Quantitative, nanoscale mapping of sp percentage and crystal orientation in carbon multilayers

Experimental and analytical techniques are introduced for the quantitative, nanoscale mapping of chemical bonding information in carbon-based materials. With these techniques, the spatial orientation of graphitic crystallites in tetrahedrally bonded amorphous carbon was imaged. Simultaneously, the percentage of sp²- and sp³-bonded carbon could be mapped quantitatively, all with spatial resolution of just a few nanometers. Two electron energy-loss spectroscopy (EELS) techniques were compared: low-loss mapping of the plasmon energy and core-loss mapping of the carbon ionization edge. The recently developed EELS acquisition routine of binned gain averaging was applied, together with multivariate statistical analysis, providing a robust method for obtaining real-space, two-dimensional bonding maps.     

Organo bifunctional silane effects on the vibration,thermal, and mechanical properties of a vinyl‐group‐containing silicone rubber/natural rubber/silica compound

A bifunctional silane (TESPD) was added to a vinyl‐group‐containing silicone rubber (SR)/natural rubber (NR)/silica compound, and the resulting mechanical, morphological, and thermal properties were compared with those of an NR/silica compound. The addition of TESPD to the silica‐filled SR/NR compound formed an SR‐silane‐silica‐silane‐NR structure that behaved as a ter‐polymer. The addition of SR into the NR improved the mechanical properties (torque maximum, modulus, elongation at break, and hardness) and thermal properties as well as the tan δ values. The SR‐silane‐silica‐silane‐NR structure exhibited advanced properties that are suitable for an automotive engine mount application, which requires good thermal and vibration absorption properties. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

Free radical activity in gamma‐irradiated polyethylene film,drawn tape and ultra‐high‐modulus fibres determined by grafting performance

Grafting rates of gaseous butadiene to a range of morphological forms of gamma‐irradiated polyethylene, including ultra‐high‐modulus fibres (UHMPE), have been measured in order to determine the availability of active free radicals over time at various temperatures. Blank experiments on unirradiated samples showed that monomer diffusion is not rate‐controlling with film and natural draw ratio tapes, but is likely to be a major factor in the control of grafting rates in UHMPE fibres. Grafting rates from monomer loss/time experiments with irradiated samples indicate that grafting is always in competition with free radical self‐annihilation, the extent being influenced by temperature, dose and morphology, including prior sample annealing. At lower temperatures, graft‐active radicals are produced over long periods of time, eg close to linear grafting rates were monitored over 20 hours for PE tape at 0 °C (50 kGy) and for gel‐spun UHMPE at 40 °C (100 kGy). At higher temperatures, grafting rates steadily decrease with time. Grafting rates are almost independent of irradiation dose in the early stages, however, the dose has an increasing positive influence as the reaction proceeds. At any given temperature and irradiation dose, the rates decrease in the series undrawn film; natural draw ratio tape; high draw ratio gel‐spun fibre; high draw ratio melt‐spun fibre. An analogy is drawn between these results and the optimum conditions required for improving the creep properties of PE tape and UHMPE fibres by acetylene‐sensitized irradiation crosslinking. Copyright © 2005 Society of Chemical Industry     

Effect of surfactant and heat treatment on morphology,surface area and crystallinity in hydroxyapatite nanocrystals

Hydroxyapatite (HA) powders were synthesized by the wet precipitation method, with and without surfactant, under identical processing parameters. These powders were then heat treated at 900 °C for 3 h in air. The detailed characterization of the powders was done by using SEM, dynamic light scattering, nitrogen adsorption, XRD, Raman spectroscopy, and FTIR techniques. The HA phase, identified by well defined PO₄^3? and OH^? ion peaks in Raman and FTIR spectra, was observed in all the powder samples. The addition of surfactant changed the morphology of the particles from spherical to needle/rod-like structure and increased the surface area up to three times (from 33 to 96 m²/g). Also, suppression in the evolution of β-TCP phase was observed along with decrease in the crystal size and crystallinity of the powder due to the addition of surfactant. Synthesized nano-HA crystals were found to have diameters and lengths in the range 10–25 nm and 75–150 nm, respectively. The heat treatment changed the architecture of the particles, increased the crystallinity and reduced the surface area to ≈7 m²/g. However, the relative increase in crystallinity was much higher for the powder synthesized with surfactant. The ratio of the average crystallite size to the crystallinity degree was about 0.53±0.07 for all the powders. The particle size distribution was bimodal and coarser for the powder synthesized without surfactant. The pore size analysis showed transformation of a predominantly mesoporous structure into a meso- plus macroporous one on heat treatment. The intensity of OH^? group peak in Raman spectra was found to be highly sensitive to the crystalline state of the HA powder and may be used to assess crystallinity.     

