Antifouling Polymer Membranes with Subnanometer Size Selectivity

Abstract

Membranes that deliver nanoscale size selectivity are desirable for applications ranging from water treatment to molecular separations. Here we describe polymer thin film composite membranes coated with amphiphilic graft copolymers consisting of a poly(vinylidene fluoride) (PVDF) backbone and poly(oxyethylene methacrylate) (POEM) side chains, PVDF-g-POEM. Transmission electron microscopy and thermal analysis reveal that these materials molecularly self-assemble into bicontinuous nanophase domains of semicrystalline PVDF, providing structural integrity, and poly(ethylene oxide) (PEO), providing selective transport channels of defined size. PVDF ultrafiltration membranes coated with PVDF-g-POEM wet instantaneously and reject >99.9% of emulsified oil from a 1000 ppm oleic acid/triethanolamine/water microemulsion feed at 66 psi without fouling. Their molecular sieving capability is demonstrated through separation of like-charged organic dyes varying in molecular dimensions by several angstroms. Thicker films of PVDF-g-POEM also act as a chromatograph, exhibiting time-dependent permeation of vitamins B2 and B12. Nonporous asymmetric membranes prepared by immersion precipitation of PVDF/PVDF-g-POEM blend solutions exhibit separation capability similar to that of the thin film composites. These new nanochannel membranes hold potential utility for both high volume and high end value liquid-based separations.

Recent progress in developing advanced membranes for emulsified oil/water separation

“…On the one hand, the hydrophilic segments are useful for improving the membrane hydrophilicity, and on the other hand, the hydrophobic segments are useful for improving their compatibility with host polymers. [45][46][47] Mayes and co-workers 48 first used a comb-like copolymer P(MMA-r-POEM) (poly(methyl methacrylate) (PMMA) back bone and poly(ethylene oxide) (PEO) side chain) as an additive. Their results demonstrated that the antifouling property of the membrane was improved greatly, whereas the membrane structure was little affected.…”

Improved Permeate Flux of PVDF Ultrafiltration Membrane Containing PVDF-g-PHEA Synthesized via ATRP

“…ATRP is utilized for polymerization of polymers containing halogen atoms and hydrophilic polymers containing styrene, (meth)acrylates, (meth)acrylamides and acrylonitrile structures as the simple polymerization method which does not require strict experiment environment, comparing to other traditional polymerization methods [12,13]. In advance, numerous graft copolymers such as poly(vinylidene fluoride)-graft-poly(ethylene glycol) methyl ether methacrylate (PVDF-g-PEGMA) and poly(vinylidene fluoride)-graft-poly(oxyethylene methacrylate) (PVDF-g-POEM) were successfully made by using ATRP method [14,15]. Blending these graft copolymers with PVDF made membranes with improved permeate flux.…”

Supported Lyotropic Liquid‐Crystal Polymer Membranes: Promising Materials for Molecular‐Size‐Selective Aqueous Nanofiltration

“…[6] More recently, Mayes and co-workers have used amphiphilic graft copolymers to generate membranes with a bicontinuous but non-ordered, nanophase-separated pore structure for aqueous nanofiltration. [7] These nanoporous materials have all shown excellent promise as functional nanofiltration (NF) media, with some systems even exhibiting molecular-sieving properties. [2,5,7] One approach to making nanoporous polymer materials that has not yet been explored for the fabrication of NF membranes is the use of polymerizable, ionic lyotropic liquid-crystal (LLC) assemblies.…”

“…[7] These nanoporous materials have all shown excellent promise as functional nanofiltration (NF) media, with some systems even exhibiting molecular-sieving properties. [2,5,7] One approach to making nanoporous polymer materials that has not yet been explored for the fabrication of NF membranes is the use of polymerizable, ionic lyotropic liquid-crystal (LLC) assemblies. Ionic LLCs have the ability to self-assemble in the presence of water into highly ordered yet fluid phase-segregated assemblies with periodic features in the 1±10 nm range.…”