Thermal Properties and Mixing State of Diol−Water Mixtures Studied by Calorimetry, Large-Angle X-Ray Scattering, and NMR Relaxation

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• 作者：Toshiyuki Takamuku ; Youichi Tsutsumi ; Masaru Matsugami ; Toshio Yamaguchi
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：October 23, 2008
• 年：2008
• 卷：112
• 期：42
• 页码：13300-13309
• 全文大小：277K
• 年卷期：v.112,no.42(October 23, 2008)
• ISSN：1520-5207

文摘

Differential scanning calorimetry (DSC) has been performed on aqueous mixtures of three diols, which involve a linear carbon chain, HO−(CH₂)_n−OH (n = 3, 4, and 5), over the whole mole fraction range of diols. The DSC results have shown the alkyl chain parity for the freezing process of the aqueous mixtures: aqueous mixtures of 1,3-propanediol (PrD) and 1,5-pentanediol (PeD) are kept in the supercooled state or vitrified over a wide mole fraction range, while those of 1,4-butanediol (BuD) are easily crystallized. The structure of PrD−water mixtures has been elucidated by using the large-angle X-ray scattering (LAXS) technique. It has been suggested that the structural change of PrD−water mixtures occurs at PrD mole fractions of x_PrD = 0.4 and 0.8: in the range of x_PrD ≤ 0.4 where the tetrahedral-like structure of water predominates, in the range of 0.4 < x_PrD < 0.8 where both PrD and water structures coexist, and in the range of x_PrD ≥ 0.8 where the inherent structure of PrD is mainly formed. ¹⁷O and ¹H NMR relaxation measurements have been made on aqueous mixtures of ethylene glycol (EG, n = 2), PrD, and BuD to clarify the dynamics of H₂¹⁷O and diol molecules. The ¹⁷O NMR relaxation rates have suggested that the rotational motion of water molecules is gradually retarded in the diol−water mixtures with increasing diol content and that the restriction of the motion is more remarkable in the order of EG < PrD < BuD. On the basis of all the results, together with comparison with those of methanol−water, ethanol−water, and 1-propanol−water mixtures previously reported, the mixing state of diol−water mixtures has been discussed at the molecular level.