Pristine Mixture Research Articles

Evaluating the role of soil EPS in modifying the toxicity potential of the mixture of polystyrene nanoplastics and xenoestrogen, Bisphenol A (BPA) in Allium cepa L.

The coexistence of emerging pollutants like nanoplastics and xenoestrogen chemicals such as Bisphenol A (BPA) raises significant environmental concerns. While the individual impacts of BPA and polystyrene nanoplastics (PSNPs) on plants have been studied, their combined effects are not well understood. This study examines the interactions between eco-corona formation, physicochemical properties, and cyto-genotoxic effects of PSNPs and BPA on onion (Allium cepa) root tip cells. Eco-corona formation was induced by exposing BPA-PSNP mixtures to soil extracellular polymeric substances (EPS), and changes were analyzed using 3D-EEM, TEM, FTIR, hydrodynamic diameter, and contact angle measurements. Onion roots were treated with BPA (2.5, 5, and 10 mgL-1) combined with plain, aminated, and carboxylated PSNPs (100 mgL-1), with and without EPS interaction. Toxicity was assessed via cell viability, oxidative stress markers (superoxide radical, total ROS, hydroxyl radical), lipid peroxidation, SOD and catalase activity, mitotic index, and chromosomal abnormalities. BPA alone increased cytotoxic and genotoxic parameters in a dose-dependent manner. BPA with aminated PSNPs exhibited the highest toxicity among the pristine mixtures, revealing increased chromosomal abnormalities, oxidative stress, and cell mortality with rising BPA concentrations. In-silico experiments demonstrated the relationship between superoxide dismutase (SOD), catalase enzymes, PSNPs, BPA, and their mixtures. EPS adsorption notably reduced cyto-genotoxic effects, lipid peroxidation, and ROS levels, mitigating the toxicity of BPA-PSNP mixtures.

Enhanced methane production during the anaerobic digestion of chicken manure through the addition of pristine and recovered biochar

This study investigates the impact of a 50:50 mixture of pristine and recovered biochar (CBC) on high-solids anaerobic digestion of chicken manure, comparing its performance with pristine biochar (PBC), recovered biochar (RBC), and a Control group. The experiment, conducted under mesophilic conditions using a 15% total solid content and 5% biochar dosage, showed that CBC treatment achieves the highest cumulative biogas production (314 mL g−1-VS) and the highest cumulative methane production o(112 mL g−1-VS) over 21 days. Further, digesters containing CBC exhibited the highest rate of COD removal (80.8%), surpassing digesters amended with PBC (71.1%), RBC (69.2%) and Control (57.8%). Although digesters amended with PBC showed a higher TAN adsorption capacity of 48 mg g−1 compared to the 32 mg g−1 of CBC, both TAN adsorption and the existing microbial population of 1.2 × 1014 microbes per gram, have allowed CBC to exhibit superior digester performance. These findings offer valuable insights for optimising anaerobic digestion processes and cutting operational costs in waste-to-energy projects incorporating biochar as an additive.

The role of algal EPS in reducing the combined toxicity of BPA and polystyrene nanoparticles to the freshwater algae Scenedesmus obliquus

