油酸、聚甲基丙烯酸甲酯修饰可磁化颗粒的磁流变液的流变行为

主要研究了拥有相同极性基团不同长度的非极性基团的表面活性剂对磁流变液流变行为的影响。分别以油酸、聚甲基丙烯酸甲酯修饰后的羰基铁粉为可磁化颗粒,硅油为载液,经过超声分散制备磁流变液。黏度测试表明,低速剪切时,颗粒表面表面活性剂层的空间位阻作用（熵斥力）起主导作用,黏度降低;高速剪切时,表面活性剂层又会增大颗粒的内摩擦,使黏度增加。通过流变模型的定量分析也印证了上述结论。磁流变测试表明,油酸为表面活性剂的磁流变液对磁场有更强烈的响应,形成更强的链束结构,屈服应力增大,而聚甲基丙烯酸甲酯的作用相反。两种表面活性剂都明显改善磁流变液的沉降稳定性能,降低了沉降速率与最终沉降量。本研究为磁流变液表面活性剂的选用提供了参考。     

Gelation, Consolidation, and Rheological Properties of Boehmite-Coated Silicon Carbide Suspensions

We have studied the gelation, consolidation, and rheological properties of boehmite-coated SiC suspensions. A boehmite-coated SiC suspension consists of SiC particles covered with a boehmite layer of a few nanometers in thickness in the suspension. Similar to boehmite suspensions, the boehmite-coated SiC suspension can gel over time. The gelation, as well as the rheological behavior of the boehmite-coated SiC suspension with respect to pH, is shown to be similar to that of a boehmite suspension. However, because of the particle-size difference, a boehmite-coated SiC suspension gels more slowly than suspensions of smaller boehmite particles. The boehmite coating improves the consolidation density of SiC, increasing the sediment density from 39 to 52 vol% and the centrifuged density from 50 to 60 vol%. It, also, makes the consolidation behavior of a boehmite-coated SiC suspension with respect to pH more consistent with the rheological behavior; i.e., lower suspension viscosity and storage modulus correlate with a higher consolidated density. In contrast, suspensions containing SiC particles partially covered with boehmite and individual boehmite particles in the suspensions show no improvement in the sediment density and no systematic correlation between the consolidation density and the rheological properties. This indicates that the complete coating of boehmite on the SiC particles is critical to the improvement in consolidation density.     

Deposition Via Dip Coating Technique of Dense Yttrium Stabilized Zirconia Layers

A deposition of yttrium stabilized zirconia layer for its use as an electrolyte in solid oxide fuel cell was performed using dip coating technique. Two commercially available surfactant systems were evaluated; nonionic surfactant which stabilizes only by steric repulsion and anionic surfactant which provides both steric and electrostatic repulsion. Dip coating process was optimized to two step deposition process. Uniform 10–15 μm thick yttria stabilized zirconia (YSZ) electrolyte layer is obtained after the final sintering step at 1400°C. Impedance spectroscopy measurements showed that selected phosphate ester based surfactant has negligible effect on the performance of the YSZ material as electrolyte.     

Rheology of Concentrated Suspensions Containing Weakly Attractive Alumina Nanoparticles

The use of nanoparticles for the fabrication of new functional ceramics and composites often requires the preparation of concentrated fluid suspensions. However, suspensions containing nanoparticles are limited in solids content because of the excluded volume formed by the dispersant adlayer around the particles. We investigated the effect of the adlayer thickness on the rheological behavior of suspensions containing model alumina nanoparticles, using dispersant molecules with deliberately tailored chain length. The apparent viscosity and yield stress of the particle suspensions were markedly decreased by increasing the dispersant length, mainly due to a reduction of the attractive forces among particles. Fluid suspensions with solids content up to 35 vol% were prepared in toluene using a dispersant length of 2.5 nm. Our experimental results and viscosity predictions based on a hard sphere model indicate that fluid suspensions with up to 43 vol% of 65 nm alumina particles could be prepared using an optimum dispersant length of about 3.6 nm.     

