INFLUENCE OF GRAVITY ON PERIKINETIC COAGULATION

Perikinetic coagulation experiments are reported which were performed under 1g and mu g conditions during a flight in a sounding rocket, for dispersions of polystyrene, quartz, and amorphous silica particles. C oagulation rates for dispersions of polystyrene, quartz, and amorphous silica are found to increase significantly under mu g conditions comp ared to 1g conditions. Another set of experiments was performed at 1g, 2g, 4g, and 7g, with different densities of the continuous phase; als o a mixture of two different polystyrene latices was used. The most pr onounced effect of gravity on coagulation rate is found for dispersion s with a small density difference, on going from 1g to 2g. In this reg ime a significant decrease in coagulation rates is observed. For the l atex mixture at pronounced density differences, gravity-induced coagul ation was observed; however, the aggregates formed did not have a last ing contact. The rate constant calculated under mu g conditions approa ches the theoretical value of von Smoluchowski. By means of a video an alysis of the perikinetic coagulation process, the formation of double ts was studied. The ''interaction time'' for two particles was found t o be longer for the density-matched dispersion. Doublets of particles are easily disrupted, and at 1g, free convection currents were observe d even at small temperature differences in the system. (C) 1998 Academ ic Press.