Both Bisphenol A (BPA) and polystyrene nanoplastics (PSNPs) are routinely found in several consumer products such as packaging materials, flame retardants, and cosmetics. The environment is seriously endangered by nano- and microplastics. In addition to harming aquatic life, nanoplastics (NPs) also bind to other pollutants, facilitating their dispersion in the environment and possibly promoting toxicity induced by these pollutants. The toxic effects of polystyrene nanoplastics (PS-NPs) and BPA were examined in this study, as well as the combined toxic impacts of these substances on the freshwater microalgae Scenedesmus obliquus. In addition, the exopolymeric substances (EPS) secreted by algae will interact with the pollutants modifying their physicochemical behaviour and fate. This work aimed to investigate how algal EPS alters the combined effects of BPA and PSNPs on the microalgae Scenedesmus obliquus. The algae were exposed to binary mixtures of BPA (2.5, 5, and 10 mg/L) and PSNPs (1 mg/L of plain, aminated, and carboxylated PSNPs) with EPS added to the natural freshwater medium. Cell viability, hydroxyl and superoxide radical generation, cell membrane permeability, antioxidant enzyme activity (catalase and superoxide dismutase), and photosynthetic pigment content were among the parameters studied to determine the toxicity. It was observed that for all the binary mixtures, the carboxylated PSNPs were most toxic when compared to the toxicity induced by the other PSNP particles investigated. The maximum damage was observed for the mixture of 10 mg/L of BPA with carboxylated PSNPs with a cell viability of 49%. When compared to the pristine mixtures, the EPS-containing mixtures induced significantly reduced toxic effects. A considerable decrease in reactive oxygen species levels, activity of antioxidant enzymes (SOD and CAT), and cell membrane damage was noted in the EPS-containing mixtures. Reduced concentrations of the reactive oxygen species led to improved photosynthetic pigment content in the cells.

Structure-function relationships of pectic polysaccharides from broccoli by-products with in vitro B lymphocyte stimulatory activity

To study structure-function relationships of pectic polysaccharides with their immunostimulatory activity, broccoli by-products were used. Pectic polysaccharides composed by 64 mol% uronic acids, 18 mol% Ara, and 10 mol% Gal, obtained by hot water extraction, activated B lymphocytes in vitro (25–250 μg/mL). To disclose active structural features, combinations of ethanol and chromatographic fractionation and modification of the polysaccharides were performed. Polysaccharides insoluble in 80 % ethanol (Et80) showed higher immunostimulatory activity than the pristine mixture, which was independent of molecular weight range (12–400 kDa) and removal of terminal or short Ara side chains. Chemical sulfation did not promote B lymphocyte activation. However, the action of pectin methylesterase and endo-polygalacturonase on hot water extracted polysaccharides produced an acidic fraction with a high immunostimulatory activity. The de-esterified homogalacturonan region seem to be an important core to confer pectic polysaccharides immunostimulatory activity. Therefore, agri-food by-products are a source of pectic polysaccharide functional food ingredients.

Experimental and numerical study on the thermal energy storage performance of a novel phase-change material for radiant floor heating systems

Thermal energy storage shows great potential for improving the energy performance of building heating systems. Phase-change materials are a promising type of storage medium for building envelopes due to their high storage capacity. However, the low thermal conductivity and easy leakage of the hydrated salts inhibit their practical application. In this study, sodium acetate trihydrate–acetamide/modified expanded graphite was prepared as a novel thermal-stable storage medium for space heating applications. Leakage protection tests showed that modified expanded graphite presented a better compatibility with hydrated salts. The thermal conductivity of the novel composite reached 1.87 W/m∙K, 4.5 times higher than that of the pristine mixture. Moreover, the PCM exhibited a great thermal reliability with a high latent heat of 161.9 kJ/kg and an acceptable supercooling degree of 2.2 °C after cycling. The thermal performance of radiant floor heating systems with different layer structures was evaluated. The heat storage and release of the storage medium were beneficial for reducing the temperature fluctuation and improving the indoor comfort. The operation cost of the system without the storage medium was 73.1% higher than that with the storage medium. This performance enhancement suggests that the novel composite is a competitive candidate for heating applications.

MaSTR™: an effective probabilistic genotyping tool for interpretation of STR mixtures associated with differentially degraded DNA.

