The permeability behavior of polyvinylpyrrolidone-modified porous silica membranes (original) (raw)
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Silica-suported polyvinylpyrrolidone filtration membranes
Journal of Membrane Science, 1996
A hybrid ceramic-polymeric membrane was developed by the growth of covalently-bonded polyvinylpyrrolidone (PVP) chains from the surface of a porous silica support membrane via a graft polymerization process. These ceramic-supported polymeric (CSP) membranes can be produced with variable surface density and length of the terminally anchored polymer chains. Hydraulic permeability measurements demonstrated the effect of the grafted chain density and length on the water permeability of the CSP membranes. The potential application of these CSP membranes for the treatment of oil-in-water emulsions, was evaluated in cross-flow filtration experiments. This preliminary evaluation indicated improved performance of a CSP membrane, relative to an unmodified support, since the CSP membrane produced a lower permeate concentration at an equivalent permeability. The improved selectivity and reduced fouling tendency is attributed to the increased hydrophilicity of the membrane surface provided by the grafted PVP chains.
Shear-induced permeability changes in a polymer grafted silica membrane
Journal of Membrane Science, 2000
The hydrodynamic response of a graft-polymerized membrane was demonstrated for a microporous silica-poly(vinylpyrrolidone) (silica-PVP) membrane. The membrane pores were modified by graft polymerizing vinyl pyrrolidone onto the membrane pore surface, resulting in a polymer surface layer of covalently tethered polymer chains. The hydraulic permeability of the modified membrane increased with increasing transmembrane pressure owing to flow-induced deformation of the grafted polymer chains. The dynamics of the modified pores was investigated by membrane hydraulic permeability studies along with a two-region hydrodynamic pore flow model. The thickness of the grafted polymer layer decreased with increasing pore-wall shear rate by up to about 47%, relative to the thickness at the zero shear limit, depending on the surface density and length of the grafted chains. Although the effective pore size of the polymer-grafted membrane was reduced by 5-36% (at the zero shear rate limit), about 18-59% of the pore size loss was regained at high pore-wall shear rates. Increasing the degree of shear-induced permeability change is feasible by increasing the ratio of the polymer chain length/pore size ratio as well as the surface density of the grafted polymer phase. The present results suggest that hydrodynamic pore size control could provide an additional useful degree of freedom in operating polymer-modified filtration membranes.
Pore-filled nanofiltration membranes based on poly(2-acrylamido-2-methylpropanesulfonic acid) gels
Journal of Membrane Science, 2005
Strong polyacid gel-filled membranes have been prepared by UV-initiated copolymerization of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and N,N -methylenebisacrylamide within the pores of a microporous polypropylene (PP) substrate. These poly(2-acrylamido-2methylpropanesulfonic acid) (PAMPS) gel-filled membranes were readily prepared with predictable amounts of the incorporated gel polymer (mass gain, MG) provided that threshold values of the degree of cross-linking and monomer concentration were exceeded. Most of the membranes showed large dimensional changes, particularly in their thickness on incorporation of the PAMPS. These changes were related to the amount of PAMPS incorporated into the membranes. In order to determine the polymer volume fractions of the incorporated gels, the partial specific volume of PAMPS (0.575 cm 3 /g) was obtained from density measurements using pycnometry. As a result of increase in thickness (volume) of the membranes, the polymer volume fractions of the PAMPS pore-filling gels were limited to values between 0.01 and 0.06, relatively low values compared to values achieved with other gel-filled membranes based on the same substrate. The Darcy permeability of PAMPS gel-filled membranes exhibits a typical relationship with polymer volume fraction, but the absolute values obtained are much lower than those of other gel-filled membranes previously studied. The lower permeability could be attributed to tightly bound water molecules along polymer chains, which effectively enlarges the hydrodynamic size of polymer chains and narrows the channels for water transport. Using the sphere model based on the Odijk's theory of semidilute polyelectrolyte solutions, the Darcy permeability of PAMPS gel-filled membranes could be calculated with good precision.
