Morphological study of a poly(3,4-ethylenedioxythiophene)/polystyrenesulfonic acid mixture by solid state 13C-CP/MAS NMR relaxometry

The nanometer morphology of a mixture of the electrically conductive polymer poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid is studied by means of solid state ¹³C-CP/MAS NMR relaxation experiments. Based on the T₁H and T_1ρH NMR relaxation decay times, determined via the chemical shift selective carbon resonances, it can be concluded that the mixture is homogeneous on the nanometer scale. Consequently, charge transport (hopping) between PEDT chains is hindered, resulting in antistatic properties.     

Experimental and theoretical investigations on petroleum-based elastomers with two cross-linking systems of different lengths viewed as bimodal networks

A review with 36 references discussing the chemistry and the structure-property relationship of elastomers cured with two cross-linking systems of different chain lengths such as sulfur and the polymerization products of p-benzoquinone and viewed as bimodal networks. These exceptional networks have shown remarkable improvements in the overall mechanical properties which are anticipated to be due to the non-Gaussian effects known for bimodal networks and evident by the anomalous upturn in the modulus values in Mooney-Rivlin stress-strain data representations. Proton and ¹³C NMR as well as energy minimization calculations were used to study the chemical structures and single chain contributions of polyquinones. Nuclei bending of these oligomers have shown to be greatly influenced by the restricted torsional behavior due to the presence of the hydrogen bonds between the benzenoid nuclei. Intrinsic atomic-level forces for the networks were evaluated using molecular dynamics techniques and showed that while the forces acting on the junction points of the cross-linking segments and the elastomeric chains had no apparent change as a consequence of the networks' bimodal formation, forces acting on the short chains of the bimodal networks are of much higher values as compared to those of unimodal networks. The presence of the relatively long polyquinone chains in the bimodal networks has caused the short sulfur chains to stretch to its maximum extensibility and no longer can increase its end-to-end distance separation by simple rotations about its skeletal bonds. Limited chain extensibility of the short chains resulting from the deformation of the bond angles and bond lengths has lead to higher potential energies. Studies on the swollen bimodal networks have validated the above conclusions since swelling of the networks will prevent the elastomeric chains from undergoing possible strain-induced crystallization during the stress-strain experiments and any abnormalities in the mechanical behavior of these networks must be therefore the result of the limited extensibility of the short chains of the networks.     

Molecular model of Estonian kukersite kerogen evaluated by C MAS NMR spectra

The chemical structure of Estonian kukersite kerogen is evaluated using a simulation of ¹³C MAS NMR spectrum. A reasonable fit to the experimental NMR spectrum is obtained by assuming a model of the geomacromolecule with empirical formula C₄₂₁H₆₃₈O₄₄S₄NCl and a set of structural elements comprising mainly alkylated phenolic structures particularly alkyl-1,3-benzenediols and condensed alicyclic rings. From the presented model new views are coming up on the carbon skeleton of kerogen and constraints on the phenol formation pathways in the retorting process, i.e. up to 80% of methylene groups in kerogen are located in aliphatic chains and the complicated mixture of phenols in the retort oil seems to result mainly from the thermal conversion of alkyl-1,3-benzenediol units originally present in kerogen.     

Fluid motion around and through a porous cylinder

The flow-field and solute transport through and around a porous cylinder is investigated numerically. The range of Reynolds number (based on the cylinder diameter and the uniform sinking rate of the cylinder) considered here is between 1 and 40 with Darcy number (Da) in the range 10^-6?Da?1.5 and porosity in the range 0.629?ε?0.999. The motivation of the present study is the application of flow through porous cylinder extensively applied in nuclear biological chemical filters as well as reduction of carbon fines in filtered water. The influence of Da on the drag coefficient, separation angle, recirculation length, streamline and vorticity pattern are investigated. The drag ratio, defined as the ratio of drag coefficient of porous cylinder to that of solid cylinder, is found to approach zero from unity as Da is increased from 10^-6 to 1.5. The separation point shifts towards the rear stagnation point as Da is increased. The time evolution of the solutal field at different Reynolds number and Darcy number is presented. A long slender concentration plume is found to evolve from the cylinder with decreasing concentration at the outer edge.     

