Fig. 3: The translational and rotational diffusion of an individual particle is described by a sphere near a non-slip wall in Stokes flow.
From: Hydrodynamic spin-orbit coupling in asynchronous optically driven micro-rotors
a Snapshots (and time-colored trajectory) of a birefringent vaterite particle viewed through crossed-polarizers, showing Brownian translation and rotation. b Near a no-slip wall (solid line), particles have lower translational diffusion Dt relative to particles in bulk, consistent across a measured size range of d = 2 − 6 μm. Inset shows the translational mean-squared displacement (MSDs) for particles with sizes d = 1.92 ± 0.11 μm and 5.92 ± 0.35 μm. The translational diffusion constants Dt obtained from these two MSDs are indicated by gray arrows in the main panel. c Rotational diffusion perpendicular to the wall, (spinning) Dr,⊥, measured using depolarization intensity decorrelation, gPA. Dr,⊥ is largely unchanged by the presence of a no-slip wall (solid line). The blue arrow indicates Dr,⊥ obtained from fitting gPA for a d = 2.31 ± 0.14 μm particle (inset). Scale bar: 5 μm. Error bars correspond to the standard deviation.
