Colloidal transport controlled by surface anchoring in active nematic fluids

Abstract

The spontaneous spatiotemporal chaotic properties of active nematic fluids provide a unique non-equilibrium environment for microscopic transport, yet achieving controllable transport within disordered turbulence remains a key challenge. The colloidal transport controlled by surface anchoring in an active nematic fluid is investigated using the method of direct-forcing fictitious domain. The control mechanism of surface anchoring angle (α=0º~90º) and active characteristic length (L c ) on colloidal transport is revealed. The results showed that although highly active turbulence dominates the decay of the velocity-related length (L vv ) in the flow (L vv ~ζ-0.41 , where ζ is the activity strength), the anchoring on the colloidal surface regulates the enrichment location, dominant orientation, and fluctuation characteristics of topological defects in the surrounding flow by breaking local rotational symmetry. The phase diagram of the defect-colloid motion indicates that macroscopic colloidal transport fundamentally depends on the competitive interplay between hydrodynamic traction and local elastic repulsion. Among these, the planar anchoring conditions (α=90º) exhibits robust co-directional driving capability that resists high-activity turbulent disturbances. The unanchored colloids strictly follow the classical scaling law D T ~Lc -1 (i.e., D T ~ζ1/2 , where D T is the colloidal diffusion coefficient). In contrast, homeotropic anchoring conditions (α=0º) maintain highly efficient long-range oriented migration (D T ~Lc -0.83 ) through weak defect interactions. Furthermore, tilted anchoring conditions (α=30° and 60°) induce strong self-rotation, making colloids susceptible to vortex capture; whereas 90° anchoring tends to trap colloids in a localized oscillatory state characterized by "high kinetic energy and low diffusion" due to the near-field "defect pinning effect." The result indicates that surface anchoring designs enable precise control over colloids, transitioning them from "directed migration" to "topological trapping." This provides crucial theoretical foundations for designing novel microfluidic systems and developing programmable soft matter materials.