Two-Dimensional Crystallization from Multicomponent Solutions.

[摘要] Most crystallizations conducted in contexts from the laboratory to industrial production involve multicomponent solutions yielding one or more phases. Because of the importance of such processes in purification and solid form engineering, understanding these crystallization behaviors is one of the greatest outstanding scientific challenges. Here a novel approach to studying this issue is explored, namely studying two-dimensional (2D) crystallization at the liquid/solid interface where the reduced dimensionality dramatically simplifies the system. During the course of investigations of 2D crystallization of aromatic primary amides bearing para substituents with long alkyl chains, a highly symmetric pattern was observed. This structure is in the plane group of p6 and contains rhombic voids even though the molecular symmetry of amide amphiphiles is Cs. These amide amphiphiles overcome the barrier to symmetry generation through forming an aggregate as a building block. This result demonstrates that a high symmetry pattern is achievable from a low symmetry building block through a proper combination of noncovalent interactions. Based on the hypothesis that amphiphile molecules can give rise to various aggregation modes potentially leading to different monolayers, 2D crystallization of an amide amphiphile containing a C18 alkyl-chain was conducted at the liquid/graphite interface. This amide amphiphile showed the ability to exist in six different forms: three close-packed structures and three nanoporous structures. The amide amphiphile was further employed to understand the phenomenon recently observed in three-dimensional crystallization that metastable polymorphs could be obtained during attempts to grow cocrystals with additives. The same phenomenon was able to be reproduced in two-dimensional crystallization from binary solutions while attempting to induce coadsorption. During the competition study between the amide amphiphile and other additive molecules, the formation of different metastable phases depending on the additive molecules was observed these are discussed in the context of kinetics and thermodynamics. During the competition study between the amide amphiphile and diheptadecyl phthalate, a new type of cocrystal that displays random mixing along one axis and periodic ordering along the other axis was discovered. The characteristics and formation process of this ;;1D-cocrystal” were examined by STM and computational models. The nature of this crystallization behavior is discussed.

[发布机构] University of Michigan

[效力级别] Chemistry

[关键词] Two-dimensional Crystallization;Chemistry;Science;Chemistry