Dynamics of growth and detachment of an isolated bubble on an inclined surface

The quasistatic growth of an air bubble nucleated on an inclined plate is investigated. Three substrates (Teflon, treated glass, and glass) are used to study the influence of the wetting conditions of the plate. The plate has been drilled to allow air injection and nucleation of the bubbles on the substrate. High-speed shadowgraphy visualizations in two perpendicular planes are used to record the evolution of the bubble shape during its growth. Experiments are conducted in quiescent water for different slopes of the plate. The bubble shape is extracted from image processing and several geometric parameters are determined. These geometric parameters are used to evaluate the forces acting on the bubble using a point-force approach. It appears that the classical expressions of the forces are valid for small slopes of the surface (less than 15◦), while the force balance is no longer verified for higher slopes. This result is linked to an elongation of the bubble foot that has to be taken into account in the modeling of the capillary force. Thus an expression for the capillary force is proposed and the force balance is used to predict the bubble detachment diameter.