A MODEL FOR ADHESION-PRODUCING INTERACTIONS OF ZINC-OXIDE SURFACES WITH ALCOHOLS, AMINES, AND ALKENES

The interactions between paint/adhesive polymers and metal surfaces th at are critical for adhesion have been studied theoretically. This stu dy used zinc oxide as a model of a galvanized steel surface, and ammon ia, water, and ethylene as models for amino, hydroxy, and unsaturated functionalities in paint/adhesive polymers. Ab initio molecular orbita l calculations were carried out on zinc oxide and zinc oxide dimer. Ge ometries were optimized at the HF/3-21G level and relative energies we re calculated by CASSCF/3-21G and by MP2 with the DZP basis set of Wac hters and Hay. Ethylene forms a stable complex with zinc oxide dimer t hat has a stabilization energy of 24.9 kcal/mol. Insertion of ethylene into zinc oxide dimer to form a stable six-membered ring adduct occur s with a surprisingly low activation energy of 8.8 kcal/mol. The bindi ng energy of ammonia with zinc oxide dimer is 38.5 kcal/mol and the ac tivation energy for insertion of ammonia forming covalent Zn-NH2 and O -H bonds is calculated to be 9.6 kcal/mol. Aminolysis of zinc oxide di mer with two ammonia molecules has a predicted barrier height of 6.7 k cal/mol. The transition structure for Zn-O bond rupture with one NH3 a nd one H2O molecule is only 1.5 kcal/mol higher in energy than the rea ctant cluster. The calculations suggest that alkenes, amines, and alco hols could readily form covalent bonds with the ZnO surface, thereby f acilitating adhesion of the polymer containing these functional groups to a galvanized surface.