Influence of a few important parameters on the rheological behaviour of silicon carbide nanoparticles dispersed aqueous suspension

In this study, investigations have been carried out on the effect of a few important parameters such as molecular weight and concentration of dispersant (polyethyleneimine) as well as that of pH on the rheological behaviour of aqueous suspension comprising silicon carbide (SiC) nanoparticles. In addition to this, the effect of particle size and addition of finer SiC particles on the rheological behaviour of SiC suspension have been examined. It is observed that viscosity of suspension increases with the increase in molecular weight of dispersant and decreases as the concentration of dispersant increases. Further, it is noticed that viscosity of the suspension progressively increases below the pH ≈?7.6 and above the pH ≈?9.3, indicating that minimum viscosity i.e. maximum stabilization of suspension is obtained within the pH range of ≈ 7.6–9.3. It has been observed that variation of SiC particle size from submicrometer to nanometer range and addition of nanometric SiC powder in SiC suspension containing coarser particles increase the viscosity significantly.     

Flow properties of haloarchaeal polysaccharides in aqueous solutions

The flow properties of the polysaccharides produced by Haloferax mediterranei^T ATCC 33500 and its super mutant Haloferax mediterranei EPS⁺⁺, R4 and EPS⁺⁺ respectively, were investigated. The R4 repeating unit is a trisaccharide containing mannose and 2-acetamido-2-deoxyglucuronic acid, ester sulphate groups are also present. In order to compare the properties of both polymers viscosimetric measurements were carried out at different integration times and using different concentrations of polymer. Under the assayed experimental conditions no effect of the time applying stress is detected for either polymer. A strong pseudoplastic behaviour is observed which is increased as the polymer concentration rises. Differences in viscosity between both polymers are due to the different molecular weights. The correlation of the experimental data using a modification of the Cross model has given very good results.     

海藻酸钠/明胶混合水溶液的流变性能

借助旋转黏度计考察了海藻酸钠/明胶混合水溶液的流变性能,发现混合溶液具有剪切变稀的非牛顿假塑性流体特征;随体系中明胶含量的增加,相应混合溶液的稠度系数增大而黏性指数下降,同时溶液的触变性能得以增强,该混合溶液体系具有协同增效性。     

Rheological properties of aqueous solutions of poly-1,2-dimethyl-5-vinylpyridinium methyl sulfate and its copolymers

Rheological properties were studied for aqueous solutions of poly-1,2-dimethyl-5-vinylpyridinium methyl sulfate and its copolymers with acrylonitrile, acrylamide, acrylic, and maleic acids in the concentration range from 1 to 10 g dL^{? 1}, temperature range from 25 to 65°C, and range of velocity gradients from 0.2 to 1.3×10 ³ sec^{? 1}. Majority of the resultant gradient dependences of the solution viscosities had a pattern typical for non-Newtonian liquids. The nature of the second comonomer affected the dynamic viscosity, its concentration, and temperature dependences. However, as the content of the second comonomer in the copolymer increased, the characteristic viscosity as well as the highest Newtonian viscosity decreased. The concentration dependences of viscosity and activation parameters of viscous flow indicate that the fluctuation network, formed in solutions of the polyelectrolytes under consideration, is much looser in comparison with solutions of the nonionic polymers. The strength of the fluctuation network increases under conditions of screening of electrostatic repulsion. The critical concentrations (crossover points) were found to be much higher than the average concentration of monomeric units within the polymeric coil and independent of the degree of polymerization or composition of the copolymer. A combination of donor and acceptor functional groups in the copolymers favors formation of additional intra- and intermolecular bonds; therefore, as the temperature rises, additional unfolding of macrocoils and strengthening of the fluctuation network takes place.     

Rheological properties of aqueous polyacrylamide solutions

A comprehensive study of the rheological properties of aqueous polyacrylamide solutions was carried out. A RheoStress RS100 Haake rheometer was used in the measurements. The concentration of polyacrylamide ranged from 0.25 to 1.0% by weight. This range is sufficiently wide to cover many of the rheological features of polyacrylamide in the lower range of concentration. The study included measurements of steady shear flow parameters, transient shear stress response, yield stress, thixotropic behavior, creep recovery, dynamic responses, and temperature effects in the range 10–50°C. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1587–1597, 1998     

Rheological properties of aqueous polyacrylamide/NaCl solutions

Rheological properties of aqueous polyacrylamide‐sodium chloride solutions are studied using RheoStress RS100. Polyacrylamide concentration was varied from 0.25 to 1.0% by weight, whereas sodium chloride ranged from 0.0 to 10 g L⁻¹. This range of concentrations is suitable to study many of the polyacrylamide‐sodium chloride rheological properties. Steady flow parameters, yield stress, thixotropic behavior, creep recovery, and dynamic tests are covered in this study. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1905–1912, 1999     

Cholesteric order in aqueous solutions of the polysaccharide Xanthan

Summary Measurements of birefringence, optical rotation and laser light diffraction show that aqueous solutions of the polyelectrolytic polysaccharide Xanthan at a concentration of 7.5 % (vol/vol) have long range order very similar to cholesteric liquid crystals. The cholesteric screw is left handed implying a rod-like conformation and right handed helicity of individual molecules. The cholesteric phase separates from a less concentrated isotropic solution and spherolites are formed.     

