Facilitated transport of olefin through solid PAAm and PAAm-graft composite membranes with silver ions

Solid poly(acrylamide) (PAAm) composite membranes containing silver ions have been investigated for olefin/paraffin separation. The propylene permeance increased significantly for a solid PAAm/AgBF₄ composite membrane with increasing loading amount of silver ions. Silver ions in solid PAAm form reversible complexes with propylene, resulting in the facilitated transport of propylene. The propylene selectivity of 100 over propane was obtained when the mole ratio of silver ions to acrylamide unit was 1. This high separation performance would be obtained predominantly because of the high loading of the propylene carrier, silver ions. PAAm-graft/AgBF₄ composite membranes were prepared in order to improve the gas permeance. Introduction of PAAm grafts on a polysulfone microporous membrane surface was confirmed by FT-IR spectroscopy. The propylene permeance was increased through the PAAm-graft/AgBF₄ membranes compared to that through of the PAAm/AgBF₄ composite membranes, indicating the formation of ultra-thin top layer.     

Facilitated oxygen transport in an ionomer membrane containing cobaltous ions

A new oxygen/nitrogen separation membrane based on an ionomer of sulfonated EPDM (ethylene-propene-diene terpolymer) containing Co²⁺ ions was synthesized and investigated. It was found that the oxygen permeability coefficient and the separation factor for O₂/N₂ of the ionomer membrane are simultaneously enhanced at lower gas pressure difference. This result is believed to be caused by a polymer coordinate complex formed in the ionomer. ESR spectra provided an evidence of the cobalt-oxygen adduct.     

Complexation mechanism of olefin with silver ions dissolved in a polymer matrix and its effect on facilitated olefin transport

Remarkable separation performance of olefin/paraffin mixtures was previously reported by facilitated olefin transport through silver-based polymer electrolyte membranes. The mechanism of facilitated olefin transport in solid membranes of AgCF3SO3 dissolved in poly(N-vinyl pyrrolidone) (PVP) is investigated. In silver polymer electrolyte membranes, only free anions are present up to the 2:1 mole ratio of [C=O]:[Ag], and ion pairs start to form at a ratio of 1:1, followed by higher-order ionic aggregates above a ratio of 1:2. At silver concentrations above 3:1, the propylene permeance increases almost linearly with the total silver concentration, unexpectedly, regardless of the silver ionic constituents. It was also found that all the silver constituents, including ion pairs and higher order ionic aggregates, were completely redissolved into free anions under the propylene environment; this suggests that propylene can be a good ligand for the silver cation. From these experimental findings, a new mechanism for the complexation reaction between propylenes and silver salts in silver-polymer electrolytes was proposed. The new mechanism is consistent with the linearity between the propylene permeance and the total silver concentration regardless of the kind of the silver constituents. Therefore, the facilitated propylene transport through silver-polymer electrolytes may be associated mainly with the silver cation weakly coordinated with both carbonyl oxygen atoms and propylene.     

Coordination structure of various ligands in crosslinked PVA to silver ions for facilitated olefin transport

The most effective ligand among -OH, -O- and -CHO for facilitated olefin transport by silver ions in room temperature crosslinked poly(vinyl alcohol) membrane has been evaluated.     

Electro-osmosis of water through a cellulose acetate membrane

Experiments on electro-osmosis of water through a cellulose acetate membrane have been reported and the data analyzed in the light of nonequilibrium thermodynamics. The linear phenomenological equations have been found to be valid. Study of the directional dependence of phenomenological coefficients has revealed the anisotropic character of the membrane. Efficiency of energy conversion for both electro-osmosis and streaming potential has been calculated and the results have been analyzed in the light of thermodynamic theories.     

Gas permeation in freeze-dried cellulose acetate membrane

Gas permeation rates for helium, nitrogen, argon, and oxygen have been studied by using freezedried cellulose acetate membrane. When the gas permeation rate in freeze-dried cellulose acetate membrane is high, the gas permeation rate through the pores is predominant. On the other hand, when this rate is small, it is predominant at the dense part, except for the pores. Therefore the gas permeation rate in freeze-dried cellulose acetate membrane can be explained by the sum of two gas permeation rates.     