The recently developed probabilistic genotyping software package MaSTR™ (SoftGenetics LLC) was used to develop statistical weight estimates for a variety of two-person STR mixture profiles with differentially degraded sources of DNA. A total of 864 analyses, on 144 two-person profiles, were performed. Mixture ratios ranged from 1:1 to 1:10, including pristine sources of DNA and various combinations of artificially degraded DNA (average size fragments of 150 or 250 bps). Quantities of DNA template were varied (0.1 to 0.5 ngs of total input) and MaSTR™ analysis was performed with eight chains of 10,000 or 40,000 iterations, with or without a conditioning profile to generate likelihood ratio (LR) values. Overall, the software performed as expected. The resulting log(LR) values for pristine mixture profiles were typically greater than 1030. Lower-quality mixture data associated with sources of DNA at ~ 0.05 ngs for each contributor resulted in peak imbalance and allelic dropout which reduced the weight in support of a contributor. This was exacerbated by higher levels of degradation, with some instances resulting in log(LR) values in support of an exclusion. These studies provide additional support for the use of probabilistic genotyping software solutions in forensic investigations, addressing concerns raised by the President's Council of Advisors on Science and Technology (PCAST).

Effect of γ-irradiation on various important physical properties of a room temperature ferroelectric liquid crystal mixture and its silver nanocomposite

A room temperature ferroelectric liquid crystal (FLC) mixture and its silver nanocomposite have been irradiated by various doses of γ-radiation from 60Co. Phase transition temperatures, dielectric permittivity, optical tilt angle, spontaneous polarization, rotational viscosity, switching time, and conductivity of the systems have been determined as a function of the irradiation dose and temperature. Phase transition temperatures and optical tilt angles of both the systems decrease significantly, more in the pristine mixture, meaning a decrease of the order parameter with irradiation. Remarkable changes are exhibited in the dielectric permittivity as well as in their molecular dynamics as confirmed by the change in Goldstone and soft mode relaxation frequencies. The conductivity of the irradiated mixture increases considerably compared to its nanocomposite probably due to the production of more ions by the radiolysis process. Spontaneous polarization, rotational viscosity, and switching time are also found to decrease linearly with irradiation dose. At the maximum absorbed dose, switching time decreases by 140 μs in the pristine mixture and 110 μs in the nanocomposite suggesting their more suitability in display applications. The concentration of the chiral dopant also influences the impact of irradiation.

Thermal stability of starch bionanocomposites films: Exploring the role of esterified cellulose nanofibers isolated from crop residue

Thermal stability and degradation kinetics were studied for glycerol plasticized starch (GPS) nanocomposites reinforced with cellulose nanofibers (CNFs) extracted from wheat straw, a crop residue. To assess the effect of surface modifications on CNFs in improving thermal degradation behavior, three types of CNFs were used viz pristine (p-CNFs), esterified (m-CNFs) and a mixture of pristine and esterified (x-CNFs) in equal ratio. Three kinetics models Ozawa-Flynn, Freidman and Kissinger’s were used to evaluate activation energy of thermal degradation for pristine and nanocomposite samples. Properties like morphology, crystallinity and water vapor permeability (WVP) were also evaluated. Morphology of m-CNF/GPS bionanocomposites films was superior as compared to other films with better interfacial bonding. Moreover, m-CNFs also exhibited 81 % reduction WVP as compared to pristine GPS films. Activation energy revealed significant enhancement i.e. as high as 52 % in thermal stability with addition of CNFs. Consequent relation between morphology and thermal stability was also established.

Very ductile polymer concrete using carbon nanotubes

Polymer concrete (PC) is a type of concrete where a polymer is used to replace cement as the binder. PC is an impermeable and chemical resistant concrete with appreciable mechanical properties. However, for most structural engineers, PC advantages do not outweigh its higher cost when compared with normal cement concrete. We report on the production of very ductile PC (measured by tensile strain at failure) with appreciable tensile strength utilizing a hybrid mixture of pristine and carboxyl (COOH) functionalized multi-walled carbon nanotubes (MWCNTs) at 2.0 wt% of epoxy resin. Experimental investigations reveal that COOH functionalization maximizes PC ductility reaching unprecedented 5.5% failure strains and increasing toughness by 184%. Fourier transformation infrared spectroscopy and dynamic modulus analysis indicate an increase in crosslinking density of the epoxy matrix up to 84% due to the carbonyl band formation induced by the COOH functionalization of MWCNTs. The significant improvement in ductility and energy absorption provides a promising platform for creating very ductile PC with attractive properties.

