Wang Li-Min, Richert Ranko
Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604, USA.
J Phys Chem B. 2005 May 12;109(18):8767-73. doi: 10.1021/jp050342x.
Glass-forming monohydroxy alcohols exhibit two dielectric relaxation signals with super-Arrhenius temperature dependence: a Debye peak and an asymmetrically broadened alpha-process. We explore the behavior of these distinct relaxation features in mixtures of such liquids by dielectric measurements. The study focuses on the viscous regime of two binary systems: 2-methyl-1-butanol with 2-ethyl-1-hexanol and 1-propanol with 3,7-dimethyl-1-octanol. We find that the logarithmic relaxation time, log(tau), of the Debye peak follows an ideal mixing law (linear change with mole fraction), even in the case of mixing structurally dissimilar components. By contrast, the log(tau) versus mole fraction curve for the alpha-process is nonlinear, indicative of slower structural relaxation relative to the expectation on the basis of ideal mixing behavior. The latter observation is analogous to the effect of composition on viscosity, heat of mixing, and glass-transition temperature, whereas the ideal mixing of log(tau) seen for the Debye peak is the exception. We conclude that the unusual ideal mixing behavior of dielectric relaxation in monohydroxy alcohols is not a result of structural similarity, but rather yet more evidence of the Debye process being decoupled from other dynamic and thermodynamic properties.
一个德拜峰和一个不对称展宽的α过程。我们通过介电测量来探究此类液体混合物中这些不同弛豫特征的行为。该研究聚焦于两个二元体系的粘性区域：2-甲基-1-丁醇与2-乙基-1-己醇以及1-丙醇与3,7-二甲基-1-辛醇。我们发现，即使在混合结构不同的组分时，德拜峰的对数弛豫时间log(τ)也遵循理想混合定律（随摩尔分数呈线性变化）。相比之下，α过程的log(τ)与摩尔分数曲线是非线性的，这表明相对于基于理想混合行为的预期，其结构弛豫较慢。后一观察结果类似于组成对粘度、混合热和玻璃化转变温度的影响，而德拜峰的log(τ)呈现理想混合则是个例外。我们得出结论，一元醇中介电弛豫这种不寻常的理想混合行为并非结构相似性的结果，而是德拜过程与其他动力学和热力学性质解耦的更多证据。