Highly-loaded silver nanoparticles in ultrafine cellulose acetate nanofibrillar aerogel

A facile method was developed to load a large amount of silver nanoparticles into a biodegradable and biocompatible cellulose acetate (CA) nanofibrillar aerogel in a controlled manner. The micro-sized CA fibrils were separated into nano-sized fibrils by salt-assisted chemical treatment in a water-acetone co-solvent to give a nanofibrillar structure with a diameter of 20-50 nm, BET surface area of 110 m²/g, and porosity of 96%. Using the high electron-rich oxygen density in the CA macromolecules and the large surface area of the CA nanoporous structure as an effective nanoreactor, the in-situ direct metallization technique was successfully used to synthesize Ag nanoparticles with an average diameter of 2.8 nm and a loading content of up to 6.98 wt%, which can hardly be achieved by previous methods. This novel procedure provides a facile and economic way to manufacture Ag nanoparticles supported on a porous membrane for various biomedical applications.     

Steady-state distribution of water in cellulose acetate membrane

The effect of hydrostatic pressure applied to a solution on one side of a membrane on the steady-state concentration distribution of permeating solvent inside the membrane has been examined with a view to distinguishing between different mechanisms of permeation in reverse osmosis. The concentration gradients found experimentally in stacks of cellulose acetate films support the view that permeation takes place by diffusion in a nonporous membrane.     

A membrane electrode reversible to zinc ions based on a polymer chelating adsorbent

The sorption of a diazocompound on a highly basic anionite has been studied. The analytical properties of the modified adsorbent have been considered. A technology has been proposed for the production of a film membrane Zn-SE utilizing modified amberlite as the ionophore. The composition of the membrane has been optimized and the main potentiometric characteristics of zinc-selective electrode have been determined. The advantages of the proposed Zn-SE construction are explained.     

Selective transport of silver ions through bulk liquid membrane using Victoria blue as carrier

Transport of Ag⁺ as Ag(CN)₂⁻ ions through a bulk liquid membrane is reported. The bulk liquid membrane used is a solution of Victoria blue (VB) in chloroform. The effects of pH of the source phase, cyanide concentration in the source phase, sodium hydroxide in the receiving phase, and VB concentration in the organic phase on the efficiency of the transport system were studied. The above system has a high selectivity for Ag⁺ and can selectively and efficiently transport Ag(CN)₂⁻ ion from aqueous solutions containing other cations such as alkali and alkaline earths, Zn²⁺, Pd²⁺, Cu²⁺, Cd²⁺,Hg²⁺, Co²⁺, Fe²⁺, Pb²⁺, Ni²⁺, and Al³⁺.     

Structure and coordination properties of facilitated olefin transport membranes consisting of crosslinked poly(vinyl alcohol) and silver hexafluoroantimonate

The high selectivity of solid‐state crosslinked poly(vinyl alcohol) (CPVA) membranes containing silver hexafluoroantimonate (AgSbF₆), with respect to olefin/paraffin mixtures, was previously reported. The structure and coordination properties of CPVA/AgSbF₆ complexes were investigated in this study with wide‐angle X‐ray scattering (WAXS), differential scanning calorimetry (DSC), X‐ray photoelectron spectroscopy (XPS), and theoretical ab initio calculations, and they were compared with those of poly(vinyl alcohol) (PVA)/AgSbF₆ complexes. Contrary to expectations, the measurements of the intersegmental d‐spacings and glass‐transition temperatures indicated that the chain mobility in the PVA/AgSbF₆ membranes was lower than that in the CPVA/AgSbF₆ membranes. The different extents of transient crosslinking in the two systems were attributed mostly to their different coordination structures; silver ions in PVA/AgSbF₆ were coordinated with hydroxyl oxygens located near the polymer main chains, whereas those in CPVA/AgSbF₆ were coordinated with aldehyde oxygens located far from the main chains. According to WAXS spectra, AgSbF₆ was completely dissolved in both PVA and CPVA, and this disrupted the crystallinity of the polymers. However, our DSC study showed that the silver ions dissolved in both polymer matrices recrystallized into silver oxide at elevated temperatures. The binding energy of Ag3d_5/2, as determined from XPS spectra, shifted to lower values with the addition of increasing amounts of the polymer matrix, indicating the increasing coordination of silver ions with polymer chains. The presence of various oxygen species with and without coordination to silver ions was confirmed from O1s XPS spectra of CPVA membranes containing silver ions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 621–628, 2004     

