Distribution Of Chemical Bonds Research Articles

Facile and cost-effective PDMS double-casting method based on curing temperature and ratio for solvent detecting applications

This study proposes a polydimethylsiloxane (PDMS) double-casting method based on curing ratio and temperature. The master mold is fabricated by first curing with high-temperature, high curing agent ratio of PDMS, followed by secondary curing with low-temperature, low-ratio PDMS to create a replica mold. The distribution of the Si–H stretch bonding and the CH3 symmetric and asymmetric stretching are altered when the curing temperature and curing ratio sequence is changed. The difference in the distribution of chemical bonds at the interface between the two molds results in double casting. Moreover, the roughness and water contact angle are measured to determine the changes in the surface properties of the master and replica molds after double casting. The double-casting method maintains the hydrophobicity of both the master and replica molds without altering the properties of PDMS. Furthermore, the one-dimensional pattern formed by the interlayer structure of the fused deposition modeling-type three-dimensional (3D) printing mold is successfully double cast. Finally, the chemical sensor for detecting the type of solvent was fabricated using the double-casting method and experimentally demonstrated. This study demonstrates a facile, simple, and cost-effective PDMS double-casting method for 3D-printed mold replicas.

Nanoscale analysis of the interface of dip layer/rubber in fiber/rubber composites

The reaction mechanism and the interfacial modulus gradient of the interfacial transition layer between the environmentally friendly dipping system (PAL) and the rubber have not been fully studied. In order to better understand the chemical structures and nano-mechanical properties of the interface between the dip layer and the rubber, we used advanced atomic force microscope (AFM) and nanoscale Fourier transform infrared spectroscopy (nano-FTIR) to perform detailed analysis in this article. The characterization of interfacial nano-mechanical properties and chemical structures is very significant for the illustration of interfacial adhesion mechanism. AFM can effectively characterize the detailed interfacial modulus gradient and the thickness of interface, while nano-FTIR can comprehensively measure the interfacial chemical structures and the distribution of chemical bonds. The results suggest that the thickness of the interface between the PAL dip layer and the rubber matrix is 175 nm, and the crosslinking density of the interfacial layer is high, which explains that the failure location of fiber/rubber composites after pull-out tests occurs on the side of the rubber matrix. Similarly, the microstructure of resorcinol-formaldehyde-latex (RFL) system was also characterized, and the preparation of RFL usually requires carcinogenic and toxic substances such as formaldehyde and resorcinol.

Elaeagnus umbellata fruit - chemical composition, bioactive compounds, and kinetic of DPPH inhibition compared to standard antioxidants


 umbellata (Autumn Olive) is a medicinal plant used in traditional Asian medicine. In this study, we examine E. umbellata, which grows in central Europe (Poland). Despite significant climatic differences in both regions, we show that the fruits have a similar chemical composition and antioxidant activity to those observed in their native areas. For the first time, we examined the fatty acid composition of E. umbellata, showing that unsaturated fatty content for as much as 88.67% of total fat. Including the content of essential polyunsaturated fatty acids was over 50% of the total fat. We also examined proximate content, the content of fat-soluble vitamins, lycopene, beta carotene, and the mineral composition of the fruit. Moreover, using FT-IR spectrometry, we have shown that the fruits of the Autumn olive can change the distribution of chemical bonds when treated with hydrogen peroxide. The fruits of E. umbellata showed dose-dependent antioxidant properties with IC50 values of 76.27 µg / ml We also investigated the kinetic antioxidant activity of E. umbellata fruits based on DPPH radical inhibition compared to standard antioxidants (vitamin c and BHT). We have shown that using available protocols to spectrophotometrically study antioxidants' reaction with the DPPH radical may underestimate the effects of the Autumn Olive fruits.

Fracture forms and multiple undulated morphology of polycarbonate LTW by introducing carbon black coated copper film

In the process of laser transmission welding (LTW) polymer with metal film as the laser absorber, few research reports related to the welding interface morphology and the causes have been published. In this study, carbon black coated copper film was selected as the laser absorber for polycarbonate (PC) laser transmission welding. Three typical fracture forms were analyzed and the relevant welding strength and width were also listed. In order to research the welding interface morphology and chemical bond distribution, the morphology of welding interface on the longitudinal section was observed by optical microscope and the tests of scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) on the cross section were performed. Dispersive bubbles and undulated copper film were found around the welding interface. To prove the causes of multiple undulating features, a thermal expansion test and thermal stress simulation analysis were done. The results indicated the expansion of PC has a more significant impact on the form of thermal stresses and the thermal stresses around the laser spot lead to the formation of multiple undulations at the weld.

