Effect of Temperature and Comonomer Content on Thermal Behavior and Crystallization Property of the Propylene–Ethylene Random Copolymers

The effects of ethylene units content and crystallization temperature on the conformations, and the thermal and crystallization behavior were investigated by a combination of Fourier transform infrared (FTIR) spectroscopy, wide angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). The characterization of FTIR spectroscopy proves that the longer helical conformation sequences of the propylene–ethylene random (PER) samples decrease, whereas the shorter helical conformation sequences increase with the increase in ethylene units content. The increase of the shorter helical conformation sequences is favorable for the formation of the γ-phase in the crystals. A group of broad endothermic peaks can be seen clearly in the DSC curves of PER copolymers, which may be associated with the melting of mixtures of the α- and γ-forms in the crystals. The melting point, crystallization temperature, and crystallinity degree of the PER copolymers decrease with the increase in ethylene units contents. Three typical melting peaks of the PER copolymers crystallized isothermally between 80°C and 130°C were observed. The two higher melting peaks result from melting of the α- and γ-phase in the crystals, whereas the materials crystallized on quenching give the lowest peak. The WAXD results confirm that the PER copolymers crystallize from the melt, as mixtures of α and γ forms, in a wide temperature range. The critical number ζ_lim of the crystallizable units for the α-form increases with the increase in crystallization temperature for PER copolymers, which is favorable for the formation of the γ phases. The amount of γ-form increases with the increase in crystallization temperature at the expense of its α component, then reaches a maximum value at the crystallization temperature of 115°C, and finally decreases with further increase in the crystallization temperature.     

Study on the Molecular Mobility in the Polyamide/SrFeO Composites by In Situ Infrared Spectroscopy

Polyamide 6(PA6) and its composite with strontium ferrite (SrFeO) magnetic powders at different concentration levels (33%, 80%) are in situ investigated by temperature-dependent Fourier transform infrared spectroscopy (FT-IR). It is found that the intensity changes of the “free” (nonhydrogen bonded) N?H stretching vibration as a function of temperature can be used to determine the glass transition (T _g) and melting temperature (T _m); whereas the hydrogen-bonded N?H stretching vibration is only sensitive to T _m. Our results reveal that high SrFeO contents increase the T _g and T _m of PA6. These observations suggest that the molecular chains of PA6 are confined with increasing content of SrFeO.     

Preparation and Mechanical and Tribological Properties of High-Density Polyethylene/Hydroxyapatite Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with hydroxyapatite nanorods (nHA) were fabricated by means of extrusion and injection molding. The thermal, mechanical, and dry sliding wear properties of HDPE-based nanocomposites filled with nHA loadings up to 20 wt% were investigated. The results of mechanical property characterization showed that nHA additions improved the hardness, elastic modulus, and yield strength of HDPE at the expense of its tensile ductility and impact strength. Thermogravimetric analysis and heat deflection temperature measurements revealed that nHA fillers are very effective to enhance the thermal stability of HDPE. The wear behavior of HDPE/nHA nanocomposites was studied using a pin-on-disk tribometer. nHA fillers of a large aspect ratio improved the wear resistance of HDPE substantially because of their load-bearing effect and the formation of a continuous transfer film on the steel counterface.     

Hybrid Particle–Continuum Simulations of Polymer Brushes in Shear Flow

A hybrid particle–continuum method is used to study the shear flow confined between two opposing walls, one of which is coated with polymer chains. Molecular dynamics (MD) is used in the particle region near the brush and Navier–Stokes (NS) equations are applied in the remaining region where the continuum assumption holds. The information exchange from the continuum region to the particle region is implemented using the constrained particle dynamics. Both Couette shear flow and oscillatory flow are considered in the present work. The effect of the shear flow on the conformational characteristics of polymer brushes is analyzed. In the overlap region, the velocities obtained from MD simulations are smoothly connected with those from NS equations. Our investigations demonstrate that the hybrid particle–continuum model is valid in exploring the shear behavior of polymer brushes.     

Half-Width Integral Method for Gas Concentration Measuring in Tunable Diode Laser Absorption Spectroscopy

ABSTRACT

We analyze the influence of random errors and absorption shape fitting errors on gas concentration measurement in tunable diode laser absorption spectroscopy. We then propose a new data processing method according to the characteristic of random errors and fitting absorption shape. This method only uses the integral value within the half width at half maximum of the fitting absorption shape to determine the gas concentration in actual measurements. Meanwhile, the O₂ transition at 13,150.197 cm^?1 is selected to measure the O₂ concentration using this method. Compared with the traditional method, the method established in this paper can accurately measure O₂ concentration.     

