Effects of composition ratio on the properties of poly(vinyl alcohol)/poly(acrylic acid) blend membrane: A molecular dynamics simulation study

Highlights: • PVA/PAA blend systems at varying composition ratio were constructed and simulated. • Properties of blend systems with different composition ratio were analyzed. • Interaction mechanism of polymer molecules in blend system was revealed. • Essential reasons for diffusion coefficient and mechanical property decreasing with addition of PAA were investigated. To investigate the effect of composition ratio on the properties for PVA/PAA blend membrane, five simulation models of PVA/PAA with different composition ratios (4/0, 3/1, 2/2, 1/3, 0/4) were constructed and simulated by using molecular dynamics (MD) simulation. The effects of composition ratio on the properties for blends were elaborated from the aspects of the compatibility, mechanical properties, binding energy, pair correlation function, and diffusion of water molecules, respectively. The result of solubility parameter indicated PVA has a good miscibility with PAA, and the static mechanics analysis shows the mechanical properties and ductility are decreased with the increase of PAA content in the blend systems. Moreover, the analysis of binding energy and pair correlation function reveal the reason why the mechanical properties of systems decrease with the additional of PAA. Additionally, the analytical results of fractional free volume is inconsistent with the diffusion ability of H₂O molecules, and the diffusion ability of H₂O molecules in blend systems has the order of 4PPVA/0PAA > 3PVA/1PAA > 2PVA/2PAA > 1PVA/3PAA > 0PVA/4PAA. The main reason for this phenomenon is that the polarity effect of carboxylic acid groups (− COOH) in PAA is stronger than that of hydroxyl groups (− OH) in PVA.