PolyTEM SIGNED

Project "PolyTEM" data sheet

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 Project objective

Controlling the polymorph (crystal structure) of crystalline materials is of vital importance to both material science and the pharmaceutical industry. Many crystal polymorphs are difficult to access, however, as polymorph is determined by both kinetics and thermodynamics. Recently, it has been observed that precipitation of crystals in confinement often leads to the formation of unusual polymorphs. For example, CaCO3 forms purely as aragonite when it is precipitated in small nano-pores. These observations suggest that confinement could offer a generic route to polymorph control. However, the fundamental mechanisms underlying this confinement effect are poorly understood. In this project, I will combine in-situ cryogenic transmission electron microscopy (cryoTEM) and liquid phase (LP) TEM to study how confinement effects give rise to polymorph control. In-situ cryoTEM allows detailed structural analysis of “snapshots” of the nucleation process, while LPTEM enables dynamic, time-resolved analysis with millisecond time resolution. Notably, although these two advanced techniques perfectly complement each other, they have never been combined to study one system. CaCO3 will form the principal focus of the study, and a graphene pocket (GP) will be used as the confinement system as it not only favours aragonite formation, but is also ideally suited to both cryoTEM and LPTEM studies. The study will reveal how CaCO3 nucleate in the GPs and develop into aragonite, and the role of surface chemistry in this polymorph control process will be investigated. The project will then be extended to functional materials (e.g., TiO2) or drug crystals (e.g., Ritonavir), in order to learn how to use confinement to control polymorph by design. The research will allow us to fully understand the formation of aragonite in nano-sized confinements and more fundamentally, will bridge the gap in knowledge about how crystal polymorph in general is controlled in confinement.