Effect of Ethylene Gycol on the Molecular Organization of H_2O in Comparison with Methanol and Glycerol:A Calorimetric Study

摘要

Excess partial molar enthalpies of ethylene glycol,H_(EG)~E,in binary ethylene glycol-H_2O,and those of 1-propanol,H_(IP)~E,in ternary 1-propanol-ethylene glycol (or metanol)-H_2O were determined at 25 deg C.From these data,the solute-solute interaction functions,H_(EG-EG)~E=N(partial deriv)H_(EG)~E/(partial deriv)_(EG))and H_(1P-1P)~E=N((partial deriv)H_(1P)~E/(partial deriv)n_(1P)),were calculated buy 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 H_2O was investigated in comparison with methanol and glycerol.We found that there are three concentration regions,in each of which the mixing scheme is quaitatively different from the other regions.Mixing scheme III operative in the solute-rich region is such that the solute moelcules 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 H_2O,respectively.Thus,the bond percolation nature of the hydrogen bond network of liquid H_2O is lost.Mixing scheme I is a progressive modification of liquid H_2O by the solute,but the basic characteristics of liquid H_2O are still retained.In particular,the bond percolation of the hydrogen bond probability and the fluctuations inherent in liquid H_2O.In contrast to glycerol,there is also a sign of a weak hydrophobic effect caused by ethylene glycol.However,how thesehydrophobic and hydrohilic effects of ethylene glycl work toether in modyfying the molecular organization of H_2O in mixing scheme I is yet to be elucidated.