Spray coating of polysulfone/poly(ethylene glycol) block polymer on macroporous substrates followed by selective swelling for composite ultrafiltration membranes

Polysulfone(PSF) is extensively used for the production of ultrafiltration(UF) membranes thanks to its high strength,chemical stability,and good processibility.However,PSF is intrinsically hydrophobic,and hydrophilic modification is always required to PSF-based membranes if they are intended to be used in aqueous systems.Facile strategies to prepare hydrophilic PSF membranes are thus highly demanded.Herein we spray coat a PSF-based amphiphilic block polymer onto macroporous substrates followed by selective swelling to prepare flat-sheet PSF UF membranes.The polymer is a triblock polymer containing PSF as the majority middle block tethered with shorter block of polyethylene glycol(PEG) on both ends,that is,PEG-b-PSF-b-PEG.We use the technique of spray coa ting to homogeneously dispense diluted triblock polymer solutions on the top of macroporous supports,instantly resulting in uniform,defect-free polymer coating layers with the thickness down to ~1.2 μm.The bi-layered composite structures are then immerged in ethanol/acetone mixture to generate mesoscale pores in the coating layers following the mechanism of selective swelling-induced pore generation,thus producing composite membranes with the mesoporous triblock polymer coating as the selective layers.This facile strategy is free from additional hydrophilic modification and much smaller dosages of polymers are used compared to conventional casting methods.The pore sizes,porositie s,hydrophilicity,and consequently the separation properties of the membranes can be flexibly tuned by changing the swelling duration and the composition of the swelling bath.This strategy combining spray coating and selective swelling is upscalable for the production of highperformance PSF UF membranes.

Preparation of polysulfone-based block copolymer ultrafiltration membranes by selective swelling and sacrificing nanofillers

Selective swelling of block copolymers of polysulfone-b-poly(ethylene glycol)is an emerging strategy to prepare new types of polysulfone ultrafiltration membranes.Herein,we prepared nanoporous polysulfoneb-poly(ethylene glycol)ultrafiltration membranes by selective swelling and further promoted their porosity and ultrafiltration performances by using CaCO_(3) nanoparticles as the sacrificial nanofillers.Different contents of CaCO_(3) nanoparticles were doped into the solution of polysulfone-b-poly(ethylene glycol),and thus obtained suspensions were used to prepare both self-supported and bi-layered composite structures.Selective swelling was performed on the obtained block copolymer structures in the solvent pair of ethanol/acetone,producing nanoporous membranes with poly(ethylene glycol)lined along pore walls.The CaCO_(3) nanoparticles dispersed in polysulfoneb-poly(ethylene glycol)were subsequently etched away by hydrochloric acid and the spaces initially occupied by CaCO_(3) provided extra pores to the block copolymer layers.The porosity of the membranes was increased with increasing CaCO_(3) content up to 41%,but further increase in the CaCO_(3) content led to partial collapse of the membrane.The sacrificial CaCO_(3) particles provided extra pores and enhanced the connectivity between adjacent pores.Consequently,the membranes prepared under optimized conditions exhibited up to 80%increase in water permeance with slight decrease in rejection compared to neat membranes without the use of sacrificial CaCO_(3) particles.

Fast Evaporation Enabled Ultrathin Polymer Coatings on Nanoporous Substrates for Highly Permeable Membranes

Thin polymer coatings covering on porous substrates are a common composite structure required in numerous applications,including membrane separation,and there is a strong need to push the coating thicknesses down to the nanometer scale to maximize the performances.However,producing such ultrathin polymer coatings in a facile and efficient way remains a big challenge.Here,uniform ultrathin polymer covering films(UPCFs)are realized by a facile and general approach based on rapid solvent evaporation.By fast evaporating dilute polymer solutions spread on the surface of porous substrates,we obtain ultrathin coatings(down to
30 nm)exclusively on the top surface of porous substrates,forming UPCFs with a block copolymer of polystyrene-blockpoly(2-vinyl pyridine)at room temperature or a homopolymer of poly(vinyl alcohol)(PVA)at elevated temperatures.Upon selective swelling of the block copolymer and crosslinking of PVA,we obtain highly permeable membranes delivering
2–10 times higher permeance in ultrafiltration and pervaporation than state-of-the-art membranes with comparable selectivities.We have invented a very convenient but highly efficient process for the direct preparation of defective-free ultrathin coatings on porous substrates,which is extremely desired in different fields in addition to membrane separation.