Anisotropic colloidal particles exhibit complex dynamics which play a crucial role in their functionality, transport, and phase behavior. In this Letter, we investigate the two-dimensional diffusion of smoothly curved colloidal rods—also known as colloidal bananas—as a function of their opening angle $\alpha$. We measure the translational and rotational diffusion coefficients of the particles with opening angles ranging from $0^{\circ }$ (straight rods) to nearly ${360}^{\circ }$(closed rings). In particular, we find that the anisotropic diffusion of the particles varies nonmonotonically with their opening angle and that the axis of fastest diffusion switches from the long to the short axis of the particles when $\alpha >{180}^{\circ }$. We also find that the rotational diffusion coefficient of nearly closed rings is approximately an order of magnitude higher than that of straight rods of the same length. Finally, we show that the experimental results are consistent with slender body theory, indicating that the dynamical behavior of the particles arises primarily from their local drag anisotropy. These results highlight the impact of curvature on the Brownian motion of elongated colloidal particles, which must be taken into account when seeking to understand the behavior of curved colloidal particles.

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• Brownian motion
• Diffusion
• Colloids
• Optical microscopy