Search

Loading and release behavior of a cationic dye, namely, safranine-T, through layer-by-layer (LbL) multilayered films of poly(diallyldimethylammonium chloride) (PDADMAC) and single/blend anionic polyelectrolytes (PEs), namely, poly(acrylic acid) (PAA), and poly(styrenesulfonate) (PSS), are described. The growths of PDADMAC/PSS-PAA multilayers and their safranine-T sorption behavior are monitored using the UV-Vis technique and discussed in terms of blend composition of anionic PEs and pH as well as their hydrophilicity and topography. The dye loading and desorption properties of the LbL films prepared from single/blend negatively charged PEs mainly depend on the interactions of PEs and safranine T. Strong interactions between PSS and safranine T result in a higher dye entrapping inside LbL films whereas either PAA-rich or single PAA-based LbL film exhibits larger dye desorption. A higher PSS content in the feed blend composition leads to an observable increase in theta(ave) and surface roughness whereas the use of PAA can yield a flatter surface due to its partially recomposed chain conformational structure at pH 11. Consequently, LbL multilayers obtained from single and blend polyanions can be considered as an encouraging material platform for the controlled release of charged species such as protein, drug, and dye. because of their tunable physicochemical and morphological properties as well as surface wettability.

Deligoz, Huseyin/0000-0002-0915-2911; Cengiz, Hacer Yesim/0000-0001-6684-7771 WOS:000560919000020 This study deals with selective separation of mono- and divalent cations from aqueous salt solutions using polymeric films based on polyethylene (PE) and polyamide6 (PA6), and two different commercial nanofiltration (NF) membranes. The diffusion rates (D) of ions (Na+ and Ca2+) , separation factors (alpha) and ion rejections (R) of the films and NF membranes are examined comparatively as well as their surface morphology and hydrophilicity. It is observed that the diffusion rates of Na+ are in the range of 0.7-1.8 x 10(-8) cm(2).s(-1) in the decreasing order of PE > NF90 > NF270 > PA6 while Ca2+ shows diffusion rates of 7.4-18.4 x 10(-8) cm(2).s(-1) in the increasing order of NF270 > NF90 approximate to PA6 > PE. Rejection values of the polymeric films and NF membranes against to Na+ and Ca2+ vary between 90% and 99.6%.The highest alpha (Ca2+/Na+) is found to be 20 for PA6 film D, alpha, and R value of both polymeric films and NF membranes are strongly affected by the existence of osmosis during diffusion-dialysis and the sizes of hydrated sodium and calcium ions. In conclusion, the film based on PA6 may be a good alternative for selective separation of mono- and divalent cations.

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 1–106 Hz. The contact angle of the silica aerogel was 106°. Moreover, the PU composite film with 7% aerogel had the highest contact angle (θ = 105°) 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 (Tg) 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 (tanδ) could be regarded as a potential dielectric constant candidate, with possible applications as a dielectric material in the microelectronics industry.

Gıda ve içecek sektöründe “sürdürülebilir üretim” ve “sıfır atık yaklaşımı” için geleneksel ayırma, saflaştırma ve derişiklendirme yöntemlerine alternatif olarak membran süreçlerinin uygulanması oldukça popüler ve gelişmekte olan bir konudur. Gıda ve içecek sektöründe uygulama çeşitliliğine bağlı olarak uygun membran süreçlerinin kullanımının yaygınlaşmasının başlıca sebepleri; (i) geleneksel yöntemlere göre işlem basamaklarını azaltarak süreci kısaltması, (ii) geleneksel yöntemde uygulanan yüksek sıcaklığa bağlı olarak gıda ve içeceklerin içerdikleri besin ve aroma bileşenlerindeki değişikliklerin minimize edilerek son ürün kalitesini arttırması, (iii) yüksek ayırma seçimliliği ve verimi, (iv) gıda içerisinde yer alan yararlı bileşenlerin zarar görmesini engelleyecek optimum koşullarda çalışma imkânı sunarak gıda güvenliğini sağlayan daha sağlıklı ve çevreci bir sistem olmasıdır. Basınç destekli mikrofiltrasyon (MF), ultrafiltrasyon (UF), nanofiltrasyon (NF) ve Ters Ozmoz (TO) membran süreçleri, geniş bir parçacık aralığında bileşenlerin etkin biçimde ayrılmasına ve dolayısıyla membran uygulamalarının gıda ve içecek sektöründe geniş bir uygulama alanı bulmasına imkan tanımaktadır. Ayrıca membran süreçleri geleneksel yöntemlere göre enerji tüketimi açısından daha ekonomiktirler. Bu derleme makalede, gıda ve içecek sektöründe yer alan alkolsüz (süt, meyve suyu, kahve vb.) ve alkollü (şarap ve bira) içeceklerde membran teknolojilerinin geleneksel yöntemlere göre sağladığı avantajlar, membran teknolojilerinin temel ilkeleri, kullanılan membran tipleri ve uygulama alanları ile endüstriyel ölçekte gerçek uygulama örnekleri hakkında detaylı bilgilere ve bu konuda yapılan çalışmalara yer verilmiştir.

Preparation and characterization of a series of polyurea (PU) coatings and their influences on layered composite materials based on rebonded polyurethane (PUr) for floor application are described in terms of the raw materials, formulation, and application performance. While PU coatings show almost the same FTIR peaks, thermogravimetric analyses results reveal that thermal stabilities of the PU coatings are slightly enhanced with the use of trifunctional polyamine compound and one step degradation takes place beyond 300 degrees C. All PU coatings have very dense, smooth, and bubble-free surfaces whereas the cross-sectional SEM images exhibit pores of different sizes. Contact angle values of all PU coatings are bigger than 90 degrees indicating that the surfaces are hydrophobic. Using propylene carbonate in the preparation of methylene diphenyl diisocyanate (MDI) prepolymer and the chain extender in the PU coating formulation impacts the mechanical and electrical properties of the PU coatings as well as layered PU/PUr composite materials. In conclusion, not only the controllable physicochemical and mechanical properties of layered PUr/PU composites but also the usage potential of recycled PU scraps in these layered composites are very promising for better floor applications.

