Preparation of self-standing polyaniline-based membranes: Doping effect on the selective ion separation and reverse osmosis properties

The selective ion transport of aqueous salt solutions including mono-, di-, trivalent cations across both doped and undoped polyaniline (PAni) membranes was described. PAni-based asymmetric membranes were prepared by the phase inversion method from the casting solution containing N-methyl pyrrolidone. It was found that the permeation rates (PR) decline in the sequence of P-R(NaCl) > P-R(MgCl2) > P-R(LaCl3). HCl-cloped PAni membrane exhibited higher permeation rates for the salts than undoped one due to its more hydrophilic nature. In reverse osmosis (RO) applications, it was observed no water permeation through undoped PAni due to less permeable and hydrophobic nature, under even at 40 bar pressure. Concerning HCl-doped PAni, this membrane showed very low water flux (J(w)) and it was found as 1.01 L m(-2) h(-1) under 40 bar pressure. On the other hand, the J increased linearly with the applied pressure. Furthermore, typical separation factor (a)values calculated from permeation rate ratios were found to be as 6.3 and 39 for Na+/Mg2+ and Na+/La3+ for HCl-doped PAni, respectively. Especially, HCl-doped PAni membrane can be used for removing rare-earth metal salts due to its high separation efficiency in high temperature applications. (C) 2007 Wiley Periodicals, Inc

Conducting composites of polyurethane resin and polypyrrole: Solvent-free preparation, electrical, and mechanical properties

Three methods were used for solvent-free preparation of conducting composites of PUR and PPy. In all cases, PUR was prepared from TDI and hydroxyl 15-W as polyol cross-linker, whereas PPy was obtained upon oxidative coupling of Py using ferric chloride as oxidant. In method 1, PPy powder was dispersed in hydroxyl. After addition of TDI the mixture was cured to yield the final product. In method 2, ferric chloride and Py were dissolved in hydroxyl and a PPy dispersion was obtained. The TDI was added and the final product was obtained upon curing. In method 3, Py was dissolved in TDI and ferric chloride dissolved in hydroxyl. Then the two solutions were mixed and cured resulting in the simultaneous formation of PPy and PUR. Method 1 led to composites with a specific electrical conductivity sigma of 10(-10) S (.) cm(-1) and a Shore A hardness of 40 to 55. Using methods 2 and 3, composites with sigma values of 10(-7) S (.) cm(-1) and a hardness of 30 to 40 were obtained. Presence of moisture increased the sigma values and decreased the hardness. Due to the solvent-free preparation, the maximum PPy content of the samples was limited to 10 wt.-%. The studies also demonstrated that the conductivity was mainly dependant on the amount of ferric chloride present in the sample and not on the PPy content, suggesting that the conductivity was ionic

Preparation, characterization and dielectric properties of polycyanurate films cyclotrimerized in the presence of different catalysts

The article deals with the preparation and characterization of a series of functional polycyanurate (PCN) films obtained from bisphenol E dicyanate (BDECy) by thermal cyclotrimerization in the presence of four different catalysts. Thermal, structural, and dielectrical analyses of PCN films are performed as well as some physical properties such as solubility, adhesion, hardness, and contact angle measurements are studied. Fourier transform infrared spectroscopy results reveal that cyclotrimerized structure is formed from BDECy not only in the presence of catalyst but also free of catalyst. While 55.5% of BDECy is cylotrimerized without catalyst, the conversion of BDECy into triazine significantly increases and reaches to 82.1% and 84.8% for PCNPh1-2 and PCNPh3-2, respectively. Thermogravimetric analysis results reveal that PCN films prepared in the presence of catalyst are thermally stable up to 240 degrees C and exhibit two degradation steps. Dielectric constant and dielectrical breakdown strength of the PCN film cyclotrimerized with 1 wt% phenol as catalyst are found to be 3.16 at 1 MHz and 194 kV/mm, respectively, while the catalyst-free PCN film has the dielectric constant of 4.92 at the same frequency. On the other hand, chemical stability, hardness, and adhesion properties of the prepared films are found to be excellent. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers

