Ultrafiltration membranes based on interpolyelectrolyte complexes: Adsorption and mass-exchange properties

Ultrafiltration membranes based on interpolyelectrolyte complexes of a sulfonated aromatic copolyamide, an acrylonitrile–N,N-dimethyl-N,N-diallylammonium chloride copolymer, and poly-N,N-dimethyl-N,N-diallylammonium chloride were prepared. The adsorption (in batch experiments and under conditions of ultrafiltration of myoglobin, lysozyme, and bovine serum albumin solutions) and mass-exchange properties of the membranes were studied. Correlation between the procedure for performing the interpolymer reaction, the composition of the complexes formed, and the characteristics of the membranes prepared was found. The protein/membrane interaction in the system studied is mainly due to Coulomb forces. The effect of the protein adsorption on the separation and transport properties of the membranes was considered. The general level of the mass-exchange properties of the membranes based on the interpolyelectrolyte complexes is higher compared to the samples containing ionic groups of like charge.     

Effect of the porous structure of sodium chloride granules on their physicochemical properties

The effect of porous structure on the strength characteristics of compacted potassium chloride granules and also on their moisture absorption and caking was studied.     

Nonstoichiometric interpolyelectrolyte complexes as colloidal dispersions based on NaPAMPS and their interaction with colloidal silica particles

Preparation and characterization of some nonstoichiometric interpolyelectrolyte complexes (NIPECs) as stable colloidal dispersions by the interaction between poly(sodium 2-acrylamido-2-methylpropanesulfonate) (NaPAMPS) and three strong polycations bearing quaternary ammonium salt centres in the backbone, poly(diallyldimethylammonium chloride) (PDADMAC) and two polycations containing N,N-dimethyl-2-hydroxypropyleneammonium chloride units (PCA₅ and PCA₅D₁), have been followed in this study as a function of the polycation structure and polyelectrolyte concentration. Complex characteristics were followed by polyelectrolyte titration, turbidity and quasi-ellastic light scattering. Almost monodisperse NIPECs nanoparticles with a good storage stability were prepared when total concentration of polyelectrolyte was varied in the range 0.85-6.35 mmol/L, at a ratio between charges (n⁻/n⁺) of 0.7. NIPECs as a new kind of flocculants were used to flocculate a stable monodisperse silica suspension. The main advantage of NIPECs as flocculants is the broad flocculation window, which is a very important aspect for industrial applications.     

Effect of thickness of the PPO membranes on the surface morphology

The effect of membrane thickness on surface morphology has been studied for the case of polyphenylene oxide (PPO) membranes cast from solutions of PPO in trichloroethylene (TCE). Both roughness and nodule size decrease with increasing membrane thickness up to a certain point after which they begin to increase. Minima in roughness and nodule size are observed for 9–11 μm thick films. These minima depend on initial polymer concentration in the casting solution. At a membrane thickness greater than 11 μm, super nodular aggregates are formed. A mechanism based on Marangoni and Rayleigh number is presented.     

Effect of PVDF characteristics on extruded film morphology and porous membranes feasibility by stretching

Three different polyvinylidene fluoride (PVDF) resins were selected to develop porous membranes through melt extrusion and stretching. The effect of the polymer rheology on chain elongation in the melt state was studied. The possibility of generating a row‐nucleated lamellar crystallization for precursor films was investigated. The arrangement and orientation of the crystalline phase were examined by wide angle X‐ray diffraction (WAXD) and Fourier Transform Infrared Spectroscopy (FTIR). The extrusion conditions and the blend compositions were adjusted to obtain uniform precursor films with appropriate morphology. Annealing, cold and hot stretching were consequently employed to generate and enlarge the pores. It was found that a proper crystalline structure of the precursor films was strongly dependent on molecular weight of PVDF and process conditions. Blending of two PVDF resins having low and high molecular weights improved the water vapor permeability of the obtained membranes. The tensile response was monitored during the stretching process for membrane development and the results revealed a distinct behavior for the membranes having low or high permeability. The membranes with low permeability did not show any significant strain hardening during stretching whereas for highly permeable membranes, a noticeable strain hardening behavior was observed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1219–1229, 2009     

