Measurement and modeling of the effect of composition ratios on the properties of poly(vinyl alcohol)/poly(vinyl pyrrolidone) membranes

To investigate the effects of composition ratios on the properties of PVA/PVP blend membrane, five models of blend membrane with the composition ratios of 4/0, 3/1, 2/2, 1/3, and 0/4 were constructed and simulated using the molecular dynamics simulation. The solubility parameters, mechanical properties, binding energy, pair correlation function, free volume and diffusion of H₂O molecules were studied, respectively. Results show that PVA has a good compatibility with PVP, the engineering modulus and binding energy decrease with the addition of PVP content. The diffusion of H₂O molecule and fractional free volume increase with the addition of PVP content, the bigger the fractional free volume, the better the diffusion ability for H₂O molecules in system. Additionally, the pair correlation functions indicate that the hydrogen bonds are more likely to be formed between H₂O molecules and polar functional groups, with the increase of PVP content. This is due to the polarity effect of amide groups (NCO) in PVP is stronger than that of hydroxyl groups (OH) in PVA. A stronger polarity effect can make the hydrogen bonds more easily to be formed between polar groups and water molecules, and this is why the hydrophilicity of membrane increases with the addition of PVP.