Fig. 2: Dynamics of colloidal molecules by purely dielectric spheres.
From: Active colloidal molecules assembled via selective and directional bonds
a Schematic illustration showing the direction of electrohydrodynamic flow (EHD) around the central dielectric sphere. The EHD flow provides an additional hydrodynamic force for colloidal bonding; it also propels the colloidal molecules. b The bond length of colloidal molecules deceases as AC frequency decreases as labeled. c The propulsion velocity of colloidal molecules increases at lower AC frequencies owing to enhanced EHD flow. The velocity increases from AB1 (black square) to AB2 (red circle) and AB3 (blue triangle) colloidal molecules due to the geometrical asymmetry. d Finite-element analysis showing that the nonuniformity of the electric field around a dielectric sphere becomes prominent at lower AC frequencies; DEP and EHD increase accordingly. Red arrows represent the direction of electric field lines. Color bar: electric field strength. e The yields of colloidal molecules of different order n, depending on the initial feed ratio of ligand and central colloid as labeled. f and g High-order colloidal molecules constantly reconfigure as the ligand particles slide along the rim of central sphere, which leads to the simultaneous velocity change, as highlighted and labeled by corresponding color. Scale bar: 4 μm. The error bars refer to the standard deviation of values for multiple experiments.