Effects of hypochlorite treatment on the surface morphology and mechanical properties of polyethersulfone ultrafiltration membranes

Polyethersulfone membranes are widely used for ultrafiltration and microfiltration especially in the dairy industry, but they are believed to degrade when exposed to the sodium hypochlorite solution that is used to sanitize the processing equipment. Such membranes were exposed to sodium hypochlorite for up to 25,000 ppm-day at 55 °C, and pH 9 and 12. Mechanical properties as measured by dynamic mechanical analysis and tensile strength did not change greatly, but surface properties measured by FTIR-ATR, field emission scanning electron microscopy and associated energy dispersive X-ray spectroscopy detected significant changes in the surface. Surface pitting was observed and was found to be most severe at pH 9. It was thought that pitting was the likely cause of degradation in performance of the membranes and that pits could act as stress raisers leading to cracking.     

Effect of thermochemical treatment on the surface morphology and hydrophobicity of heterogeneous ion-exchange membranes

A comparative analysis is performed on the effect thermochemical treatment in aqueous, alkali, and acid media has on the surface morphology and hydrophobicity of swelling heterogeneous ion-exchanged membranes. A correlation between changes in surface morphology and hydrophobicity is established. It is shown that under prolonged (50 h) membrane thermal treatment above room temperature, hydrophobicity is reduced due to substantial enlargement of cavities and cracks resulting from the partial destruction of inert binder (polyethylene) and reinforcing poly-?-caproamide fabric (capron).     

Effect of the structure of Ti-Sb-O catalysts on their acid-base properties,surface oxygen binding energy,and catalytic properties in propylene ammoxidation

The structure of Ti-Sb-O catalysts, namely, a solid solution of antimony ions in rutile-type TiO₂ and the titanium antimonate TiSb₂O₆, is characterized by X-ray diffraction, high-resolution electron microscopy, calorimetry, and IR spectroscopy. The structure effects on the acid-base properties and the surface oxygen binding energy are considered, as well as the correlation of these characteristics with the catalytic properties of the Ti-Sb-O system in propylene ammoxidation. The solid solution has a regular crystal structure. As a consequence, the surface has high concentrations of strong aprotic acid and strong basic sites and is characterized by a high surface oxygen binding energy. In the titanium antimonate structure, extended crystallographic shear defects cause a marked enrichment of the surface with antimony and, accordingly, an increase in the relative concentration of weak aprotic acid sites and a decrease in the surface oxygen binding energy. The changes of the structure and acid-base properties of the surface in passing from the solid solution to TiSb₂O₆ result in an increase in the acrylonitrile selectivity.     

Effect of tacticity and morphology on the formation of persistent electrical polarization in polar polymer membranes

Persistent electrical polarization (heterocharged electret formation) has been studied as a function of stereotacticity, crystallinity, and molecular weight in membranes of poly(vinyl alcohol) (PVA) prepared via different synthetic routes. Membranes of PVA–sodium polystyrenesulfonate (PSSNa) and PVA–poly(vinyl acetate) (PVAc) copolymers and PVA–PVAc–PSSNa were also investigated. The degree of persistent polarization a pure PVA membrane can support, was found to vary according to isotactic > syndiotactic > heterotactic triad concentrations. Increases in crystallinity tend to decrease persistent polarization, and such changes in crystallinity are probably responsible for the above observed order, since measurements of persistent polarization on noncrystalline PVA–PSSNa membranes were found to vary according to syndiotactic > heterotactic > isotactic with regard to the PVA. Within PVA–PSSNa membranes the presence of acetate groups reverses the behavior of PSSNa from anhancer to an inhibitor of electret formation. The results all support a model in which heterocharged electret formation involves an ion displacement in the direction of the applied field and stabilization of this ion displacement by local hydrogen bonding.     

