Fig. 9.2 — Digital video microscopy

(a) Original and (b) thresholded digital image of a ternary mixture of silica spheres (radii a = 1.55, 2.31 and 3.16 μm) freely diffusing on the bottom of a sample cell. The circles in (a) and the symbols in (b) represent the measured position and size of the particles. (c) Particle trajectories relative to an acquisition time of 10 s and (d) corresponding mean squared displacements (MSDs). Note in (d) that the MSDs loosely cluster around three values, corresponding to the three particle sizes.