Papers by Keyword: Molecular Structure

Abstract: Polycarboxylate superplasticizers (PCEs) with different molecular structure had been synthesized and characterized by FT-IR. PCEs were mainly included polyester (Type A), polyether (Type B) and ester ether copolymer (Type C). The application properties, adsorption behaviors and hydration process were investigated. The TOC was used to measure the adsorption amount, and crystal components in the hydration products were detected by XRD analysis. Test showed that Type B had the excellent performance, including large water reduction rate and strong adsorption capacity. The ester group in the molecular structure of Type A and C could improve the fluidity retention of cement paste, but the hydrolysis of ester group also weakened adsorption capacity on cement particles. In addition, in the cement-water-PCEs system, the difference of molecular structure would affect the early hydration process of cement slurry. For example, research indicated that the main hydration peak and maximum elevated temperature was delayed by adding PCEs. Through the examination of hydration products, it revealed that the intensity of calcium hydroxide (CH) and ettringite (AFt) peaks with Type B was higher than the other. The concrete application performance results indicated that PCEs had the basically equal contribution to the compressive strength. Keywords molecular structure; ester group; adsorption; hydration products; compressive strength

Abstract: Polyurethane (PU) gel was synthesized based on methylene diphenyl diisocyanate (MDI) and polyols corporation with 1,1,1-Tris(hydroxymethyl)propane (TMP) as a crosslinking agent. The chemical structure of synthesized polyurethane gel was investigated using Fourier-transform infrared spectroscopy (FTIR). The effects of curing temperature, curing time, and crosslinking concentration on the degree of swelling, gel content and hardness of polyurethane gel are investigated. In addition, the crosslink density and average molecular weight between crosslinking points were determined using the Flory-Rehner equation. The results revealed that the curing temperature had more pronounced effect on degree of swelling and gel content than curing time. As the curing temperature increased the degree of swelling and gel content in polyurethane gel increased. Curing time seem to have a complicated effect on crosslink density and average molecular weight between crosslinking points. The hardness of polyurethane gel tends to increase with increasing crosslinking concentration and curing time.

Abstract: Calculation of molecular structure and related vibrational spectra of the isopropyl nitrate was carried out by means of density functional theory (DFT) by employing the Gaussian 03 mathematical package. The molecular geometries were fully optimized by using the Becke's three-parameter hybrid exchange functional combined with the Lee–Yang–Parr correlation functional (B3LYP) and using the 6-31G(d) basis set. By scanning the dihedral angles around C-O and C-C bonds, two energetically most favorable conformers of isopropyl nitrate - TG, GT forms were found. Calculations of the frequencies and forms of normal oscillations of the obtained forms of isopropyl nitrate are performed. The spectral features of the conformational state of isopropyl nitrate and the spectral effects of the formation of intramolecular H...ONO₂ hydrogen bonds have been revealed.

Abstract: The quality stability of the natural rubber is a key point to its use in the industries and some special fields. However, due to storage hardening caused by the complicated molecular structure of natural rubber and non-rubber component, the quality uniformity is still not controlled in the nowadays rubber factory. In the previous research, storage hardening phenomena are extensively examined but the special mechanism is controversial and detail information is need to be further revealed. The dynamic evolution of accelerated storage properties and molecular structure of natural rubber have been investigated. The results show that △P increased slowly at first but then increased apparently and PRI has no direct relationship with △P. The storage time of 24 h is the critical storage period in which besides the △P and PRI, the P₀, gel content and molecular weight also has obvious transformation. △P has a negative apparent correlation with ester content but protein content is relatively of no account in storage hardening process.