Characterization of crystallinity,orientation, and mechanical properties in biaxially stretched poly(p-phenylene sulfide) films

In this paper, we describe the preparation and structural characterization of biaxially oriented poly(p-phenylene sulfide) (PPS) films. These films were prepared in a biaxial stretching machine at various stretching temperatures, rates, and stretching ratios. Selected samples were constrained annealed at elevated temperatures. The state of orientation was determined by wide angle X-ray diffraction (pole figure determination) and birefringence measurements. The results are expressed in terms of the biaxial orientation functions (?,?). Mechanical properties (tensile modulus, tensile strength, and elongation to break) were obtained as a function of processing conditions and direction in the plane of the films.     

Morphology,crystallinity, and electrochemical properties of in situ formed poly(ethylene oxide)/TiO2 nanocomposite polymer electrolytes

A method to produce nanocomposite polymer electrolytes consisting of poly(ethylene oxide) (PEO) as the polymer matrix, lithium tetrafluoroborate (LiBF₄) as the lithium salt, and TiO₂ as the inert ceramic filler is described. The ceramic filler, TiO₂, was synthesized in situ by a sol–gel process. The morphology and crystallinity of the nanocomposite polymer electrolytes were examined by scanning electron microscopy and differential scanning calorimetry, respectively. The electrochemical properties of interest to battery applications, such as ionic conductivity, Li⁺ transference number, and stability window were investigated. The room‐temperature ionic conductivity of these polymer electrolytes was an order of magnitude higher than that of the TiO₂ free sample. A high Li⁺ transference number of 0.51 was recorded, and the nanocomposite electrolyte was found to be electrochemically stable up to 4.5 V versus Li⁺/Li. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2815–2822, 2003     

Quantification of carbonyl compounds in oxidized low-linolenate,high-stearate and common soybean oils

The carbonyl compounds in five oxidized soybean oils (SBO) of various fatty acid compositions were determined. Three were from common normal soybean varieties, and two were from lines developed from new mutant varieties. One mutant line had a linolenate (18:3) content of 3.5% (A5), and one had a stearate (18:0) content of 24% (A6). SBO were stored at 28 C and 60 C. Trichlorophenylhydrazones (TCPH) of carbonyls formed during oxidation were quantified and tentatively identified by gas chromatography. The storage temperature and the composition of the oils affected the types and amounts of volatiles produced. Hexanal was the major volatile in the oils in both storage tests. After 60 C storage, 2- and/or 3-hexenal was present only in the oil with the highest 18:3 content (BSR 101, 18:3=9%). The amounts of the carbonyls formed in A5 were 2 to 5 times less than the amounts formed in BSR 101. The amounts of many of the carbonyls were converted into relative flavor potency by using reported data. Hexanal was the major contributor to flavor. After storage at 28 C, 2- and/or 3-hexenal was the second most intense flavor compound regardless of the 18:3 content of the oil. The amount of a compound and the threshold value did not always predict its flavor importance according to the flavor potency data.     

Effect of clay on vulcanization,network structure,and technical properties of natural rubber in the presence of silane coupling agents

The presence of silane coupling agents do not cause a change in network structure in clay-filled natural rubber vulcanizates, both in sulfur vulcanization and peroxide vulcanization systems. However, the improvement in technical properties in the presence of silane coupling agents is more in the peroxide vulcanization system and is accompanied by enhanced polymer—filler interactions. Scanning electron microscopy (SEM) studies have been made in order to understand the failure behavior.     

Quantification,characterization and fatty acid composition of lysophosphatidic acid in different rat tissues

The amount and composition of lysophosphatidate present in different rat tissues have been estimated by an internal standard method in which a synthetic unnatural isomer (1-heptadecanoyl-rac-glycerol-3-phosphate) was added to the total lipid extracts, and the fatty acid composition of purified lysophosphatidate was determined. Lipids from tissues were extracted under acidic conditions, and the lysophosphatidate was purified by solvent partitions followed by thin-layer chromatography in multiple solvent systems. The purified lipid was shown to be 1-acyl-sn-glycerol-3-phosphate by chromatographic and chemical analysis, by its resistance to hydrolysis when treated with phospholipase A₂ and also by its complete conversion to 1-acyl-sn-glycerol when treated with alkaline phosphatase. The fatty acid consituents of this lipid were determined by gas-liquid chromatography of the derived methyl esters. The concentrations (nmol/g of tissue) of lysophosphatidate in various tissues were: 86.2±4.2 in brain, 60.3±6.3 in liver, 46.4±6.5 in kidney, 30.6±5.0 in testis, 22.3 in heart and 19.3 in lung. Mostly (80%) saturated fatty acids were found to be present in this lyso lipid. A significantly high level of stearic acid was present in this lipid from all the tissues (50–60% in liver, kidney, brain and testis, and about 40% in heart and lung) compared to plamitic acid (10–15% in liver, kidney and brain and 25–30% in testis, heart and lung). The fatty acid compositions of phosphatidic acid, the putative product of lysophosphatidate acylation, from different tissues were also determined and palmitate was found to be the major saturated fatty acid. These results suggest that tissue lysophosphatidic acid is not only formed byde novo biosynthesis but is also generated via the breakdown of phospholipids such as phosphoinositides.     