The influence of high-energy ball milling on the heterogeneous reaction kinetics in the Ti-Si system

The high-temperature (1300–1600 K) kinetics for the Ti-Si reactive system were investigated using electro-thermal analysis. The influence of short-term (1–3 min) high-energy ball milling (HEBM) of Ti+0.6Si heterogeneous powder mixtures on the kinetic parameters was also studied. It was shown that HEBM leads to a significant decrease of the apparent activation energy (Ea) of the solid-state reaction between silicon and titanium. For the non-milled mixture, Ea is 339 ± 63 kJ/mol, while after 3 min of HEBM it drops more than twice to 148 ± 12 kJ/mol. The reaction initiation temperature also decreases with an increase of HEBM time: from 1467 ± 62 K for the pristine mixture to 1110 ± 42 K after 3 min of mechanical treatment. The conclusion was made that a decrease of crystalline size and an increase of the crystal lattice defect concentration, which in combination enhance the grain boundary diffusion, can be responsible for the high reactivity of the mechanically activated mixtures.

Follow-up observations of extremely metal-poor stars identified from SDSS

The most metal-poor stars in the Milky Way witnessed the early phases of formation of the Galaxy, and have chemical compositions that are close to the pristine mixture from Big Bang nucleosynthesis, polluted by one or few supernovae. Only two dozen stars with ([Fe/H]< -4) are known, and they show a wide range of abundance patterns. It is therefore important to enlarge this sample. We present the first results of an effort to identify new extremely metal-poor stars in the Milky Way halo. Our targets have been selected from low-resolution spectra obtained as part of the Sloan Digital Sky Survey, and followed-up with medium resolution spectroscopy on the 4.2 m William Herschel Telescope and, in a few cases, at high resolution on the the 9.2 m Hobby-Eberly Telescope. Stellar parameters and the abundances of magnesium, calcium, iron, and strontium have been inferred from the spectra using classical model atmospheres. We have also derived carbon abundances from the G band. We find consistency between the metallicities estimated from SDSS and those from new data at the level of 0.3 dex. The analysis of medium resolution data obtained with ISIS on the WHT allow us to refine the metallicities and in some cases measure other elemental abundances. Our sample contains 11 new metal-poor stars with [Fe/H] < -3.0, one of them with an estimated metallicity of [Fe/H] ~ -4.0. We also discuss metallicity discrepancies of some stars in common with previous works in the literature. Only one of these stars is found to be C-enhanced at about [C/Fe]~+1, whereas the other metal-poor stars show C abundances at the level of [C/Fe]~+0.45.

Partial resetting of the U-Th-Pb systems in experimentally altered monazite: Nanoscale evidence of incomplete replacement

