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What happens when nanoparticles collide?
When there is a significant amount of particles, the Brownian motion brings them collide. The phenomenon of coagulation forms aggregates maintaining particles to each other by forces of attraction (Van der Waals). This leads to an instability of aerosol (composed of small particles), an overall increase in the size of aggregates associated with a decrease in the concentration of particles in the air.
Visualization of the mechanism of coagulation kinetics of nanoparticles (10, 30 and 50 nm).
The more the size of the aggregate increases, the less sensitive to the thermal diffusion it is: speed and mean displacement decrease. Beyond 5x102 nm, the force of gravity is no longer negligible: an agglomerate of one micron could be deposited on the ground in a few tenths of seconds.