Novel hydrogel pore-filled composite membranes with tunable and temperature-responsive size-selectivity

Abstract

Hydrogel pore-filled composite membranes (HPFCM) based on polyethylene terephthalate (PET) track-etched membranes with pore diameters between 200 and 5000 nm and temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were successfully prepared. A premodification of the pore walls by grafted linear PNIPAAm led to stable anchoring of crosslinked PNIPAAm prepared in a subsequent step. Proper tuning of photopolymerization conditions resulted in a desired microstructure of the hydrogels and thus tailored barrier properties of the composite membranes. The very interesting separation performance of HPFCM was due to diversification of the hydrogel network that caused adjustable sieving properties via synthesis conditions and also largely switchable barrier properties in response to the temperature. The interplay between the immobilized hydrogel and various pore sizes of the membrane support was also investigated. The base membrane provides mechanical support and confines the hydrogel within its pores, and it thus allows using the hydrogel mesh size for size-selective solute transport. Completely stable and selective HPFCM were only obtained with base pore sizes of about 2 mm or smaller. The size-selectivity (molecular weight cut-off) of the same HPFCM was higher under diffusive than under convective flow conditions; this is presumably mainly caused by elasticity deformation of the hydrogel network. The apparent cut-off from diffusion experiments was well correlated to the mesh-size of the hydrogel determined from the Darcy model applied to permeability data obtained under convective flow conditions. Upon temperature increase beyond 32 C, flux increased and rejection decreased very strongly; this remarkable change between macromolecule-size selective ultrafiltration and microfiltration/filtration behavior was fully reversible.

Temperaturgesteuerte Wasserfiltration mit Mikrogel‐modifizierten Hohlfasermembranen

“…[2,3] Eine Methode zur Synthese von porengefüllten kompositen "trackedetched" Poly(ethylenterephthalat)(PET)-Membranen wurde von Ulbricht und Mitarbeitern verçffentlicht. [4] Die Kompositmembranen wurden mittels In-situ-Photopolymerisation von Poly(N-isopropylacrylamid)(PNIPAAm)-Hydrogelen hergestellt und zeichneten sich durch temperaturabhängige Permeabilität sowie temperaturabhängigen Rückhalt aus. Hydrogel-beschichtete Membranen für die Wasserfiltration konnten La et al mittels Photopolymerisation von Poly(ethylenglycol)diacrylat (PEGDA) und einem funktionellen, Ammoniumsalz (RNH 3 Cl) enthaltenden Monomer herstellen.…”

“…Anzumerken ist jedoch, dass alle hier vorgestellten Membranmodifikationen mit Hydrogelen auf komplexen chemischen Verfahren basieren, beispielsweise auf der photoinitiierten "grafting from"-Polymerisation. [1][2][3][4][5][6][7] Die Realisierung von kontrollierten chemischen Reaktionen in der Tiefe der Membran oder der porçsen Stützstruktur stellt eine schwer zu lçsende Herausforderung dar.…”

Redox-responsive polymeric membranes via supermolecular host–guest interactions

“…Besides our research, Abetz et al have employed polyvinylpyridine to fabricate pH-responsive membranes [25,26]. Wandera et al, Adrus et al and Yang et al employed poly(N-isopropylacrylamide) to prepare thermo-responsive membranes [17,19,27,28]. Hoare et al reported magnetically triggered nanocomposite membranes based on superparamagnetic nanoparticles [21].…”

“…Furthermore, serious smart membranes have been reported to act in response to changes in electric fields [29] and ionic strength [30,31]. So far, the most popular strategy to fabricate stimuli-responsive membranes is to prepare copolymers of inherent stimuli-responsive properties [17,19,23,24,[27][28][29][30].…”

“…Therefore, the design of smart membranes with apparently redox-responsive hydraulic permeability is urgent desired. Nowadays, enormous effort has been made in the development of stimuli-responsive membranes with controllable permeability for the application of water treatment [16,17], separation [18,19], controlled drug delivery [20,21] and so on. These membranes are able to show a pre-determined responsive permeability to various external stimuli.…”