Abstract  A new polythiophene derivative has been synthesized by both chemical and electrochemical oxidative polymerization of the monomer 3,4-ethylenedithiathiophene (EDTT). Both methods produce a polymer which is completely soluble in 1-methyl-2-pyrrolidinone (NMP) and partly soluble In tetrahydrofuran (THF) and chloroform. The FT-IR spectra of the neutral polymer indicate a regular structure formed via alpha,alpha coupling of thiophene rings. The new polymer shows two absorption bands at 341 nm and 413-419 nn in NMP solution in the UV-vis region. Photoexcitation of the polymer in dilute NMP solution results in a broad band luminescence with peak at ca. 552 nm. The redox behavior of the polymer was studied by cyclic voltammetry in 0.1 M (Bu(4)N)ClO4 acetonitrile solution. The average molecular weights have been determined by gel permeation chromatography (GPC) to be M(n) similar to 3.03 x 10(3) and M(n) similar to 4.75 x 10(3) for the chemically and electrochemically synthesized polymer, respectively. Electron spin resonance data are reported. Thermal gravimetric analysis studies show that the new polymer is stable in nitrogen up to 276 degrees C. The chemically doped (with FeCl4-) polymer and the electrochemically doped (with ClO4-) polymer show electrical conductivity of 0.1 and 0.4 S/cm at room temperature, respectively. These results are compared to some previously characterized polythiophenes.

Abstract  Poly (L-lactic acid) (PLLA) membranes were fabricated through immersion precipitation method. 1, 4-dioxane (DX), N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF), N, N-dimethyl-acetamide (DMAc), and DX/NMP, DX/DMF and DX/DMAc were used as solvents severally. With a focus on the PLLA/DX/NMP/H2O system, the effect of solvent mixture on PLLA membrane was investigated by altering the ratio of DX/NMP. Various membrane morphologies were obtained, which were further correlated by mean of solubility parameter and viscosity of casting solution. It was found that the membrane cast with DX/NMP (1/1) exhibited ideal structure and better performance compared with membranes cast with same concentration of PLLA.

Abstract  Single-walled carbon nanotubes (SWNTs) were dispersed in N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), and NN-dimethylacetamide (DMA), respectively. The nonlinear optical properties of SWNT dispersions were studied using the open aperture Z-scan technique at 532 nm. The nonlinear extinction coefficients strongly increase with increasing SWNT concentration. In the three dispersions, the DMF dispersions show the strongest nonlinear extinction effect. In conjunction with this, the optical limiting performance is also superior for the DMF dispersions. Compared with DMF and DMA, NMP has a much better debundling effect for SWNTs; however, the optical limiting properties of the NMP dispersions is inferior. The SWNT dispersions seem to attenuate the intense light more effectively, as is shown by the stronger optical limiting response compared to the zinc plithalocyanine solution, at the same concentration. The static light scattering experiment revealed that the DMF dispersions have the largest average bundle size. The main origin of the optical limiting effect of the SWNT dispersions is due to the solvent and/or carbon vapor bubble-induced nonlinear scattering. Our results show that the average bundle size of SWNTs in combination with the physical properties of the solvent dominate the nonlinear extinction and optical limiting properties of SWNT dispersions.

Abstract  Nonlinear optical and optical limiting properties of a range of single-walled carbon nanotube dispersions prepared in N-methyl-2-pyrrolidinone (NMP) were studied using the open aperture Z-scan technique at 532 nm. As the appropriate thermodynamic properties of the solvents are much more important than the bundle size of nanotubes for improving the optical limiting performance, the solvent parameters were controlled by either changing the temperature of the dispersions or blending a secondary solvent. While the optical limiting performance can be varied freely by increasing or decreasing the temperature from room temperature to 100 degrees C, the reduction of temperature below the freezing point of NMP and then down as far as -80 degrees C has little influence on the limiting. performance. As a result of adding a small amount of organic solvent into the NMP dispersions, the nonlinear optical responses were enhanced significantly clue to the reduction of surface tension and other parameters. By contrast, the addition of water leads to a decrease in the optical limiting response. Nanotube dispersions in water/surfactant exhibit a similar limiting performance to the nanotubes in NMP. Our results reveal that the optical limiting performance of the nanotube dispersions can be engineered by adjusting the solvent properties. Because the carbon nanotube dispersions are typical of the thermally induced light scattering dominated optical limiting materials, we believe the conclusions tit not only the nanotubes but also other nanomaterials with the similar limiting mechanism.

