基于多链模型的磁流变弹性体剪切模量的数值分析

Based on the magnetic interaction energy, using derivative of the magnetic energy density, a model is proposed to compute the magnetic-induced shear modulus of magnetorheological elastomers. Taking into account the influences of particles in the same chain and the particles in all adjacent chains, the traditional magnetic dipole model of the magnetorheological elastomers is modified. The influence of the ratio of the distance etween adjacent chains to the distance between adjacent particles in a chain on the magnetic induced shear odulus is quantitatively studied. When the ratio is large, the multi-chain model is compatible with the single chain model, but when the ratio is small, the difference of the two models is significant and can not be neglected. Making certain the size of the columns and the distance between adjacent columns, after constructing the computational model of BCT structures, the mechanical property of the magnetorheological elastomers composed of columnar structures is analyzed. Results show that, conventional point dipole model has overrated the magnetic-induced shear modulus of the magnetorheological elastomers. From the point of increasing the magnetic-induced shear modulus, when the particle volume fraction is small, the chain-like structure exhibits better result than the columnar structure, but when the particle volume fraction is large,the columnar structure will be better.     

Damping of Magnetorheological Elastomers

The damping property of magnetorheological (MR) elastomers is characterized by a modified dynamic mechanical-magnetic coupled analyzer. The influences of the external magnetic flux density, damping of the matrix, content of iron particles, dynamic strain, and driving frequency on the damping properties of MR elastomers were investigated experimentally. The experimental results indicate that the damping properties of MR elastomers greatly depend on the interfacial slipping between the inner particles and the matrix. Different from general composite materials, the interfacial slipping in MR elastomers is affected bythe external applied magnetic field.     

超细金属铁颗粒的高分子修饰及其悬浮液的磁流变性能

报道以γ射线辐照方法合成出具有良好分散性的高分子复合金属铁粒子.分别选择十二烷基硫酸钠、溴化十六烷基三甲基铵、Tween-80、TritonX-200和OP-10等表面活性剂和有机单体、无机铁颗粒一起制备乳状液,通过对这种含有超细金属铁颗粒乳状液稳定性的比较,以寻求合适的乳化剂.并对以TritonX-200为乳化剂时合成出的高聚物复合铁颗粒进行了XRD、TEM和IP表征.还将实验中所获得的高聚物复合铁粒子与粒径相同的未经修饰的纯铁粒子分别制成了悬浮液,对两者的悬浮性能进行了比较,同时,也将高聚物复合铁粒子制成的悬浮液与Fe3O4-PMMA复合粒子悬浮液两者的屈服应力随磁场变化情况进行比较研究.     

Effect of Cyclic Deformation on Magnetorheological Elastomers

Fatigue properties of magnetorheological elastomer (MRE) samples were investigated based on cis-polybutadiene rubber by using a fatigue test machine. Three MRE samples with iron particles mass fraction of 60%, 70%, and 80% were fabricated, and their properties dependence of three strain amplitudes (50%, 75%, and 100%) were measured. The absolute magnetorheological (MR) effect, storage modulus, and loss modulus of MRE samples after fatigue were evaluated by a modified dynamic mechanical analyzer. The results revealed that MR effect, storage modulus, and loss modulus of MREs containing 80% iron particles depended strongly on the strain amplitudes and the number of cycles, while storage mod-ulus and loss modulus of MREs containing 70% iron particles also depended on the strain amplitudes and the number of cycles but not as strongly as sample which contains 80% iron particles, but the properties of MREs containing 60% iron particles after cyclic deforma-tion were almost independent of the fatigued conditions. In order to investigate the fatigue mechanism of MREs, the sample was carried out with a quasi-static tensile testing and its surface morphology during testing was observed in situ by scanning electron microscopy.     

Radiation Vulcanization of Magnetorheological Elastomers Based on Silicone Rubber

The fabrication of magnetorheological （MR） elastomers was studied by two vulcanization methods, including heat vulcanization （HV） and radiation vulcanization （RV）, were employed to fabricate MRE samples. The dynamical mechanical properties were characterized by using a dynamic mechanic analyzer. In particular, both the MR effect and its durability were investigated. The experimental results showed that RV samples have large magnetoinduced modulus, large zero-field modulus, and good durability property of MR effect. To explain these results, cubic deformation and plasticizer migration were analyzed. Large magneto-induced modulus of RV sample results from cubic deformation during vulcanization process. And the plasticizer migration results in better durability of MR effect.     

The evaluation and implementation of magnetic fields for large strain uniaxial and biaxial cyclic testing of Magnetorheological Elastomers

Magnetorheological Elastomers (MREs) are “smart” materials whose physical properties are altered by the application of magnetic fields. In previous studies the properties of MREs have been evaluated under a variety of conditions, however little attention has been paid to the recording and reporting of the magnetic fields used in these tests [1]. Currently there is no standard accepted method for specifying the magnetic field applied during MRE testing. This study presents a detailed map of a magnetic field applied during MRE tests as well as providing the first comparative results for uniaxial and biaxial testing under high strain fatigue test conditions. Both uniaxial tension tests and equi-biaxial bubble inflation tests were performed on isotropic natural rubber MREs using the same magnetic fields having magnetic flux densities up to 206 mT. The samples were cycled between pre-set strain limits. The magnetic field was switched on for a number of consecutive cycles and off for the same number of following cycles. The resultant change in stress due to the application and removal of the magnetic field was recorded and results are presented.     