牛顿介质浓悬浮体的流变性质

<正>浓悬浮体广泛出现于石油、化工、材料、食品等工业领域中,例如煤浆、油墨、涂料、填充高分子、果酱等.为了解决这些材料的某些工艺问题,常需要了解其流变性质.另一方面,悬浮体理论的发展始于只适用于稀悬浮体的Einstein方程,人们对浓悬浮体复杂的流变行为尚缺乏全面和规律的认识.本文通过对碳酸钙悬浮体流变性能的研究,讨论了分散相浓度和表面改性的影响,得到粒子悬浮体流变性的一些基本认识,亦为各种工业悬浮体的流变表征提供了一种实验方法.     

Rheological Behavior of Coating Colors: Influence of Thickener

In this work we have investigated the effect of rheology modifiers on the rheological properties of concentrated (65 solids mass%) kaolin suspensions and six different coating colors. Measurements have been performed on kaolin‐based suspensions, without rheology modifier and with either a classic cellulose thickener or associative polymers. It was noticed that suspensions containing a thickener had a much larger viscosity and storage and loss moduli than suspensions containing no rheology modifier. The enhancement of the rheological properties was found to be much more important for the suspensions containing the associative polymer. These observations have been related to steric stabilization of the suspensions, and to the occurrence of entanglements and bridging when the associative polymer was used as the thickener. The influence of the thickener on the rheological properties of the coating colors was found to be similar to that observed for the concentrated kaolin suspensions.     

添加剂对酸性硅溶胶及料浆胶凝与流变行为的影响

以酸性硅溶胶及其结合料浆为研究对象,通过对比胶凝时间、黏度、触变环面积、剪切应力等流变参数,研究了聚丙烯酰胺、氢氧化镁、柠檬酸三铵等对酸性硅溶胶及结合料浆流变行为、凝聚过程的作用规律。结果表明:氢氧化镁电离出Mg²⁺促进了酸性硅溶胶的缩合反应,对酸性硅溶胶胶凝过程的影响较为显著;氢氧化镁添加量的增加,增大了胶凝速度,酸性硅溶胶的稳定性下降。聚丙烯酰胺作为阴离子表面活性剂,通过空间位阻效应,缔合溶胶中的氢键,在溶胶中形成三维网络结构,同时聚丙烯酰胺水解吸附在溶胶胶团颗粒表面,加快了SiO₂粒子的絮凝,提高了酸性硅溶胶及其结合料浆的黏度。控制柠檬酸三铵的含量低于10 mg/mL,有助于降低硅溶胶结合料浆的黏度,提高体系的稳定性。     

Influence of organic admixtures on the rheological behaviour of cement pastes

The rheological properties of cementitious pastes used to proportion Self-Consolidating Concretes (SCC) have been examined, in particular, the influence of High range water reducing admixture (HRWRA) with that of Viscosity Modifying Admixtures (VMAs) have been compared. HRWRAs are known to have dispersing effects on the cement particles through steric and/or electrostatic repulsion, while the effects of VMAs are expected to stabilise the paste by increasing the viscosity of the aqueous solution. Both transient and steady state rheological behaviour of the cementitious pastes proportioned with different dosages of HWRA and VMA were considered. Experimental results show that the influence of VMAs on rheological properties is actually minor compared to that of HRWRAs. These results are discussed in the framework of rheology of concentrated suspensions.     

Phase Behavior of Polyelectrolyte Complexes and Rheological Behavior of Alumina suspensions for Direct Ink Writing

Polyelectrolyte complexes have a bright prospect for fabricating 3D periodic structures by direct ink writing. The phase behavior of complexes containing poly(acrylic acid) and poly(ethylenimine) and rheological behavior of Al₂O₃ colloidal suspensions are characterized. The results reveal that the pH value of solution takes an important role on the phase behavior of polyelectrolyte complexes. When the [COOH]:[NH_x] ratio is higher than or lower than the critical value of 0.6, the pH range of turbid complex solutions narrows down and meanwhile moves to acidic or alkaline region, respectively. The addition of pH regulators prompts polyelectrolyte exchange reaction and soluble complexes are suitable for preparation of cera‐mic suspensions. The polyelectrolyte suspensions with linear viscoelasticity at lower shear stress and good fluidity at higher shear stress are identified for direct ink writing of 3D structures with microsized feature.     