Effect of coagulant temperature and composition on surface morphology and mass transfer properties of cellulose acetate hollow fiber membranes

Cellulose acetate (CA) hollow fibers were spun via the dry‐jet wet spinning technique under various external coagulant compositions and temperatures. The surface morphology of the resulting hollow fiber was examined using field emission scanning electron microscopy (FESEM) and tapping mode atomic force microscopy (TMAFM). The pure water permeability (PWP) and the retention of dextran of the hollow fiber were also measured. The results showed that both the temperature and composition can affect greatly the surface morphology and hence the permeation performance of hollow fiber membranes when the temperature was over 55°C and the dimethyl formamide (DMF) content was higher than 15%. The on‐line draw ratio increased with the coagulant temperature and DMF content (in the range of 0 to 10%) in the external coagulant. The ultimate tensile strength also increased when the fibers were coagulated in 5–10% DMF and at 70°C. The PWP increased with the DMF content in the coagulant and the coagulant temperature. The retention of dextran decreased with the increase of the DMF content in the coagulant and the coagulant temperature. Copyright © 2005 John Wiley & Sons, Ltd.     

Influence of the physicochemical treatment procedure on the morphology and properties of the polyvinyl chloride film surface

Atomic-force microscopy was applied to examination of the topography of the surface of polyvinyl chloride films treated by corona discharge and nitrogen-oxygen plasma at atmospheric pressure. The structure of the modified surface was examined, as well as the influence of the surface activation method on the possibility of its subsequent chemicophysical functionalization.     

Design of materials for solid oxide fuel cells,permselective membranes,and catalysts for biofuel transformation into syngas and hydrogen based on fundamental studies of their real structure,transport properties,and surface reactivity

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Effect of the surface modification of polymer membranes on their microbiological fouling

Composite polymer membranes with chemically different surfaces are prepared by the photochemical modification of Millipore microfiltration poly(vinylidene fluoride) and polysulfone membranes using 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-hydroxyethyl methacrylate, and 2-(dimethylamino)ethyl methacrylate quaternized with methyl chloride. It is shown that, during the filtration of an E. coli suspension, the membrane flux substantially decreases with time owing to the fouling of the membrane surface by bacterial cells. The membranes with the hydrophilic surface are less susceptible to fouling than hydrophobic membranes, while the ability to recover the performance upon washing is higher for the membranes with a chemically neutral surface than for charged membranes. It is shown that the susceptibility of membranes to microbiological fouling reduces with a decrease in the roughness of the membrane surface. It is established that the membranes modified with the quaternized 2-(dimethylamino)ethyl methacrylate possess antibacterial properties. These membranes proved to be the most efficient in the filtration of natural surface water in a noncontinuous regime, a result that is explained by the ability of membranes to prevent the formation of a fouling biofilm on their surfaces.     

Investigation of electrical properties of the electrical double layer on porous glasses

A series of Controlled Porosity Glasses was employed to investigate their electrical surface properties. Surface charge density and adsorption of electrolyte ions were examined, in order to link initial glass composition and physicochemical properties with its surface electrical double layer characteristics. Results prove the increase of surface boron concentration and consequently growing of negative charge and adsorption properties. Authors find it more complicated to explain characteristics of positive charge changes, which require further investigation.     

Control over the morphology of porous polymeric membranes for flow through biosensors

Porous membranes have been developed by photo-polymerisation-induced phase separation of a monomer/solvent mixture. Characterised by a large open surface area reaching up to about 50 m²/g, these membranes are suitable for flow through biosensor applications in the field of molecular diagnostics. The effects of the polymerisation conditions and the phase separation on the resulting structures are discussed. SEM analysis and BET surface area measurements revealed that morphology can be well controlled by adjusting monomer concentration and UV intensity. Membranes functionalised with epoxy and amine groups show high coupling efficiency of oligo-DNA and large hybridisation efficiency.     

