Vyazovkin Sergey, Dranca Ion
Department of Chemistry, University of Alabama at Birmingham, 901 South 14 Street, Birmingham, Alabama 35294, USA.
J Phys Chem B. 2005 Oct 6;109(39):18637-44. doi: 10.1021/jp052985i.
The alpha- and beta-relaxation processes in amorphous indomethacin have been studied by using differential scanning calorimetry. The beta-process has been detected as a small endothermic peak that emerges before the glass transition step when reheating samples previously annealed in the temperature region -20 to +5 degrees C. The activation energy of the beta-process is approximately 57 kJ mol(-1), and shows an increase with increasing temperature as it approaches the glass transition region. In the glass transition region, the effective activation energy of relaxation decreases with increasing temperature from 320 to 160 kJ mol(-1). Heat capacity measurements have allowed for the evaluation of the cooperatively rearranging region in terms of the linear size (3.4 nm) and the number of molecules (90). The beta-relaxation fades below -30 degrees C, which provides a practical estimate for the lower temperature limit of physical instability in indomethacin. It is demonstrated experimentally that nucleation of indomethacin takes place in the temperature region of the beta-relaxation.
采用差示扫描量热法研究了非晶态吲哚美辛中的α和β弛豫过程。β过程被检测为一个小的吸热峰，当重新加热先前在-20至+5℃温度区域退火的样品时，该峰出现在玻璃化转变步骤之前。β过程的活化能约为57 kJ mol⁻¹，并且随着温度接近玻璃化转变区域而增加。在玻璃化转变区域，弛豫的有效活化能随着温度升高从320 kJ mol⁻¹降至160 kJ mol⁻¹。通过热容测量，可以根据线性尺寸（3.4 nm）和分子数量（90）评估协同重排区域。β弛豫在-30℃以下消失，这为吲哚美辛物理不稳定性的较低温度极限提供了一个实际估计。实验证明，吲哚美辛的成核发生在β弛豫的温度区域。
