Quantum-mechanical study of interaction between polycarbonate and M0.5Al0.5N(0 0 1) surfaces (M = Ti, V, Cr)

Interaction of polycarbonate with M0.5Al0.5N(0 0 1) surfaces (M = Ti, V, Cr) is systematically explored using density functional theory. All functional groups of polycarbonate, namely carbonic acid, benzene, phenol, and propane, are considered. While benzene, phenol, and propane exhibit low affinity to Ti0.5Al0.5N(0 0 1), carbonic acid (H2CO3) strongly reacts dissociating into CO2+ and 2OH−. This is enabled by strong covalent-ionic bonds span by C from CO2+ and surface N and metal atoms as well as O from OH− and surface metal atoms. The absolute value of the adsorption energy for carbonic acid decreases from −1.76 to −0.72 eV molecule−1 as Ti is replaced with Cr, implying that its affinity to M0.5Al0.5N(0 0 1) diminishes. This may be understood based on the electronic structure. The covalent-ionic bonds between the reaction products and surface atoms are weakened as the valence electron concentration is increased. These results are of relevance for the decomposition behavior observed during extrusion and molding of polycarbonate.