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Rotation of magnetic particles inside the polymer matrix of magnetoactive elastomers with a hard magnetic filler
Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Rotation of magnetic particles inside the polymer matrix of magnetoactive elastomers with a hard magnetic filler G.V. Stepanov a,n, D.Yu. Borin b, P.A. Storozhenko a a b
State Scientific Research Institute of Chemistry and Technology of Organoelement Compounds, 105118 Moscow, Russia TU Dresden, Magnetofluiddynamics, Measuring and Automation Technology, Dresden 01062, Germany
art ic l e i nf o
a b s t r a c t
Article history: Received 14 July 2016 Accepted 26 July 2016
We propose the results of research on the magnetic properties of magnetoactive elastomers containing particles of a hard magnetic filler. According to our understanding, the mechanism of re-magnetizing of the composite is based on two competing processes, being the re-magnetizing of the magnetic filler and mechanical rotation of particles inside of the polymer matrix. & 2016 Elsevier B.V. All rights reserved.
Keywords: Magnetorheology Magnetopolymer elastic composites Ferrogels Magnetoactive elastomers
1. Introduction
2. Samples and setup
Inspired by the increasing intensity of utilization in active damping devices, substantial studies of magnetorheological and magnetoactive elastomers—MREs and MAEs respectively—have been conducted over the last years [1–4]. By their composition the materials feature a polymer matrix filled with high- or low-coercivity magnetic particles varying in size in the range 1–100 mm. While patents dedicated to magnetic elastomers most frequently mention both types of fillers, there are few publications containing descriptions of elastomers based on high-coercivity powders [5,6]. Results of the first systematic studies of such materials including the basic rheological and magnetic characteristics of the MREs were previously published and are described in a number of publications [7–11]. The principal philosophy of this research topic is the possibility to avoid using heavy magnets for inducing magnetic fields inside the elastomer. A field appears inside the specimen after its magnetizing, as a result of which the material permanently gains the necessary damping and rheological properties. As indicated by the results, the material exhibits a set of specific magnetorheological properties, among which is its anomalous way of magnetizing and demagnetizing. In addition, our measurements unveiled the fact that the coercive force of the composite is significantly lower in comparison to that of the pure magnetic filler used as a component. In the current study we experimentally consider the mechanism of the re-magnetizing of the MAE based on a hard magnetic filler.
We prepared our samples according to the standard procedure based on mixing a powder of FeNdB and liquid silicone semiproduct followed by polymerizing in a mold [10]. At the same time, powders of carbonyl iron were frequently introduced into the mixtures with the purpose of providing a higher degree of homogeneity and develop materials with better magnetorheological properties. The elastic modulus of the matrix was modified using a dilution of the liquid rubber component with a silicone oil. Magnetic measurements were conducted utilizing a vibrating sample magnetometer (Lake Shore 7407).
n
Corresponding author. E-mail address: [email protected] (G.V. Stepanov).
3. Results and discussion It is a known fact that the dilution of magnetic powders leads to increased coercive forces resulting from lower densities of the studied materials and thus from reduced demagnetizing factors. Therefore, comparison of the similar parameters of different magnetic powders requires the equality of their densities. Measurements performed within the frames of our research indicated that the MAE samples exhibited significantly lower magnitudes of coercive force than pure powders, which is contradictory to theory. In our experiments we used powders diluted with an inert substance and expected higher values of the parameter. This is well seen from Table 1. The decreasing of the coercive force may probably be explained by the rotation of particles of the magnetic filler inside the matrix. As the concentration of the filler decreases, there remain more polymer separating single particles resulting in their easier
http://dx.doi.org/10.1016/j.jmmm.2016.07.051 0304-8853/& 2016 Elsevier B.V. All rights reserved.
Please cite this article as: G.V. Stepanov, et al., Journal of Magnetism and Magnetic Materials (2016), http://dx.doi.org/10.1016/j. jmmm.2016.07.051i
G.V. Stepanov et al. / Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Table 1 Particles concentration and coercivity of the composite. FeNdB concentration in the polymer matrix (%)
Coercivity of the composite
100 80 75
1900 1700 1400
Fig. 2. Dependence of the average coercive force of MAE on its shear modulus. Point 1 refers to the coercive force of an FeNdB powder with a value of 3300 Oe.
