A fundamental understanding of the bubble sliding mechanism underneath a surface is complex and associated with the shape of the surface (inclination and curvature), roughness and surface tension as well as wettability. Although wettability also has a significant impact on the bubble sliding mechanism, it is extremely difficult to characterise this parameter on a downward facing submerged surface as it involves a hysteresis of the contact angle and the wetting by sliding along the surface. The notion of wettability is based on the concept of an equilibrium state between the interfacial surface tension of the three phases and the presence of an equilibrium contact angle. This contact angle is the angle between the solid surface and the liquid-gas interface [19], which can be described by Young’s equation (Cluster report four). However, Young’s equation is based on a single contact angle and for a perfectly homogeneous and ideal situation. For a real system, like downward facing inclined submerged surface, the contact angle of the bubble can take several values [20]. The difference between the higher and the lower value of this dispersion is called the contact angle hysteresis and the durations of such phenomena are almost instantaneous as previously discussed. Recently, tremendous advances have been realized. It is established that measured dynamic angle is not a representative of the true angle of contact due to the effects of viscosity on the outline of the meniscus next to the moving contact line. Additional studies are, therefore, vital to establish the precision of the dimensions of the dynamic contact angle. Such studies are also needed to ascertain the physical properties of the system that affects the dynamic contact angle. In this report, attention is given to determine experimentally the dynamic contact angle and validate the results with our numerical predictions. It should be noted the wetting of the surface is neglected at this stage.

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