QUANTITATIVE IRRAS ANALYSIS OF ACID-BASE INTERFACIAL INTERACTIONS IN VARIOUS POLYMER/METAL MODEL SYSTEMS - RELEVANCE TO ADHESION

The physical interactions of polymers with inorganic substrates are determined by two major contributions : Van der Waals forces and acid-base interactions, taken in the most general ''Lewis'' electron acceptor-donor sense. The present work shows that the microscopic exothermic interfacial energy changes corresponding to bond formation, i.e. the work of adhesion, can be very appreciably increased by the creation of interfacial acid-base interactions. Practically, polymers such as paly(ethylene-co-vinyl acetate) (EVA), terpene-phenol resins (TPR), polethylene oxide (PEO) and polymethylmethacrylate (PMMA), and some of their blends, were solution cast on basic (aluminium oxide) and acidic (hydroxylated glass) substrates. Acid-base interfacial mechanisms (nature of the interfacial bonds and enthalpy of adduct formation through electron exchange) are evidenced by Fourier transform infrared reflection absorption spectroscopy (IRRAS). Moreover, it is shown that, on one hand, modification of the electron donor ability of the polymer functionnalities reveals the amphoteric character of the substrate and on the other hand, modification of the electron donor ability of the substrate changes the nature of the species involved in interfacial adduct formation. Then, practical adhesion tests (peel experiments performed in a chosen liquid medium), were carried out in order to correlate the nature and strength of interfacial acid-base bonds with simultaneous increases in adhesive strengths. Thermodynamic considerations on adhesion phenomena in liquid media allowed us to propose coherent values of the acid-base work of adhesion, W-ab, and of the density of acid-base sites through the knowledge of the enthalpy of adduct formation, Delta H-ab, previously determined.