Fig. 1. Hysteresis loop of a composite material with a rigid (1) and soft (2) polymer matrix (Samples 1 and 4).
rotation. At the same time, the elasticity of the polymer matrix features an important factor affecting the behavior of the material; for the capability of the matrix to deform defines how strongly the particles are confined. Comparison of typical hysteresis loops of composite materials based on rigid and soft polymer matrices is presented in Fig. 1. Studies of the full magnetization curve of the material also unveiled an anomalous shape of the hysteresis loop. The given character of the curve is probably caused by the rotation of particles inside the elastic matrix too when the composite is placed in an external field, as a result of which the particles get magnetized and form chain-like structures lining up along the force lines. At the same time, field reversal makes the particles flip over to get their momenta parallel to the newly established influence and does not lead to their re-magnetizing. A detailed study of the dependency of the coercive force of the composite material on the elastic modulus of its polymer matrix demonstrated the decreasing of the former as the latter gets lower. Important to note, this reduction is significant. So, measurements unveiled a 5-time weakening of the coercive force in the set of samples with matrix elasticities dropping from 90 to 1 kPa. At the same time, the coercive force is subjected to the most significant changes in the area of 20 kPa. The obtained data are presented in Table 2 and Fig. 2. Owing to the well-pronounced asymmetric configuration of the hysteresis loop of MAE, which are in Fig. 3, while Fig. 2 demonstrates average values of the coercive forces. This phenomenon points to the existence of a mechanism of magnetizing and re-magnetizing of the composite. In the process Table 2 Elastic modulus and coercive force of the studied composite samples. Sample
1
2
3
4
5
E, kPa Hc , Oe
90 2900
40 2700
20 2100
6 700
1 650
Fig. 3. Asymmetric hysteresis loop of a composite material with a soft polymer matrix (Sample 3).
of re-magnetizing the particles inside the matrix suffer partial remagnetizing, whereas the remaining ones flip to get their momenta parallel to the external field to continue to magnetize further. Most clearly these processes are seen in materials with moderate elasticities when placed in moderate magnetic fields, which creates the possibility for competition between re-magnetizing and flipping. As the elasticity modulus gets lower, the shape of the hysteresis loop is defined practically only by the value of the elastic modulus of the matrix, whereas the coercive force depends on this property of the polymer conditionally. As can be seen from Fig. 3, the hysteresis loop is noticeably asymmetric. Primary magnetizing occurring during measurements lines up the magnetized particles in a certain direction, being the preferable orientation of light magnetizing. After the direction of the external field has been changed the particles flip resulting in an increased tension inside the matrix trying to turn them in the previous direction. When the particles return to their previous position, in which they were initially embedded in the matrix and then magnetized, the process goes more easily and the coercive force of the reversal part of the loop appears to be lower. In fact, we deal not with a light magnetizing axis, but with a concrete direction of light magnetizing. The most expressed difference in the behavior of the MAE with a soft (sample 4) and hard (sample 1) matrix can be observed on
Please cite this article as: G.V. Stepanov, et al., Journal of Magnetism and Magnetic Materials (2016), http://dx.doi.org/10.1016/j. jmmm.2016.07.051i
G.V. Stepanov et al. / Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
of the re-magnetization of the magnetoactive elastomers with a hard magnetic filler is based on two competing processes being the re-magnetizing of the magnetic filler and mechanical rotation of particles inside of the polymer matrix. In order to prove this conclusion, microstructural study of the elastic composites under magnetic field influence as well as theoretical approaches are required.
Acknowledgements Financial support by Deutsche Forschungsgemeinschaft (DFG) under Grant Bo 3343/1–1 within PAK 907 and support of RFBR under Grant 16–53-12009 providing the basis for our investigations is gratefully acknowledged.
