Statistical and rheological evaluation of the effect of salts in partially hydrolyzed polyacrylamide solutions

Partially hydrolyzed polyacrylamide (PHPA) is the most common anionic copolymer used in Enhanced oil recovery (EOR), but the use of this polymer presents some limitations in the presence of divalent cations. The objective of this work was to evaluate the thermal stability of PHPA in brines containing Na⁺, Mg²⁺, and Ca²⁺ cations (isolated or combined). In this study, the PHPA used at a concentration of 2500 mgL⁻¹ has a MW of 20 × 10⁶ Da. The stability of the polymeric solutions was monitored through rheological analyses for 180 days at 70°C, in the absence of oxygen, using a central composite rotational design. In the absence of dissolved oxygen and cations, the PHPA solution was basically the same as that observed over a period of 30 days. It was observed that Ca⁺² ion had the greatest influence on reducing the viscosity of PHPA in all cases. Polymeric solutions with Total dissolved solids (TDS) greater than 1000 mg L⁻¹ showed complete degradation of the polymer in 180 days. The statistical data corroborate the rheological results, showing that only the main effect of Na⁺ was not statistically significant and that the concentrations of Mg²⁺ and Ca²⁺ presented statistically significant effects in their linear components and quadratic components.     

Inward Migration of Glass‐Modifier Cations During Heat Treatment Under an N2 Atmosphere

An Na⁺/Ca²⁺‐deficient layer is observed to form on the glass surface region up to a depth of hundreds of nanometers when a soda‐lime‐silicate glass is heat treated under an N₂ atmosphere near its glass‐transition temperature. The measurements were performed using X‐ray photoelectron spectroscopy with C₆₀‐ion sputtering (C₆₀‐XPS) and dynamic secondary‐ion mass spectrometry (D‐SIMS) with consideration of the mass and charge balances. The increase in the amount of hydrogen is substantially less than the decrease in the total charge due to the loss of modifier cations in the Na⁺/Ca²⁺‐deficient layer; furthermore, the oxygen concentration in this layer is lower than the bulk value, suggesting that the silanol groups in the surface layer of the glass are dehydrated. A high‐concentration layer of Ca²⁺ is also confirmed in the dehydration layer of the glass heat treated under an N₂ atmosphere, suggesting that Na⁺ and Ca²⁺ ions migrate inward into the glass via an ion‐exchange reaction with protons, which migrate toward the surface from the bulk. We also confirmed that a thicker Na⁺/Ca²⁺‐deficient layer is formed on glass surfaces with higher water content. Our results suggest that the dehydration of the silanol groups is the driving force of the inward migration of Na⁺ and Ca²⁺ ions.     

Influence of K+ and Na+ ions on the degradation of wet‐spun alginate fibers for tissue engineering

A synthetic type of wet‐spun alginate fibers were immersed in simulated body fluid(SBF) composed of K⁺, Na⁺, and Ca²⁺ cations with various concentrations. Experimental measurements revealed that Na⁺ had a greater impact on degradability than that of K⁺ ion. The finding was further confirmed by the characterization of mass loss, ICP, XRD, and theoretical analyses. The degradation process and mechanism were demonstrated through the research on swelling behavior and mass loss. Besides, the wet‐spun alginate fibers were characterized by FT‐IR, XRD, and SEM. The results showed that the degradation mechanism could be attributed to the ion‐exchange between Ca²⁺ of the synthetic alginate fibers and Na⁺, K⁺ of the solutions under the osmotic pressure. The synthetic fibers were swelled and then degraded faster with the presence of Na⁺ ion presented greater influence on degradability compared with K⁺ ion. The degradation results of a mechanical rupture of fibers due to excessive water uptake without the occurrence of any chemical changes in the spun alginates structure. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44396.     

Poly[poly(oxypropylene) phosphate] macroionophores for transport and separation of cations in a hybrid: Cation‐exchange polymer and liquid membrane system

