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 Nov 7;151(17):174503. doi: 10.1063/1.5125138.
Dielectric susceptibility data of vapor-deposited films of iso-propylbenzene (IPB) and n-propylbenzene (NPB) have been recorded across a wide range of deposition temperatures, T, mostly below the glass transition temperature, T. The results for the real and imaginary components of dielectric susceptibility are compared with recently published results for 2-methyltetrahydrofuran (MTHF). Common to all three systems are the following: (i) increased kinetic stability seen as higher onset temperature for the transformation to the liquid state for T ≈ 0.85T; (ii) the reduction of the dielectric loss (χ″) for as-deposited glasses, a signature of increased packing density that is maximal for T ≈ 0.85T; and (iii) a reduced level of the storage component (χ') for as-deposited glasses, an effect that is almost deposition temperature invariant for T < T. Material specific behavior is observed when heating the as-deposited films to 1.2T: IPB and NPB transform directly into the ordinary liquid state if judged on the basis of dielectric susceptibility, whereas MTHF has been reported to enter an unusual liquid state prior to a liquid-liquid transition at higher temperatures. These results are discussed in the context of the curious scattering results reported by Ishii et al. for some benzene derivatives, which hint at a liquid-liquid transformation.
已记录了在广泛的沉积温度范围内，T，主要低于玻璃化转变温度，T 的异丙基苯（IPB）和正丙基苯（NPB）蒸气沉积薄膜的介电常数数据。介电常数实部和虚部的结果与最近发表的 2-甲基四氢呋喃（MTHF）的结果进行了比较。所有这三个系统的共同点如下：（i）转变为液体状态的动力学稳定性增加，即对于 T ≈ 0.85T，起始温度更高；（ii）沉积玻璃的介电损耗（χ″）降低，这是堆积密度增加的特征，在 T ≈ 0.85T 时达到最大值；（iii）沉积玻璃的存储成分（χ'）降低，对于 T < T，这种效应几乎与沉积温度无关。当将沉积的薄膜加热到 1.2T 时，会观察到特定于材料的行为：如果根据介电常数判断，IPB 和 NPB 直接转化为普通液态，而 MTHF 据报道在更高温度下发生液-液转变之前进入了一种异常液态。这些结果在 Ishii 等人报告的一些苯衍生物的奇特散射结果的背景下进行了讨论，这些结果暗示存在液-液转变。
