Polymeric membranes with good solvent stability and scalability have been intensively
explored for application to diverse organic solvent nanofiltration (OSN) separation processes.
The target is a solvent stable membrane with a high solvent permeance and an effective
separation between products and impurities. This work focuses on the fabrication of composite
membranes incorporating ultrathin nanofilms, with fast solvent transport and controllable pore
structure via interfacial polymerization. These nanofilms were studied for use in hydrocarbon
separations and for iterative synthesis.
Novel amines, with an internal hydrophilic group and one/two external hydrophobic chains,
were successfully synthesized through a two-step reaction. The amphiphilic amines selfassembled
into vesicle structures in an aqueous solution and were then utilized to fabricate
ultrathin nanofilms. Compared to literature-reported membranes, these highly crosslinked
polyamide membranes with hydrophobic domains demonstrated ultrafast transport for nonpolar
solvents as well as a tight molecular weight cut-off (MWCO) of 400Da. When varying
the hydrophobic fluorine chains to alkyl chains, the membranes produced much higher
hydrocarbon solvent permeance due to the ‘structure-like’ interaction between the solvent
molecules and attached oligomers within vesicles. Thus, these nanostructures can be tuned for
the desired application. In general, these membranes incorporating vesicles are highly stable in
crude oil systems, with 5 times higher permeance than literature reported membranes with the
same selectivity.
Exploiting the self-assembled domains formed by vesicles, chemical etching was conducted to
manually create nanopores in the nanofilms. The surface of the membranes changed from
hydrophobic to hydrophilic after the removal of vesicles. By controlling the size and number
of these hydrophobic domains, the MWCOs of the membranes could be simply adjusted. The etched membranes showed a high acetonitrile permeance with a high separation factor between
the large molecules (hubs) and the small molecules (building blocks) when applied in an
iterative synthesis process, compared with other reported membranes. This approach could be
used as a strategy to create highly stable porous membranes, with controllable pore sizes, to
achieve a clear separation.