Poly[poly(oxypropylene) phosphate]s (PPOPP, M_n = 5800, 8100, 10,400), with different POP units (400, 1200, 2000), were synthesized and applied as cation‐selective macroionophores in a multimembrane hybrid system (MHS). The solution of PPOPP in dichloroethane formed the flowing liquid membrane (FLM) circulating between two polymer cation‐exchange membranes, and subsequently, between two polymer‐made pervaporation (PV) membranes. It was found that the PPOPP macroionophores activate the preferential transport of Zn²⁺ cations from aqueous solutions containing competing Cu²⁺, Ca²⁺, Mg²⁺, K⁺, and Na⁺ cations. The following separation orders were observed for PPOPPs with POP‐400 and POP‐1200: Zn²⁺ > Cu²⁺ ? Ca²⁺, Mg²⁺, K⁺, Na⁺, and for PPOPP with POP‐2000: Zn²⁺ > Cu²⁺,Ca²⁺ ? Mg²⁺, K⁺, Na⁺. Always, the particular cations are separated as: Zn²⁺ > Cu²⁺, Ca²⁺ > Mg²⁺, and K⁺ > Na⁺. The properties of PPOPPs were compared to respective transport and separation characteristics corresponding to those of respective poly(propylene glycol)s and poly(oxypropylene) bisphosphates. The results of investigation indicate that the bifunctional character of PPOPPs is caused by the presence of ionizable groups and probably pseudocyclic POP structures. By comparing the separation of cations in the simple MHS[FLM] system and the system supported by pervaporation unit [MHS[FLM‐PV] it was found that continuous dehydration of an organic FLM improves the system overall performance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1436–1445, 2004     

Transfer of Monovalent and Divalent Cations in Salt Solutions by Electrodialysis

Abstract

The selectivity mechanism of transport of Na⁺, Ca²⁺ and Mg²⁺ through commercial monovalent‐cation permselective membranes is investigated in batch electrodialysis experiments with synthetic salt solutions containing monovalent and divalent cations. The role of hydration energy, steric effect, kinetic effect as well as effects of permselectivity of cation exchange membrane has been elucidated with electrodialysis of single solutions (NaCl, CaCl₂, MgCl₂). The mechanism of interferences is investigated in (Na⁺/Ca²⁺, Na⁺/Mg²⁺, Ca²⁺/Mg²⁺ and Na⁺/Ca²⁺/Mg²⁺) mixtures.     

Calcium ion modulates protein release from chitosan‐hyaluronic acid poly electrolyte gel

Polyelectrolyte complex (PEC) of chitosan (CH) and hyaluronic acid (HA) are widely used for skin, cartilage, and bone tissue engineering. However, no reports are seen on their response at high ionic media, like increased Ca²⁺ where they are likely to be exposed in the form of bone constructs and the influence of these ions on modulating the release of incorporated entities such as drugs and growth factors. Here, we prepared freeze dried scaffolds of PEC of CH and HA (CH‐HA) and characterized them by FTIR, TGA, SEM, and ESEM. FITC conjugated BSA, designated as FA, was incorporated into the PEC to study the release properties in response to Ca²⁺. The swellability of CH‐HA and the extent of drug release from the matrix, FA loaded CH‐HA was studied in deionised water and aqueous Na⁺ and Ca²⁺ solutions. Swelling and drug release were high for the matrix in aqueous Ca²⁺ whereas it was remarkably low in water and Na⁺. Drug released was found to increase with concentrations of Ca²⁺ (0.02–1.0M) indicating that CH‐HA is a promising matrix for Ca²⁺ responsive delivery of agents to accelerate healing of bone cracks, which is known to release high amount of Ca²⁺. POLYM. ENG. SCI., 55:2089–2097, 2015. © 2015 Society of Plastics Engineers     

FTIR-ATR studies of diffusion and perturbation of water in polyelectrolyte thin films. Part 4. Diffusion, perturbation and swelling processes for ionic solutions in SPEES/PES membranes

We report diffusion rates and equilibrium concentrations of water in a polyelectrolyte SPEES/PES film using ATR/FTIR spectroscopy. The data for water obtained by fitting spectral intensities to a dual mode diffusion model in the presence of different counter ions (at 0.2 mol dm⁻³) follow the order Li⁺>Cs⁺>Na⁺>Ca²⁺>K⁺. Diffusion is progressively slower for higher concentrations of NaCl (0.2-0.85 mol dm⁻³) and the NO₃⁻ counter anion leads to a faster diffusion rate than for Cl⁻ at the same concentration. Both water uptake and diffusion rates are broadly consistent with expectations based on the differential degrees of swelling, caused by changes in the SO₃⁻/SO₃⁻ interpolymer chain repulsive forces leading to a decrease in volume diffusion compared with the value for pure water. Direct spectral measurements of the degree of swelling confirm that the process does occur, although the order of the swelling amounts does not map directly onto that of the diffusion rates. This is probably because the interfacial dissociation processes are hydration dependent.     

