Entropic Nature of the Debye Relaxation in Glass-Forming Monoalcohols

Abstract

The dynamics and thermodynamics of the Debye and structural (α) relaxations in isomeric monoalcohols near the glass transition temperature T g are explored using dielectric and calorimetric techniques. The α relaxation strength at T g is found to correlate with the heat capacity increment, but no thermal signals can be detected to link to the Debye relaxation. We also observed that the activation energy of the Debye relaxation in monoalcohols is quantitatively correlated with that of the α relaxation at the kinetic T g , sharing the dynamic behavior of the Rouse modes found in polymers. The experimental results together with the analogy to the Rouse modes in polymers suggest that the Debye process in monoalcohols is an entropic process manifested by the total dipole fluctuation of the supramolecular structures, which is triggered and driven by the α relaxation.

Isomeric effects in structure formation and dielectric dynamics of different octanols

“…Furthermore, it was reported that ring-chain transformations take place on the timescale of the Debye relaxation, an observation interpreted to correspond to fluctuations of the Kirkwood factor 67 . These notions were recently corroborated and extended to include not only the temperature but also the pressure dependence of the Debye relaxation 68 or to emphasize that despite a lacking calorimetric signature, the Debye process, like the Rouse modes in polymers, is entropic in nature 24 . It should be emphasized that the observation of Debye relaxations is by no means restricted to monohydroxy alcohols but well-known also for water and other dielectric liquids featuring large relaxation strengths ∆ 69 .…”

“…This microstructure is controlled by the length 4,5 and the branching 6 of the carbon tail and the position of the hydroxyl group 7 and can be classified by cyclic, linear or more complex associates like lassos and branched chains or loops. Interestingly, the ap-pearance and dominant type of structural arrangements are supposed to dependent on temperature [8][9][10] and pressure [11][12][13] as inferred from dielectric spectroscopy [14][15][16][17][18][19] , rheology [20][21][22] , calorimetry 23,24 , vibrational spectroscopy 25,26 , molecular dynamics simulations [27][28][29][30] and a combination of experimental and theoretical methods [31][32][33][34] . An overview can be found in Böhmer et al 3 .…”

Measurement and analysis of Debye relaxation dynamics of <i>n</i>-propanol, <i>n</i>-butanol and <i>n</i>-octanol

“…子的扩散运动 [8,17] ；图中主要显示的是本文重点关注的 Debye 弛豫，同时为了便 于 α 弛豫的观察，𝜀′是采用对数轴呈现的。α 弛豫和 Debye 弛豫在𝜀′曲线上表现 为台阶式变化，而在𝜀′′上则表现为一个弛豫峰，二者是一一对应的。这些结果都 与其他文献中所得到单羟基醇液体的介电谱信息相一致 [4,5] α 弛豫和 Debye 弛豫这两个过程反映的都是分子中等效电偶极子在外电场作 用下所产生的取向运动，其中 α 弛豫与液体玻璃化转变相对应 [2,3,10] ，体现的是 分子协同运动，而 Debye 弛豫则认为与单羟基醇中氢键分子链内羟基运动有关 [4-7, 10, 15] ，Xu 等 [18]…”

Mediating the slow dynamics of polyacrylates by small molecule-bridged hydrogen bonds

“…[6][7][8] Given that it is weakly constrained by inter-chain entanglements, this mode is entropic in nature and has a weak dependence on the temperature. 9,10 The sub-Rouse mode has a length scale intermediate between the a-relaxation and Rouse mode, which is cooperative like a-relaxation albeit to a lesser degree. 2,3,11 As temperature sweeps through a crossover temperature T B (at about 1.2T g ), its relaxation dynamics changes from one Vogel-Fulcher-Tamman law to another.…”

“…In contrast to the enthalpic a-relaxation that can be detected by most traditional techniques, the entropic effects 12,14 associated with slow dynamics (i.e., sub-Rouse and Rouse modes) can only be detected using a few techniques, such as dielectric 10,11,[15][16][17][18] and mechanical 9,[19][20][21][22] spectroscopy. Dielectric spectroscopy monitors the reorientation of molecular dipoles.…”