Dielectric relaxation and crystallization of nanophase separated 1-propanol-isoamylbromide mixture.
Dielectric relaxation and crystallization of nanophase separated 1-propanol-isoamylbromide mixture.
复制标题
纳米相分离的 1-丙醇-异戊基溴混合物的介电弛豫和结晶。
DOI：
10.1063/1.2761898
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
G. P. Johari
中科院分区：
文献类型：
--
作者：
G. Power;J. Vij;G. P. Johari
通过介电谱在宽频率和温度范围内研究了液-液相分离对 1-丙醇和异淀粉溴明显均匀混合物的分子弛豫的影响，并实时研究了其结晶动力学。与之前一样，该混合物显示出两个广泛分离的弛豫过程，其中由于异淀粉溴的定向扩散而较快的弛豫以及由于1-丙醇的定向扩散而较慢的弛豫。在混合物中，异淀粉溴化物的取向极化 Deltaepsilon 对介电常数的比例贡献与纯状态下的大致相同，但 1-丙醇的介电常数在 120 K 时降低了约 3 倍。随着温度降低，这种差异保持恒定。异淀粉溴的弛豫时间 tau 及其分布参数与纯液体相同，但 1-丙醇的弛豫时间 tau 较长，并且随着 T 的降低而增加，在 119 K 时约为纯液体值的 130 倍。这与异构庚醇的发现相反，异构庚醇的 tau 值有所下降。外推表明，在 T>151 K 时，混合物中 1-丙醇的 tau 值可能会低于纯液体中的 tau 值（异淀粉溴组分在达到该温度之前结晶）。这表明混合物中 1-丙醇的 Tg 对应于 10(3) s 的 Tg 将高于纯液体中的 Tg。混合物中两种组分的结晶以不同的速率发生，1-丙醇保持部分未结晶，而异淀粉溴完全结晶。任何剩余液体异淀粉溴的tau在结晶态存在下不会改变，而混合物中剩余液体1-丙醇的tau减少。混合物在异淀粉溴中以亚微米或纳米尺寸的醇聚集体进行相分离，不影响后者的弛豫动力学，同时其自身的ε减小并且tau增加。简要描述了各种松弛机制的发现结果。
The effects of liquid-liquid phase separation on molecular relaxation of an apparently homogeneous mixture of 1-propanol and isoamylbromide has been studied by dielectric spectroscopy over a broad frequency and temperature range, and its crystallization kinetics investigated in real time. The mixture shows two widely separated relaxation processes, as before, with the faster relaxation due to the orientational diffusion of isoamylbromide and the slower due to that of 1-propanol. In the mixture, the scaled contribution to permittivity from orientation polarization, Deltaepsilon, of isoamylbromide is about the same as in the pure state, but that of 1-propanol decreases by a factor of approximately 3 at 120 K. As the temperature is decreased, this difference remains constant. The relaxation time, tau, of isoamylbromide and its distribution parameter remains the same as for the pure liquid, but that of 1-propanol is longer and increases with decrease in T, becoming approximately 130 times the pure liquid's value at 119 K. This is in contrast to the finding for an isomeric heptanol, whose tau had decreased. Extrapolation suggests that at T>151 K, tau of 1-propanol in the mixture may become less than that in the pure liquid (the isoamylbromide component crystallizes before this temperature could be reached). This indicates that Tg corresponding to tau of 10(3) s for 1-propanol in the mixture would be higher than in the pure liquid. Crystallization of the two components in the mixture occurs at different rates and 1-propanol remains partially uncrystallized while isoamylbromide completely crystallizes. tau of any remaining liquid isoamylbromide does not change in the presence of crystallized states while tau of residual liquid 1-propanol in the mixture is reduced. The mixture phase separates in submicron or nanosize aggregates of the alcohol in isoamylbromide, without affecting the latter's relaxation kinetics, while its own epsilon(s) decreases and tau increases. Consequences of the finding for various relaxation mechanisms are briefly described.