The objective of the study is to investigate the electrochromic performances of layer-by-layer (LbL) multilayered thin film electrode prepared from linear polyethylene imine (LPEI) and poly(3,4-ethylenediox-ythiophene):polystyrene sulfonate (PEDOT:PSS) on PET-ITO substrate in the presence of different types of electrolytes. For this purpose, the electrochromic behaviors of (LPEI/PEDOT:PSS) 10 is performed in LiClO4/propylene carbonate (PC) and two different ionic liquids (IL) namely N-methylimidazolium tetrafluoroborate (Melm-BF4) and 2-hydroxy ethyl ammonium formate (2-HEAF), as a function of IL content and scanning rate. The optical contrast value of (LPEI/PEDOT:PSS) 10 film is determined as 58.4% in the existence of 10 wt% of 2-HEAF as the electrolyte. The coloration efficiency of this film is determined as 606.7 cm(2)/C, which this value was greater approximately four times than 1 M LiClO4/PC. According to the obtained results, 2-HEAF has been evaluated as a suitable electrolyte alternative for (LPEI/PEDOT:PSS) 10 film due to its better optical contrast and coloration efficiency compared to other electrolytes. Research Fund of the Istanbul University-Cerrahpasain Istanbul/Turkey [49085] This work is supported by the Research Fund of the Istanbul University-Cerrahpasain Istanbul/Turkey. Project Number: 49085. WOS:000582116500007 2-s2.0-85092488443

This article concerns with the effect of external salt addition on the structural, morphological and electrochemical properties of linear poly(ethylene imine) (LPEI) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) based LbL assembled films that is a cathodic color changing electrode for electrochromic device. For this purpose, cationic and anionic commercial polyelectrolytes (PEs) with/without 0.3 M NaCl were deposited on PET-ITO with automatized dip coating system. From QCM-D, it was found that the multilayer deposition became larger for LbL assembled films obtained from salt-free PEs. While the dissipation change (Delta D) of (LPEI/PEDOT:PSS)(10/NaCl) (150 x 10(-6)) exhibited relatively soft/flexible structure compared to the (LPEI/PEDOT:PSS)(10) (110 x 10(-6)), AD changes became more obvious during PEDOT:PSS adsorption. Furthermore, it was determined that the film thickness and surface roughness values were highly dependent on the number of deposited bilayers whereas they dropped with the addition of salt to LPEI. The root mean square roughness (R-q) of (LPEI/PEDOT:PSS)(10), (LPEI/PEDOT:PSS)(20) and (LPEI/ PEDOT:PSS)(40) were found to be 28 nm, 41.7 nm and 61.5 nm, respectively, while R-q of (LPEI/PEDOT:PSS)(20)(/NaCl) was 14.2 nm. All LbL mutilayered films had hydrophilic character and the average contact angle value of (LPEI/PEDOT:PSS)(20)(/NaCl) was found to be 66 degrees due to the presence of salt within the multilayers. In addition, ion transport rate increased if the external salt was added to PE. Concerning the salt effect on colorancy of LbL multilayers, all films showed reversible color changes between blue and transparent/pale blue and (LPEI/PEDOT:PSS)(20) exhibited darker blue in the colored state whereas (LPEI/PEDOT:PSS)(20/NaCl) had more translucent in the bleached state. Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [2214A/2014-2] Merve Okutan would like to thank The Scientific and Technological Research Council of Turkey (TUBITAK) for grant The International Research Fellowship Programme (for PhD students) 2214A/2014-2. WOS:000488954800013 2-s2.0-85069964555

The fabrication of LbL (layer by layer) self-assembled thin films is attracting attention for various applications. Hence, the detailed characterization of these films is very vital. In this study, interaction between the conjugate/non-conjugated polyelectrolyte pairs, final film compositions and viscoelastic behavior of the LbL multilayer thin films are determined using the quartz crystal microbalance dissipation (QCM-D) technique. Firstly, anodic color changing polyaniline (PAni) based LbL films as electrodes are coated on flexible PET-ITO substrate and extensive characterizations are performed. Secondly, electrochemical characterization of these films in LiClO4/PC electrolyte is carried out. It is found from QCM-D and UV–vis analyzes that the films can be successfully coated on PET-ITO surface. Film thicknesses of (PAni/PAA)10, (PAni/PAA)20 and (PAni/PAA)40 films are determined from SEM images and they are found to be approximately 160, 240 and 410 nm, respectively. Ra roughness values of the same films are determined to be 6.56, 14.4 and 13.7 nm from AFM analysis. Also, cyclic voltammetry (CV) analysis reveals a significant reduction and oxidation peaks of the electroactive polymer. It is observed that (PAni/PAA)20 LbL film efficiently changed blue/green to light yellow/transparent color in LiClO4/PC liquid electrolyte over the potential range from ?0.1 to 0.5 V vs Ag wire. © 2018 Elsevier B.V. Türkiye Bilimsel ve Teknolojik Araştirma Kurumu, TÜBITAK: 2214A/2014-2 Merve Deniz would like to thank The Scientific and Technological Research Council of Turkey (TUBITAK) for grant The International Research Fellowship Programme (for PhD students) 2214A/2014-2 . 2-s2.0-85058148705

Polymers based on ionic conducting materials have important interest because of their potential applications in polymer electrolytes and membranes for fuel cell application. PVdF-co-HFP poly(viniliden-co-hexafluoropropylene) was chosen as a polymer matrix because of its high ionic conductivity and better mechanical properties. Polymer matrix composites were prepared with various amounts of LiClO4 salt by a solution casting method. The sample-ionic conductivity measurements were recorded by AC impedance analyzer at different frequencies from 0.1 Hz to 20 MHz and at different temperatures from 273 to 373 K. The changes of nanoscopic free volume and free volume fraction in these materials were investigated in terms of temperature from 273 to 373 K using Positron Annihilation Lifetime Spectroscopy (PALS) and Simha-Somcynsky (SS) Hole Theory. The free volume had a bump at about 3% in weight percentage of the salt and there is a slight increase after 10%. The effects of weight percentages of LiClO4 and temperature were investigated. The mechanism of the ac ionic conductivity was presented in terms of the free volume models, however thermo-occupancy function justifies the best accurate representation of the data.

