Abstract  Cellulose triacetate (CTA) membranes for forward osmosis (FO) were fabricated in this study. The fundamental engineering and science of CTA membrane formation were explored by casting the membranes from different solvent systems and characterizing the membranes' morphology using advanced tools such as positron annihilation spectroscopy (PAS). N-Methyl-2-pyrrolidone (NMP) and dioxane were used as the solvents for CTA in the membrane fabrication process. It was found that the choice of solvents for membrane fabrication significantly affects the morphology of as-cast membranes and their FO performance. The CTA membrane cast using NMP as the main solvent has shown poor NaCl rejection but high water flux, whereas the CTA membrane cast using dioxane as the main solvent has excellent NaCl rejection but low water flux. SEM and PAS data reveal that the sublayer of CTA membranes cast from dioxane has a close-cell and much denser structure compared to that cast from NMP. As a result, the former has a significantly lower water flux than the latter in the FO process (5 vs. 27 LMH) using a 2 M NaCl draw solution. Surprisingly, with the addition of acetic acid into the dioxane/acetone solvent system, the resulting membrane has a significantly more porous and open-cell sublayer structure. In addition to the pore forming ability of acetic acid, FTIR spectra confirm the formation of acetic acid/dioxane complexes in the casting solution. Thus, as validated by PAS spectra, the free volume of the active layer of the resultant CTA membranes increases after the addition of acetic acid into the dioxane/acetone casting solution and the water flux increases to 23 LMH using a 2 M NaCl draw solution. Molecular simulations were also conducted to examine CTA polymeric chains in different solvent systems and to witness different CTA chain behaviors in these solvents that leads to significant differences in the as-cast membranes' morphology. (C) 2012 Elsevier B.V. All rights reserved.

Abstract  The gas solubility of hydrogen sulfide in aqueous solutions of 32.5 wt.% N-methyldiethanolamine (MDEA) and 12.5 wt.% diethanolamine with 4, 6, and 10 wt.% 2-amino-2-methyl-1-propanol, at 313.15, 343.15, and 393.15 K, has been measured, using a volumetric method for the analysis of the liquid phase, over a range of pressure from 2.5 to 1036 kPa. The experimental results of the gas solubility are given as the partial pressure of H2S against its mole ratio a (mol H2S/mol total alkanolamine) and mole fraction of H2S at each temperature studied. Enthalpies of solution of H2S have been derived from the pressure-temperature concentration data. Experimental solubility data obtained in our laboratory for H2S and CO2 are compared, and it is possible to establish that the aqueous solutions of MDEA, DEA, and AMP studied in this work are highly selective towards H2S under the same conditions of pressure and temperature. (C) 2004 Elsevier B.V. All rights reserved.

Abstract  Using a laser monitoring observation technique, the solubilities of 4-methylbenzoic acid in N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, trichloromethane, acetic acid, and water were measured by a synthetic method at temperatures ranging from 288 K to 370 K at atmospheric pressure. A solubility equation was proposed and verified by experimental results. Differential scanning calorimetry experiments were also performed and discussed.

Abstract  The density, speed of sound, refractive index, viscosity, and surface tension values of binary mixtures formed by N-methyl-2-pyrrolidone (NMP) + 1-amino-2-propanol (MIPA) {or bis(2-hydroxypropyl)amine (DIPA)} were determined at several temperatures from (293.15 to 323.15) K The excess volumes were determined using the density values, and the calculated data have been fitted with a Redlich-Kister equation.

Abstract  The development of organic devices requires the fabrication of thin films, and inkjet printing has been shown to be a suitable method to reach this goal. This work describes the printing process and characterisation of polyaniline (PANI) printed on bond and photographic papers using a desktop inkjet thermal printer. To enable printing, a solution composed by PANI, n-methyl-2-pyrrolidone, ethylene glycol, alcohol and water must be prepared. PANI is printed on bond and photographic paper and then doping of PANI is performed by hydrochloric acid vapour exposure. Micro-Raman spectroscopy showed that PANI printed on paper keeps its basic characteristics. The results from electrical measurements showed that the surface resistivity of the printed PANI samples decreases by increasing the printing number, i.e. the number of layers that were deposited, and depends slightly on the paper type. A stretched semicircle followed by a linear upward tail, attributed to Warburg impedance combined with other intrinsic mechanisms of PANI on porous media, are always present on the Cole-Cole plots obtained for doped-PANI on bond paper. It was shown that these parameters significantly change with the relative humidity, opening the possibility to apply PANI/paper-based devices as humidity sensors. (C) 2012 Elsevier B.V. All rights reserved.

