Over the years, several methods have been developed to modify polymer surfaces for improved adhesion, wettability, printability, dye uptake, etc. These include mechanical treatments, wet-chemical treatments, exposure to flames, corona discharges, and glow discharge plasmas. A basic objective of any such treatment is to remove loosely bonded surface contamination and to provide intimate contact between the two interacting materials on a molecular scale, for molecular energies across an interface decrease drastically with increasing intermolecular distance . The simplest method that one can envisage for improving adhesion is to mechanically roughen a surface, thereby enhancing the total contact area, and mechanical interlocking, which is one of several basic mechanisms that have been proposed to explain adhesion. Theoretical adhesion models have been proposed by various authors to account for a wide range of related experimental observations (for reviews of these theories, see, for example, refs 6 and 7); they are, very briefly: (i) the adsorption or chemical reaction theory, which states that bond strength
is mainly determined by physi-or chemisorption at the interface; (ii) the electrostatic theory of Deryagin , which is based on contact charging
when two dissimilar materials are intimately joined; (iii) the diffusion theory of Voyutskii , which claims that the bond strength of
polymers is governed by diffusion across their interface; (iv) the Theological theory of Bikerman , which states that the performance
of a bonded system is governed by the mechanical properties of the materials comprising the joint, and by local stresses in the joint; and
(v) the mechanical interlocking or ‘hooking’ theory, based on the micro geometry of the interface, as already mentioned above.