Rheological and Electrokinetic Properties of Sodium Montmorillonite Suspensions

Because of their particular electric surface properties and crystal structure, most clay minerals possess a very high ion exchange capacity. Furthermore, the surface charge distribution is anisotropic: while faces of the laminar clay particles have a negative, pH-independent charge, edges may be positive or negative, depending on pH. In this work, we propose to contribute new data on particle-particle interaction and charge distribution, by means of measurements of the low-frequency dielectric dispersion (LFDD) of the clay suspensions. Because of the nonspherical shape of clay particles, there are no theoretical models capable of explaining the experimental relaxation spectra. Hence, we limit ourselves to obtaining indirect information by comparing LFDD spectra in different experimental conditions. The quantities of interest in LFDD are the value of the low-frequency dielectric constant, epsilon'(r)(0), and the characteristic or relaxation frequency, omega(cr). These two parameters were measured varying the weight fraction, straight phi, of clay (0.5, 1, and 1.5% w/v) and the pH of the dispersion medium (5, 7, and 9), while maintaining the ionic strength constant ([NaCl]=10(-4) M). It was found that the characteristic relaxation frequency of the dielectric constant was pH-dependent, with a significant minimum at pH 7 in all cases. The results are interpreted as the superposition of two independent relaxation phenomena, associated with edges and faces. With respect to the weight fraction influence, we have found a linear behavior of epsilon'(r)(0) with straight phi at pH 9, indicating the existence of no significant interaction between particles. However, at pH 7 a slight deviation of linearity is observed, and at pH 5 we observe a clearly nonlinear behavior, indicating a stronger degree of interaction between particles. This is in good agreement with the initial assumption that at acid pH values, the electric surface charge of faces is negative, whereas the edges possess a positive charge, thus favoring attractive face-to-edge interaction. Copyright 2000 Academic Press.     

Rheological Behavior of Titanium Dioxide Suspensions

The rheological properties of titanium dioxide dispersed in water are measured over a wide range of powder concentrations, temperatures, and pH values. The value of intrinsic viscosity of titanium dioxide measured with an Ubbelohde capillary viscometer is 3.55, which is useful for determining the shape and aggregation property of the particles. The yield stress and steady shear viscosity of titanium dioxide with broad and narrow particle size distributions were measured over a wide range of solid volume fractions on a Brabender rheometer. It is observed that the rheological properties of the suspensions are quite different due to the difference in particle size distributions. Quemada, Casson, and Zhou's models were used to fit the experimental data and useful parameters were obtained. Calculated data are also in good agreement with the experimental data. As expected, the shear viscosity and yield stress decrease with increasing temperature. But when the temperature is around 50 degrees C, yield stress increases with increasing temperature while shear viscosity exhibits a complex behavior. The phenomena are very interesting and special. The Peclet number was used to analyze the shear thickening behavior. Models were also used to describe the shear viscosity under different temperatures and the master plots of the reduced variables eta/eta(infinity) vs t(c)gamma; at different temperatures are superimposed, which means the agreement is fair and the models are suitable to describe the rheological properties of titanium dioxide suspensions. pH effects were investigated on a Rheometrics RFS-II rheometer and it was found that pH can change the surface charge of the particles, which also affects the rheological behavior. The pH at which maximum shear viscosity and yield stress occur is in concordance with the isoelectric point. Copyright 2001 Academic Press.     

Rheological Behavior of the Melts for Polyethylene-based Montmorillonite Nanocomposites

IntroductionOwing to their special structures or morphologies,polymer-based montmorillonite nanocomposites exhibitsome particular characteristics,such as,physical,thermal,and mechanical properties,induced by theaddition of very small amounts of inorganic …     

Rheological Properties of Silica Particle Suspensions in Mineral Oil

The rheological properties of particles suspended in a non‐polar mineral oil have been investigated as a function of volume fraction of particles, particle size, surface properties and shear rate. Three different types of particles were investigated; glass microspheres, monodisperse silica particles and fumed silica. The suspensions showed shear thinning behavior at higher volume fractions, and the viscosity increased with decreasing particle size. The hydrophobic particles display lass shear thinning effects. The relative viscosity of all the suspensions was well fitted to the Krieger and Dougherty model.     

