Preparation and properties of electrospun PAN/Fe3O4 magnetic nanofibers

Polyacrylonitrile (PAN)/Fe₃O₄ composite nanofibers were prepared via the electrospinning of the PAN spinning solutions with magnetite Fe₃O₄ nanoparticles. The experimental results showed that the morphology and diameter of the nanofibers strongly depended upon concentrations of PAN and salt additives in the spinning solutions. A suitable PAN concentration and LiCl additives could effectively prevent the occurrence of beads in the electrospinning process and affected the diameters of the electrospun nanofibers. The breaking strength and breaking strain decreased when the magnetite Fe₃O₄ nanoparticles were incorporated. The prepared PAN/Fe₃O₄ nanofibers were superparamagnetic at room temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Superabsorbent polymeric materials. I. Swelling behaviors of crosslinked poly(sodium acrylate-co-hydroxyethyl methacrylate) in aqueous salt solution

A series of crosslinked poly(sodium acrylate-co-hydroxyethyl methacrylate) based on sodium acrylate (SA), 2-hydroxyethyl methacrylate (HEMA), and N,N′-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The resultant crosslinking polymers are xerogellants. This work investigates not only the absorbency or swelling behavior for these xerogellants composed of different ratios of HEMA/SA in water, but also the effects of various salts and pH values on the swelling properties. Experimental results indicate that the absorbency in deionized water decreases with an increase in the HEMA in copolymeric gel, which is related to the degree of expansion of the network and the strength of the hydrophilic group. The absorbency in the chloride salt solutions decreases with an increase in the salt concentration (swelling is 50 times for the IA group chloride salt solutions, but is less than 5 times for the IIA group salt solution), owing to the osmosis of water and ions between the polymeric gel and the external solution. A decrease in the extent of swelling occurs for divalent and trivalent chloride salt solutions. For the salt solutions of the same ionic strength, the swelling amount has the following tendency: LiCl(aq) = NaCl(aq) = KCl(aq), CaCl₂(aq) < SrCl₂(aq) < BaCl₂(aq), and Fe³⁺ > Ca²⁺ > Zn²⁺ > Cu²⁺. These orders are related to the complexing ability between metallic cations and the carboxylate group in the polymeric chains. Finally, the adsorption of ferric ion by these gels is also investigated. © 1996 John Wiley & Sons, Inc.     

Effect of using different precursors on electrospinning of CaCu3Ti4O12

In this study, the rheological behavior of electrospinning solutions containing different copper and calcium salts (Cu(NO₃)₂·3H₂O, CuCl₂, Ca(NO₃)₂·4H₂O and CaCl₂) were investigated. To find out the suitable electrospinning solution for producing the high purity CaCu₃Ti₄O₁₂ nanofibers, solutions containing different copper and calcium salts were prepared and CaCu₃Ti₄O₁₂ fibers with different morphological and size were produced. The results showed that the nature of the metals complexes in the ceramic solutions had an obvious effect on the rheological behavior of the electrospinning solutions. FTIR spectras of the electrospinning solutions demonstrated that the interaction between the metal ions and carbonyl groups in the polyvinylpyrrolidone unit occurred and the polyvinylpyrrolidone chains underwent conformational variations. Intensity of the interaction between the metal ions and polymer chains in chloride salts solutions is more than nitrate salts solutions in order to the viscosities of chloride solutions that are more than nitrate solutions. So, thinner high purity polycrystalline CaCu₃Ti₄O₁₂ nanofibers with diameters ranging <200 nm were successfully synthesized by selecting a novel solution containing copper and calcium nitrates after sintering at 900 °C for 4 h.     

