Showing papers in "Polymers for Advanced Technologies in 2005"
TL;DR: In this paper, the authors summarized and reviewed the research on electromagnetic interference (EMI) shielding with intrinsically conducting polymers (ICPs), mainly polyaniline (PANI) and polypyrrole (PPY), and their composites in various frequency ranges.
Abstract: This paper summarizes and reviews the research on electromagnetic interference (EMI) shielding with intrinsically conducting polymers (ICPs), mainly polyaniline (PANI) and polypyrrole (PPY), and their composites in various frequency ranges. ICPs are new alternative candidates for EMI shielding applications due to their lightweight, corrosion resistance, ease of processing, and tunable conductivities as compared with typical metals. More importantly, the dominant shielding characteristic of absorption other than that of reflection for metals render ICPs more promising materials in applications requiring not only high EMI shielding effectiveness but also shielding by absorption, such as in stealth technology. Copyright © 2005 John Wiley & Sons, Ltd.
510 citations
TL;DR: In this paper, a spin-loading asymmetric cellulose acetate (CA) hollow fiber membrane was examined using a scanning electron microscope and the silver content in the fiber was measured using an inductively coupled plasma atomic emission spectrometer.
Abstract: Silver-loading asymmetric cellulose acetate (CA) hollow fiber membrane was spun via the dry jet-wet spinning technique. The spinning solution was prepared by dissolving AgNO3 and CA in N,N-dimethylformamide (DMF). The silver ions were reduced in the spinning dope into silver nano-particles. The morphology of the resulting hollow fibers was examined using a scanning electron microscope and the silver content in the fiber was measured using an inductively coupled plasma atomic emission spectrometer. The antibacterial activities were evaluated. These hollow fibers had a sponge-like structure and dense inner and outer surfaces. At a 50 k magnification, the pore on the skin layer was not observable, while the nodule size was smaller than 10 nm. The residual silver content of as-spun hollow fiber was about 60% of the original silver added in the polymer solution. After immersing in water bath for 180 days, the silver content in the bulk of the hollow fibers decreased to 60% and the silver content on the surface reduced to 10%, yet still showed antibacterial activity against Escherichia coli and Staphylococcus aureus. After permeating with water for 5 days, the silver content in the hollow fibers decreased, and did not show antibacterial activity against E. coli and S. aureus. Thus, silver content must be periodically replenished after permeation. The proper range of AgNO3 in the spinning solution for CA hollow fiber should be about 100–1000 ppm. Copyright © 2005 John Wiley & Sons, Ltd.
360 citations
TL;DR: A set of preparation techniques which allow to introduce simultaneous specific functions into such nanoobjects has been developed recently as mentioned in this paper, including electrospinning and co-electrospinning of nanofibers as well as template methods utilizing eletrospun nanofiber or porous substrates.
Abstract: Nanofibers and nanotubes based on polymers offer a broad range of applications in areas such as photonics, sensorics, catalysis or medicine and pharmacy. A set of preparation techniques which allow to introduce simultaneous specific functions into such nanoobjects has been developed recently. These include electrospinning and co-electrospinning of nanofibers as well as template methods utilizing eletrospun nanofibers or porous substrates. These techniques yield infinitively long nanofibers and nanotubes with well defined aspect ratios respectively with diameters down to a few ten nanometers. These nanofibers and nanotubes can be functionalised, among others by using biodegradable materials or via the incorporation of nanoparticles or precursor molecules, in such a way that applications for tissue engineering, for catalysis, photonics and sensorics become available. Copyright # 2005 John Wiley & Sons, Ltd.
274 citations
TL;DR: In this article, the effects of ZnO nanoparticles on the physical properties of polystyrene (PS)/zinc oxide (ZnO) nanocomposites were investigated.
