Jakobsen Bo, Maggi Claudio, Christensen Tage, Dyre Jeppe C
DNRF Centre Glass and Time, IMFUFA, Department of Sciences, Roskilde University, Postbox 260, DK-4000 Roskilde, Denmark.
J Chem Phys. 2008 Nov 14;129(18):184502. doi: 10.1063/1.3007988.
Shear-mechanical and dielectric measurements on the two monohydroxy (monoalcohol) molecular glass formers 2-ethyl-1-hexanol and 2-butanol close to the glass-transition temperature are presented. The shear-mechanical data are obtained using the piezoelectric shear-modulus gauge method covering frequencies from 1 mHz to 10 kHz. The shear-mechanical relaxation spectra show two processes, which follow the typical scenario of a structural (alpha) relaxation and an additional (Johari-Goldstein) beta relaxation. The dielectric relaxation spectra are dominated by a Debye-type peak with an additional non-Debye peak visible. This Debye-type relaxation is a common feature peculiar to monoalcohols. The time scale of the non-Debye dielectric relaxation process is shown to correspond to the mechanical structural (alpha) relaxation. Glass-transition temperatures and fragilities are reported based on the mechanical alpha relaxation and the dielectric Debye-type process, showing that the two glass-transition temperatures differ by approximately 10 K and that the fragility based on the Debye-type process is a factor of 2 smaller than the structural fragility. If a mechanical signature of the Debye-type relaxation exists in these liquids, its relaxation strength is at most 1% and 3% of the full relaxation strength of 2-butanol and 2-ethyl-1-hexanol, respectively. These findings support the notion that it is the non-Debye dielectric relaxation process that corresponds to the structural alpha relaxation in the liquid.
本文展示了在接近玻璃化转变温度时，对两种单羟基（单醇）分子玻璃形成剂2-乙基-1-己醇和2-丁醇进行的剪切力学和介电测量。剪切力学数据是使用压电剪切模量测量法获得的，测量频率范围为1 mHz至10 kHz。剪切力学弛豫谱显示出两个过程，它们遵循结构（α）弛豫和额外的（乔哈里-戈尔茨坦）β弛豫的典型情况。介电弛豫谱以一个德拜型峰为主，还可见一个额外的非德拜峰。这种德拜型弛豫是单醇特有的常见特征。非德拜介电弛豫过程的时间尺度与机械结构（α）弛豫相对应。基于机械α弛豫和介电德拜型过程报告了玻璃化转变温度和脆性，结果表明两个玻璃化转变温度相差约10 K，并且基于德拜型过程的脆性比结构脆性小2倍。如果这些液体中存在德拜型弛豫的力学特征，其弛豫强度分别至多为2-丁醇和2-乙基-1-己醇完全弛豫强度的1%和3%。这些发现支持了这样一种观点，即与液体中的结构α弛豫相对应的是非德拜介电弛豫过程。