Research Article| June 01, 2016 Partial resetting of the U-Th-Pb systems in experimentally altered monazite: Nanoscale evidence of incomplete replacement Alexis Grand’Homme; Alexis Grand’Homme 1ISTerre (Institut des Sciences de la Terre), University Grenoble Alpes, 38058 Grenoble Cedex 9, France Search for other works by this author on: GSW Google Scholar Emilie Janots; Emilie Janots * 1ISTerre (Institut des Sciences de la Terre), University Grenoble Alpes, 38058 Grenoble Cedex 9, France *E-mails: janotse@ujf-grenoble.fr; anne.magali.seydoux@univ-st-etienne.fr. Search for other works by this author on: GSW Google Scholar Anne-Magali Seydoux-Guillaume; Anne-Magali Seydoux-Guillaume * 2Laboratoire Magmas et Volcans LMV (UMR 6524 CNRS-UBP-UJM1 IRD), 42023 Saint-Etienne, France *E-mails: janotse@ujf-grenoble.fr; anne.magali.seydoux@univ-st-etienne.fr. Search for other works by this author on: GSW Google Scholar Damien Guillaume; Damien Guillaume 2Laboratoire Magmas et Volcans LMV (UMR 6524 CNRS-UBP-UJM1 IRD), 42023 Saint-Etienne, France Search for other works by this author on: GSW Google Scholar Valérie Bosse; Valérie Bosse 3Laboratoire Magmas et Volcans LMV (UMR 6524 CNRS-UBP-UJM-IRD), 63038 Clermont-Ferrand, France Search for other works by this author on: GSW Google Scholar Valérie Magnin Valérie Magnin 1ISTerre (Institut des Sciences de la Terre), University Grenoble Alpes, 38058 Grenoble Cedex 9, France Search for other works by this author on: GSW Google Scholar Geology (2016) 44 (6): 431–434. https://doi.org/10.1130/G37770.1 Article history received: 08 Feb 2016 rev-recd: 12 Apr 2016 accepted: 12 Apr 2016 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Alexis Grand’Homme, Emilie Janots, Anne-Magali Seydoux-Guillaume, Damien Guillaume, Valérie Bosse, Valérie Magnin; Partial resetting of the U-Th-Pb systems in experimentally altered monazite: Nanoscale evidence of incomplete replacement. Geology 2016;; 44 (6): 431–434. doi: https://doi.org/10.1130/G37770.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Alteration experiments on natural monazite crystals (Manangotry standard, Madagascar) under alkali conditions at 300, 400, 500 and 600 °C and 200 MPa were conducted to clarify mechanisms behind incomplete resetting of U-Th-Pb geochronological systems in monazite replaced by dissolution and precipitation processes. Above 400 °C, experimental products show typical replacement textures: a compositionally distinct monazite rim, referred as altered rim, surrounds the primary monazite (Mnz1). Isotopic and electron microprobe U-Th-Pb in situ dating of the altered rim yields intermediate ages between pristine monazite (555 Ma) and complete experimental resetting (0 Ma). Lead is systematically detected in altered rims, with concentration decreasing from 400 °C to 600 °C. The origin of incomplete resetting is elucidated with transmission electron microscope images that reveal an incomplete replacement of Mnz1 by a secondary monazite (Mnz2) within the altered rim. With increasing temperature, the size and volume of the Mnz2 within the altered rim become more important. Because no structural Pb or Pb nanoinclusions were observed, Pb in the altered rim is attributed to the Mnz1 component. Partial resetting of U-Th-Pb systems depends on the nanomixture of different Mnz1 proportions in the analyzed volume, and explains the higher rejuvenation at 600 °C than at lower temperatures. Although microanalytical techniques have the spatial resolution to date micrometer-sized rims, they are unable to resolve a nanoscale mixture of pristine and secondary monazite that could occur in altered rims formed by fluid-driven replacement, especially at low temperatures. Porosity and/or inclusions and complex age scattering in zoned monazite are significant markers that can indicate a possible nano-sized partial replacement. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Radical copolymerization of 2-methoxy-4-formylphenyl (meth)acrylates with L-(−)-menthyl (meth)acrylates

The radical copolymerization of 2-methoxy-4-formylphenyl (meth)acrylates with L-(−)-menthyl (meth)acrylates has been studied, and the reactivity ratios have been determined. It has been found that the bulk copolymerization of these monomers% results in insoluble copolymers when the content of 2-methoxy-4-formylphenyl (meth)acrylates in the pristine mixture exceeds 36 mol % and conversion exceeds ∼30%. However, in the course of this reaction, soluble copolymers are formed in solution.