Abstract  The effects of dope flow rate and flow angle within a spinneret during spinning hollow fiber membranes on the morphology, water permeability and separation performance of poly(ethersulfone) ultrafiltration hollow fiber membranes were investigated. For this purpose, two spinnerets with different flow angles were designed and used. The dope solution, containing polyethersulphone (PES)/N-methyl-2-pyrrolidone (NMP)/diethylene glycol (DG) with a weight ratio of 23/41/36, which was very close to its cloud point (binodal line), was used in order to speed up the coagulation of nascent fibers so that the relaxation effect on molecular orientation was reduced. The wet-spinning process was purposely chosen to fabricate the hollow fibers without extra drawing. Therefore, the effects of gravity and elongation stress on fiber formation could be significantly reduced and the orientation induced by shear stress within the spinneret could be frozen into the wet-spun fibers. Experimental results suggest that higher dope flow rates (shear rates) in the spinneret produce UF hollow fiber membranes with smaller pore sizes and denser skin layers due to the enhanced molecular orientation. Hence, the pore size and the water permeability decrease, but the solute separation increases. Hollow fibers spun from a conical spinneret have smaller mean pore sizes with larger geometric standard deviations, thus exhibiting lower water flux and greater solute separation than hollow fibers spun from a traditional straight spinneret. In addition. SEM studies indicate macrovoids response differently for the 90degrees straight and 60degrees conical spinnerets when increasing the dope flow rate. Macrovoids can be significantly suppressed and almost disappear in the 90degrees spinneret at high dope flow rates. This phenomenon cannot be observed for the 60degrees conic spinneret. (C) 2004 Elsevier B.V. All rights reserved.

Abstract  This paper demonstrates a methodology for preparing patterned graphene films through the destabilization of dispersed graphene in N-methyl-pyrrolidone (NMP) by addition of water, which causes the graphene to be trapped at the interface of NMP/hexane. The trapped graphene film is transferred onto the patterned wetting/nonwetting surface through dip-coating process. The quality of graphene film is studied by scanning electron microscopy and atomic force microscopy. The sheet resistance of graphene film is 1.49 x 10(2) k Omega/square with surface coverage of 70% measured by the four-probe method. Field effect transistor based on such patterned graphene film is then fabricated. The current on/off ratio of devices is 1.24 with field-effect hole mobility of 159 cm(2)/Vs.

Abstract  La0.6Sr0.4Co0.2Fe0.8O3-alpha (LSCF) perovskite powders having a submicrometer size were synthesized by a sol-gel autocombustion method. From these powders, the gastight LSCF hollow-fiber membranes with a highly asymmetric structure comprising a dense layer of thickness ca. 88 mu m integrated with a porous substrate were fabricated in a single step through a phase inversion/sintering technique with a mixture of N-methyl-2-pyrrolidone (NMP) and water as internal coagulant. Oxygen permeation fluxes through the obtained hollow-fiber membranes were measured under air/He gradients at different temperatures. The results indicate that the highly asymmetric hollow-fiber membranes possess an oxygen permeation flux of 0.11-2.19 mL cm(-2) min(-1) in the temperature range of 650-1000 degrees C, which is 2.6-10.5 times higher than that of the sandwich-structured hollow-fiber membranes. Oxygen permeation in the hollow-fiber membranes is limited primarily by the surface exchange reactions at lower temperatures, but ionic bulk diffusion will have a rate-limiting effect at temperatures higher than 900 degrees C.