Thermosensitive and ampholytic hydrogels for salt solution

A series of N‐isopropylacrylamide/[[3‐(methacryloylamino)propyl]dimethy(3‐sulfopropyl)ammonium hydroxide] (NIPAAm/MPSA) copolymer hydrogels were prepared with various compositions. Swelling of the hydrogels in water, aqueous NaCl, KCl, CaCl₂, and MgCl₂ solutions was studied. NIPAAm/MPSA hydrogels have a higher degree of swelling in water and salt solutions than that of poly(N‐isopropylacrylamide) (PNIPAAm). Also, NIPAAm/MPSA hydrogels are more salt resistant when deswelling in salt solutions. For <7 mol % MPSA, the formed hydrogels retain both temperature reversibility and high swelling. A higher content of MPSA (>11 mol %) leads to better salt resistance but a decrease in thermosensitivity. The swelling of NIPAAm/MPSA hydrogel in 0.05M NaCl is non‐Fickian. In NaCl and KCl aqueous solutions, the zwitterionic hydrogels do not show obvious antipolyelectrolyte swelling behavior, whereas in divalent salt CaCl₂ and MgCl₂ solutions, the swelling ability of NIPAAm/MPSA hydrogels is enhanced at low salt concentration, then decreases with further increase in salt concentration. The lower critical solution temperatures of NIPAAm/MPSA hydrogels are also affected by concentrated salt solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2032–2037, 2003     

Experimental Study of the Salt Effect in Vapor/Liquid Equilibria Using Headspace Gas Chromatography

The salt effect on vapor/liquid equilibrium for an ethanol/water system was studied at 70 °C using the Headspace Gas Chromatography technique. The azeotropic point of the system was eliminated in the presence of the salts studied. All the salts investigated in this work exhibited a salting out effect which followed the order of NH₄Cl > NaCl > CaCl₂ and which increased with increasing salt concentration. Good agreement with Furter's equation was observed for the experimental data with unsaturated NaCl salt. The salt effect parameter, determined from Furter's equation, was found to be a function of the liquid concentration.     

The effect of physiologically relevant additives on the rheological properties of concentrated Pluronic copolymer gels

The high concentration triblock copolymer poly(ethylene oxide)₉₉-poly(propylene oxide)₆₉-poly(ethylene oxide)₉₉ (Pluronic F127) aqueous solutions with the addition of different components commonly used in physiologically relevant applications were characterized by rheological measurements, differential scanning calorimetry (DSC) and small angle X-ray/neutron scattering. The sol-gel transition temperature, as well as the storage modulus of the F127 solution depend both on the concentration of polymer and of clay. Above the gel transition, the storage modulus of the solutions increased with clay concentration. Yield strain is independent of polymer and clay concentrations. Two different kinds of inorganic salts, sodium chloride (NaCl) and calcium chloride (CaCl₂) were added into the polymer and polymer-clay solutions. The sol-gel transition temperature decreased noticeably, but the storage modulus decreased only a small amount with increasing concentration of inorganic salts. Addition of salts to polymer-clay solutions resulted in precipitation of the clays which decreased the modulus. No effect on the mechanical properties was observed with the addition of common serum proteins. However, addition of 0.5-10% glucose decreased the transition temperature between 3° and 7°, without significantly affecting the modulus. The depression of the transition temperature by glucose was similar to that found with salts and indicated that the mechanism, namely competition for water, may be similar.     

Stability of a boron-doped diamond electrode in molten chloride systems

Stability of a boron-doped diamond as an oxygen evolution electrode material was evaluated at 773 K in molten LiCl–KCl (58.5:41.5 mol%), LiCl–KCl (75:25 mol%), LiCl–CaCl₂ (64:36 mol%), LiCl–NaCl–CaCl₂ (52.3:13.5:34.2 mol%). In molten LiCl–KCl systems, the BDD is stable at 773 K regardless of the concentration of oxide ion and the composition of the melt. In molten LiCl–CaCl₂ and LiCl–NaCl–CaCl₂, the BDD electrode is less stable than in molten LiCl–KCl systems.     