Abstract: Polystyrene (PS)/zinc oxide (ZnO) nanocomposites were prepared by solution mixing, followed by film casting. The effects of ZnO nanoparticles on the physical properties of PS were investigated. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) showed that ZnO nanoparticles were homogeneously dispersed in the PS matrix. The introduction of 5 wt% ZnO increased slightly the glass transition temperature by 2.3°C. Thermal gravimetric analysis thermograms showed that the thermal stability of PS was enhanced with increasing ZnO content. Neither shift nor sharpening of absorption band was detected by infrared spectra. ZnO nanoparticles had little effect on the wide-angle X-ray diffraction (WAXD) pattern of PS. The transmittance of ultraviolet light was decreased with increasing ZnO content. PS/ZnO nanocomposites exhibited a small reduction in tensile strength and elongation to break. However, a significant enhancement in tensile modulus was achieved when 5 wt% ZnO was introduced. In the FESEM images of the tensile fractured surface, localized plastic deformation was observed for PS, while the site from which ZnO was pulled out was usually observed in the nanocomposites. Copyright © 2006 John Wiley & Sons, Ltd.
151 citations
TL;DR: An overview of the recent literature on flame retardancy of poly(vinyl chloride) (PVC) is presented in this article, where a short overview of mechanisms of thermal decomposition of PVC, especially those which lead to char formation, is also presented because this gives insight into the mechanisms of flame retardant action.
Abstract: This paper presents an overview of the recent literature on flame retardancy of poly(vinyl chloride) (PVC). A short overview of mechanisms of thermal decomposition of PVC, especially those which lead to char formation, isalso presented because this gives insight into the mechanisms of flame retardant action. New developments in the area are mostly focused on combinations of various flame retardants and smoke suppressants in the search for synergistic effects. Because different additives show different mechanisms of action, synergistic combinations are very probable. New developments in phosphate ester plasticizers are reported in the literature.
136 citations
TL;DR: In this article, a coupling reaction of both macrodiols of polylactide (PLLA-diol) and poly(glycolide-co-caprolactone) (PGC)-diols in the presence of 1,6-hexanediisocyanate as coupling agent was investigated and the copolymers were found to be thermoplastic and easily soluble in common solvents.
Abstract: In this study, biodegradable shape-memory polymers—polylactide-co-poly(glycolide-co-caprolactone) multiblock (PLAGC) copolymers—were synthesized by the coupling reaction of both macrodiols of polylactide (PLLA-diol) and poly(glycolide-co-caprolactone) (PGC-diol) in the presence of 1,6-hexanediisocyanate as coupling agent. The copolymers formed were found to be thermoplastic and easily soluble in common solvents. The compositions of the copolymers were determined by 1H-NMR and the influences of segment lengths and contents of both macrodiols on the properties of the PLAGC copolymers were investigated. It was found that the copolymers had adjustable mechanical properties which depended on contents and segment lengths of both macrodiols. The copolymers showed such good shape-memory properties that the strain fixity rate (Rf) and the strain recovery rate (Rr) exceed 90%. By means of adjusting the compositions of the copolymers, PLAGC copolymers with transition temperatures around 45°C could be obtained. The degradation rate determination showed that the PLAGC copolymers have fast degradation rates, the mechanical strengths of the PLAGC copolymers would be completely lost within 1–2 months depending on molecular weights and contents of the both segments of PLLA and PGC. Copyright © 2005 John Wiley & Sons, Ltd.
118 citations
TL;DR: In this paper, the authors present a review of the ST and SFE values expressed in dyn/cm for a number of polymers, minerals, oxides and clays, and also deal with the calculation of ST based on parachor values and other polymer properties obtained from a DIPPR database accompanied and coupled with QSPR software entitled TSAR.
Abstract: This paper presents a review of the ST and SFE values expressed in dyn/cm for a number of polymers, minerals, oxides and clays. The review also deals with the calculation of ST based on parachor values and other polymer properties obtained from a DIPPR database accompanied and coupled with QSPR software entitled TSAR. Data are also given on the ST of clays.
The three components of the ST, the apolar Lifshitz–van der Waals component and the two polar (electron-donor and electron-acceptor) components of the various clays are also presented, as calculated by the van Oss et al. equation.
Substitution of the cations in the innerlayer of clays by other inorganic cations is reviewed. Data are given on the effect of introducing organic ammonium cations into the clays and how they affect MMT, laponite, and talc.
The effect of temperature on the ST of small molecules and on polymers is discussed, and a formula for this effect is shown. The effect of surface crystallinity on ST is discussed.
The effect of chemical composition, structure and molecular weight are discussed as well. Systems for the estimation of ITs are reviewed, in relation to the ST values of the components.
