Multiwall carbon nanotubes (MWCNTs) have been functionalized via addition of undecyl (C11-) radicals generated by thermal decomposition of lauroyl peroxide. The functionalized MWCNTs (C11-MWCNTs) ...were characterized by Raman, IR spectroscopy, and thermogravimetric analysis (TGA). Isotactic polypropylene (iPP) and syndiotactic polypropylene (sPP) nanocomposites containing both purified and alkyl-functionalized MWCNTs have been synthesized via in situ polymerization method with the use of C 2- and C s -symmetry zirconocenes activated by MAO in liquid propylene medium. The effect of incorporating C11-MWCNTs on structural, electrical, and mechanical properties of the polypropylene-based nanocomposites has been studied. Analysis of electrical properties in the microwave range elucidates interfacial transformations in the composites induced by MWCNT functionalization and evaluates relative aspect ratios for the filler particles in different systems. The synthesized materials demonstrate improved filler dispersion and mechanical characteristics as a result of nanotube chemical functionalization. The MWCNT functionalization leads to markedly improved nanocomposite plasticity and noticeable enhancement of sPP tensile modulus.
Isotactic polypropylene and elastomeric stereoblock polypropylene nanocomposites containing 0.1−3.5 wt % multiwall carbon nanotubes (MWCNTs) have been synthesized via the in situ polymerization ...approach using MAO-activated C 2- and C 1-symmetry ansa-zirconocenes, a technique that has not been previously reported in literature. Fracture morphology examination of the nanocomposites revealed very efficient distribution of the MWCNTs within the isotactic polypropylene matrix, yet interfacial adhesion level and the reinforcement efficiency were dependent on the nanotube loadings. The elastomeric stereoblock polypropylene/MWCNT and the isotactic polypropylene-based nanocomposites exhibited different morphologies depending on the synthesis peculiarities. For isotactic polypropylene, Youngʼs modulus increased by ∼22% even at 0.1 wt % MWCNT loading, and further modulus growth was observed at higher filler contents. Relatively low permittivity values and considerable dielectric losses in microwave range infer that the obtained nanocomposites can find use as efficient electromagnetic shielding materials and microwave absorbing filters. Outstanding improvement of thermal stability (∼60 °C at maximum weight loss rate temperature) has been achieved for isotactic polypropylene upon incorporating only 3.5 wt % of carbon nanotubes.
A new approach combining Raman spectrometry and laser induced breakdown spectrometry (LIBS) within a single laser event was suggested. A pulsed solid state Nd:YAG laser running in double pulse mode ...(two frequency-doubled sequential nanosecond laser pulses with dozens microseconds delay) was used to combine two spectrometry methods within a single instrument (Raman/LIBS spectrometer). First, a low-energy laser pulse (power density far below ablation threshold) was used for Raman measurements while a second powerful laser pulse created the plasma suitable for LIBS analysis. A short time delay between two successive pulses allows measuring LIBS and Raman spectra at different moments but within a single laser flash-lamp pumping. Principal advantages of the developed instrument include high quality Raman/LIBS spectra acquisition (due to optimal gating for Raman/LIBS independently) and absence of target thermal alteration during Raman measurements. A series of high quality Raman and LIBS spectra were acquired for inorganic salts (gypsum, anhydrite) as well as for pharmaceutical samples (acetylsalicylic acid). To the best of our knowledge, the quantitative analysis feasibility by combined Raman/LIBS instrument was demonstrated for the first time by calibration curves construction for acetylsalicylic acid (Raman) and copper (LIBS) in gypsum matrix. Combining ablation pulses and Raman measurements (LIBS/Raman measurements) within a single instrument makes it an efficient tool for identification of samples hidden by non-transparent covering or performing depth profiling analysis including remote sensing.
