Figure 17.4 — Depletion interactions between colloidal particles Figure 17.4 — Depletion interactions between colloidal particles. (a) The large spheres are surrounded by a depletion region from which the smaller spheres are excluded, shown by the grey line. When the large spheres are close together, the total excluded volume decreases and, thus, the volume available to the small spheres increases. (b) With a higher volume fraction, the small spheres form a layered shell structure around the larger spheres. (c) Measured depletion interaction free energy as a function of small sphere volume fraction φS.Reprinted figures from Crocker et al., Phys. Rev. Lett. 82, 4352–5. Copyright (1999) by the American Physical Society.