Abstract  The phase behavior of 1-glyceryl monoleyl ether (GME) in mixtures of water and the solvents 1,5-pentanediol (POL) or N-methyl-2-pyrrolidone (NMP) was investigated by ocular inspection, polarization microscopy, and small-angle X-ray diffraction (SAXD). Phase diagrams were constructed based on analyses of more than 200 samples prepared using the two different solvents at 20 °C. The inverse hexagonal phase formed by GME in excess of water was transformed into the cubic and sponge phase with the increasing amount of each solvent. Particularly POL allowed for the formation of an extended sponge phase area in the phase diagram, comprising up to 70% POL-water mixture. The phase behavior using NMP was found to be similar to the earlier investigated solvent propylene glycol. The extended sponge phase for the POL system was attributed to POLs strong surface/interfacial activity with the potential to stabilize the polar/apolar interface of the sponge phase. The cubic and sponge phases formed using POL were further studied by NMR in order to measure the partitioning of POL between the lipid and aqueous domains of the phases. The domain partition coefficient K (lipid domain/aqueous domain) for POL in cubic and sponge phases was found to be 0.78 ± 0.14 and constant for the two phases.

Abstract  La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) hollow fiber membrane precursors were prepared by spinning a starting Suspension containing 68.75 wt % LSCF powders, 6.25 wt % polyethersulfone (PESf), and 25.0 wt % N-methyl-2-pyrrolidinone (NMP) at room temperature using deionized water and tape water as the internal and external coagulants, respectively. High temperature sintering was carried Out in a range of 1200-1500 degrees C to study the influences of the sintering process oil the properties of the LSCF hollow fiber membranes including the microstructure, crystalline phase, mechanical strength, as well as the oxygen permeability. Mechanical strength of the LSCF hollow fibers increased with increasing sintering temperature and reached a maximum of 115 MPa at 1500 degrees C sintering temperature. To obtain gastight LSCF hollow fiber membranes, the sintering temperature must be higher than 1250 degrees C, and the sintering time must be longer than 2 h. However, higher than 1350 degrees C sintering temperature would facilitate the formation of sulfate impurity phases, resulting in noticeable reduction of oxygen permeation flux. The optimum sintering temperature should be around 1300 degrees C, and the sintering time should be within the range of 2-4 h to obtain the gaslight and high flux LSCF hollow fiber membranes.

Abstract  OBJECTIVES: The exposure of seven workers and three on-site study examiners to N-methyl-2-pyrrolidone (NMP) was studied in an adhesive bonding compound and glue production facility.

METHODS: Airborne NMP was analysed by personal and stationary sampling on activated charcoal tubes. NMP and its main metabolites, 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI), were analysed in pre-shift and post-shift spot urine samples by gas chromatography-mass spectrometry. The workers were examined with respect to irritation of the eyes, the mucous membranes and the skin, and health complaints before and after the work-shift were recorded.

RESULTS: The time-weighted average concentration of NMP in most work areas varied between 0.2 and 3.0 mg/m3. During the manual cleaning of stirring vessels, valves and tools, 8-h TWA exposures of up to 15.5 mg/m3 and single peak exposures of up to 85 mg/m3) were observed. NMP and its metabolites were detected in two pre-shift urine specimens. NMP and 5-HNMP concentrations in post-shift urine samples of five workers and three on-site study examiners were below 125 microg/g creatinine and 15 mg/g creatinine, respectively, while two vessel-cleaning workers showed significantly higher urinary NMP concentrations of 472 and 711 microg/g creatinine and 5-HNMP concentrations of 33.5 and 124 mg/g creatinine. 2-HMSI was detectable in four post-shift samples (range: 1.6-14.7 mg/g creatinine). The vessel cleaner with the highest NMP exposure reported irritation of the eyes, the upper respiratory tract and headaches.

CONCLUSIONS: The results of this study indicate a relatively low overall exposure to NMP in the facility. An increased uptake of NMP occurred only during extensive manual vessel cleaning. Health complaints associated with NMP exposure were recorded in one case and might be related to an excessive dermal exposure due to infrequent and inadequate use of personal protective equipment.

