• • Surface tension thresholds dictate transport direction: aqueous ethanol droplets with surface tensions ≥39.73 mN/m (0–20 vol%) undergo sustained reverse transport on hard cilia, while those with ≤28.85 mN/m (60–100 vol%) exhibit forward transport, establishing a critical surface tension window for directional control.
• • Cilia spacing modulates bidirectional behavior: at 0.6 mm center-to-center spacing, 40 vol% ethanol droplets (30.11 mN/m) achieve bidirectional transport, whereas 0.8 and 1.0 mm spacings yield reverse transport and 0.2–0.4 mm spacings yield forward transport, enabling programmable motion paths.
• • Temperature-responsive elastic modulus and stiffness of TRAS provide a reversible mechanism to tune asymmetric three-phase contact line and viscous resistance, overcoming the fixed-geometry limitations of conventional asymmetric surfaces.
• • The TRAS platform enables long-range bidirectional bubble transport without external power sources, offering a scalable route for enhancing heat transfer efficiency in electrolyzers and mineral flotation cells where bubble directionality is critical.