New insights into the impact of nanoscale surface heterogeneity on the wettability of polymeric membranes

The impact of surface nanoscale physical heterogeneity on the wettability of polymeric membranes is still elusive. Conventional wettability analysis includes quantifying the membrane surface roughness using AFM followed by measuring the apparent equilibrium contact angle of DI water over the membrane surface. Here, we present a novel experimental approach, solely based on contact angle analysis, to elucidate the impact of surface heterogeneity on the wettability of dense polymeric membranes. The proposed approach involves evaluation of equilibrium and advancing contact angles of at least three non-polar liquids over the membrane surface. Using this information, the wettability parameters including the surface roughness-ratio, frictional pinning force, and the dispersive surface tension component of the polymeric membranes were successfully quantified. The comparison with the conventional approach showed that there are 10%-20% discrepancies between the AFM-based and contact angle-based wettability parameters. The results revealed that the AFM measurements strongly depend on the size of the scanned area, particularly for samples with large surface heterogeneity. Furthermore, the water flux decline due to colloidal fouling was found to be in good agreement with the results of our proposed model. This study can provide new insights into developing advanced membrane materials with desired surface wettability and antifouling property.