水分子对初始碳烟颗粒形成过程影响的分子动力学模拟

采用LAMMPS软件，基于ReaxFF，以十氢化萘、萘、2-甲基蒽、1-乙基芘为催化油浆的模型化合物研究了600～2500 K温度下催化油浆形成初始碳烟颗粒的过程，考察了2500 K时水分子对初始碳烟颗粒形成过程的影响。研究表明温度在600 K时模型化合物分子主要是物理聚集成核。温度在900～1700 K时模型化合物分子处于聚集和分离的动态过程，无法从单体向碳烟颗粒转变。温度高于2100 K时主要是化学成核，模型化合物分子碳氢键先断裂，然后碳碳键断裂产生大量短碳链，碳链经成键和环化形成初始碳烟颗粒。温度在2500 K时水分子抑制模型化合物分子化学成核，随着体系氢碳比的增加，抑制初始碳烟颗粒形成的作用增强。水分子产生氢自由基和氢氧自由基，这些基团会直接导致模型化合物分子的侧链断裂和碳碳键断裂形成大量短碳链。碳链继续与氢自由基和氢氧自由基作用形成一氧化碳、二氧化碳、氢气、甲烷等而被消耗，水分子的作用为促进短碳链形成和抑制短碳链向形成初始碳烟颗粒的方向进行。     

Synthesis of polyynes by dehydrohalogenation of chlorinated paraffins

A mixture of chlorinated iso- and n-paraffins having from 22 up to 30 carbon atoms and 70% chlorine content was dehydrohalogenated with alcoholic solutions of KOH, NaOH, LiOH, MeOK and EtONa in heterogeneous phase and under different conditions. In agreement with thermodynamic calculations, FT-IR and electronic spectra (by the 1st derivative of the absorption curve) provide clear evidence about the formation of long polyyne segments (acetylenic carbyne domains) conjugated with residual double bonds. More in detail, FT-IR spectra show a neat absorption band at 2180–2190 cm^–1 due to triple bonds stretching while it is shown the strict analogy between electronic spectra recorded on the dehydrohalogenation products of chlorinated paraffins and the well known ene-polyynes like isomycomicyn and dodeca-2,10-diene-4,6,8-triyne.     

Some aspects of existence of elementary carbon with sp-hybridized bonds

The existence of elementary carbon with sp-hybridized bonds was shown to be impossible if its single chains cannot be retained in a sufficient mutual distance. The course of synthesis of the nuclei of a skeleton from carbon macromolecules in sp state is discussed on the basis of experimental data which characterize the products of reduction of poly(tetrafluoroethylene) (PTFE) with Li-amalgam (WAXS, SAXS, Li-content, densities of reduction products, adsorption measurements). Cubic crystallities of LiF, growing during the reduction from Li⁺ and F⁻ ions to the size of 3.3 nm, were shown as structure-determining elements. A novel polymeric compound of carbon with lithium is formed by PTFE reduction. A structural scheme of this compound, based on narrow monolayer ribbons of six-membered rings, is proposed. Lithium atoms bound to the edge-atoms hinder the extension of the ribbons to a graphite-like sheet. Many physico-chemical properties of the carbon skeleton (nongraphitic state, surface area, adsorption capacity, easy oxidability) can be explained on the basis of the proposed mechanism of its synthesis.     

Molecular dynamics in polyester- or polyether-urethane networks based on different diisocyanates

Different non-conventional polyurethane networks crosslinked with a hyperbranched polyester (Boltorn^®H40) were synthesised with an aim to determine the influence of the polyurethane chemical structure as well as of the length of the linear chains between crosslinking centres on molecular relaxations in such systems. For that purpose, both polyether- and polyester-type macrodiols as well as two different diisocyanates were used to synthesise the connecting polyurethane chains between crosslinks. Molecular dynamics were investigated by dielectric spectroscopy and by dynamic mechanical analysis. It was found that the changes of the repeating macrodiol-diisocyanate unit number (i.e. length of the polyurethane linear chains) practically did not affect the molecular relaxations. This effect was explained by the formation by hydrogen bonds between urethane groups of similar, independent of the polyurethane linear chain length, physical networks, which control the molecular mobility. By contrast, the chemical nature of the precursors strongly influences the molecular relaxation associated with glass transition, and to some extent also the sub-glass secondary relaxation processes occurring in the investigated networks.     

