Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
J Chem Phys. 2010 Jan 28;132(4):044504. doi: 10.1063/1.3294703.
Dielectric relaxation spectroscopy of glass forming liquids normally exhibits a relaxation scenario that seems to be surprisingly general. However, the relaxation dynamics is more complicated for hydrogen bonded liquids. For instance, the dielectric response of monoalcohols is dominated by a mysterious Debye-like process at lower frequencies than the structural alpha-relaxation that is normally dominating the spectra of glass formers. For polyalcohols this process has been thought to be absent or possibly obscured by a strong contribution from conductivity and polarization effects at low frequencies. We here show that the Debye-like process, although much less prominent, is also present in the response of polyalcohols. It can be observed in the derivative of the real part of the susceptibility or directly in the imaginary part if the conductivity contribution is reduced by covering the upper electrode with a thin Teflon layer. We report on results from broadband dielectric spectroscopy studies of several polyalcohols: glycerol, xylitol, and sorbitol. The findings are discussed in relation to other experimental observations of ultraslow (i.e., slower than the viscosity related alpha-relaxation) dynamics in glass formers.
玻璃形成液体的介电弛豫光谱通常表现出一种似乎非常普遍的弛豫情况。然而，对于氢键液体，弛豫动力学更为复杂。例如，单醇的介电响应在低于结构α弛豫的频率范围内由一种神秘的德拜型过程主导，而结构α弛豫通常主导着玻璃形成体的光谱。对于多醇，人们认为该过程不存在，或者可能由于低频下电导和极化效应的强烈贡献而被掩盖。我们在这里表明，尽管德拜型过程不太明显，但它也存在于多醇的响应中。如果通过用薄聚四氟乙烯层覆盖上电极来减少电导贡献，则可以在介电常数实部的导数中或直接在虚部中观察到该过程。我们报告了对几种多醇（甘油、木糖醇和山梨糖醇）进行宽带介电光谱研究的结果。这些发现与其他关于玻璃形成体中超慢速（即比与粘度相关的α弛豫慢）动力学的实验观察结果进行了讨论。