Desorption kinetics of lithium amide/magnesium hydride systems at constant pressure thermodynamic driving forces

Lithium amide and magnesium hydride are lightweight materials with high hydrogen-holding capacities and thus they are of interest for hydrogen storage. In the present work mixtures with initial molar compositions of (LiNH2 + MgH2) and (2LiNH2 + MgH2) were ball milled with and without the presence of 3.3 mol% potassium hydride dopant. Temperature programmed desorption, TPD, analyses of the mixtures showed that the potassium hydride doped samples had lower onset temperatures than their corresponding pristine samples. The dehydrogenation kinetics of the doped and pristine mixtures was compared at 210 °C. In each case a constant pressure thermodynamic driving force was applied in which the ratio of the plateau pressure to the applied hydrogen pressure was set at 10. Under equivalent conditions, the (LiNH2 + MgH2) mixture desorbed hydrogen about 4 times faster than the (2LiNH2 + MgH2) mixture. The addition of potassium hydride dopant was found to have a 25-fold increase on the desorption rates of the (2LiNH2 + MgH2) mixture, however it had almost no effect on the desorption rates of the (LiNH2 + MgH2) mixture. Activation energies were determined by the Kissinger method. Results showed the potassium hydride doped mixtures to have lower activation energies than the pristine mixtures.

Aligned 3D human aortic smooth muscle tissue via layer by layer technique inside microchannels with novel combination of collagen and oxidized alginate hydrogel

Tissue engineering of the small diameter blood vessel medial layer has been challenging. Recreation of the circumferentially aligned multilayer smooth muscle tissue has been one of the major technical difficulties. Some research has utilized cyclic stress to align smooth muscle cells (SMCs) but due to the long time conditioning needed, it was not possible to use primary human cells because of expeditious senescence occurred . We demonstrate rapid buildup of a homogeneous relatively thick (30-40 μm) aligned smooth muscle tissue via layer by layer (LBL) technique within microchannels and a soft cell-adhesive hydrogel. Using a microchannelled scaffold with gapped microwalls, two layers of primary human SMCs separated by an interlayer hydrogel were cultured to confluence within the microchannels. The SMCs aligned along the microchannels because of the physically constraining microwalls. A novel double layered gel consisting of a mixture of pristine and oxidized alginate hydrogel coated with collagen was designed to place between each layer of cells, leading to a thicker tissue in a shorter time. The SMCs penetrated the soft thin interlayer hydrogel within 6 days of seeding of the 2nd cell layer so that the entire construct became more or less homogeneously populated by the SMCs. The unique LBL technique applied within the micropatterned scaffold using a soft cell-adhesive gel interlayer allows rapid growth and confluence of SMCs on 2D surface but at the same time aligns the cells and builds up multiple layers into a 3D tissue. This pseudo-3D buildup method avoids the typical steric resistance of hydrogel embedding.

Photo-and pressure-induced transformations in the linear orthorhombic polymer of C60

Stability of the linear orthorhombic polymer of C60 under pressure and laser irradiation is studied by Raman scattering and X-ray diffraction measurements. The Raman spectrum at ambient pressure remains unchanged, in the time scale of the experiment, up to an intensity of 3200 W/cm2 of the 514.5 nm line of an Ar+ laser, but irreversible changes are observed at higher intensities. The Raman spectra recorded at increased pressure show similar irreversible changes even at the laser intensity as low as 470 W/cm2. The X-ray diffraction and Raman measurements of the pressure-treated samples, performed after pressure release, show that the nonirradiated material does not exhibit any changes in the crystal structure and phonon spectra. This behavior indicates a pressure-enhanced photo-induced transformation to a new polymeric phase characterized by a Raman spectrum that differs from those of the other known polymeric phases of C60. The Raman spectra of the phototransformed linear orthorhombic polymer of C60 were measured at a pressure of up to 29 GPa. The pressure dependence of the Raman mode frequencies show singularities near 4 GPa and 15 GPa, respectively, related to a reversible phase transition and an irreversible transformation to a metastable disordered phase. The diffuse Raman spectrum of the disordered phase does not exhibit substantial changes with an increase in pressure up to 29 GPa. The high-pressure phase transforms to a mixture of pristine and dimerized C60, after pressure release and exposure to ambient conditions for 30 h.

