聚邻苯二胺/蒙脱土纳米复合材料的合成及其电流变效应

用乳液共混插层法制备了聚邻苯二胺/蒙脱土纳米复合材料微粒,通过IR、XRD及TEM对其结构进行了表征。 结果发现,邻苯二胺插入蒙脱土层间聚合后,导致蒙脱土片层之间的剥离,形成纳米复合材料。 将其分散在甲基硅油中(体积分数,22%)配制成无水电流变液,该复合材料表现出较大的协同效应,具有较好的电流变行为。实验结果表明在外加电场下,其电流变效应比聚邻苯二胺、蒙脱土均有显著提高。 在3 kV/mm(DC, 74.5 s-1)时,剪切强度达8.27 kPa;同时抗沉降性极好,静置60 d沉淀率小于3%。介电性能测试表明,聚邻苯二胺/蒙脱土纳米颗粒的介电常数和介电损耗较蒙脱土和聚邻苯二胺均有一定提高,电导率也达到了最佳范围。     

Polar‐Molecule‐Dominated Electrorheological Fluids Featuring High Yield Stresses

Recent works on the development of various electrorheological (ER) fluids composed of TiO₂, Sr? Ti? O, and Ca? Ti? O particles coated with C? O/H? O polar groups are summarized, in which an extremely large yield stress up to 200 kPa is measured and the dynamical yield stress reaches 117 kPa at a shear rate of 775 s^?1. Moreover, unlike that of traditional dielectric ER fluids, the yield stress displays a linear dependence on electric field strength. Experimental results reveal that it is the polar molecules adsorbed onto the dielectric particles that play the decisive role: the polar‐molecule‐dominated ER effect arises from the alignment of polar molecules by the enhanced local electric field in the gap between neighboring particles. The pretreatment of electrodes and the contrivance of new measuring procedures, which are desirable for the characterization and practical implementation of this material, are also discussed. The successful synthesis of these fluids has made many of the long since conceived applications of the ER effect available.     

Sol-Gel Preparation of Graphite/TiO2 Composite Particles and Their Electrorheological Effect

Graphite/TiO2 composite particles were obtained by sol-gel technique in this paper. The structure and characteristic of the composite particles are analyzed by XRD, SEM and TG-DTA. The electrorheological properties of the ER fluid containing the particles were measured by a Couette-type rheometer under shear rates of 1～136 s-1 and AC electric fields of 0～3 kV/mm. The experimental results show that the leaking current density of the ER fluid is higher than that of pure titanium dioxide particles dispersed in damping oil. The shear yield stress of the ER fluid increases with increasing electric field and exhibits a typical Bingham flow behavior. The suspension demonstrates an excellent ER performance (τ/τ0=1200) compared with conventional ER fluids (τ/τ0 ≤500). The sedimentation of the ER fluid is improved obviously due to the coating effect of the particles.     

Synthesis and characterization of polysaccharide phosphates based electrorheological fluids

Polysaccharide phosphate particles were synthesized via an esterification process with various molar concentrations of phosphoric acid using both cellulose and potato starch. The particles were characterized with thermogravimetric analysis, scanning electron microscopy, and an inductively coupled plasma-mass spectrometer. These particles were then dispersed in a silicone oil to make anhydrous electrorheological (ER) fluids. Each sample of polysaccharide particles used in this study exhibits thermal stability and possesses excellent ER properties when measured as functions of both particle concentration and electric field strength by a rheometer equipped with a high voltage generator. A difference in the flow behavior for both potato starch and cellulose-phosphates-based ER fluids was also identified.     

