Rheological properties and dispersion stability of magnetorheological (MR) suspensions

In the present article, the rheological responses and dispersion stability of magnetorheological (MR) fluids were investigated experimentally. Suspensions of magnetite and carbonyl iron particles were prepared as model MR fluids. Under an external magnetic field (H ₀) and a steady shear flow, the yield stress depends upon H ₀ ^3/2. The Yield stress depended on the volume fraction of the particle (φ) linearly only at low concentration and increased faster at high fraction. Rheological behavior of MR fluids subjected to a small-strain oscillatory shear flow was investigated as a function of the strain amplitude, frequency, and the external magnetic field. In order to improve the stability of MR fluid, ferromagnetic Co-γ-Fe₂O₃ and CrO₂ particles were added as the stabilizing and thickening agent in the carbonyl iron suspension. Such needle-like particles seem to play a role in the steric repulsion between the relatively large carbonyl iron particles, resulting in improved stability against rapid sedimentation of dense iron particles. Furthermore, the additive-containing MR suspensions exhibited larger yield stress, especially at higher magnetic field strength. Received: 4 April 2000 Accepted: 6 November 2000     

添加剂在毛细管电泳分离DNA中的作用研究进展

使用无胶筛分介质的毛细管电泳（包括毛细管阵列电泳和微芯片电泳）是最重要的DNA分离技术之一。在低粘度的无胶筛分介质中加入某种添加剂是一种有效且简单的克服填充困难和提高DNA分离性能的方法。本文就各种添加剂（如多羟基化合物、粘土、金纳米粒子、乳胶粒等）对提高无胶筛分介质中DNA的分离性能的作用进行了综述。     

Use of two-dimensional liquid chromatography in the analysis of additives in cellulose acetate polymer

Summary The capability of elution-elution multi-dimensional liquid chromatography was investigated. A column scaling approach was evaluated for the quantification of low-molecular-weight additives in cellulose acetate. A small-bore (1-mm i.d.) gel-permeation column was used to separate the higher-molecular-weight polymer from the lower-molecular-weight components. Once separated these additives were transferred to a C₁₈ reversed-phase column via a switching valve. The reversed-phase system successfully separated and quantified individual additives.Analysis time for an ultraviolet inhibitor, Tinuvin^®P, in cellulose acetate, including re-equilibration, was approximately 30 minutes. Both accuracy and precision were good. Precision over a three day period was about 1.5%.     

Saponification then GC for Determination of Irganox 1010 and Irganox 1076 in a Polymer Matrix

A gas chromatographic method has been established for determination of Irganox 1010 and 1076 after saponification. The analytes were saponified with methanolic potassium hydroxide, acidified with hydrochloric acid, and the solvent was removed by rotary evaporation. The dry residue was dissolved in xylene and analyzed by GC with flame-ionization detector (FID). Compounds were separated on a polar (Carbowax 20 M) capillary column and nitrogen was used as carrier gas and make-up gas. This method has a relatively large linear dynamic range, 50–3,000 and 100–1,600 mg L⁻¹ for Irganox 1010 and 1076, respectively, and limits of detection (LOD) were 20 and 40 mg L⁻¹, respectively. The effect of conditions such as saponification temperature, and concentration and volume of potassium hydroxide were studied.     

Dual capillary gas chromatographic analysis of alcohols and methyl tert-butyl ether in gasolines

A gas chromatographic method has been developed for the identification and direct determination of alcohols and methyl tert-butyl ether (MTBE) in gasolines. The technique involves simultaneous injection of the gasoline without any sample preparation onto two fused silica capillary columns of differing polarities. The method permits simultaneous determinations of methanol, ethanol, 2-propanol, tert-butanol, 1-propanol, sec-butanol, 1-butanol, and MTBE. By using an automatic sampler in combination with electronic pressure programming and BASIC programming, the determinations were performed automatically and reproducibly with a relatively short analysis time.     

Identification and quantification of (polymeric) hindered-amine light stabilizers in polymers using pyrolysis-gas chromatography-mass spectrometry and liquid chromatography-ultraviolet absorbance detection-evaporative light scattering detection

Direct analysis of polymers containing polymeric hindered amine light stabilizers (HALS) by using pyrolysis coupled to GC-MS is applied successfully for fast and straightforward identification of these HALS additives. Each of the HALS additives shows different pyrolysis gas chromatograms containing characteristic pyrolysis products. As a result, HALS additives with very similar chemical structures, e.g. Chimassorb 944 and Chimassorb 2020, can be distinguished. A HPLC method with both ultraviolet (UV) and evaporative light scattering detection (ELSD) is developed to quantify the various HALS additives in extracts of polymers. The critical factor of the HPLC method is the use of a basic amine, like n-hexylamine, as a solvent additive to facilitate the elution of HALS additives. The various HALS additives can be distinguished according to retention time and peak shape and by using different detection methods. The suitability of the developed methods is demonstrated by the analytical performance of the HPLC method and the identification and determination of the actual content of HALS additives in polyolefines using pyrolysis GC-MS and HPLC. The HPLC method can also be used for the determination of the specific migration of HALS additives from food contact materials.     

