Work

Impact of wettability onto the growth of air bubbles at micro-cavities on silicon wafers: Experiments, simulations, and analytical solutions

Year: 2024

Type: article

Abstract: • Wettability impacts the shape of surface bubbles and their speed of growth in supersaturated solutions. • Simulations show non-uniform distributions of dissolved air around surface bubbles that deviate from a hemispherical shape. • A novel bubble shape parameter derived from simulations is introduced into classical theory to fit the experimental results. The surface wettability influences the oversaturation-driven growth of gas bubbles on the surface via the contact angle. Larger contact angles on hydrophobic surfaces compared to hydrophilic ones lead to faster growth of bubbles nucleating at microcavities of identical size. Cylindric micro-cavities were etched in silicon wafers as nucleation sites. Afterward, the surfaces were functionalized to obtain different wettability characterized by contact angle. The growth of air bubbles was recorded using microscopic shadowgraphy. The bubble growth at micro-cavities can be separated into a pinning stage and an expansion stage. On more hydrophobic surfaces, the duration of the pinning stage is shorter, and the bubble grows with a larger contact angle during the expansion stage, both contributing to faster bubble growth. A shape-dependent factor derived from simulations vividly describes the average mass flux into the bubble caps of given contact angles, providing a clear explanation of the impact of wettability on bubble growth.

Source: Journal of Colloid and Interface Science

DOI: 10.1016/j.jcis.2024.12.133