Gelation of chitin and chitosan dispersed suspensions under electric field: effect of degree of deacetylation

Herein, the effect of the degree of deacetylation (DD) on the gelation of the chitosan dispersed suspension as an electrorheological (ER) fluid under an electric field is presented. The fluids were prepared by dispersing the chitin and the chitosan particles having various DDs into silicone oil, and they were evaluated under various electric fields. The alignment of chitosan particles in the fluid was also observed using an optical microscope under the electric field. The formed fibrous structure between electrodes are though to continue to the viscosity increase, because an attempt to move one electrode relative to the order would be hindered by the drag of the dangling fibrils. A noteworthy result is that the region of the frequency for gel state of the ER fluids increased in the order of chitosan DD 99.3, 93.4, 73.2, 83.8, and 87.3% under electric fields while the modulus of the fluids increased in the reverse order. This order was well-matched with the result of dielectric constants and yield stresses of ER fluids. The study of influence of DD on the gelation of the chitosan dispersed suspension under an electric field shows the relevance of the chemical composition of the heteropolysaccharide (chitin-chitosan copolymer) to the rheological and electric properties of ER suspensions.     

电流变体特性及电流变体应用器件的进展

本文详细评述了电流变体(ERF)材料的组成、工作机理及其流变力学性能,提出以Bingham塑性体来近似描述电流变体的流变特性,综述了电流变体在智能材料、汽车离合器、液压阀门等器件中的应用,给出了含电流变体的双层智能复合材料梁单层、双层加电状态对其振动特性的影响,设计了含电流变体的主动控制式减振器,并对其在外加电场作用下的减振性能进行了评价。     

Electrorheological properties of poly(acrylonitrile) microspheres coated with multiwall carbon nanotubes

Poly(acrylonitrile) (PAN) particles coated with functionalized multiwall carbon nanotubes (fMCNTs) were prepared and applied to electrorheological (ER) fluids. First, carboxylic acid groups were introduced on the multiwall carbon nanotubes by chemical oxidation method. Then, nitrile groups on the surface PAN particles were modified to amine groups by Co catalysis reaction. Finally, fMCNTs were anchored on the surface of polymer particles by covalent bonding between carboxylic acid groups on fMCNTs and amine groups on particles. fMCNTs attached polymeric microspheres were characterized by scanning electron microscopy and optical microscopy. The ER properties of fMCNTs modified microspheres were measured under controlled electric fields. Although the amount of fMCNTs anchored on the surfaces of microspheres was 1 wt.% of polymers, good ER properties were observed. This improvement may be caused by fMCNTs enhancing the electrical properties of polymer microspheres.     

硫酸改性TiO2粒子的表征与电流变性能研究

采用硫酸溶液浸渍TiO₂干凝胶的方法制备了硫酸改性的TiO₂粒子, 并组成了具有显著电流变性能的电流变材料. 用FT-IR、XRD、比表面积分析仪等表征了样品结构, 并测试了其电流变性能. 结果表明：由于硫酸根对晶粒生长的阻碍作用, 与纯TiO₂粒子相比, 硫酸改性的TiO₂粒子的晶粒尺寸降低, 比表面积提高, 并含有大量的强极性键SO. 当电场强度为3kV/mm时, 纯TiO₂粒子电流变液的场致剪切应力与零场剪切应力之比（τ_E/τ₀）仅为80, 而硫酸改性TiO₂电流变液的τ_E/τ₀高达500. 产生这些现象可归因于硫酸改性TiO₂粒子带来的结构改变赋予其明显的界面极化能力.     

智能复合材料结构的主动振动控制

本文提出应用电流变体(Electro-Rheological Fluids)材料作为复合材料结构振动主动控制的材料,针对含电流变体材料的智能复合材料悬臂梁,进行了振动的主动控制,测试了智能复合材料悬臂梁在外加电场作用下,弹性模量、衰减系数、固有频率等振动特性的变化,同时,针对不同的梁材料,给出了材料变化对梁振动控制的影响.     