Abstract  N-Methyl-2-pyrrolidone (NMP) is a versatile organic solvent frequently used for surface cleaning such as paint stripping or graffiti removal. Liquid NMP is rapidly absorbed through the skin but dermal vapour phase absorption might also play an important role for the uptake of the solvent. This particular aspect was investigated in an experimental study with 16 volunteers exposed to 80 mg/m(3) NMP for 8 h under either whole-body, i.e. inhalational plus dermal, or dermal-only conditions. Additionally, the influence of moderate physical workload on the uptake of NMP was studied. The urinary concentrations of NMP and its metabolites 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI) were followed for 48 h and analysed by gas chromatography-mass spectrometry (GC-MS). Percutaneous uptake delayed the elimination peak times and the apparent biological half-lives of NMP and 5-HNMP. Under resting conditions, dermal-only exposure resulted in the elimination of 71 +/- 8 mg NMP equivalents as compared to 169 +/- 15 mg for whole-body exposure. Moderate workload yielded 79 +/- 8 mg NMP (dermal-only) and 238 +/- 18 mg (whole-body). Thus, dermal absorption from the vapour phase may contribute significantly to the total uptake of NMP, e.g. from workplace atmospheres. As the concentration of airborne NMP does not reflect the body dose, biomonitoring should be carried out for surveillance purposes.

Abstract  The use of polymethylmethacrylate (PMMA) to reinforce vertebral bodies (Vertebroplasty) leads to an increase in the Young's modulus of the augmented vertebral body. Fractures in the adjacent vertebrae may be the consequence thereof. Hence, PMMA with a reduced Young's modulus may be suitable for vertebroplasty. The goal of this study was to produce and characterize stiffness-adapted PMMA cements. Modified PMMA bone cements were produced by adding N-methyl-pyrrolidone (NMP). Young's modulus, yield strength, polymerization temperature, setting time, and hardening behavior of different cements were analyzed. Focus was on the mechanical properties of the material after different storage conditions (in air at room temperature and in PBS at 37 degrees C). The Young's modulus decreased from 2670 MPa (air)/2384 MPa (PBS) for the regular cement to 76 MPa (air)/320 MPa (PBS) for a material composition with 60% of the MMA substituted by NMP. Yield strength decreased from 85 MPa (air)/78 MPa (PBS) to 2 MPa (air)/24 MPa (PBS) between the regular cement and the 60% composition. Polymerization temperature decreased from 70 degrees C (regular cement) to 48 degrees C for the 30% composition. The hardening behavior exhibited an extension in handling time up to 200% by the modification presented. Modification of PMMA cement using NMP seems to be a promising method to make the PMMA cement more compliant for the use in cancellous bone augmentation in osteoporotic patients: adjustment of its mechanical properties close to those of cancellous bone, lower polymerization temperature, and extended handling time.

Abstract  Novel polylactide (PLA) microspheres endowed with hydrophilic and bioadhesive surfaces as injectable formulations for the controlled release of fenretinide were prepared, using a novel technique based on the co-precipitation of PLA with gelatin, at the interface of a liquid dispersion formed by the addition of N-methylpyrrolidone containing PLA and dextrin (DX), towards an aqueous solution of gelatin (G). The resulting PLA-G-DX microspheres were compared with others prepared by the same technique using polylactide-co-glycolide (PLGA), with or without DX, and with or without phosphatidylcholine. Of the different systems, the PLA-G-DX microspheres had the best morphological, dimensional and functional characteristics. They had the highest drug loading, and their drug release was the most efficient over time without any burst effect. Their in vitro anti-tumoural activity was strongly enhanced with respect to the pure fenretinide. This paralleled the increased drug concentration inside the cells due to their marked bioadhesion to the tumour cell membranes as indicated by scanning electron microscope images.