Multi-scale study on mechanical property and strength prediction of aeolian sand concrete

The aim of this work is to promote the utilization of aeolian sand for concrete production. The workability and mechanical property of aeolian sand concrete (ASC) is studied. The effect mechanisms of aeolian sand on the mechanical property of concrete are revealed from multiple scales. For the macro scale, use the pressure tester to test the compressive strength. For the mesoscopic, use the scanning electron microscope (SEM) to observe the structure of the interface transition zone (ITZ) and the nuclear magnetic resonance (NMR) to test the pore structure. Meanwhile, the distribution of chemical bonds is analyzed by the Fourier transform infrared (FT-IR) spectrometer and the microstructure of hydration products are characterized by the SEM for the microscopic. The results show that using parts of aeolian sand can improve the working and mechanical property of concrete. The physical influence mechanism is that it perfects the gradation of the aggregate and increases the density of concrete, reduces the effect of aggregate size and micro-region bleeding, improves the structure of ITZ and pores. For the chemical, it may accelerate the hydration reaction speed of cement and change the microstructure of hydration products. Finally, a strength prediction model of ASC is established based on the published and tested data, which agrees well with the tested result.

Atomistic simulations of the equation of state and hybridization of liquid carbon at a temperature of 6000 K in the pressure range of 1-25 GPa.

The equation of state and the structure of liquid carbon are studied by molecular simulation. Both classical and quantum molecular dynamics (QMD) are used to calculate the equation of state and the distribution of chemical bonds at 6000 K in the pressure range 1-25 GPa. Our calculations and results of other authors show that liquid carbon has a fairly low density on the order of 1.2-1.35 g/cm3 at pressures about 1 GPa. Owing to the coordination number analysis, this fact can be attributed to the high content of sp1-bonded atoms (more than 50% according to our ab initio computations). Six empirical potentials have been tested in order to describe the density dependence of pressure and structure at 6000 K. As a result, only one potential, ReaxFF/lg, was able to reproduce the QMD simulations for both the equation of state and the fraction of sp1, sp2, sp3-bonded atoms.

Examining the effect of physical fields on the adhesive strength of protective epoxy composite coatings

We examined and substantiated the effect of treating the compositions in the electromagnetic field and with ultrasound on the adhesive strength of epoxy composites that contain highly dispersed particles of ferro-, para- and diamagnetic nature. It was established experimentally that the optimal content of highly dispersed fillers is 6 mass fractions. The studies conducted confirm the prospects of using the treatment of compositions in physical fields for obtaining epoxy composite protective coatings. The given technology enables to ensure high adhesive strength (60–70 MPa) of bonds between a coating and a metal base, to increase the degree of structuring (G=99.7 %) and to reduce by 65 % internal stresses in coatings. We achieved an increase in the number of physical-chemical bonds between an epoxy polymer binder and the surface of highly dispersed particles by increasing the mobility of segments of macromolecules and improving the interaction between components of the system under the influence of external physical fields. By using the electron microscopy method, we registered a uniform distribution of ferro- and paramagnetic particles in epoxy composites after treating the compositions in the electromagnetic field. This occurs due to the orientation of the dipole segments of macromolecules in a force field and the uniform distribution of chemical bonds in the structure of epoxy composite. The received epoxy composite coatings with highly dispersed powders after treating the compositions in the physical field are characterized by defect-free structure. Epoxy composite coatings could be used as wear- and corrosion resistant coatings for parts of machines and mechanisms in automotive and instrument-making industries, as well as in the oil and gas sector. Such parts can operate under conditions of temperature gradient, mechanical stresses, deformations and aggressive impacts.