Data on the ST of high-energy materials are presented. The changes in these values upon interaction with low-energy surfaces are discussed. Copyright © 2005 John Wiley & Sons, Ltd.
95 citations
TL;DR: In this paper, a casting solution of polyvinylpyrrolidone (PVP) in various solvents [N,N-dimethylacetamide (DMAc), N,Ndimethylformamide (DMF) and 1-methyl-2-pyrrinolidone(NMP) was manufactured from a casting solutions of the polymer, PVP, and immersing the prepared films in different non-solvents.
Abstract: Polysulfone (PS) and polyethersulfone (PES) ultrafiltration membranes were manufactured from a casting solution of the polymer, polyvinylpyrrolidone (PVP) in various solvents [N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) and 1-methyl-2-pyrrolidone (NMP)] by immersing the prepared films in different non-solvents [water, 2-butanol, mixture of water and 2-butanol, mixture of water and 2-propanol (IPA) and mixture of water and 1-butanol].
The influences of various solvents and non-solvents on morphology and performance of the prepared membranes were analyzed by scanning electron microscopy (SEM) and separation experiments using milk as the feed. Copyright © 2005 John Wiley & Sons, Ltd.
90 citations
TL;DR: In this article, polyacrylonitrile (PAN) was blended with polyvinylidine fluoride (PVDF) at various ratios and made into membranes, and the hemocompatibility of the resulting membranes was evaluated based on human plasma proteins adsorption, platelet adhesion, thrombus formation, and blood coagulation time.
Abstract: Polyacrylonitrile (PAN) was blended with polyvinylidine fluoride (PVDF) at various ratios and made into membranes. The hemocompatibility of the resulting membranes was evaluated based on human plasma proteins adsorption, platelet adhesion, thrombus formation, and blood coagulation time. The PAN/PVDF blends exhibited partial miscibility according to the inward shifting of their two glass transition temperatures. The microstructures of blend membranes examined using atomic force microscopy (AFM) indicated that the roughness increased with the PVDF content, and the phase separation was too severe to form a membrane when the PVDF content was more than 30%. The water contact angle of PAN/PVDF blend membranes increased with the PVDF content. By blending with 20wt% apolar PVDF the adsorption of blood proteins could be reduced, and hence the platelet adhesion and thrombus formation was also reduced. However, when the PVDF content was 30wt%, severe thrombogenicity was observed due probably to the more porous structure of blend membrane. These results demonstrated that the hemocompatibility would be improved for PAN/PVDF blend membranes with appropriate hydrophilicity and roughness. Copyright # 2005 John Wiley & Sons, Ltd.
86 citations
TL;DR: Porous polylactide (PLA) microspheres were fabricated by an emulsion-solvent evaporation method based on solution induced phase separation in this paper, where the pore size was in the range of decade micrometers.
Abstract: Porous polylactide (PLA) microspheres were fabricated by an emulsion-solvent evaporation method based on solution induced phase separation. Scanning electron microscopy (SEM) observations confirmed the porous structure of the microspheres with good connectivity. The pore size was in the range of decade micrometers. Besides large cavities as similarly existed on non-porous microspheres, small pores were found on surfaces of the porous microspheres. The apparent density of the porous microspheres was much smaller than that of non-porous microspheres. Fabrication conditions such as stirring rate, good solvent/non-solvent ratio, PLA concentration and dispersant (polyvinyl alcohol, PVA) concentration had an important influence on both the particle size and size distribution and the pore size within the microspheres. A larger pore size was achieved at a slower stirring rate, lower good solvent/non-solvent ratio or lower PLA concentration due to longer coalescence time. Copyright © 2005 John Wiley & Sons, Ltd.
84 citations
TL;DR: In this paper, the effects of the polymerization variables on the swelling capacity of the products were investigated, and it was found that, in a certain range of the monomers mol ratio, increase of AMPS content was surprisingly accompanied with swelling reduction.
