Conclusions
The effects of the PAN substrate on the IP-film formation were investigated while highlighting the role of the surface hydrophilicity. The hydrophilicity of the PAN substrate was first modified by implementing the alkaline treatment and characterized by the contact-angle measurement. The surface of the PAN substrate modified by the alkaline treatment was further tuned by the deposition of different polyelectrolytes to vary the degree of hydrophilicity. All the modified PAN substrates were employed to fabricate the TFC membranes via IP and the formed IP layers were compared to correlate the film formation with the degree of hydrophilicity. The following conclusions can be drawn from the characterization results:
  1. The PAN substrate with a relatively hydrophilic surface could result in delamination when employed to fabricate the TFC membrane via IP, whereas the integrity of the IP layer can be improved by decreasing the surface hydrophilicity.
  2. The deposition of various polycations onto the surface of the PAN substrate can change the wettability to different degrees, thereby offering a tool for the IP-based fabrication of TFC membranes with a hydrophilic PAN substrate.
  3. The comparative study of evaluating the TFC membranes with different PAN substrates indicated that a relatively hydrophilic substrate would favor the enhancement of the water-flux efficiency when employed in an FO process.
All the modified PAN substrates were also examined by SEM and AFM; the characterization results confirmed that the variations in the geometrical characteristics were negligible. Therefore, it is reasonable to believe that the effects of the modified PAN substrates on the IP-film formation were primarily attributed to the changes in the surface wettability. The application of polyelectrolyte deposition not only provided an approach to investigating the effects of the surface hydrophilicity, but also opened new paradigm for optimizing the fabrication of TFC membranes via IP.