Surface states of PVA/chitosan blended hydrogels

Hydrogels were prepared from blends of poly(vinyl alcohol) (PVA) and chitosan in varying proportions. Electron spectroscopy analysis of the resulting hydrogel membranes, cast on glass plates, revealed that the chitosan component was concentrated on the surface of the air-surface side of the membranes and was nearly constant from 10 to 40 wt% of chitosan content of the blends. The increasing water-contact angle on the hydrogel surface with increasing chitosan content indicated that the chitosan molecules were more hydrophobic than were PVA molecules. The zeta-potential in the air-surface side of the hydrogels increased to reach a constant value at more than 10 wt% chitosan content at all experimental pH values (3.0, 5.0, and 7.2). Electron-probe micro-analyzer results showed that the two-dimensional distribution of the chitosan component on the surface of the air-surface side of the Chitosan-15 sample was heterogeneous when it was compared with that on the surface of the air-surface side of the Chitosan-40 sample; the chitosan component on the surface of the Chitosan-15 sample was localized in islands. Observations of the Chitosan-15 sample by confocal laser-scan microscope gave the same results. (C) 2000 Elsevier Science Ltd. All rights reserved.