Abstract: Novel hydrogels based on zwitterionic monomer [3-(methacrylamido)propyl] dimethyl (3-sulfopropyl) ammonium hydroxide (MPDSAH) and a strong acid monomer (2-acrylamido-2-methylpropane sulfonic acid, AMPS) were synthesized through solution polymerization under normal conditions to achieve nearly quantitative gel yield. The structure of the gels was confirmed using infrared spectroscopy. Thermal properties were simultaneously studied by differential scanning calorimetry and thermogravimetric analysis (DSC/TGA). The effects of the polymerization variables on the swelling capacity of the products were investigated. It was found that, in a certain range of the monomers mol ratio, increase of AMPS content was surprisingly accompanied with swelling reduction. The swelling exhibited lower sensitivity to the crosslinker concentration (range 0.6–1.2 wt%) compared with the conventional superabsorbents. However, in contrast with the conventional acrylic acid-based superabsorbents, the neutralization degree of AMPS part of the new gels had only a small enhancing effect on their swelling capacity. The effect of total monomer concentration on the hydrogel absorbency was also studied. The fully ionic hydrogels showed an unusual pH-independency behavior, so that their absorbency was nearly unchanged in a wide range of pH. Such unexpected behavior was also observed for the swelling in the ionic environments with various ionic strengths. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, a multifunctional superabsorbent composite from acrylic acid, acrylamide (AM), sodium humate (SH) and attapulgite (APT), PAA-AM/SH/APT, was synthesized by aqueous solution polymerization, using N,N′-methylenebisacrylamides (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator.
Abstract: A novel multifunctional superabsorbent composite from acrylic acid (AA), acrylamide (AM), sodium humate (SH) and attapulgite (APT), PAA-AM/SH/APT, was synthesized by aqueous solution polymerization, using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator. In this paper, not only the effects of the ratio of AA to AM, SH and APT content on the saturated water absorbency, but also various swelling behaviors of the composite were systematically investigated. The results show that comprehensive performances of the superabsorbent are improved by introducing functional components into a poly(acrylic acid-acrylamide) (PAA-AM) network. Functionality of the composite in practice was also investigated by studying the release of SH and by growing Elymus dahuricus Turcz (a kind of grass) plants in soil with and without using the superabsorbent composite. The roots and stems of Elymus dahuricus Turcz were found to be sturdier compared with the plants grown without the superabsorbent composite. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, two closely related polyimide foams (TEEK-H series and TEEK-L series) were investigated for density effects and closed versus open cell effects on the thermal, mechanical, and flammability properties.
Abstract: Activity at the NASA Langley Research Center (LaRC) has focused on developing low density polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohol at room temperature. Monomer blends may be used to make a variety of polyimide foams with varying properties. The first foaming process developed consisted of thermal cycling the polymer precursor residuum and allowing the inflation of the particles to interact to create the foam. This process has resulted in foam structures with higher percentages of open cell content. Another innovative foaming process has been developed that begins with partially inflated microspheres, “friable balloons”, with incomplete polymer molecular weight gain, which when fully cured into a foam results in more closed cell structures.
In a research study performed by NASA Kennedy Space Center (KSC) and LaRC, two closely related polyimide foams, TEEK-H series and TEEK-L series, (4,4′-oxydiphthalic anhydride/3,4′-oxydianiline and 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride/4,4′-oxydianiline) were investigated for density effects and closed versus open cell effects on the thermal, mechanical, and flammability properties. Thermal conductivity data under the full range of vacuum pressures indicate that these materials are effective insulators under cryogenic conditions. Contributing factors such as cell content, density, and surface area were studied to determine the effects on thermal conductivity. Cone calorimetry data indicated decreased peak heat release rates for the closed cell system, TEEK-H friable balloons, compared to the TEEK foams with higher open cell content. Mechanical properties including tensile strength and compressive strength indicated that the materials have good structural integrity. Foams with more open cell content resulted in greater tensile and compressive strengths than the closed cell foams. The maximum closed cell content achieved in the “friable balloon” system was 78% at a foam density of 0.048 gm/cm3. Published in 2005 by John Wiley & Sons, Ltd.
TL;DR: In this paper, sterically stabilized magnetite nanoparticles in polydimethylsiloxane (PDMS) carrier fluids have been prepared for potential biomedical applications, where the PDMS stabilizers were adsorbed onto the magnetite surfaces via the carboxylate groups in an interfacial reaction at an acidic pH.
