Nanoscaled free volume holes and slow release of urea for poly(vinyl alcohol)/urea composite films

Abstract

Poly(vinyl alcohol) coated urea films were prepared by simple tape casting. The crystallinity of the films decreased with increasing urea weight content, and hydrogen bonds were formed between PVA and urea. The size of nanoscaled free volume holes in the amorphous region were measured by positron annihilation lifetime spectroscopy, and it was found that the mean size of the free volume increased with increasing urea content. About 80 % of the urea was released from the composite film after 25 h in liquid water. The increased free volume holes supplied diffusion channels for water and urea molecules, ensuring efficient urea release from the PVA coating.