Abstract  Aramid macroscale fibers, also called Kevlar fibers, exhibit extremely high mechanical performance. Previous studies have demonstrated that bulk aramid macroscale fibers can be effectively split into aramid nanofibers (ANFs) by dissolution in dimethylsulfoxide (DMSO) in the presence of potassium hydroxide (KOH). In this paper, we first introduced the ANFs into the structure of graphene nanosheets through non-covalent functionalization through π-π stacking interactions. Aramid nanofiber-functionalized graphene sheets (ANFGS) were successfully obtained by adding the graphene oxide (GO)/DMSO dispersion into the ANFs/DMSO solution followed by reduction with hydrazine hydrate. The ANFGS, with ANFs absorbed on the surface of the graphene nanosheets, can be easily exfoliated and dispersed in N-methyl-2-pyrrolidone (NMP). Through a combination of these two ultra-strong materials, ANFs and graphene nanosheets (GS), the resultant ANFGS can act as novel nanofillers for polymer reinforcement. We used the ANFGS as an additive for reinforcing the mechanical properties of poly(methyl methacrylate) (PMMA). With a loading of 0.7 wt% of the ANFGS, the tensile strength and Young's modulus of the ANFGS/PMMA composite film approached 63.2 MPa and 3.42 GPa, which are increases of ∼84.5% and ∼70.6%, respectively. The thermal stabilities of ANFGS/PMMA composite films were improved by the addition of ANFGS. Additionally, the transparencies of the ANFGS/PMMA composite films have a degree of UV-shielding due to the ultraviolet light absorption of the ANFs in the ANFGS.

Abstract  There is an increasing commercial demand for naturally sourced indigo that meets the purity standards set by the synthetic product. This study concerns the indigo made from leaves of woad (Isatis tinctoria L.), and in particular its interaction with particulate impurities arising from soil and plant materials. Also, a more reliable method using N-methyl-2-pyrrolidone has been developed for the spectrophotometric determination of indigo. In a novel application of fluorescence spectroscopy, indoxyl intermediates in indigo formation are shown to be stable for minutes. The main indigo precursor from woad can be adsorbed onto Amberlite XAD16 in conformity with a Langmuir isotherm, but indigo precursors break down on this and other resin beads to yield indigo and red compounds. Indigo made from indoxyl acetate aggregates into particles, the size distribution of which can be modified by the inclusion of a fine dispersion of calcium hydroxide. Bright field microscopy of indigo products made under defined conditions and scanning electron microscopy combined with energy-dispersive X-ray analysis reveal the relationship of indigo with particulate materials. A model illustrating the interaction of indigo with particulate contaminants is developed on the basis of the results obtained, and recommendations are made for improving the purity of natural indigo.

Abstract  Epoxyols are generally accepted as crucial intermediates in lipid oxidation. The reactivity of tert-butyl (9R,10S,11E,13S)-9, 10-epoxy-13-hydroxy-11-octadecenoate (11a,b) toward lysine moieties is investigated, employing N(2)-acetyllysine 4-methylcoumar-7-ylamide (12) as a model for protein-bound lysine. The prefixes R and S denote the relative configuration at the respective stereogenic centers. Independent synthesis and unequivocal structural characterization are reported for 11a,b, its precursors, and tert-butyl (9R,10R,11E, 13S)-10-(¿5-(acetylamino)-6-[(4-methyl-2-oxo-2H-chromen-7-yl)amino ]-6 -oxohexyl¿amino)-9,13-dihydroxy-11-octadecenoate (13a-d). Reactions of 11a,b and 12 in 1-methyl-2-pyrrolidone (MP) and MP/water mixtures at pH 7.4 and 37 degrees C for 56 days show formation of the aminols 13a-d to be favored by an increased water content. The same trend is observed for hydrolytic cleavage of 11a,b to tert-butyl (E)-9,10, 13-trihydroxy-11-octadecenoate (14) and tert-butyl (E)-9,12, 13-trihydroxy-10-octadecenoate (15). Under the given conditions, aminolysis proceeds via an S(N)2 substitution, in contrast with the S(N)1 process for hydrolysis. In the MP/water (8:2) incubation, 15. 8% of 12 has been transformed to 13a-d and 10.5% of 11a,b hydrolyzed to the regioisomers 14 and 15 after 8 weeks, respectively. Aminolysis of alpha,beta-unsaturated epoxides by lysine moieties therefore is expected to be an important mode of interaction between proteins and lipid oxidation products.

Abstract  In this study, uniform nitrogen-doped carbon quantum dots (N-CDs) were synthesized through a one-step solvothermal process of cyclic and nitrogen-rich solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethyl-imidazolidinone (DMEU), under mild conditions. The products exhibited strong light blue fluorescence, good cell permeability and low cytotoxicity. Moreover, after a facile post-thermal treatment, it developed a lotus seedpod surface-like structure of seed-like N-CDs decorating on the surface of carbon layers with a high proportion of quaternary nitrogen moieties that exhibited excellent electrocatalytic activity and long-term durability towards the oxygen reduction reaction (ORR). The peak potential was -160 mV, which was comparable to or even lower than commercial Pt/C catalysts. Therefore, this study provides an alternative facile approach to the synthesis of versatile carbon quantum dots (CDs) with widespread commercial application prospects, not only as bioimaging probes but also as promising electrocatalysts for the metal-free ORR.

