Investigation on enhancement of electrical,dielectric and ion transport properties of nanoclay-based blend polymer nanocomposites

Polymer Bulletin - An intercalated blend polymer nanocomposite (PNC) films based on blend (PEO–PVC), LiPF6 as salt and modified montmorillonite (MMMT) as nanoclay are prepared via solution...     

Investigations on nylon 4 membranes: Synthesis and transport properties. II. Transport properties of nylon 4 polymer membranes

The reverse osmosis, ultrafiltration, and dialysis properties of nylon 4 membranes to separations of sodium chloride, urea, a series of ethylene glycols and other compounds in the aqueous phase were investigated. The nylon 4 membranes were prepared from a formic acid solution with and without organic or inorganic additives. The effects of polymer concentration, amount of additives, casting time, and temperature on the membrane performance in terms of salt separation and product rate were investigated. The tensile properties of the nylon 4 membranes in both the dry and wet states were determined. It was found that the highest salt separation of a 0.1% sodium chloride solution did not exceed 53.3%. However, these membranes showed some intersting dialysis properties which were comparable to those of commercial cellophane and cellulose acetate membranes.     

Water transport in ion exchange membranes

Water transport across ion exchange membranes has been studied experimentally. Water transference numbers were obtained from streaming potential measurements for cation and anion exchange membranes. At low salt concentration the water transference number reaches a limiting value which for the cation exchange membranes seems to be closely correlated with the cation—water friction in infinite dilute solutions.The observed water transference number for a given anion exchange membrane does not seem to be much dependent on the type of coion even at concentrations where the membrane is no longer perfectly permselective.     

Effects of thermal annealing on the optical properties of Ar ion irradiated ZnS films

Ar-ion-implantation to a dose of 1×10¹⁷ ions/cm² was performed on cubic ZnS thin films with (111) preferred orientation deposited on fused silica glass substrates by vacuum evaporation. After ion implantation, ZnS films were annealed in flowing argon at different temperatures from 400 to 800 °C. The effects of ion implantation and post-thermal annealing on the structural and optical properties of ZnS films were investigated by X-ray diffraction (XRD), photoluminescence (PL) and optical transmittance measurements. XRD reveals that the diffraction peaks recover at ∼500 °C. The optical transmittances show that the bandgap of ZnS films blueshifts when annealed below 500 °C, and redshifts when annealed above 500 °C. PL results show that the intrinsic defect related emissions decrease with increasing annealing temperature from 400 to 500 °C, and increase with increasing annealing temperature from 500 to 800 °C. The observed PL emissions at 414 and 439 nm are attributed to the transitions of Zn_i→V_Zn and V_S→VBM, respectively.     

Enhanced transport properties in polymer electrolyte composite membranes with graphene oxide sheets

Polymer electrolyte membranes have been widely investigated for high performance fuel cells. Here, we report the synthesis of ionic conductive Nafion/graphene oxide (GO) composite membranes for application in direct methanol fuel cells. GOs interact with both the non-polar backbone and the polar ionic clusters of Nafion because of their amphiphilic characteristics attributable to hydrophobic conjugation and hydrophilic functional groups. Accordingly, GO sheets serve to modify the microstructures of two domains of Nafion. In particular, the transport properties of Nafion are favorably manipulated by the incorporation of GO. This modulated the ionic channels of Nafion and decrease methanol crossover while preserving ionic conductivity. Furthermore, strong interfacial interactions due to the insertion of GO nanofillers into the Nafion matrix improve the thermal and mechanical properties of the material. In particular, we exploit Nafion/GO composite membrane as electrolyte material for direct methanol fuel cell (DMFC) in order to resolve current issue of methanol crossover. This composite membrane-based DMFC compared to the Nafion 112-based DMFC remarkably enhanced cell performance, especially in severe operating conditions.     

