Bioinspired Temperature-Responsive Anisotropic Cilia Surface for Flexible Manipulation of Underwater Bubbles
Underwater bubble manipulation is critical for water electrolysis, heat transfer, and mineral flotation, yet existing strategies relying on buoyancy or Laplace gradient forces from asymmetric surface geometries suffer from limited flexibility and narrow applicability. This work introduces a temperature-responsive anisotropic cilia surface (TRAS) that achieves bidirectional long-range bubble transport by modulating elastic modulus and stiffness. The TRAS enables precise control over the asymmetric three-phase contact line and viscous resistance, facilitating reversible bubble motion. Experimental validation using aqueous ethanol droplets with varying surface tensions (73.16 mN/m for 0 vol% to 22.27 mN/m for 100 vol%) on cilia with center-to-center spacings of 0.2–1.0 mm reveals that transport direction depends on both cilia spacing and liquid surface tension. Droplets of 0 vol% and 20 vol% ethanol exhibit sustained reverse transport on hard cilia, while 60 vol%, 80 vol%, and 100 vol% solutions show sustained forward transport. Notably, 40 vol% ethanol droplets display bidirectional transport at 0.6 mm spacing, reverse transport at 0.8 and 1.0 mm, and forward transport at 0.2 and 0.4 mm. These results demonstrate that tuning surface tension and cilia spacing provides a versatile platform for directional bubble manipulation, with promising applications in heat transfer, electrochemistry, and gas handling systems.