Power G, Vij J K, Johari G P
Laboratory of Advanced Electronic Materials, Department of Electronic and Electrical Engineering, Trinity College, University of Dublin, Dublin 2, Ireland.
J Chem Phys. 2007 Sep 7;127(9):094507. doi: 10.1063/1.2761898.
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.
通过介电谱在较宽的频率和温度范围内研究了液-液相分离对1-丙醇和异戊基溴明显均匀混合物分子弛豫的影响，并实时研究了其结晶动力学。如前所述，该混合物显示出两个广泛分离的弛豫过程，较快的弛豫归因于异戊基溴的取向扩散，较慢的弛豫归因于1-丙醇的取向扩散。在混合物中，异戊基溴取向极化对介电常数的标度贡献Δε与纯态时大致相同，但1-丙醇的贡献在120K时降低了约3倍。随着温度降低，这种差异保持不变。异戊基溴的弛豫时间τ及其分布参数与纯液体时相同，但1-丙醇的弛豫时间更长，且随温度降低而增加，在119K时约为纯液体值的130倍。这与一种异构庚醇的研究结果相反，其τ值降低了。外推表明，在T>151K时，混合物中1-丙醇的τ可能小于纯液体中的τ（异戊基溴组分在达到该温度之前就结晶了）。这表明混合物中1-丙醇对应于10³s的τ的玻璃化转变温度将高于纯液体中的。混合物中两种组分的结晶速率不同，1-丙醇部分未结晶而异戊基溴完全结晶。在存在结晶态的情况下，任何剩余液态异戊基溴的τ不变，而混合物中残余液态1-丙醇的τ降低。混合物在异戊基溴中以亚微米或纳米尺寸的醇聚集体形式相分离，不影响后者的弛豫动力学，而其自身的ε(s)减小且τ增加。简要描述了该发现对各种弛豫机制的影响。
