Direct measurement of interaction force between solid surface and air bubble: Relationship between interaction force and contact angle

Estimating the hydrophobicity of a solid surface is important for flotation process. Measuring the contact angle or interaction force between air bubbles and a solid surface has been widely used for evaluating the hydrophobicity of surfaces. However, the correlation between the contact angle and interaction force was not be fully explained because contact angle was measured on a macroscale surface and interaction force was measured on a microscale surface (ranging nm(2) - mu m(2)) using atomic force microscopy. In this study, we directly measured the macroscale surface - air bubble interaction force in terms of attachment force and detachment energy. We then correlated our measured attachment force and detachment energy values with the static contact angle of specimen surface. The attachment force (F-a) and detachment energy in phase 2 (E-2) represented the hydrophobicity of specimen surface. And F-a and E-d in phase 2 were found to have an exponential relationship until 90 degrees of the surface contact angle.