A dramatic increase in the surface tension of water with decreasing temperature in the supercooled liquid region has appeared as one of the many anomalies of water. This claimed anomaly characterized by the second inflection point at about +1.5 °C was observed in older surface tension data and was partially supported by some molecular simulations and theoretical considerations. In this study, two independent sets of experimental data for the surface tension of water in the temperature range between +33 and -25 °C are reported. The two data sets are mutually consistent, and they lie on a line smoothly extrapolating from the stable region. No second inflection point and no other anomalies in the course of the surface tension were observed. The new data lies very close to the extrapolated IAPWS correlation for the surface tension of ordinary water, which hence can be recommended for use, e.g., in atmospheric modeling.

Measurements of the surface tension of supercooled water down to −25°C have been reported recently (Hrubýet al. J. Phys. Chem. Lett. 2014, 5, 425−428). These experiments did not show any anomalous temperature dependence of the surface tension of supercooled water reported by some earlier measurements and molecular simulations. In the present work, this finding is confirmed using a counterpressure capillary rise method (the counterpressure method) as well as through the use of the classical capillary rise method (the height method). In the counterpressure method, the liquid meniscus inside the vertical capillary tube was kept at a fixed position with an in-house developed helium distribution setup. A preset counterpressure was applied to the liquid meniscus when its temperature changed from a reference temperature (30°C) to the temperature of interest. The magnitude of the counterpressure was adjusted such that the meniscus remained at the same height, thus compensating the change of the surface tension. One advantage of the counterpressure method over the height method consists of avoiding the uncertainty due to a possible variation of the capillary diameter along its length. A second advantage is that the equilibration time due to the capillary flow of the highly viscous supercooled water can be shortened. For both the counterpressure method and the height method, the actual results are relative values of surface tension with respect to the surface tension of water at the reference temperature. The combined relative standard uncertainty of the relative surface tensions is less than or equal to 0.18%. The new data between −26 and +30°C lie close to the IAPWS correlation for the surface tension of ordinary water extrapolated below 0.01°C and do not exhibit any anomalous features. ■ INTRODUCTIONThe surface tension of supercooled liquids, in particular, water and aqueous mixtures, is an important property both in academia and in industry. It plays an essential role in atmospheric research of the nucleation and growth of water droplets 1 and ice crystals. 2 It is known that water in clouds can persist in a supercooled liquid form at temperatures down to −38°C. 3 Manka et al. 4 recently showed that liquid water nanodroplets rather than ice crystals form by homogeneous nucleation at temperatures down to −73°C. Reliable data for the surface tension of supercooled aqueous systems are also important in technical applications such as operation of wind turbines, 5 aircraft icing, 6 or design of secondary refrigeration systems operating with brine. 7 Compared to other fluids, water shows several anomalies at low temperatures, e.g., the well-known maximum in the liquid density at +4°C at atmospheric pressure. The unusual behavior of liquid water becomes more distinct in the metastable supercooled region below 0°C. For instance, the isobaric heat capacity and the isothermal compressibility seemingly diverge (or approach a sharp maximum) when extrapolated to temperatures around −45°C, i.e., below the homogeneous nuc...

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The TOTEM Experiment will measure the total pp cross-section with the luminosityindependent method and study elastic and diffractive scattering at the LHC. To achieve optimum forward coverage for charged particles emitted by the pp collisions in the interaction point IP5, two tracking telescopes, T1 and T2, will be installed on each side in the pseudorapidity region 3.1 ≤ |η| ≤ 6.5, and Roman Pot stations will be placed at distances of ±147 m and ±220 m from IP5. Being an independent experiment but technically integrated into CMS, TOTEM will first operate in standalone mode to pursue its own physics programme and at a later stage together with CMS for a common physics programme. This article gives a description of the TOTEM apparatus and its performance.

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