Abstract: Dispersions of sterically stabilized magnetite nanoparticles in polydimethylsiloxane (PDMS) carrier fluids have been prepared for potential biomedical applications. Trivinylsiloxy-terminated PDMS was functionalized with mercaptoacetic acid or mercaptosuccinic acid to afford PDMS stabilizers containing either three or six carboxylic acid groups, respectively, at one chain-end. Magnetite nanoparticles were synthesized by a chemical co-precipitation reaction of FeCl2 and FeCl3 with hydroxide at pH 9‐10. Subsequently, the PDMS stabilizers were adsorbed onto the magnetite nanoparticle surfaces via the carboxylate groups in an interfacial reaction at an acidic pH. The complexes were characterized with transmission electron microscopy to establish an average particle diameter of 7.4 � SD 1.7nm and approximately spherical shape. Complexes containing up to 67wt% magnetite were prepared using these PDMS stabilizers, resulting in maximum saturation specific magnetizations of � 50emug � 1 . The polymer-magnetite nanoparticle complexes could be dispersed in PDMS oligomers to afford polysiloxane ferrofluids. Copyright # 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, the proton conductivities of block copolyimide membranes were measured as functions of the relative humidity and temperature using four-point-probe electrochemical impedance spectroscopy.
Abstract: In this article novel sulfonated block copolyimides with various diamine compositions and block chain lengths were synthesized by chemical imidization using a two-pot procedure. The proton conductivities of the block copolyimide membranes were measured as functions of the relative humidity and temperature using four-point-probe electrochemical impedance spectroscopy. The proton conductivity of the membranes strongly depended on the block chain lengths and increased with an increase in the block chain lengths. The proton conductivity of NTDA-BDSA-b-6FAP (112/48) as the block copolyimide membrane was approximately 0.35 S cm−1 which indicated a higher value when compared to that determined for Nafion®. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: The entropically-driven ring-opening polymerization of macrocyclic monomers is a relatively new method of polymer synthesis that exploits the well-known phenomenon of ring-chain equilibria as mentioned in this paper.
Abstract: The entropically-driven ring-opening polymerization of macrocyclic monomers (> ca. 14 ring atoms per repeat unit) and/or macrocyclic oligomers is a relatively new method of polymer synthesis that exploits the well-known phenomenon of ring-chain equilibria. It attracts interest because of its novel features. For example, these ring-opening polymerizations emit no volatiles and little or no heat. This review considers the principles of entropically-driven ring-opening polymerizations, gives selected examples and discusses potential applications. The latter include micromolding, high throughput syntheses and the synthesis of supramolecular polymers. Copyright (c) 2005 John Wiley T Sons, Ltd.
TL;DR: Frontal polymerization (FP) is a particular technique in which the heat released by the exothermal reaction of monomer to polymer conversion is exploited to promote the formation of a hot traveling front able to propagate and self-sustain the reaction.
Abstract: Polymeric products are largely used for consolidation of stone in the field of cultural heritage. Nevertheless, the main problem of polymeric compounds is related to their macromolecular nature, it being difficult for a polymer to penetrate inside the pores which may have a very small diameter. These considerations are the starting points for in situ polymerization. According to this technique, not the pre-formed polymer, but the monomer is introduced into the stone and it is polymerized in situ in a subsequent step.
Frontal polymerization (FP) is a particular technique in which the heat released by the exothermal reaction of monomer to polymer conversion is exploited to promote the formation of a hot traveling front able to propagate and self-sustain the reaction.
In the present work, FP is performed inside the pores of the stone and the results lead to the conclusion that the hot front is still active in the presence of an inorganic material which dissipates partially the heat released during the polymerization. In addition some recent applications of FP are discussed in comparison with the traditional polymerization for the in situ consolidation and protection of stones. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this paper, a poly(acrylic acid)/sodium humate superabsorbent composite was synthesized by aqueous solution polymerization of acrylic acid using N, N'-methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator in the presence of sodium humate.