An RNA‐Cleaving Catalytic DNA Accelerated by Freezing

The EtNa DNAzyme was isolated during the isopropanol precipitation step of an in vitro selection effort. Although inactive with the intended cofactor, its RNA cleavage activity was observed under a few conditions. With Na⁺, EtNa was highly active in ～50 % ethanol, whereas in water, it was highly active with Ca²⁺. In this work, we showed that the EtNa DNAzyme was accelerated by freezing in water in the presence of Na⁺. The apparent K_d value reached 6.2 mm Na⁺ under the frozen condition, over 20 times tighter than that in water at room temperature. With 10 mm Na⁺, EtNa had a cleavage rate of 0.12 h^?1 after freezing at ?20 °C. This effect was unique to EtNa, as all other tested DNAzymes were inhibited by freezing except for the Na⁺‐specific NaA43. Freezing also inhibited EtNa if Ca²⁺ was used. We attributed this to the concentrations of EtNa and Na⁺ in the micropockets between ice crystals, but divalent metals might misfold DNA. Overall, we have systematically studied the effect of freezing on the RNA‐cleavage activity of DNAzymes. The DNAzyme sequence and the metal ion species are both crucial to determine the effect of freezing.     

Pervaporation separation of water–ethanol mixtures using metal‐ion‐exchanged poly(vinyl alcohol) (PVA)/sulfosuccinic acid (SSA) membranes

Poly(vinyl alcohol)/sulfosuccinic acid (PVA/SSA) membranes in the hydrogen form were converted to monovalent metal ion forms Li⁺, Na⁺, and K⁺. The effect of exchange with metal ions was investigated by measuring the swelling of water–ethanol (10/90) mixtures at 30 °C and by the pervaporative dehydration performance test for aqueous ethanol solutions with various ethanol concentrations at 30, 40, and 50 °C. In addition, electron spectroscopy for chemical analysis (ESCA) analysis was carried out to study the quantity of metal ions in membranes. From the ESCA analysis, the lithium ion quantity in the resulting membranes is greater than that of any other metal ions in question because of the easy diffusion of a smaller metal ion into the membrane matrix. The swelling ratio was in the following order: PVA/SSA‐Li⁺ > PVA/SSA‐Na⁺ > PVA/SSA‐K⁺ membranes. For pervaporation, the PVA/SSA‐Na⁺ membrane showed the lowest flux and highest separation factor for all aqueous ethanol solutions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1867–1873, 2002     

Ion exchange properties and selectivity of PSS in an electrochemically switchable PPy matrix

A composite of polypyrrole (PPy) and polystyrenesulfonate (PSS) exchanges cations and is a promising material for the technical application of water softening. The ion exchange properties of electrochemically prepared PPy(PSS) are studied by investigating the polymer using a electrochemical quartz crystal microbalance (EQCM) and by analysing the solution surrounding the polymer by atomic adsorption spectroscopy (AAS). The exchange of cations by PPy(PSS) is found to be caused by three driving forces: electrochemical oxidation/reduction of PPy; chemical oxidation of PPy by dissolved oxygen; gradients of cation concentration between polymer and solution. The ion selectivity of PPy(PSS) is investigated and ion exchange isotherms for the binary systems Ca²⁺/Na⁺ and Ca²⁺/Mg²⁺ are determined.     

Polarographic studies of cadmium(II) ions binding in aqueous polyelectrolyte solutions

Polarographic behaviour of cadmium(II) ions in aqueous solutions of polyacrylic acid with and without indifferent electrolyte (potassium chloride) has been examined. Data for polyacrylic acid were compared with those for the monomer. The diffusion current of polarographic reduction of cadmium(II) ions in the range 0 ? [KCl] < 0.2 N in the presence of polyelectrolytes depends upon the concentration and degree of polymer neutralization and also upon the nature of cation (Na⁺, K⁺) in the polyacrylate salt.     

Application of jojoba wax bound to polyethylene membranes and hollow fibers in ion‐exchange and pervaporation processes

Chlorosulfonated polyethylene membranes and hollow fibers were reacted with allylic amino jojoba to bind the wax chemically to the polymer. The modified membranes and hollow fibers were then tested in the ion‐exchange and pervaporation processes, respectively. The jojoba‐bound polyethylene membranes were selective in preventing transfer of divalent ions such as Ca²⁺ and Mg²⁺, while monovalent ion such as K⁺ and Na⁺ could penetrate the membranes. The flux of the monovalent ions depended on the amount of jojoba bound to the polymer, which acted as a barrier to the ions (the monovalent ions could be eluted by acid washing). The concentration of ions (in the range of 0.05–1.0 N) in the feed solution had little effect on the flux. Preliminary results of pervaporation of a dioxane/water mixture through hollow fibers made of jojoba‐bound chlorosulfonated polyethylene show separation of the dioxane from the water with a separation factor of 6. This technique can be applied to remove residual organic solvents in the purification of industrial waste water. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 763–768, 2001     

Use of the empirical Hill equation for characterization of the effect of added cations on the viscosity of aqueous solutions of partially hydrolyzed polyacrylamide

Summary An empirical method based on the Hill equation has been developed to characterize the effects of added cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺) on the viscosities of aqueous solutions of partially hydrolyzed polyacryl-amide.     

