Experimental characterization and viscoelastic modeling of isotropic and anisotropic magnetorheological elastomers

The paper presents experimental research and numerical modeling of dynamic properties of magnetorheological elastomers (MREs). Isotropic and anisotropic MREs have been prepared based on silicone matrix filled by micro-sized carbonyl iron particles. Dynamic properties of the isotropic and anisotropic MREs were determined using double-lap shear test under harmonic loading in the displacement control mode. Effects of excitation frequency, strain amplitude, and magnetic field intensity on the dynamic properties of the MREs were examined. Dynamic moduli of the MREs decreased with increasing the strain amplitude of applied harmonic load. The dynamic moduli and damping properties of the MREs increased with increasing the frequency and magnetic flux density. The anisotropic MREs showed higher dynamic moduli and magnetorheological (MR) effect than those of the isotropic ones. The MR effect of the MREs increased with the rise of the magnetic flux density. The dependence of dynamic moduli and loss factor on the frequency and magnetic flux density was numerically studied using four-parameter fractional derivative viscoelastic model. The model was fitted well to experimental data for both isotropic and anisotropic MREs. The fitting of dynamic moduli and loss factor for the isotropic and anisotropic MREs is in good agreement with experimental results.     

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.     

Enhancement in Magnetorheological Effect of Magnetorheological Elastomers by Surface Modification of Iron Particles

In order to obtain magnetorheological (MR) elastomers with high magnetorheological effect, a family of anisotropic rubber-based MR elastomers was developed using a new form of chemical modification. Three different kinds of surfactants, i.e. anionic, nonionic and compound surfactants, were employed separately to modify iron particles. The MR effect was evaluated by measuring the dynamic shear modulus of MR elastomer with a magneto-combined dynamic mechanical analyzer. Results show that the relative MR effect can be up to 188% when the iron particles are modified with 15% Span 80. Besides the surface activity of Span 80, however, such high modifying effect is partly due to the plasticizing effect of Span 80. Compared with the single surfactant, the superior surface activity of compound surfactant makes the relative MR effect reach 77% at a low content of 0.4%. Scanning electron microscope observation shows that the modification of compound surfactant results in perfect compatibility between particles and rubber matrix and special self-assembled structure of particles. Such special structure has been proved beneficial to the improvement of the relative MR effect.     

Novel highly elastic magnetic materials for dampers and seals: Part I. Preparation and characterization of the elastic materials

The new generation of magnetic elastomers represents a new type of composites, consisting of small (mainly nano and micron‐sized) magnetic particles dispersed in a highly elastic polymeric matrix. The combination of polymers with magnetic materials displays novel and often enhanced properties. Highly elastic magnetic composites are quite new and understanding of the behavior of these materials depending on the composition, external conditions, and the synthesis processes is still missing. Thus, the aim of this work is the study of fundamental principles governing the preparation of these materials as well as their structure and elastic properties. Copyright © 2007 John Wiley & Sons, Ltd.     

Viscoelasticity of suspensions of magnetic particles in a polymer: effect of confinement and external field

We study the suspensions of magnetic particles, the precursor state of magnetic gels and elastomers. We use magnetic particles with a permanent magnetization which is high enough to overcome thermal energy and low enough to guarantee a long live time of the sample. These particles form a space-filling structure at very low volume fractions (approximately 0.5 vol %), which modifies the viscoelastic response of the matrix significantly. In confined geometry the particles form clusters of a size that depends on the sample thickness. Even small external fields induce a strong anisotropy in the mechanical and optical properties of the suspension. The action of the applied magnetic field induces a gel-like response in one direction but leaves the other directions liquidlike. The viscosity is a very sensitive mechanical test for the anisotropy of the material. Light scattering data confirm our mechanical results.     

Influence of particle coating on dynamic mechanical behaviors of magnetorheological elastomers

In this paper, core-shell structured poly methyl methacrylate (PMMA) coated carbonyl iron (CI) particles were prepared to study the influence of particle coating on the dynamic properties of magnetorheological elastomers (MREs). The CI-PMMA composite particles were encapsulated via an emulsion polymerization method. Two MRE samples were prepared with CI-PMMA composite particles and CI particles, respectively. Their microstructure was observed by using a scanning electron microscope (SEM). Dynamic properties of these two samples under various strain and magnetic fields were measured with a dynamic mechanical analyzer (DMA). The experimental results indicate that the MRE sample with CI-PMMA composite particles has larger storage modulus, smaller loss factor and smaller Payne effect than that of the sample with only CI particles. The analysis indicates that the use of CI-PMMA particles would increase the bond strength between particles and matrix. These experimental results were also verified by the SEM images.     

