Gabriel Jan P, Thoms Erik, Guiseppi-Elie A, Ediger M D, Richert Ranko
School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, USA.
Department of Electrical and Computer Engineering, College of Engineering, Anderson University, 316 Boulevard, Anderson, South Carolina 29621, USA.
J Chem Phys. 2022 Jan 28;156(4):044501. doi: 10.1063/5.0080373.
The dielectric relaxation behavior of the molecular glass former butyronitrile is revisited by measuring both bulk samples cooled from the melt and samples obtained by physical vapor deposition. We find that the dielectric constant in the viscous regime of the bulk liquid is much higher than reported previously, reaching ε = 63 at T = 103 K, i.e., just above the glass transition temperature T = 97 K. By contrast, varying the deposition temperature and rate of vapor-deposited samples leads to dielectric constants in a range between 4.5 and 63 at T = 103 K. Values much below ε = 63 persist for thousands of seconds, where the dielectric relaxation time is about 0.1 s. The observations can be interpreted by the formation of clusters in which pair-wise anti-parallel dipole orientation is the preferred state at temperatures well below the glass transition. These non-crystalline clusters are long-lived even above T, where the remaining volume fraction is in the state of the equilibrium polar liquid.
通过测量从熔体冷却的块状样品以及通过物理气相沉积获得的样品，重新研究了分子玻璃形成剂丁腈的介电弛豫行为。我们发现，块状液体粘性区域的介电常数比之前报道的要高得多，在T = 103 K时达到ε = 63，即略高于玻璃化转变温度T = 97 K。相比之下，改变气相沉积样品的沉积温度和速率会导致在T = 103 K时介电常数在4.5至63之间。远低于ε = 63的值会持续数千秒，此时介电弛豫时间约为0.1 s。这些观察结果可以通过簇的形成来解释，在低于玻璃化转变温度的温度下，成对反平行偶极子取向是簇中的优选状态。这些非晶簇即使在T以上也是长寿命的，此时剩余体积分数处于平衡极性液体状态。
