Kawakami Kohsaku, Harada Takuji, Yoshihashi Yasuo, Yonemochi Etsuo, Terada Katsuhide, Moriyama Hiroshi
†International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
J Phys Chem B. 2015 Apr 9;119(14):4873-80. doi: 10.1021/jp509646z. Epub 2015 Mar 25.
Fragility is a measure of the departure from non-Arrhenius behavior for supercooled liquids and glasses, and various simple methods are available for its quantification. However, the obtained values usually do not agree with each other. One of the purposes of this study was to compare the fragility values obtained by different methodologies. Thermodynamic fragility (FT) is a simple concept that is evaluated from the heat capacity change at the glass transition temperature (Tg). Dynamic fragility is evaluated using three methodologies in this study: extrapolation of the configurational entropy (Sc) to the Kauzmann temperature (Tk) (FDC), ramp-rate dependence of Tg (FDTg), and that of the fictive temperature (Tf) (FDTf). FT and FDC of 19 pharmaceutical compounds were correlated, whereas FDTg and FDTf did not correlate with either of them. This result seems reasonable because both FT and FDC are calculated from thermodynamic parameters in the quasi-equilibrium state, but FDTg and FDTf are likely affected by kinetics as well. Another goal of this study was to find the correlation between the glass-forming ability (GFA) and fragility. FDTg was shown to correlate with GFA, presumably because both were determined on the balance of thermodynamic and kinetic factors. This correlation suggests that fragile glass has low GFA. Furthermore, the relevance of fragility to isothermal crystallization is discussed. Compounds with small FDTg and FDTf tended to exhibit pressure-controlled crystallization, for which better storage stability can be expected relative to temperature-controlled compounds. Fragility was shown to be a useful parameter practically as well as scientifically.
脆性是衡量过冷液体和玻璃偏离非阿累尼乌斯行为的一个指标，有多种简单方法可用于对其进行量化。然而，所得到的值通常彼此不一致。本研究的目的之一是比较通过不同方法获得的脆性值。热力学脆性（FT）是一个简单的概念，可根据玻璃化转变温度（Tg）下的热容变化来评估。本研究使用三种方法评估动态脆性：将构型熵（Sc）外推至考兹曼温度（Tk）（FDC）、Tg 的升温速率依赖性（FDTg）以及虚构温度（Tf）的升温速率依赖性（FDTf）。19种药物化合物的FT和FDC具有相关性，而FDTg和FDTf与它们两者均无相关性。这个结果似乎是合理的，因为FT和FDC都是根据准平衡态的热力学参数计算得出的，但FDTg和FDTf可能也受动力学影响。本研究的另一个目标是找出玻璃形成能力（GFA）与脆性之间的相关性。结果表明FDTg与GFA相关，大概是因为两者都是由热力学和动力学因素的平衡决定的。这种相关性表明脆性玻璃的GFA较低。此外，还讨论了脆性与等温结晶的相关性。具有较小FDTg和FDTf的化合物倾向于表现出压力控制结晶相对于温度控制的化合物，预计其具有更好的储存稳定性。结果表明，脆性在实际应用和科学研究中都是一个有用的参数。
