Work of peel

Based on the arguments presented thus far, it would seem that, for a given PSA, the work of adhesion, and thus the peel force, should decrease systematically as the surface energy of the release coating is decreased. Therefore, fluorochemical containing polymers should provide the lowest release forces. In practice, these generalities often do not hold, due to other factors, such as interfacial dynamics and rheological considerations. 

The skin is usually degreased with alcohol followed by a mild acetone scrub. After cleaning, Jessner s solution is appUed to the face with a sable brush, cotton tipped apphcators, cotton balls, or 2 X 2 gauze sponges. The author prefers the use of cotton tipped applicators. Typically, the cheeks are treated first, working from medial to lateral areas followed by application to the chin and forehead area. For superficial peeling, two coats are usually applied. Additional coats increase the depth of peeling. 

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] ... 

The search for the key to the universe might eventually come to an end. But it is also possible that understanding the workings of nature is like peeling off the layers of an onion one by one and that the quest will go on for as long as there are scientists. 

The interaction of two substrates, the bond strength of adhesives are frequently measured by the peel test [76]. The results can often be related to the reversible work of adhesion. Due to its physical nature such a measurement is impossible to carry out for particulate filled polymers. Even interfacial shear strength widely applied for the characterization of matrix/fiber adhesion cannot be used in particulate filled polymers. Interfacial adhesion of the components is usually deduced indirectly from the mechanical properties of composites with the help of models describing composition dependence. Such models must also take into account interfacial interactions. 

Fig. 11. Dependence of the peel strength of tin plate/epoxy systems on coating thickness for coatings cast from DTPM and methyl cello-solve. These theoretical curves were constructed using experimental values for modulus, critical coating thickness, solvent evaporation rate, solution concentration and interfacial work of adhesion96 (Reprinted from Ref. 96, p. 123 by cautesy of Plenum Press)...

Fig. 11. Normalised enhanced adhesive strength wyw as a function of the surface density, a, for two PDMS elastomers in contact with silicon wafers covered with irreversibly adsorbed chains. Wis the thermodynamic work of adhesion, W=2y, with ythe surface tension of PDMS, 7=21.6 mN m"1 at 25 °C. The filled symbols correspond to a molecular weight between crosslinks in the elastomer Mc=24.2 kg mol-1 while Mc=10.2 kg mol-1 for the open symbols. The adhesive strength, G, has been measured by peel tests performed at a very low velocity of the propagation of fracture, 0.17 im/s. The molecular weight of the surface anchored chains is Mw=242 kg mol-1...

This is the definitive reference for all engaged in chemical peels in cosmetic practice, based on one author s extensive experience in research, practice and teaching. It contains the results of over fifteen years of work with peels and coxers all tyjDcs of treatment and all t qaes of peel, paying attention to the science underlying their use, as well as to preparation, application and... 

The adhesion of metal layers deposited onto polymer surfaces is determined by the concentration and the bond strength of the chemical and physical interactions between the metal atoms and the functional (polar) groups at the polymer surfaces. Each type of functional group produces individual metal-polymer interactions, and makes a specific contribution depending on its concentration to the interfacial adhesion and consequently to the related shear or peel strength of metal-polymer systems (see Fig. 18.1). Thus for each type x of metal-functional group interaction a, the work of adhesion is calculated with Eq. (1), with A=area, I = Loschmidfs constant, and C = concentration. 

The total work of adhesion Wt, follows by summation over all types of interaction [Eq. (2)], presenting the correlation with the macroscopically measured adhesive bond strength, here the peel strength. 

Effectively, when viscoelastic losses are negligible (i.e., when performing experiments at very low peel rate or high temperature), 4>-> 1 and G must tend toward IV. However, the resulting threshold value Gq is generally 100 to 1000 times higher than the thermodynamic work of adhesion, IV. 

This is an important aspect and would at least partly explain in a manner somewhat different from the more accepted explanations why Go is generally 100 to 1000 times higher than the thermodynamic work of adhesion [48], It indicates that G E(v, T). Apart from this the interesting consideration still holds that the flexibility at the interface is inversely proportional to both the intrinsic fracture energy and to the peel adhesion strength at least where the effect of is minimized. 

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