Rotating Soft Macrogrooved Interfaces for Programmable Transport and Rebound‐Driven Sorting

ABSTRACT Groove‐guided liquid transport on biological surfaces demonstrates how structural patterns regulate droplet motion. Inspired by this principle, a rotating soft annular macrogrooved substrate is designed. The coupling of substrate compliance and rotation‐induced shear produces a unique rebound regime, where droplets undergo a single and low‐amplitude bounce that is absent on both rigid and non‐rotating substrates. A combined theoretical and experimental analysis establishes the upper and lower limits of this regime. Remarkably, the contact time exhibits a non‐monotonic dependence on the rotational capillary number, with up to a 25% reduction at intermediate values. Building on this controllable rebound and transport, a multifunctional droplet manipulation platform is demonstrated. First, high‐fidelity directional transport with millimeter‐scale precision validates the platform's accuracy. Second, a radial distribution system enables rapid modulation of solution concentrations through spatial deposition. Third, label‐free droplet sorting is realized across a broad range of viscosities and sizes with minimal mass loss for highly viscous liquids. As a proof‐of‐concept for real‐world processing, bovine milk droplets with different fat contents are separated, revealing sensitivity to subtle compositional differences. Finally, this tunable interface integrating transport and sorting in a single system is realized, enabling quantitative property‐based droplets analysis and advancing next‐generation droplet manipulation technologies.