Relationship between structure and transport in cellulose acetate desalination membranes

Several experimental techniques, including measurements of salt rejection, water flux, birefringence, and membrane opaqueness, were used to characterize the structure and performance of typical cellulose acetate desalination membranes. The results indicate that optimum salt rejection and water flux characteristics are related to the presence of molecular orientation effectively perpendicular to the membrane surface. An alignment-type flow mechanism involving water contained within the oriented structure is consistent with the observed structural and transport phenomena. The various membrane fabrication procedures apparently have significant effects on the development of molecular orientation in the thin surface layers of the membrane.     

Combined sorption/transport of sodium dodecyl sulfate and hydrochloric acid in a blend of cellulose acetate butyrate with cellulose acetate hydrogen phthalate

The transport of hydrochloric acid (0.001-0.1 M) and sodium dodecyl sulfate (0.001-0.1 M) has been measured through a membrane consisting of a blend of cellulose acetate butyrate and cellulose acetate hydrogen phthalate. The cellulose derivative blend is suggested to suffer an alteration in the degree of hydrophobicity when in equilibrium with sodium dodecyl sulfate (SDS) through hemimicelle formation. An increase in surface hydrophobicity of the blend when in equilibrium with SDS solution was observed by fluorescence measurements using the vibronic bands of the probe pyrene, as well as by water desorption kinetics; a decrease of the effective diffusion coefficients from 1.2 × 10⁻¹¹ m² s⁻¹ in the absence of SDS to approximately 2 × 10⁻¹³ m² s⁻¹ in its presence was found. The value obtained for the mutual diffusion coefficient of HCl in the concentration range 0.001-0.1 M (D=4.2×10⁻¹⁴ m² s⁻¹) shows also that the membrane presents hydrophobic features. The flux of SDS in the blend membrane at different pH values shows two distinct permeation rates depending on the cmc. However, from the calculation of permeability coefficients at SDS concentrations below the cmc a clear decrease in P is found, whilst, at concentrations above the cmc the permeability coefficients are nearly constant, only showing a slightly increase. The diffusion coefficients of SDS in the blend increase over the whole SDS concentration range analysed and show an effective diffusion coefficient 2-3 orders of magnitude below the diffusion coefficients of SDS in aqueous solutions. This fact suggests that the only diffusing species are SDS unimers. The presence of HCl in the SDS bulk solution has the effect of increasing the permeability and diffusion coefficients. Mutual analysis of permeation and diffusion coefficients and sorption isotherms shows that, on decreasing the pH, the interactions between SDS and the polymer network decrease. This is also reflected in a clear decrease of the hydrophobic interactions between the diffusing and polymeric species, provoked by a decrease in the unimer-unimer association.     

Integrated photografted molecularly imprinted polymers with a cellulose acetate membrane for the extraction of melamine from dry milk before HPLC analysis

In this study, a new separation technique based on membrane extraction is described for the determination of melamine in dry milk. The water‐compatible cellulose acetate membrane, which is photografted by melamine imprinted nanospheres, was prepared by placing the membrane into the polymerization solution containing methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as cross‐linker, acetonitrile as porogen, and melamine as the template molecule. The characterization of the polymeric membrane was performed by Fourier transmission infrared spectroscopy and scanning electron microscopy. This integrated composite membrane was used as a solid‐phase extraction medium for the extraction of melamine from dry milk samples. Various parameters affecting the extraction efficiency of the membrane were evaluated. The results showed higher binding capacity for melamine imprinted membranes in comparison with the nonimprinted membranes. High‐performance liquid chromatography analysis showed that the extraction of melamine from dry milk by the photografted cellulose acetate membrane had a linear calibration curve in the range of 0.02–11.80 μg/mL with an excellent precision of 2.73%. The limit of detection and quantification of melamine was 0.007 and 0.020 μg/mL, respectively. The recoveries of melamine were in the range of 88.7–94.8%.     