Rheological properties of poly(ethylene oxide) aqueous solutions

This article describes the rheological properties of certain poly(ethylene oxide)s dissolved in water-based solvents. The experimental results show that the rheological properties in aqueous solutions are significantly affected by the solvent properties, which have been changed by the use of ethanol–water mixtures and electrolyte solutions and by the variation of the ambient pressure and temperature. The variation of the temperature and pressure is seen to change the polymer chain configuration and also the interactions of polymer segments with the solvent molecules. This gives rise to distinctive and apparently unusual rheological properties for these systems with the variation of the ambient temperature and pressure. The study generally illustrates that the rheology of these systems are, to a large degree, influenced by the hydrogen bonding in the solvent and between the solvent as well as the polymer. At a first-order level, the increase of the pressure and the temperature and also the addition of electrolytes, and the inclusion of an aqueous diluent, produce comparable effects. In essence, these changes seem to disrupt the hydrogen bonding structure in the solutions and, hence, the solvent quality in a comparable fashion. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 419–429, 1998     

黏度法测试UHMWPE黏均分子量实验过程探讨

研究和分析了黏度法测量UHMWPE黏均分子量过程中各个环节对测试结果的影响,整个操作过程的各种主客观因素都可能引入实验误差,只有严格控制好测试过程中的每一个环节,才能保证测试结果的准确性和可靠性。     

Corrosion behaviour of hafnium diboride in aqueous solutions

A dense HfB₂ ceramic material was prepared by hot pressing in the presence of 2.5 wt.% Si₃N₄, as a sintering aid. The microstructure consisted of a fine HfB₂ matrix with refractory secondary phases (BN, HfO₂, Hf(C,N,O)) and Si, mainly located at the triple points. The material corrosion behaviour in acid and alkaline solutions of chlorides and sulphates was investigated by means of several experimental techniques, that is potentiodynamic polarization curve recording and potentiostatic tests coupled to solution chemical analysis, scanning electron microscope (SEM) observations and X-ray photoelectron spectroscopy (XPS) surface chemical characterization. Sintered HfB₂ undergoes an electrochemical corrosion attack of the HfB₂ phase and a chemical corrosion attack, mainly localized on the secondary phases. In acid sulphate solution a strong corrosion attack on the diboride phase occurs which leaves a secondary phase skeleton. In acid chloride solution and in alkaline chloride and sulphate solutions, the rate of secondary phase dissolution is quicker than the dissolution rate of the primary diboride phase and an intergranular corrosion attack morphology occurs. The Si phase dissolves relatively fast only in alkaline solutions. In analogy with the corrosion behaviour of ZrB₂, corrosion of HfB₂ phase is thought to produce both soluble and insoluble (hafnium and boron oxides) corrosion products. In acid sulphate solution the soluble corrosion products are mainly boric acid and a sulphate complex of Hf(IV). In the other solutions they are mainly constituted by boric acid (or borates, depending on the solution pH). The high corrosion rates detected in acid sulphate solution are due to the marked stability of the soluble sulphate complex of Hf(IV).     

Rheological properties of aqueous solutions of sodium carboxymethylcellulose and methylhydroxypropylcellulose blends

It was found that a specific feature of aqueous solutions of Na-CMC and MHPC is the presence of a viscosity extremum for a polymer ratio of 80:20 wt. % and in treating the MHPC solution in a rotary-pulsed activator at the rate of 300 rpm. It was hypothesized that an increase in the size of the coils of the MHPC macromolecules as a result of improvement of the thermodynamic quality of the solvent in the first case and their stretching in the second case is the cause of the increase in the viscosity of the solutions. Films spun from solutions, characterized by anomalous high viscosity values, have high strength and elasticity. __________ Translated from Khimicheskie Volokna, No. 5, pp. 41–44, September–October, 2006.     

Macroscopic observation of thermal behavior of concentrated solution of coal extracts

The solvent extracts of Upper Freeport and Illinois No.6 coals were mixed with N-methyl-2-pyrolidinon (NMP) and annealed at 353 K to produce the gelatinous materials. Differential scanning calorimetric measurements revealed that the materials can hold significant amounts of nonfreezable NMP (as much as 3 g NMP per 1 g coal extracts) which disperse in the materials on a molecular scale, indicating the materials are not phase separated. The thermal behaviors were measured macroscopically as a function of the extract concentration using a needle penetrometer during heating from 223 to 360 K. The penetration-temperature curves were analyzed to estimate the apparent viscosity (η_a). During the penetrations, η_a was decreased very rapidly, approximately four orders of the magnitude by a temperature increase of 20 K, suggesting that the coal extracts-NMP mixtures undergoes a gel to sol transition. The heats of dissociation of crosslinks (ΔH_m) were estimated by applying Eldridge-Ferry equation. The ΔH_m of coal extracts-NMP mixtures was relatively small, i.e. approximately 10 kJ/mol, whereas the ΔH_m of polyvinyl alcohol-NMP gel in which the hydrogen bonds contribute the formation of the physical network structures, was about 65 kJ/mol. Not the specific interaction such as hydrogen bonds, but weak interactions such as van der Waals force were likely to contribute the formation of the coal extracts-NMP gel.     

