WETTING AND SCALING RESISTANCE OF MICROPOROUS MEMBRANES

Membrane distillation (MD) has garnered attention as a viable technology for treating hypersaline water, wastewater, and seawater by utilizing low-grade thermal energy to transport water vapor through hydrophobic microporous membranes. In the MD process, one side of hydrophobic microporous membranes directly contacts heated feed water, while the other side is in contact with the cold cleaned water. However, the application of MD desalination has significant issues, which limit its practical application. First, membrane pore wetting can lead to contamination of the treated water. Second, scaling is another challenge in MD process. Moreover, most microporous membranes used in MD have been modified with materials that are toxic, such as per- and polyfluoroalkyl substances (PFAS). Therefore, it is of great importance to understand the mechanism governing membrane pore wetting and develop novel method to fabricate microporous membranes with high wetting and scaling resistance. In this work, the influence of various surfactants with different charges and molecular structures on membrane pore wetting was studied. It is found that the properties of surfactants have significant influence on the wetting potential. Our results suggest that contact angle and surface tension are not suitable for predicting the wetting resistance of microporous membranes for MD process. Furthermore, we have developed a new method, which enables the fabrication of PFAS-free microporous membranes using polydimethylsiloxane (PDMS) brush. Our membranes display improved wetting and scaling resistance when comparing to the commercially available hydrophobic membranes.