Superabsorbent polymeric materials IX: Effect of cationic structure on swelling behavior of crosslinked poly(sodium acrylate‐co‐cationic monomers) in aqueous salt solutions

Two series of xerogels based on sodium acrylate (SA), trimethyl methacrylamidopropyl ammonium iodide (TMMAAI), trimethyl methacryloyloxyethyl ammonium iodide (TMMAI), and N,N′‐methylene‐bis‐acrylamide (NMBA) as a crosslinker were prepared by inverse suspension polymerization. The water absorbency and swelling kinetic behavior for these xerogels in water or various saline solutions were investigated. The results showed that the swelling behaviors of these absorbents are related to their chemical structures, their compositions, and the type of external salt solutions. There would be effective improvement in the water absorbency of these two gel series by copolymerizing SA with a small amount of cationic monomer (TMMAAI or TMMAI). The initial absorption rates in deionized water were found to be faster for TM series gels than for TA series gels. The two series of superabsorbents had a tendency to absorb water in dilute nitrate aqueous solutions in the order: Fe³⁺, Ni²⁺, Ca²⁺, Cu²⁺, and Na⁺ for Fe(NO₃)₃, Ni(NO₃)₂, Ca(NO₃)₂, Cu(NO₃)₂, and NaNO₃ aqueous solution, respectively. The absorbency and initial absorption rate for these gels were related to the gel compositions and salt concentrations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1827–1837, 2001     

Composite cation exchangers

Sulfonated phenol formaldehyde resins containing different amounts of sulfonated sawdust were prepared. The thermal and chemical stabilities, scientific weight capacity, and apparent capacities for the exchange of Na⁺, Ca²⁺, and Mg²⁺ at different concentrations were detemined for both H⁺ and Na⁺ forms of resins. Composites containing up to 30%–50% of sawdust, while being very much cheaper, are comparable in their properties to the pure polymeric resin. Thus, cheaper exchangers can be prepared by substituting part of the polymer by sawdust.     

Simultaneous Determination of the Permeability of a Nafion Membrane to Formic Acid and Water

The simultaneous diffusion of formic acid and water through Nafion was measured for four formic acid concentration differentials (1–17.5 M) and for two counter‐ions in the membrane (H⁺ and Ba²⁺). An iterative method based on Fick's law is presented to calculate the volumes and concentrations of the solutions as a function of time. Besides the initial conditions, the input parameters are two diffusion coefficients, one of formic acid and one of water, which were adjusted to fit the experimental data. Once the difference in liquid fraction between the two types of membranes is taken into account, the diffusion coefficient of formic acid through Nafion appears independent of the nature of the counter‐ion and the conductivity of the formic acid solution. The diffusion coefficient of water is 10 times higher than the formic acid diffusion coefficient and is systematically lower in membranes in the Ba²⁺ form than in H⁺ form.     

Viscous and Interfacial Behaviors,and AFM Morphologies of a Tetra-Polymer in Aqueous Solutions for Enhanced Oil Recovery

An acrylamide-based tetra-polymer (PAVO) containing a macro-monomer APEO: allyl-capped octylphenoxy poly(ethylene oxide) and vinyl biphenyl (VP), was measured in 30 g/L NaCl with static light scattering. The result shows that the molecular weight is low and the polymer chains are expanded. The apparent viscosities are much higher in 90 g/L NaCl than in water for PAVO at polymer concentrations higher than 1 g/L, the salt-thickening effects induced by the Na⁺, Ca²⁺, and Mg²⁺ ions are exhibited, and both surface and interfacial tensions are low in water and 90 g/L NaCl. In order to reveal the mechanism giving rise to solution properties for this polymer, the effects of polymer concentration on associating behaviors of the polymer chains in water and in 90 g/L NaCl, were investigated by the ultraviolet spectral analysis using pyrene as a probe. Resistance factor and residual resistance factor are remarkably higher in 120 g/L salt for PAVO than for HPAM. Atomic force microscope (AFM) morphologies of PAVO in water show that the expanded polymer chain bundles are formed at the polymer concentrations of 0.5–1.5 g/L, which demonstrates that the introduction of the APEO macro-monomer together with VP can make the polymer chains expanded.     

