Effect of Ethylene Glycol on the Molecular Organization of H₂O in Comparison with Methanol and Glycerol: A Calorimetric Study

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• 作者：Koga ; Yoshikata
• 关键词：Ethylene glycol– ; H2O ; methanol ; or glycerol– ; H2O ; excess partial molar enthalpy ; enthalpic interaction ; mixing schemes ; effect on the molecular organization of H2O
• 刊名：Journal of Solution Chemistry
• 出版年：2003
• 出版时间：2003
• 年：2003
• 卷：32
• 期：9
• 页码：803-818
• 全文大小：132 KB

文摘

Excess partial molar enthalpies of ethylene glycol, H^E_EG, in binary ethylene glycol–H₂O, and those of 1-propanol, H^E_IP, in ternary 1-propanol–ethylene glycol (or methanol)–H₂O were determined at 25°C. From these data, the solute–solute interaction functions, H^E_EG−EG = N(∂H^E_EG/∂n_EG) and H^E_1P−1P = N(∂H^E_1P/∂n_1P), were calculated by graphical differentiation without resorting to curve fitting. Using these, together with the partial molar volume data, the effect of ethylene glycol on the molecular organization of H₂O was investigated in comparison with methanol and glycerol. We found that there are three concentration regions, in each of which the mixing scheme is qualitatively different from the other regions. Mixing scheme III operative in the solute-rich region is such that the solute molecules are in a similar situation as in the pure state, most likely in clusters of its own kind. Mixing scheme II, in the intermediate region, consists of two kinds of clusters each rich in solute and in H₂O, respectively. Thus, the bond percolation nature of the hydrogen bond network of liquid H₂O is lost. Mixing scheme I is a progressive modification of liquid H₂O by the solute, but the basic characteristics of liquid H₂O are still retained. In particular, the bond percolation of the hydrogen bond network is still intact. Similar to glycerol, ethylene glycol participates in the hydrogen bond network of H₂O via-OH groups, and reduces the global average of the hydrogen bond probability and the fluctuations inherent in liquid H₂O. In contrast to glycerol, there is also a sign of a weak hydrophobic effect caused by ethylene glycol. However, how these hydrophobic and hydrophilic effects of ethylene glycol work together in modifying the molecular organization of H₂O in mixing scheme I is yet to be elucidated.