Characterization of crystalline cellulose in biomass: Basic principles, applications, and limitations of XRD, NMR, IR, Raman, and SFG

Cellulose is among the most important and abundant biopolymers in biosphere. It is the main structural component of a vast number of plants that carries vital functions for plant growth. Cellulose-based materials have been used in a variety of human activities ranging from papers and fabrics to engineering applications including production of biofuels. However, our understanding of the cellulose structure in its native form is quite limited because the current experimental methods often require separation or purification processes and provide only partial information of the cellulose structure. This paper aims at providing a brief background of the cellulose structure and reviewing the basic principles, capabilities and limitations of the cellulose characterization methods that are widely used by engineers dealing with biomass. The analytical techniques covered in this paper include x-ray diffraction, nuclear magnetic resonance, and vibrational spectroscopy (infrared, Raman, and sum-frequency-generation). The scope of the paper is restricted to the application of these techniques to the structural analysis of cellulose.     

Analysis of coherence,strain, thermal vibration and preferred orientation in carbons by X-Ray diffraction

In ideal graphitic layers the inter-atomic (or inter-unit cell) distances l and the number of atoms (or unit cells) n(l) at a distance from any atom (or unit cell) chosen as origin may be represented by sets l and n(l) which define the structure. In the defective lattice theory presented here the structure of diffusely scattering (the so-called amorphous) carbons are likewise defined by the two sets, however n(l)'s are modified by a probability (coherence probability) function g(l) and l's are modified for dispersion (strain effects). It is shown that the coherence probability function can be determined from the atomic radial distribution curves without a priori knowledge of distortion and temperature diffuse scattering. Analytical expressions have been developed that permit analysis of distortion and temperature diffuse scattering from the observed profiles of the diffuse peaks and from the atomic radial distribution functions. In analyzing the distortion, Gauss', Gauchy's and Laplace's distributions are considered. It is demonstrated that distortion could be responsible for the diffuseness of the diffraction profiles of carbons to a greater extent than the coherence probability, the so-called domain or particle size effect. It is also shown that the integrated intensities, I(φ), of the (00l) reflections of anisotropic, e.g. pyrolytic, carbons are related to the angle φ that the diffraction vector makes with the pole of the sample by I(φ) = K exp (?p²sin²φ) in which K is the proportionality constant and p is the characteristic parameter of the sample. The equation has a reasonably sound physical basis and has been found to be applicable to samples having a wide range of preferred orientations.     

Effects of polydimethylsiloxane grafting on the calcification,physical properties,and biocompatibility of polyurethane in a heart valve

Segmented polyurethane (PU) has proven to be the best biomaterial for artificial heart valves, but the calcification of polyurethane surfaces causes serious problems in long‐term implants. This work was undertaken to evaluate the effects of polydimethylsiloxane (PDMS) grafting on the calcification, biocompatibility, and blood compatibility of polyurethane. A grafted polyurethane film was compared with virgin polyurethane surfaces. Physical properties of the samples were examined using different techniques. The hydrophobicity of the polyurethane films increased as a result of silicone modification. The effects of surface modification of polyurethane films on their calcification and fibroblast cell (L 929) and platelet behavior were evaluated in vitro. Fourier transform infrared spectroscopy indicated the direct involvement of the polyether soft segments of the polymer in the calcification process. Scanning electron microscopy of films indicated that grafting of silicone rubber to the surface of polyurethane successfully prevented the calcification process. The morphology of fibroblast cells that adhered to the PU films and modified films was similar to that of controls and showed the same proliferation. On the other hand, grafting PDMS onto PU did not affect the amount of platelets that adhered to the polyurethane surfaces. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 758–766, 2005     

Origin of the 2450 cm Raman bands in HOPG, single-wall and double-wall carbon nanotubes