Abstract  To investigate the benefits of pretreatment in pyrolysis of heavy fractions, a feedstock in the range of gas oil has undergone aromatic extraction at different temperatures and solvent/oil ratios with n-methyl-2-pyrrolidone as the solvent. The raffinate with least aromatic content in addition to the original feed were subjected to steam cracking at different operating conditions to compare their product distributions with respect to the individual effects of temperature, flow rate, and dilution ratio. The experimental design was carried out with the use of the central composite design methodology. We find that the yields of ethylene, propylene, and butylenes increase by more than 10% upon dearomatization. The liquid products with five or more carbon atoms decrease by 13% on average. From desirable products, only butadiene reduced by about 18% upon extraction. Furthermore, a practical selectivity factor was proposed to support the preference of low residence time cracking and more generally to scrutinize the performance of the steam cracking process. Simulation results suggested a 2-fold increase in furnace run length in possible application of this treatment in a real olefin plant.

Abstract  Generating power from HyperCoal is a high- efficiency process in which the organic portion of coal is extracted with industrial solvents at a temperature around 360 degrees C and fed to a gas turbine directly. This study sought to establish a selection index for identifying subbituminous coals that give high extraction yields. Subbituminous coals were extracted at 360 degrees C with flowing industrial solvents, and we investigated the relationship between the extraction yield and the quantity of oxygen-containing functional groups in the coal. The extraction yield with a polar solvent, crude methylnaphthalene oil ( CMNO), increased with the quantity of carboxylate groups bridged by metal cations, such as Ca2+ and Mg2+ (COOM). The correlation coefficient between the extraction yield and the quantity was 0.82. Acid treatment of coal before extraction released COOM cross-links, increasing the extraction yield. These results suggest that the thermal extraction of lowrank coals strongly depends on the cross-links rather than the hydrogen bonds. Therefore, the thermal extraction yields of low- rank coals can be estimated from the quantity of COOM in the original coals. The intercept of the regression line between the quantity of COOM and the extraction yield with CMNO was 57.8%. This value is the average extraction yield for low- rank coals with free COOM.

Abstract  Infinite dilution activity coefficients y(i)(infinity) have been measured for various solutes (alkanes. alkenes. cycloalkanes, cycloalkenes. aromatics. alcohols, ketones, esters, ethers, and water) in the five ionic liquids 1-methyl-3-methyl-imidazolium methylsulfate [MMIM](+)[CH3SO4](-). 1-methyl-3-methyl-imidazolium methoxyethylsulfate [MMIM](+)[CH3OC2H4SO4](-). 1-methyl-3-methyl-imidazolium dimethylphosphate [MMIM](+)[(CH3)=PO4](-), N-ethylpyridinium bis(trifluoromethylsulfonyl) imide [C5H5NC2H5](+)[(CF3SO2)(2)N](-), and pyridiniumethoxyethylsulfate [C5H5NH](+)[C2H5OC2H4OSO3](-) in the temperature range from 303.15 to 373.15 K. Additionally. densities of the investigated ionic liquids were measured in the temperature range from 293.15 to 353.15 K. Using all available gamma(i)(infinity)-data, the selectivities S-ij(infinity)= gamma(i)(infinity)/gamma(i)(infinity) and the capacities k(i)(infinity) = 1/gamma(i)(infinity) at infinite dilution were determined for different separation problems not only for ionic liquids, but also N-methyl-2-pyrrolidone (NMP) and ethylene glycol. (C) 2004 Elsevier B.V All rights reserved.

Abstract  We used X-ray photoelectron spectroscopy (XPS) to examine structural changes in the chemical form of nitrogen in coal induced by thermal extraction with organic or industrial solvents (HyperCoal (HPC) production). Changes during solvent extraction depended on the chemical form of nitrogen in the coal. HyperCoal nitrogen primarily consisted of pyrrole nitrogen (pyrrole-N), with less pyridine nitrogen (pyridine-N) and no quaternary nitrogen (quaternary-N). The extracted residue contained pyridine-N and quaternary-N as well as pyrrole-N. Quaternary-N decreased during extraction, while the amount of pyridine-N increased, and relatively a little change was observed in pyrrole-N. It is thought that much of the quaternary-N decomposed during thermal extraction and was converted to pyridine-N. (C) 2012 Elsevier B.V. All rights reserved.