Here, Layer-by-Layer (LbL) films of PDADMAC and single/blend PAA/PSS were described for the drug loading/release platform. For this purpose, the effects of chemical composition of LbL film and drug type on loading/release properties were studied as a function of blend composition, pH and ionic strength of the polyelectrolytes (PEs)/releasing medium using QCM-D and UV–vis analyses. 15 % and 23 % (w/w) IBF-Na and DCF-Na loading were found without multilayer decomposition for LbL multilayers of (PDADMAC5.5/PAA5.5)10 while lower drug loadings were observed for PAA/PSS blend or single PSS containing LbL films. Drug sorption results obtained by QCM-D and UV–vis analyses were fitted very well. In-vitro studies, the loaded drugs were mostly released from the LbL films within 5 min. It was evaluated that IBF/DCF-Na release% of LbL multilayered films can be controlled as a function of pH, ionic strength, and single/blend composition as well as hydrophilicity, morphology, and topography of these films. In conclusion, these films may be good candidates as encouraging platforms for pH stimuli drug loading/release applications.

Deligoz, Huseyin/0000-0002-0915-2911 WOS:000525303900030 Development of antistatic thermoplastic elastomer composites is gaining much interest in scientific and industrial aspects. In this contribution, a novel type of polyester-block-ether copolymer (PEBE), PEBE with ionic liquid (PEBE-IL) and quaternized PEBE (PEBE-Q) were synthesized, characterized and compounded with a commercial bottle grade polyester (PET) resin. It was found that the surface resistivity of the PET composite films was around 10(9)-10(10) Omega/sq. The addition of the PEBE copolymers as an antistatic agent into PET matrix resulted in almost 10(6) times enhancement in surface resistivity compared to neat PET film. Among the PET films with an antistatic agent, it was emphasized that PEBE-IL and ionic liquid doping to PET matrix led to a relatively lower crystallization degree, surface resistivity, contact angle and breaking force with a translucent appearance compared to neat PET film. Furthermore, it was illustrated that antistatic PET films with fine-tune physical, mechanical and morphological properties can be achieved by choosing appropriate antistatic agent type and amount.

In this study, it was aimed to prepare a series of PVdF-co-HFP based electrolytes with different LiClO4 loadings and to investigate their chemical and electrical properties in detail. For this purpose, PVdF-co-HFP based electrolytes with different LiClO4 loadings (1–20 weight %) were prepared using solution casting method. X-ray diffraction (XRD), differential scanning calorimetry, and thermogravimetric (TGA) –differential thermal and dielectric spectroscopy analysis of PVdF-co-HFP/LiClO4 were performed to characterize their structural, thermal, and dielectric properties, respectively. XRD results showed that the diffraction peaks of PVdF-co-HFP/LiClO4 electrolytes broadened and decreased with LiClO4. TGA patterns exhibited that PVdF-co-HFP/LiClO4 electrolytes with 20 wt % of LiClO4 had the lowest thermal stability and it degraded above 473 K, which is highly applicable for solid polymer electrolytes. Dielectric constant, dielectric loss, and conductivities were calculated by measuring capacitance and dielectric loss factor of PVdF-co-HFP/LiClO4 in the range from 10 mHz to 20 MHz frequencies at room temperature. In consequence, conductivities of PVdF-co-HFP/LiClO4 increased significantly with frequency for low loading of LiClO4 while they only slightly changed with higher LiClO4 addition. On the other hand, dielectric constant values of PVdF-co-HFP/LiClO4 films decreased with frequency whereas they rose with LiClO4 addition. The dielectric studies showed an increase in dielectric constant and dielectric loss with decreasing frequency. This result was attributed to high contribution of charge accumulation at the electrode–electrolyte interface. The electrolyte showed the maximum conductivity of 8 × 10−2 S/cm at room temperature.

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?1–107 Hz between 20°C and 200°C. PCN/epoxy blends up to 50% epoxy resin show a good stability of dielectric constant in this frequency band for 200°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 (0.1–103 Hz) due to the interfacial polarization governed by Maxwell–Wagner–Sillars effect. POLYM. ENG. SCI., 58:820–829, 2018. © 2017 Society of Plastics Engineers. © 2017 Society of Plastics Engineers

Supercritical deposition (SCD) is used to prepare carbon-supported Pt nanoparticles as electrocatalysts for proton exchange membrane fuel cells (PEMFCs). Dimethyl(1,5-cyclooctadiene)platinum(II) (Pt(cod)me 2 ) is adsorbed from supercritical carbon dioxide (scCO 2 ) solutions onto Vulcan VX-72 at 13.2 MPa and 50 °C. The adsorbed metal precursor is converted to its metal form via three different routes: thermal conversion in N 2 at ambient pressure (route 1), thermal conversion in scCO 2 (route 2), or chemical conversion in H 2 at ambient pressure (route 3). Sequential SCD is used in routes 1 and 3. The mean diameters of the synthesized Pt nanoparticles are smallest for route 1 and largest for route 3. Nano-scale morphology of the electrocatalysts is characterized using transmission electron microscopy (TEM), revealing narrower Pt particle size distributions for the catalyst prepared via route 1 than for those synthesized by routes 2 and 3. Electrocatalyst prepared using route 1 showed the best performance both in specific activity (measured via cyclic voltammetry) and in PEMFC tests among electrocatalysts prepared using different routes.