Effect of Polyvinylpyrrolidone Additions on the Rheology of Aqueous,Highly Loaded Alumina Suspensions

The control of the rheological behavior of highly loaded ceramic/polymer suspensions affords the development of near‐net shape forming techniques. In this study, suspensions containing sub‐micrometer diameter alumina (up to 56 vol%) were fabricated using an anionic dispersant (≈4 vol%) and water‐soluble polyvinylpyrrolidone (PVP). The amount and ratio of molecular weights of PVP in the suspension were varied to influence flow behavior. The final pH of the system, ≈9.5, was higher than the isoelectric point (IEP) of alumina implying that the alumina powder possesses a negative surface charge. In the case of alumina at this pH, PVP does not adsorb onto the surface of the powder. The flow behavior of the PVP‐containing suspensions displayed yield‐pseudoplastic characteristics that closely agreed with the Herschel–Bulkley fluid model. The addition of PVP significantly changed the rheology of the system, increasing the shear yield stress and altering flow behavior. Interparticle interaction approximations of the suspensions were modeled to correlate with experimental observations.     

Synthesis of exfoliated acrylonitrile-butadiene-styrene copolymer (ABS) clay nanocomposites: role of clay as a colloidal stabilizer

Acrylonitrile-butadiene-styrene copolymer (ABS) clay nanocomposites were synthesized using two clays (sodium montmorillonite, laponite). Both colloidal stability and mechanical properties of the nanocomposites were dependant on aspect ratios of clays. Laponite, a low aspect ratio clay, reduced particle sizes of ABS clay nanocomposite latexes, enhanced colloidal stabilities, and increased viscosity of the latexes. The colloidal stability of ABS clay latexes may result from four factors. Firstly, the electrostatic repulsion forces originated from surface charges of clays and anionic surfactant contribute to colloidal stability. Secondly, laponite layers separate sodium montmorillonite layers and polybudadiene latex particles preventing the coagulation. Thirdly, the laponite layers adsorbed on latexes act like steric barriers against coagulation. Fourthly, increased viscosity reduces latex mobility, lowering collision possibility among latex particles. Resultant ABS clay nanocomposites showed exfoliated structures, and their mechanical properties related to the relative weight ratio of sodium montmorillonite to laponite: as portions of sodium montmorillonite increased, dynamic moduli of the nanocomposites increased, because sodium montmorillonite has higher aspect (length/thickness) ratio than laponite.     

Effect of dispersants on the rheology of aqueous silicon carbide suspensions

The effect of cationic and anionic dispersants on aqueous suspensions of as-received and surface-modified silicon carbide particles has been studied via observation of the rheological behaviour. Only the cationic dispersants were effective for the as-received SiC, with polyethyleneimine being superior to Hyamine 2389 probably as a result of a greater electrosteric interaction. SiC particles modified using Al(NO₃)₃ behaved like alumina and so could be dispersed using the anionic dispersants ammonium polyacrylate and polymethacrylate. Such dispersions displayed no heteroaggregation when alumina was added, although the order of mixing could significantly affect the rheological behaviour of the suspension. Nevertheless, the suspensions appeared robust to slight fluctuations in pH.     