Atomic oxygen functionalization of double walled C nanotubes

The interaction of atomic oxygen with double walled C nanotubes at room temperature was studied by high resolution photoemission spectroscopy with synchrotron radiation. The nature of the chemical species formed on the nanotube sidewalls was followed from the initial adsorption up to advanced oxidation stages, whereas the thermal evolution of the O-related chemical species was monitored by fast photoemission. At the beginning of oxidation O atoms preferentially chemisorb forming C-O-C bonds, in ether and epoxy structures, which originate different components in the O1s spectra and exhibit different thermal stability. The onset of sp² lattice distortion is attested by the appearance of C-C bonds intermediate between sp² and sp³ configurations. The formation of double and triple C-O bonds is favored at later oxidation stages, and is accompanied by increasing lattice amorphization and decreasing emission in the Fermi level region. After annealing at 950 °C the O1s signal disappears and the presence of lattice defects emerges from the C1s line shape. This result, together with the chemical inertness of the deoxygenated nanotubes towards CO and O₂ adsorption suggests that the dangling bonds are promptly healed by thermal annealing and only stable topological defects are retained in the nanotube lattice.     

Plasma polymerization in mixture system of tetramethyltin and ammonia gas

Summary Plasma polymerization in a mixture system of tetramethyltin (TMT) and ammonia (NH₃) gas was investigated by elemental analysis, IR spectroscopy, and ESCA in comparison with that in a mixture system of tetramethylsilane (TMS) and NH₃ gas. NH₃ gas contributed to the formation of polymers containing much tin, less carbon and hydrogen, and negligible nitrogen element. IR and ESCA spectra showed acceleration in dehydrogenation and /or dealkylation of carbon chains and in oxidation of tin element by NH₃ gas. While, plasma polymerization in the TMS/NH₃ mixture system showed incorporation of nitrogen residues as amido and amino groups as well as dehydrogenation and dealkylation. This descrepancy in chemical structure between polymerizations in the TMT/NH₃ and the TMS/NH₃ system might result from Sn-N bonds susceptible to moisture to form oxidized Sn.     

Average density of chain atoms at points along the contour of freely jointed chains

The density of chain atoms in the volume element dV centered on atom i has been obtained for short and long freely jointed (FJ) chains. The Gaussian distribution function is used for long chains, and Treloar's corrections to this distribution are imposed for short chains. For long FJ chains, the density of chain atoms is a maximum when atom i is located midway along the contour of the chain, and it is a minimum when atom i is any of the three atoms at either end of the chain. The ratio of these densities is 2. Short FJ chains can exhibit qualitatively different behavior, with the site of the maximum density shifting from the middle to the end of the chain when the number of bonds decreases from 8 to 7. This shift is imposed by the strong deviations from the Gaussian distribution when n is small.     

Ultrafast sol–gel synthesis of graphene aerogel materials

Graphene aerogels derived from graphene-oxide (GO) starting materials recently have been shown to exhibit a combination of high electrical conductivity, chemical stability, and low cost that has enabled a range of electrochemical applications. Standard synthesis protocols for manufacturing graphene aerogels require the use of sol–gel chemical reactions that are maintained at high temperatures for long periods of time ranging from 12 h to several days. Here we report an ultrafast, acid-catalyzed sol–gel formation process in acetonitrile in which wet GO-loaded gels are realized within 2 h at temperatures below 45 °C. Spectroscopic and electrochemical analysis following supercritical drying and pyrolysis confirms the reduction of the GO in the aerogels to sp² carbon crystallites with no residual carbon–nitrogen bonds from the acetonitrile or its derivatives. This rapid synthesis enhances the prospects for large-scale manufacturing of graphene aerogels for use in numerous applications including sorbents for environmental toxins, support materials for electrocatalysis, and high-performance electrodes for electrochemical capacitors and solar cells.     