Lithium ion transport through nonaqueous perfluoroionomeric membranes

The transport properties of lithiated perfluorinated ionomers imbibed with nonaqueous solvents and solvent mixtures were studied. Polymeric ion‐exchange membranes have potential use in the next generation single‐ion secondary lithium polymer batteries, where the lithiated form of the membrane is used as a polymer electrolyte. The novelty of the approach for lithium battery applications lies in the advantage offered by a transference number of unity, no additional salt (e.g., LiPF₆) is needed, and the excellent physical and chemical stability of the fluoropolymers. Ion‐exchange membranes were converted to the Li⁺ salt form and analyzed for total conversion using FT‐IR. Nonaqueous solvents and solvent mixtures were imbibed into the membranes in a glove box, and the uptake was measured over time. A four‐point probe was used to determine the ionic conductivity based on impedance measurements performed over a frequency range of 10 to 35,000 Hz. Conductivities exceeding 10^?4 S/cm with transference numbers of unity were achieved making these ionomeric membranes potentially useful in rechargeable lithium polymer batteries.     

Structural,dielectric and transport properties of samarium-doped cobaltites

Cobaltites have gained considerable importance in the field of material science, due to their valuable dielectric, biological and magnetic properties. This work highlights the importance of samarium (Sm) doping to enhance the structural and dielectric properties of bismuth calcium cobaltite. All samples were synthesized using the co-precipitation technique and were sintered at 750 °C for 2 h. X-Ray Diffraction (XRD) analyses, as well as Fourier-transform infrared spectroscopy, are used to realize the monoclinic structure of all samples. In addition, XRD analysis was used to determine the lattice strains, lattice constant, crystallite size, the volume of a unit cell, and dislocation density. This analysis shows that Sm doping increases the dislocation density and lowers the average crystallite size. The AC conductivity, (σ_ac), dielectric constant (ε), and loss tangent tan (δ) for all samples were measured at various fixed frequencies and in the variable frequency range (100Hz – 3 MHz). The obtained results are also discussed using the non-linear modified Debye function and Jonscher's power law. The composition Bi₂Ca_1.95Sm_0.05CoO₆ proves to be the better dielectric material at 350 °C–600 °C as it achieves a high value for dielectric constant while maintaining the lower dielectric loss than that of other compositions. Bi₂Ca_1.95Sm_0.05CoO₆ acquires a higher value for σ_ac than the previously reported σ_ac values of Ca_2-xY_xCo₂O₅. These qualities make the aforementioned specimen highly preferable for energy applications.     

Gas transport properties of polyaniline membranes

The transport properties of He, H₂, CO₂, O₂, N₂, and CH₄ gases in solvent cast, HCl doped, and undoped polyaniline (PANi) membranes were determined. Measurements were carried out at 40 psi pressure from 19°C to 60°C. An excellent correlation was found between the diffusion coefficients and the molecular diameters of gases. The solubility coefficients of gases were found to correlate with their boiling points or critical temperatures. The sepa-ration factors for CO₂/N₂ and CO₂/CH₄ are dominated by the high solubility of CO₂. These correlations enable us to predict the permeability, diffusion, and solubility coefficients of other gases. After the doping-undoping process, the fluxes of gases with kinetic diameters smaller than 3.5 Å increased but those of larger gases decreased. This results in a higher separation factor for a gas pair involving a small gas molecule and a larger one. © 1996 John Wiley & Sons, Inc.     

Polyorganophosphazene membranes: preparation and transport properties

Polyphenoxyphosphazene, polycumylphenoxyphosphazene, polybutylphenoxyphosphazene and their copolymers were synthesized. Asymmetric and homogeneous membranes for liquid-liquid and gas separations were prepared. The ultrafiltration membranes were characterized by a cut-off higher than 100,000 Daltons. The gas separation membranes, tested with O₂, N₂, CO₂ and CH₄, were characterized by permeabilities similar to the ones of rubbery polymers and selectivities similar to the ones of glassy polymers.     