Fig. 4. Magnetic susceptibility of the MAE with a hard magnetic filler based on the hard (Sample 1) and soft (Sample 4) polymer matrix as a function of an applied magnetic field. Direct (1) and reverse (2) curves of the hysteresis loop are given.
the dependencies of the magnetic susceptibility on an applied magnetic field. These dependencies are shown in Fig. 4 for two kinds of samples. As can be seen from the plot, the maximum of the susceptibility is evidently shifted to the range of the low fields for the sample with a soft matrix. The field strength corresponding to the highest susceptibility is ∼250 Oe for the MAE with a soft polymer matrix and ∼4000 Oe for the MAE with a hard polymer matrix. The last value approximately corresponds to the susceptibility of the FeNdB powder. Moreover, the magnetic susceptibility of the MAE with a soft polymer matrix is much higher than the one for the MAE with a hard matrix. These differences are related to the re-orientation (rotation) of the filler particles inside the polymer matrix during the change of the field direction. Particles of the filler in the sample with a soft matrix are not completely remagnetized, but can rotate according to the change of the field direction. The individual particles in the soft matrix are oriented along the applied field instantaneously after the beginning of the magnetization process. The direction of their magnetic moments remains constant and the moments can be only increased with an increase of the field strength.
4. Conclusion and outlook In our study we have experimentally shown that the mechanism
References [1] M.R. Jolly, J.D. Carlson, B.C. Muñoz, T.A. Bullions, The magnetoviscoelastic response of elastomer composites consisting of ferrous particles embedded in a polymer matrix, J. Intell. Mater. Syst. Struct. 7 (6) (1996) 613–622. [2] M. Kallio, The Elastic and Damping Properties of Magnetorheological Elastomers, 565, Espoo: VTT Publications, 2005. [3] G.V. Stepanov, S.S. Abramchuk, D.A. Grishin, L.V. Nikitin, E.Y. Kramarenko, A. R. Khokhlov, Effect of a homogeneous magnetic field on the viscoelastic behavior of magnetic elastomers, Polymer 48 (2007) 488–495. [4] G. Stepanov, D. Borin, Y. Raikher, P. Melenev, N. Perov, Motion of ferroparticles inside the polymeric matrix in magnetoactive elastomers, J. Phys.: Condensed Matter 20 (20) (2008) 204121. [5] L. Lanotte, G. Ausanio, C. Hison, V. Iannotti, C. Luponio, C.J. Luponio, State of the art and development trends of novel nanostructured elastomagnetic composites, J. Optoelectron. Adv. Mater. 6 (2) (2004) 523–532. [6] J.-H. Koo, A. Dawson, H.-J. Jung, Characterization of actuation properties of magnetorheological elastomers with embedded hard magnetic particles, J. Intell. Mater. Syst. Struct. 23 (9) (2012) 1049–1054. [7] G. Stepanov, A. Chertovich, E. Kramarenko, Magnetorheological and deformation properties of magnetically controlled elastomers with hard magnetic filler, J. Magn. Magn. Mater. 324 (21) (2012) 3448–3451. [8] D.Y. Borin, G.V. Stepanov, S. Odenbach, Tuning the tensile modulus of magnetorheological elastomers with magnetically hard powder, J. Phys.: Conference Series 412 (1) (2013) 012040. [9] D.Y. Borin, G.V. Stepanov, Oscillation measurements on magnetoactive elastomers with complex composition, J. Optoelectron. Adv. Mater. 15 (2013) 249–253. [10] G. Stepanov, D. Borin, E. Kramarenko, V. Bogdanov, D. Semerenko, P. Storozhenko, Magnetoactive elastomer based on magnetically hard filler: Synthesis and study of viscoelastic and damping properties, Polym. Sci. Ser. A 56 (5) (2014) 603–613. [11] E.Y. Kramarenko, A.V. Chertovich, G.V. Stepanov, A.S. Semisalova, L. A. Makarova, N.S. Perov, A.R. Khokhlov, Magnetic and viscoelastic response of elastomers with hard magnetic filler, Smart Mater. Struct. 24 (3) (2015) 035002.