A model for the permeation characteristics of porous membranes with grafted polyelectrolyte brushes
Journal of Colloid and Interface Science, 1991
The hydraulic permeability and neutral solute diffusion characteristics of a membrane made up of plane parallel channels whose walls are covered by a terminally grafted weak polyelectrolyte are studied theoretically. The measurable quantities of interest, namely the hydraulic and diffusion thicknesses, as well as the selectivity of the pore are predicted in terms of the polymer brush conformations provided by the recent polyelectrolyte brush theory (Misra et aL, Macromolecules 22, 4173 (1989)). The effects of the brush grafting density, pH, ionic strength, and solute size are investigated. The Debye-Bueche-Brinkman model which visualizes the wafted layer as an obstacle course composed of randomly distributed spherical segments is employed to study both momentum and mass transfer through the channel. The hydrodynamic thickness is found to be a much better characteristic of polymer conformation for brushes than for homopolymer adsorption. This is due to the slower decay of the segment density in brushes-almost parabolic as opposed to almost exponential in homopolymers. Also, the streaming potential is found to be negligibly small due to the highly retarded flow in the polymer brush region where the mobile charge density is high. Concerning the solute permeability, one obtains, in accord with the recent experimental data (Kim and Anderson, J. Membr. Sci. 47, 163 (1989)), that the resistance to diffusive transport is less than that for momentum transport, except for fairly large solutes (solute size ~ two times the segment size). Finally, the computations also reveal that a significant enhancement in selectivity between solutes of different sizes can be achieved with polyelectrolyte grafted membranes.
In the current work, we report a novel low fouling mixed matrix membranes (MMMs) that comprise polyethylenimine coated silica nanoparticles (SiO 2-g-PEI) and polyethersulfone membrane for Ultrafiltration application. The hydrophilic SiO 2-g-PEI was synthesized via grafting polyethylenimine (PEI) molecules onto the surfaces of silica nanoparticles (SiO 2 NPs). Later on, NPs were embedded within a PES polymeric matrix at disparate ratios by the phase inversion method to obtain modified MMMs. Modified SiO 2-g-PEI were characterized by Fourier transform infrared spectroscopy (FTIR), Field Emission Scanning electron microscopy (FE-SEM) and energy dispersive X-ray (EDX) spectroscopy, whereas the MMMs were characterized via FE-SEM, EDX, FTIR-ATR, and contact angle (CA). Moreover, this study presents the proposed interaction mechanism between the contents of PES/SiO 2-g-PEI and the interaction mechanism of each PES/SiO 2-g-PEI membrane with molecules of water. Results disclosed that MMMs prepared with 0.7 wt% nanoadditives possessed optimum characteristics and performance with 82.56% surface porosity, 41 ± 2 • CA, and higher mean pore size (41.04 nm). The pure water permeation permeability of this membrane showcased more than 7-fold enhancement with 97% retention to BSA if compared to pristine PES. Besides, the M0.7 manifested a stable performance during the prolonged operation, greater flux recovery ratio (94%) and was less prone to fouling by the protein solution. These results significantly override those obtained by pristine PES membrane and suggest a promising potential of SiO 2-g-PEI on tailoring membrane performance.
Modeling of the Salt and pH Effects on the Permeability of Grafted Porous Membranes
Macromolecules, 1996
A simple theoretical model describing the effects of pH and salt concentration on the permeability and counterion transport number of variable permeability membranes has been presented and validated experimentally for the case of poly(vinylidene fluoride) membranes graft modified with poly(acrylic acid) chains by radiation-induced grafting. The model incorporates explicitly the statistical conformations of a polyacid chain grafted onto the pore surface. The electrostatic interactions between the bound charges in the chains are screened according to the Debye-Huckel theory. The charged capillary model for porous membranes is then used to evaluate the permeability and counterion transport number of the membrane. This theoretical approach is able to describe the experimental trends observed for a range of KCl concentrations and pH values when the grafting ratios are low. In particular, the fact that the membrane permeability changes by several orders of magnitude when the properties of the external solution are varied can be rationalized in terms of very simple physical principles.