Characterization of amorphous Zr–Si–C thin films deposited by DC magnetron sputtering

Zrx(SiyC1–y)1–x films with different Si/C atomic ratios and Zr contents were deposited using non-reactive dc-magnetron co-sputtering. All films exhibited an X-ray amorphous structure with a complex distribution of chemical bonds. The presence of Zr in the films reduced the amount of CC and SiC bonds but favored the formation of ZrC and ZrSi bonds. The mechanical and electrical properties were dependent on the bond distribution in the amorphous structure and a linear relationship between film hardness and the relative amount of SiC bonds was observed. The addition of Zr in films also gave rise to an increase in metallic character resulting in a lower electrical resistivity. Analysis of the tribofilm showed that a low friction coefficient was favored by the formation of a lubricating a-C layer and that the formation of zirconium and silicon oxides in the more Zr-rich films has a detrimental effect on the tribological performance.

Ultrathick, low-stress nanostructured diamond films

We describe a hot-filament chemical vapor deposition process for growing freestanding nanostructured diamond films, ∼80μm thick, with residual tensile stress levels ≲90MPa. We characterize the film microstructure, mechanical properties, chemical bond distribution, and elemental composition. Results show that our films are nanostructured with columnar grain diameters of ≲150nm and a highly variable grain length along the growth direction of ∼50–1500nm. These films have a rms surface roughness of ≲200nm for a 300×400μm2 scan, which is about one order of magnitude lower than the roughness of typical microcrystalline diamond films of comparable thickness. Soft x-ray absorption near-edge structure (XANES) spectroscopy indicates a large percentage of sp3 bonding in the films, consistent with a high hardness of 66GPa. Nanoindentation and XANES results are also consistent with a high phase and elemental purity of the films, directly measured by x-ray and electron diffraction, Rutherford backscattering spectrometry, and elastic recoil detection analysis. Cross-sectional transmission electron microscopy reveals a large density of planar defects within the grains, suggesting a high rate of secondary nucleation during film growth. These films represent a new class of smooth, ultrathick nanostructured diamond.

Characteristics of C4F8 plasmas with Ar, Ne, and He additives for SiO2 etching in an inductively coupled plasma (ICP) reactor

We have characterized the effect of adding Ar, Ne, and He noble gases to C4F8 inductively coupled plasmas for SiO2 etching. The systematic variation of their ionization potentials, metastable energy levels, and mass of the dominant ion in C4F8/X% discharges (X=He, Ne, or Ar) containing a high percentage of the noble gas provides a means to evaluate the relative importance of gas phase and surface processes in the etching of SiO2. The total ion flux, ion composition, FC deposition and etching rates, and composition of the surface reaction layer formed on Si or SiO2 in these discharges show systematic differences as a function of process parameters because of the different electron impact ionization thresholds for Ar, Ne, and He gases, and differences in the mass of the dominant ion for discharges containing a large proportion of the noble gas. For given experimental conditions (600 W and 20 mTorr for most of this work), Ar addition gives rise to the largest ion current density, and He to the smallest ion current density. When the noble gases are added to C4F8, the Ar+ ion flux contributes the largest percentage and He+ the smallest percentage of the total ion flux for the same dilution of C4F8 with the noble gases. Ion compositional analysis shows that CF+, CF3+, and CF2+ are the dominant ionic fluorocarbon (FC) species (in order of importance), and that they show similar trends as a function of added Ar, Ne, and He percentage. The fluxes of the more highly dissociated C+, F+, and SiFx+/COFx+ ions are greater when Ne and He are added to C4F8 than for Ar addition. Ion energy distributions of all ions are displaced to lower energies for C4F8/Ar discharges as compared with C4F8/Ne or C4F8/He plasmas. Infrared laser absorption spectroscopy was used to determine absolute densities of neutral CF, CF2, and COF2 radical species as a function of gas composition. The densities of CF2 and COF2 radical species were enhanced when Ne and He were added to C4F8 in comparison to Ar addition. Fluorocarbon deposition rates on unbiased Si substrates were measured and greater for C4F8 discharges with Ne or He additives than when Ar was added. Upon rf biasing of the substrates, the ion energies required for etching to take place are lowest for C4F8/Ar discharges, followed by C4F8/He and C4F8/Ne discharges. A comparison of x-ray photoelectron spectra of SiO2 surfaces exposed to C4F8/X% discharges at −10 V self-bias voltage shows pronounced differences in the chemical bond distribution of fluorocarbon films which can be explained by differences in momentum transfer to the surface and the associated bond breaking of deposited fluorocarbon layers on the surface. A comparison of SiO2 and Si etching rates in C4F8/X% discharges shows that for C4F8/Ne discharges containing more than 70%Ne the highest SiO2/Si but lowest SiO2/resist etching rate ratio is obtained.

