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 de termined by two major contributions : Van der Waals forces and acid-ba se interactions, taken in the most general ''Lewis'' electron acceptor -donor sense. The present work shows that the microscopic exothermic i nterfacial energy changes corresponding to bond formation, i.e. the wo rk of adhesion, can be very appreciably increased by the creation of i nterfacial acid-base interactions. Practically, polymers such as paly( ethylene-co-vinyl acetate) (EVA), terpene-phenol resins (TPR), polethy lene oxide (PEO) and polymethylmethacrylate (PMMA), and some of their blends, were solution cast on basic (aluminium oxide) and acidic (hydr oxylated glass) substrates. Acid-base interfacial mechanisms (nature o f the interfacial bonds and enthalpy of adduct formation through elect ron exchange) are evidenced by Fourier transform infrared reflection a bsorption spectroscopy (IRRAS). Moreover, it is shown that, on one han d, modification of the electron donor ability of the polymer functionn alities reveals the amphoteric character of the substrate and on the o ther hand, modification of the electron donor ability of the substrate changes the nature of the species involved in interfacial adduct form ation. Then, practical adhesion tests (peel experiments performed in a chosen liquid medium), were carried out in order to correlate the nat ure and strength of interfacial acid-base bonds with simultaneous incr eases 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 sit es through the knowledge of the enthalpy of adduct formation, Delta H- ab, previously determined.