Investigation of particle pairing in liquids

Abstract

During the development of a particle interferometric method to size and characterize particles as small as 0.03 μm in liquids, early tests indicated that particles might be traveling as nontouching pairs in some instances. A plausible mechanism for pairing is the van der Waals attraction between particles, an attraction opposed by the double layer repulsion due to ions in the liquid. Electrostatic attraction could also produce transient pairings, followed by agglomeration. Particle pairs would be expected to have different dynamic, electrostatic, statistical, and optical characteristics from single particles. The behavior of particle pairs might be informative with regard to chemical and flow conditions in the liquid. The statistics of particles arriving in nontouching pairs was derived and compared with our data. For highly dilute tap water, there was statistically significant evidence for pairs, with an estimated 0.3% of the particles appearing in pairs. Similar tests did not show the existence of pairs in suspensions of 0.343-μm polystyrene latex. The small fraction of pairs found would not have significant effects in most circumstances nor require alteration of particle counting and analysis methods. © 1991.