Some studies of the diffusion of steroids across a cellulose acetate membrane

Summary The diffusion of four steroids across a cellulose acetate membrane has been examined and from the variation of diffusion rate with temperature the energies of activation have been estimated. The energies of activation are compared with solubility and partition data and it suggested the relative hydrogen bonding ability of the four steroids is of considerable importance in governing the diffusion rate.     

Facilitated transport of saccharides through a supported liquid membrane containing a neutral lipophilic resorcinarene carrier

The facilitated transport of several types of saccharidess has been studied across a supported liquid membrane containing a resorcinarene carrier. The rate-determining step is believed to be the migration of a carrier-saccharide-water ternary complex in the organic solvent. The transport kinetics obey a saturation law, that allows the calculation of the stability constants of the various complexes. The stability constants are related to the saccharide structures: important factors are chain length, configuration and substitution of key hydroxyl groups.     

Stabilization of ferrocene leakage by physical retention in a cellulose acetate membrane. The fructose biosensor.

The prevention of ferrocene leakage from an electrode by physical retention of mediator in a matrix of cellulose acetate membrane is reported. Five types of the cellulose acetate membranes were prepared, containing 1.8%, 5.3%, 8.5%, 20.0% of ferrocene and a membrane containing 1.8% of ferrocene and 0.05 % of Nafion in the matrix. Ferrocene embedded membranes were successfully applied in the construction of a fructose biosensor by immobilization of PQQ-dependent fructose dehydrogenase (FDH). The biosensor comprising a cellulose acetate membrane with 1.8% of ferrocene and 0.05% of Nafion had good stability characteristics, retained almost 40% of the initial response after 8 h of continuous use with an initial sensitivity of 226 nA mM(-1) and response time of 75 s.     

Effect of a static magnetic field on ion transport in a cellulose membrane

A cellulose membrane was exposed to the static magnetic field (SMF) in the presence of KCl solution and ion transport through the membrane was measured before and after the SMF exposure. SMF at 0.24 T significantly enhanced the rate of ion transport, especially after the first exposure (p<0.05), while the increased ion transport rate did not return to the initial basal level after exchange of the aqueous medium. These results suggest that an irreversible, temporal conformation change took place on the cellulose membrane or on the water bound to the cellulose surface. The accelerating effect of SMF on the ion transport seems to have occurred as a result of stabilized hydration layer on the cellulose surface.     

Primary-particle-beam-induced reduction of silver acetate in glycerol solutions to form a silver mirror

The liquid SIMS mass spectra of silver acetate dissolved in a glycerol matrix is discussed, with emphasis on the formation of a ‘silver mirror’ on the surface of the glycerol droplet owing to reduction of the silver acetate. Silver clusters containing up to three silver atoms have been observed from this mirrored surface; Ag₃⁺ cluster ions are not observed in the spectrum when conditions are such that the mirror is not formed. For example, use of a slightly oxidizing matrix (o-nitrophenyl octyl ether or m-nitrobenzylalcohol) prevents formation of the ‘mirror’; only Ag⁺ is sputtered from this surface.     

Grafting of caprolacton to cellulose acetate by reactive processing

Cellulose acetate was successfully modified with caprolacton in an internal mixer at temperatures between 120 and 220 °C, and reaction times between 5 and 45 min in the presence of tin-octoate catalyst. The efficiency of modification and the structure of the product were analyzed by SEC, ¹H NMR, and FTIR spectroscopy. Significant modification of cellulose acetate did not occur at low temperatures, below 180 °C. Grafting efficiency increased with increasing temperature and time. The extent of grafting could be estimated from the amount of material extracted from the samples by toluene and by FTIR analysis, from the relative intensity of -CH₂- and -CH₃ vibrations. The amount of polycaprolacton homopolymer is relatively low at the end of the reaction; the efficiency of grafting is good. Although high temperature and long reaction time favor grafting, considerable degradation of the product occurs under these conditions. Quantitative analysis showed that the average length of grafted oligomeric caprolacton chains is around 3 monomer units. The chains attached to the CA backbone internally plasticize the polymer leading to a considerable decrease of its glass transition temperature.