Abstract: A novel poly(acrylic acid)/sodium humate superabsorbent composite was synthesized by aqueous solution polymerization of acrylic acid using N, N'-methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator in the presence of sodium humate. The effects on water absorbency such as initial monomer concentration, degree of neutralization of acrylic acid, amount of crosslinker, initiator and sodium humate, etc. were investigated. The water absorbency of the superabsorbent composite synthesized under optimal synthesis conditions with a sodium humate content of 20% exhibited an absorption of 1268 g H2O/g sample and 93 g H2O/g sample in distilled water and in 0.9 wt% NaCl solution, respectively. Swelling rate and water retention tests were also carried out. The results show that sodium humate, as a kind of functional filler, can enhance comprehensive properties of superabsorbent composite and reduce the product cost significantly. Copyright (c) 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, a detailed investigation of the effects of cellulose amount and solvent (aqueous NaOH) concentration on MCC solubility has been presented, and the results show that an optimal NaOH concentration range can always be found to give the best solution of MCC having a certain weight.
Abstract: A cost-effective and environmentally friendly method to dissolve microcrystalline cellulose (MCC) has been utilized. A detailed investigation of the effects of cellulose amount and solvent (aqueous NaOH) concentration on MCC solubility has been presented. In the experiments, NaOH solutions with concentrations ranging from 3.7 to 18.6 wt% have been employed to dissolve MCC with various weights. The results show that an optimal NaOH concentration range can always be found to give the best solubility of MCC having a certain weight. The solubility monotonically decreases with either the decreasing or increasing of NaOH concentration away from the optimal concentration range. In addition, the optimal concentration range of NaOH for dissolving cellulose has been shown to shrink as the amount of MCC increases. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: A series of water-soluble N-substituted poly(alkylanilines) (PNAAs) have been enzymatically synthesized with a variety of groups, from methyl to n-butyl.
Abstract: A series of water-soluble N-substituted poly(alkylanilines) (PNAAs) have been enzymatically synthesized with a variety of groups, from methyl to n-butyl, such as poly(N-methylaniline), poly(N-ethylaniline), poly(N-butylaniline) and poly(N-phenylethanolamine). The syntheses were made in the presence of poly(4-sodium styrene sulfonate) (SPS) as a template and horseradish peroxidase (HRP) as a catalyst. The size and type of the groups have a great effect on the properties of the final polymers. UV-vis spectroscopy and cyclic voltammetry measurements confirmed that for enzymatically synthesized PNAAs/SPS complexes, the electroactivity increased with the bulkiness of the substituents. These polymers have been studied in the doped and undoped states by FT-IR and UV-vis spectroscopy. Also these polymers show multiple and reversible optical transitions that can be ascribed to the formation of polaron and bipolaron states. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: The NCO-terminated prepolymers, prepared by reacting a mixture of poly(tetramethylene glycol) and fumed nanosilica with 4,4′-diphenylmethane diisocyanate, were chain-extended with 1,4- butanediol to yield polyurethane-silica nanocomposites as mentioned in this paper.
Abstract: The NCO-terminated prepolymers, prepared by reacting a mixture of poly(tetramethylene glycol) and fumed nanosilica with 4,4′-diphenylmethane diisocyanate, were chain-extended with 1,4- butanediol to yield polyurethane-silica nanocomposites. The nanosilica particles were well dispersed in the polyurethane matrix up to 3 wt%. The polyurethane chains in the interfaces were covalently linked to the nanosilica surfaces through urethane bonds. Introduction of the nanosilica into the polyurethane enhanced both tensile strength and elongation of the resulting nanocomposite films. Especially, the elongation at break of the nanocomposite films containing 1 wt% nanosilica was 3.5 times greater than that of the pure polyurethane films. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, the stability of metal insulator semiconductor (MIS) transistors based on α-sexithiophene was investigated and the kinetics of the threshold voltage shift upon application of a gate bias was determined.
Abstract: An investigation into the stability of metal insulator semiconductor (MIS) transistors based on α-sexithiophene is reported. In particular the kinetics of the threshold voltage shift upon application of a gate bias has been determined. The kinetics follow a stretched-hyperbola type behavior, in agreement with the formalism developed to explain metastability in amorphous–silicon thin film transistors. Using this model, quantification of device stability is possible. Temperature-dependent measurements show that there are two processes involved in the threshold voltage shift, one occurring at T≈220 K and the other at T≈300 K. The latter process is found to be sample dependent. This suggests a relation between device stability and α-sexithiophene deposition parameters. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this article, two kinds of chitosan derivatives, crosslinked chitosa derivatives and supported palladium complexes (CL-CTS-Pd) were synthesized and characterized by X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), differential thermal analysis (DTA), etc.