磁性Fe3O4微粒表面有机改性

在分散聚合法制备复合磁性微球过程中,采用硅烷偶联剂KH 570对磁性Fe3O4微粒进行表面改性.红外光谱(FTIR)、光电子能谱(XPS)分析结果表明,偶联剂与磁性微粒表面以化学键形式结合.改性后,Fe3O4微粒与单体及其聚合物之间具有良好的亲和性,采用改性后的磁性微粒可以显著改善磁性微球的性能指标.     

磁性Fe_3O_4微粒表面有机改性

在分散聚合法制备复合磁性微球过程中 ,采用硅烷偶联剂 KH- 570对磁性 Fe_3O_4微粒进行表面改性 .红外光谱 (FTIR)、光电子能谱 (XPS)分析结果表明 ,偶联剂与磁性微粒表面以化学键形式结合 .改性后 ,Fe_3O_4微粒与单体及其聚合物之间具有良好的亲和性 ,采用改性后的磁性微粒可以显著改善磁性微球的性能指标 .     

对苯二异氰酸酯基聚氨酯弹性体交联度对其形态与摩擦性能的影响

聚氨酯弹性体的摩擦性能在诸如船舶、汽车、生物医用等领域具有十分重要的意义,而通过化学修饰策略实现该类材料摩擦性能的精细设计,仍具有十分迫切的研究需求和广泛的应用前景。 本工作以对苯二异氰酸酯(PPDI)与聚四氢呋喃醚二醇(PTMG)为原料,通过调节1,4-丁二醇与三羟甲基丙烷两种扩链交联剂的混合比例,采用预聚体法合成了具备不同交联度的PPDI基聚氨酯弹性体。 其中,傅里叶变换衰减全反射光谱(FTIR-ATR)、广角X射线衍射(WAXD)、差示扫描量热仪(DSC)等表征结果表明,聚氨酯弹性体中硬段和软段的结晶度随交联度的提升均呈下降趋势。 同时,力学测试表明,材料的弹性模量随之降低,而PPDI基聚氨酯弹性体摩擦系数则明显增大。 此外,滞后回环曲线表明,交联度的改变影响了PPDI基聚氨酯弹性体的阻尼特性,而聚氨酯弹性体阻尼的差异在其摩擦性能对速率的依赖关系中则有所体现。 本工作由此提出,利用不同交联度下PPDI基聚氨酯中软硬段结晶度的变化,在对材料弹性模量和损耗模量进行可控调节的同时,能够实现对其摩擦性能的改变,为PPDI基聚氨酯弹性体的摩擦性能调控提供了一种简单有效的途径。     

酞菁钴/铁纳米填充母粒组成的磁流变液性能

采用有机/无机原位（insitu）复合方法制备得出酞菁钴/铁纳米填充母粒,与甲基硅油组成磁流变液（MRS）。MRS的附加动态剪切应力（Δτ)与分散介质浓度、外加磁场强度呈正比例关系;剪切速率对Δτ的影响表明磁致流变为链状结构特征;Δτ对温度不敏感;MRS对外加磁场有可逆的开/关变化特征,无记忆效应,磁流变响应时间小于0.1s。     

聚苯胺颗粒材料的表面改性

用改性的溶胶-凝胶法制备了表面包覆有一定厚度的钛酸钡薄膜的聚苯胺,通过TEM和FT-IR分析方法研究了其形貌及微结构,并探讨了改性聚苯胺材料的电流变性能.FT-IR研究结果表明,在聚苯胺与钛酸钡之间存在着N－O间的氢键作用.TEM研究结果表明,改性聚苯胺粒子的直径在1.0～1.5 μm之间.此外,包覆工艺显著改善了材料的介电性能和电流变性能,为制备出高性能的电流变材料提供了一条可行的途径,值得进一步研究.     

Magneto‐sensitive Elastomers in a Homogeneous Magnetic Field: A Regular Rectangular Lattice Model

A theory of mechanical behaviour of the magneto‐sensitive elastomers is developed in the framework of a linear elasticity approach. Using a regular rectangular lattice model, different spatial distributions of magnetic particles within a polymer matrix are considered: isotropic, chain‐like and plane‐like. It is shown that interaction between the magnetic particles results in the contraction of an elastomer along the homogeneous magnetic field. With increasing magnetic field the shear modulus, G, for the shear deformation perpendicular to the magnetic field increases for all spatial distributions of magnetic particles. At the same time, with increasing magnetic field the Young's modulus, E, for tensile deformation along the magnetic field decreases for both chain‐like and isotropic distributions of magnetic particles and increases for the plane‐like distribution of magnetic particles.

