solute on the respective fluctuations. These data were interpreted in terms of mixing schemes learned earlier in this laboratory by using the data of excess partial molar enthalpy, entropy, and volume, and the respective alcohol-alcohol interaction functions, i.e., the composition derivatives of partial molar quantities. Key words: aqueous methanol, ethanol, and propan-1-ol;fluctuation density; normalized fluctuation; partial molar fluctuations of alcohol.

Excess partial molar enthalpies of 2-butoxyethanol and water in 2-butoxyethanol–water mixtures

Excess partial molar enthalpies of 2-butoxyethanol (BE) and water, [Formula: see text](I = BE or H2O), were measured from 25 to 35 °C in the entire concentration range. The results indicated that there are three concentration regions bounded at about xB = 0.02 and xB = 0.5, xB being the mole fraction of BE. In each region, the concentration and temperature dependence of [Formula: see text] (I = BE or H2O), is distinctively different from those in the other regions, and appears to support the following views: In the water-rich region, xB < 0.02, BE molecules cause an enhancement in the structure of water, and this effect spans a long range via a structurally enhanced network of water. The solute–solute (BE–BE) interaction is repulsive and of a long range character in terms of enthalpy. As xB increases, the repulsive solute–solute interaction becomes stronger sharply to the threshold value, xB ≈ 0.017, whereupon the mode of such mixing no longer becomes possible. In the intermediate range, 0.02 < χB < 0.5, a new scheme whereby BE molecules tend to associate is predominant. Two clathrate-like aggregates of the types h[BE(H2O)k] with k = 55 and 4 may exist together with BE clusters (BE)n In the third region, 0.5 < xB, BE molecules are exactly in the same environment as in pure liquid, while water molecules are almost in the same environment as in pure water. The solution consists of BE and water clusters. Keywords: excess partial molar enthalpy, 2-butoxyethanol–water.