Temperature-actuated changes in wettability at elastomer/water interfaces

Surface modification of 1,4-polybutadiene and cis-1,4-polyisoprene to introduce polar functional groups provided surfaces that reconstructed reversibly against water as a function of temperature. These surfaces became hydrophobic in contact with hot water, but their original hydrophilicity returned upon equilibration against cold water. Repeated cycling between hot and cold water, however, led to a damping of this reversibility. A series of parallel experiments on both the interfacial and bulk behavior of these elastomers strongly indicated that this damping was due to the alignment of extended interfacial chains during temperature cycling and to a decay of the restoring force on the interfacial chains under extension. These studies thus demonstrate that the interfacial behavior of elastomers can display close analogies to the bulk viscoelastic properties of the solid.     

Novel highly elastic magnetic materials for dampers and seals: part II. Material behavior in a magnetic field

The combination of polymers with magnetic particles displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The magnetic field sensitive elastomers represent a new type of composites consisting of small particles, usually from nanometer range to micron range, dispersed in a highly elastic polymeric matrix. In this paper, we show that in the presence of built‐in magnetic particles it is possible to tune the elastic modulus by an external magnetic field. We propose a phenomenological equation to describe the effect of the external magnetic field on the elastic modulus. We demonstrate the engineering potential of new materials on the examples of two devices. The first one is a new type of seals fundamentally different from those used before. In the simplest case, the sealing assembly includes a magnetoelastic strip and a permanent magnet. They attract due to the magnetic forces. This ensures that due to high elasticity of the proposed composites and good adhesion properties, the strip of magnetoelastic will adopt the shape of the surface to be sealed, this fact leading to an excellent sealing. Another straightforward application of the magnetic composites is based on their magnetic field dependent elastic modulus. Namely, we demonstrate in this paper the possible application of these materials as adjustable vibration dampers. Copyright © 2007 John Wiley & Sons, Ltd.     

Magnetoactive elastomer based on magnetically hard filler: Synthesis and study of viscoelastic and damping properties

This work is focused on the magnetic response of magnetoactive elastomer (MAE) based on silicone polymer matrices filled with magnetic particles of magnetically hard NdFeB-alloy. Viscoelastic properties of MAE were studied by the method of oscillation shear. After magnetization in an external magnetic field of 2 T MAE samples demonstrate more than two-time increase in the storage and loss moduli and 25% increase in the loss factor. Performed study of the damping properties of the materials has shown that the oscillation time of the pendulum hammering the magnetized sample is in two times shorter than in case of the non-magnetized sample. Viscoelastic and damping properties of MAE are defined by magnetic interactions between the magnetized particles of the magnetic filler.     

聚氨酯弹性体的相区相容性和阻尼性能研究

合成了一系列含有不同软段的聚氨酯嵌段共聚物及接枝共聚物,并测试了其动态力学性能,结果表明,聚氨酯共聚物的相容性与大分子的链结构有关,接枝链的存在对聚氨酯嵌优共聚物相空性和阻尼性能有很大影响。     

Elastomer/LDH nanocomposites: Synthesis and studies on nanoparticle dispersion, mechanical properties and interfacial adhesion

Layered double hydroxides (LDHs) based elastomer nanocomposites have been synthesized and characterized in terms of nanoparticle dispersion, mechanical properties and interfacial adhesion. Since LDH has basic hydroxyl groups on its surface, its potential as reinforcing filler in elastomers and in additionally a crosslinking agent in carboxylated elastomers has been investigated in details. For this purpose, two different elastomers having widely different polarities and functional groups (e.g., ethylene propylene diene terpolymer, i.e. EPDM and carboxylated nitrile rubber, i.e. XNBR) have been used as the matrix. The pristine LDH based on Mg and Al was modified with decane sulfonate by the regeneration method. The morphological analysis of the nanocomposites (done by X-ray diffraction analysis and electron microscopy) shows that in both matrices LDH particles are dispersed in three different forms, i.e. as primary particles, as exfoliated layers and as soft clusters formed by both of them. However, their relative proportion differs drastically in the two matrices. We have shown in this study that the LDH can significantly improve the mechanical properties in both the system. In XNBR/LDH nanocomposites containing no conventional metal oxide curative, this improvement is very prominent due to secondary interaction between LDH and XNBR matrix indicating that LDH can crosslink carboxalated elastomers. It is also observed that LDH particle promotes strain-induced crystallization in XNBR/LDH. The fracture surface analysis shows that in XNBR/LDH nanocomposite very stable polymer-filler interface is formed and tensile failure takes place through the matrix rather than through the interface. In case of EPDM/LDH nanocomposites the opposite is observed and the polymer matrix hardly wets the surface of the LDH particle.     

