Power G, Vij J K, Johari G P
Laboratory of Advanced Electronic Materials, Department of Electronic Engineering, Trinity College, University of Dublin, Dublin 2, Ireland.
J Chem Phys. 2007 Jan 21;126(3):034512. doi: 10.1063/1.2409929.
To gain insight into the effects of liquid-liquid phase separation on molecular relaxation behavior we have studied an apparently homogeneous mixture of 5-methyl-2-hexanol and isoamylbromide by dielectric spectroscopy over a broad temperature range. It shows two relaxation regions, widely separated in frequency and temperature, with the low-frequency relaxation due to the alcohol and the high-frequency relaxation due to the halide. In the mixture, the equilibrium dielectric permittivity epsilon(s) of the alcohol is 41% of the pure state at 155.7 K and epsilon(s) of isoamylbromide is approximately 86% of the pure state at 128.7 K. The difference decreases for the alcohol component with decreasing temperature and increases for the isoamylbromide component. The relaxation time tau of 5-methyl-2-hexanol in the mixture at 155.7 K is over five orders of magnitude less than in the pure state, and this difference increases with decreasing temperature, but tau of isoamylbromide in the mixture is marginally higher than in the pure liquid. This shows that the mixture would have two T(g)'s corresponding to its tau of 10(3) s, with values of approximately 121 K for its 5-methyl-2-hexanol component and approximately 108 K for its isoamylbromide component. It is concluded that the mixture phase separates in submicron or nanometer-size aggregates of the alcohol in isoamylbromide, without affecting the latter's relaxation kinetics, while its own epsilon(s) and tau decrease markedly.
为深入了解液 - 液相分离对分子弛豫行为的影响，我们通过介电谱在较宽温度范围内研究了5 - 甲基 - 2 - 己醇和异戊基溴的一种看似均匀的混合物。它显示出两个弛豫区域，在频率和温度上有很大差异，低频弛豫归因于醇，高频弛豫归因于卤化物。在该混合物中，155.7 K时醇的平衡介电常数ε(s)是其纯态时的41%，128.7 K时异戊基溴的ε(s)约为其纯态时的86%。随着温度降低，醇组分的这种差异减小，而异戊基溴组分的差异增大。155.7 K时混合物中5 - 甲基 - 2 - 己醇的弛豫时间τ比其在纯态时少五个数量级以上，且这种差异随温度降低而增大，但混合物中异戊基溴的τ略高于其在纯液体中的值。这表明该混合物会有两个对应于其10³ s的τ的玻璃化转变温度（Tg），其5 - 甲基 - 2 - 己醇组分的值约为121 K，异戊基溴组分的值约为108 K。得出的结论是，该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)和τ显著降低。