Synthesis and Properties of a Novel Branched Polyether Surfactant

A novel branched polyether surfactant (TPE) was prepared by anion polymerization with different proportions of propylene oxide (PO) and ethylene oxide (EO) using 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane as a core. The structures and average molecular weight (M _n ) of the TPE were characterized by ¹H NMR and GPC. The cloud point was determined by turbidimetry in the presence of inorganic salts. Inorganic salts decreased the cloud point of TPE polyether in the following order: Na₂CO₃ > Na₂SO₄ > NaCl > CaCl₂ > MgCl₂. The effects of inorganic salts (NaCl, MgCl₂, CaCl₂, and NaSCN) and temperature on the surface activity of TPE in aqueous solution were investigated by surface tension measurements. The surface activity parameters and the thermodynamic parameters were calculated from surface tension data. Similar to the effect of increasing temperature, the salting-out inorganic salts such as NaCl, MgCl₂, and CaCl₂ favor the micellization and increase the maximum surface excess concentration, while the salting-in NaSCN has the opposite effect. The influence of NaCl on the morphology of micelles was investigated by TEM. The micellization is entropy-driven at low temperature and enthalpy-driven at higher temperature. The TPE polyether has large surface activity and can be used as a demulsifier to break up crude oil emulsions.     

Reverse osmosis applied to the recovery of water from aqueous salt solutions

A cellulose acetate membrane was applied to the study of reverse osmosis on aqueous solutions of LiCl, NaCl, KCl, CaCl₂, SrCl₂ and BaCl₂. This membrane, 71 microns thick and having an effective diameter of 1 1/2 in. was mounted within a specially constructed cell, made of stainless steel and designed to withstand pressures up to 1500 psi. The cell consisted of two chambers, which were separated by the membrane, and a porous plate supporting it. Solutions of 0·05 N, for all of these salts, were used to establish the osmotic pressure of each solution, the water fluxes through the membrane, and the extent of salt rejection. These variables were also determined for NaCl normalities of 0·2 and 0·6. On a single pass basis, the salt rejections ranged from 76% for KCl up to 95% for CaCl₂. The results are discussed in terms of the size of the hydrated cation. The water fluxes for all these solutions were found to be essentially the same and were independent of the type of salt. For solutions of 0·05 N, the water fluxes ranged from zero at the osmotic pressure up to about 44 × 10^?5 g sec^?1cm^?2 (8·8 gal day^?1ft^?2) at 800 psi and 77°F. Also, for the 0·05 N-NaCl solution, the temperature was varied from 77°F to 120°F. The results of this temperature study show that the extent of salt rejection remains essentially fixed, while the water flux at any given pressure at 120°F becomes nearly double that of 77°F.     

Effects of pH and Neutral Salts on the Adsorption of the Poly(ethylene glycol terephthalate) Condensates Toward Poly(ethylene terephthalate) Fiber

This study deals with the effects of pH and neutral salts on the adsorption of PET fiber with four kinds of poly(ethylene glycol terephthalate) condensated from dimethyl terephthalate (DMT) and poly(ethylene glycol) (PEG). The surface properties of the aqueous solution, the contact angle of polyol‐treated PET fabrics, and its parameters were also discussed. The pH of the solution or the adding of neutral salt in the polyol solution largely affected the contact angle of polyol‐treated PET fabrics as well as the surface tension of the solution. A lower pH of the polyol solution or adding neutral salts in the solution showed a lower surface tension and a lower contact angle that resulted in a better adsorption between polyol and poly(ethylene terephthalate) fibers. The lower pH of the solutions and a higher valence of the added neutral salt in the solution showed a largely positive effect on the adsorption parameters, and the order of effectiveness is Al₂(SO₄)₃ > MgSO₄ > Na₂SO₄.     