Several divalent cations together with tetravalent Ti4+ ion were replaced by two trivalent Fe3+ ions of barium hexaferrite in the form of BaFe10M2+Ti4+O19. Samples were prepared by using solid state reaction route and 1 wt% B2O3 was added to inhibit the crystal growth at lower temperatures. Magnetic, dielectric and microwave properties of samples were investigated by X-ray crystallography, scanning electron microscopy, magnetization and near field microwave measurements. Magnetization measurements revealed that saturation magnetization of the cation substituted samples is less than that of the pure barium hexaferrite. Except Co2+ substituted barium hexaferrite, coercivities of the samples are nearly 1 kOe. While measurement of dielectric constants of Zn2+, Mn2+, Co2+ and Cu2+ substituted samples yields a significant enhancement ( approximate to 10-10(2) times) with respect to Ni2+ substituted barium hexaferrite in permittivity through local polarization of Fe3+ electronic charges activated with nearby divalent ions. It is suggested that Zn2+ and Mn2+ substitution acts to reduce the electron hopping probability between Fe2+ and Fe3+. All samples have approximately the same microwave absorption properties in such a way that minimum reflection loss (RL) of -10 dB occurs at 15 GHz. Meanwhile, Zn2+ and Mn2+ substituted samples have quite wide absorption bandwidths of 4 GHz at - 10 dB. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Preparation of multilayered polyelectrolyte and polyelectrolyte blend films and their drug uptake/release properties are studied using quartz crystal microbalance-dissipation (QCM-D). Polyvinylamine hydrochloride (PVA), polystyrene sulfonate sodium salt (PSS), and polyacrylic acid (PAA) were used as polyelectrolytes. Either films of the pure polyelectrolytes (PVA/PSS and PVA/PAA) or blends (PVA/PAA–PSS) were used. Our studies indicate that multilayer growth and drug loading/release properties of ibuprofen (IBF) can be successfully followed using QCM-D. Simultaneous UV–vis and QCM-D studies also show that the blend composition of the films always differs from the mixture composition of the dipping solution independent of pH of the dipping solutions. While PAA is more adsorbed at pH 5.5, PSS is almost completely adsorbed at pH 1.7. On the other hand, it is found that the films prepared from polyelectrolytes at pH 1.7 without salt are stable in neutral and acidic pH, while the lbl blend films prepared at pH 5.5 with or without salt decompose at pH 2 and 11. Pure PVA/PAA films exhibit a faster release of IBF than those of pure PVA/PSS and blend films due to the fact that the pH probably triggered a burst disintegration. IBF release characteristics of blend films differ from pure systems and a two-step release behavior is observed. It is emphasized that hydrogen bonding between PAA and IBF has an important role for the retarded IBF release from the blend films if PSS lead to hydrophobic interactions with the drug. In conclusion, pH stimuli lbl assembled films are prepared and their drug loading/release can be fine-tuned depending on multilayer structure.

Recently, there has been renewed interest in tungsten oxide based electrochromic (EC) materials. A variety of studies related to these materials have been reported, however, no serious studies so far have been reported on the electrochromic effect of tungsten oxide that is synthesized by solution combustion method. The major advantage of this process is the ease and simplicity with preparing nanosize oxides. Herein, the principal objective of this project was to produce uniform and adhesive tungsten oxide thin films from as-synthesized powder by solution combustion route for EC device. Although extensive research has been carried out on EC properties of tungsten oxide, limited study exists in e-beam evaporated tungsten oxide thin film studies for smart window application. Therefore, tungsten oxide thin films were deposited from our own produced powder by e-beam evaporation. To present the effect of new powder on the properties of the thin films, their physical and morphological properties were compared with thin film deposited by commercial tungsten oxide powder. Finally, electrochemical and optical characteristics of an all-solid-state EC device with a structure of glass/ITO/SCS-WO3/Nafion/ITO/glass with high optical transmittance modulation (63% at 550 nm) was fabricated. This study has been one of the first attempts to thoroughly examine in detail of tungsten oxide powder synthesized by solution combustion method for EC active layer. These findings contribute in several ways to our understanding of solution combustion synthesized powder to be used for production of EC active layer of thin film and provide a basis for developing and designing energy-efficient EC active materials and devices. WOS:000480665600004 2-s2.0-85067929573

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°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. © 2012 Society of Plastics Engineers.

We reported on the synthesis and detailed physicochemical characterization of poly(1-vinyltriazole)-grafted iron oxide nanoparticles. Superparamagnetic iron oxide nanoparticles (SPION) were fabricated by gel-to-crystalline conversion method. Telomerization of poly(1-vinyltriazole) on iron oxide nanoparticles was achieved via silanization process. XRD analysis confirmed the crystalline phase as magnetite, and FT-IR analysis confirmed the presence of PVTri on nanoparticles. Particle morphology was observed to be polygonic, due to the synthesis process, while average size estimated from TEM micrographs is 7 nm. Agreement between crystallite size estimated from XRD and particle size from TEM affirms single crystalline character of these nanoparticles. Dependence of conductivity on temperature showed a strong evidence for thermally activated polarization mechanism. Temperature and frequency dependence of dielectric permittivity revealed interfacial polarization and temperature-assisted-reorganization effects. Magnetic evaluation showed non-saturation and superparamagnetic characteristics of nanoparticles as well as magnetic particles being single domains. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

In this contribution, four comparative methods are described for the preparation of catalyst coated membranes (CCMs) via using layer-by-layer (LbL) technique. In the first method, LbL composite membrane is immersed into H 2 PtCl 6 solution followed by reduction to metallic Pt. Secondly, Pt–C (Hispec 3000) dispersed in the positively charged polyelectrolyte is assembled onto the membrane support. Thirdly, anionic polyelectrolyte with external salt is used for the preparation of CCM. In the fourth method, reductive precipitation of platinum salt loaded on Vulcan XC complexes within LbL multilayer in the presence of Nafion solution takes place. From SEM analysis, it is observed that the polyelectrolytes are deposited onto both sides of the pre-treated Nafion ® 117 membrane successfully with Pt loadings of 0.023 μg cm −2 and 0.15 μg cm −2 for CCMs prepared according to method 1 reduced in 10 and 30 min, respectively. Single cell performance of MEA-6 based on CCM (PAH/PSS–H 2 PtCl 6 –Vulcan XC72–Nafion) prepared according to method 4 displays the best output performance (98 mW cm −2 ) due to the improved contact between the catalyst layer and the membrane. Furthermore the cell performance of MEA-6 is significantly improved (18%) due to creating new path for fuel and catalyst interaction (three phase boundary) compared to pristine Nafion ® 117 based MEA.