Please cite this article as: G.V. Stepanov, et al., Journal of Magnetism and Magnetic Materials (2016), http://dx.doi.org/10.1016/j. jmmm.2016.07.051i
Contents lists available at ScienceDirect
Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm
Rotation of magnetic particles inside the polymer matrix of magnetoactive elastomers with a hard magnetic filler G.V. Stepanov a,n, D.Yu. Borin b, P.A. Storozhenko a a b
State Scientific Research Institute of Chemistry and Technology of Organoelement Compounds, 105118 Moscow, Russia TU Dresden, Magnetofluiddynamics, Measuring and Automation Technology, Dresden 01062, Germany
art ic l e i nf o
a b s t r a c t
Article history: Received 14 July 2016 Accepted 26 July 2016
We propose the results of research on the magnetic properties of magnetoactive elastomers containing particles of a hard magnetic filler. According to our understanding, the mechanism of re-magnetizing of the composite is based on two competing processes, being the re-magnetizing of the magnetic filler and mechanical rotation of particles inside of the polymer matrix. & 2016 Elsevier B.V. All rights reserved.
Keywords: Magnetorheology Magnetopolymer elastic composites Ferrogels Magnetoactive elastomers
1. Introduction
2. Samples and setup
Inspired by the increasing intensity of utilization in active damping devices, substantial studies of magnetorheological and magnetoactive elastomers—MREs and MAEs respectively—have been conducted over the last years [1–4]. By their composition the materials feature a polymer matrix filled with high- or low-coercivity magnetic particles varying in size in the range 1–100 mm. While patents dedicated to magnetic elastomers most frequently mention both types of fillers, there are few publications containing descriptions of elastomers based on high-coercivity powders [5,6]. Results of the first systematic studies of such materials including the basic rheological and magnetic characteristics of the MREs were previously published and are described in a number of publications [7–11]. The principal philosophy of this research topic is the possibility to avoid using heavy magnets for inducing magnetic fields inside the elastomer. A field appears inside the specimen after its magnetizing, as a result of which the material permanently gains the necessary damping and rheological properties. As indicated by the results, the material exhibits a set of specific magnetorheological properties, among which is its anomalous way of magnetizing and demagnetizing. In addition, our measurements unveiled the fact that the coercive force of the composite is significantly lower in comparison to that of the pure magnetic filler used as a component. In the current study we experimentally consider the mechanism of the re-magnetizing of the MAE based on a hard magnetic filler.
We prepared our samples according to the standard procedure based on mixing a powder of FeNdB and liquid silicone semiproduct followed by polymerizing in a mold [10]. At the same time, powders of carbonyl iron were frequently introduced into the mixtures with the purpose of providing a higher degree of homogeneity and develop materials with better magnetorheological properties. The elastic modulus of the matrix was modified using a dilution of the liquid rubber component with a silicone oil. Magnetic measurements were conducted utilizing a vibrating sample magnetometer (Lake Shore 7407).
n
Corresponding author. E-mail address: [email protected] (G.V. Stepanov).
3. Results and discussion It is a known fact that the dilution of magnetic powders leads to increased coercive forces resulting from lower densities of the studied materials and thus from reduced demagnetizing factors. Therefore, comparison of the similar parameters of different magnetic powders requires the equality of their densities. Measurements performed within the frames of our research indicated that the MAE samples exhibited significantly lower magnitudes of coercive force than pure powders, which is contradictory to theory. In our experiments we used powders diluted with an inert substance and expected higher values of the parameter. This is well seen from Table 1. The decreasing of the coercive force may probably be explained by the rotation of particles of the magnetic filler inside the matrix. As the concentration of the filler decreases, there remain more polymer separating single particles resulting in their easier
http://dx.doi.org/10.1016/j.jmmm.2016.07.051 0304-8853/& 2016 Elsevier B.V. All rights reserved.
Please cite this article as: G.V. Stepanov, et al., Journal of Magnetism and Magnetic Materials (2016), http://dx.doi.org/10.1016/j. jmmm.2016.07.051i
G.V. Stepanov et al. / Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Table 1 Particles concentration and coercivity of the composite. FeNdB concentration in the polymer matrix (%)
Coercivity of the composite
100 80 75
1900 1700 1400
Fig. 2. Dependence of the average coercive force of MAE on its shear modulus. Point 1 refers to the coercive force of an FeNdB powder with a value of 3300 Oe.