Synthesis and swelling behavior of crosslinked copolymers of neutralized maleic anhydride with other monomers

A series of novel copolymer superabsorbents based on maleic anhydride (MLN), acrylamide (AAM), hydroxyethyl methacrylate (HEMA), and N,N′‐methylenebisacrylamide (NMBA) were prepared by inverse‐suspension polymerization. The influence of the reaction parameters on the water absorption was investigated to improve the understanding and to identify the optimum reaction conditions. The water absorbences or swelling behaviors for these absorbents in various salt solutions and various alcohol solutions were studied. The tendency of the absorbency for these absorbents in salt and alcohol solutions is in the order Na⁺ > Ca²⁺ > Al³⁺ for NaCl, CaCl₂, and AlCl₃ aqueous solutions and a glycerol > glycol > methanol > ethanol solution, respectively. This article also explains the IR and SEM characterization of the water‐absorbing copolymers and their practical use in soil for water retention. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2725–2731, 2003     

Rheological characteristics of foamed gel for mine fire control

Foamed gel as a new type of fire extinguishing material is used to prevent the spontaneous combustion of coal. In order to make a comprehensive study on rheological characteristics of foamed gel for mine fire control, by using type NDJ‐5s digital viscometer, the factors such as mass concentration of the mixture mixed by thickener and crosslinker, foaming multiple, added salts (NaCl, CaCl₂, AlCl₃), pH value and temperature having influences on the rheological properties of foamed gel have been investigated in this paper. It can be found that foamed gel shows the characteristic of non‐Newtonian fluids and has shear‐thinning properties. With increasing of mass concentration of the mixture, the thixotropy response becomes more significant. When the foaming multiple reaches 20, the apparent viscosity gets the maximum value. The obvious viscosity characteristic of ‘polyelectrolyte solution’ is observed in aqueous salt solutions when added salts are put into the solution. Under different conditions of pH values, foamed gel has higher sensitivity to acid than alkaline. Zero shear viscosity, depending on temperature, decreases with the temperature increasing. Meanwhile, the fire performances of foamed gel are studied experimentally and theoretically. Copyright © 2014 John Wiley & Sons, Ltd.     

Spider-net within the N6, PVA and PU electrospun nanofiber mats using salt addition: Novel strategy in the electrospinning process

Electrospun nanofibers are promising candidates in the nanotechnological applications due to the advantages of the nanofibrous morphology. Therefore, many attempts were reported to modify the electrospun mats to gain more beneficial properties. In the present study, we are introducing a strategy to synthesize electrospun polymeric nanofiber mats containing spider-net binding the main nanofibers. Addition with long stirring time of a metallic salt having tendency to ionize rather than formation of sol–gel in the host polymer solution reveals to synthesize a spider-net within the electrospun nanofibers of the utilized polymer. Nylon6, polyurethane and poly(vinyl alcohol) have been utilized; NaCl, KBr, CaCl₂ and H₂PtCl₆ have been added to the polymeric solutions. In the case of nylon6 and poly(vinyl alcohol), addition of the inorganic salts resulted in the formation of multi-layers spider-network within the electrospun nanofibers mats. The synthesized spider-nets were almost independent on the nature of the salt; the optimum salt concentration was 1.5 wt%. The metallic acid led to form trivial spider-nets within both of nylon6 and poly(vinyl alcohol) nanofibers. In a case of polyurethane, few spider-nets were formed after salt addition due to the low polarity of the utilized solvents. According to TEM analysis, the synthesized spider-net consisted of joints; the later issued from the main nanofibers at Taylor's cone zone. The spider-net improved the mechanical properties and the wetability of the nylon6 nanofiber mats, accordingly a mat having amphiphilic feature has been prepared.     

A novel thermosensitive polymer, poly(methyl 2-propionamidoacrylate), with geminal substituents

A novel thermosensitive polymer, poly(methyl 2-propionamidoacrylate) (PMPA), was prepared and the phase transition behavior in an aqueous solution was studied. PMPA have geminal substituents of propionamide and methoxy carbonyl in each monomer unit. It was found that PMPA shows the lower critical solution temperature (LCST) at 50.6 °C sharply. The LCST of PMPA was almost independent of the polymer concentration above 40 g/l, while, below 40 g/l, it decreased with the increasing polymer concentration. The effect of salt addition (NaCl, NaBr, and Na₂SO₄) on the LCST was also studied. The LCST of PMPA linearly decreased with the increasing concentration of each salt. The salting-out effect of these salts was in line with the Hofmeister series: Na₂SO₄>NaCl>NaBr.     