恒压驱动流下电流变液动力学可视化试验研究

针对动态场下电流变效应机理可视化试验研究工作较少的现状,设计并制造了一个可视化试验台。通过试验观察了电流变液在外电场和流动场耦合作用下的场致亚微观动态结构变化。试验结果表明,耦合场下的动力学过程中,电流变液的流变行为主要受极化力和液动力的影响;链结构的屈服断裂最先发生在极板附近,即表征出速度滑移的微流动特征,其屈服断裂也就是电流变液的屈服强度。试验还验证了俘获效应。     

The giant electrorheological effect in suspensions of nanoparticles

Electrorheology (ER) denotes the control of a material's flow properties (rheology) through an electric field. We have fabricated electrorheological suspensions of coated nanoparticles that show electrically controllable liquid-solid transitions. The solid state can reach a yield strength of 130 kPa, breaking the theoretical upper bound on conventional ER static yield stress that is derived on the general assumption that the dielectric and conductive responses of the component materials are linear. In this giant electrorheological (GER) effect, the static yield stress displays near-linear dependence on the electric field, in contrast to the quadratic variation usually observed. Our GER suspensions show low current density over a wide temperature range of 10-120 degrees C, with a reversible response time of <10 ms. Finite-element simulations, based on the model of saturation surface polarization in the contact regions of neighbouring particles, yield predictions in excellent agreement with experiment.     

钛酸钙系电流变液在直流电场下静态剪切的应力响应

研究了直流电场下钛酸钙系电流变液在静态剪切模式下的力学响应,得到了材料在静态剪切模式下的应力应变关系,讨论了材料温度、电压和剪切应变对应力的影响,以理论推导和实验数据拟合的方法得出了剪切应力与剪切应变、温度以及电场强度等参数的半经验数学关系式.理论值对比实验结果表明,剪切应力表达式与实验结果符合较好,可以用于预测材料在静态剪切模式下的剪切应变,温度和电场强度对剪切应力的影响.     

New Dispersed Phase of Electrorheological Fluids:TiO2 Coating Graphite Particles

Electrorheological (ER) fluids have a great p otelltial for maily applications because of ER effect:changing from a liquid-laal state to a solid-like statewhen an electric field is applied to them. However,large scale of utilization of MR fluids has not been realized for lack of excellent ER systems. Part of thedndculty in developing high performance ER fluidslies in the difficulty of finding a single material thatcan fulfill all the electrical and mechalilcal requiremellts of ER fluids su…     

电流变弹性体夹层结构梁的动力学仿真研究

对电流变弹性体夹层悬臂梁在不同电场控制下的振动响应特性和可控性进行研究。将电流变弹性体等效为一种具有电控力学性能的粘弹性阻尼材料,基于Hamilton原理建立了三层电流变弹性体夹层梁的有限元动力学方程,仿真分析了其在不同外加电场控制下的振动特性。分析结果显示,随着外加电场强度的增加,电流变弹性体夹层梁的固有频率不断增大,振动幅值却不断减小。表明电流变弹性体夹层梁具有与电流变液夹层梁相似的可控振动响应特性,能在外加电场作用下实现对结构振动的实时控制。     

The influence of solid-phase concentration on the performance of electrorheological fluids in dynamic squeeze flow

The yield stress of electrorheological (ER) fluids increases by orders of magnitude when electric field is applied across them. In the absence of the field, ER fluids behave as Newtonian fluids. This paper is concerned with an experimental investigation to determine the rheological performance of ER fluids, consisting of a dielectric liquid carrier with a range of solid-phase concentration. The ER fluid was contained in a squeeze cell, which during motion subjects the fluid to both compressive and tensile loading. The results were analysed in terms of the capacity for the transmission of imposed forces across the fluid and showed a great dependence on the applied D.C voltage and the weight fraction of the dispersed solid-phase. In addition, the implications of the results to vibration control, where the ER fluid is employed in an engine mount, are discussed.     

Influence of liquid phase on nanoparticle-based giant electrorheological fluid

We show that the chemical structures of silicone oils can have an important role in the giant electrorheological (GER) effect. The interaction between silicone oils and solid nanoparticles is found to significantly influence the ER effect. By increasing the kinematic viscosity of silicone oils, which is a function of siloxane chain length, sol-like, gel-like and clay-like appearances of the constituted ER fluids were observed. Different functional-group-terminated silicone oils were also employed as the dispersing media. Significant differences of yield stress were found. We systematically study the effect of siloxane chain lengths on the permeability of oils traveling through the porous spaces between the particles (using the Washburn method), oils adsorbed on the particles' surface (using FT-IR spectra), as well as their particle size distribution (using dynamic light scattering). Our results indicate the hydrogen bonds are instrumental in linking the silicone oil to GER solid particles, and long chain lengths can enhance the agglomeration of the GER nanoparticles to form large clusters. An optimal oil structure, with hydroxyl-terminated silicone oil and a suitable viscosity, was chosen which can create the highest yield stress of ～300?kPa under a 5?kV?mm(-1) DC electric field.     