Abstract  We analyzed the solid-state C-13 cross-polarization/magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectra of three types of coal samples that had been immersed in toluene or n-hexane for 1 h. The coal samples were from the United States (Upper Freeport (UF) reserve, 86 wt % carbon, and Wyodak (WY) reserve, 75 wt % carbon), and Australia (Yallourn (YL) reserve, 65 wt % carbon). The spectra of toluene- and n-hexane-immersed UF and n-hexane-immersed WY coals were identical to the spectra of the corresponding fresh coals: sorbed molecule peaks were not observed, which indicates that almost all the molecules in these coals were in a mobile state. The spectra of toluene- and n-hexane-immersed YL coal and toluene-immersed WY coal showed peaks for toluene and n-hexane, demonstrating that some of the molecules were bound relatively strongly to the coal. The C-1 carbon of toluene was not observed in the CP/MAS NMR spectra of toluene-immersed YL and WY coals, so it is possible that the toluene molecules observed in the NMR spectra were bound to these coals at the methyl or C-4 carbon through an OH(coal)-pi(toluene) interaction. In the CP/MAS spectrum of n-hexane-immersed YL, the C-3 carbon of n-hexane was observed, but the C-1 and C-2 carbons were not. This result indicates that n-hexane molecules may bind to the coal only at C-3, whereas the C-1 and C-2 carbons remain more mobile. For YL coal immersed in toluene or n-hexane, or WY coal immersed in toluene, the observed peak intensities of toluene or n-hexane in the coals were smaller than expected, given the content. This result indicates that a proportion of the toluene or n-hexane molecules in the coal interacted relatively strongly with the coals via OH-pi bonding and that the remaining molecules were in a mobile state and interacted weakly with the coals by pi-pi bonding or some other weak interaction.

Abstract  Electron spin resonance (ESR) spectroscopy has been used as a method to study membrane fouling during ultrafiltration (UF). Bovine serum albumin (BSA) and polyethylene oxide (PEO), with and without TEMPO (spin probe), solutions in water were used as the feed in the UF experiments. Asymmetric membranes were prepared by phase inversion technique using casting solutions of polyethersulfone (PES) in n-methyl pyrrolidone (NMP). Polyvinyl pyrrolidone (PVP) was added as a nonsolvent additive. The fouling of the membrane was dependent on the size and shape of the macromolecular solute and the operating feed pressure. Tt was also observed that the mobility of the deposited macromolecular solute in the membrane pore became the least in a certain range of pore size of UF membranes and this minimum mobility was also dependent on the operating pressure. (C) 2000 Elsevier Science B.V. All rights reserved.

Abstract  In this paper we test our proposed methodology for a calibration procedure for mass determination by size exclusion chromatography. A sample is coarsely fractionated oil column and when the fractions are examined by matrix assisted laser desorption-ionisation mass spectrometry a direct variation of molecular mass with retention is found. Importantly the chromatograms produced when using N-methyl-2-pyrrolidinone as eluant are found to be free from solute association effects over a wide range of concentrations. The examination of a gasifier char is presented as a unique application of this chromatographic system. (C) 1998 Elsevier Science Ltd. All lights reserved.

Abstract  This paper reports the fractionation and subsequent examination of two, very different coal derived materials, a coal tar pitch and a commercial liquefaction extract. These were separated on the basis of their retention in a typical preparative size exclusion chromatography apparatus using THF as the eluent. Matrix assisted laser desorption mass spectrometry, using the small molecules of the sample as matrix, has been used to examine the various fractions from preparative s.e.c. and the peak mass intensities have been used to define an absolute calibration of the s.e.c. separation. Limitations of the methods are discussed. The u.v.-fluorescence spectra of the fractions were recorded and trends in the spectra are described. The fractions were also analyzed by size exclusion chromatography employing N-methyl-2-pyrrolidinone as the chromatographic eluent. The main advantages of this system over traditional solvents is the avoidance of surface adsorption effects observed with THF and the more complete solution of coal-derived material. (C) 1998 Elsevier Science Ltd. Ail rights reserved.

