Surface tension of seawater at low temperatures including supercooled region down to – 25 °C

Abstract

The experimental apparatus used for the measurement of surface tension of supercooled water using a capillary rise technique [Hrubý et al. J. Phys. Chem. Lett 5 (2014) 425 and Vinš et al. J. Phys. Chem. B 119 (2015) 5567] was modified for the measurements with seawater. New data for the surface tension of IAPSO seawater standard were collected for a salinity range from 10 g/kg to 38 g/kg and at temperatures from 30 °C down to −25 °C. The reported measurements are relative to the surface tension of pure water at the reference temperature of 15 °C. The combined standard uncertainty of the relative surface tension is better than 0.30%. The new data do not indicate any anomaly in the temperature trend of the surface tension of low-temperature and supercooled seawater down to temperature of −25 °C. The data agree with other literature data measured at stable conditions above 0 °C. Recent correlation by Nayar et al. [J. Phys. Chem. Ref. Data 43 (2014) 043103], considered as a potential standard for the surface tension of seawater, shows a very good agreement with the new data both in the stable region and under the metastable supercooled conditions. The differences between the correlation and the experimental data are entirely within the experimental uncertainty. Consequently, the recommended range of validity of the correlation by Nayar et al. can be extended into the supercooled region down to −25 °C for salinity up to 38 g/kg. In addition, an alternative correlation for the surface tension of seawater compatible with the recent correlation by Pátek et al. [J. Chem. Eng. Data 61 (2016) 928] for pure water is introduced. The new correlation has the same form as that by Nayar et al., however with slightly modified coefficients. Both correlations for seawater provide comparable results over the temperature and salinity ranges of the available experimental data.