In Situ Study of Buried Metal–Polymer Interfaces Exposed to an Aqueous Solution by an Integrated ATR-FTIR and Electrochemical Impedance Spectroscopy System

This study investigates the interfacial bonding variations of carboxylic polymers on Zn surfaces upon exposure to an aqueous solution by means of an integrated ATR-FTIR and electrochemical impedance spectroscopy (EIS) analysis in Kretschmann geometry. In situ ATR-FTIR probes water molecules reaching Zn surfaces and subsequent interfacial bonding degradation at the hidden polymer–metal interfaces. Furthermore, EIS characterizes the polymer film capacitance and resistance determining the exposed polymer bulk and metal–polymer interfacial changes. Consequently, the integrated ATR-FTIR and EIS system is used to resolve the processes of polymer saturation with water and interfacial bonding degradation complementarily and simultaneously. Additionally, two types of carboxylic polymers, i.e., a polyester and a cured unsaturated polyester, are applied on a set of differently pretreated Zn samples to evaluate the effects of the curing process and surface pretreatments on water transport within the polymer structure and subsequent interfacial bonding degradation. Furthermore, Zn surface hydroxyl fractions are calculated by means of X-ray photoelectron spectroscopy (XPS) and correlated to the interfacial bonding degradation process. The results show that the hydroxyl fraction is a determining factor in accomplishing proper initial and durable interfacial bonding. Additionally, the polymer curing process plays an important role in barrier performance against water.