A methodology to determine the adhesion force of arbitrarily shaped drops with convex contact lines

• Model for measuring drop adhesion force was developed.
• No assumption for shape of contact line needed except convexity.
• No assumption for variation of contact angle along contact line is needed.
• New contact line model was experimentally validated.

The adhesion force of drops deposited on smooth solid surfaces can be found by integration along the contact line of the liquid–vapor surface tension acting on an infinitesimal contact line element, projected on the substrate plane (γ||). Approximate relations available in the literature are applicable only for drops with specific contact line shapes (e.g. circular, elliptical, parallel-sided, or contact lines with at least one axis of symmetry). However, in most applications drops are exposed to a combination of forces and the contact line may have any arbitrary shape. In this study, a model is developed to calculate the adhesion force of drops with arbitrary shape. The contact line shape and contact angle values are found using side view images taken at different azimuthal angles (around the drop). The model is applicable to drops of any shape, as long as contact line is convex, and takes into account the perspective errors during imaging.

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