The acid-base concept in adhesion science

The adhesion between two materials is the manifestation of the forces at work across the interface. A high level of adhesion is sought in joints, coatings or at the metal-oxide interfaces discussed in the previous chapter. It is of special importance, due to economical implications, in the glue industry - mechanical joints are more and more often being replaced by, or used in parallel with, adhesive joints - and in the paint and glass industries. 

Two parameters characterize the quality of a joint its resistance to separation and its resistance to ageing. Reactions, such as the hydrolysis of interfacial bonds, induced by external agents, are often responsible for premature ageing (Ishida and Koenig, 1980 Gan et al, 1986 Stein and Prutzman, 1988 Brewis and Kinloch, 1983). The resistance to separation, on the other hand, is measured by various peeling tests. It depends upon several factors  

An hydroxylated surface may, thus, be a proton donor (Bronsted acid)  

An acidic pKi and a basic pK2 are associated with the equilibrium constants Ki and K2 of these two reactions. Electrochemical measurements allow a determination of the isoelectric point of the surface IEPS) which is the pH value of a solution in contact with the surface which yields an equal concentration of MOH J and M0 sites. The surface then bears a net zero charge and the proton concentration is equal to  

A high lEPS value reveals a strong surface basicity, while a value close to zero is characteristic of a strong acidity. Parks (1965) compiled lEPS 

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