Figure 2. Dynamics of an isolated colloidal roller.

(a) Local packing fraction φ(r), averaged over the azimuthal angle φ, plotted as a function of the radial distance. The dashed line indicates the radius of the circular chamber. (b) Probability distribution function of the roller velocities measured from the individual tracking of the trajectories. (c) Autocorrelation of the roller velocity 〈v_i(t)·v_i(t+T)〉 plotted as a function of v₀T for packing fractions ranging from φ₀=6 × 10⁻³ to φ₀=10⁻². Full line: best exponential fit. (d) Superimposed trajectories of colloidal rollers bouncing off the edge of the confining circle. Time interval: 5.3 ms (E₀/E_Q=1.1, φ₀=6 × 10⁻³). Same parameters for the four panels: R_c=1.4 mm, E₀/E_Q=1.1, φ₀=6 × 10⁻³.