Liquid-vapor surface tension

Liquid vaporization cycle, 8 42 Liquid-vapor surface tension, 12 3 Liquid viscosity... 

In two-component liquid the change in the liquid-vapor surface tension is given by... 

The work of Bangham and Rozouk (6) also showed that ft e always has a value, TTe O. The studies by Harkins (8) and co-workers showed that ft e always exceeds the liquid-vapor surface tension by a factor of about 3 to 4, and that the contact angle tended to approach zero (C0S/ff2s 1.0). This being so ... 

It has generally been observed that urethane systems, which are cured on the surface of some low energy materials, are also free from adhering to them, i.e. they are self-releasing. Materials which show this characteristic relative to urethanes in a very effective way include at least three different types of plastics polytetrafluoroethylene, polyethylene, and polypropylene. These materials all have a defined critical surface tension sc less than about 30 dynes/cm. Assuming that this value is near, the liquid vapor surface tension lv value of an effective IMR urethane systems, then the work of adhesion as given by Equation 4 is as follows ... 

Here Vm is the condensed molar volume (34.68 cm3/mol for nitrogen) 7 is the liquid-vapor surface tension (8.72 X 10 3 N/m for nitrogen) R is the gas constant T is the temperature p is the pressure of nitrogen above the sample po is the saturation vapor pressure of nitrogen at temperature T and n is a unitless factor. The contact angle 0 is assumed to be zero, and the value of n is set to 2 for the desorption branch of the isotherm. The pore radius is then calculated from rp by adding the thickness of the adsorbed layer present before capillary condensation takes place. This thickness (t) is calculated by using the Halsey (5) equation ... 

Fig. 12. Critical temperature difference vs. bulk liquid-vapor surface tension.

It is known that the surface property of a solid is determined by its surface free energy. The relationship between contact angle (CA) and the surface tensions (y) has been described by Young s equation, cos0 = (ysv — ysi)/)dv. in which 6 is the contact angle, ysv. ysi. Y y are the solid-vapor, solid-liquid and liquid-vapor surface tensions, respectively. However, this equation is only applicable for an ideal plane, and measurements of WCA on real surfaces reveal that the WCA of a given... 

Another advantage of working in a liquid environment is the opportunity to study kinetic phenomena or to conduct experiments on the adsorption of surfactants. Figure 2.28 shows the liquid/vapor surface tension (easily measured, as we have just seen) and its solid/liquid counterpart (determined by way of the JKR method) as functions of the surfactant concentration in a system comprised of silicone, water, and heptaethyleneglycoldo-decylether. ... 

The liquid-vapor surface tension was calculated using the Kirkwood-Buff formula which in the geometry used in our system is given by [41]... 

However, this method requires a separate simulation to obtain liquid-vapor surface tension values and is therefore computationally intensive. More description of this method can be found elsewhere (Grzelak and Errington 2008). 

Values for the liquid-vapor surface tension can and have been obtained experimentally [30] by fitting the measured profile to the profile calculated by Bashforth and Adams [29]. In this manner one obtains p, and thus c, if the volume of the droplet and the liquid and vapor densities are also known. 

Contact angle measurements can also be used to obtain information about adsorption of surfactants on solid surfaces (in our case on fiber materials). In such a case contact angles have to be measured as a function of the surfactant concentration c. Under certain circumstances, but generally if the liquid-vapor surface tension is larger than the solid surface tension no adsorption of the liquid vapor on the solid surface takes place, and therefore the solid surface tension will stay constant with changing surfactant concentration. The Young equation [Eq. (3)] becomes therefore ... 

Dip coating. A solution or a sol dispersion of the precursor is first prepared. Then the substrate is vertically introduced in the solution or dispersion and slowly pulled out the covered substrate is then dried and the film formed upon calcination. The method has been used to prepare anatase, brookite, or rutile films [61]. The width of the film depends on the pulling rate, viscosity, and density of the liquid medium, its concentration, the liquid-vapor surface tension, and the temperature. 

Liquid/Vapor Surface Tension of the Methanol/Water Mixture.97... 

Liquid/Vapor Surface Tension of the Methanol/Water Mixture Surface tension values were previously measured at different mass fractions of methanol in water at constant temperature from 293 to 323 K, and are available in the literature (Vazquez et al., 1995). Bubble point tests here were conducted over a colder range of temperatures ( 275-295 K), so measurements from Vazquez et al. (1995) at 293 K are used to... 

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