Graphical abstract
Combining Raman and laser induced breakdown spectroscopy by double pulse lasing
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-Dimethylformamide (DMF) is often used as a liquid medium for the exfoliation of graphene for further use in a wide range of fields of science and technology: biomedical research, the ...technology of materials for electronics, and polymer composites. However, the nature of the processes of exfoliation of graphene sheets from the surface of micron-sized graphite particles and the subsequent stabilization of its dispersion has hardly been studied. In this work, the stages of graphene suspension formation in DMF and its mixture with aqua molecules under the action of ultrasonic irradiation were investigated. Characterization of graphene suspensions was carried out using transmission electron microscopy (TEM), dynamic light scattering (DLS), FTIR spectroscopy, Raman spectroscopy, and UV-Vis spectroscopy. The presence of aqua in the colloid system leads to the predominant formation of 3D graphene sheets with larger linear dimensions than in pure DMF. The defectiveness of the basal plane of graphene sheets obtained by exfoliation in pure DMF is significantly lower than in a mixture with aqua, while the edge defectiveness in both cases is rather low. A comprehensive analysis of the spectral data and TEM results with electron diffraction shows that in both cases graphene in suspensions is multilayer. However, if in pure DMF the graphene suspension was formed in one stage and its layering did not exceed five, then in the presence of aqua the formation of the dispersed phase occurred in two stages. At the second stage, a partial association of the sheets from finer fraction increases the sizes of graphene sheets,
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, the particles with higher surface energy were attached to larger ones or associated with each other. Perhaps this is because aqua molecules included in the complexes and removed from the global hydrogen bond system, tend to restore these bonds and, thus, facilitate the fusion of the smallest and lightest graphene sheets.
In pure DMF, the graphene layering is mainly limited to 5 layers; in the aqua presence, partial association of the lightest graphene sheets with the highest surface energy occurs.
Staphylococcus aureus is an extremely infectious and malignant pathogen among many bacteria species. The aim of this work is to provide a robust classification model that would be able to identify S. ...aureus independent of the culture growth stage and the variations in bacteria concentration in suspension and also one that would be able to identify the pathogen among both taxonomically close species of the same genus and taxonomically distant species of different genera, using Fourier transform infrared spectroscopy (FTIR). In total, the spectra of 141 isolates of 17 bacteria have been used. Based on a combination of principal component analysis (PCA) and linear discriminant analysis (LDA), an identification model providing 100% sensitivity and 98% specificity was built. Inherent reliability and flexibility of the model have been shown. The proposed method of analysis allows us to get closer to the diagnostic requirements in the field of clinical microbiology, and it can be utilized for typing of other pathogenic bacteria species.
Composite materials of isotactic polypropylene and graphene nanoplatelets were synthesized by in situ polymerization in liquid propylene with the use of metallocene catalyst system. Graphene ...nanoplatelets were prepared by chemical oxidation of graphite and subsequent reduction. Preliminary ultrasonic treatment of GNP suspensions in toluene results in better dispersion of particles, both in liquid polymerization medium and in polymer matrix. GNP particles consist of 3–5 graphene layers and have aspect ratio 40. In composites with pristine GNP particles their aspect ratio is 110, whereas ultrasonic processing reduces aspect ratio to 40–50. Ultrasonic processing provides, apparently, a more uniform distribution of GNP particles, which in nanocomposite are largely individualized. This change of aspect ratio of filler particles and their aggregates results in different properties of composites with pristine and sonicated GNP. Percolation threshold for composites with pristine GNP is 0.25 vol.%. In composites with sonicated GNP percolation threshold is 2–3 vol.%. This is due to reduction in the size of filler particles aggregates and much more uniform distribution of particles in polymer matrix after ultrasonic treatment.
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Carbon‐containing nanosize solid‐state phase have been produced in the atmospheric pressure microwave (MW) plasma ignited in the gas bubbles in liquid alkanes CnH2n+2 (n = 7, 8, 10, 15, 16). Gas ...bubbles are generated by flow of argon. According to SEM data, the solid‐state products are represented by particles having dimensions in the range of 100–200 nm. Raman spectra of the sooty‐like unpurified solid products permit to categorize them as sp3+sp2 mixed forms of carbon comprising mainly an “damaged grapheme” along with a “few‐layer” graphite nanoparticles. NMR spectra of the solid products show strong aromatization and formation of various unsaturated molecular fragments. FTIR‐ATR spectra indicate that the carbonaceous nanoparticles are contaminated with minor amounts of different hydrocarbon residues and oxidized species.