Analysis of localization and chemical status of minor elements in a mammalian cell using soft X-ray contact microscopy

We have developed computer-assisted procedures for mapping minor light elements and their chemical bond information from a set of soft X-ray transmission images of biological specimens. Minor light elements such as Ca, S and P play an important role in the biological function and structure in a cell. Contact X-ray microscopy with an electric zooming tube covering wide wavelength range from the K absorption edge of S to the L absorption edge of P is applied to elemental mapping. The procedure of elemental mapping depends basically on the subtraction of the contribution of major elements such as C, O and N in intracellular absorption spectra to find the presence of the absorption edges of minor elements. The results of simulation experiments were presented. Chemical bond imaging utilizes a XANES spectrum corresponding to a specific chemical bond. Since the intensity is relatively low for minor elements, the ratio between absorption at the peak and at the bottom, which represents the chemical bond distribution, becomes small. We developed the computer program for the enhancement of very small ratio value. This procedure was applied to the S-S and S-C bond imaging at the S-K absorption edge.

Physical and chemical threshold behavior in chalcogenide networks: 119Sn Mössbauer spectroscopy of Ge(Sn)–As–Se glasses

Lamb–Mössbauer factors can serve as sensitive probes of vibrational network dynamics and, as such, are suited to examine the rigidity percolation concept in covalent networks. This is shown by detailed temperature dependent Mössbauer spectroscopic data obtained on 119Sn dopants in the ternary Ge–As–Se glass system. Significant increases of Lamb–Mössbauer factors and effective Mössbauer lattice temperatures are observed, when the average coordination number 〈r〉 reaches the critical value of 2.4 bonds per atom, as predicted by percolation theory. Detailed inspection of three compositional series reveals, however, that this universality is superimposed by a distinct chemical threshold behavior, related to a sudden change in the chemical bond distribution in the selenium-poor region of the composition diagram. Trends observed for both the 119Sn Lamb–Mössbauer factors and isomer shifts indicate that this "‘chemical effect’' diminishes network connectivity, resulting in the conversion of Sn(IV)Se4/2 units to Sn(II)Se3/2- groups. In the Ge–Sn–Se system, where data could be obtained at glass compositions well above 〈r〉=2.67, no evidence was found for the previous suggestion that this average coordination number corresponds to a percolation threshold associated with a transition from two- to three-dimensional connectivity.

Speciation Equilibria and Chemical Bond Distribution in Chalcogenide Glasses. A 31P Spin Echo and MAS-NMR Study of the System Phosphorus-Selenium-Tellurium

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSpeciation Equilibria and Chemical Bond Distribution in Chalcogenide Glasses. A 31P Spin Echo and MAS-NMR Study of the System Phosphorus-Selenium-TelluriumCarri Lyda, Thomas Tepe, Jason Leone, Hellmut Eckert, and Mark RaffettoCite this: J. Phys. Chem. 1994, 98, 36, 9063–9071Publication Date (Print):September 1, 1994Publication History Published online1 May 2002Published inissue 1 September 1994https://doi.org/10.1021/j100087a039RIGHTS & PERMISSIONSArticle Views67Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (747 KB) Get e-Alerts

Chemical bond distribution in chalcogenide glasses. A 31P MAS and spin-echo NMR study of glasses in the phosphorus-germanium-selenium system

Glasses in the phosphorus-germanium-selenium system have been prepared at compositions within the entire glass-forming region and their properties have been measured by differential scanning calorimetry and 31P nuclear magnetic resonance (NMR) spectroscopy, using spin-echo and magic-angle spinning (MAS) techniques. The glass transition temperature, T g, is a monotonic function of the average coordination number, 〈 r〉, with a distinct change in slope, d T g/d〈 r〉, near 〈 r〉 = 2.4, the theoretically expected percolation threshold. The NMR results are consistent with a structure in which phosphorus and germanium atoms compete for bonding to the selenium atoms but are otherwise randomly distributed. After taking into account the bonding requirements of the germanium atoms, which form tetrahedral GeSe 4 2 units, the presence of germanium in these glasses is found to have a secondary effect on the phosphorus environment. Based on the compositional dependence of the 31P- 31P dipolar second moments, it is suggested that the formation of P-bonded phosphorus atoms is more favored than in binary PSe glasses. 31P MAS-NMR data show that the presence of germanium tends to reduce the concentration of four-coordinated Se= PSe 3 2 units. This effect is attributed to the decrease in available selenium and to the fact that the coordinatively saturated GeSe 4 2 units are unable to provide intermolecular stabilization for the four-coordinated species.

