The cooperative dynamics of the H-bond system in 2-propanol/water mixtures: Steric hindrance effects of nonpolar head group
The cooperative dynamics of the H-bond system in 2-propanol/water mixtures: Steric hindrance effects of nonpolar head group
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DOI：
10.1063/1.1620996
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发表时间：
2003-11
影响因子：
4.4
通讯作者：
Takaaki Sato;R. Buchner
中科院分区：
文献类型：
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作者：
Takaaki Sato;R. Buchner
我们已经确定了复杂的2-丙醇/水混合物的介电谱，采用时域反射法在整个混合范围内在0.1 mV/GHz范围内，在20 °C，25 °C和30 °C。在特定浓度下，借助于波导干涉测量法，频率范围扩展到89 GHz。过量活化自由能ΔGE、焓ΔHE和熵ΔSE以及它们的偏摩尔量ΔGiE、ΔHiE和ΔSiE [i=2-丙醇（2 PA）和水（W）]由协同过程的弛豫时间τ1导出。在富水区，ΔHE和ΔSE表现出明显的行为，并具有较大的正值，这表明“时间平均”数和氢键强度增加。2-丙醇/水的τ1明显大于1-丙醇/水，导致ΔH和ΔS的最大值大10%。这表明非极性基团对支链异丙基单元的空间位阻作用比直链正丙基单元的空间位阻作用更有效。
We have determined the complex dielectric spectra of 2-propanol/water mixtures employing time domain reflectometry for the entire mixing range in 0.1⩽ν/GHz⩽25 at 20 °C, 25 °C, and 30 °C. At the specific concentrations, a frequency range was expanded up to 89 GHz with the help of waveguide interferometry. The excess activation free energy, ΔGE, enthalpy, ΔHE, and entropy, ΔSE, and their partial molar quantities, ΔGiE, ΔHiE, and ΔSiE [i=2-propanol (2PA) and water (W)] were derived from the relaxation time of the cooperative process, τ1. In the water-rich region, ΔHE and ΔSE exhibit conspicuous behavior with large positive values, which suggests an increase of the “time averaged” number and the strength of H-bonds. τ1 becomes considerably larger for 2-propanol/water than that for 1-propanol/water, resulting in ∼10% larger maxima of ΔH and ΔS. This indicates that the steric hindrance caused by the nonpolar group is more efficient for the branched isopropyl unit than that for the linear n-propyl moiety in prev...