The second order Raman signals around the G′-band region of graphite and carbon nanotubes have been investigated at more than 15 excitation laser lines. Two distinct Raman bands have been observed around 2700 cm⁻¹; a prominent one is due to the so-called G′-band and the other is a weak band around 2450 cm⁻¹. Both two bands can be from the double resonance process involving two phonons around the K-point in the phonon dispersion of a two-dimensional graphite. The 2450 cm⁻¹-band has exhibited little power dependence, whereas the intensity of G′-band has shown large photon energy dependence as already reported. The 2450 cm⁻¹-band and the G′-band correspond to non-dispersive q = 0 and fully-dispersive q = 2k, respectively. From the phonon dispersion and the corresponding phonon frequency, the 2450 cm⁻¹-band can be assigned as an overtone mode of LO phonon (i.e. 2LO). This is revealed by calculated Raman spectra of graphite with proper electron-phonon matrix elements. The present study is the first report on the origin and assignment of the 2450 cm⁻¹-band, which is based on the double resonance Raman scattering.     

Effect of crystallinity on structural,thermal, and in vitro dissolution properties of Na2O-CaO-Nb2O5/MgO-P2O5 glass-ceramics

The impact of the crystallinity on structural, thermal, and in vitro dissolution properties were examined for Na₂O-CaO-Nb₂O₅/MgO-P₂O₅ glasses/glass-ceramics. Glass-ceramics were synthesized via a spontaneous crystallization process. The Nb content in the materials increased with melting temperature, furthermore, the crystallinity is proportional to the Nb content. The presence of crystalline niobates and phosphates is confirmed by FTIR analysis which is consistent with XRD. The FTIR results indicate that the phosphate network is built of different proportions of Q², Q¹, and Q⁰ units, depending on the amount and type of crystalline phase. Most of the samples show an improvement in thermal stability. The in vitro dissolution test showed that the highest mass loss for most of the samples occurred during the first 6 days of immersion in the PBS solution. The presence of small phosphate crystals favors the deposition of hydroxyapatite on samples’ surfaces while the larger niobate crystals dissolve more readily.     

Kinetics of,free radical modification of polyolefins in extruders – chain scission,crosslinking and grafting

Free radical reactions, carried out in polymer melts, have become a popular method of chemically modifying polyolefins. The elementary free-radical reactions which are relevant in the chemical modification of polyolefins at high temperatures in extruders, such as chain transfer to polymer via primary and polymer radicals, β-scission, double bond addition and bimolecular termination, affect chain scission, long chain branching, crosslinking and grafting. This brief review will discuss some of the work focused on the kinetics and mathematical modelling of these reactions.     

Cooling of fibres and yarns in melt-spinning,with allowance for their transverse vibration

Conclusions Transverse yarn vibrations intensify yarn cooling as a result of increasing the heat transfer coefficient, and also cause nonuniformity in diameter due to a periodic displacement of the solidification point along the yarn length.A reduction in yarn diameter nonuniformity is possible by increasing the frequency of mechanical vibrations and decrease the diameter gradient along the yarn.The nonuniformity of complex yarn diameter when it undergoes transverse vibrations is less than the nonuniformity of the individual filaments due to their vibration in different phases.Translated from Khimicheskie Volokna, No. 3, pp. 33–35, May–June, 1985.     

Quantification of gypsum crystal nucleation,growth, and breakage rates in a wet flue gas desulfurization pilot plant

The aim of this work is to study the influence of nucleation, growth and breakage on the particle size distribution (PSD) of gypsum crystals produced by the wet flue gas desulfurization (FGD) process. The steady state PSD, obtained in a falling film wet FGD pilot plant during desulfurization of a 1000 ppm(v) SO₂ gas stream, displayed a strong nonlinear behaviour (in a ln(n(l)) vs. l plot) at the lower end of the particle size range, compared to the well‐known linear mixed suspension mixed product removal model. A transient population balance breakage model, fitted to experimental data, was able to model an increase in the fraction of small particles, but not to the extent observed experimentally. A three‐parameter, size‐dependent growth model, previously used for sodium sulphate decahydrate and potash alum, was able to describe the experimental data, indicating either size‐dependent integration kinetics or growth rate dispersion. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

The reaction of tetrakis(trimethylsiloxy)silane,QM4, and hexakis(trimethylsiloxy)disiloxane,Q2M6, with sodium hydroxide in ethanol

The reaction of the two model polyorganosiloxanes. QM₄ and Q₂M₆, with ethanolic sodium hydroxide is reported (Q=SiO_{4 2} andM=Me₃SiO_{1 2}). Removal of theM groups from QM₄ was rapid and led to the formation of a sodium silicate species which was insoluble in organic solvents. The reaction with Q₂M₆, however, was incomplete and gave hybrid structures of the type Q₂M₆ (O_{1 2}Na). A possible pathway for the formation of the sodium silicate species from QM₄ is proposed.