Bubble detachment from patterned solid surfaces: Roles of wettability contrast and domain geometry

Bubble detachment from solid surfaces plays a vital role in technologies such as electrolytic hydrogen production for clean energy and flotation recovery of critical minerals. However, the interfacial physics governing three-phase contact line during detachment on heterogeneous surfaces remains poorly understood. This study investigates the influence of wettability contrast and domain geometry on bubble detachment using patterned silicon substrates. Two types of surfaces were microfabricated: homogeneous hydrophobic substrates and composite substrates with a central domain (hydrophilic or hydrophobic) surrounded by a contrasting exterior. Circular, square, and triangular patterns were designed with constant perimeter and varying enclosed area. High-speed video microscopy and quantitative image analysis were used to determine detachment parameters, including contact angle, contact radius, and bubble volume over time. For surfaces with hydrophobic exteriors and hydrophilic interiors, the three-phase contact line retracted inward and pinned at the boundary, stabilizing the bubble and delaying detachment. This yielded the largest detachment volumes, contrasting with previous reports where superhydrophobic interiors enabled rapid retraction without pinning. In reverse configurations (hydrophilic exterior, hydrophobic interior), pinning was ineffective, resulting in unstable bubble behavior. Additionally, detachment volume scaled with contact area at fixed perimeter, with circular patterns producing the largest bubbles. These findings challenge classical capillary models and highlight the critical role of wettability contrasts and boundary geometry in bubble detachment - offering new insights for enhancing efficiency in hydrogen production and the flotation-based recovery of critical minerals. Pinning of bubble contact controls detachment, but largest bubbles detach when pinned at wettability dividing lines between hydrophobic exterior and hydrophilic interior, yielding detaching volume scaling with contact area under fixed perimeter. • Bubble detachment on patterned surfaces with wettability contrast investigated. • Pinning at hydrophobic exterior-hydrophilic interior boundary yields largest volumes. • Detaching volume scales with contact area under fixed perimeter. • Sharp corners accelerate bubble detachment from patterned domains. • Insights enhance bubble physics beyond classical theories for emerging applications.