Institute of Physics, University of Silesia, Katowice, Uniwersytecka 4, 40-007, Poland.
J Chem Phys. 2011 Aug 28;135(8):084507. doi: 10.1063/1.3626027.
The complex relative permittivity of a non-crystallizable secondary alcohol, 5-methyl-2-hexanol, is measured over a wide range of temperatures and pressures up to 1750 MPa (17.5 kbar). The data at atmospheric pressure (P = 0.101 MPa) are analyzed in terms of three processes, and the results are in complete agreement with that of O. E. Kalinovskaya and J. K. Vij [J. Chem. Phys. 112, 3262 (2000)]. Process I is of the Debye type and process II is of the Davidson-Cole type, whereas process III is identified as the Johari-Goldstein relaxation process. For pressures of ∼500 MPa and higher, processes I and II are seen to merge into each other to form a single dominant process which unambiguously cannot be resolved into more than one process. The dielectric relaxation strength of process I decreases slightly initially with pressure and when the two processes have merged at elevated pressures, the total relaxation strength increases with increase in pressure. Process III is better resolvable at higher pressures especially above T(g) in the supercooled liquid state for the reason that the separation in the time scales between the dominant and the JG relaxation process increases at elevated pressures. Surprisingly we find a change in the slope in the plot of log τ(JG) vs. 1/T for P = 1750 MPa. The results for the relaxation time of alcohols are compared with the Kirkwood correlation factor, g, and it is found that higher is the g, lower is the relaxation time for process I, and it is more of the Debye type. On a reduction in g brought about by an increase in pressure at lower temperatures, the dominant process becomes non-Debye though extensive hydrogen bonding is still present. The dielectric strength of the merged processes increases with increase in pressure. The values of the steepness index, m = |d log τ/d(T(g)/T)|(T = Tg) for processes I and II are different for P = 0.1 MPa. However the value of m, for the composite process, which is a merger of processes I and II, for P = 1750 MPa is almost the same for process II at P = 0.1 MPa. From the results of the activation volume, activation enthalpy, and a comparison of the relaxation times with the g factor, we conclude that both processes I and II are significantly affected by hydrogen bonding and both contribute to the structural relaxation.
非晶化仲醇 5-甲基-2-己醇的复介电常数在很宽的温度和压力范围内（高达 1750 MPa（17.5 kbar））进行了测量。在大气压力（P = 0.101 MPa）下的数据用三个过程进行了分析，结果与 O.E. Kalinovskaya 和 J.K. Vij 的结果完全一致[J. Chem. Phys. 112, 3262 (2000)]。过程 I 是德拜型，过程 II 是戴维森-科尔型，而过程 III 则被确定为 Johari-Goldstein 弛豫过程。对于约 500 MPa 及更高的压力，过程 I 和 II 合并成一个单一的主导过程，这个过程显然不能被分解成多于一个过程。过程 I 的介电弛豫强度最初随压力略有下降，当两个过程在较高压力下合并时，总弛豫强度随压力的增加而增加。在较高的压力下，过程 III 更容易分辨，特别是在过冷液体状态下的 Tg 以上，原因是在较高压力下，主导和 JG 弛豫过程之间的时间尺度分离增加。令人惊讶的是，我们发现 1750 MPa 时 log τ(JG) 与 1/T 的关系图的斜率发生了变化。醇的弛豫时间的结果与 Kirkwood 相关因子 g 进行了比较，发现 g 越高，过程 I 的弛豫时间越短，它更具有德拜型。在较低温度下，压力升高导致 g 降低，主导过程虽然仍存在广泛的氢键，但不再是德拜型。合并过程的介电强度随压力的增加而增加。过程 I 和 II 的陡度指数 m = |d log τ/d(T(g)/T)|(T = Tg)在 P = 0.1 MPa 时不同。然而，对于 P = 1750 MPa 时的合并过程（过程 I 和 II 的合并），其值 m 与 P = 0.1 MPa 时的过程 II 几乎相同。从活化体积、活化焓的结果以及与 g 因子的弛豫时间的比较，我们得出结论，过程 I 和 II 都受到氢键的显著影响，并且都对结构弛豫有贡献。
