Polyamide thickness and roughness have been identified as critical properties that affect thin-film composite membrane performance for reverse osmosis. Conventional formation methodologies lack the ability to control these properties independently with high resolution or precision. An additive approach is presented that uses electrospraying to deposit monomers directly onto a substrate, where they react to form polyamide. The small droplet size coupled with low monomer concentrations result in polyamide films that are smoother and thinner than conventional polyamides, while the additive nature of the approach allows for control of thickness and roughness. Polyamide films are formed with a thickness that is controllable down to 4-nanometer increments and a roughness as low as 2 nanometers while still exhibiting good permselectivity relative to a commercial benchmarking membrane.
Nanofiber-supported thin film composites
(TFC) for forward osmosis
(FO) have shown great promise as viable FO membranes in comparison
to commercially available forward osmosis membranes. In numerous studies
on the subject, nanofiber supports for TFC membranes are commonly
made by electrospinning. In this study, we have chosen a different
nanofiber medium to use as a support for a FO TFC membrane. This nonwoven,
which is a commercially available nanofiber mat, is from E.I. du Pont
de Nemours and Company (DuPont). This unique nanofiber-based nonwoven
is produced as long rolls and is unsupported, unlike other nanofiber
products that are produced on top of a typical spunbond or wetlaid
nonwoven due to the lack of mechanical integrity. The DuPont PES material
demonstrated better strength than typical electrospun materials and
was used to support a polyamide selective layer formed by in situ
interfacial polymerization. The DuPont PES TFC membrane was tested
in FO and found to generate twice the water flux and one-tenth the
reverse solute flux compared to a commercial TFC FO membrane. The
membrane was also found to match the performance of laboratory-based
electrospun-nanofiber-supported TFC but exhibited better selectivity
and strength.
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