The permeability behavior of polyvinylpyrrolidone-modified porous silica 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.

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.

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.

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.

Journal of Colloid and Interface Science, 1992

The effect of solvent power and flow rate on the permeability of a size exclusion chromatography (SEC) column packed with a novel polyvinylpyrrolidone (PVP)-grafted porous silica resin was studied. The PVP-silica resin was prepared from a porous silica size exclusion resin onto which a terminally anchored PVP layer was graft polymerized. The terminally anchored PVP layer was synthesized via a free radical graft polymerization method. The permeability of the PVP-grafted silica columns was determined from simple flow rate-pressure drop measurements. Qualitatively, as the solvent power increased, the permeability of the PVP-silica-packed column decreased. This behavior was consistent with the expected higher degree of swelling of PVP with increasing solvent power. The permeability was also lower for longer PVP surface-anchored chains. The change in the permeability of the PVP-grafted columns with shear stress was negligible, consistent with the estimate of a dense brush-like surface coverage by terminally anchored PVP molecules. The possibility of controlling the surface conformation of the PVP layer by changing the solvent power and possibly shear rate (for nonbrush coverage) suggests an additional degree of freedom in operating SEC columns. The use of polymer-silica matrix resins in size exclusion chromatography may be of special interest since one can tailor-design the surface by controlling the degrees of surface density and grafted polymer molecular weight.

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.

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.

Journal of Membrane Science, 2005

Morphological properties of hydrophilic and hydrophobic Shirasu-porous-glass (SPG) membranes were investigated over a wide range of mean pore sizes (0.252-20.3 µm) by liquid permeability measurements, scanning electron microscopy and Hg porosimetry. Hydrophobic modification of membrane surface was made by surface coating with silicone resin. The results are discussed using the non-uniform capillary bundle model of membrane permeability. The mean pore tortuosity of 1.28 was kept constant over the whole range of mean pore sizes investigated. The SEM images confirmed that the geometry of pore network was similar for all SPG membranes, irrespective of their mean pore size. The span of pore size distribution ranged from 0.28 to 0.68 and the number of pores per unit cross-sectional-2membrane area from 10 9 to 10 13 m-2. The membrane resistance was unchanged after surface treatment with silicone resin, which means that the pores were not plugged by the resin, even in the submicron range of mean pore sizes.

Journal of Polymer Research, 2013

In this study, the effects of various solvents on the structure and permeation properties of polysulfone-silica nanocomposite membranes were investigated. Silica nanoparticles were prepared by the sol-gel method through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS). Polysulfone-silica nanocomposite membranes were prepared by the thermal phase inversion method. N-methyl pyrrolidone (NMP), N,N-dimethyl acetamide (DMAc) and tetrahydrofuran (THF) were used as solvents. Based on the experimental results, it was observed that the CO 2 /N 2 and O 2 / N 2 selectivities increased in the presence of silica nanoparticles in all cases. However, the permeabilities of the applied gases decreased, except for CO 2 . Based on the obtained selectivity data, permeability data, and favorable dispersion of silica nanoparticles in the polymer matrix, the results indicate that NMP is the best solvent for polysulfone-silica membrane preparation. The obtained CO 2 permeability and CO 2 /N 2 selectivity of the polysulfone-silica (5 wt%) membrane prepared using NMP as the solvent were 7 barrers and 35, respectively.

Advances in Polymer Technology, 2020

The grafting of pH-responsive poly(acrylic acid) (PAA) brushes was carried out on the surface of a commercial TFC-PA membrane using surface-initiated atom transfer radical polymerization (SI-ATRP). Poly(t-butyl acrylate) was polymerized through the SI-ATRP method followed by its acid hydrolysis to form PAA hydrophilic polymer brushes. Surface morphology, permeation flux, salt rejection, and pore sizes were investigated. The contact angle for water was reduced from 50° for a pristine membrane to 27° for the modified membrane due to a modification with the hydrophilic functional group and its brush on membrane surfaces. The flux rate also increased noticeably at lower pH values relative to higher pH for the modified membranes, while the flux remains stable in the case of pristine TFC-PA membranes. There is slight transition in the water flux rate that was also observed when going from pH values of 3 to 5. This was attributed to the pH-responsive conformational changes for the grafted ...