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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >The Glass Transition and Dielectric Secondary Relaxation of Fructose-Water Mixtures
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The Glass Transition and Dielectric Secondary Relaxation of Fructose-Water Mixtures

机译：果糖-水混合物的玻璃化转变和介电二次弛豫

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Broad-band dielectric measurements for fructose-water mixtures with fructose concentrations between 70.0 and 94.6 wt% were carried out in the frequency range of 2 mHz to 20 GHz in the temperature range of-70 to 45 °C.Two relaxation processes,the alpha process at lower frequency and the secondary beta process at higher frequency,were observed.The dielectric relaxation time of the alpha process was 100 s at the glass transition temperature,T_g,determined by differential scanning calorimetry(DSC).The relaxation time and strength of the beta process changed from weaker temperature dependences of below T_g to a stronger one above T_g.These changes in behaviors of the beta process in fructose-water mixtures upon crossing the T_g of the mixtures is the same as that found for the secondary process of water in various other aqueous mixtures with hydrogen-bonding molecular liquids,polymers,and nanoporous systems.These results lead to the conclusion that the primary a process of fructose-water mixtures results from the cooperative motion of water and fructose molecules,and the secondary beta process is the Johari-Goldstein process of water in the mixture.At temperatures near and above T_g where both the alpha and the beta processes were observed and their relaxation times,tau_(alpha)and tau_(beta),were determined in some mixtures,the ratio tau_(alpha)/tau_(beta)is in accord with that predicted by the coupling model.Fixing tau_(alpha)at 100 s,the ratio tau_(alpha)/tau_(beta)decreases with decreasing concentration of fructose in the mixtures.This trend is also consistent with that expected by the coupling model from the decrease of the intermolecular coupling parameter upon decreasing fructose concentration.
机译：在2 mHz至20 GHz的频率范围内，-70至45°C的温度范围内，对果糖浓度为70.0至94.6 wt％的果糖-水混合物进行宽带介电​​测量。用差示扫描量热法（DSC）测定，在玻璃化转变温度T_g下，α过程的介电弛豫时间为100 s。 β过程从低于T_g的较弱温度依赖性变化为高于T_g的较强温度依赖性。果糖-水混合物中的β过程的行为与混合物的T_g相交时的变化与水的二次过程相同在具有氢键分子液体，聚合物和纳米孔系统的各种其他水性混合物中。这些结果得出以下结论：果糖-水的主要过程Xtures是水和果糖分子协同运动的结果，次生β过程是混合物中水的Johari-Goldstein过程。在接近T_g的温度下，观察到α和β过程及其弛豫时间，在某些混合物中确定了tau_α和tau_β，比率tau_α/tau_β与耦合模型所预测的一致。在100 s处固定tau_α，比率tau_ α/tau_β随着混合物中果糖浓度的降低而降低。这一趋势也与耦合模型所预期的趋势一致，即当果糖浓度降低时，分子间耦合参数的降低。

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