Electrocapillary measurements by drop-time technique: Comparison of calibration methods

Abstract

This paper considers the drop-time technique in electrocapillary measurements and focuses on calibration methods required to convert the drop-time t of a mercury electrode into the value of the interfacial tension γ. The relationships between t and γ, described in the literature, are reviewed and six calibration methods identified. On the basis of high-precision drop-time electrocapillary measurements carried out in 0.1moll−1 KCl aqueous solution, with γ values known from the absolute measurement method, the performance of the calibration methods, expressed in terms of measurement bias and uncertainty, is evaluated and compared. Better performance is observed for the methods that involve a nonlinear model such as γ=αtβ fitted to calibration data, instead of a single-point linear calibration commonly used. The measurement uncertainty U⩽0.12mNm−1 evaluated with these advanced calibration approaches corresponds to the level of accuracy achieved with the classical capillary electrometer.