Abstract
Polymer crosslinking imbues chemical stability to thin films at the expense of lower molecular transportation rates. Here in this work we deployed molecular dynamics simulations to optimise the selection of crosslinking compounds that overcome this trade-off relationship. We validated these simulations using a series of experiments and exploited this finding to underpin the development of a pervaporation (PV) desalination thin-film composite membrane with water fluxes reaching 234.9 ± 8.1 kg m−2 h−1 and salt rejection of 99.7 ± 0.2 %, outperforming existing membranes for pervaporation and membrane distillation. Key to achieving this state-of-the-art desalination performance is the spray coating of 0.73 μm thick crosslinked dense, hydrophilic polymers on to electrospun nanofiber mats. The desalination performances of our polymer nanocomposites are harnessed here in this work to produce freshwater from brackish water, seawater and brine solutions, addressing the key environmental issue of freshwater scarcity.
Highlights
Polymer crosslinking imbues chemical stability to thin films at the expense of lower molecular transportation rates
Longer chains and asymmetrical structures minimized the formation of carboxylic dimers between polymeric crosslinkers (P(AA-AMPS) and P(AASS)), enabling esterification reactions that underpin crosslinking with polyvinyl alcohol (PVA) chains
Here, in this work, we overcome the detrimental effect of polymer crosslinking on molecular transportation rates across a thin polymer film by optimizing the molecular structure and the amount of facilitated transport functional groups on crosslinking compounds via molecular dynamics simulations
Summary
Polymer crosslinking imbues chemical stability to thin films at the expense of lower molecular transportation rates. In this work we deployed molecular dynamics simulations to optimise the selection of crosslinking compounds that overcome this trade-off relationship We validated these simulations using a series of experiments and exploited this finding to underpin the development of a pervaporation (PV) desalination thin-film composite membrane with water fluxes reaching 234.9 ± 8.1 kg m−2 h−1 and salt rejection of 99.7 ± 0.2 %, outperforming existing membranes for pervaporation and membrane distillation. PV, a thermally driven process with energy costs that are identical to the higher end of SWRO energy costs, can utilize low grade (waste heat from industrial processes) or renewable (from solar or geothermal energy) heat to drive water separations from seawater at 40–75 °C, while the use of hydrophilic polymers in PV can overcome the detriments of fouling plaguing MD membranes[5] Such membranes typically exist as thin-film composites (TFCs) where hydrophilic polymers are deposited as dense selective layers on to porous supports. The deposition of this composite as a selective layer on nanofibrous PAN supports via spray coating yielded TFC membranes with desalination performances that outperformed current PV desalination[6,16] (by a factor of 3–20-fold), state-of-the-art vacuum[3], and direct contact MD membranes[17]
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