Modification of transport properties of ion exchange membranes,XIII. Surface-modified cation exchange membranes prepared from polyamines and a copolymer membrane containing p-stryenesulfonyl chloride

A membrane precursor was prepared by the copolymerization of p-styrenesulfonyl chloride and divinylbenzene in the presence of a poly(vinyl chloride) supported cloth. The surface of the membrane was treated with various amines, and then the sulfonyl chloride groups in the internal part of the membrane were hydrolyzed with an aqueous sodium hydroxide solution in organic methanol or acetone solvent. Hydrolysis conditions were examined for the introduction of the sulfonic acid groups. The membrane modified by ethylenediamine exhibited slightly bipolar properties during the electrodialysis of seawater. Surface-modified membranes using tetraethylenepentamine exhibited excellent monovalent cation permselectivity, low membrane electric resistance, and long performance durability during the electrodialysis of seawater.     

The mechanism of liquid transport through swollen polymer membranes

The pressure-driven transport of liquids employed in reverse osmosis has been shown to occur by a solution-diffusion mechanism in highly swollen polymer membranes. A theory based on this mechanism was successfully used earlier to correlate permeation fluxes for such membranes. Positive confirmation of this theory is provided here by direct measurement of the proposed concentration gradient. A study of the temperature dependence of the liquid diffusion coefficient in the polymer membrane has provided additional evidence of a hydrodynamic regime of diffusion in highly swollen membranes. It is also shown that the proposed ceiling flux in reverse osmosis is equal to the pervaporation flux.     

Structural, optical and bioactive properties of calcium borosilicate glasses

Glass of composition 40SiO₂–20B₂O₃–30CaO–10M₂O₃ (M = Al, Cr, Y and La) were prepared by the splat quenching technique to investigate the effect of M₂O₃ on their bioactivity, structural and optical properties. Y₂O₃ and Cr₂O₃ containing glasses formed a crystalline hydroxyapatite (HA) layer after dipping in simulating body fluid (SBF) for 25 days. On the other hand, HA layer could not form in Al₂O₃ and La₂O₃ glasses. However, during soaking in SBF solution, these glasses exhibit higher dissolution rate, lower density and increased optical band gap as compared to unsoaked glasses. Their oxygen molar volume was also higher than for Y₂O₃ and Cr₂O₃ glasses. The change in composition affects the cross-link formation in the glass matrix and finally its durability and bioactivity in SBF. The results show that M₂O₃ plays an important role in controlling chemical durability and bioactivity of the glasses.     

Structural investigation of low energy ion irradiated Al2O3

The present study is undertaken to investigate the ion irradiation impact on the structural properties of α-Al₂O₃ which is one of the potential insulator used for ITER-like reactors. 300 keV Ar⁶⁺ ion beam with varying fluence is used to irradiate Al₂O₃ polycrystalline material in bulk form. Structural damage to α-Al₂O₃ due to ion irradiation is investigated by grazing incidence XRD (GIXRD), micro-RAMAN and photoluminescence spectroscopy. Further, the surface morphology of irradiated and pristine samples is studied using atomic force microscopy. GIXRD data reveal the radiation induced damage at low fluence and structural improvement at higher fluence up to 1 × 10¹⁶ ions/cm². Annealing effect is explained by temperature rise during irradiation and due to partial grain growth of Al₂O₃ at 1 × 10¹⁶ ions/cm². It is important to note that there is no sign of amorphization even at the highest fluence 1 × 10¹⁶ ions/cm² used in this study. The explanation is supported by the Raman characterization results. Detailed peak assessment of photoluminescence spectra is presented. Photoluminescence characterization results are corroborated with XRD results. The present study reveals the radiation hardness of polycrystalline Al₂O₃ material in the low energy ion regime.     

