Bubble pinch‐off on biphilic and superhydrophobic surfaces

Abstract In this work, we experimentally measured the pinch‐off of a gas bubble on a biphilic surface, which consisted of an inner circular superhydrophobic region and an outer hydrophilic region. The superhydrophobic region had a radius of R SH varying from 2.8 to 19.0 mm, where the large R SH modeled an infinitely large superhydrophobic surface. We found that during the pinch‐off, the contact line had two different behaviors: for small R SH , the contact line was fixed at the boundary of superhydrophobic and hydrophilic regions, and the contact angle gradually increased; in contrast, for large R SH , the contact angle was fixed, and the contact line shrank toward the bubble center. Furthermore, we found that regardless of bubble size and contact line behavior, the minimum neck radius collapsed onto a single curve after proper normalizations and followed a power–law relation where the exponent was close to that for bubble pinch‐off from a nozzle. The local surface shapes near the neck were self‐similar. Our results suggest that the surface wettability has a negligible impact on the dynamics of pinch‐off, which is primarily driven by liquid inertia. Our findings improve the fundamental understanding of bubble pinch‐off on complex surfaces.