Riechers Birte, Guiseppi-Elie A, Ediger M D, Richert Ranko
School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287-1604, USA.
Department of Biomedical Engineering, The Dwight Look College of Engineering, Texas A&M University, College Station, Texas 77843, USA.
J Chem Phys. 2019 Jun 7;150(21):214502. doi: 10.1063/1.5091796.
This work reports results gained from dielectric spectroscopy on the organic molecular glass-former 2-methyltetrahydrofuran (MTHF), which was deposited onto an interdigitated electrode device by physical vapor deposition. By a suitable selection of preparation parameters (deposition temperature, deposition rate, and annealing conditions), various states of MTHF could be created: ultrastable glass, a liquid state with unusual dielectric properties, or the ordinary liquid state as obtained by supercooling. Observations on kinetic stability as well as on the suppression of dielectric loss in the ultrastable state resemble previous findings for other molecular glass-formers. Remarkably, after annealing just above T, all vapor-deposited films of MTHF display a static dielectric constant in the liquid state (ε) that is up to a factor of two below that of the ordinary bulk liquid. A structural transition to the ordinary liquid-cooled state of MTHF occurs at temperatures far above its conventional T, indicative of polyamorphism: the formation of an unusual structure that is achieved by physical vapor deposition and that differs from the ordinary liquid state obtained by supercooling. The present results also reveal that the dielectric constant of the as deposited glass (ε) is reduced to practically the value of the squared refractive index, n.
本研究报告了通过介电谱对有机分子玻璃形成剂2-甲基四氢呋喃（MTHF）进行研究所得的结果，该物质通过物理气相沉积法沉积在叉指电极装置上。通过适当选择制备参数（沉积温度、沉积速率和退火条件），可以产生MTHF的各种状态：超稳定玻璃态、具有异常介电性质的液态或通过过冷获得的普通液态。对超稳定状态下的动力学稳定性以及介电损耗抑制的观察结果与其他分子玻璃形成剂的先前研究结果相似。值得注意的是，在略高于T的温度下退火后，所有气相沉积的MTHF薄膜在液态下的静态介电常数（ε）比普通本体液体的介电常数低至两倍。MTHF向普通液态冷却状态的结构转变发生在远高于其传统T的温度下，这表明存在多晶型现象：通过物理气相沉积形成的一种异常结构，它不同于通过过冷获得的普通液态。目前的结果还表明，沉积态玻璃的介电常数（ε）实际上降低到了折射率平方n的值。
