Chemical valves based on poly(4-vinylpyridine)-filled microporous membranes (original) (raw)
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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.
Langmuir, 1999
The partial molar volume, V h , and the partial specific volume, ν j, were estimated for more than 25 polyelectrolyte structures. The materials investigated by density measurements in highly diluted aqueous solutions (c < 10 -2 monomol/L) included both synthetic polyelectrolytes and chemically modified natural polymers. Through a detailed analysis, related to the chemical structure and macromolecular parameters, a linear dependence between the copolymer composition and the partial volumes could be identified for diallyldimethylammonium chloride/acrylamide copolymers. Additivity could also be shown for sodium cellulose sulfate having various degrees of substitution. For a homologous series of poly(vinylbenzyltrialkylammonium chloride)s, a linear correlation between the molar mass of the monomer unit and the partial molar volume was obtained. No influence of the degree of polymerization was observed as long as the contour length exceeds the Debye length. The experimental results were used to evaluate the general applicability of the additivity schemes of Durchschlag and Zipper, as well as Gianni and Lepori, to polyelectrolytes. Agreement between experimental and calculated partial volumes strongly depends on the chemical structures. In the case of the synthetic polycations, the deviations are in a similar range for both models though somewhat smaller for the Gianni/Lepori model. The use of the Durchschlag/Zipper model yields much better agreement for the anionic biopolymers with deviations generally less than 3%. The tendency of the empirical models is correct; however, the precision may be improved by regressing of parameters from the experimental results. The new experimental data may also be useful in polyelectrolyte characterization.
Acid/base properties of poly(4-vinylpyridine) anchored within microporous membranes
Journal of Membrane Science, 1999
Membranes consisting of poly(4-vinylpyridine) anchored within the pores of microporous polypropylene and polyethylene membranes exhibit a very large, fully reversible change in permeability over a very narrow pH range (pH valve). A detailed examination of the acid/base properties of the incorporated poly(4-vinylpyridine) has been undertaken in order to understand the factors affecting the position (pH) at which this valve operates. It was shown that the position and magnitude of the valve is the same when either HCl, H 3 PO 4 , or CH 3 COOH are used to adjust the acidity of the feed solution, indicating that pH of the aqueous phase is the major determining factor controlling the valve operation with these acids. However, the valve behavior of the membrane with H 2 SO 4 was found to be completely different than with the other acids in that the valve both closed at a substantially higher pH than with the other acids and then fully re-opened when the pH was decreased below 3. Potentiometric titrations of membranes containing poly(4-vinylpyridine) and control experiments involving solutions/suspensions of the homopolymer in water were undertaken. It was found that there are substantial differences in the protonation of poly(4vinylpyridine) both in terms of its environment (membrane bound or in solution) as well as with the acid used. The differences in the pK observed between H 2 SO 4 and the other acids are discussed in terms of conformational changes of poly(4vinylpyridine) which are induced by both protonation and the counter-ion (anion) present. The results of potentiometric titrations parallel the valve behavior of the membranes. The conformational changes underlying the pH valve effects in different acids were visualized by atomic force microscopy and followed by thickness changes in the membranes. # 1999 Elsevier Science B.V. All rights reserved. 0376-7388/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. P I I : S 0 3 7 6 -7 3 8 8 ( 9 8 ) 0 0 2 1 9 -1
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1993
The protonation of two polyelectrolytes with carboxyl groups, grafted on porous cellulose and polyurethane supports, was evaluated by potentiometry, titration calorimetry and Fourier transform IR (FT-IR) spectroscopy in aqueous media. The large potentiometric hysteresis loops observed were indicative of interactions between functional groups of the graft chains and the substrate.
Nanofiltration using pore-filled membranes: effect of polyelectrolyte composition on performance
Separation and …, 2001
Several series of membranes composed of microporous poly(propylene) substrates filled with polyelectrolyte gels of different chemical structure, polymer concentration and charge densities have been prepared in order to examine the effect of polyelelctrolyte composition on the performance of these membranes in nanofiltration. The membranes were made by two different routes involving either in situ chemical cross-linking of poly(4-vinylpyridine) or poly(vinylbenzyl chloride), or by in situ polymerization of acrylic acid with tetra(ethylene glycol) diacrylate or N,Nmethylenebisacrylamide as cross-linking agents in the pores of the substrates. The resulting pore-filled membranes were characterized by the concentration (volume fraction) of the polyelectrolyte in the pores, ion exchange capacity (charge density), water content, and thickness. The different series of membranes were tested under pressure to determine their hydrodynamic permeabilities and salt separation properties (NaCl). It was found that there was a good correlation between hydrodynamic (Darcy) permeability and gel polymer concentration that holds irrespective of the gel polymer chemistry in the pore-filling gels. Membranes with different pore-filling gels, whether positively or negatively charged, followed the same relationship. The separation properties of the membranes are very good and the salt rejection was found to be practically constant over a wide range of permeabilities (gel concentrations). It was also found that the increase in the nominal charge density above approximately 0.2 mmol/cm 3 of the swollen gel had a negligible effect on the separation properties of the gel-filled membranes. The results of this study provide a basis for the further design and optimization of polyelectrolyte filled membranes for nanofiltration applications.