Abstract: Two kinds of chitosan derivatives, crosslinked chitosan and crosslinked chitosan condense with salilylaldehyde, supported palladium complexes (CL-CTS-Pd and CL-S-CTS-Pd) were synthesized and characterized by X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), differential thermal analysis (DTA), etc. These complexes are efficient catalysts for the Heck reaction under atmospheric conditions and can be easily recovered and reused. The detailed studies show that the catalyst CL-S-CTS-Pd is much more efficient than CL-CTS-Pd under the same conditions. CL-S-CTS-Pd keeps its catalytic activity in the Heck reaction of acrylic acid with iodobenzene even at a low temperature (60°C) or with tiny amounts of the catalyst (0.05 mol%Pd). Yields of making cinnamic acid were even as high as 75.3% in the Heck reaction of acrylic acid with iodobenzene using CL-S-CTS-Pd that was recovered 10 times. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: Graphite-polymer nanocomposites were prepared by melt blending of various graphites (virgin graphite, expandable graphites, and expanded graphite) with polystyrene and its copolymers as mentioned in this paper.
Abstract: Graphite-polymer nanocomposites were prepared by melt blending of various graphites (virgin graphite, expandable graphites, and expanded graphite) with polystyrene and its copolymers (acrylonitrile-butadiene-styrene (ABS) and high-impact polystyrene (HIPS)). Nanocomposites were characterized by X-ray diffraction, cone calorimetry, thermogravimetric analysis and evaluation of mechanical properties. Nanocomposite formation occurs at higher loadings (3–5%) of expandable graphites but not for virgin or expanded graphite. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this paper, self-assembled honeycomb polycarbonate films were deposited on polymer piezoelectric (poled polyvinylidene fluoride) substrates under a fast dip-coating process.
Abstract: Self-assembled honeycomb polycarbonate films were deposited on polymer piezoelectric (poled polyvinylidene fluoride) substrates under a fast dip-coating process. Ordered structures with micro-scaled pores dispersed in the polycarbonate matrix were obtained, demonstrating 2D hexagonal packaging. Theoretical model explaining self- assembling process is proposed. Fabricated structures have a potential as 2D tunable photonic crystals. Photonic bandgap location was estimated. Visible-IR transmittance spectrum of the self-assembled films was studied with a FTIR spectrometer. Diffraction properties of the honeycomb patterns were investigated. High transparency of the components makes possible IR optics applications of obtained structures.
TL;DR: In this article, a flame retardant (4-diphenylphosphoryloxyphenoxy)(4-hydroxymhenoxy)cyclotriphosphazene (PPPZ) was prepared and characterized by FT-IR, 31P-NMR and 1HNMR spectroscopy.
Abstract: A novel flame retardant (4-diphenylphosphoryloxyphenoxy)(4-hydroxyphenoxy)cyclotriphosphazene (PPPZ) was prepared and characterized by FT-IR, 31P-NMR and 1H-NMR spectroscopy. Polyurethanes that contained aromatic phosphate groups attached to cyclotriphosphazene, with various phosphorus contents, were prepared from PPPZ, poly(propylene glycol), 1,4-butanediol, and 2,4-toluene diisocyanate by one-step polymerization. The polymers prepared were characterized by FT-IR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and oxygen index (LOI) measurements. The effect of the concentration of PPPZ on the thermal behavior of the polyurethane was studied. The results indicated that the glass transition temperature (Tg) of the polyurethane increased with the concentration of PPPZ. The PPPZ-containing polyurethanes exhibited slightly higher temperatures of degradation and higher char yields than PPPZ-free polyurethanes. Moreover, the LOI of the polyurethanes increased with increasing PPPZ content. Also studied was the possible mechanism of the flame retardancy. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this paper, the thermal behavior of a series of poly(ethylene oxide) (PEO)/stearic acid blends was investigated by means of differential scanning calorimetry (DSC), modulated temperature DSC, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) for application as thermal energy storage materials.
