Analysis of Surface Structures in Nitrogen-Containing Polymer Systems by Ion Scattering Spectroscopy

Low-energy ion scattering spectroscopy (LEIS or ISS) combined with molecular mechanics calculations is used to predict the structure and orientation of functional groups at the topmost surface for a group of nitrogen-containing polymers. ISS of poly(2-vinylpyridine) (P2VP), poly(4-vinylpyridine) (P4VP), and ethylated P2VP gives N/C scattered ion intensity ratios which reflect the position of the nitrogen in the planar side group. The N/C scattered intensity ratios were 0.404 ± 0.025 for P4VP, 0.01 ± 0.02 for P2VP, and 0.42 ± 0.025 for ethylated P2VP. Results are explained through the use of conformational energy calculations classical concepts such as “shadowing” and “shielding” effects, and molecular modeling. X-ray photoelectron spectroscopy (XPS or ESCA) data show no differences between P2VP (ortho nitrogen) and P4VP (para nitrogen). ISS of poly(vinylpyrollidone) (PVPyr) and poly(vinylcarbazole) (PVK) is used to complement the work done on the pyridine polymers. The combined data support a polymer orientation in which the polymer backbone is exposed to the vacuum at the vacuum/surface interface. These results are possible because of the extreme surface sensitivity of the ISS technique.