Co-motion of catalytic tubes and host droplets on superhydrophobic surfaces

Abstract

The ability to convert chemical energy into directed motion is a defining feature of living systems and a central goal in the design of synthetic active matter. Here, we report a self-propelling system in which a millimeter-sized tube is confined within a hydrogen peroxide droplet on a superhydrophobic surface. The tubes are synthesized via chemical garden self-assembly and catalyze the decomposition of the peroxide to water and oxygen gas. The resulting droplet-tube cell exhibits diverse dynamic behaviors, including propeller-like spinning, orbital rotation, and long-range translational jumps, driven by the asymmetric growth and bursting of internally generated gas bubbles. These motions are sensitive to hydrogen peroxide concentration, which governs both the internal gas production rate and the system's active lifetime. This system offers a simple yet versatile platform for exploring confined catalysis, emergent motility, and the design of soft, fuel-containing active materials.