     

Effect of carbon black on the mechanical performances of magnetorheological elastomers

Several magnetorheological elastomer (MRE) samples, with different weight percentages of carbon black, were fabricated under a constant magnetic field. Their microstructures were observed by using an environmental scanning electron microscope (SEM), and their mechanical performance including magnetorheological (MR) effect, damping ratio and tensile strength were measured with a dynamic mechanical analyzer (DMA) system and an electronic tensile machine. The experimental results demonstrate that carbon black plays a significant role in improving the mechanical performance of MR elastomers. Besides the merits of high MR effect and good tensile strength, the damping ratio of such materials is much reduced. This is expected to solve a big problem in the application of MR elastomers in practical devices, such as in adaptive tuned vibration absorbers.     

Flexo-Ionic Effect of Ionic Liquid Crystal Elastomers

The first study of the flexo-ionic effect, i.e., mechanical deformation-induced electric signal, of the recently discovered ionic liquid crystal elastomers (iLCEs) is reported. The measured flexo-ionic coefficients were found to strongly depend on the director alignment of the iLCE films and can be over 200 µC/m. This value is orders of magnitude higher than the flexo-electric coefficient found in insulating liquid crystals and is comparable to the well-developed ionic polymers (iEAPs). The shortest response times, i.e., the largest bandwidth of the flexo-ionic responses, is achieved in planar alignment, when the director is uniformly parallel to the substrates. These results render high potential for iLCE-based devices for applications in sensors and wearable micropower generators.     

Surface Modification and Contact Interaction of Particles

Abstract

The effects of particle surface modification by ambient media and surfactant adsorption on the cohesive forces in the immediate contacts between individual particles have been studied with the CF (cohesive force) apparatus. The values of the free energy of interaction in direct coagulation contacts between particles of various types in liquids of different polarity and in the presence of various surfactants have been measured. They cover a broad range of several orders of magnitude; these interactions define the rheological properties of concentrated thixotropic systems and their stability with respect to peptization. A similar experimental technique has been used for studying active media influences on various physico‐chemical processes of particle bridging and formation of the phase contacts responsible for the mechanical properties of related solid structures and their resistance to fracture. The effect of the adsorption induced decrease in strength and durability of such porous structures with phase contacts and compact solids is considered.     

邻苯二酚-四乙烯五胺改性超高分子量聚乙烯纤维

应用Cat-TEPA改性超高分子量聚乙烯(UHMWPE)纤维,在难黏附的纤维表面形成均匀涂层.采用透射电子显微镜(TEM)、红外光谱(FTIR)、X射线光电子能谱(XPS)、X射线衍射(XRD)、示差扫描量热(DSC)、热重分析(TGA)和静态接触角测试等手段对其结构和性能进行了表征,并通过单丝拔出实验研究改性前后纤维与环氧树脂之间的界面剪切强度(IFSS),探索了反应物配比、反应时间对表面性能的影响,并确定最佳改性条件.结果表明Cat-TEPA共沉积改性未影响纤维的结晶和热稳定性,改性后纤维表面浸润性得到改善,且适当增加反应时间和TEPA含量能够提高纤维和树脂之间的IFSS,当Cat-TEPA摩尔比为1:4,反应时间为24 h时效果最佳,与未改性纤维相比,界面剪切强度提升约44%.     

Application of Magnetorheological Fluid Damper in Rotor Vibration Control

A shear mode magnetorheological (MR) fluid damper used for rotor vibration control is designed, and the theoretical model of a cantilever rotor system with the MR fluid damper is established. The imbalance properties of the rotor system is studied theoretically and experimentally. It is found from the study that as the magnetic field strength in the MR fluid damper increases, the damping and stiffness of the damper are increased. The vibration amplitude of the rotor system is decreased at the critical speed, and the critical speed of the rotor system is increased with the increasing of applied magnetic field. The rotor vibration when passing through the critical speed can be controlled by using simple on/off control method.     

聚乙二醇包裹羰基铁核壳粒子的制备及水基磁流变液的性能

以羰基铁粉(CI)为原料用共溶胶-凝胶反应制备CI/聚乙二醇核壳复合粒子，并将其与水组成了磁流变液. 用SEM、TEM、FT-IR和VSM表征了核壳复合粒子的微观结构和静磁特性，并测试了水基磁流变液的性能. 结果表明，核壳复合粒子表面有SiO_x和聚乙二醇的包覆层，它有较好的亲水性和优良的软磁特性，用它组成的水基磁流变液具有抗沉降性优良、零场粘度低、磁流变效应显著等特点.     

聚天冬氨酸修饰对磁性氧化铁纳米粒子稳定性及脑MRI造影效果的影响

<正>超顺磁性氧化铁(Superparamagnetic iron oxide,SPIO)作为医用磁共振成像(Magnetic resonance imaging,MRI)造影剂,可以有效地改变人体组织中质子的自旋-自旋弛豫时间,从而增强磁共振成像的对