Drop shape visualization and contact angle measurement on curved surfaces

The shape and contact angles of drops on curved surfaces is experimentally investigated. Image processing, spline fitting and numerical integration are used to extract the drop contour in a number of cross-sections. The three-dimensional surfaces which describe the surface–air and drop–air interfaces can be visualized and a simple procedure to determine the equilibrium contact angle starting from measurements on curved surfaces is proposed. Contact angles on flat surfaces serve as a reference term and a procedure to measure them is proposed. Such procedure is not as accurate as the axisymmetric drop shape analysis algorithms, but it has the advantage of requiring only a side view of the drop–surface couple and no further information. It can therefore be used also for fluids with unknown surface tension and there is no need to measure the drop volume. Examples of application of the proposed techniques for distilled water drops on gemstones confirm that they can be useful for drop shape analysis and contact angle measurement on three-dimensional sculptured surfaces.

Graphical abstractStatic, as-placed contact angles are estimated from side views of sessile drops on curved surfaces without need of any preliminary information. Figure optionsDownload full-size imageDownload high-quality image (83 K)Download as PowerPoint slideHighlights► Drop shape on curved surfaces is visualized. ► Contact angle is determined on flat and curved surfaces with no a priori information. ► Contact angle measurement on three-dimensional sculptured surfaces is performed. ► Gemstones wettability is analyzed.