Abstract: The thermal behavior of a series of poly(ethylene oxide) (PEO)/stearic acid blends was investigated by means of differential scanning calorimetry (DSC), modulated temperature DSC, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) for application as thermal energy storage materials. It has been found that PEO/stearic acid blends are efficient polymer-based phase change materials that can be applied in the temperature range 55.7–75.2°C with the enthalpy of phase transition values in the range of 202.8–252.3 J/g. The PEO/stearic acid blend (1:3 w/w) exhibits a senergistic effect—its value of enthalpy of melting and crystallization is higher than those of pure components. The origin of this promising effect was investigated by FT-IR and SEM techniques to ascertain the influence of hydrogen bonds on the sample's supramolecular morphology. Copyright © 2005 John Wiley & Sons, Ltd.
TL;DR: In this paper, a bilayer dermal equivalent was fabricated by combining the collagen/chitosan porous scaffold with a silicone membrane, and the results proved that the water vapor permeability of this bilayer derivative was close to normal adult skin.
Abstract: A bilayer dermal equivalent was fabricated by combining the collagen/chitosan porous scaffold with a silicone membrane. The macroscopic shapes and microstructures of the collagen/chitosan scaffolds with or without silicone membrane were illustrated. Water-uptake was characterized by the phosphate buffered saline (PBS)-immersion test. It was found that the glutaraldehyde treated scaffold had a higher water-uptake ratio than that of the thermal treatment. The water vapor permeability of the bilayer dermal equivalent was tested under different humidities at room temperature. The results proved that the water vapor permeability of this bilayer dermal equivalent was close to normal adult skin. Investigation of the mechanical performance found that the bilayer dermal equivalent had a tensile stress of 0.1 MPa and a strain of 30% in the wet state. In vitro cell culture demonstrated that the bilayer dermal equivalent presented in this study did not show any cytotoxicity. Copyright © 2006 John Wiley & Sons, Ltd.
TL;DR: In this article, two conventional methods: low temperature solution polycondensation and short period reflux conditions were performed under microwave conditions with a small amount of o-cresol that acts as a primary microwave absorber.
Abstract: Epiclon [3a,4,5,7a-tetrahydro-7-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-1,3-isobenzofurandione] (1) was reacted with L-methionine (2) in acetic acid and the resulting imide-acid 3 was obtained in high yield The diacid chloride 4 was prepared from diacid derivative 3 by reaction with thionyl chloride Thermostable poly(amide-imide)s containing epiclon structure were synthesized by reacting of diacid chloride 4 with various aromatic diamines Polymerization reaction was performed by two conventional methods: low temperature solution polycondensation and short period reflux conditions In order to compare conventional solution polycondensation reaction methods with microwave-assisted polycondensation, the reactions were also carried out under microwave conditions with a small amount of o-cresol that acts as a primary microwave absorber The reaction mixture was irradiated for 6 min with 100% radiation power Several new optically active poly(amide-imide)s with inherent viscosity ranging from 015 to 036 dl/g were obtained with high yield All of the above polymers were fully characterized by 1H-NMR, FT-IR, elemental analyses and specific rotation techniques Some structural characterizations and physical properties of these new optically active poly(amide-imide)s are reported Copyright © 2005 John Wiley & Sons, Ltd
TL;DR: In this paper, the properties of hyperbranched polymers with linear oligomers for preparing organic-inorganic hybrids, BoltornTM H20 and linear polyester hexa-acrylate (EB830) were selected as organic components for preparing UV-curable transparent hybrid materials using 3-(trimethoxysilyl) propylmethACrylate as a coupling agent via a sol-gel process.
Abstract: To compare the properties of hyperbranched polymers with linear oligomers for preparing organic-inorganic hybrids, hyperbranched aliphatic polyester (BoltornTM H20) and linear polyester hexa-acrylate (EB830) were selected as organic components for preparing UV-curable transparent hybrid materials using 3-(trimethoxysilyl) propylmethacrylate as a coupling agent via a sol-gel process. The prehydrolyzed product of tetraethoxysilane was used as an inorganic component. The effects of inorganic content on the morphologies, thermal behaviors, photopolymerizaiton kinetics and mechanical properties of the hybrids were investigated. The results show that for hyperbranched polyester-based hybrids, the organic phase shows much better compatibility with inorganic phase even at high inorganic component content due to its special spheral shape and plenty of functional end groups, compared with linear EB830-based hybrids. Copyright © 2004 John Wiley & Sons, Ltd.