Pressure-induced transformations in the linear orthorhombic polymeric phase of C 60

The pressure-induced transformations in the linear orthorhombic polymer of C 60 have been studied by in situ Raman scattering. The simultaneous application of pressure and laser irradiation results in fast photo-transformation of the 1D-O polymer at pressures as low as ∼0.3 GPa. The pressure dependence of the Raman modes of the photo-transformed polymer shows singularities near ∼4 GPa and ∼15 GPa, related to reversible phase transition and transformation to a metastable highly disordered phase, respectively. The diffuse spectrum of the disordered phase does not exhibit essential changes for increasing pressure up to 29 GPa. The recovered high-pressure phase transforms to a mixture of pristine and dimerized C 60 within ∼30 h.

Pressure-induced transformation and phonon modes of the two-dimensional rhombohedral polymer ofC60:A Raman spectroscopic study

The Raman spectra and stability of the two-dimensional rhombohedral (2D-R) polymeric phase of ${\mathrm{C}}_{60}$ have been studied as a function of pressure up to \ensuremath{\sim}30 GPa at room temperature. The pressure dependence of the phonon frequencies is rather smooth and reversible to $Pl~15\mathrm{GPa}.$ At higher pressure the initially sharp and distinct Raman peaks become very broad and diffuse and the material undergoes an irreversible transformation to a new rather disordered phase. The intensity of the ${A}_{g}(2)$ pentagonal pinch (PP) mode rapidly decreases in the pretransitional pressure range and vanishes in the new phase. The high-pressure phase is recovered at normal conditions but is metastable and transforms under heating to a mixture of pristine and dimerized ${\mathrm{C}}_{60}$ as was evident by their Raman spectrum. The quenching of the PP mode, the retention of the molecular cage, and the irreversibility of the transition are the indications that the new high-pressure phase may be formed by random covalent bonding between ${\mathrm{C}}_{60}$ molecular cages in adjacent polymeric sheets of the 2D-R polymer of ${\mathrm{C}}_{60}.$

Structural stability of the rhombohedral 2D polymeric phase of C 60 studied by in situ Raman scattering at pressures up to 30 GPa

The structural stability of the rhombohedral two-dimensional (2D) polymeric phase of C 60 has been studied as a function of pressure up to ∼30 GPa at room temperature by means of in situ Raman scattering. An irreversible transformation to a new disordered phase was observed at a pressure of ∼15 GPa. The intensity of the A g(2) pentagonal pinch (PP) mode rapidly decreases in the pre-transitional pressure range while the Raman spectrum of the transformed material becomes very diffuse. The high-pressure phase recovered to normal conditions is metastable and transforms under heating to a mixture of pristine and dimerized C 60 as can be seen by their Raman spectra. The retention of the fullerene molecular cage at high pressure and quenching of the PP-mode are the indications that the high-pressure phase may be associated with a random creation of new polymeric bonds between the molecules in adjacent polymeric planes of the 2D-rhombohedral phase of C 60.

Electrochemical impedance measurements of p-doped polyacetylene in LiGaCl 4CH 3NO 2 medium

Impedance measurements have been carried out on new oriented polyacetylene during electrochemical intercalation in a LiGaCl 4CH 3NO 2 medium. The electrocapillary approach of the intercalation process into pyrographite, a well-defined host material, is extrapolated to polyacetylene. Results are discussed on the basis of galvanostatic, cyclic voltammetry and a.c. impedance measurements. In the case of a constant current charge of polyacetylene, it is seen that Nyquist diagrams obtained for different dopant concentrations ( y) are typical of the capacitive behaviour of a blocking porous electrode. We can conclude that intercalation into polyacetylene is mainly a capacitive process: for 0 < y ⩽ 0.02, the measured capacity varies with the ratio doped (CH) x /undoped (CH) x ; for 0.02 < y < 0.05, the capacity of the electrode remains constant although X-ray studies show that the sample is a mixture of pristine and doped (CH) x . The low-frequency internal capacitance is thus related to the diffusion of the intercalated species through the external doped part of the fibrils.