聚合物二元体系动态力学性能的估算

动态热机械分析是多相聚合物体系的一个重要研究手段.分析动态力学性能可以研究共混高聚物的相容性、复合材料的界面特性以及高分子运动机理等.本文综述了聚合物二元体系,即填充、纤维增强、共混体系动态力学性能的估算方法.在填充体系中,分别概述有无界面作用两种情况,当存在界面作用时,界面作用越强,模量越大,阻尼越小.对纤维增强体系,讨论了玻璃纤维有无取向的情况下模量和阻尼的估算.特别对于聚合物二元共混体系,分"海-岛"结构和双连续相两种情况,分别讨论了模量与阻尼的估算.     

Magnetoswitchable controlled hydrophilicity/hydrophobicity of electrode surfaces using alkyl-chain-functionalized magnetic particles: application for switchable electrochemistry

Magnetic nanoparticles consisting of undecanoate-capped magnetite (average diameter approximately 4.5 nm; saturated magnetization, M(s), 38.5 emu g(-1)) are used to control and switch the hydrophobic or hydrophilic properties of the electrode surface. A two-phase system consisting of an aqueous buffer solution and a toluene phase that includes the suspended capped magnetic nanoparticles is used to control the interfacial properties of the electrode surface. The magnetic attraction of the functionalized particles to the electrode by means of an external magnet yields a hydrophobic interface that acts as an insulating layer, prohibiting interfacial electron transfer. The retraction of the magnetic particles from the electrode to the upper toluene phase by means of the external magnet generates a hydrophilic electrode that reveals effective interfacial electron transfer. The electron-transfer resistance and double-layer capacitance of the electrode surface upon the attraction and retraction of the functionalized magnetic particles to and from the electrode, respectively, by means of the external magnet were probed by Faradaic impedance spectroscopy (R(et) = 170 Omega and C(dl) = 40 microF sm(-2) in the hydrophilic state of the electrode and R(et) = 22 k Omega and C(dl) = 0.5 microF sm(-2) in the hydrophobic state of the interface). The magnetoswitchable control of the interface enables magnetic switching of the bioelectrocatalytic oxidation of glucose in the presence of glucose oxidase and ferrocene dicarboxylic acid to "ON" and "OFF" states.     

Structural morphology developments in the interfacial phase of heterocoagulated composite particles: dynamic mechanical measurements

The dynamic mechanical properties of polymeric composites composed of poly (methyl methacrylate) continuous-phase and various inclusion types of heterocoagulated composite particles were investigated in order to relate them to the morphology of shell region of composite particles. Using the heterocoagulation process, large particles were encapsulated with various types of small particles: (1) conventional linear-type polymer particles; (2) crosslinked polymer particles; and (3) reactive polymer particles capable of forming crosslinked structure, whereby the interfacial properties of the composite become modified. These composite particles were subsequently annealed to form continuous shell regions and then mixed with matrix particles. It is shown that chain diffusion movement of the small particles having different chain characteristics influences the network formation at the interfacial shell region. The ability of maintaining interfacial domain structure depends on the degree of network formation.     

The effects of rigid polystyrene particles on the glass transition characteristics and mechanical wave attenuation of styrene‐butadiene rubber: Particle size and acoustic mismatch

Glass transition characteristics and mechanical wave attenuation of the neat and filled styrene‐butadiene rubber (SBR) containing 10 wt % of rigid monosize polystyrene particles of various diameters from several hundred microns down to several tens of nanometers were investigated by dynamic mechanical thermal analysis, impedance tube, and ultrasonic spectroscopy. The results showed the matrix damping capacity and the breadth of glass transition increase by reducing the size of rigid particles due to the matrix‐particles interfacial area increase as the major governing parameter. Matrix glass transition broadening toward higher temperatures was attributed to the increased dynamic heterogeneity induced by fillers, whereas the damping capacity increase was assigned to contribution of interfacial friction loss mechanism. The proposed postulation was confirmed based on the calculated temperature distribution of the relaxing matrix volume fraction. Sound wave attenuation by the matrix and PS particles filled systems led to a broad absorption peak for the former and appearance of a secondary absorption peak at lower frequencies for the latter. Intensity of this secondary peak was highest for the system containing PS nanoparticles. Finally, ultrasonic attenuation enhanced by the PS particle size to wavelength ratio increase according to α_sca ～ (d/λ)^0.38 scaling law and declined by replacing the dense particles with larger hollow PS particles. Comparison of the normalized attenuation of the PS particle filled SBR in various mechanical wave attenuation regimes implied low sensitivity to particle size in vibration, mild differentiation in the sound, and finally severe differentiation in the ultrasound regimes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 82–88, 2010     

