Work of Adhesion Wa

Most of the various strategies which have been proposed to predict relative adhesive interfacial strength are based on thermodynamics. One may define, without ambiguity, as shown in Fig. 3, a thermodynamic work of adhesion , Wa,... 

Fig. 3. Definition of thermodynamic work of adhesion, Wa (a) disjoining surfaces in vacuum (b) disjoining surfaces in fluid medium m and (c) disjoining surfaces in presence of vapors from adhesive.

The work of adhesion was determined from the a versus P measurements (see Eq. 11). The work of adhesion between two rubber spheres was found to be 71 4 mJ/m. The work of adhesion reduced to 6.8 0.4 mJ/m in the presence of 0.01 M solution of dodecyl sulfate. Using these measurements of adhesion between rubber in air and a surfactant solution, Johnson et al. [6] provided the first direct experimental verification of the Young s equation (Eq. 40). They also measured... 

In an attempt to determine the applicability of JKR and DMT theories, Lee [91] measured the no-load contact radius of crosslinked silicone rubber spheres in contact with a glass slide as a function of their radii of curvature (R) and elastic moduli (K). In these experiments, Lee found that a thin layer of silicone gel transferred onto the glass slide. From a plot of versus R, using Eq. 13 of the JKR theory, Lee determined that the work of adhesion was about 70 7 mJ/m". a value in clo.se agreement with that determined by Johnson and coworkers 6 using Eqs. 11 and 16. 

Contact Angle (0) and the Work of Adhesion (Wa) for the Control and the Modified EPDM Surfaces... 

The force needed to break the mineral-air interface is called the work of adhesion, WA, and is equal to the work needed to separate the mineral-air interface and produce in place air-water and mineral-water interfaces. This, in other words, may be represented with interfacial tensions in place as ... 

In a similar manner, an expression for the interfacial tension, Yf can be written using the geometric mean definition for work of adhesion, Wa (see Figure 8), and the Girifalco-Good interaction parameter (17-18), as. 

Wetting can be quantitatively expressed in terms of the thermodynamic work of adhesion, Wa. of a liquid to a solid using the Dupre equation... 

Harkins defines two terms, the work of cohesion We which is the work done when a bar of liquid of unit cross sectional area is pulled apart against the cohesive forces. It is thus numerically equal to twice the sur ce energy of the liquid. The work of adhesion Wa is similarly defined as the work required to pull apart a composite bar consisting of half of one liquid and half of the other, at the place of junction. 

The contact angle has a significant effect on repellency. The work of adhesion, Wa, required to remove the droplets, ignoring viscoelastic effects is ... 

Also, Fowkes [90] and Good [91] developed a novel technique for the determination of the work of adhesion, Wa, by employing the surface free energy obtained from the contact angle value in the system of solid-liquid using... 

Dupre equation — The equation gives the work of adhesion Wa b between two immiscible liquids A and B Wa b = Pa v + yp, v - Pa-b. where y denotes the interfacial tensions between the different phases (A-V liquid A-vapor A, B-V liquid B-vapor B, A-B liquid A-liquid B). 

When the optimal conditions are satisfied, i.e., a well-controlled atmosphere, a pure, homogeneous and smooth solid surface and an accurate measurement system, the Young contact angle and the liquid surface energy can be derived with an accuracy of 3 deg and 2% respectively allowing the work of adhesion (Wa = [Pg.144]

According to the definition of the work of adhesion Wa in terms of bond energies (equation (1.12) with A = M and B = AO), Wa is proportional to em-ao where em-ao is an average interaction energy between M atoms and oxide ions. Clearly, Wa is proportional to an absolute bond energy while AHf(MO) is proportional to a difference of bond energies. As a result, the interfacial quantity to be used in a correlation with AHc(mo) should not be Wa but the work of immersion W, which, taking into account its definition (equation (1.54)) and expressions (1.9) to (1.11) of <7SV and [Pg.208]

The forces responsible for adhesion/release are intermolecular, and are usually referred to as secondary valence forces. In many cases, however, they can also be primary, that is, those of direct chemical bond. In any event, the force of separation Fs is shown to be a function of two factors work of adhesion Wa, and the distance of bond separation d. Taylor and... 

Direct measurements on the work of adhesion Wa have also been summarized by Krauss (11). Values of Wa are also calculatable with reasonable accuracy for systems free of direct chemical bond as is shown later in "Equation 3 . The separation distance d for high energy systems where Fmax exists has been estimated by McKelvey... 

Figure 6-3 illustrates the situation of a liquid soil adhering to a substrate in the presence of air. The reversible work to remove the liquid oily soil O from the substrate, the work of adhesion Wa (equations 6.12 and 6.13) is given by the expressions... 

Adsorption of surfactant and other bath components (e.g., inorganic ions) at the substrate-liquid and particle-liquid interfaces. This causes a decrease in the work required to remove the particle from the substrate, since the free energy change per unit area involved in this process is the work of adhesion Wa (Chapter 6, Section IB), given in this case by the expression... 

Fowkes proposed in 1964 that the work of cohesion, W), and the work of adhesion, Wa, can be separated into their dispersion, d, polar, p, induction, i, and hydrogen-bonding, h components ... 

Table 13. Correlation of extrapolated adhesive strength a0 with work of adhesion Wa for various HPC film-substrate combinations [61]...

According to Dupre, the work of adhesion, Wa, is a characteristic of the similarity between neighboring phases, i.e., it shows the degree of saturation in the uncompensated surface forces upon contact. The interfacial energy, gi2, on the contrary describes the intensity of the remaining uncompensated interactions at the interface between neighboring phases. 

A comparison of Young s equation with the definition of the work of adhesion, Wa, given by eq. (III. 1), yields... 

To solve this equation the adsorption isotherm needs to be measured over a wide range of partial pressures and integrated. As a result the work of adhesion Wa, the free energy JG and the dispersive and polar surface energy, y s and y s can be obtained. 

Values for the approximate work of adhesion, WA, of each polymer for each test liquid are indicated in Table IV. They were calculated... 

Interfacial equilibrium work of adhesion was calculated using the values of polar and dispersive components of the surface energy according to the relation ... 

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