Abstract  A synthetic polymer, polyvinylpyrrolidone (PVP - E 1201) primarily finds applications in the pharmaceutical and food industries due to its resistance and zero toxicity to organisms. After ingestion, the substance passes through the organism unchanged. Consequently, it enters the systems of municipal wastewater treatment plants (WWTP) without decomposing biologically during the waste treatment process, nor does it attach (through sorption) to particles of activated sludge to any significant extent, therefore, it passes through the system of a WWTP, which may cause the substance to accumulate in the natural environment. For this reason the paper investigates the potential to initiate aerobic biodegradation of PVP in the presence of activated sludge from a municipal wastewater treatment plant. The following agents were selected as the initiators of the biodegradation process - co-substrates: acrylamide, N-acethylphenylalanine and 1-methyl-2-pyrrolidone, a substance with a similar structure to PVP monomer. The biodegradability of PVP in the presence of co-substrates was evaluated on the basis of biological oxygen demand (BOD) as determined via a MicroOxymax O-2/CO2/CH4 respirometer. The total substrate concentration in the suspension equaled 400 mg.dm(-3), with the ratio between PVP and the co-substrate being 1:1, while the concentration of the dry activated sludge was 500 mg.dm(-3). Even though there was no occurrence of a significant increase in the biodegradation of PVP alone in the presence of a co-substrate, acrylamide appeared to be the most effective type of co-substrate. Nevertheless, a recorded decrease in the slope of biodegradation curves over time may indicate that a process of primary decomposition was underway, which involves the production of metabolites that inhibit activated sludge microorganisms. The resulting products are not identified at this stage of experimentation.

Abstract  The pendant drop method, combined with efficient temperature control of the measuring cell, allows high precision measurements of both surface tension and interfacial tension. The surface tensions and liquid densities of mixtures of cyclohexane + heptane, cyclohexane + propanone, and toluene + propanone have been determined at a normal pressure of 1 bar over the temperature range from 287 K to 317 K. The surface tension data could be parametrized with a cubic polynomial. Gibbs excess surface concentrations are derived from our experimental data, and the influence of activity coefficients is discussed. The high precision pendant drop apparatus allows accurate measurements of the interfacial tension in systems with liquid-liquid phase separation. In binary mixtures of heptane + N,N-dimethylformamide, heptane + N-methyl-2-pyrrolidone, and decane + N,N-dimethylformamide, the interfacial tension was measured over a wide temperature range close to the critical solution point. The densities of the corresponding liquid phases were obtained by buoyancy measurements. The accuracy of the density measurements is Deltarho = +/-0.0001 g(.)cm(-3) for the vibrating tube densimeter; for the buoyancy measurements we find Deltarho = +/-0.0005 g(.)cm(-3). The reproducibility of the surface tension measurements is generally better than Deltasigma = +/-0.50% at the 95% confidence level. Standard deviations for all experimental values are given in the tables. The resulting data are parametrized using polynomial and Wegener expansion type equations.

Abstract  Integral asymmetric polyetherimide (PEI) hollow fiber membranes were prepared using N-methyl-2-pyrrolidone (NMP) as a solvent and ethanol as a nonsolvent-additive (NSA). Two polymer dopes with polymer concentrations 30 and 25 wt% and the coagulation value 1.0 g were formulated. The mass ratio of ethanol NMP in these polymer dopes was 0.2. Water was used as both an internal and external coagulant. Hollow fibers with an outer diameter of about 600 mu m and an inner diameter of about 300 mu m were prepared at different air-gaps. The membrane structure and gas separation properties were examined. The results reveal that the length of air-gap plays an important role in the spinning process and greatly affects the membrane separation performance. Non-coated asymmetric membranes with He/N-2 selectivity as high as about 90 were obtained within an optimum range of air-gap lengths. After silicone-coating, the membranes prepared exhibit outstanding selectivity and moderate permeation flux. Gas permselection properties for N-2, CH4, Ar, CO2, O-2, H-2, and He through the PEI membranes were investigated in some detail as a function of pressure and temperature. (C) 1998 Elsevier Science B.V.