The paper is concerned with the investigation of oxygen transport in layer-by-layer (LbL) self assembly of polystyrene sulfonic acid sodium salt (PSS) and polyallylamine hydrochloride (PAH) on Nafion membrane depending on the number of deposited bilayers, ion type within the multilayers and temperature. It is observed from SEM analysis that the polyelectrolyte layers growth on each side of Nafion membrane regularly. The oxygen permeability ( P O 2 ) of (PAH–PSS)20 is 691 cm3/(m2 day bar) at 25 °C while P O 2 of pristine Nafion is 2329 cm3/(m2 day bar) at the same temperature. This significant reduction (70.3%) in gas permeability can be explained by the formation of LbL multilayers which both restrict the mobility of gas through the polymer matrix and adjust gas solubility properties in conjunction with ion–dipole interaction between the polar phase of Nafion and the secondary ammonium groups of PAH. (PAH/PSS)20–Na+ and (PAH/PSS)20–H+ exhibit 64.4% and 52.3% reduction in oxygen permittivity at 25 °C in comparison with the pristine Nafion®117, respectively, while the proton conductivities of these membranes are 106.9 and 136.9 mS/cm. Promisingly, it is found that the membrane selectivity values (Φ) of all multilayered membranes in both H+ and Na+ form are much higher than that of perfluorosulfonated ionomer. The thickness of deposited bilayers dominates the diffusion and solubility properties of oxygen through the composite membrane while the major effect of surface hydrophilicity is not observed on oxygen permeability.

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°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°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°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 © 2011 John Wiley & Sons, Ltd.

Some approaches are applied for lowering methanol diffusion which leads a reduced cell performance for direct methanol fuel cells (DMFCs). In this contribution, investigation of the salt addition and acid treatment effects on the transport properties of chitosan (CHI) and poly(acrylic acid) (PAA) based polyelectrolyte complexes (PEC) are reported. Acid treated PEC membranes (PEC5-H + ) with externally added salt are found to be suitable for DMFCs due to low methanol permeability (4.6 × 10 −8 cm 2 s −1 ), acceptable conductivity (12.9 mS cm −1 ) and membrane selectivity (28.1 × 10 4 S s cm −3 ). The ionic interaction of the PEC and H 2 SO 4 not only provides an enhancement in methanol barrier properties but also results in a positive effect in mechanical integrity until 230 °C. The oxidative and hydrolytic stability of PEC membranes can be acceptable for DMFCs in which diluted methanol was used. Above all, the cost effectiveness and controllable synthesis technique of acid treated PECs make their applicability in DMFC quite attractive.

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.

The paper deals with the synthesis and characterization of a new type of acid doped highly conductive complex membrane based on sulfonated polyimide (sPI) and ionic liquid (IL) for high temperature anhydrous fuel cells. For this purpose, 2,4-diaminobenzene sulfonic acid (2,4-DABSA) is reacted with benzophenontetracarboxylic dianhydride (BTDA) to yield sulfonated poly(amic acid) (sPAA) intermediate. Subsequently, IL is added into sPAA to form an interaction between sulfonic acid and imidazolium group of IL followed by acid doping. The ionic conductivity of acid doped sPI/IL complex polymer membrane is higher than that of IL containing composite membranes reported in the literature (5.59 × 10 −2 S cm −1 at 180 °C). Furthermore, dynamic mechanical analysis (DMA) results of acid doped sPI/IL complex membrane show that the mechanical strength of the complex product is slightly changed until 350 °C due to the formation of ionic interactions between sulfonic acid groups of sPI and imidazolium groups of IL. Consequently, the ionic interaction not only provides high ionic conductivity with excellent thermomechanical properties (the storage module of 0.91 GPa at 300 °C) but also results in a positive effect in long term conductivity stability by blocking IL migration through the membrane.

Highly proton conductive and mechanically stable Nafion ® 112 based composite membranes with suppressed methanol permeability were prepared via Layer-by-Layer (LbL) technique for fuel cell applications. It was observed from UV–vis results that the polyelectrolyte layers growth on Nafion membrane surface regularly. (PAH/PSS) 20 –H + with 0.01 M NaCl exhibited 39.9% reduction in methanol permittivity and nearly 2 times higher proton conductivity (0.152 S cm −1 ) than that of untreated Nafion ® 112. Promisingly, it was found that the membrane selectivity ( Φ ) values of all multilayered composite membranes in proton form prepared from polyelectrolytes comprising NaCl were higher than that of both untreated and chemically treated Nafion ® 112. Furthermore, the mechanical and thermal properties of the composite membrane obtained from polyelectrolytes free salt were enhanced due to the interaction between the polar phase of Nafion and anionic/cationic charges of polyions.

The paper is concerned with the formation of Layer-by-Layer (LbL) self-assembly of highly charged polyvinyl sulfate potassium salt (PVS) and polyallylamine hydrochloride (PAH) on Nafion membrane to obtain the multilayered composite membranes with both high proton conductivity and methanol blocking properties. Also, the influences of the salt addition to the polyelectrolyte solutions on membrane selectivity (proton conductivity/methanol permeability) are discussed in terms of controlled layer thickness and charge density. The deposition of the self-assembly of PAH/PVS is confirmed by SEM analysis and it is observed that the polyelectrolyte layers growth on each side of Nafion membrane regularly. (PAH/PVS) 10 –Na + and (PAH/PVS) 10 –H + with 1.0 M NaCl provide 55.1 and 43.0% reduction in lower methanol permittivity in comparison to pristine Nafion, respectively, while the proton conductivities are 12.4 and 78.3 mS cm −1 . Promisingly, it is found that the membrane selectivity values ( Φ ) of all multilayered composite membranes in H + form are much higher than those of Na + form and perfluorosulfonated ionomers reported in the literature. These encouraging results indicate that composite membranes having both superior proton conductivity and improved methanol barrier properties can be prepared from highly charged polyelectrolytes including salt for fuel cell applications.

A series of highly proton conductive electrolyte membranes with improved methanol barrier properties are prepared from polyallylamine hydrochloride (PAH) and polystyrene sulfonic acid (PSS) including salt by Layer-by-Layer (LbL) method. The effects of added salt type (NaCl, MgCl 2 ) and salt concentration (1.0 M, 0.1 M) on proton conductivity ( σ ) and methanol barrier properties of the LbL self-assembled composite membranes are discussed in terms of controlled layer thickness and charge density. Furthermore, the influences of ion type in the multilayered composite membranes are studied in conjunction with physicochemical and thermal properties. The deposition of the self-assembly of PAH/PSS film on Nafion is followed by UV–Vis spectroscopy and it is observed that the polyelectrolyte layers growth on both sides of Nafion membrane regularly. (PAH/PSS) 5 –Na + and (PAH/PSS) 5 –H + with 1.0 M NaCl exhibits 49.6 and 27.8% reduction in lower methanol permittivity in comparison with the pristine Nafion ® 117, respectively, while the proton conductivities are 12.97 and 74.69 mS cm −1 . Promisingly, it is found that the membrane selectivity values ( Φ ) of all multilayered membranes in H + form are much higher than that of salt form (Na + and Mg 2+ ) and perfluorosulfonated ionomers reported in the literature. Also, we find out that the use of polyelectrolytes with high charge density causes a further improvement in proton conductivity and methanol barrier properties simultaneously. These encouraging results indicate that upon a suitable choice of LbL deposition conditions, composite membranes exhibiting both high proton conductivity and improved methanol barrier properties can be tailored for fuel cells.

