The effects of specific interactions on the surface structure and composition of miscible blends of poly(vinyl alcohol) and poly(N-vinyl-2-pyrrolidone)

Poly(vinyl alcohol) (PVAL)/poly(N-vinyl-2-pyrrolidone) (PVP) blends were studied by differential scanning calorimetry (d.s.c.), Fourier transform infrared spectroscopy (FTi.r.), and X-ray photoelectron spectroscopy (XPS). A single glass transition temperature (T-g) was observed for all PVAL/PVP blends, suggesting that PVAL/PVP blends are miscible within the compositions considered. The specific interaction (hydrogen bonding) between PVAL and PVP was investigated by d.s.c. and FTi.r. The surface chemical composition of the blends was studied by XPS. The XPS result showed that PVAL is enriched on the surface of the PVAL/PVP blends in spite of the formation of intermolecular hydrogen bonds between the C=O in PVP and the OH in PVAL. The intermolecular hydrogen bonds also induce a change of 0.3-0.4 eV in the Ols binding energy difference between the oxygen atoms in the carbonyl and hydroxyl groups. It can be concluded that the formation of the intermolecular hydrogen bonds is a major factor for the miscibility of the PVAL/PVP blends in the bulk and that the difference in the surface energy between PVAL and PVP is the dominant factor that controls the surface composition of the blends. (C) 1998 Elsevier Science Ltd. All rights reserved