Abstract  ne open-circuit voltage increases substantially and stability of dye-sensitized TiO2 solar cells is improved when polymer gel containing poly (vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP) in N-methyl-2-pyrrolidone replaces commonly used solvents such as acetonitrile (ACN) and 3-methoxypropionitrile (MPN). The energy conversion efficiency of the cell with 6 wt % PVdF-HFP is comparable to that obtainable in ACN and in MPN. The promising effect of PVdF-HFP as a gelator is attributed to its interaction with Li+ ions. (C) 2004 The Electrochemical Society.

Abstract  Two related propositions addressing the interpretation of size-exclusion chromatograms of heavy hydrocarbon liquids have been examined. First. that peaks observed at, the exclusion (short, retention time) limits of size exclusion chromatography (SEC) columns. when using 1-methyl-2-pyrrolidinone (NMP) as eluent, are due to aggregation brought about by sample polarity. Second, that the addition of salts such as LiBr to the NMP eluent dissipates ionic binding forces and causes the disaggregation of polar clusters. The resulting shift to longer elution times (smaller masses) is then interpreted as representing those of the disaggregated sample molecules. However, in earlier work, we observed that the addition of this salt shifted chromatograms to retention times later than the permeation limits of the analytical columns. The salt appeared to have increased surface interactions between the sample and column packing. Thus, the addition of the salt directly to the SEC eluent did not allow distinguishing, between any possible disaggregation effect and its adverse effect on the size mechanism. In this work, we have attempted to separate the two effects. The samples were fractionated by planar chromatographv (PC) using solvents with dissolved salts: LiBr or tetrabutylammonium acetate (TBAA). Any presumed disaggregation would be expected to take place during the planar chromatographic separation. The fractions were then recovered from the plates and characterized by SEC. Three coal-derived liquids were investigated. The results indicated that the salty solvents were able to mobilize more large-mass material than the solvent alone because the increased polarity of the Salty solvent was better able to displace larger molecules from the polar sites of the silica. SEC showed these fractions to be of larger apparent MM than those recovered in PC using untreated solvents. No evidence of disaggregation was found due to the use of salts.

Abstract  A petroleum atmospheric pressure distillate residue and three tars derived from different coals using different severities of thermal treatment were separated into seven fractions using column chromatography on silica and sequential elution by the solvent sequence pentane, toluene, acetonitrile, pyridine, 1-methyl-2-pyrrolidinone (NMP) and water. The fractions from the four extractions have been compared using size exclusion chromatography (SEC) in NMP as eluent and by synchronous ultra-violet-fluorescence (UV-F). This paper concerns the pentane and toluene soluble fractions only since these are the least polar fractions. By SEC, the size of the aromatic molecules increased from the first pentane soluble fractions to the toluene-soluble fractions, with the petroleum residue fractions of larger size than the equivalent fractions from coal liquids. The three coal tars showed significant differences, indicating that temperature Of pyrolysis had a significant effect on the molecular size. Synchronous UV-F spectra of the four sets of fractions, in solution in NMP, again showed significant differences between the petroleum residue and the coal tars, as well as amongst the three coal tars. In general, the petroleum residue fractions contained smaller aromatic clusters than the coal liquid fractions. These low-polarity fractions contained material excluded from the column porosity in SEC that was unlikely to consist of aggregates of polar molecules.

Abstract  Two series of sulfonated polybenzothiazoles containing naphthalene, derived from either 2,2-bis(4-carboxyphenyl) hexafluoropropane (6FA) or 2,6 naphthalene dicarboxylic acid (NA) were synthesized by polycondensation with non-sulfonated monomer 2,5-diamino-1,4-benzenedithiol dihydrochloride (DABDT) and sulfonated monomer 4,8-disulfonyl-2,6-naphthalene dicarboxylic acid (DSNA). The sPBT-6FA series polymers containing DSNA were soluble in polar aprotic solvents such as dimethyl sulfoxide or 1-methyl-2-pyrrolidinone, whereas sPBT-NA65 with NA was not soluble in common polar aprotic solvents. Therefore, the incorporation of both the naphthalene and flexible hexafluoroisopropylidene units enhanced the solubility of the sPBT polymer series. The polymers were evaluated as proton exchange membranes and exhibited excellent dimensional stability, high thermal and oxidative stabilities, good mechanical properties, and high proton conductivities. The proton conductivities of sPBT-6FA65 were 025 S cm(-1) at 80 degrees C in water and 0.018 S cm(-1) at 120 degrees C under 35% RH. (C) 2015 Elsevier B.V. All rights reserved.

