Surface characterization and quantitative study of poly(4-vinyl phenol) and poly(4-vinyl pyridine) blends by XPS and ToF-SIMS

Hydrogen bonding between poly(vinyl phenol) (PVPh) and poly(4-vinyl pyridine) (PVPy) was studied by time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Systematic studies were performed on various blends of PVPh and PVPy in different solvents, including ethanol and N,N-dimethylformamide (DMF). Both X-ray photoelectron spectroscopy and contact angle results showed no surface segregation of any component for the blends and complexes of PVPy and a low molecular weight PVPh. Excess of PVPh was found at the surface of the blends when a high molecular weight PVPh was used. However, after annealing at 90°C in a vacuum oven for five days, the surface and bulk compositions are the same. These findings reveal that the surface of blends of high molecular weight polymers may not be in the thermodynamic equilibrium state. The peak intensity of the characteristic pyridyl ions of the blends, especially the PVPh/PVPy complexes, such as the peak at m/z=106, was greatly enhanced by the hydrogen bonding. The quantitative relationship between the ion intensity and the surface composition was studied. A linear relationship was established between the intensity ratio of some of the characteristic ions and the surface concentration determined by XPS.