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:
- 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.
- 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.
- 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.