Non-linear Viscoelastic Rheological Properties of PCC/PEG Suspensions

The shear thinning and shear thickening rheological properties of PCC/PEG suspension were investigated with the increase of oscillatory amplitude stress at different constant frequencies. The results show that the complex viscosity was initially independent of stress amplitude and obvious shear thinning occurred, then dramatic shear thickening took place after reaching the minimum viscosity. Typically, in a constant frequency of 5 rad/s, the elastic modulus, viscous modulus, and tanδ （δ is the out-of-phase angle） vs. the stress amplitude was investigated. It is found that the elastic modulus initially appeared to be independent of stress amplitude and then exhibited a rapid decrease, but the viscous modulus was independent of amplitude stress at lower amplitude stress. After reaching the minimum value the viscous modulus showed a rapid increase. On the other hand, tanδ increased from 0.6 to 92, which indicates that the transition from elastic to viscous had taken place and tanδ showed a steep increase when shear thickening occurred. Lissajous plots are shown for the dissipated energy vs. different maximum stress amplitude in the shear thinning and shear thickening regions. The relationship of dissipated energy vs. maximum stress amplitude was determined, which follows a power law. In the shear thinning region the exponent was 1.91, but it steeply increases to 3.97 in the shear thickening region.     

类水滑石/蒙脱土体系的特殊粘弹性和触变性研究

本文对由类水滑石（HTlc） /钠质蒙脱土（MT）组成的复杂体系的粘弹性和触变性进行了详细的研究,我们共研究了两种Fe-Mg-Al- HTlc样品,从样品1到样品2,Al 对 Fe的比例保持不变,而Mg2+的含量逐渐增加。研究发现,随着类水滑石中Mg2+的含量增加,HTlc/MT分散体系的结构强度逐渐增加;触变环的实验结果也表明,随着类水滑石中Mg2+的含量增加,HTlc/MT分散体系的触变程度逐渐增加。由此我们可以得到这样的结论,通过调节类水滑石金属的配比我们就可以对类水滑石/蒙脱土体系的流变性进行宏观的调节。     

表面活性剂对氧化锰悬浮体系流变学振荡行为的影响

对介孔氧化锰的溶胶-凝胶法合成和用表面活性剂（脂肪醇聚氧乙烯醚, AEO_9)的模板合成过程中所得的悬浮体系的流变性质进行了对比研究。结果表明： 上述体系均具有触变性,且无论是否预剪切,其表观粘度均随时间作周期性振荡; 同时上述体系的储能模量G'和损耗模量G"亦具有周期性的振荡行为。但表面活性剂 AEO_9的引入使体系的触变性大为减弱,屈服值明显降低,凝胶结构强度减弱。同 时还发现引入AEO_9的模板合成过程中,不仅体系的表观粘度及G'大幅度下降,且 G'与G"的振荡周期显著增大,振幅亦明显减小。这说明体系中两亲分子与无机物存 在较强的相互作用,作者还对这些现象进行了讨论。     

Mg-Al类水滑石/高岭土分散体系流变振荡现象研究

恒剪切速率(DL)实验发现Mg-Al类水滑石(HTlc)/高岭土(kaolinite)分散体系中存在流变震荡现象,即粘度随时间发生周期性升高和降低的变化.研究了HTlc/kaolinite分散体系的质量比(R)、剪切速率、pH、无机盐及聚合物等因素对振荡现象的影响,发现较高的DL与无机盐含量均可使震荡现象消失.pH值及...     

Correlation between Conformational Parameters and Rheological Properties of Molten Syndiotactic Polypropylenes

Summary: New rheological results with molten polypropylenes of different degrees of syndiotacticity are presented. The temperature dependence of their dynamic viscoelastic functions is correlated with the characteristic ratio. Relaxation time and Newtonian viscosity values are plotted as a function of molecular weight. The very high values of both rheological parameters found for the most syndiotactic polypropylenes are explained considering the reptation model, which links conformational parameters with the viscoelastic response in the molten state.

Disengagement or reptation time as a function of molecular weight.     

Effect of pH and Salt on Rheological Properties of Aerosil Suspensions

Ionic strength and pH will influence the zeta potential of suspended particles, and consequently particle interactions and rheological properties as well. In this study the rheological properties and aggregation behaviour of Aerosil particles dispersed in aqueous solutions with various pH and salt concentration were studied. The potential energy was estimated by the DLVO theory and short range hydration forces and compared to the experimentally determined zeta potential. The strongest attraction between particles occurs at the isoelectric point (pH 4) and resulted in large aggregates, which gave relatively higher values of viscosity, yield stress, moduli, and shear thinning effects. The relative viscosity as a function of volume fraction was fitted to the Krieger and Dougherty model for all the suspensions. Oscillation measurements showed that the suspensions display elastic behaviour at low pH and viscous behavior at high pH. Furthermore, suspensions with high salt content had higher storage moduli. A power law dependency of storage moduli with volume fraction could be used to indicate the interaction strength between particles.     