Electrospun polyacrylonitrile nanocomposite fibers reinforced with Fe3O4 nanoparticles: Fabrication and property analysis

The manufacturing of pure polyacrylonitrile (PAN) fibers and magnetic PAN/Fe₃O₄ nanocomposite fibers is explored by an electrospinning process. A uniform, bead-free fiber production process is developed by optimizing electrospinning conditions: polymer concentration, applied electric voltage, feedrate, and distance between needle tip to collector. The experiments demonstrate that slight changes in operating parameters may result in significant variations in the fiber morphology. The fiber formation mechanism for both pure PAN and the Fe₃O₄ nanoparticles suspended in PAN solutions is explained from the rheologial behavior of the solution. The nanocomposite fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectrophotometer, and X-ray diffraction (XRD). FT-IR and XRD results indicate that the introduction of Fe₃O₄ nanoparticles into the polymer matrix has a significant effect on the crystallinity of PAN and a strong interaction between PAN and Fe₃O₄ nanoparticles. The magnetic properties of the nanoparticles in the polymer nanocomposite fibers are different from those of the dried as-received nanoparticles.     

Synthesis,characterization, and swelling behavior of superabsorbent hydrogel from sodium salt of partially carboxymethylated tamarind kernel powder‐g‐PAN

Polyacrylonitrile (PAN)‐grafted sodium salt of partially carboxymethylated tamarind kernel powder (Na‐PCMTKP‐g‐PAN, %G = 413.76 and %GE = 96.48) was prepared using the established optimal reaction conditions for ceric‐initiated graft copolymerization of acrylonitrile onto Na‐PCMTKP (DS = 0.15) in a homogeneous medium. The graft copolymer was hydrolyzed by 0.7N KOH solution at 90–95°C to yield the superabsorbent hydrogel H‐Na‐PCMTKP‐g‐PAN. The nitrile groups of Na‐PCMTKP‐g‐PAN were completely converted into a mixture of hydrophilic carboxamide and carboxylate groups during alkaline hydrolysis, followed by in situ crosslinking of the grafted PAN chains. The products were characterized spectroscopically and morphologically. The swelling behavior of the unreported superabsorbent hydrogel, H‐Na‐PCMTKP‐g‐PAN, was studied by carrying out its absorbency measurements in low‐conductivity water, 0.15M salt (NaCl, CaCl₂, and AlCl₃) solutions, and simulated urine (SU) at different timings. The swelling behavior of the hydrogel in different swelling media followed the second‐order kinetics. The values of the various swelling characteristics were reported. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Behavior of gas bubbles in aqueous electrolyte solutions

A system was investigated in which a swarm of air bubbles was dispersed in aqueous electrolyte solutions. the salts used were: NaCl, NaBr, NaI, Na₂SO₄, Na₃PO₄ LiCl, MgCl₂, MgSO₄, CaCl₂, AlCl₃ and Al₂(SO₄₃. The effects of the salts on the interfacial area of dispersion and on the oxygen transfer coefficient were investigated at various salt concentrations. The results showed a definite dependence of the surface area of dispersion on the valence of the ionic species and salt concentrations. A very satisfactory correlation was obtained for all the salts with the use of ionic strength as the correlating parameter. The mechanism of the coalescence-preventing action of the salts was discussed and explained on the basis of ion—water interactions. The oxygen mass transfer coefficient was found to be only slightly dependent on the presence of electrolytes in the range of concentrations used in this work. The importance and possible practical application of the results were briefly discussed.     

