Surface Between Water and its Vapor or Air

The surface tension of water with respect to water vapor is listed as a function of the temperature at the standard pressure (0.1 MPa) in Table 1.2. The value with respect to air is lower by 0.03 % at room temperature (Richards and Carver 1921). Compared with other liquids the value is quite large y = 71.96 mN m at 25 °C, exceeded only by that of hydrogen peroxide, 73.7 mN m , and approached only by other highly hydrogen bonded liquids such as glycerol, 63.3 mN m ethylene glycol, y =48.0mN m and formamide y = 58.2 mN m Other common liquids have definitely lower values, mostly in the range of 20-40 mN m (Marcus 1998). 

The temperature dependence of the surface tension of liquids is expressed well in terms of an empirical equation involving the critical temperature Tc (Guggenheim 1945)  

The proportionality coefficient yo is a function of the critical temperature 7, the critical density Pc, and the acentric factor (o. For water, however, this expression is only approximate between 0 and 100 °C (with yo = 157.7 mN m ) and a more accurate description is in terms of a linear dependence on (1 

One way to deal with the molecular aspects of the surface tension of a liquid is via the scaled particle theory (SPT) of Reiss et al. (1960). Mayer (1963) obtained an expression from this treatment, reformulated here as follows  

assuming that the SPT is applicable to macroscopic quantities, Mayer (1963a) related the surface tension of a liquid to its isothermal compressibility. He reformulated Eq. (4.3) again as  

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