Particle growth in aqueous suspensions: the influence of surface energy and polarity

The aggregation of drug particles in suspensions can cause products to be spoiled. In this paper the role of surface energetics in controlling the dispersion of powders in water is considered, by use of a spreading coefficient. The contact angles, surface energies and the polarities were determined for a series of barbiturate powders. Contact angles were measured using a Wilhelmy plate technique. Aqueous suspensions of each powder were prepared and the change in particle size was monitored over a period of hours and days. By extrapolation the limiting size of the aggregates was calculated and this was related to the original particle size of each powder.