Liu Tianyi, Cheng Kevin, Salami-Ranjbaran Elmira, Gao Feng, Li Chen, Tong Xiao, Lin Yi-Chih, Zhang Yue, Zhang William, Klinge Lindsey, Walsh Patrick J, Fakhraai Zahra
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
J Chem Phys. 2015 Aug 28;143(8):084506. doi: 10.1063/1.4928521.
We detail the formation and properties associated with stable glasses (SG) formed by a series of structural analogues of 1,3-bis(1-naphthyl)-5-(2-naphthyl)benzene (α,α,β-TNB), a well-studied SG former. Five compounds with similar structural properties were synthesized and physical vapor-deposited with a constant deposition rate at various substrate temperatures (Tdep) in the range between 0.73 Tg and 0.96 Tg. These molecules include α,α,β-TNB, 3,5-di(naphthalen-1-yl)-1-phenylbenzene (α,α-P), 9-(3,5-di(naphthalen-1-yl)phenyl)anthracene (α,α-A), 9,9'-(5-(naphthalen-2-yl)-1,3-phenylene)dianthracene (β-AA), and 3,3',5,5'-tetra(naphthalen-1-yl)-1,1'-biphenyl (α,α,α,α-TNBP). Ellipsometry was used to study the transformations from the as-deposited glasses into ordinary glasses (OG). The stability of each film was evaluated by measuring the fictive temperature (Tf) and density difference between the as-deposited glass and OG. It is demonstrated that all five molecules can form SGs upon vapor deposition in this temperature range. In-depth studies on the dependence of the stability of as-deposited glasses upon Tdep were performed with three molecules, α,α,β-TNB, α,α-P, and α,α-A. The general trends of stability were comparable at the same Tdep/Tg for these three compounds. Similar to previous studies on α,α,β-TNB, vapor-deposited glasses of α,α-P and α,α-A formed the most stable structures around Tdep = 0.8-0.85 Tg. The most stable glass of each molecule showed the lowest thermal expansion coefficient compared to OG and a positive optical birefringence. However, the SGs of α,α-A were less stable compared to α,α-P and α,α,β-TNB at the relative Tdep/Tg. Based on Arrhenius extrapolation of the aging time, as a measure of stability, the most stable α,α-A glass was only aged for a few years as opposed to hundreds or thousands of years for other glasses. We hypothesize that the reduced stability is due to slower mobility at the free surface of α,α-A glass compared to the other two molecules.
我们详细阐述了由1,3 - 双（1 - 萘基）- 5 - （2 - 萘基）苯（α,α,β - TNB，一种经过充分研究的稳定玻璃形成剂）的一系列结构类似物形成的稳定玻璃（SG）的形成及性质。合成了五种具有相似结构性质的化合物，并在0.73Tg至0.96Tg范围内的不同衬底温度（Tdep）下以恒定沉积速率进行物理气相沉积。这些分子包括α,α,β - TNB、3,5 - 二（萘 - 1 - 基）- 1 - 苯基苯（α,α - P）、9 - （3,5 - 二（萘 - 1 - 基）苯基）蒽（α,α - A）、9,9' - （5 - （萘 - 2 - 基）- 1,3 - 亚苯基）二蒽（β - AA）和3,3',5,5' - 四（萘 - 1 - 基）- 1,1' - 联苯（α,α,α,α - TNBP）。使用椭偏仪研究了从沉积态玻璃向普通玻璃（OG）的转变。通过测量沉积态玻璃与OG之间的虚构温度（Tf）和密度差来评估每种薄膜的稳定性。结果表明，在该温度范围内气相沉积时，所有五种分子都能形成SG。对α,α,β - TNB、α,α - P和α,α - A这三种分子的沉积态玻璃稳定性对Tdep的依赖性进行了深入研究。对于这三种化合物，在相同的Tdep/Tg下，稳定性的总体趋势具有可比性。与先前对α,α,β - TNB的研究类似，α,α - P和α,α - A的气相沉积玻璃在Tdep = 0.8 - 0.85Tg左右形成最稳定的结构。与OG相比，每种分子最稳定的玻璃表现出最低的热膨胀系数和正的光学双折射。然而，在相对Tdep/Tg下，α,α - A的SGs比α,α - P和α,α,β - TNB的稳定性更低。基于老化时间的阿伦尼乌斯外推法（作为稳定性的一种度量），最稳定的α,α - A玻璃仅老化了几年，而其他玻璃则老化了数百年或数千年。我们推测稳定性降低是由于α,α - A玻璃的自由表面处的迁移率比其他两种分子慢。
