Brownian Motion Lab

Below are movies of polystyrene particles with diameter of 0.5 mm, 1.1 mm and 1.9 mm diffusing in water and water-glycerol mixtures of different ratios.

0.5 mm particles in water, 50/50 glycerol-water, 75/25 glycerol-water, glycerol

1.1 mm particles in water, 50/50 glycerol-water, 75/25 glycerol-water, glycerol

1.9 mm particles in water, 50/50 glycerol-water, 75/25 glycerol-water

0.5 mm, 1.1 mm, and 1.9 mm in water

0.5 mm, 1.1 mm, and 1.9 mm in 75/25 glycerol-water

Notice that some particles have halos around them. This is caused by the fact that the particles are doing Brownian motion also in the z direction, not only in the x-y plane. The halo is an optical effect seen when the particle is slightly out of focus.