Abstract  Graphene platelets (GnPs) are a class of novel 2D nanomaterials owing to their very small thickness (∼3 nm), high mechanical strength and electric conductivity (1460 S cm(-1)), and good compatibility with most polymers as well as cost-effectiveness. In this paper we present a low-cost processing technique for producing modified GnPs and an investigation of the electrical and mechanical properties of the resulting composites. After dispersing GnPs in solvent N-methyl-2-pyrrolidone, a long-chain surfactant (Jeffamine D 2000, denoted J2000) was added to covalently modify GnPs, yielding J2000-GnPs. By adjusting the ratio of GnPs to the solvent, the modified GnPs show different average thickness and thus electrical conductivity ranging from 694 to 1200 S cm(-1). To promote the exfoliation and dispersion of J2000-GnPs in a polymeric matrix, they were dispersed in the solvent again and further modified using diglycidyl ether of bisphenol A (DGEBA) producing m-GnPs, which were then compounded with an epoxy resin for the development of epoxy/m-GnP composites. A percolation threshold of electrical volume resistivity for the resulting composites was observed at 0.31 vol%. It was found that epoxy/m-GnP composites demonstrated far better mechanical properties than those of unmodified GnPs of the same volume fraction. For example, m-GnPs at 0.25 vol% increased the fracture energy release rate G1c from 0.204 ± 0.03 to 1.422 ± 0.24 kJ m(-2), while the same fraction of unmodified GnPs increased G1c to 1.01 ± 0.24 kJ m(-2). The interface modification also enhanced the glass transition temperature of neat epoxy from 58.9 to 73.8 °C.

Abstract  In situ forming implants (ISFI) have shown promise in delivering adjuvant chemotherapy following minimally invasive cancer therapies such as thermal ablation of tumors. Although ISFI systems have been thoroughly investigated for delivery of high molecular weight (Mw) therapeutics, little research has been conducted to optimize their design for delivery of low Mw drugs. This study examined the effect of varying the formulation components on the low Mw drug release profile from a ISFI consisting of poly(D,L-lactide-co-glycolide) (PLGA), fluorescein (model drug), and excipient dissolved in 1-methyl-2-pyrrolidinone (NMP). Effects of varying PLGA Mw, excipient concentration, and drug loading were studied. Additionally, solubility studies were conducted to determine the critical water concentration required for phase inversion. Results demonstrated that PLGA Mw was the most significant factor in modulating low Mw drug release from the ISFI systems. ISFI formulations comprised of a low Mw (16 kDa) PLGA showed a significantly (p < 0.05) lower burst release (after 24 h), 28.2 +/- 0.5%, compared with higher Mw PLGA (60 kDa), 55.1 +/- 3.1%. Critical water concentration studies also demonstrated that formulations with lower Mw PLGA had increased solubility in water and may thus require more time to phase invert and release the drug.

Abstract  In this study, a comparison between neat poly(vinylidene fluoride) (PVDF) membrane and composite (PVDF-Nanoclay and PVDF-PVP-Nanoclay) membranes is presented. All membranes were synthesized by the phase inversion process, using 18% PVDF, n-methylpyrrolidone as solvent and water as the non-solvent. Demineralized water cross-flow permeation tests were conducted to evaluate the membranes performance. Scanning electron microscopy (SEM) images of the membranes surface and cross-section and water contact angle measurements were used to estimate additives effects on membranes morphology. The results indicate that dopant addition affected membrane permeate flux and morphology. The 4% nanoclay composite membrane resulted in the highest ultrapure water permeability (0.9130 m(3).m(-2).h(-1).MPa-1), lower hydraulic resistance (3.27x10(+12).m(-1)), lower contact angle (87.1 degrees) and highest surface porosity (0.95%). Furthermore, it was verified that the membrane surface porosity increased with increasing clay nanoparticles concentrations. It was observed that the morphology of the membranes with clay nanoparticle addition is characterized by a thin surface layer, with macro-pores, a thin bottom layer, which has a sponge-like structure with micro-pores and a thick intermediate layer, with finger-like pores and macro-pores. It was also verified that the introduction of PVP promotes a denser morphology compared with membranes without it. Based on the SEM surface and cross-sectional images and permeability tests, it became evident that the internal pore morphology plays an important role in membrane performance, because the higher the frequency and extent of the finger-like pores in the intermediate layer the higher is the membrane permeability. These preliminary results indicated that the use of nanoclay as an additive for membrane casting is a promising procedure for improving membrane performance for water and wastewater treatment.