Synthesis and properties of imidazole-grafted hybrid inorganic-organic polymer membranes

Imidazole rings were grafted on alkoxysilane with a simple nucleophilic substitute reaction to form hybrid inorganic-organic polymers with imidazole rings. Proton exchange membranes (PEM) based on these hybrid inorganic-organic polymers and H₃PO₄ exhibit high proton conductivity and high thermal stability in an atmosphere of low relative humidity. The grafted imidazole rings improved the proton conductivity of the membranes in the high temperature range. It is found that the proton conductivities increase with H₃PO₄ content and temperature, reaching 3.2 × 10⁻³ S/cm at 110 °C in a dry atmosphere for a membrane with 1 mole of imidazole ring and 7 moles of H₃PO₄. The proton conductivity increases with relative humidity (RH) as well, reaching 4.3 × 10⁻² S/cm at 110 °C when the RH is increased to about 20%. Thermogravimetric analysis (TGA) indicates that these membranes are thermally stable up to 250 °C in dry air, implying that they have a good potential to be used as the membranes for high-temperature PEM fuel cells.     

聚偏氟乙烯纳米多孔膜结构调控及离子传递特性

在纳微米尺度调控膜孔结构对发展高性能膜分离材料具有重要意义。使用半结晶性高分子材料聚偏氟乙烯（PVDF）,利用非溶剂诱导相分离（NIPS）、蒸汽诱导相分离（VIPS）、溶剂蒸发诱导相分离（EIPS）方法,成功制备了不同形貌的多孔膜。提出了根据聚合物的结晶生长机制调控膜孔结构概念,根据溶剂蒸发时间调控结晶生长。利用SEM和BET对膜孔形貌进行表征,XRD和DSC对结晶进行检测,氢离子（H⁺）和四价钒离子（VO²⁺）以及其他常用离子的扩散系数表征传质特性。在溶剂蒸发诱导结晶的过程中,随着溶剂蒸发时间的延长,膜断面的球晶比例逐渐增加,最后至球晶完全融合,膜孔结构发生了显著变化,且膜的结晶度和结晶形态随之发生变化,离子选择性能随膜孔尺寸减小而逐渐增大。     

Structural,magnetic, and optical properties of nano-sized Ni0.85Se

Nanocrystalline Ni_0.85Se was synthesized by a hydrothermal method. X-ray diffraction analysis by Rietveld method indicated that Ni_0.85Se has a NiAs-type hexagonal structure. Narrow crystallite size distribution with an average area-weighted size of 〈ɛ_F〉 = 8.5 nm is obtained by Warren-Averbach method. Structural analysis revealed deformed Se atoms octahedron with the shortest distance between Se atoms in adjacent planes 〈Se–Se〉_adj smaller than between nearest neighbors in layer plane 〈Se–Se〉_nea, and a rather short interatomic distance between the transition metal atoms 〈Ni–Ni〉. The optical property of Ni_0.85Se was studied by UV-spectroscopy. Magnetic measurement shows a ferromagnetic phase transition for Ni_0.85Se below 14 K.     

Structural and transport properties of polydimethylsiloxane based polyurethane/silica particles mixed matrix membranes for gas separation

Mixed matrix membranes of synthesized polyurethane (PU) based on toluene diisocyanate (TDI), polydimethylsiloxane (PDMS) and polytetramethylene glycol (PTMG) with polyvinyl alcohol based polar silica particles were prepared by solution casting technique. The homogeneity and thermal properties of the prepared PDMS-PU/silica membranes were characterized using scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The SEM micrographs confirmed the distribution of silica particles in the polymer matrix without agglomerations. Gas permeation properties of membranes with different silica contents were studied for pure CO₂, CH₄, O₂, He and N₂ gases. The obtained results indicated the permeability of the condensable and polar CO₂ gas was enhanced whereas permeability of other gases decreased upon increasing the silica content of the mixed matrix membranes. The permeability of CO₂ and its selectivity over N₂ was increased from 68.4 Barrer and 22 in pure PDMS-PU to 96.7 Barrer and 64.4 in the mixed matrix membranes containing 10 wt% of the silica particles.     

