Solid-vapor interfacial tension

A drop of liquid at rest on a solid surface is under the influence of three forces or tensions. As shown in Fig. 10.2, the circumference of the area of contact of a circular drop is drawn toward the center of the drop by the solid-liquid interfacial tension, 7sl- The equilibrium vapor pressure of the liquid produces an adsorbed layer on the solid surface that causes the circumference to move away from the drop center and is equivalent to a solid-vapor interfacial tension, ygy- The interfacial tension between the liquid and vapor, y y, essentially equivalent to the surface tension y of the... 

In this Young s expression, the solid-vapor interfacial tension, ysv is the surface tension of the solid in equilibrium with the vapor of the wetting liquid. If ys is the surface tension of the solid against its own vapor or in vacuum, then [72]... 

The Wenzel Eq. (21) was derived by assuming that the roughness increases the surface solid/liquid and solid/vapor interfacial tensions by the factor r, the surface roughness coefficient, so that the effective interfacial tensions become ry L Tsv and by direct substitution into Young s equation yields,... 

Liquid/vapor interfacial tension Solid/vapor interfacial tension Curvature ( = 1/r)... 

This appendix presents computation of resultant solid/liquid and solid/vapor interfacial tensions from the methanol/water binary mixture bubble point data from Chapter 4. Governing equations are presented for deriving the Langmuir isotherms for the S/L and S/V data. The goodness of fits are also discussed for both cases. 

FIGURE D.1 Solid/Vapor Interfacial Tension as a Function of Liquid/Vapor Interfacial Tension for Binary Methanol/ Water and Stainless Steel 304 System. 

The bubble point tests conducted in methanol/water mixtures were worked up to show properties of the three-phase interfaces along the complex contact line in SS304 LAD screens. In particular, the variation with F2 of the solid/vapor interfacial tension /sv differed from that of the solid/liquid interface j/sl- The data are consistent with the Langmuir isotherm description of the thermodynamics of adsorption. The result of the analysis is that the co-areas Amin are 0.32 nm /molecule for the SS304— vapor interface and 1.77 nm /molecule for the SS304—solution interface. This implies that that methanol molecules form a dense, liquid-like monolayer at the interface of SS304 with the vapor phase, while the methanol molecules are very dilute in the interface between SS304 and the solution of methanol/water. 

Wetting can also be considered as a capillary phenomenon. The inner wall of the capillary may be defined as hydrophilic if the capillary rise of water is positive. This implies that the advancing contact angle of water is less than 90. This criterion is much less stringent than the previous one, and hydrophilicity would imply that the solid-vapor interfacial tension is greater than the solid-water interfacial tension. 

DETERMINATION OF THE SOLID-VAPOR INTERFACIAL TENSION OF BENZOPHENONE AND BIBENZYL USING THE FREEZING FRONT TECHNIQUE... 

This expression shows that the excess free energy decreases if (1) the liquid-vapor interfacial tension, y, decreases, (2) if the liquid-solid interfacial tension, Yj, decreases, and (3) the solid-vapor interfacial tension, y,, increases. 

Note that adsorption of surfactant molecules results in a dcCTcasing of solid-liquid interfacial tension, that is, y , - y > 0. However, adsorption of surfactant molecules on the bare hydrophobic interface in front of the moving meniscus results in a local increase of the solid-vapor interfacial tension, that is, y°sv lZ< 0- The initial contact angle on the bare hydrophobic interface is assumed to be bigger than %I2, that is, y - y , < 0. 

It is assumed that the imbibition process goes sufficiently fast, and transfer of the surfactant molecules on the bare surface in front of the moving meniscus can be neglected because this process goes much slower (see Section 5.2). Hence, the solid-vapor interfacial tension, y does not depend on the surfactant concentration and remains equal to its value at zero concentration. It is also taken into account in Equation 5.42 that Ys/(Cm) is a decreasing function of the surfactant concentration. Equation 5.42 shows that P(C ,) = Y(C .)cos0a(C ,) isanincreasing function of the concentration, with the maximal value, = P(Q mcX reached at CMC and the minimal value, = Ysv(0)-Ys((0X reached at zero surfactant concentration. 

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