Bond formation at polycarbonate | X interfaces (X = T-i, Al, TiAl) probed by X-ray photoelectron spectroscopy and density functional theory molecular dynamics simulations

To investigate the bond formation at polycarbonate (PC) | X interfaces (X = Ti, Al, TiAl) by X-ray photoelectron spectroscopy, thin metallic layers were deposited onto PC substrates by direct current magnetron sputtering. Additionally, changes in the chemical state of the polymer were studied systematically by density functional theory molecular dynamics simulations of a PC dimer interacting with the corresponding metallic surfaces. These predictions were confirmed by experiments, indicating a higher reactivity at PC | Ti interfaces: Ti reacts with all functional groups of PC, forming numerous interfacial C-Ti and (C-O)-Ti bonds, whereas Al exhibits selective reactivity as only (C-O)-Al bonds with the carbonate group are formed. However, integrated crystal orbital Hamilton population (ICOHP) calculations indicate a significantly higher interfacial bond strength for (C-O)- Al bonds compared to (C-O)-Ti and C-Ti bonds (ICOHP differences up to 3.1 eV). By multiplying the experimentally determined relative interfacial bond concentration with the theoretically determined maximum bond strength as an indicator for adhesion, the PC | Ti interface exhibits a -1.9 and -1.4 times larger value compared to the PC | Al and the PC | TiAl interface, respectively. Thus, Ti thin films are the preferential choice as adhesion layers for PC.