Characterization of N,N-dimethylacrylamide/2-methoxyethylacrylate copolymers and phase behaviour of their thermotropic aqueous solutions

Dimethylacrylamide (DMA) has been copolymerized with 2-methoxyethylacrylate (MOEA) and solutions of the products were analysed by FTIR to yield derived reactivity ratios r_DMA = 1.11 ± 0.13 and r_MOEA = 0.63 + 0.10. The measured glass transition temperatures T_g of PDMA and PMOEA were 395 K, and 242 K, respectively. These and the values of T_g for the copolymers accorded well with the Fox relationship. Cloud point curves for copolymers in water were established over a wide range of concentration, solubility decreasing with increase in temperature. For these reversibly thermotropic solutions, the lower critical solution temperature (LCST) increased from 9°C to 80°C with decrease in content of MOEA in the copolymer from 91.1 mol% to 38.6 mol%.     

无规共聚聚丙烯的流变性能研究

采用毛细管流变仪对无规共聚聚丙烯(PP-R)的流变行为进行了具体分析。结果表明:PP-R的黏度随温度变化的敏感性不大;随着剪切速率的提高,PP-R的黏度明显降低(剪切变稀);入口压力降(P0)与温度和剪切速率均有关温,度升高P,0减小剪,切速率增大P,0升高。     

双醛淀粉流变性的研究

双醛淀粉毒性低、化学反应活性高,广泛应用于各种工业,是一种很重要的化工原料,而双醛淀粉的流变性会对双醛淀粉的应用产生重大的影响.本文研究了不同pH下制备双醛淀粉的流变性,结果表明:溶液呈胀流型,提高剪切速率,粘度略有增加,pH3.5下制备双醛淀粉的粘度比pH7下制备双醛淀粉的粘度低.     

Molecular dynamics simulation of PAMAM dendrimer in aqueous solution

The properties of ethylenediamine (EDA) cored and amine surface poly(amidoamine) (PAMAM) dendrimers of generation 1 through 7 in the explicit solvent were studied by the atomistic force field based molecular dynamics. Since amines are assumed to be protonated the simulation condition is designed to represent the dilute alkali solution. All the generations are spherical in shape, while the higher generations show edges or slightly polyhedral shape. The density profile indicates that the dendrimers are constant density spheres and the densities are independent of generation in this aqueous solution. The scaling properties of the radius of gyration with the numbers of atoms and solvent accessible surface with radius of gyration indicate the PAMAM dendrimers are densely compact structures which result from the highly flexibility confirmed by the terminal group distribution. Dynamic behaviors such as autocorrelation function of the squared radius of gyration and mean square displacement were also studied too.     

Electrochemical behaviour of cobalt in aqueous solutions of different pH

A systematic study of the corrosion and passivation behaviour of cobalt in aqueous solutions of different pH was carried out. Open circuit potential measurements, polarization experiments and electrochemical spectroscopic (EIS) investigations were employed. The experimental results show that the metal surface is always covered by a native passive film which consists of CoO. The formation of the oxide film obeys a two-electron charge transfer process. The dissolution of the barrier film is controlled by the pH of the solution. In neutral and basic solutions the barrier film is stable. In these media a barrier film thickening with the formation of secondary layer is considered. In acidic solutions, the passive film is unstable and dissolves via a pure chemical process. The mechanism of the corrosion and passivation processes taking place at the electrode/electrolyte interface in the different solutions is discussed. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to confirm the electrochemical measurements and the suggested mechanisms.     

Weighted intrinsic viscosity relationships for polysaccharide mixtures in dilute aqueous solutions

The weighted intrinsic viscosities of polysaccharide mixtures in dilute aqueous solutions have been studied. The purpose of this investigation is to demonstrate that average intrinsic viscosities would scale with the weight fraction of the individual components for polysaccharide mixtures in 0.5N NaOH_(aq). The polysaccharides examined in this study were composed of polymers differing in their molecular weights, degree of branching, and bond linkages. Excellent agreement between theory and experiment was observed for the three different mixed polymer systems examined. This observation validates certain aspects of proposed theoretical treatments which employ this fundamental assumption and allows for further advances in experimental analytical developments of water-soluble polymer systems.     

HDPE树脂流变参数与分子量分布的关系研究

测定了4种高密度聚乙烯(HDPE)树脂的分子量及其分布,研究了其毛细管流变行为和动态流变行为,并分析了得到的流变参数和分子量分布的关系。结果表明:仅在较低挤出速度或较高温度条件下,用毛细管流变测得的非牛顿指数才能用作分子量分布的量度;用动态流变测得的剪切变稀指数、流变多分散指数、幂率指数均可在一定程度上反映了HDPE树脂分子量分布的大小,其中幂率指数与分子量分布的相关性最好(相关系数r2=0.994)。