Spectral, electrical conductivity and biological activity properties of some new azopyrimidine derivatives and their complexes

The electronic absorption spectra of 5-(o-substituted phenylazo)-6-amino-2-thiouracils and 6-(o-substituted phenylazo)-5-aminouracils containing different substituents are studied at different pH's. The dissociation constants are evaluated and discussed. Phenomenon of tautomerism is more supported by (1)H NMR and (13)C NMR spectra. The electrical conductivity of some ligands and their Co(II), Ni(II) and Cu(II) complexes in the temperature range 293-150K favoured their semiconducting properties where the metal ion forms a bridge to facilitate the flow of the current. The biological activity of some ligands and their complexes are tested against a number of Gram-positive and Gram-negative bacteria. The results showed that some of the compounds have a well considerable activity against some of the organisms.     

Effect of coagulating agent viscosity on the kinetics of formation,morphology, and transport properties of cellulose nanofiltration membranes

Low-viscous coagulating agents are tradionally used to precipitate polymers from their solutions and obtain films and fibers from them; they represent, as a rule, the combinations of solvent and nonsolvent of the polymer used. At the same time, since the structure of the precipitated polymer is formed under non-equilibrium conditions, the influence of the coagulant viscosity can be quite substantial. The influence of the viscosity of the medium on the formation of structure, morphology, and transport characteristics of the precipitated polymer is studied by example of forming of the cellulose membranes from solution in N-methyl-morpholine N-oxide using some proton-donor coagulants. In this regard, the interdiffusion processes proceeding at the contact of cellulose solutions and coagulating agents (water, propylene glycol, glycerin) are explored using the laser interferometry method. Varying the precipitator viscosity allows one to change the rate of formation and correspondingly the morphology of the cellulose films. In turn, the membrane structure determines its transport characteristics, which were assessed by the filtration of aprotic media with anionic dyes—Orange II and Remazol Brilliant Blue R. The application of the low-viscous precipitator provides the formation of a uniform film structure in the bulk, but leads to development of defects close to the surface, while a viscous medium promotes the formation of a relatively thin dense shell on the films.     

Effect of an aprotic solvent on the properties and structure of ion-exchange membranes

The effect of the aprotic solvent dimethylacetamide on the equilibrium and transport properties of heterogeneous (MK-40, MA-40, and MA-41) and homogeneous (MF-4SK) ion-exchange membranes is investigated. On the basis of concentration dependences of the conductivity and diffusion permeability of membranes, model calculations of transport-structural parameters that reflect the structural and kinetic characteristics of conducting phases of the swollen polymer are performed. The effect of the aprotic solvent on the flow of current through the structural fragments of the ion-exchange material is estimated. The causes of changes that are induced in the properties of the membranes by the aprotic solvent are ascertained.     

Effect of filler morphology and surface chemistry on the rheological properties of filled polypropylenes

The effect of filler size, shape and surface chemistry is investigated for mineral-filled polypropylene. Viscosity, first normal stress difference and dynamic properties are all considered. It is shown that, other things being equal, viscosity decreases as filler size increases, the filler surface is made hydrophobic or the shape of the filler is changed from ‘blocky’ to ‘platey’. The first normal stress difference is found to be relatively insensitive to such changes.     

Effect of the structure of copper(II) complexes, adsorbed on the surface of SiO2, on their catalytic activity in ozone decomposition

We describe the composition, structure, and catalytic activity in the reaction of ozone decomposition for copper(II) complexes with acido ligands and immobilized Schiff’s bases (propyl benzaldimine derivatives) that are anchored on silica (silica gel, aerosil). We demonstrate methods for controlling their catalytic activity. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 1, pp. 55–60, January–February, 2006.