Cation Permeability of Voltage-Gated Hair Cell Ca2+ Channels of the Vertebrate Labyrinth

Some hearing, vestibular, and vision disorders are imputable to voltage-gated Ca²⁺ channels of the sensory cells. These channels convey a large Ca²⁺ influx despite extracellular Na⁺ being 70-fold more concentrated than Ca²⁺; such high selectivity is lost in low Ca²⁺, and Na⁺ can permeate. Since the permeation properties and molecular identity of sensory Ca²⁺ channels are debated, in this paper, we examine the Na⁺ current flowing through the L- and R-type Ca²⁺ channels of labyrinth hair cells. Ion currents and cytosolic free Ca²⁺ concentrations were simultaneously monitored in whole-cell recording synchronous to fast fluorescence imaging. L-type and R-type channels were present with different densities at selected sites. In 10 nM Ca²⁺, the activation and deactivation time constants of the L-type Na⁺ current were accelerated and its maximal amplitude increased by 6-fold compared to physiological Ca²⁺. The deactivation of the R-type Na⁺ current was not accelerated, and its current amplitude increased by 2.3-fold in low Ca²⁺; moreover, it was partially blocked by nifedipine in a voltage- and time-dependent manner. In conclusion, L channel gating is affected by the ion species permeating the channel, and its selectivity filter binds Ca²⁺ more strongly than that of R channel; furthermore, external Ca²⁺ prevents nifedipine from perturbing the R selectivity filter.     

The thermodynamic properties of sodium and potassium dissolved in their molten chlorides,bromides, and iodides

The saturated vapour pressures are measured as a function of temperature and alkali metal concentration for the liquid solutions Na + NaCl, Na + NaBr, Na + NaI, K + KCl, K + KBr, and K + KI. The sodium and potassium partial pressures are determined. The expressions for their temperature dependence are obtained. Vaporization heats, activity coefficient, partial excess enthalpies and entropies are calculated from the experimental data for sodium and potassium in these solutions. Equations are derived for the redox potential as a function of temperature and the alkali metal concentration in the melts. The cathodic polarization of an iron electrode in molten NaCl, KCl, and NaBr is investigated. The steady-state alkali metal concentration in the cathode layer of the electrolyte is shown to be linear in the current density, varying from ～ 300 to 10⁴ A m^?2. The effective alkali metal diffusion coefficients estimated from the linear relation are much greater than the diffusion coefficients of the cations Na⁺ and K⁺ in the same molten salts. The cathode potentials are found to become nearly independent of the current density when it exceeds ～ 10⁴ A m^?2, the steady-state metal concentration in the cathode layer of the electrolyte being still far from saturated.     

Pharmacological Dissection of the Crosstalk between NaV and CaV Channels in GH3b6 Cells

Thanks to the crosstalk between Na⁺ and Ca²⁺ channels, Na⁺ and Ca²⁺ homeostasis interplay in so-called excitable cells enables the generation of action potential in response to electrical stimulation. Here, we investigated the impact of persistent activation of voltage-gated Na⁺ (Na_V) channels by neurotoxins, such as veratridine (VTD), on intracellular Ca²⁺ concentration ([Ca²⁺]_i) in a model of excitable cells, the rat pituitary GH3b6 cells, in order to identify the molecular actors involved in Na⁺-Ca²⁺ homeostasis crosstalk. By combining RT-qPCR, immunoblotting, immunocytochemistry, and patch-clamp techniques, we showed that GH3b6 cells predominantly express the Na_V1.3 channel subtype, which likely endorses their voltage-activated Na⁺ currents. Notably, these Na⁺ currents were blocked by ICA-121431 and activated by the β-scorpion toxin Tf2, two selective Na_V1.3 channel ligands. Using Fura-2, we showed that VTD induced a [Ca²⁺]_i increase. This effect was suppressed by the selective Na_V channel blocker tetrodotoxin, as well by the selective L-type Ca_V channel (LTCC) blocker nifedipine. We also evidenced that crobenetine, a Na_V channel blocker, abolished VTD-induced [Ca²⁺]_i elevation, while it had no effects on LTCC. Altogether, our findings highlight a crosstalk between Na_V and LTCC in GH3b6 cells, providing a new insight into the mode of action of neurotoxins.