Plastron-mediated growth of captive bubbles on superhydrophobic surfaces

Captive bubbles on a superhydrophobic (SH) surface have been shown to increase in volume via injection of air through the surrounding plastron. The experimental contact diameter against volume trends were found to follow that predicted by the Surface Evolver simulation generally but corresponded with the simulated data at contact angle (CA) = 158° when the volume was 20 μL but that at CA = 170° when the volume was increased to 180 μL. In this regime, there was a simultaneous outward movement of the contact line as well as a small reduction in the slope that the liquid–air interface makes with the horizontal as air was injected. At volumes higher than 180 μL, air injection caused the diameter to reduce progressively until detachment. The inward movement of the contact line in this regime allowed the bubble body to undergo shape deformations to stay attached onto the substrate with larger volumes (300 μL) than predicted (220 μL at CA = 170°) using simulation. In experiments to investigate the effect of translating the SH surface, movement of captive bubbles was possible with 280 μL volume but not with 80 μL volume. This pointed to the possibility of transporting gas-phase samples on SH surfaces using larger captive bubble volumes.