Polymorphic Phase Transformation Pathways under Nanoconfinement: Flufenamic Acid
Polymorphic Phase Transformation Pathways under Nanoconfinement: Flufenamic Acid
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DOI：
10.1021/acs.cgd.0c01207
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发表时间：
2020-11-04
影响因子：
3.8
通讯作者：
Ward, Michael D.
中科院分区：
文献类型：
--
作者：
Zhang, Keke;Fellah, Noalle;Ward, Michael D.
氟灭酸（FFA）是一种高度多晶型的化合物，迄今为止有9种形式。当在可控孔隙玻璃（CPG）中在纳米级限制下进行熔融结晶时，有利于形成极不稳定的FFA形式VIII。在限制下，形式VIII足够稳定以允许测量其熔点，其随着孔径的减小而降低，符合雅阁-汤姆森关系，使得能够测定本体形式的另外难以捉摸的熔点。此外，各种多晶型物之间的转化途径取决于孔径，对于嵌入30-50-nm直径孔中的纳米晶体，其转化途径为VIII -> II -> I型，而在100-200 nm孔中，其转化途径为VIII -> IV -> III型。相比之下，VIII型在公牛中直接转化为III型。尽管先前的报道已经证明纳米限制可以改变（热力学）多晶型稳定性排名，但这些结果说明纳米级限制可以阻止和改变相变动力学，使得可以观察到其他隐藏的途径。
Flufenamic acid (FFA) is a highly polymorphic compound, with nine forms to date. When melt crystallization was performed under nanoscale confinement in controlled pore glass (CPG), the formation of the extremely unstable FFA form VIII was favored. Under confinement, form VIII was sufficiently stable to allow the measurement of its melting point, which decreased with decreasing pore size in accord with the Gibbs-Thomson relationship, enabling determination of the otherwise elusive melting point of the bulk form. Moreover, the transformation pathways among the various polymorphs depended on pore size, proceeding as form VIII -> form II -> form I for nanocrystals embedded in 30-50-nm diameter pores, and form VIII -> form IV -> form III in 100-200 nm pores. In contrast, form VIII converts directly to form III in the bulls- Whereas previous reports have demonstrated that nanoconfinement can alter (thermodynamic) polymorph stability rankings, these results illustrate that nanoscale confinement can arrest and alter phase transformations kinetics such that otherwise hidden pathways can be observed.