Removal of Indigo Carmine and Pb(II) Ion from Aqueous Solution by Polyaniline

In this work, we report the synthesis of polyaniline emaraldine salt (PAni-ES) by a chemical oxidative polymerization method. The obtained PAni-ES samples prepared under different conditions were used for the removal of indigo carmine anionic dye and Pb(II) ion from aqueous solutions. The results also showed that the pseudo-second-order kinetic model fitted better than the data obtained from pseudo-first-order model for the adsorption of anionic dye and Pb(II) ion onto PAni-ES. The fit of the data for indigo carmine and Pb(II) ion adsorption onto PAni-ES suggested that the Langmuir model gave closer fittings than Freundlich model

Triethylene Glycol Stabilized CoFe2O4 Nanoparticles

We report on the synthesis and detailed composition, thermal, micro-structural, ac-dc conductivity performance and dielectric permittivity characterization of triethylene glycol (TREG) stabilized CoFe2O4 nanoparticles synthesized by polyol method. XRD analysis confirmed the inorganic phase as CoFe2O4 with high phase purity. Microstructure analysis with TEM revealed well separated, spherical nanoparticles in the order of 6 nm, which is also confirmed by X-ray line profile fitting. FT-IR analysis confirms that TREG is successfully coated on the surface of nanoparticles. Overall conductivity of nanocomposite is approximately two magnitudes lower than that of TREG with increase in temperature. The ac conductivity showed a temperature dependent behavior at low frequencies and temperature independent behavior at high frequencies which is an indication of ionic conductivity. The dc conductivity of the nanocomposites and pure TREG are found to obey the Arrhenius plot with dc activation energies of 0.258 eV and 0.132 eV, respectively. Analysis of dielectric permittivity functions suggests that ionic and polymer segmental motions are strongly coupled in the nanocomposite. TREG stabilized CoFe2O4 nanoparticles has lower epsilon' and epsilon '' than that of pure TREG due to the doping of cobalt. As the temperature increases, the frequency at which (epsilon '') reaches a maximum shifted towards higher frequencies. On the other hand, the activation energy of TREG for relaxation process was found to be 0.952 eV which indicates the predominance of electronic conduction due to the chemical nature of TREG. Contrarily, no maximum peak of tan delta was observed for the nanocomposite due to the being out of temperature and frequency range applied in the study

Influence of epoxy addition on the thermal, mechanical, and dielectrical properties of polycyanurate films

In the study, polycyanurate (PCN)/epoxy resin (ER) blends are prepared to enhance the physical properties of cyanate ester resins. The effects of curing schedule and blend composition on their thermal, mechanical, and dielectrical properties of cured PCN/epoxy blend films are examined. FTIR analysis of the cured blend films exhibits the expected cyanurate and oxazolidinone peaks in all blend compositions except the film thermally treated for 1 h in the presence of 1% phenol. TGA results show that the thermal stability decreases with epoxy content in the blend film. From SEM analyses, it is observed that all films have very dense, smooth, and bubble free surface without phase separation. For the pure PCN, the dielectric constants are found to be 3.54-5.91 in the range of 10(-1)-10(7) Hz between 20 degrees C and 200 degrees C. PCN/epoxy blends up to 50% epoxy resin show a good stability of dielectric constant in this frequency band for 200 degrees C, which is close to the dielectric constant of the homopolymerized PCN. Beyond this percentage of epoxy resin, dielectric constants of PCN/epoxy blends greatly increase at low-frequency region (0.1-10(3) Hz) due to the interfacial polarization governed by Maxwell-Wagner-Sillars effect. POLYM. ENG. SCI., 58:820-829, 2018. (c) 2017 Society of Plastics Engineer