Gas transport properties of electrospun polymer nanofibers

Although the basic principles of gas flow through unidirectional fibers have been widely studied and well understood since the 1950s, questions arise when these principles are applied to electrospun polymer nanofibers. Classic theories based on orderly packed coarse fibers are inadequate in accounting for the influences of random fiber distribution and slip flow. In this work, a mechanistic model in terms of fiber volume fraction and fiber radius is presented to determine the through-plane permeability of electrospun nanofiber layers. The fibrous system is subdivided into a series of cells of orthogonal fibers with random volumes. A single factor is proposed to quantify the effect of randomness of fiber distribution on flow behaviors. When the fiber radius is comparable with the mean free path of air molecules, the slip flows in the nanoscale fibrous media are particularly explored. The solutions obtained are successfully validated through comparison with experimental and numerical results. It is demonstrated that the through-plane permeability of electrospun nanofibers is enhanced by the slip effect and randomly distributed fibers are more permeable than ordered structures.     

Structural refinement,optical and microwave dielectric properties of BaZrO3

In this work, barium zirconate (BaZrO₃) ceramics synthesized by solid state reaction method and sintered at 1670 °C for 4 h were characterized by X-ray diffraction (XRD), Rietveld refinement, and Fourier transform infrared (FT-IR) spectroscopy. XRD patterns, Rietveld refinement data and FT-IR spectra which confirmed that BaZrO₃ ceramics have a perovskite-type cubic structure. Optical properties were investigated by ultraviolet–visible (UV–vis) absorption and photoluminescence (PL) measurements. UV–vis absorption spectra suggested an indirect allowed transition with the existence of intermediary energy levels within the band gap. Intense visible green PL emission was observed in BaZrO₃ ceramics upon excitation with a 350 nm wavelength. This behavior is due to a majority of deep defects within the band gap caused by symmetry breaking in octahedral [ZrO₆] clusters in the lattice. The microwave dielectric constant and quality factor were measured using the method proposed by Hakki–Coleman. The dielectric resonator antenna (DRA) was investigated experimentally and numerically using a monopole antenna through an infinite ground plane and Ansoft's high frequency structure simulator software, respectively. The required resonance frequency and bandwidth of DRA were investigated by adjusting the dimension of the same material.     

Morphology and properties of perfluorosulfonic acid polymer/perfluorocarboxylic acid polymer blend membranes

A melt‐extruded method has been used to prepare blend membranes of Perfluorosulfonic Acid Polymer (PFSA) and Perfluorocarboxylic Acid Polymer (PFCA) with different combination ratios. Fourier Transform Infrared (FT‐IR) and X‐ray Diffraction (XRD) analyses have showed that the chemical structure and crystallization behaviour of both polymers remained unchanged in the blend membrane, and the crystallinity has been increased for the blend membrane with a higher weight fraction of PFCA. According to the results obtained from Scanning Electron Microscope (SEM), PFSA and PFCA polymers are well compatible, forming mixed aggregates containing both sulphonyl and carboxyl ions. Surprisingly, a membrane containing a 50:50 ratio of PFSA/PFCA has showed microphase separation, and it possesses the smallest ionic cluster size among all the blend membranes prepared, as illustrated by the Small Angle X‐ Ray Scattering (SAXS) analysis. In addition, when the PFCA content was increased, the ion exchange capacity (IEC) for blend membranes remained the same, while their water uptake and proton conductivity have decreased rapidly. Compared with the PFSA/PFCA two‐layered membrane, this PFSA/blend/PFCA membrane not only maintained respectable electrolysis property, also exhibited significantly higher peel strength, especially after the hydrolization process; plus, it has showed excellent resistance to the peeling damage under the operational conditions of chlor‐alkali electrolytic cells. POLYM. ENG. SCI., 55:180–189, 2015. © 2014 Society of Plastics Engineers