The impact of low-surface-energy functional groups on oil fouling resistance in membrane distillation

Recent progress in developing anti-fouling membranes suggests that integrating low-surface-energy functional groups into a hydrophilic matrix can generate a robust fouling resistant surface that not only mitigates the attachment, but also facilitates the detachment, of hydrophobic foulants. Excellent anti-fouling performance with such surfaces with heterogeneous surface energy has been reported in pressurized membrane processes. However, the impact of low-surface-energy functional groups on the membrane fouling resistance in membrane distillation (MD) has not been investigated and is the goal of the current study. In this study, we compared the fouling behaviors between a reference hydrophobic polyvinylidene fluoride (PVDF) membrane and three composite membranes with chitosan based hydrogel surface but different amount of perfluoroalkyl functional groups. We first fabricated and characterized the three composite membranes, then challenged them in MD experiments with a crude-oil-emulsion as the feed solutions, and finally conducted force spectroscopy to probe the interaction between an oil droplet and the three composite membranes as well as the reference PVDF membrane. The results from MD fouling tests and force spectroscopy suggest that incorporating perfluoroalkyl functional groups into the hydrogel matrix did significantly improve the anti-fouling performance and reduce oil adhesion onto the membrane surface as long as they were not excessive on the surface.