ABSTRACT Gas entrapment during dynamic wetting on microstructured surfaces critically determines coating uniformity and interfacial transport in photoresist deposition. This study systematically investigates gas–liquid–solid interactions during droplet spreading on hydrophilic quartz micro-grooved substrates using high-speed microscopic imaging and theoretical modeling. A multistage evolution is observed, where a primary central air pocket fragments into secondary and micro-scale bubbles as groove width decreases. A two-dimensional capillary–compression model and an implicit 3D relation are developed to describe gas encapsulation at the groove center under atmospheric pressure. Results reveal a critical geometric transition: gas entrapment becomes unavoidable when the groove width falls below 20 μm and the aspect ratio (AR) exceeds 0.25. The inclination of the advancing three-phase contact line is identified as the dominant factor governing cavity closure. Furthermore, once the AR exceeds 2, reducing groove width enhances the apparent hydrophobic response more effectively than increasing groove height. Vacuum-assisted experiments demonstrate that lowering ambient pressure significantly suppresses bubble formation, identifying an optimal vacuum pressure window of -50 to -80 kPa for photoresist wetting. These findings elucidate the fundamental mechanisms of wetting-induced gas entrapment and provide quantitative guidelines, including specific geometric limits and pressure setpoints, for defect-free photoresist coating and controlled microbubble generation.
Li et al. (Wed,) studied this question.