带相反电荷胶体颗粒混和悬浮体的流变学性能

研究了带相反电荷的粘土颗粒和MMH(铝、镁混合金属氢氧化物)颗粒形成的混和悬浮体的流变学性能,考察了盐对混合体系流变学性能的影响.结果表明,当粘土质量分数为1%时,悬浮体为牛顿型流体;当质量分数升至2%时,悬浮体表现出固体的弹性响应;特定粘土含量的悬浮体中,随着MMH量的增加,混合体系的屈服值和弹性模量亦增加,表明凝胶结构增强.向混合体系中加入NaCl,弹性模量、屈服值和粘度等流变参数均降低.与单组分粘土悬浮体或MMH悬浮体相比,双组分混合体系的结构恢复很快.     

镁铝类水滑石/阳离子淀粉分散体系流变学振荡行为研究

采用稳态剪切和小振幅振荡剪切实验研究了镁铝类水滑石化合物(Mg-Al HTlc)/阳离子淀粉(CS)分散体系(HTlc与CS质量之比R分别为0, 0.02, 0.05和0.08)的流变学性质．实验结果表明: 上述体系在实验pH值(5～11)范围内均为剪切稀释非牛顿流体, 其中, Mg-Al HTlc/CS (R＝0, 0.02和0.05)分散体系的流变曲线符合幂律模型, 而Mg-Al HTlc/CS (R＝0.08)体系符合Herschel-Bulkley模型. 上述体系先于1000 s^－1剪切180 s, 再于1 s^－1(或者3 s^－1)低速剪切时均表观出粘度随时间周期变化的振荡现象. 振荡现象缘于CS分子结构的周期变化. pH值、剪切速率和HTlc含量的变化可以改变振荡周期(频率)和振幅. 低pH值条件下, Mg-Al HTlc/CS (R＝0.08)体系先于1000 s^－1剪切180 s, 再于小振幅振荡剪切(剪切应力0.03 Pa, 频率0.5 Hz)时储能模量G?和损耗模量G?也表现出随时间周期变化的振荡现象.     

HDPE氧化交联与动态流变行为

研究了高密度聚乙烯(HDPE)熔体在200℃的动态流变行为,比较了空气、氮气及加入抗氧剂B215情况下体系动态粘弹行为的差异.研究表明,在空气环境中,HDPE在低频区域出现特征粘弹行为.随着测试前热处理时间的延长,动态储能模量(G')明显增加,在低频率(ω)区域lgG'～lgω关系呈现平台特征.同时损耗角tanδ变小并出现极大值.在氮气环境中,上述特征粘弹行为存在但不明显.在加入抗氧剂的条件下,特征粘弹行为完全消失.这些现象归因于高温下HDPE的氧化导致其发生交联.     

Influence of Monovalent Electrolytes on Rheological Properties of Gelled Colloidal Silica Suspensions

Rheological responses of the gelled (G) Snowtex 20 silica suspensions in the presence of LiCl, NaCl, and KCl have been investigated as functions of concentrations of silica and salt at pH 9.8 in terms of the Hofmeister series effect. The primary silica particle is isolated, and it is coagulated to form a gel above at 0.1, 0.3, and 0.5 M concentrations of LiCl, NaCl, and KCl, respectively, when the silica volume fraction φ is beyond 1.0%. The resulting G silica suspensions are classified into a strong‐link gel and their power‐law dependences of the critical strain as well as the storage modulus on the silica volume fraction were compared with the predictions by the fractal gel model. The resulting power‐law exponents of the critical strain are negative, this is in agreement with that predicted by the fractal model, and their magnitudes decrease with an increase in salt concentration, irrespective of the salt. Moreover, the magnitude of the power‐law exponent for the critical strain is well related to the Hofmeister series effect, namely it decreases in the order Li⁺, Na⁺, and K⁺, and the least hydrated K⁺ adsorbs in great enough in amount to create a less flexible network structure in the G silica suspension due to stronger attraction between the silica particles. Moreover, the stronger attraction, on the other hand, should be responsible for both the larger storage modulus and the higher power‐law exponent of the silica volume fraction dependence on the storage modulus. Therefore, the Hofmeister series effect is useful to understand the rheological properties of the G Snowtex 20 silica suspensions.     

