The importance of aspect ratio in profile analysis tensiometry

The latest developments in profile analysis tensiometry (PAT) for determining surface tension and interfacial viscoelastic parameters involve the determination of a digital interface profile and its best fit with the Young–Laplace equation. In this short communication, we show that the results for surface tension and other interfacial parameters determined by PAT are extremely sensitive to the (aspect) ratio of length to width of a pixel. Fine calibration (to five decimal digits) for the aspect ratio required to obtain physically consistent results is not always achieved with conventional numerical procedures due to nanometer resolution limit of optical imaging devices but can be manually adjusted using the known surface tension of pure water and/or surfactant solutions at reference temperature.

(Left) Unreal variation of surface tension of water as measured with unadjusted aspect ratio and cyclic variation of bubble volume. (Right) Consistent surface tension of water as measured with adjusted aspect ratio and cyclic variation of bubble volume.Figure optionsDownload as PowerPoint slide