Abstract  Aniline/o-anisidine copolymer (P(An-co-oAs))-intercalated GO composite was synthesized by the delamination/reassembling method in N-methyl-2-pyrrolidone (NMP) solvent, and was characterized by FTIR, XRD, DSC, SEM, TGA, conductivity and cyclic voltammetry. XRD and FTIR spectra indicate that the P(An-co-oAs) exists as a monolayer of outstretched chains in the gallery of GO due to the hydrogen bonds between -NH, =N and -OCH3 groups of P(An-co-oAs) and the oxygen functional groups of the GO layers. The results of thermal analysis show that no de-intercalation of P(An-co-oAs) from GO occurred during heating. Its electrical conductivity has reached 1.9 X 10(-2) S/cm, which is by 3 orders of magnitude higher than that of GO. The intercalation of P(An-co-oAs) also has a pronounced effect on the stabilization of electrochemical response in relation to the GO matrix and P(An-co-oAs). (C) 2005 Elsevier Ltd. All rights reserved.

Abstract  We report the first synthesis of step-growth aromatic polyamide (PA) aerogels made using amine end-capped polyamide oligomers cross-linked with 1,3,5-benzenetricarbonyl trichloride (BTC). Isophthaloyl chloride (IPC) or terephthaloyl chloride (TPC) were combined with m-phenylenediamine (mPDA) in N-methylpyrrolidinone (NMP) to give amine-capped polyamide oligomers formulated with up to 40 repeat units. Addition of the cross-linker, BTC, typically induces gelation in under 5 min. Solvent exchange of the resulting gels into ethanol followed by supercritical CO2 drying gives colorless aerogels with densities ranging from 0.06 to 0.33 g/cm(3), compressive moduli between 5 and 312 MPa, and surface areas as high as 385 m(2)/g. Dielectric properties were also measured in the X-band frequency range. It was found that relative dielectric constant decreased with density as seen with other aerogels with the lowest relative dielectric constant being 1.15 for aerogels with densities of 0.06 g/cm(3). Because of their superior mechanical properties, these aerogels can be utilized in a number of aerospace related applications, such as insulation for rovers, habitats, deployable structures, and extravehicular activity suits, as well as low dielectric substrates for antennas and other electronics. Because of potentially lower cost relative to polyimide and other polymer aerogels, they also have potential for use in more terrestrial applications as well, such as insulation for refrigeration, building and construction, and protective clothing.

Abstract  The effect of heterogeneity of a dope polymer solution on membrane morphology has been investigated. Heterogeneity was developed in polyethersulfone solutions of either gamma-butyrolactone (gamma-BL) or a mixed solvent of gamma-BL/N-methyl-2-pyrrolidone, which exhibit gelation and/or phase separation with aging time. Two different processes for membrane preparation have been employed; Process I, heterogeneity-developed dope solution was cast on a glass plate with a knife for uniform thickness, and immediately immersed into a nonsolvent form of the membrane. Process LI, a dope solution was cast on a glass plate and then aged in a closed environment. After a certain aging time, it was immersed into a nonsolvent to be coagulated. The developed heterogeneity was destroyed markedly during casting in Process I, whereas the heterogeneity was maintained until the moment of immersion into a coagulation medium in Process II. Membranes prepared by Process I were finger-like regardless of the aging time, whereas Process II yielded macrovoid-free and sponge-like membranes having enhanced gas permeance and mechanical strength at long aging times. From these results, it was concluded that the morphology and transport properties of a membrane were able to be controlled by the solution structure, in particular, the solution heterogeneity in the cast film. (C) 1999 Elsevier Science B.V. All rights reserved.