Use of Organic Solvents as Additives in Inductively Coupled Argon Plasma with Atomic Emission Spectrometric Detection

Abstract

The effect of nitric acid/organic aerosols on the emission intensity of metals from the first row transition series, plus Cd and Pb was investigated. The addition of organic solvents to reference solutions diminished the aerosol mean drop size, by reducing the surface tension of the solutions. Correlation between signal intensity and BEC with the main physical characteristics (surface tension and viscosity) of the nitric acid/acetic acid and nitric acid/alcohol solutions was studied. Analytical curves (0–2.0 fig ml^?1) were evaluated using a matrix matching procedure, and detection limits indicated an improvement (ca 40%) in analytical performance as well as in linearity, sensitivity and precision.     

Co‐electroosmotic capillary electrophoresis of basic proteins with 1‐alkyl‐3‐methylimidazolium tetrafluoroborate ionic liquids as non‐covalent coating agents of the fused‐silica capillary and additives of the electrolyte solution

The paper reports the results of a study carried out to evaluate the use of three 1‐alkyl‐3‐methylimidazolium‐based ionic liquids as non‐covalent coating agents for bare fused‐silica capillaries and additives of the electrolyte solutions (BGE) for CE of basic proteins in the co‐EOF separation mode. The three ionic liquids are differentiated from each other by the length of the alkyl group on the imidazolium cation, consisting of either an ethyl, butyl or octyl substituent, whereas tetrafluoroborate is the common anionic component of the ionic liquids. Coating the capillary with the ionic liquid resulted in improved peak shape and protein separation, while the EOF was maintained cathodic. This indicates that each ionic liquid is effective at masking the protein interaction sites on the inner surface of the capillary, also when its adsorption onto the capillary wall has not completely neutralized all the negative charges arising from the ionization of the silanol groups and the ionic liquid is not incorporated into the BGE employed for separation. Using the coated capillaries with BGE containing the ionic liquid employed for the coating, at concentration low enough to maintaining the EOF cathodic, both peak shape and protein separation varied to different extents, based on the particular ionic liquid used and its concentration. Fast and efficient separation of the model basic protein mixture in co‐electroosmotic CE is obtained with the 1‐butyl‐3‐methylimidazolium tetrafluoroborate coated capillary and 100 mM acetate buffer (pH 4.0) containing 4.4 mM 1‐butyl‐3‐methylimidazolium tetrafluoroborate as the BGE.     

Influence of the RE2O3 (RE = Y,Gd) and CaO nanoadditives on the electromagnetic properties of nanocrystalline Co0.2Ni0.3Zn0.5Fe2O4

The present work reports the influence of the nanoadditives Y₂O₃, Gd₂O₃, and CaO on the magnetic, electrical and dielectric properties of sintered nanoferrites Co_0.2Ni_0.3Zn_0.5Fe₂O₄. All powders were synthesized via the polyol method. XRD analysis showed that except the nanoferrite which was obtained by in an one-post procedure, subsequent calcinations of the as-produced additives were necessary to obtain nanocrystals of the desired phases. The mean particle size inferred from TEM images of the nanoadditives sintered at 1000 °C ranges from 87 nm for Y₂O₃ to 126 nm for CaO. IR spectroscopy provided useful information on the nature of the core and the surface chemistry of the as-produced additives and their associated annealed powders. Upon sintering, it was found that the incorporation of 5 wt.% additives remarkably increased the densification of the doped materials. The most important increase in densification was observed with CaO due to its larger particles. dc M-H hysteresis loops taken at 300 K revealed a superparamagnetic behavior of the produced ferrite/nanoadditives. Additionally, as expected, the ferrite/nanoadditives showed reasonable saturation magnetization and high Curie temperature. The electrical and dielectric properties, namely the resistivity, the loss factor, and the relation frequency were found to be clearly affected by doping. The resistivity decreased with increasing temperature indicating a semiconducting behavior. Further, at room temperature, the highest resistivity was observed with Y₂O₃. The major role was attributed to the high fraction of insulating Y₂O₃ owing to its smallest particles combined with the low Fe²⁺ concentration in the ferrite nanoparticles taking advantages of the moderate sintering temperature. In addition, the dc conductivity was found to follow the Arrhenius law with a slope change observed at the Curie temperature. Further, all the additives clearly affected the ac conductivities of the pure ferrite. The variation of the dielectric permittivity with frequency and temperature was explained on the basis of M-W type of interfacial polarization. Additionally, at high frequencies, the lower dielectric loss was found with Y₂O₃ doping. It was found to be of about 10 times lower than the undoped material and much larger than reported for similar undoped bulk ferrites.     

添加剂对AP/Al热分解影响的红外光谱与热分析研究

采用傅里叶变换红外吸收光谱(FTIR)和差示扫描量热法(DSC)研究了草酸铵(AO), 碳酸锶(SC)及复配的草酸铵/碳酸锶等添加剂对复合固体推进剂主要组分高氯酸铵(AP)的作用机理。红外分析表明：草酸铵使AP各吸收峰消失的温度延后。碳酸锶在凝聚相中与AP的分解产物高氯酸发生反应生成比较稳定的产物高氯酸锶,IR光谱证实了高氯酸锶的存在。DSC分析结果表明：草酸铵的加入使AP高温阶段的分解放热峰向高温方向移动,但对AP低温阶段的分解放热峰没有影响。碳酸锶的加入使AP两个阶段的分解放热峰均向高温方向移动。草酸铵/碳酸锶的加入,虽然使AP的分解放热峰均向高温方向移动,但是实验发现,在常压下草酸铵/碳酸锶的组合配方没有发挥对AP高温分解的协同作用。基于上述实验探讨了草酸铵和碳酸锶抑制AP分解的作用机理。