Chemical Bond Distribution and Short Range Order in Non-Oxide Ciialcogenide Glasses. Results from NMR Spectroscopy

AbstractSolid-state 31p MAS-NMR provides powerful insights into the local order of phosphorus selenide based glasses. Specifically, it allows a quantitative characterization of the melt equilibrium PSe3/2 + Se -> Se=PSe3/2 describing the stability of four-coordinate P atoms. Using this technique, the effect of isovalent substitution by As, and Te, and of other glass constituents Ge and TI on this equilibrium and on the quantitative phosphorus speciation is studied in detail.

3D chemical model for geological macromolecules

This study defines a chemical representation of the kerogen macromolecule based on data from physicochemical analyses. The model should permit: creation of various schematic drawings representing an average macromolecule; future integration of new analytical results (for instance on structures of biomarkers or biopolymers); and determination of the distribution of chemical bonds. The models developed in this study can be represented in a 3D space, using classical chemical symbols, in the form of cyclic groups linked to each other by aliphatic chains. One cyclic group is a connected set of aromatic, naphthenoaromatic or naphthenic rings. These cyclic groups are constructed using basic elements such as atoms and bonds defined by their length and direction. Modeling of kerogen is done in three successive steps. A library is first created to define atoms, bonds and cyclic groups. Secondly, starting from a set of equations describing the analytical results, cyclic and aliphatic groups are chosen in the appropriate stoechiometric amount to match the analytical data. Finally the construction is done: cyclic groups are placed randomly in a 3D space, connections are made by aliphatic chains, and functional groups are added. The molecular modeling software Xmol TM can be operated on APOLLO stations. It allows the creation of libraries, the calculation of chemical bonds corresponding to the analyses and the construction of macromolecules. An example is given for a type III kerogen at the beginning of diagenesis.

31P Dipolar NMR Approaches Towards the Development of Structural Principles in Non-Oxidic Glasses.

AbstractWhile the utility of solid state NMR to provide structural information in amorphous systems is well established in silicate and borate glasses, the systematic application of modern NMR techniques to non-oxidic systems has just begun. One of the central issues in these types of glasses is the question of the chemical bond distribution and the existence of short range order. The present study utilizes the selective measurement of homonuclear 31p.31P dipole-dipole couplings via spin echo decay to address this issue in the glass systems P-Se, PSe- Ge and CdGeAs2-xPx. The results indicate that the first two systems are characterized by a high degree of chemical ordering. The chemical bond distribution in CdGeAs2-xPx glasses is found to deviate considerably from that in the stoichiometry-analog crystalline materials.

Optical anisotropy of polyisobutene

The distribution of chemical bonds in polyisobutene results in a theoretically zero optical and electrical anisotropy of the polymer according to bond polarizability additivity principles as conventionally applied, irrespective of polymer chain conformation. Non-zero values of the segmental anisotropy (∼4.4 × 10 −40 C 2m 2/J) derived from strain-optical birefringence on the polymer in the rubbery state have been recently reported by Liberman et al. who suggest qualitatively that severe crowding of the chemical groups in the polymer affects the anisotropies of the group polarizabilities and gives the observed non-zero segmental anisotropy. We have measured optical, electrical and magnetic anisotropies for the pure liquid polymer using techniques of flow birefringence, depolarized light scattering, electro-optic birefringence and magneto-optic birefringence. Segmental optical anisotropies so derived agree with those measured by Liberman et al. and results of the above measurements taken as a whole lead to an origin for the observed anisotropy which requires locality dependent values of optical and electrical bond polarizability anisotropies to be used in the calculation of the polyisobutene polarizability anisotropy. Our explanation of the polarizability locality dependence differs from the steric overlap suggestion of Liberman et al. and depends upon the electric field interaction between dipoles induced in polarizable bonds.