Effects of magnetic particles and carbon black on structure and properties of magnetorheological elastomers

Isotropic magnetorheological elastomers (MREs) consisting of ethylene-propylene-diene monomer (EPDM), carbon black and two different micron-sized iron particles (carbonyl iron powder (CIP) and bare iron powder (BIP)) were prepared for dynamic automotive applications such as tunable engine mounts, vibration absorbers and suspension bushings. The sample that contains 5 phr CIP and 60 phr carbon black has the best tensile strength, elongation at break and elastic modulus and the highest MR effect of 77%. Based on SEM and EDS, homogenous distribution of single CIP and its aggregates of 8 μm and larger BIP aggregates of 15–20 μm were observed with 30 phr loadings of CIP and BIP, respectively. EPDM/carbon black/CIP MREs show significant property improvements compared to EPDM/carbon black/BIP MREs. The system containing CIP particles has substantially lower damping factor, Payne effect, elastic modulus, hardness, aggregation behavior and higher tensile strength and elongation at break values compared to BIP system.     

Modification of carbonyl iron particles by carboxyl-containing polydimethylsiloxanes

The possibility of preparing magnetic particles with the “core–shell” structure was demonstrated. The procedure is based on the treatment of carbonyl iron particles with polydimethylsiloxanes (PDMS) containing terminal or distributed over the chain carboxyl groups attached via the alkyl or aryl spacer. The presence of carboxyl-containing PDMS grafted to the surface of carbonyl iron particles was revealed by electron microscopy. Magnetorheological fluids and magnetic elastomers containing magnetic particles with the “core–shell” structure were obtained, and their rheological properties were studied.     

The Enhanced MR Effect of Dense Magnetic Particles Suspensions Consisting of Superfine α-Fe Particles

It is reported that magnetorheological (MR) effect was enhanced when superfineα-Fe particles and other nanosize particles were added to suspensions of dense micron magnetic particles. The effect of adding superfine particles on dynamics shear stress, sedimentation stability and structure of solidified MR of magnetic suspensions were studied. The experiment showed considerable increase of shear stress and much stability of sedimentation when the suspension consisting of superfine particles. The enhanced MR effect by superfine particles dealt with the properties, weight ratio and scale of superfine particles.     

线形低密度聚乙烯／废胶粉热塑弹性体动态硫化性能研究

利用动态硫化法制备了线形低密度聚乙烯(LLDPE)/废胶粉(GTR)热塑弹性体。重点研究了两种交联剂:硫和过氧化二异丙苯(DCP)对共混物性能的影响。加入一定量的苯乙烯-丁二烯-苯乙烯(SBS)共聚物作为增容剂。结果表明,经过DCP动态硫化后的共混物的力学性能比简单共混的共混物有明显的提高,而加入硫磺体系对共混物力学性能影响不大甚至有所下降。通过红外光谱、热分析(DSC)和扫描电镜(SEM)对共混物的热行为和表面形态研究表明,加入DCP交联剂使LLDPE、SBS和胶粉之间发生了交联反应,从而增加了胶粉颗粒与LLDPE间的界面相容性,使其热塑性弹性体的力学性能得以提高。     

Model filled rubber. II. Particle composition dependence of suspension rheology

Monodisperse size colloidal particles varying in chemical composition were synthesized by emulsifier‐free emulsion polymerization. Using a stress‐controlled rheometer, the rheological behavior of colloidal suspensions in a low molecular weight liquid polysulfide was investigated. All suspensions exhibited shear thinning behavior. The shear viscosity, dynamic moduli, and yield stress increased as interactions between particles and matrix increased. The rheological properties associated with network buildup in the suspensions were sensitively monitored by a kinetic recovery experiment. We propose that interfacial interactions by polar and hydrogen bonding between particles and matrix strongly promote affinity of matrix polymer to the filler particles, resulting in adsorption or entanglement of polymer chains on the filler surface. A network structure was formed consisting of particles with an immobilized polymer layer on the particle surface with each particle floc acting as a temporary physical crosslinking site. As the interfacial interaction increases, the adsorbed layer thickness on the filler particles, hence, the effective particle volume fraction, increases. As a result, the rheological properties were enhanced in the order PS < PMMA < PSVP. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 815–824, 1999