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 concentrated solutions of agarose in ionic liquid

The rheological properties of agarose solutions were examined under the effect of entanglement coupling between agarose chains. Agarose solutions were prepared by using an ionic liquid 1‐butyl‐3‐methylimidazolium chloride as a solvent. The concentration of agarose was varied from 1.1 × 10¹–2.1 × 10² kg m^?3. The master curves of the angular frequency (ω) dependence of the storage modulus (G′) and the loss modulus (G″) showed a rubbery region in the middle ω region and a flow region at low ω region, respectively. The molecular weight between entanglements (M_e) for agarose was calculated from the plateau modulus. Moreover, M_e for agarose melt was determined to be 2.3 × 10³ from the concentration dependence curve of M_e. By using well‐known empirical relations in polymer rheology, information on molecular characteristics of sample agarose was derived. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Rheological behavior of polymer solutions during fabric coating

The overall performance of coated products is determined by the intrinsic material properties in solution and processing conditions. To characterize the behavior of these materials, the viscosity of polymers in solution at various concentrations was measured and the experimental data were fitted with the Carreau model. The results describe the rheological behavior of coating materials, and provide a basis for the modeling of polymer flow during the coating process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hydrodynamic properties of aqueous dextran solutions

The hydrodynamic performance of aqueous dextran solutions, including the rheological and thixotropic properties, were investigated. Three kinds of dextrans with different molecular weights were employed to examine the effects of the molecular weight, concentration, temperature, and so forth on the hydrodynamic properties of aqueous dextran solutions. The results showed that an aqueous solution of a dextran with a high molecular weight of 5.223 × 10⁵ at a high concentration of 30 wt % had pseudoplastic properties, in contrast to the conclusions of other researchers finding that aqueous dextran solutions were Newtonian liquids. The viscosity of the aqueous dextran solutions decreased with temperature, and the activation energy was calculated to be 16,849.2 J/mol with a 10 wt % dextran (weight‐average molecular weight = 5.223 × 10⁵) solution. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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 behavior of hydrolyzed polyacrylamide solution flowing through a molecular weight adjusting device with porous medium☆

The separate-layer injection in different interlayers and the injection of the same-molecular-weight polymer solution in a layer are necessary in the polymer flooding process because of heterogeneous multilayer sandstone reservoirs in EOR projects.To alleviate the matching problems between the layer permeability and the injected polymer molecular weight,a molecular weight adjusting device with porous medium was designed on the basis of mechanical degradation principle.In terms of four variables(polymer concentration,pore diameter,length of shear component and flow rate),the rheological behavior of hydrolyzed polyacrylamide(HPAM)solution flowing through the device was investigated in detail.The change of these variables is able to control the shear rate of HPAM solutions through ceramic foam,and achieve the desired degree of shear degradation and the final rheological parameters—viscosity loss,viscoelasticity and pressure drop.Therefore,a linear relationship between viscosity loss and shearing rate was established so as to obtain the targeted viscosity easily.Field tests in the Daqing Oil Field showed that the polymer molecular weight could drop 20%to 50%.In a word,the results could guide the industrial application of the novel device and the further study of polymer degradation flowing through the porous medium.     

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).     

Measurement and correlation of physical properties of aqueous solutions of tetrabutylammonium hydroxide,piperazine and their aqueous blends

The density, viscosity and refractive index of aqueous solutions of tetrabutylammonium hydroxide (TBAOH), pi-perazine (PZ) and their aqueous blends are determined at several temperatures (303.15 to 333.15 K). All these measured physicochemical properties decreases with an increase in temperature. The density data is used to cal-culate the coefficient of thermal expansion and excess molar volume of al aqueous binary and ternary solutions. The coefficient of thermal expansion increases with increase in temperatures and concentrations. The negativity of excess molar volume for al the aqueous solution decreased with increase in temperature. Each physical prop-erty is correlated with temperature by least square method and the corresponding coefficients for each property are presented. The prediction values from correlations for the physical properties are in good agreement with the experimental values.     

醚化海藻酸钠-丙烯酸-聚乙烯醇高吸水树脂在环境介质中的溶胀行为

以N,N-亚甲基双丙烯酰胺为交联剂,过硫酸铵-亚硫酸氢钠为引发剂,采用水溶液法合成了醚化海藻酸钠-丙烯酸-聚乙烯醇高吸水性树脂.考察比较了树脂在不同pH值缓冲溶液和盐溶液中的平衡含水率.结果表明,在酸性介质中,凝胶的溶胀过程为—COO^-的质子化过程控制,溶胀过程表现出non-Fickian动力学行为; 在碱性介质中,溶胀过程主要由溶剂扩散控制,表现出Fickian动力学行为,随着pH值升高,凝胶的平衡含水率升高; 在离子强度相近时,树脂在pH缓冲溶液中的溶胀率比在单价盐离子溶液中低,但比在二价盐溶液中高.对聚合物-溶剂的相互作用机理进行了探讨.     

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%.     

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.