Microwave plasma in liquid dielectrics is new area of plasma processing. In this paper, we focus on characterization of carbon nanoparticles produced in microwave discharge in liquid alkanes. It was shown that nanoparticles can be classified as the damaged graphene.
Native fibrinogen is a key blood plasma protein whose main function is to maintain hemostasis by virtue of producing cross-linked fibrin clots under the influence of thrombin and fibrin-stabilizing ...factor (FXIIIa). The aim of this study was to investigate mechanisms of impairment of both the molecular structure and the spatial organization of fibrinogen under ozone-induced oxidation. FTIR analysis showed that ozone treatment of the whole fibrinogen molecule results in the growth of hydroxyl, carbonyl, and carboxyl group content. A similar analysis of fibrinogen D and E fragments isolated from the oxidized protein also revealed transformation of distinct important functional groups. In particular, a remarkable decay of N–H groups within the peptide backbone was observed along with a lowering of the content of C–H groups belonging to either the aromatic moieties or the aliphatic chain CH2 and CH3 units. The model experiments performed showed that the rather unexpected decay of the aliphatic CH units might be caused by the action of hydroxyl radicals, these being produced in the water solution from ozone. The observed dissimilarities in the shapes of amide I bands of the fibrinogen D and E fragments before and after ozone treatment are interpreted in terms of feasible local conformational changes affecting the secondary structure of the protein. Taken as a whole, the FTIR data suggests that the terminal D fragments of fibrinogen are markedly more susceptible to the ozone-induced oxidation than the central E fragment. The data on elastic and dynamic light scattering provide evidence that, in the presence of FXIIIa, both the unoxidized and the oxidized fibrinogen molecules bind to one another in an “end-to-end” fashion to form the flexible covalently cross-linked fibrinogen homopolymers. The γ and α polypeptide chains of the oxidized fibrinogen proved to be involved in the enzymatic cross-linking more readily than those of unaffected fibrinogen. The experimental data on fibrinogen oxidation acquired in the present study, combined with our earlier findings, make it reasonable to suppose that the spatial structure of fibrinogen could be evolutionarily adapted to some reactive oxygen species actions detrimental to the protein function.
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•Damage of the chemical and spatial structure of fibrinogen under oxidation is studied.•The fibrinogen D region is more sensitive to oxidation compared to the E region.•End-to-end interaction of fibrinogen molecules forms coiled-like homopolymers.•Oxidized fibrinogen is more easily affected by FXIIIa than the pristine protein.
The plasma fibrin-stabilizing factor (pFXIII) function is to maintain a hemostasis by the fibrin clot stabilization. The conversion of pFXIII to the active form of the enzyme (FXIIIа) is a multistage ...process. Ozone-induced oxidation of pFXIII has been investigated at different stages of its enzyme activation. The biochemical results point to a decrease of an enzymatic activity of FXIIIа depending largely on the stage of the pFXIII conversion into FXIIIа at which oxidation was carried out. UV-, FTIR- and Raman spectroscopy demonstrated that chemical transformation of cyclic, NH, SH and S–S groups mainly determines the oxidation of amino acid residues of pFXIII polypeptide chains. Conversion of pFXIII to FXIIIa proved to increase protein sensitivity to oxidation in the order: pFXIII<pFXIII activated by thrombin<pFXIII in the presence of calcium ions<FXIIIa. The dynamic light scattering data indicate that the three-dimensional structure of pFXIII becomes loosened due to oxidative modification. ESR spectroscopy data also point to conformational changes of the fibrin-stabilizing factor under oxidation. Taking into account these new findings it seems reasonable to assume that the inhibitory/carrier FXIII-B subunits can serve as scavengers of ROS. Hypothetically, this mechanism could help to protect the key amino acid residues of the FXIII-A subunits responsible for the enzymatic function of FXIIIa.
•Oxidation of pFXIII at different stages of its activation is studied.•Protein sensibility to oxidation depends on interaction of A and B heterosubunits.•B subunits protect key amino acid residues of A subunits during ROS attack.•For the first time, B subunits are suggested to perform antioxidant function.