表面活性剂对TiO2水悬浮体稳定及流变性质的影响

在陶瓷的制备过程中,通常需将陶瓷粉末分散于水中形成陶瓷浆后再浇铸成型.研究表明[1],陶瓷浆的分散、稳定及流变性质直接影响到成品的性能.因此,研究分散稳定剂对该浆料性质的影响有着重要意义.本文利用电泳和流变学方法研究了TiO2在表面活性剂的水溶液中浓浆体的分散稳定性及流变性质.     

Rheological Properties of Silica Suspensions in Aqueous Solutions of Block Copolymers and Their Water-Soluble Components

Dynamic moduli of fumed silica suspensions in aqueous solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers and PEO homopolymers were measured as a function of surface coverage. Since the block copolymers and PEO are adsorbed on the silica surface through hydrogen bonding between the ether oxygen and the silanol group on the silica surface, the interaction between the silanol groups, which is dominant for the aggregation of silica particles, should be prohibited. Dynamic moduli in the silica suspensions were strongly related to the stability of the silica suspensions and the block copolymer, and the longest PEO portion was useful for stabilizing the silica particles. However, the PEO homopolymer did not support stability of the silica particles, suggesting that chain conformation of the PEO portion in the block copolymer is different from that for the PEO homopolymer. Copyright 2001 Academic Press.     

流变学法研究表面活性剂与HPAM的相互作用

流变学法研究表面活性剂与HPAM的相互作用;聚合物;表面活性剂;相互作用;流变学方法     

Effect of Montmorillonite on the Crystallization,Rheological and Physical Behavior of Polyamide-6/Polylactic Acid Blends

Organic montmorillonite (OMMT)/polyamide-6 (PA6)/polylactic acid (PLA) composites were prepared via a step melt compounding process using a twin screw. The effect of OMMT content on the crystallization behavior, as well as rheological and mechanical properties of the composites was carried out by differential scanning calorimetry, differential mechanical analysis, and using an advanced rheometer and a material testing machine. The crystallization behavior of the polymers was studied using a dynamic rheology method, which allowed to determine the onset of nucleation and obtain semiquantitative data on the nucleation density. The results revealed that the interaction between the OMMT and the PA6/PLA inhibits the molecular chain segment motion, which reduces the nucleation temperature, the crystal growth temperature, the melting temperature and the glass transition temperature of the samples. However, the PA6/PLA/OMMT composites showed better mechanical properties than the PA6/PLA composites.     

Rheological and Electrical Properties of Oxidized Carbon Black Suspensions in Vaseline Oil under Shear and Vibration

The results of investigations of the rheological characteristics and electrical resistance of the suspensions of carbon black in vaseline oil under the effects of shear and vibration were presented. The investigations are carried out on an original unit that allowed one to simultaneously subject the suspensions to shear deformation and orthogonal vibration. The electrical resistance was also measured in an ac pulsed low-voltage mode. Possible mechanisms of the suspension conductivity were considered depending on the regime of dynamic action.     

纳米离子材料中离子相互作用与流变性能调控

制备了2种离子相互作用强度不同的纳米离子材料(相对强度SiO_2-SIT-M2070SiO_2-SIT-Ethomeen).结果表明,分散相SiO_2在纳米离子材料中稳定存在,未出现聚集.纳米离子材料中外层低聚物的结晶受到抑制,且离子相互作用越强,结晶抑制作用越明显,对动态流变性质也有显著影响.在相同固含量条件下,纳米离子材料SiO_2-SIT-Ethomeen的动态剪切模量和黏度比SiO_2-SIT-M2070小1~3个数量级.在动态大应变剪切条件下,高固含量的SiO_2-SIT-M2070表现出软玻璃流变学特性;而SiO_2-SIT-Ethomeen体系表现出强应变过冲现象,并且随着固含量的升高,其动态模量和黏度出现极大值时所对应的应变值逐渐减小,而且应变过冲的程度逐渐变小.因此通过调节组分间离子相互作用可有效地调节纳米离子材料的流变特性.