In this study, 8 mol% yttria-stabilized zirconia (8YSZ), ceria-, and scandia-doped YSZ powders were synthesized by the reverse microemulsion method. The powders were calcined at 1000°C and sintered at 1450°C. The crystalline properties and microstructure of the samples were characterized by X-ray diffraction and SEM methods, respectively. Oxygen ionic conductivities of the samples were measured by electrochemical impedance spectroscopy in the temperature range 250–375°C. Grain interior and grain boundary resistivities were also calculated. Particle sizes of YSZ and Sc-doped YSZ were found to be

The paper is concerned with the deposition of self-assembled polyelectrolyte multilayer on Nafion membrane by layer-by-layer (LbL) technique with lowered methanol cross-over for direct methanol fuel cell (DMFC) applications. The formation of self-assembled multilayered film on Nafion was characterized by UV–vis spectroscopy and it was found that the polyelectrolyte layers growth on the Nafion surface regularly. Furthermore, the proton conductivity and methanol cross-over measurements were carried out for characterization of the LbL self-assembled composite membranes. The results showed that the concentration and pH of the polyelectrolytes significantly affect the proton conductivity and methanol barrier properties of the composite membranes. 10−1 monomol polyelectrolyte concentration and pH 1.8 was found to be optimum deposition conditions considering proton conductivity and methanol permeation properties of the LbL self-assembled composite membranes. The methanol permeability of the 10 bi-layers of PAH1.8/PSS1.8 deposited LbL self-assembly composite membrane was significantly suppressed and found to be 4.41 × 10−7 cm2/s while the proton conductivity value is in acceptable range for fuel cell applications.

A series of sulfonated homo- and random co-polyimides (co-SPI) based on 2,4-diaminobenzenesulfonic acid (2,4-DABS) and 2,5-diaminobenzenesulfonic acid (2,5-DABS) has been synthesized via conventional two-step polyimidization method. 2,4-DABS and 2,5-DABS were used as sulfonated diamine compounds, 4,4′-oxydianiline (ODA) and 4,4′-diaminodiphenyl sulfone (DDS) were used as non-sulfonated diamine compounds. Mixtures of sulfonated and non-sulfonated diamine compounds were reacted with benzophenonetetracarboxylic dianhydride (BTDA) to obtain co-SPI membranes. Molar ratios of sulfonated to non-sulfonated diamine were systematically varied to produce copolymers of controlled compositions. The co-SPIs were evaluated for thermal oxidative stability, ion exchange capacity (IEC), water uptake, proton conductivity, solubility, and hydrolytic stability. Proton conductivity and hydrolytic stability of the co-SPIs were compared with the fully aromatic polyimide, homo-SPIs (BTDA/2,4-DABS and BTDA/2,5-DABS). Regarding thermogravimetric analysis (TGA) analysis, it is concluded that desulfonation temperature in the range of 200–350°C suggests high stability of sulfonic acid groups. co-SPIs with 40 mol% of 2,4-DABS showed similar or higher proton conductivity than Nafion® 117 in water. Proton conductivity values of the co-SPIs were mainly a function of IEC and water uptake. Consequently, the optimum concentration of 2,4-DABS was found to be in the range of 30–40 mol% from the viewpoint of proton conductivity, IEC, and hydrolytic stability. Copyright © 2008 John Wiley & Sons, Ltd.

A series of random sulfonated copolyimides containing aliphatic linkages (co-SPIAs) with controlled degrees of sulfonic acid groups were synthesized via a conventional two-step polyimidization method. 2,4-Diaminobenzene sulfonic acid (2,4-DABS) and 1,6-diaminohexane (DAH) were used as sulfonated aromatic diamine and nonsulfonated aliphatic diamine compounds, respectively. Mixtures of diamine compounds were reacted with benzophenonetetracarboxylic dianhydride (BTDA) to obtain the co-SPIAs. The molar ratios of DAH/2,4-DABS were systematically varied to produce copolymers with controlled compositions that contained up to 70 mol % sulfonic acid moieties. The co-SPIAs were evaluated for thermal oxidative stability, ion-exchange capacity (IEC), water uptake, proton conductivity, solubility, and hydrolytic stability. The proton conductivity and hydrolytic stability of the co-SPIAs were compared with the fully aromatic polyimide, sulfonated homo-polyimide (homo-SPI) (BTDA/2,4-DABS). From thermogravimetric analysis, we observed desulfonation temperatures in the range 200–350°C, which suggested a high stability of the sulfonic acid groups. The co-SPIAs with 40–70 mol % 2,4-DABS showed higher proton conductivity than Nafion 117 in water. The proton conductivity values of the co-SPIAs were mainly a function of IEC and water uptake. Furthermore, the hydrolytic stability of the 2,4-DABS-based sulfonated polyimide membranes were improved by the introduction of the nonsulfonated diamine with aliphatic linkages. The optimum concentration of 2,4-DABS was found to be around 40 mol % from the viewpoint of proton conductivity, IEC, and hydrolytic stability. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Composites of PUR and IL were prepared and specific conductivities and Shore A hardness were determined. IL were based on 1-alkyl-3-methylimidazolium salts with counterions BF - 4 , PF - 6 , triflate, or ethylsulfate. Presence of IL increased the conductivity by five orders of magnitude. Variation of alkyl chain length and nature of counterions only had little effect on the conductivity. Presence of IL had a plasticizing effect, which was most pronounced for the IL with dodecyl groups and PF - 6 as counterion. In broadband dielectric measurements, the complex conductivity showed a characteristic dispersion that is caused by the interplay between (hopping) transport of charge carriers and electrode polarization.