Abstract  Gas solubility data have been determined for carbon dioxide in binary mixtures of physical plus chemical solvents. The physical solvent studied is N-methylpyrrolidone, whereas the chemical solvents are monoethanolamine and diethanolamine. The mixtures studied were N-methylpyrrolidone with monoethanolamine 15 wt % and with diethanolamine 15 and 30 wt %. The data were obtained at several temperatures ranging from 298 to 373 K in the pressure range 20-2200 kPa. The experimental results are reported as the partial pressure of carbon dioxide against its mole fraction in the liquid phase. Values of the enthalpy of solution of carbon dioxide were derived from the experimental data.

Abstract  The possibility of using R124 (2-chloro-1,1,1,2,-tetrafluoroethane, CHClFCF3) and organic absorbents as working fluids in absorption heat pumps was investigated. Various classes of organic compounds, ail commercially available, were tested as absorbents for possible combination with R124; the absorbents included DMAC (N',N'-dimethylacetamide, C4H9NO), NMP (N-methyl-2-pyrrolidone, C5H9NO), MCL (N-methyl epsilon-caprolactam, C7H13NO), DMEU (dimethylethylene urea, C5H10N2O), and DMETEG (dimethylether tetraethyleneglycol, C10H22O5). To evaluate the performance of a candidate refrigerant-absorbent pair in a refrigeration or heat pump cycle. the thermophysical properties of the pure components and the mixture and the equilibrium and transport properties have to be determined. either from experimental data or by prediction methods. The thermal stability of the refrigerant-absorbent must also be tested, A method for the calculation of the concentration in the liquid and gas phases and the excess thermodynamic properties of the mixture as a function of the system temperature and pressure based on our experimental setup is described. On the basis of vapor-liquid equilibrium measurements, density and viscosity measurements and thermostability testing, enthalpy-concentration diagrams were constructed. The performance characteristics of the investigated working fluids in terms of the coefficient of performance (COP) and the circulation ratio (f) were calculated for a single-stage absorption cycle, In terms of overall performance (COP, f and stability) R124-DMAC was found to be the superior combination, followed by R124-NMP, R124-DMEU and R124-MCL (the three pairs for which stability problems were found al high temperatures), and finally by R124-DMETEG. (C) 1997 Elsevier Science Ltd and IIR.

Abstract  The modifications afforded by several chemical treatments to the main functional groups of a bituminous coal vv ere characterized by diffuse reflectance infrared spectroscopy. The starting materials were the polyanions and potassium coal adducts obtained from the parent coal, treated with potassium according to the Sternberg and Lazarov reactions. The results show the differences in the reactive sites involved in these reactions and in the behaviour of these sites during protonation or alkylation. Some of the typical functional groups introduced (or modified) can be active acceptor sites during hydrogen transfer from tetralin at low temperature (315 degrees C) in conditions avoiding thermal bond cleavage. Taking into account the semiquantitative results of the i.r. analysis, the participation of several active sites in the total hydrogen transfer was estimated, indicating the role of quinonic, aromatic and alkyl groups. Copyright (C) 1996 Elsevier Science Ltd.

Abstract  High quality graphene sheets were produced from graphite by liquid phase exfoliation using N-methyl-2-pyrrolidone (NMP) and a subsequent thermal treatment to enhance the exfoliation. The exfoliation was enhanced by treatment with organic solvent and high thermal expansion producing high yields of the high-quality and defect-free graphene sheets. The graphene was successfully deposited on a flexible and transparent polymer film using the vacuum filtration method. SEM images of thin films of graphene treated at 800 degrees C showed uniform structure with no defects commonly found in films made of graphene produced by other techniques. Thin films of graphene prepared at higher temperatures showed superior transmittance and conductivity. The sheet-resistance of the graphene film treated at 800 degrees C was 2.8 x 10(3) k Omega/square with 80% transmittance. (C) 2012 Elsevier B. V. All rights reserved.