Air-entraining actions of anionic surfactants in portland cement pastes

The air-entraining actions of a number of anionic surfactants in cement pastes were studied in order to determine whether precipitated calcium surfactants influence the air-entrainment process. Air contents of pastes containing both soluble and precipitated calcium surfactants were higher than those containing only soluble calcium surfactants, thus indicating that precipitated material contributed towards air-entrainment. It was shown further that the precipitated calcium surfactant could re-dissolve appreciably during mixing and supply additional surfactant ions in solution to replace those adsorbed on cement. It was concluded that these additional ions contributed to air-entrainment by further adsorption on cement particles and by augmenting the foam capacity of the mixing water.     

Modifying the rheological behavior of associative triblock copolymers in aqueous media through surfactant additives

The rheological behavior of aqueous micellar solutions of a triblock copolymer, bearing two small hydrophobic end-blocks of polybutadiene and a large hydrophilic middle block of poly(sodium methacrylate), was studied in the presence of a cationic (dodecyl trimethyl ammonium bromide) or an anionic (sodium dodecyl sulfate) surfactant. Depending on the concentration and the charges of the interacting (with the water soluble middle block) surfactants, the rheological behavior of the triblock copolymer micelles (which resemble compact spheres, based on scattering studies) can be altered dramatically. The surfactant additives can either solidify a liquid-like system (low triblock concentration, dominated by loops) or alternatively liquefy a gel (high triblock concentration, dominated by bridges). Apparently, the hydrophobic tails of the surfactants prefer to join the hydrophobic polybutadiene cores of the triblocks, whereas by increasing the surfactant concentration the core functionality can be changed. In addition interactions between the oppositely charged hydrophilic surfactant heads and middle blocks can yield complexes producing new hydrophobic domains. These findings suggest possibilities for controlling complex fluid rheology.     

Viscoelastic Behavior of Alkyl Ether Sulfate Systems Containing Nanosized Colloidal Silica

Surfactant systems incorporating wormlike micelles (WLM) are utilized in both industrial and consumer products. While the viscoelastic behavior of such systems provides for many desired end-use properties, there is often a need to further modify the rheological properties of such systems. These WLM systems behave much like polymer systems. Furthermore, incorporation of nanosized particles results in interaction of nanoparticles with the large WLM structures altering the rheological behavior. While there are a number of studies that have focused on the effect of particles on the rheological behavior in cationic surfactant systems, fewer studies have been done on systems containing anionic surfactants. In this study, relaxation behaviors in systems containing sodium alkyl ether sulfate and sodium carbonate were studied. The anionic surfactant was an alkyl ether sulfate with an average chain length of 12 carbons and one ethoxy group. WLM behavior was achieved through the addition of sodium carbonate. Ludox TMA, a nanosized colloidal silica, was employed at different concentrations in the WLM systems. Temperature was varied between 5 and 45°C. While characterization of relaxation in terms of the Maxwell model adequately described data below the threshold of ωτ ~1, the model failed to adequately describe behavior at higher frequencies. A modified expression with an additional relaxation mode adequately described relaxation throughout the frequency range studied. It was also found that zero-shear viscosities generally increased with an increase in silica concentration, and relaxation times decreased. Measurements of relaxation due to a compressive stress via ultrasonic attenuation measurements in the surfactant/particle systems are also discussed.     

Temperature induced gelation of concentrated ceramic suspensions: rheological properties

Concentrated, sterically stabilised ceramic suspensions have been reversibly gelled by changing the temperature. Using an amphiphilic polymer, Hypermer KD3, as dispersant for alumina and alumina-silicon carbide whisker composite mixtures in pentanol resulted in a transition from dispersed to flocculated state close to room temperature. The collapse of the adsorbed polymer layer with decreasing solvency (temperature) in the marginal solvent pentanol induces flocculation when the long-range van der Waals force overcomes the remaining steric repulsion. Temperature induced gelation (TIG) of concentrated suspensions has a drastic effect on the rheological properties. At temperatures above 30°C, the suspensions have a low viscosity and negligible elasticity. When the temperature is lowered below 20°C, the viscosity increases significantly and the viscoelastic behaviour becomes predominantly elastic. The elasticity and the associated particle network strength are sufficiently high for a highly concentrated gelled suspension to support its own weight. The potential use of TIG as a novel forming method was discussed with relation to other new shaping techniques. ©     