基于可视化的电流变动力学中的俘获效应

本文设计并制造了一个动力学可视化试验台。试图通过可视化试验来观察电流变液在多场耦合作用下的俘获效应,进而研究电流变悬浮液的力学性能与场致亚微观结构的动态耦合关系。试验研究结果表明,采集到的动态变化映像验证了电流变液在动态耦合场下其电流变效应与俘获效应有关,即流动介质的固相分率φ、密度ρ以及颗粒的堆积形式N由于俘获效应的存在从而发生改变。     

Guided self-assembly of nanostructured titanium oxide

A series of nanostructured titanium oxide particles were synthesized by a simple wet chemical method and characterized by means of small-angle x-ray scattering (SAXS)/wide-angle x-ray scattering (WAXS), atomic force microscope (AFM), scanning electron microscope (SEM), transmission electron microscope (TEM), thermal analysis, and rheometry. Tetrabutyl titanate (TBT) and ethylene glycol (EG) can be combined to form either TiO(x) nanowires or smooth nanorods, and the molar ratio of TBT:EG determines which of these is obtained. Therefore, TiO(x) nanorods with a highly rough surface can be obtained by hydrolysis of TBT with the addition of cetyl-trimethyl-ammonium bromide (CTAB) as surfactant in an EG solution. Furthermore, TiO(x) nanorods with two sharp ends can be obtained by hydrolysis of TBT with the addition of salt (LiCl) in an EG solution. The AFM results show that the TiO(x) nanorods with rough surfaces are formed by the self-assembly of TiO(x) nanospheres. The electrorheological (ER) effect was investigated using a suspension of titanium oxide nanowires or nanorods dispersed in silicone oil. Oil suspensions of titanium oxide nanowires or nanorods exhibit a dramatic reorganization when submitted to a strong DC electric field and the particles aggregate to form chain-like structures along the direction of applied electric field. Two-dimensional SAXS images from chains of anisotropically shaped particles exhibit a marked asymmetry in the SAXS patterns, reflecting the preferential self-assembly of the particles in the field. The suspension of rough TiO(x) nanorods shows stronger ER properties than that of the other nanostructured TiO(x) particles. We find that the particle surface roughness plays an important role in modification of the dielectric properties and in the enhancement of the ER effect.     

Electrorheological properties of pumice/silicone oil suspension

Pumice particles-based electrorheological (ER) suspensions were prepared in silicone oil and its ER behavior was investigated as a function of shear rate, electric field strength, concentration and temperature. Sedimentation stabilities of suspensions were determined. ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. Yield stress of pumice suspensions increased linearly with increasing applied electric field strength and with concentrations of the particles. The pumice suspensions show a typical shear thinning non-Newtonian viscoelastic behavior, in which viscosity of suspension decreased sharply with increasing shear rate. Effect of high temperature onto ER activity of pumice/silicone oil system was also investigated.     

Fabrication of ammonium persulfate coated silica microsphere via chemical grafting and its electrorheology

Silica/ammonium persulfate (APS) microspheres were fabricated by coating APS on the surface of ~2 μm sized silica particles and applied as a candidate for electrorheological (ER) materials. The morphologies of these particles were observed by SEM. Chemical compositions and structure of the particles were confirmed by EDS and FT-IR. Thermogravimetric analysis was used to examine the amount of APS coating on the silica particles. A 10 vol% ER fluid based on the fabricated particles was prepared by dispersing them into hydroxyl group-terminated silicone oil. Typical ER properties were obtained using a rotational rheometer under an applied electric field at a controlled shear rate test. These properties were also correlated with its dielectric spectra.