Fig. 1. Hysteresis loop of a composite material with a rigid (1) and soft (2) polymer matrix (Samples 1 and 4).
rotation. At the same time, the elasticity of the polymer matrix features an important factor affecting the behavior of the material; for the capability of the matrix to deform defines how strongly the particles are confined. Comparison of typical hysteresis loops of composite materials based on rigid and soft polymer matrices is presented in Fig. 1. Studies of the full magnetization curve of the material also unveiled an anomalous shape of the hysteresis loop. The given character of the curve is probably caused by the rotation of particles inside the elastic matrix too when the composite is placed in an external field, as a result of which the particles get magnetized and form chain-like structures lining up along the force lines. At the same time, field reversal makes the particles flip over to get their momenta parallel to the newly established influence and does not lead to their re-magnetizing. A detailed study of the dependency of the coercive force of the composite material on the elastic modulus of its polymer matrix demonstrated the decreasing of the former as the latter gets lower. Important to note, this reduction is significant. So, measurements unveiled a 5-time weakening of the coercive force in the set of samples with matrix elasticities dropping from 90 to 1 kPa. At the same time, the coercive force is subjected to the most significant changes in the area of 20 kPa. The obtained data are presented in Table 2 and Fig. 2. Owing to the well-pronounced asymmetric configuration of the hysteresis loop of MAE, which are in Fig. 3, while Fig. 2 demonstrates average values of the coercive forces. This phenomenon points to the existence of a mechanism of magnetizing and re-magnetizing of the composite. In the process Table 2 Elastic modulus and coercive force of the studied composite samples. Sample
1
2
3
4
5
E, kPa Hc , Oe
90 2900
40 2700
20 2100
6 700
1 650
Fig. 3. Asymmetric hysteresis loop of a composite material with a soft polymer matrix (Sample 3).
of re-magnetizing the particles inside the matrix suffer partial remagnetizing, whereas the remaining ones flip to get their momenta parallel to the external field to continue to magnetize further. Most clearly these processes are seen in materials with moderate elasticities when placed in moderate magnetic fields, which creates the possibility for competition between re-magnetizing and flipping. As the elasticity modulus gets lower, the shape of the hysteresis loop is defined practically only by the value of the elastic modulus of the matrix, whereas the coercive force depends on this property of the polymer conditionally. As can be seen from Fig. 3, the hysteresis loop is noticeably asymmetric. Primary magnetizing occurring during measurements lines up the magnetized particles in a certain direction, being the preferable orientation of light magnetizing. After the direction of the external field has been changed the particles flip resulting in an increased tension inside the matrix trying to turn them in the previous direction. When the particles return to their previous position, in which they were initially embedded in the matrix and then magnetized, the process goes more easily and the coercive force of the reversal part of the loop appears to be lower. In fact, we deal not with a light magnetizing axis, but with a concrete direction of light magnetizing. The most expressed difference in the behavior of the MAE with a soft (sample 4) and hard (sample 1) matrix can be observed on
Please cite this article as: G.V. Stepanov, et al., Journal of Magnetism and Magnetic Materials (2016), http://dx.doi.org/10.1016/j. jmmm.2016.07.051i
G.V. Stepanov et al. / Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
of the re-magnetization of the magnetoactive elastomers with a hard magnetic filler is based on two competing processes being the re-magnetizing of the magnetic filler and mechanical rotation of particles inside of the polymer matrix. In order to prove this conclusion, microstructural study of the elastic composites under magnetic field influence as well as theoretical approaches are required.
Acknowledgements Financial support by Deutsche Forschungsgemeinschaft (DFG) under Grant Bo 3343/1–1 within PAK 907 and support of RFBR under Grant 16–53-12009 providing the basis for our investigations is gratefully acknowledged.