Abstract: Due to the physical, chemical, biological characteristics and high biocompatibility, the hydrogels based on plant polysaccharides and proteins became a sought-after material in many fields. Such hydrogels are the water swelling biopolymer matrices that react reversibly on minor changes in composition and in the external environment. However, the mechanical and electrical properties of "pure" hydrogels inhibit their wide practical application. One of approachs to improve their properties is the usage of carbon nanotubes, which provide good electrical conductivity and can significantly improve the characteristics of materials. The effects of carbon nanotubes on electric conductivity and mechanic properties of hydrogels based on natural biopolymers (gelatin and κ-carrageenan) of different composition were investigated. The electrical conductivity of the gels was studied using InoLab Cond 7310 SET1 conductometer. The rheological properties of hydrogels were investigated by Anton Paar MCR 302 rheometer. Such characteristics as temperature, frequency and amplitude dependencies of the storage modulus and the loss modulus of hydrogels were obtained. It was found that the addition of carbon nanotubes led to the increase in electrical conductivity of hydrogels. The morphology and rheological properties of studied hydrogels alter significantly in the presence of carbon nanotubes. The obtained data indicate the possibility of a purposeful change in electrical and mechanical properties of hydrogels by the addition of carbon nanotubes.

Abstract: The topology of electron density is a sketch that gives a clear picture about electronic distribution and details information of natural molecular bonding. In quantum mechanics or particularly in quantum chemistry, the electron density is a measure of the probability of an electron occupying at any infinitesimal element of space surrounding at any given point.Studies about the topology of electron density in Cd_0.5Zn_0.5S at plane (101) were conducted by the application of density functional theory (DFT) within linear augmented plane wave (LAPW) by using the WIEN2k software. In this calculation, generalized gradient approximation (GGA) methods were used to calculate the exchange-correlation potential of the electrons. Based on this calculation, the topology of electron density were presented in a contour plot (2D) and also inarelief map plot (3D) in order to see the way electron density, ρ of Cd_0.5Zn_0.5S defines the gradient field and hence the bonding type. From these plots, we identified the bond paths that coincide with the contours of electron to suggest that Cd_0.5Zn_0.5S exhibited characteristics of covalent and a slightly ionic bond character.

Abstract: β-Sialonwhiskers which the molecular structuralformula of β-Sialonis Si₃Al₃O₃N₅(z = 3) were synthesized from fly ash and graphite under appropriate technological conditions by carbothermal reduction–nitridation process. The effects of carbon content, reaction temperature and reaction time on synthesis ofβ-Sialonwere analysed by XRD, SEM techniques. The results proved that, the condition of the carbon content over 80% is the best parameter to promote theβ-Sialon powder production. Compared to other kinds of temperature, 1430 °C is the optimal temperature to promoteβ-Sialon powder generation. Compared to 3h, holding time of 6h is promoting theβ-Sialon powder generation.The main morphology of β-Sialon was rod-like whisker.

Abstract: Pathological changes in animal models of autoimmune hepatitis and liver cells were similar to the mechanism of injury and viral hepatitis, the thesis of the active component of several common liver substances studied, wild chrysanthemum extract has anti-bacterial, anti-viral, pharmacological effects such as anti-inflammatory and immune liver and nerve protection, Dicliptera polysaccharide with excellent hepatoprotective activity of the liver that can be used as an adjunct to clinical medicine. Introduction

Abstract: This research, natural rubber containing different gel contents were prepared by deproteinization and saponification treatment from high ammonium natural rubber latex. Deproteinization natural rubber was further treated as acetone extraction and then transesterification. It was founded that gel content and molecular weights of treated natural rubber were decreased and almost absented for transesterification treatment. Rheological respond on small amplitude oscillating shear (SAOS) and large amplitude oscillating shear (LAOS) deformation of treated natural rubber were captured by using rubber process analyzer (RPA 2000). Firs harmonic rheological properties, storage modulus, G and loss modulus, G decreased as gel content and molecular weight decreased. It was believed that gels, explicitly branching points, were destroyed after the natural rubber was deproteinized, transesterification, or saponification according to the molecular structure of natural rubber presumed by Tanaka et al, which functional groups contain protein and fatty acid are participated in branching to forming gel structure. It was concluded that gel content as the same as molecular structure of natural rubber could be characterized as rheological behavior.

Abstract: Water-soluble phenolic resin was prepared using sodium hydroxide and ammonia as catalysts. The molecular structure of water-soluble phenolic with different molecular weight was studied by infrared spectrum and the mechanism was discussed. The results show that addition reaction and polycondensation synchronize in the reaction process, while addition reaction dominates in the early stage while polycondensation dominates in the later stage.