Characterization of Colloidal Stability during Precipitation Reactions

Methods of characterizing colloidal interaction potentials of nanoscale silver particles during their formation are discussed. Silver sols are produced by the borohydride reduction of silver perchlorate, and their colloidal stability is found to vary both with reaction conditions and over the course of the reaction. Stability ratios are estimated using two independent techniques for a variety of reaction conditions and interpreted in terms of pair potentials consisting of van der Waals attractions and electrostatic repulsions. At low temperatures (<15 °C), the particles are highly charged. At higher temperatures (>15 °C), surface potentials decrease. At the end of the reaction where borohydride is converted to borate by oxidation with water, the particle surface changes, possibly forming an oxide layer resulting in a decrease in surface potential.