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Thermodynamic Property of Aqueous Solutions

We are studying the mixing schemes in aqueous solution by novel methodology using calorimetric and vapor pressure measurements. Excess partial molar enthalpy of X, HXE, and excess chemical potential of X, mXE can be determined from calorimetry and vapor pressure measurement, respectively. Excess partial molar entropy can be calculated from HXE and mXE. In terms of enthalpy, for example, we evaluate enthalpic X-X interaction function, HX-XE from differentiation of HXE from amount of X. For binary 1-propanol (1P)-H2O, HX-XE shows a sharp peak abnormally (Fig. 1). Dr. Koga (The University of British Columbia) et al. earlier concluded that this peak abnormally indicates hydration bond percolation threshold, i.e. the whole hydrogen bond network of H2O is percolated in the H2O-rich region and not percolated in the 1P-rich region.

Recently we evaluate x1P- and xS-dependence of these quantities in ternary 1P-H2O-S in order to learn about the effects of S on the molecular organization of H2O. Presence of S induces the peak pattern to change. The induced changes are used to learn about the effect of S on H2O, e.g. hydrophobic, hydrophilic or amphiphilic (Fig. 2). We can also learn hydrophobicity or hydrophilicity of S by comparison with degree of the shift of the peak anomaly. Thus we study the effects of S in aqueous solution using the thermodynamic behavior of 1P as a probe.

Fig. 1 x1P-dependence of Enthalpic 1P-1P interaction function for 1P-H2O at 25 oC

Fig. 2. Schematic graph of the x1P-dependences of H1P-1PE for binary 1P-H2O (O) and ternary 1P-H2O-S (A-C).

Reference. Y. Koga, Solution Thermodynamics and its Application to Aqueous Solutions: A Differential Approach. Elsevier, Amsterdam (2007).

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