The strength of interfacial bonding between polymers and inorganic substrates is very appreciably enhanced when polymers are acidic and substrates are basic, or vice versa. The interaction is of two kinds, an increased thermodynamic work of adhesion resulting from large exothermic interactions at the interface, and an increased tensile strength resulting from electrical charge injection into the polymer from the substrate.
The exothermic interfacial interactions between acidic and basic sites are easily measured by calorimetry or by infrared spectral shifts. The enthalpies of adsorption can be correlated and predicted by the Drago equation, −Δ H = CACB+ EAEB, where the CA and EA for the acidic member can be measured by enthalpies determined with basic molecular probes of known CB and EB. Heats of adsorption of polymers onto inorganic substrates are precisely predictable with the above equation once E and C values are known for the polymer and substrate.