Dupre energy of adhesion

Let us make some examples with adherence of glass ball on polyurethane. The Dupre energy of adhesion - 2... 

Dwell times generally increase the adherence force, and Fig. 10 shows the increase of w with contact time between glass and polyurethane (26). Between two polymers (auto-hesion ) this effect is ascribed to interdiffusion of chains by reptation theory and experiments (27-29) lead to a (hence a Dupre energy of adhesion, see below)... 

It is easily understood that a good adhesive must wet and clean the adherend, have a high Dupre energy of adhesion, a high viscosity, and no residual stress. To wet... 

These same forces also insure the adhesion between two solids and the work to break these bonds is the Dupre energy of adhesion (or thermodynamic work of adhesion) w = 7, + 72 712 where 7j and 72 are the surface energies and interfacial energy. (In-... 

Water adsorption decreases the Dupre energy of adhesion, and hence the viscoelastic losses according to Eq. (54). This point was verified by measuring the rolling resistance 91 of a glass cylinder rolling on an inclined sample (G — 91//) as a function of velocity for various... 

So far, we have assumed that the threshold value Gq for vanishing crack speed is the Dupre energy of adhesion w for adherence, or twice the surface energy y for fracture of homogeneous bodies. Indeed, for adherence of glass on polyurethane, crack propagation was observed for G > w and crack healing for G < vi. (4,63,64)... 

The theoretical curves, 1, corresponding to a non-contaminated rubber surface, are obtained by the following procedure. For each ball, the critical release altitude was accurately measured so that the mean value of the parameter , product of the temperature factor and the Dupr energy of adhesion, was correctly determined ... 

The process of viscoelastic braking just described has certain parallels with the dynamic adhesion of elastomers. When, for example, a rubber strip is peeled from a rigid substrate, the effective, or apparent, work of adhesion, W, is usually much greater than the intrinsic, or reversible, energy of adhesion, Wq, given by the Dupre equation [15] ... 

Thns the strain energy release rate is effectively an instantaneous value of Dupre s energy of adhesion, with 6 = 0(0 instead of the equilibrium value. The sign reversal in the left-hand side of Eq. (18) when compared to Eq. (15) is due simply to the fact that we have a closing crack with a spreading liquid. 

It seems essential that the energies of adhesion of the systems involved, the possibility of a contraction of the liquid film in negative systems and the contact angle (Fig. 27) are not taken into account in these relations. This may account for the great differences between calculated and experimental data. Combining the equations after Dupre and after Young yields the following simple relation for the work of adhesion ... 

It may be obvious to relate the equation of Young and Dupre (Equihion 8.3) to the Gibbs energy of adhesion between S and L It follows from Equation 5.11... 

The Young-Dupre equation for the free energy of adhesion is obtained by combining Eqs. (1) and (5a) ... 

Thermodynamically, a relationship of the free energy of adhesion per unit area of a solid-liquid pair is that it is equal to the work required to separate a unit area of the solid-liquid interface, thus creating a unit area of a liquid and solid interface (Figure 7.5(b)). This relationship is the well-known Dupre equation, as follows ... 

Clearly, the interfacial tensions and the adsorption state of all three D-faces contribute to this specific excess Helmholtz free energy of adhesion. In comparison, Dupre s rule (Dupre 1865) for the reversible specific work of adhesion... 

After Gibbs, we relate the free energy values of the liquid (subscript L) film between two identical solid (S) surfaces Gfiim. interfadal 0sl, and of the interaction F sLS) = F (represented by modulus) afiim = 2gsl — F . The Dupre rule states for the energy of adhesion W(sl) = W Gsl + = Os + Ol (no adsorption takes place). With model... 

If we separate two blocks of different materials 1 and 2, the energy difference that equals the adhesive energy (also called Dupre work of adhesion) will be given by... 

The van der Waals and other non-covalent interactions are universally present in any adhesive bond, and the contribution of these forces is quantified in terms of two material properties, namely, the surface and interfacial energies. The surface and interfacial energies are macroscopic intrinsic material properties. The surface energy of a material, y, is the energy required to create a unit area of the surface of a material in a thermodynamically reversible manner. As per the definition of Dupre [14], the surface and interfacial properties determine the intrinsic or thermodynamic work of adhesion, W, of an interface. For two identical surfaces in contact ... 

This equation has been known for over a century it was given by Young2 (without proof ) and by Dupre 3 it can be deduced also from Laplace s theory of Capillarity, or indeed from any theory of the cohesive forces, since it can be obtained from consideration of energies only. Until recent years it has been little noticed, which is unfortunate, as the meaning of the contact angles is much clarified when the work of adhesion is introduced, and the surface tensions of the solid surfaces, which are not measurable, are eliminated. Most authors are now, however, expressing their results in terms of the work of adhesion or of closely related expressions. 

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