Chemical Engineering Journal, 2000
Diffusion permeability of the composite polypyrrole/polyethylene (PPy/PE) membranes in relation to various low-molecular weight electrolytes (hydrochloric acid, potassium chloride or sodium hydroxide) was studied. PPy/PE membranes were prepared by oxidative polymerization of pyrrole in the presence of FeCl 3 . They differed in the thickness of PPy layers deposited on both the membrane and pore surfaces and in porosity. It was shown that changes of porous, hydrophilic and ion exchange properties of the membranes affect their diffusion permeability to electrolytes in the same way as was demonstrated earlier for diffusion permeability of microporous ion exchange Neosepta membranes in relation to proteins [M. Bleha, G. Tishchenko, Y. Mizutani, N. Ohmura, in: A. Dyer, M.J. Hudson, P.A. Williams (Eds.), Progress in Ion Exchange. Advances and Applications, Cambridge, 1997, pp. 211-218]. It means that there is an optimum combination of PPy content and membrane porosity ensuring the maximum fluxes of electrolytes through the membranes. At low (<2 h) and high (>6 h) duration of pyrrole polymerization the diffusion permeability of PPy/PE membranes is low. In the first case, PPy covers mainly the outer membrane surfaces; the surface of pores remain hydrophobic because pyrrole has no time for penetrating into them. In the second case, PPy forms thick layers on both the membrane and pore surfaces resulting in their blocking. It was found that the diffusion transport of acid and alkali accompanied with removing of Fe from the PPy/PE membranes. The influence of Fe-containing compounds presenting in the PPy/PE membranes on their diffusion permeability in alkaline or acidic conditions is discussed.
Influence of inorganic fillers on the compaction behaviour of porous polymer based membranes
Journal of Membrane Science, 2004
The influence of TiO 2 as inorganic filler in poly(vinylidene fluoride) (PVDF) and polyamideimide (PAI) membranes on various permeation processes has been investigated. PAI/TiO 2 membranes could be prepared without any post-treatment. Furthermore, PAI membranes with 40 wt.% TiO 2 could withstand a temperature treatment at 180 • C with only minor decrease in fluxes. The pore size distribution of the thus treated membranes remained practically unchanged.
Morphological control of porous membranes based on aromatic polyether/water soluble polymers
Journal of Applied Polymer Science, 2016
This work describes the development of porous membranes based on blends of an aromatic polyether bearing main and side chain pyridine units (AP) with hydrophilic ionic polymers, like poly(sodium 4-styrenesulfonate) (PSSNa) and its acid form (PSSH), or non-ionic like polyvinylpyrrolidone and polyethylene glycol. Porous membranes were obtained after the removal of the water soluble polymers from the respective blend. The effect of various parameters such as water soluble polymer used (pore former), blend composition, casting solvent, and solvent evaporation level on porous structure formation was studied thoroughly. Specifically, SEM examination for the aforementioned systems indicated various porous morphologies depending on experimental conditions as well as thermodynamic and kinetic parameters occurring during their formation. The thermal properties of the membranes were influenced by the kind of the pore former, as revealed by thermogravimetric analysis. Special attention was paid to the systems AP/ PSSNa and AP/PSSH to evaluate their miscibility via dynamic mechanical analysis and ATR-FTIR spectroscopy. AP/PSSNa membranes have been preliminary used to test the water permeability for water purification. The tests revealed high water flux values at increased PSSNa concentrations.
Organically-modified ceramic membranes for solvent nanofiltration: fabrication and transport studies
Grafting of mesoporous-alumina membranes with monovinyl terminated polydimethylsiloxane (PDMS), using 3-mercaptopropyltriethoxysilane (MPTES) as a linking agent, is described. The grafting performance of the organic moieties on-alumina powders was studied by FTIR. Contact angle measurements and solvent permeability tests were used to characterize the membrane properties. The results indicated that grafting reactions were successfully carried out. The toluene permeability of the membrane was reduced from 5.3 to 2.1 L/m 2 .h.bar after grafting with the polymer. No degradation of the membrane material was observed after chemical stability tests in toluene for 6 days at room temperature and at elevated temperatures (up to 90ûC).