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Title: The study of organic crystals by atomic force microscopy
Author: Chow, Ernest Ho Hin
ISNI:       0000 0004 5364 7350
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2014
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Organic crystals are found in everyday goods such as foods, drugs, dyes, and agricultural products. To better understand the solid-state behaviour of organic crystals, the study of their surfaces is crucial, as several reactions occur at the interface between the crystal surface and its immediate environment. While atomic force microscopy (AFM) is a useful tool for studying surfaces, it is not a common technique for studying organic crystals. The rst part of this report aims to address problems of imaging organic crystals by AFM which arise from the nature of the imaging technique and the material property of organic crystals. Methods of detecting and predicting the likelihood of the problems encountered in imaging organic crystals are suggested in order for a more accurate interpretation of the information obtained by this technique. The e ect of humidity on aspirin crystal surfaces is then investigated by AFM. The growth of new features on the surface is believed to be a result of the hydrolysis of aspirin molecules. Mechanisms are suggested based on the observed surface response of aspirin, where surface defects and the mobility of surface molecules are believed to be important factors a ecting reactivity. The last section investigates the solid-state photochemical reaction of anthracene, which is a reaction that should not occur according to the topochemical postulate. The surface response of anthracene crystals to UV light was studied, and the results indicate strong reactivity at sites of surface defects, which is likely due to photodimerisation. A similar mechanism that described the behaviour of aspirin surfaces was suggested for this reaction. In summary, both reactions that were studied provided a better insight towards understanding the solid-state reactivity of organic crystals. The proposed surface mechanisms imply that surface defects and the presence of humidity or solvent vapour are very likely to play a role in determining reactivity. Further studies on the origin of defects are suggested in order to better control the behaviour of organic crystals in the solid-state.
Supervisor: Not available Sponsor: Pfizer Institute of Pharmaceutical Materials Science
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: atomic force microscopy ; chemistry ; surface chemistry ; crystal defects ; pharmaceutical ; organic crystals ; solid-state chemistry ; photochemical ; anthracene ; aspirin ; NSAIDs