Structural changes in ethanol-water mixtures: Ultrasonics, Brillouin scattering and molecular dynamics studies

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• 作者：A. Asenbaum^a ; ^{augustinus.asenbaum@sbg.ac.at} ; C. Pruner^a ; Emmerich Wilhelm^a ; ^b ; M. Mijakovic^c ; L. Zoranic^c ; F. Sokolic^c ; B. Kezic^d ; A. Perera^d
• 关键词：Water ; Ethanol&ndash ; water mixtures ; Ultrasonics ; Brillouin scattering ; Sound dispersion ; Molecular dynamics
• 刊名：Vibrational Spectroscopy
• 出版年：2012
• 期刊代码：113_09242031
• 类别：ms
• 出版时间：May, 2012
• 卷：60
• 期：Complete
• 页码：102-106
• 文件大小：509 K

摘要

Mixing of two hydrogen-bonded liquids may lead to significant composition dependent changes of liquid microscopic structure, which in turn will be reflected by changes of the corresponding thermodynamic, thermophysical and spectroscopic properties. For the liquid system {x_EtOHC₂H₅OH + (1 鈭?#xA0;x_EtOH)H₂O} at ambient temperatures and pressures, we show that major structural rearrangements occur in the composition range of 0.15 < x_EtOH < 0.20, where x_EtOH denotes the ethanol mole fraction. Most interestingly, in this region, the excess enthalpy shows a minimum, the excess heat capacity at constant pressure shows a maximum, and both the ultrasonic speed and the hypersonic speed exhibit a maximum. In fact, molecular dynamics (MD) simulation results indicate the saturation of ethanol clustering in this low ethanol mole fraction region. The corresponding change of structural/vibrational dynamics is detected by Brillouin scattering, i.e. it is reflected by the observed sound dispersion in the composition region 0.15 < x_EtOH < 0.65, where simulations show micro-segregated distributions of water and ethanol domains that form a bi-continuous mixture. At larger ethanol mole fractions, we found chain-like hydrogen-bonded water clusters.