Fig. 4. Magnetic susceptibility of the MAE with a hard magnetic filler based on the hard (Sample 1) and soft (Sample 4) polymer matrix as a function of an applied magnetic field. Direct (1) and reverse (2) curves of the hysteresis loop are given.
the dependencies of the magnetic susceptibility on an applied magnetic field. These dependencies are shown in Fig. 4 for two kinds of samples. As can be seen from the plot, the maximum of the susceptibility is evidently shifted to the range of the low fields for the sample with a soft matrix. The field strength corresponding to the highest susceptibility is ∼250 Oe for the MAE with a soft polymer matrix and ∼4000 Oe for the MAE with a hard polymer matrix. The last value approximately corresponds to the susceptibility of the FeNdB powder. Moreover, the magnetic susceptibility of the MAE with a soft polymer matrix is much higher than the one for the MAE with a hard matrix. These differences are related to the re-orientation (rotation) of the filler particles inside the polymer matrix during the change of the field direction. Particles of the filler in the sample with a soft matrix are not completely remagnetized, but can rotate according to the change of the field direction. The individual particles in the soft matrix are oriented along the applied field instantaneously after the beginning of the magnetization process. The direction of their magnetic moments remains constant and the moments can be only increased with an increase of the field strength.
4. Conclusion and outlook In our study we have experimentally shown that the mechanism
References [1] M.R. Jolly, J.D. Carlson, B.C. Muñoz, T.A. Bullions, The magnetoviscoelastic response of elastomer composites consisting of ferrous particles embedded in a polymer matrix, J. Intell. Mater. Syst. Struct. 7 (6) (1996) 613–622. [2] M. Kallio, The Elastic and Damping Properties of Magnetorheological Elastomers, 565, Espoo: VTT Publications, 2005. [3] G.V. Stepanov, S.S. Abramchuk, D.A. Grishin, L.V. Nikitin, E.Y. Kramarenko, A. R. Khokhlov, Effect of a homogeneous magnetic field on the viscoelastic behavior of magnetic elastomers, Polymer 48 (2007) 488–495. [4] G. Stepanov, D. Borin, Y. Raikher, P. Melenev, N. Perov, Motion of ferroparticles inside the polymeric matrix in magnetoactive elastomers, J. Phys.: Condensed Matter 20 (20) (2008) 204121. [5] L. Lanotte, G. Ausanio, C. Hison, V. Iannotti, C. Luponio, C.J. Luponio, State of the art and development trends of novel nanostructured elastomagnetic composites, J. Optoelectron. Adv. Mater. 6 (2) (2004) 523–532. [6] J.-H. Koo, A. Dawson, H.-J. Jung, Characterization of actuation properties of magnetorheological elastomers with embedded hard magnetic particles, J. Intell. Mater. Syst. Struct. 23 (9) (2012) 1049–1054. [7] G. Stepanov, A. Chertovich, E. Kramarenko, Magnetorheological and deformation properties of magnetically controlled elastomers with hard magnetic filler, J. Magn. Magn. Mater. 324 (21) (2012) 3448–3451. [8] D.Y. Borin, G.V. Stepanov, S. Odenbach, Tuning the tensile modulus of magnetorheological elastomers with magnetically hard powder, J. Phys.: Conference Series 412 (1) (2013) 012040. [9] D.Y. Borin, G.V. Stepanov, Oscillation measurements on magnetoactive elastomers with complex composition, J. Optoelectron. Adv. Mater. 15 (2013) 249–253. [10] G. Stepanov, D. Borin, E. Kramarenko, V. Bogdanov, D. Semerenko, P. Storozhenko, Magnetoactive elastomer based on magnetically hard filler: Synthesis and study of viscoelastic and damping properties, Polym. Sci. Ser. A 56 (5) (2014) 603–613. [11] E.Y. Kramarenko, A.V. Chertovich, G.V. Stepanov, A.S. Semisalova, L. A. Makarova, N.S. Perov, A.R. Khokhlov, Magnetic and viscoelastic response of elastomers with hard magnetic filler, Smart Mater. Struct. 24 (3) (2015) 035002.
Please cite this article as: G.V. Stepanov, et al., Journal of Magnetism and Magnetic Materials (2016), http://dx.doi.org/10.1016/j. jmmm.2016.07.051i