Interaction Between Neuroglobin and Caffeine by Multispectroscopic Methods

The interaction between neuroglobin (Ngb) and caffeine was studied by spectroscopy. UV-Vis spectra revealed that caffeine did not influence the native hexa-coordinated heme structure of neuroglobin. Fluorescence spectra indicated that caffeine could quench the intrinsic fluorescence of neuroglobin through static quenching mechanisms. The calculated thermodynamic parameters showed that the electrostatic force was the main intermolecular force in the reaction. Results also indicated that the microenvironmental changes of tryptophan and tyrosine residues within neuroglobin are inapparent. Furthermore, the circular dichroism (CD) spectra implied that caffeine could induce the formation of α-helix structure of neuroglobin.     

Study on the Interaction Between Oxymatrine and Tungstosilicic Acid by Resonance Rayleigh Scattering and Its Analytical Applications

In the 0.1 mol · L^?1 hydrochloric acid solution, oxymatrine reacted with tungstosilicic acid to form a 2:1 ion-association complexes. This results in a great enhancement of resonance Rayleigh scattering. The maximum resonance Rayleigh scattering wavelength was located at 393 nm. Resonance Rayleigh scattering intensity was proportional to the concentration of oxymatrine in the range of 1.5–26.4 µg · mL^?1, and the detection limit (3σ) was 0.23 µg · mL^?1. The optimum conditions and the effects of coexisting substances on the reaction were investigated. The method shows a wide linear range and high sensitivity, and was applied to the determination of oxymatrine in marine capsules and human urine samples with satisfactory results. Therefore, a highly sensitive, simple, and quick method has been developed for the determination of oxymatrine.     

Interaction between isoamyl adenine and rice cytokinin oxidase

Cytokinin (CTK) dehydrogenase is responsible for regulating the endogenous CTK content by oxidative removal of the side chain. Herein, we have applied fluorescence method to study the interaction between CTK dehydrogenase and CTK in vitro and obtain some parameters of their interaction. We found that addition of isopentenyl adenine can quench the fluorescence of CTK dehydrogenase, and the quenching mechanism was to be a static quenching procedure. We have measured the number of binding sites n and the apparent binding constant K and have calculated the thermodynamics parameter ΔH, ΔG, and ΔS by fluorescence quenching method. Based on thermodynamics parameter’s results, we concluded that their binding reaction was both entropy driven and the enthalpy driven, and the Van der Waals force and hydrogen bond force played a major role in the interaction. Based on the synchronous fluorescence spectrometry results, we demonstrated that the binding site between isopentenyl adenine and CTK dehydrogenase is in the microenvironment of both tryptophan and tyrosine. The fluorescence signal of coenzyme, flavin adenine dinucleotide, decreases gradually with the addition of isopentenyl adenine. And this method can be used for isopentenyl adenine routine assay. Under optimized experimental parameters, the linear segment increases from 0.6 µM to 100 µM with a regression equation of ΔF = 0.04 + 0.15c_ip (r = 0.999, c_ip in µM) with the detection limit of 0.15 µM iP.     

Preconcentration and Separation of Gold(III) from Ore Samples by Solid-Phase Extraction Prior to Its Catalytic Fluorescent Determination

ABSTRACT

A new catalytic kinetic fluorescent quenching method for the determination of trace gold(III) was investigated. The method was based on the catalytic effect of gold on oxidation of 3-(3′-methylphenyl)-5- (2′-arsenoxylphenylazo) rhodanine by hydrogen peroxide in potassium hydrogen phthalate–hydrochloric acid (pH = 3.4). Under the optimum conditions, the great decrease of fluorescence intensity has a linear relationship against the concentration of gold in the range of 0 to 12.0 µg·L^?1 with a detection limit of 6.0 × 10^?10g·L^?1. The coexistent metal ions can be separated, and gold can be enriched by TBP resin of solid-phase extraction, which greatly improves the selectivity and sensitivity of the system. The method can be used to determine trace amounts of gold in ore samples successfully with satisfactory results.     

The Electronic Absorption Spectra of Binuclear Complexes,[Cu(o-phen) (sal)No3 and [Cu2 (sacch)4(im)4] Crystal

The electronic absorption spectra of crystals of the title componds were recorded and the experimental results were explained quantitatively with the ligand field theory and the radial wave function of bound Cu(II) cation. With these spactra, the range of magnetic interactions between two Cu(II) ions of the title compounds are discussed.