Characterisation of the Morphological and Surface Properties of Organic Micro-Crystalline Particles

The surface properties of single and agglomerated micro-crystals are characterised using the micro-focus X-ray beams available at a third generation synchrotron light source together with other laboratory facilities. The influence of the crystallisation environment, on the resultant product crystals is studied by both varying the cooling rates during crystallisation and through the addition of impurities and cross-correlated with the morphology and size changes. Unmodified urea crystallised in 99% ethanol produce needle-like crystals whilst addition of 4% of biuret in crystallisation of urea produce a more prismatic crystal shape. At faster cooling rates smaller sized crystals are produced and vice versa. Dispersive surface energy analysis using inverse gas chromatography (IGC) shows that unmodified urea has lower dispersive surface energy than urea modified by biuret. The dispersive surface energy also increases as the cooling rates increased. Both the morphology changes and surface energy measurements are validated using molecular modelling. The morphological prediction intermolecular force calculations of unmodified urea and urea modified by biuret are used to calculate a weighted value for the whole crystals’ dispersive surface energies. The results are in good agreement with experimental results from IGC. The sorption of urea crystals on water moisture showed that unmodified urea samples adsorbed water higher than urea modified by biuret by the observation of the percentage of mass change with respect to the relative humidity. The study of variability within powdered samples was found that no significant different in the unit cell parameters values of each single crystals. The orientation relationship between agglomerated micro-crystalline particles of aspirin showed the agglomerates tend to interact at the faces that have ability to form bonding. In urea samples, most of the agglomerates are mostly aligned due to epitaxy growth of the crystals. The XMT experiment also was carried out on agglomerated α-LGA and the 3-dimensional (3D) shape the samples were obtained.