Quantifying the impact of silica hydrophilicity and loading on membrane surface properties through response surface methodology

In porous mixed matrix membrane formation, identifying the effect of filler/additive loading is essential to enhance the membrane surface properties, especially pore size, porosity, and hydrophilicity. However, there is a limited investigation on the direct correlation between filler loading and specific membrane properties (i.e., is filler loading affecting pore size more prominently than porosity and hydrophilicity or vice versa), leading to extensive laboratory experiments. Hence, this work aims to quantify the correlation of filler loading on pore size, porosity, and hydrophilicity. Porous membranes with different hydrophilic and hydrophobic silica loadings (0-3 wt%) with different polymer concentrations (12-15 wt%) were prepared, and their impact on the pore size, porosity, and contact angle was studied using response surface methodology. The analysis of variance results revealed a significant correlation between hydrophobic silica loading and pore size and porosity, with p-value of 0.03 for the former and 0.01 for the latter, respectively. Moreover, according to analysis, hydrophobic silica loading was identified as a significant factor affecting porosity. Conversely, the hydrophilic silica loading exhibited significant correlations, with p-values of 0.0045, 0.0267, and 0.0001 for pore size, porosity, and contact angle, respectively, thus concluding that loading of hydrophilic silica is crucial in determining contact angle and porosity. The confirmatory test validated that the developed models are reliable, with a maximum deviation of 10.7% for pore size, 7.5% for porosity, and 8.5% for contact angle. These statistical correlations offer valuable insights into membrane formation, surpassing the qualitative approaches typically reported.