Possible Anomaly in the Surface Tension of Supercooled Water: New Experiments at Extreme Supercooling down to -31.4 °C

The surface tension of water is suspected to show a substantial increase at low temperatures, which is considered to be one of the many anomalies of water. The second inflection point (SIP) anomaly, originally claimed to be at around -8 °C, was experimentally refuted down to -25 °C by Hrubý et al. ( , 5, 425-428). Recent molecular simulations predict the SIP anomaly near or even below the homogeneous freezing limit of around -38 °C. To contribute to an ongoing discussion about the SIP anomaly, new experiments focused on extreme levels of supercooling were carried out in this study. Unique experimental data down to -31.4 °C were collected using two measuring techniques based on the capillary rise method. A significant deviation from the extrapolated IAPWS formulation R1-76(2014) for surface tension of ordinary water was detected below -20 °C. Contrary to previous data, new experiments provide room for an anomaly in the course of surface tension in the deeply supercooled region.