Studying Chemisorption at Metal–Polymer Interfaces by Complementary Use of Attenuated Total Reflection–Fourier Transform Infrared Spectroscopy (ATR-FTIR) in the Kretschmann Geometry and Visible–Infrared Sum-Frequency Generation Spectroscopy (SFG)

The molecular configuration and chemistry at the zinc/zinc oxide–polyester interface were studied by using two complementary spectroscopic techniques: attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR) and sum-frequency generation (SFG) spectroscopy. It was shown that ATR-FTIR should be considered as a (3D) interphase-sensitive technique with probing depths of 250–400 nm in the headgroup region (2000–1200 cm–¹). On the other hand, SFG is known to be a (2D) interface-sensitive technique. The ATR-FTIR measurements showed that carboxylate groups are formed within the near-interface region of the polyester phase. SFG measurements showed that the carboxylic acid groups are stable at the polymer–zinc/zinc oxide interface. In addition, in situ ATR-FTIR and SFG measurements have been conducted when exposing the polyester–zinc/zinc oxide system to D₂O. The exposure to D₂O is observed to lead to an additional conversion of ester and carboxylic acid groups to carboxylate groups. The comparison of the SFG and ATR-FTIR measurements shows that this conversion occurs much slower at the polyester–zinc/zinc oxide interface than in the bulk of the polyester. Finally, the strengths and limitations as well as the complementarity of both techniques are discussed.