Elucidation of Viscosity Reduction Mechanism of Nano Alumina Suspensions with Fructose Addition by DSC

Control of the rheological properties of the nanoparticle suspensions is challenging. In this study influence of the solids content and the fructose addition on the viscosity of nano alumina suspensions have been investigated by low temperature differential scanning calorimetry (LT‐DSC), rheometry, and zeta potential measurements. Analysis of the water melting events in LT‐DSC revealed useful information for explaining the rheological behavior of the nanoparticle suspensions. It was shown that the bound water layer has a negligible effect on the viscosity of micrometer‐size particle suspension while it increases the effective solid content of alumina nanoparticle suspensions significantly leading to high viscosities. The presence of fructose modifies the bound water layer, decreases the effective solids content, hence resulting in viscosity reduction. Fructose addition lowers the pH of the suspension, but has a negligible effect on the zeta potential. The origin of the bound water, and electrostatic and steric effects of the fructose addition on the viscosity are discussed.     

Investigation of Crystal Morphology and Shock Sensitivity of Cyclotrimethylenetrinitramine Suspension by Rheology

Crystal morphology and shock sensitivity of a series of cyclotrimethylenetrinitramine (RDX) particles suspended from ethylene glycol were investigated. Flow rheology was employed to measure the rheological properties of the suspensions at constant temperature; it was observed that the stress‐shear rate and viscosity behavior of the suspensions were controlled by the particle morphology. The viscosity of the RDX suspensions changed with the roundness/smoothness of RDX crystals at all applied shear rates. The suspensions containing crystals with smoother morphology showed reduced viscosity. When the viscosity data was compared to the shock sensitivity results from the RS‐RDX Round Robin study, a good correlation was obtained. This study has validated the use of flow rheology to indicate the morphology and shock sensitivity of crystalline particles.     

The rheological behavior and surface charging of gelcasting alumina suspensions

Aim of this work is to investigate the effect of monomers containing either carboxylate (ammonium acrylate) or acrylamide (hydroxymethylacrylamide) functional groups on the surface charging and rheological behavior of alumina suspensions. The rheological behavior was investigated by changing the concentrations of dispersant (ammonium polyacrylate) and monomers in the suspensions. The zeta potential of alumina suspensions containing each of the different monomers was measured as a function of dispersant additions. The suspension rheological behavior varied significantly depending on the monomer type, which could be explained in terms of repulsive forces, pH changes and additive interactions.     

Comparative study of the dispersion of three oxide pigments with sodium polymethacrylate dispersants in alkaline medium

The adsorption of sodium polymethacrylate (NaPMA) dispersants onto three oxide powders (hematite, goethite and rutile) in alkaline medium has been investigated together with the resulting stabilization of the suspensions. Under basic conditions of waterborne coatings formulation, hematite and rutile are negatively charged whereas goethite is almost neutral. Adsorption isotherms, electrophoretic mobility, particle size, IR spectroscopy and rheological measurements were used to investigate the polymer–pigments interactions. It was found that adsorption of the anionic NaPMA polymer on the three pigments was still possible even at pH above the isoelectric point (IEP). Depending on the pH and the type of oxide, electrostatic interactions, chemical complexation at the surface or/and hydrogen bonding were suggested to be the predominant contributions to the adsorption process. The adsorption at high pH was enough for preventing particles aggregation and ensuring an efficient stabilization of the suspensions. The viscosity measurements performed at pH close to the IEP's also suggested that besides the electrostatic stabilization, the NaPMA polymers provided a steric stabilization. The steric effect was larger with the polymers of higher molar mass. The comparison of the three oxide showed that the affinity for the surface site came mainly from chemical interaction with acidic surface sites in the order rutile > goethite > hematite. The strong adsorption on rutile came from the aluminum treatment of its surface.