TEM studies of the crystal growth of indanthrone pigments
The aim of this work was to study the crystal growth of indanthrone during the pigmentation process. The colouring properties of a pigment are dependent on the chemical and crystallographic structure of the pigment. However, other factors are known to affect these properties including particle size, particle size distribution and level of dispersion in the chosen application medium. The parameters which affect the growth of the pigment particles were investigated with the emphasis placed on the mechanism by which growth took place. The final form of the crystals after growth was also investigated in this thesis. High and low magnification imaging and diffraction were studied on the CTEM (conventional transmission electron microscope) whilst PEELS (parallel electron energy loss spectroscopy) and DPC (differential phase contrast) studies took place on the VG HB5 STEM (scanning transmission electron microscope). In addition to these studies, x-ray diffraction and surface area analysis techniques were employed. The low magnification CTEM work gave good information on the size, shape and size distribution of the pigment particles and enabled detailed analysis of the level of growth attained under varied reaction conditions. Parameters varied during these reactions included choice of solvent, solvent concentration, reaction time and the method used for removing the solvent. Methyl benzoate and nitrobenzene were found to be effective in promoting crystal growth in indanthrone whilst isopropanol proved to be extremely ineffective. The rate of growth was found to be affected by, among other things, the concentration of the solvent and the time it was in contact with the pigment. The most likely method of growth has been identified as ripening followed by coalescence. Initially, larger particles grow at the expense of the smaller particles - the smaller ones go into solution and are then able to aid the growth of the larger particles.