Synthesis of carbon nanostructures from residual solids waste tires

This article presents the results of the synthesis and morphological characterization of carbon nanostructures obtained from the decomposition of residual solid from waste tires (RSWT) in quartz tubes under reduced pressure (1.33 Pa) at 900°C for 15 min. The synthesis led to the formation of two phases, a fragmented solid black powder composed of multi‐walled carbon nanotubes (MWCNTs), onion‐type fullerenes, and spheres, and a very bright metallic dark film. Analysis by microscopy (SEM and TEM) showed that the MWCNTs had an average diameter of approximately 25 nm and a length greater than 100 nm while the diameter of the onion‐type fullerenes was found to be 8 nm. The nanospheres showed different diameters ranging from 500 nm to 1.5 μm, and some had a metallic core surrounded by layers of carbon. The infrared spectra of the nanotubes exhibited absorption bands at 1558 and 1458 cm^?1, corresponding to C?C and C? C bonds, and signals at 3438 and 1080 cm^?1 related to the OH and C? O groups from oxidized graphite as it was identified in the dark film. The Raman spectra of the carbon nanostructures present D and G‐bands at 1331 and 1597 cm^?1, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and dye separation performance of ferromagnetic hierarchical porous carbon

Ferromagnetic hierarchical porous carbon (FHPC) with nickel particles embedded in the hierarchical porous carbon skeleton was synthesized. The hierarchical macro–mesoporous skeleton was formed by dissolving a salt template of Na₂CO₃ and the ferromagnetic nickel particles were produced by in situ carbothermal reduction of nickel oxide. The saturation magnetization, remnant magnetization and coercive force of FHPC are 11.3 emu g⁻¹, 2.3 emu g⁻¹ and 55.7 Oe. The ferromagnetic property enables the magnetic separation of the FHPC from water. The surface chemical environments of the FHPC consist of different oxygen functional groups, like –OH, >COO and >CO groups, as well as a trace amount of aliphatic species of –CH₃ or -CH_2^- structures. Dye separation performance of the FHPC was investigated using methylene orange, and the adsorption capacity was 0.16 mg m⁻² with the adsorption kinetics constant of 2.2 m² mg⁻¹ min⁻¹, which is superior to that of magnetic carbon spheres.     

Phase behaviors of bidisperse nanoparticle/block copolymer mixtures in dilute solutions

The complex microstructures of bidisperse nanoparticles/diblock copolymer mixtures in dilute solutions have been investigated by a theoretical approach which combines the self-consistent field theory (SCFT) and the density functional theory (DFT). Special attention is payed to the role played by the block ratio and the interaction parameters between each component in the mixture. It is shown that the conformational entropy of the polymer chains, the block ratio of the diblock copolymer, the chemical difference between two kinds of particles and the steric packing effect of the particles play important roles in determining the morphologies of the systems. It is found that with the increase of the block ratio, the mixture undergoes a morphological transition from compound micelles to spherelike micelles. The increase of chemical difference between the two kinds of particles can promote the formation of “a jujube set in a cake”. When the selectivity of the particles is changed, another type of micelle emerges. Specifically, in the case where the particles are nonselective to the A- and B-blocks, ordered structures from the phase separation between the two types of particles emerge inside the micelles formed by the amphiphilic diblock copolymers in solutions.     

Linear carbon chains encapsulated in multiwall carbon nanotubes: Resonance Raman spectroscopy and transmission electron microscopy studies

In this paper we report the characterization of linear carbon chains encapsulated in multiwalled carbon nanotubes by using Raman spectroscopy and transmission electron microscopy. The chains are characterized by strong vibrational peaks around 1850 cm⁻¹ and both the frequency and intensity of these peaks were found to be dependent on laser excitation energy. Furthermore, resonance Raman spectroscopy was used for constructing the resonance window of the linear carbon chains. The Raman spectroscopy data showed that long chains have lower highest occupied molecular orbital–lowest unoccupied molecular orbital energy gaps and weaker carbon–carbon bonds. Besides the spectroscopy evidence for the linear carbon chain, we used scanning transmission electron microscopy/electron energy loss spectroscopy analysis of the nanotube cross section to unambiguously show the existence of a 1D structure present within the innermost carbon nanotube with an unprecedented clarity compared to previous reports on this kind of system.     