ROMP-based boron nitride composites

The present work focuses on the investigation of the thermal and dielectric properties of composites obtained by surface-modified hexagonal boron nitride (hBN) and ring-opening metathesis polymerization (ROMP) based polymer. A new kind of high performance composites was developed based on using amino silane functionalized hBN (AS-hBN) and bromine functional group possessing homo and copolymers synthesized via ROMP pathway. Aminosilane capped boron nitride (BN) and bromine bearing polymer backbone enhance the interaction between filler and the polymer chains. The effects of surface-modified BN (AS-hBN) and its content on the dielectric properties, and thermal resistance of composites, are systematically investigated and discussed. The resultant composites possess high electrical break over voltages. While all of the ROMP-based films exhibit low value in a wide frequency range, in the case of the composite with 20% AS-hBN and poly(bromooxanorbornene-co-cyclooctadiene) (ROMP-BN-6) displays very low dielectric constants in around 1.5 up to 1 MHz at 20 degrees C. This value is significantly lower than that of common polymer dielectrics, which is usually in the range of 3-6. Besides the lowest dielectric constant of ROMP-BN-6, it has also the smallest dielectric loss tangent even at high temperatures. Tan of ROMP-BN-6 is 0.003 and 0.0067 at 10 Hz-1 MHz at 20 degrees C, respectively. Thermal stability of polymers was also improved by introducing surface-modified hBN. Polymers bearing 20% AS-hBN are highly thermally stable up to similar to 350 degrees C and gave 25% char yield at 800 degrees C. (C) 2017 Wiley Periodicals, Inc

Structural and dielectrical characterization of low-k polyurethane composite films with silica aerogel

In this study, a hydrophobic silica aerogel was synthesized via one-step surface modification and polymer composite films based on a polyurethane (PU) matrix were prepared by doping with silica aerogel powder (at 2%, 3%, 5%, and 7% by weight = w/w%). The structural, thermal, morphological, and surface properties of the silica aerogel and PU composite films containing aerogel were investigated by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), scanning electron microscopy, and tensiometry. The dielectric properties of the silica aerogel and PU composite films containing the aerogel were determined over a temperature range of 293-423 K and a frequency range of 1-10(6) Hz. The contact angle of the silica aerogel was 10(6). Moreover, the PU composite film with 7% aerogel had the highest contact angle (theta = 105 degrees) among the composite samples, which was similar to contact angle of the silica aerogel. The dielectric constants and dielectric losses decreased with the frequency for all of the samples, whereas they increased with the temperature. The polarization regions and relaxation times were determined for all of the samples using the Cole Cole equation. The glass-transition temperatures (T-g) were determined for the silica aerogel and PU composite films containing aerogel by dielectric spectroscopy and compared with the DSC results. The dielectric constants were lower for the PU composite films than the PU film. The dielectric constant for the PU composite film doped with 2% silica aerogel was 2.9 at 10 MHz. Thus, the PU composite with a low dielectric constant and dielectric loss factor (tan delta) could be regarded as a potential dielectric constant candidate, with possible applications as a dielectric material in the microelectronics industry

Synthesis and characterization of anhydrous conducting polyimide/ionic liquid complex membranes via a new route for high-temperature fuel cells

The paper deals with the synthesis and characterization of a new series of anhydrous conducting acid-doped complex membranes based on polyimide (PI) and ionic liquid (IL) for high-temperature fuel cells via a new route. For this purpose, three imidazolium-based ILs (RIm+BF4-) with different alkyl chain lengths (R=methyl, ethyl, and butyl) are added into polyamic acid (PAA) intermediate prepared from the reaction of benzophenonetetracarboxylic dianhydride and diaminodiphenylsulfone in different COOH/imidazolium molar ratios (n?=?0.5, 1, and 2). Then, the thermally imidized complex membrane was doped with H2SO4. The conductivities of acid-doped PI/IL complex membranes prepared by taking n of 1 are found to be in the range of 10-4-10-5?S?cm-1 at 180 degrees C, whereas the acid-free PI/IL complex membranes show the conductivity at around 10-9-10-10?S?cm-1. Thermogravimetric analysis results reveal that the acid-doped PI/IL complex membranes are thermally stable up to 250 degrees C. Dynamic mechanical analysis results of the acid-doped ionically interacted complex membrane show that the mechanical strengths of the PI/IL complex membranes including 1-methyl imidazolium tetrafluoroborate (MeIm-BF4) and 1-ethyl 3-methyl imidazolium tetrafluoroborate (EtIm-BF4) are comparable with those of pristine PI until 200 degrees C. Furthermore, it can be clearly emphasized that the ionic interaction between carboxylic acid groups of PAA's and IL's cations offers a positive role in long-term conductivity stability by preventing the IL migration at high temperatures. On the other hand, preliminary methanol permeability tests of the acid-doped membranes show that they can also be considered as an alternative for direct methanol fuel cells. Copyright (c) 2011 John Wiley & Sons, Ltd