The reaction of myristic acid (MA) and isopropyl alcohol (IPA) was carried out by using both homogeneous and heterogeneous catalysts. For a homogeneously catalyzed system, the experimental data have been interpreted with a second order, using the power-law kinetic model, and a good agreement between the experimental data and the model has been obtained. In this approach, it was assumed that a protonated carboxylic acid is a possible reaction intermediate. After a mathematical model was proposed, reaction rate constants were computed by the Polymath* program. For a heterogeneously catalyzed system, interestingly, no pore diffusion limitation was detected. The influences of initial molar ratios, catalyst loading and type, temperature, and water amount in the feed have been examined, as well as the effects of catalyst size for heterogeneous catalyst systems. Among used catalysts, p-toluene sulfonic acid (p-TSA) gave highest reaction rates. Kinetic parameters such as activation energy and frequency factor were determined from model fitting. Experimental K values were found to be 0.54 and 1.49 at 60°C and 80°C, respectively. Furthermore, activation energy and frequency factor at forward were calculated as 54.2 kJ mol−1 and 1828 L mol−1 s−1, respectively. © 2008 Wiley Periodicals, Inc. 40: 136–144, 2008

Cobalt Ferrite (CoFe2O4) nanoparticles coated with oleic acid were synthesized by polyol method. The structures of the nanoparticles were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared with Attenuated Total Reflectance Unit (FTIR -ATR). Thermal and morphological properties of nanoparticles were determined by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmitting electron microscopy (TEM) respectively. The dielectric constant and dielectric loss of the nanoparticles were determined in the frequency range of 10 Hz–20 MHz and within the temperature range of 293 K–423 K. It was observed that AC conductivity σ(ω) α ωs. (0

Three methods were used for solvent-free preparation of conducting composites of PUR and PPy. In all cases, PUR was prepared from TDI and hydroxol 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 hydroxol. After addition of TDI the mixture was cured to yield the final product. In method 2, ferric chloride and Py were dissolved in hydroxol and a PPy dispersion was obtained. Then TDI was added and the final product was obtained upon curing. In method 3, Py was dissolved in TDI and ferric chloride dissolved in hydroxol. 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 a of 10 -10 S · cm -1 and a Shore A hardness of 40 to 55. Using methods 2 and 3, composites with σ values of 10 -7 S · cm -1 and a hardness of 30 to 40 were obtained. Presence of moisture increased the σ 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 dependent on the amount of ferric chloride present in the sample and not on the PPy content, suggesting that the conductivity was ionic.

Four different types of cross-linked polyimides based on 4,4-diphenylmethane diisocyanate (MDI) were prepared by the reaction of different types of conventional poly(amic acid) intermediates with MDI as a cross-linking agent. Subsequently, they were thermally imidized in order to obtain corresponding cross-linked polyimide structure. The results of FTIR-ATR showed that MDI can effectively react with carboxylic acid groups of PAA to form cross-linked polyimide films. TGA, FTIR-ATR and SEM analyses were carried out for characterization of cross-linked polyimide (CPI) films. Moreover, the electrical properties such as dielectric breakdown strength, dielectric constant, I–V characteristics and loss factor of MDI based cross-linked polyimides have been checked. In addition, some physical properties such as water uptake, adhesion, hardness and solubility properties of the films were investigated. The results showed that all CPI films have good insulating properties such as high dielectric breakdown voltage, low loss factor (tan δ), leakage density and excellent physical properties.

A series of conventional polyimide (CPI) films, based on pyromellitic dianhydride (PMDA) and benzophenonetetracarboxylicdianhydride (BTDA), were prepared by a two step process, and their dielectrical constant, dielectrical loss, and DC conduction behaviors were studied at different frequencies and voltages. Their dielectrical breakdown voltage, water uptake, and solubility properties were also investigated. The effects of chemical structure and water uptake on the electrical properties of the films are discussed in detail. The dielectric constants of the CPI films vary between 2.93 and 3.72 at 1 MHz frequency and they are in the following decreasing order: BTDA-DDS > BTDA-DDE > PMDA-DDS > PMDA-DDE. The structure and thermal and oxidative stability of films were analyzed by FTIR-ATR and TGA, respectively. The results showed that all CPI films have good insulating properties, such as high dielectric breakdown voltage, low dielectric constant with stability for long period of frequency, and low leakage density. Our results concerning electrical properties also suggest that electron hopping is responsible for AC conduction and Poole-Frenkel mechanism is predominant for DC conduction of all CPI films.

A novel cross-linked polyimide (CPI) has been prepared by imidization of cross-linked poly(amic acid) (CPAA). In this work, the Ac conductivity and dielectric properties of this polyimide are presented comparitively with those of conventional polyimide (PI), in the 0.2–100 kHz frequency range and 300–463 K temperature interval. Although the frequency and temperature dependencies of dielectric constant of both conventional and cross-linked polyimides show the same behaviour, the dielectric constant of CPI takes lower values. The Ac conduction studies suggest that electron hopping is responsible for conduction of the PI and CPI films. The activation energy calculated in 296–353 K temperature interval and the s-relaxation was also observed for CPI.

A novel type of a Si-containing poly(urethane-imide) (PUI) was prepared by two different methods. In the first method, Si-containing polyurethane (PU) prepolymer having isocyanate end groups was prepared by the reaction of diphenylsilanediol (DSiD) and toluene diisocyanate (TDI). Subsequently the PU prepolymer was reacted with pyromellitic dianhydride (PMDA) or benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl pyrolidone (NMP) to form Si-containing modified polyimide directly. In the second method, PU prepolymer was reacted with diaminodiphenylether (DDE) or diaminodiphenylsulfone (DDS) in order to prepare an amine telechelic PU prepolymer. Finally, the PU prepolymer having diamine end groups was reacted with PMDA or BTDA to form a Si-containing modified polyimide. Cast films prepared by second method were thermally treated at 160 °C to give a series of clear, transparent PUI films. Thermogravimetric analysis indicated that the thermal degradation of PUI starts at 265 °C which is higher than degradation temperature of conventional PU, confirming that the introduction of imide groups improved the thermal stability of PU. To characterize the modified polyimides and their films, TGA, FTIR, SEM and inherent viscosity analyses were carried out. The dielectrical properties were investigated by the frequency–capacitance method. Dielectric constant, dielectric breakdown strength, moisture uptake and solubility properties of the films were also investigated.