Solution properties of polyelectrolytes
Journal of Chromatography A, 1993
Quantitative evaluation of elution volumes (V,) of polyelectrolytes in salt-containing eluents was performed, taking into account electric double-layer effects and the effective radius of polyions, and assuming that polyelectrolytes behave as rigid hydrodynamic spheres and that the geometry of gel pores is cylindrical. A polynomial V, dependence on ionic strength (I) was obtained, namely a second order one in Z-"'. The semi-empirical polynomial coefficients depend on column characteristics, namely V, (interstitial volume), VP (total pore volume) and a (mean pore radius), as well as on effective coil radius (R,) and on k (a parameter related to the electric effects). Fair correlations between predicted and measured elution volumes for uncharged polymers hold, at least for the polyelectrolyte-gel systems tested here: polyelectrolytes poly(L-glutamic acid), sodium poly(styrene sulphonate) and poly(acrylic acid); gels Spherogel TSK PW4000 and Ultrahydrogel 250.
polyelectrolytes a review in drug delivery and dynamics study 6
Polyelectrolytes are polymers of oppositely charged ions and their properties differ profoundly than their repeating units. Over recent years, much advancement has been made in the synthesis, characterization, and application of polyelectrolytes and polyelectrolyte complexes (PECs). It has many applications as flocculation agents, dispersant agents, and as super-plasticizers. In this article, the synthesis, types, characteristics, and application of PECs mainly for drug delivery and dynamics study are reviewed. Polymers that contain repeating electrolyte units i.e. polycations or polyanions, at near-neutral pH are called polyelectrolytes [1], which incorporate significant molecules, for example, DNA and other naturally available polymers. These groups charged the polymers after dissociation in aqueous solution and are physically and chemically similar to both electrolytes and polymers. Their solutions are conductive, like salts and viscous like polymer's solutions. Polymers are classified into various types, such as based on origin, composition, molecular architecture, and electrochemistry. Around a hundred years ago, the investigation of polyelectrolyte complexes started [2] but is being revived a short time ago on account of many different types of work that require immense knowledge of the field. One such line is the layer-by-layer (LbL) aggregation of electrolyte units, invented by Decher [3], which leads to many possible applications in the fields of catalysis, membranes, and biomedicine. The concept of polyelectrolyte complexes as a significant contributor to drug delivery vehicle design may be useful because of its improvements made a few decades back [4-7]. The properties of the starting materials and the reacting environment both affect the synthesis, shape and characteristics of polyelectrolyte complexes [8-16]. The formed shape of the PEC or for any charged group is usually depicted in figure 1. Oppositely charged polyelectrolytes get together by shaping inseparable ion pairs, and the rest unbonded charged particles are balanced by small counter-ions to makeup separable ion pairs. Water molecules enclose many ion pairs in the hydration layer because this phenomenon generally occurs in the aqueous phase. Polyelectrolytes are polymers of oppositely charged ions and their properties differ profoundly than their repeating units. Over recent years, much advancement has been made in the synthesis, characterization, and application of polyelectrolytes and polyelectrolyte complexes (PECs). It has many applications as flocculation agents, dispersant agents, and as super-plasticizers. In this article, the synthesis, types, characteristics, and application of PECs mainly for drug delivery and dynamics study are reviewed.
Journal of Membrane Science, 2004
Pressure-driven transport of dilute electrolytes in microporous membranes containing terminally-anchored charged poly(amino acids) (PAA) has been investigated through both experimental characterization and model evaluation. The membrane pore structure was modified via single-point covalent attachment of either negatively (poly(l-glutamic acid) or PLGA) or positively-charged polypeptides (poly(l-arginine) or PLA and poly(l-lysine) or PLL) allowing for separations using microporous materials (i.e. cellulosic, silica/polyethylene composites). Thus, efficient exclusion of ionic species can be achieved in open membrane platforms with considerably lower pressure requirements than conventional NF. For instance, the solute rejection of 0.5 mM solutions of environmentally-toxic species, such as divalent oxyanions of As(V) and Cr(VI), using a PLGA functionalized silica support (pore size ∼100 nm) was >80% at 0.7 bar. The effects of solute type, concentration, pH, polypeptide loading and pore coverage of the attached macromolecule on the observed solute rejection and hydraulic permeability have been examined. In addition, immobilization of PLGA allows for conformation-based alteration of membrane separation properties upon changes in pH. These morphological transitions were investigated through application of permeability data to a two-region pore model describing solvent transport. This allows for theoretical evaluation of the effective thickness of the polypeptide-containing pore region. Ion transport was then modeled using a two-dimensional approach based on the extended-Nernst Planck equations coupled with Donnan equilibrium principles. The required parameters are the effective membrane surface charge density and the PAA pore coverage as determined through permeability studies. This analysis allows for evaluation of the fixed membrane charge density based on solute rejection data, as well as, estimation of the electrostatic properties of the immobilized poly(amino acids) (i.e. pK a shifts, pH dependent thickness of polymer containing pore region).
Ultrathin self-assembled polyelectrolyte membranes for pervaporation
Journal of Membrane Science, 1998
Ethanol±water pervaporation through new composite membranes with ultrathin self-assembled polyelectrolyte separating layer is described. The composite membranes were prepared by alternating electrostatic adsorption of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate sodium salt) (PSS) on a porous PAN/PET supporting membrane (a polyethylene terephthalate¯eece coated with a thin layer of polyacrylonitrile). The sealing of the pores of the supporting membrane was studied by gas¯ow measurements. Pervaporation experiments were carried out under variation of the preparation and operation conditions. Generally it was found that the separation capability considerably increased, when the composite membrane was annealed at temperatures above 608C, while the¯ux simultaneously decreased. The same was found, when the number of PAH/PSS layers was increased. Raising the pervaporation temperature led to both an increase of the¯ux and the separation factor. The highest separation factor of 70 was found at a low water content of the feed of 6.2% (w/w). The corresponding¯ux was 230 g m À2 h À1 . Pervaporation was feasible up to a water content of 24% (w/w) in the feed. At higher values, hydrolysis set in resulting in partial desorption of the separating layer. # 1998 Elsevier Science B.V. All rights reserved.