An experimental study of the influence of weak convection on perikinetic coagulation

A remarkably increased coagulation rate for 2-mu m PS spheres was previousl y reported for a perikinetic coagulation experiment performed under microgr avity conditions (1998, R. Folkersma, A. J. G. van Diemen, and H. N. Stein, J. Colloid Interface Sci. 206, 482); from this experiment, it was assumed that the leading factor slowing the coagulation process under normal gravit ation was free convection due to gravity (1998, R. Folkersma, and H. N. Ste in, J. Colloid Interface Sci. 206, 494). To test the influence of free conv ection as a single-effect factor on the coagulation process, a ground-based experiment was constructed. The coagulation rate of 2-mu m PS spheres disp ersed in water was determined by measuring the turbidity of the dispersion solution while convection-driven flows in the solution were checked with a visual magnification system. We found that it was possible to cease free co nvection-driven particle flows on the ground, as long as the experiments we re carefully operated. The strength of convection was controlled by changin g the temperature gradient applied to the sample cell. By monitoring both t he coagulation rate and convection-driven flows simultaneously, our experim ents showed that weak free convection (maximum speed <150 mu m/s) actually has negligible effects on the coagulation rate. (C) 2000 Acadenic Press.