Shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids*

We present diffusiophoresis of ellipsoidal particles induced by ionic solute gradients. Unlike the common belief that diffusiophoresis is shape-independent, here we show that this assumption breaks down when the thin Debye layer approximation is relaxed. Using particle tracking microscopy, we find that the diffusiophoretic mobility of ellipsoids is sensitive to the eccentricity and the orientation of the ellipsoid relative to the imposed solute gradient. We show that such shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids can be easily captured by modifying previous theories for spheres.