Kearns Kenneth L, Swallen Stephen F, Ediger M D, Sun Ye, Yu Lian
Department of Chemistry, School of Pharmacy, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
J Phys Chem B. 2009 Feb 12;113(6):1579-86. doi: 10.1021/jp808665t.
Indomethacin glasses of varying stabilities were prepared by physical vapor deposition onto substrates at 265 K. Enthalpy relaxation and the mobility onset temperature were assessed with differential scanning calorimetry (DSC). Quasi-isothermal temperature-modulated DSC was used to measure the reversing heat capacity during annealing above the glass transition temperature Tg. At deposition rates near 8 A/s, scanning DSC shows two enthalpy relaxation peaks and quasi-isothermal DSC shows a two-step change in the reversing heat capacity. We attribute these features to two distinct local packing structures in the vapor-deposited glass, and this interpretation is supported by the strong correlation between the two calorimetric signatures of the glass to liquid transformation. At lower deposition rates, a larger fraction of the sample is prepared in the more stable local packing. The transformation of the vapor-deposited glasses into the supercooled liquid above Tg is exceedingly slow, as much as 4500 times slower than the structural relaxation time of the liquid.
通过物理气相沉积在265 K的基板上制备了具有不同稳定性的吲哚美辛玻璃。用差示扫描量热法（DSC）评估了焓松弛和迁移率起始温度。采用准等温温度调制DSC测量高于玻璃化转变温度Tg退火期间的可逆热容量。在沉积速率接近8 Å/s时，扫描DSC显示两个焓松弛峰，准等温DSC显示可逆热容量的两步变化。我们将这些特征归因于气相沉积玻璃中两种不同的局部堆积结构，并且玻璃到液体转变的两个量热特征之间的强相关性支持了这种解释。在较低的沉积速率下，更大比例的样品以更稳定的局部堆积制备。气相沉积玻璃在Tg以上转变为过冷液体的过程极其缓慢，比液体的结构弛豫时间慢多达4500倍。
