Hydroxyapatite suspensions were prepared in water, isopropyl alcohol, and hexadecane representing polar, semipolar, and nonpolar media, respectively. A range of dispersants were added and pH was adjusted where appropriate in an attempt to modify stability against sedimentation and hence provide suspensions suitable for ink-jet printing and other colloidal processing methods. Stability was assessed by sedimentation tests and by optical microscopy of the fractal patterns that form in drainage films on glassware surfaces. This novel method was made quantitative by simple but effective image processing methods and the two approaches correlated well. The interpretation of drainage films needs to be tested for generality on other powders but could provide a rapid method (within seconds) of screening flocculation behavior which, when assisted by elementary image processing methods of the type described here, could be used for high-throughput screening. It allows a nanoscopic process to be viewed by eye. This is possible because the fractal hierarchy of agglomeration allows the results of processes occurring at the ultimate particle scale to be observed at the millimeter scale.
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