Fully hydrolyzed PVA F-17A (98.0%–99.5% degree of hydrolysis)
was purchased from OCI Co. Ltd (Incheon, Korea). PAA (average
molecular weight 5000) was purchased from Wako Pure Chemical
Industries Ltd (Osaka, Japan). All materials were used without
further purification.
PVA and PAA were physically mixed to yield PVA/PAA blends in
ratios of 100/0, 99/1, 95/5, 90/10 and 80/20 by weight. The mixtures
(10 g) were dissolved in deionized water (90 g) by stirring at 90 ∘C
for 4 h to give the respective PVA/PAA solutions, which were then
cooled to room temperature. Each solution was bar-coated onto a
glass substrate using a bar-type automatic film-coating apparatus
(KIPAE E&T Co. Ltd, Hwasung, Korea) that could accurately control
film thickness. The coated films were pre-dried in a drying oven
at 70 ∘C for 24 h, followed by heat treatment at 150 ∘C for 1 h in a
drying oven. The film thickness was maintained at 60±1 μm to aid
in evaluating physical properties