Lyotropic liquid crystalline solutions of hydroxypropyl cellulose in water: Effect of salts on the turbidity and viscometric behavior

Effect of addition of salt on the viscometric behavior of the dilute or concentrated aqueous solution of hydroxypropyl cellulose (HPC) was determined by means of an Ubbelohde or a cone-plate viscometer. That effect on the turbidity of the dilute system was also determined. As salts, NaCl, LiCl, and thiourea were chosen. The turbidity and viscometric behavior for the dilute system, and the viscometric behavior for the concentrated system were greatly affected by salt type and concentration. With increasing NaCl or LiCl concentration, the cloud point decreased, [η] showed a maximum, Huggins' constant k′ showed a minimum, and the shear viscosity for concentrated isotropic solutions showed a maximum. The 45 wt % solution with no salt showed a viscometric behavior which was characteristic of lyotropic liquid crystals; however, with increasing NaCl concentration, a critical temperature at which the shear viscosity showed a maximum with respect to temperature shifted to lower temperature. This behavior was due to an increase in the turbidity, not due to a phase transformation. On the other hand, an addition of thiourea did not affect so greatly the turbidity and viscometric behavior as an addition of NaCl or LiCl did. We speculated different actions of NaCl and thiourea.     

Thermal Behavior of Nitrocellulose with Inorganic Salts and their Mechanistic Action

In this study, we investigated the effects of inorganic salts on the stability of NC and its reaction mechanism. Under isothermal conditions at 120 °C in an O₂ atmosphere, the induction time period for NC heat release was prolonged in the presence of Li₂CO₃, Na₂CO₃, CaCO₃, Mg(OH)₂, Ca(OH)₂, and MgO, all of which produce alkaline saturated solutions with a pH value of 10–12. In addition, the induction time period depended on this pH value. This suggests that these salts stabilized NC by neutralizing acids that would otherwise accelerate the hydrolysis of the O‐NO₂ bond. However, Sr(OH)₂ ⋅ 8H₂O and K₂CO₃, which produce strongly alkaline saturated solutions with pH>13, decreased the induction time period. It is possible that these strong bases caused alkaline decomposition of NC. In addition, for Sr(OH)₂ ⋅ 8H₂O, the released water of crystallization appeared to be related to NC destabilization. SrCO₃, NaHCO₃, K₂SO₄, CaSO₄, ZnSO₄, NaCl, CaCl₂, AgCl, and NaNO₂, which produce near‐neutral saturated solutions, slightly decreased the NC induction time period. The NC induction time period with these salts depended upon the solubility of the added salt. This may indicate that in the presence of these inorganic salts, the boiling point of water is increased, which reduces the vaporization of water from NC and thus accelerates the hydrolysis of NC.     

Increasing viscosity in entangled polyelectrolyte solutions by the addition of salt

The viscosity of several polyelectrolytes is measured in both salt free solutions and solutions in the high salt limit. At low polymer concentrations, the zero shear rate viscosity decreases as much as 100-fold upon addition of a monovalent salt, namely NaCl. However, as polymer concentration increases, the viscosity difference between polymer in salt free and in monovalent salt solution diminishes. Further, the zero shear rate viscosity becomes independent of added monovalent salt at the critical polyelectrolyte concentration c_D. Above c_D, the addition of monovalent salt increases the zero shear rate viscosity of the entangled polyelectrolyte solutions. The viscosity increase agrees with viscosity scaling theory for polyelectrolytes in the entangled regime. Polyelectrolytes exhibiting an increase in viscosity above c_D in the presence of monovalent salt include three natural anionic polyelectrolytes (xanthan, carrageenan, welan), one synthetic anionic polyelectrolyte (hydrolyzed polyacrylamide), and one natural cationic polyelectrolyte (chitosan). Generally, these polyelectrolytes are relatively high molecular weight (>1 M Dalton), which makes c_D experimentally accessible (e.g., c_D = 0.2 wt% for xanthan). The magnitude of the viscosity increase is as high as 300% for xanthan and nearly independent of monovalent salt concentration in the high salt limit. The increase in viscosity in monovalent salt solution and magnitude of c_D appear to be heavily influenced by the molecular characteristics of the polymers such as monomer weight, molecular structure, and chain conformation.