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 ɛ′ 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 °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 δ of ROMP-BN-6 is 0.003 and 0.0067 at 10 Hz–1 MHz at 20 °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 ∼350 °C and gave 25% char yield at 800 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45658.

Bu calisma 2007-2008 yilari arasinda, Ordu ili Merkez, Gulyali, Ulubey, Persembe, Fatsa, Kabaduz, Unye ve Ikizce ilcelerinde yetistirilen karayemis genotiplerinin ozelliklerini belirlemek ve umitvar tipleri secmek amaciyla yurutulmustur. Tiplerin seciminde kullanilmistir. Tartili derecelendirmede salkimdaki meyve sayisi, meyve iriligi, meyve agirligi, meyve et/cekirdek orani, suda cozunur kuru madde miktari, tat, burukluk durumu, cekirdegin meyve etinden ayrilma durumu ve meyvede birorneklilik gibi kriterler kullanilmistir. Yapilan degerlendirme sonucunda O-20, O-44, O-64, O-37 ve O-105 karayemis genotiplerinin digerlerinden daha ustun oldugu saptanmis, genotiplerin ortalama salkimdaki meyve sayilari 3,3-27,3 adet; meyve irilikleri 18,0020,55 mm; meyve agirliklari 4,31-6,24 g; meyve et/cekirdek oranlari 10,79-16,08; suda cozunur kuru madde miktari %16,20-25,00 arasinda bulunmustur

The paper presents the results of the research on a new polymer-membrane and gel electrolytes for electrochromic devices. A complementary solid-state electrochromic device consisting of cathodically coloring working electrode of WO3 and anodically coloring counter electrode of NiO films is prepared to compare the effects of gel or membrane forms of carboxymethyl cellulose (CMC) polymer electrolyte on the electrochromic properties of devices. The performance evaluations of the complementary solid-state electrochromic devices indicate good reversibility, low power consumption of +/- 3V in colored state, high variation of transmittance changing of 64% in gel electrolyte, and lower 7% in membrane electrolyte and good memory effect under open-circuit conditions. CMC based electrolytes can be used as an ion-conducting medium and be a good candidate for complementary electrochromic devices owing to, the improved properties as well as its cheapness.

In this study, two approaches are compared to develop nanostructured membrane electrode assemblies (MEA) using layer-by-layer (lbl) technique. The first is based on the direct deposition of polyallylamine hydrochloride (PAH) and sulfonated polyaniline (sPAni) on Nafion support to prepare lbl composite membrane. In the second approach, sPAni is coated on the support in the presence of platinum (Pt) salt, Nafion solution and Vulcan for obtaining catalyst containing membranes (CCMs). SEM and UV-vis analysis show that the multilayers are deposited on both sides of Nafion successfully. Although H-2/O-2 single cell performances of acid doped lbl composite membrane based MEA are found to be at the range of 126 and 160 mW cm(-2) depending on the number of deposited layers, the cell performance of MEA obtained from catalyst containing lbl self-assembled thin membrane (PAH/sPAni-H+)(10-Pt) is found to be 360 mW cm(-2) with a Pt utilization of 720 mW mgPt(-1). This performance is 82% higher as compared to original Nafion((R))117 based MEA (198 mW cm(-2)). From the cell performance evaluations for different structured MEAs, it is mainly found out that the use of lbl CCMs instead of composite membranes and fabrication of thinner electrolytes result in a higher H-2/O-2 cell activity due to significant reduction in ohmic resistivity. Also, it is observed that the use of sPAni slightly improves the cell performance due to an increased probability of the triple phase contact and it can lead to superior physicochemical properties such as conductivity and thermal stability. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40314.

The development of composite membranes and catalyst containing membranes (CCMs) with low methanol permittivity attracts a great deal of research attention for achieving higher performance in direct methanol fuel cells (DMFCs). Here, the fabrication and DMFC performance of composite and catalyst containing membranes (CCM) via layer-by-layer (lbl) technique are demonstrated. lbl composite and catalyst containing membrane based membrane-electrode assemblies (MEAs) show quite impressive cell performance. While the single cell performances of lbl composite membrane based MEAs are found to be in the range of 19.5 and 22 mW cm(-2), DMFC performance of MEA obtained from Pt containing self-assembled 10 bilayer of polyallylamine hydrochloride and polyvinylsulfonic acid, (PAH/PVS-H+)(10-pt), is found to be 24 mW cm(-2). This performance is nearly 65.5% higher compared to pure Nafion((R)) 112 based MEA. Inductive coupling plasma-mass spectroscopy (ICP-MS) result shows that Pt particles incorporate inside lbl multilayers with a loading of 0.28 mu gcm(-2). From the analyses of the performance evaluations, it is emphasized that the use of thin lbl catalyst containing membranes can be possible and quite promising in DMFC applications instead of thicker membranes due to their improved methanol barrier properties as well as proton conductivity. (c) 2013 Elsevier Ltd. All rights reserved.

Co1-xZnxFe2O4 spinel nanoparticles with Zn concentrations of x = 0.0, 0.2 were prepared by a hydrothermal route in the presence of triethylene glycol (TEG). The structural, magnetic, electrical and dielectric properties of the prepared nanoparticles were studied. The XRD results confirmed the formation of single spinel ferrite structure with crystallite size 9 and 10 nm for x = 0.0 and 0.2 compositions respectively. The lattice parameter (a) increased with increasing Zn concentration. Temperature and frequency dependent electrical and dielectric properties of the prepared ferrites have also been investigated. Our findings show that overall conductivity of Co0.8Zn0.2Fe2O4 nanoparticle is lower than that of CoFe2O4 and roughly in the range of 10(-11)-10(-7) S cm(-1) depending strongly temperature and frequency owing to the formation of stable electric bonds between the Zn2+ and Fe2+ ions, which localizes Fe2+ charge carriers. 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. dc conductivity of Co0.8Zn0.2Fe2O4 nanoparticle are found to obey the Arrhenius plot and can be classified into two regions over with activation energy of 0.113 and 0.163 eV in the ranges of 20-40 degrees C and 70-120 degrees C, respectively when CoFe2O4 has an activation energy of 0.245 eV. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.

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.