Thalassiosira pseudonana diatom as biotemplate to produce a macroporous ordered carbon-rich material

Ordered macroporous-mesoporous carbonaceous materials were produced as a direct replica of the Thalassiosira pseudonana diatom by infiltration of the skeleton with furfuryl alcohol. The final carbon-rich material preserves the macropores of the diatom acting as bio-template and new hierarchical macro-mesopores appears as the silica is eliminated through chemical etching. The final solid can be described as an organized array of carbon macrotubes. In order to understand the progressive silica etching and the subsequent effect on the final carbon material, different etching reagents have been used. Moreover, the similar pore topology of T. pseudonana and the well known MCM-41 mesoporous silica (hexagonal ordered arrays of non-interconnected pores), allowed us to consider this system as a micrometric model to understand in 3-D the carbon replication of MCM-41 silicas.     

Chemical bonds in carbon fibres

In reporting the results of an examination of the mechanism of formation of chemical bonds in carbon fibres, the following conclusions can be drawn: — the existing concepts concerning curved hybrid bonds and σ-, π-bonds do not explain their compatibility with the high thermal stability of carbon fibres; — the concept of formation of chemical bonds in carbon fibres because of the gravitational effect of atoms with energy corresponding to the energy of chemical bond formation due to the high value of the gravitational constant of 1.6·10⁻²⁸ cm³/g·sec²) caused by the high density of the substance in the atom of 10¹²–10¹³g/cm³, is substantiated; — the gravitational constant is calculated with the equation of the dynamics of orbital motion for the potential energy; the values obtained are in satisfactory agreement with the results of the calculation based on tensiometric and spectroscopic data. __________ Translated from Khimicheskie Volokna, No. 6, pp. 41–44, November–December, 2006.     

Interpenetrating bimodal networks

Sequential interpenetrating networks (IPN's) were obtained from a tetrafunctionally end-linked network [prepared from hydroxyl-terminated poly(dimethylsiloxane) (PDMS) chains having a number-average molecular weight of 21.3 × 10³ g mol^?1] by swelling it with very short vinyl-terminated PDMS chains (～450 g mol^?1), which were then themselves tetrafunctionally end linked, Simultaneous IPN's were prepared from a mixture of the same two types of PDMS chains, with different end-linking agents and catalysts for the two separate reactions. In elongation studies, both types of IPN's showed upturns in modulus which were similar to those shown by the usual bimodal networks, which are prepared from mixtures of chains having identical end groups, and are thus entirely interconnected. The sequential IPN's have values of the high deformation modulus close to those of the interconnected networks, possibly because their lack of connectivity is compensated for by the stretching of the long chains by the short-chains used to form the second network, Values of the ultimate strength are smaller for the IPN's, thus demonstrating the advantage of direct bonding between the long and short network chains. The simultaneous IPN's, however, have unusually large extensibilities, which makes their energies for rupture comparable to those of the corresponding interconnected bimodal networks.     

Precise characterization of cuticular compounds in youngDrosophila by mass spectrometry

Cuticular hydrocarbons of youngDrosophila flies are singular with very long chains and complex diene mixtures. A precise characterization of these substances was carried out by epoxidation and analysis of the products by GC-MS with negative chemical ionization. InD. melanogaster, double bonds of dienes are more probable at carbon positions 11 or 13 and 21 or 23. InD. simulans, double bonds are shifted more towards the interior of the chain. Such a difference is also found among monoenes of both species. The analyses of monoenes and dienes confirm the similarity of cuticular compounds of young flies of both sexes in both species. A main cuticular compound ofD. erecta females, 9, 23-tritriacontadiene, is also presented.