结晶
无定形固体
材料科学
溶解
晶体生长
化学工程
涂层
结晶学
玻璃化转变
化学物理
化学
Crystal(编程语言)
纳米技术
聚合物
复合材料
工程类
程序设计语言
计算机科学
作者
Lei Zhu,Letitia Wong,Lian Yu
摘要
Amorphous solids are generally more soluble and faster dissolving than their crystalline counterparts, a property useful for delivering poorly soluble drugs. Amorphous drugs must be stable against crystallization, for crystallization negates their advantages. Recent studies found that crystal growth in amorphous indomethacin is orders of magnitude faster at the free surface than through the bulk and this surface-enhanced crystallization can be inhibited by an ultrathin coating. Herein, we report a second system that exhibits the same phenomena. Crystal growth at the free surface of amorphous nifedipine (NIF) was at least 1 order of magnitude faster than that through the bulk below the glass transition temperature Tg (42 degrees C). A thin coating of gold (10 nm) reduced the surface crystal growth rate to the bulk crystal growth rate. Surface-enhanced crystal growth was more pronounced near and below Tg than substantially above Tg, which suggests that this growth mode is more important for the glassy state. Our results support the view that a thin layer of molecules near the surface have higher mobility than the bulk molecules and can enable faster crystal growth. The higher mobility of surface molecules and the resulting fast crystal growth can be suppressed by an ultrathin coating.
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