Institute of Physics, University of Rostock, Wismarsche Str. 43-45, 18051 Rostock, Germany.
J Chem Phys. 2013 Jan 14;138(2):024501. doi: 10.1063/1.4773354.
Vapor-deposited glasses of toluene and ethylbenzene have been characterized by in situ ac chip-nanocalorimetry. The high sensitivity of this method allows the detection of small changes in the heat capacity of nanogram size samples. We observe that vapor-deposited glasses have up to 4% lower heat capacities than the ordinary glass. The largest heat capacity decrease and the most kinetically stable glasses of toluene and ethylbenzene are observed in a range of deposition temperatures between 0.75 T(g) and 0.96 T(g). Compared to larger molecules, deposition rate has a minor influence on the kinetic stability of these glasses. For both toluene and ethylbenzene, the kinetic stability is strongly correlated with the heat capacity decrease for deposition temperatures above 0.8 T(g). In addition, ac-nanocalorimetry was used to follow the isothermal transformation of the stable glasses into the supercooled liquid at temperatures slightly above T(g). Toluene and ethylbenzene stable glasses exhibit a constant transformation rate which is consistent with the growth front mechanism recently demonstrated for tris-naphthylbenzene and indomethacin. The kinetic stability of the most stable toluene and ethylbenzene glasses is comparable to that observed for other stable glasses formed by vapor deposition.
采用原位 ac 芯片微量热法对甲苯和乙苯的气相沉积玻璃进行了表征。该方法具有较高的灵敏度，可检测纳克级样品热容的微小变化。我们观察到气相沉积玻璃的热容比普通玻璃低 4%。在 0.75 T(g)至 0.96 T(g)之间的沉积温度范围内，甲苯和乙苯的玻璃化转变温度下降最大且动力学稳定性最高。与较大分子相比，沉积速率对这些玻璃的动力学稳定性影响较小。对于甲苯和乙苯，在高于 0.8 T(g)的沉积温度下，动力学稳定性与热容下降呈强相关。此外，ac 微量热法还用于研究在稍高于 T(g)的温度下，稳定玻璃等温转变为过冷液体的过程。甲苯和乙苯稳定玻璃的转变速率保持恒定，与最近报道的三萘基苯和吲哚美辛的生长前沿机制一致。最稳定的甲苯和乙苯玻璃的动力学稳定性与通过气相沉积形成的其他稳定玻璃相当。
