- Email: [email protected]
Magnetorheological characteristics of nanoparticle-added carbonyl iron system
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 303 (2006) e290–e293 www.elsevier.com/locate/jmmm
Magnetorheological characteristics of nanoparticle-added carbonyl iron system B.J. Parka, I.B. Janga, H.J. Choia,, A. Pichb, S. Bhattacharyab, H.-J. Adlerb a
b
Department of Polymer Science and Engineering, Inha University, Incheon 402-751, Korea Institute of Macromolecular Chemistry and Textile Chemistry, Dresden University of Technology, D-01062 Dresden, Germany Available online 20 February 2006
Abstract Magnetorheological (MR) fluid, suspension of magnetic carbonyl iron (CI) and magnetic additives in mineral oil, were prepared. The novel core–shell structured additives, comprising monodisperse polystyrene (PS) spheres as cores and magnetite as shells, were fabricated by surfactant-free emulsion polymerization. This MR fluid with bimodal particles was suspended in mineral oil and their MR characteristics were examined via a rotational rheometer in a parallel plate geometry equipped with a magnetic field supplier. MR properties of the bimodal MR fluid with magnetic additive exhibit similar magnetic and MR properties compared to MR fluid consisting of pristine CI, but with much improved dispersion stability. r 2006 Elsevier B.V. All rights reserved. PACS: 81.05.Ni; 82.70-y; 81.07.Pr; 75.50.-y Keywords: Magnetorheology; Carbonyl Iron; Core/shell; Additive
1. Introduction Magnetorheological (MR) fluids are regarded as one of the smartest materials, since they exhibit remarkable characteristics of changing their flow properties under the application of an external magnetic field [1–3]. When MR fluid is subjected to a magnetic field, MR fluids can be reversibly transformed from a fluid-like to a solid-like state within milliseconds because of the forming chain cluster of the magnetic particles [4]. Since its first discovery, there have been a large number of studies on MR characteristics and its potential applications including active controllable dampers, torque transducers, and position controllers [5,6] along with its electrical counterpart [7,8]. Despite these potential applications, there are only few commercially available devices due to the lack of suitable fluids. MR fluid must have certain features including noncorrosive, active over a broad temperature range, stable against settling, irreversible flocculation, chemical stability, and high magnetic saturation [9]. Furthermore, it should Corresponding author. Tel.: +82 32 860 7486; fax: +82 32 865 5178.
E-mail address: [email protected] (H.J. Choi). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.01.084
have a large field-induced yield stress with small apparent viscosities in the absence of an applied magnetic field [10]. However, main drawback is the sedimentation in the equipment due to high density mismatch, because MR fluids in general contain high-density particles (e.g., iron, ferrites) dispersed in a liquid carrier with a low density. In order to resolve these problems, we synthesized magnetic nanoparticles, the composite particles with polymeric core particles covered by Fe3O4 (magnetite) shell, as additive. These core–shell particles were prepared by controlled precipitation of inorganic precursors onto the core particles [11]. Several studies have been conducted on the preparation of composite particles consisting of cores covered with shell of different chemical composition. Such materials may exhibit a few unique magnetic, optical, catalytic, chemical, electric, adsorptive properties and therefore have aroused extensive scientific and technological interest [12]. Composites with magnetic property were prepared by twostep procedure. At first, highly monodisperse polystyrene (PS)-acetoacetoxyethyl methacrylate (AAEM) microspheres were synthesized by surfactant-free emulsion polymerization [13] and then magnetite nanoparticles have been deposited onto the preformed polymeric cores
ARTICLE IN PRESS B.J. Park et al. / Journal of Magnetism and Magnetic Materials 303 (2006) e290–e293
e291
providing formation of magnetic shell. After all, since lower particle density of the nanoparticles could be accomplished, sedimentation stability in MR fluids was found to be enhanced with addition of certain amounts of the nanoparticles. 2. Experimental
3. Results and discussion Fig. 1 shows the surface morphology of both PS-AAEM particles and SAM composite particles (inset). Average particle size of the spherical PS-AAEM nanoparticles was observed to be about 200 nm. Surface of the SAM composite shows rough morphologies with many tiny particles compared with the smooth surface morphologies of typical polymer particle. It can be seen that the
Fig. 1. SEM images of PS-AAEM. Inset is the SAM image.
4
2 M (emu/g)
Both styrene (ST) (Fluka, USA) and AAEM (Aldrich, USA) were purified by vacuum distillation prior to use. Sodium peroxydisulfate (SPDS) and 2,20 -azobis (2-methylpropyonamidine) dihydrochloride (AMPA), iron (III) chloride (FeCl3), and iron (II) chloride (FeCl2) (Aldrich, USA) were used as received. Aqueous ammonium hydroxide (NH4OH) (40%) (Fluka, USA) was also used. Double-wall glass reactor equipped with stirrer and reflux condenser was purged with nitrogen. Distilled water (170 g) and appropriate amounts of ST (19 g) and AAEM (1 g, 5% to ST) were added into a reactor and stirred at room temperature. After 10 min, the temperature was increased to 70 1C and aqueous solution of initiator (0.3 g SPDS in 10 g water) was added to initiate the PS-AAEM copolymerization process. The PS-AAEM latexes were prepared at ca.10% solid content. Diluted PS-AAEM dispersions were placed into stirred reactor and mixture was stirred for 15 min under nitrogen flow at 25 1C. Solutions of FeCl2 and FeCl3 were prepared in separate flasks and added to stirred dispersion under nitrogen blanket (molar ratio FeCl3:FeCl2 was kept constant at 2:1). Aqueous NH4OH solution was added dropwise to initiate the magnetite formation process. Immediately after the addition of base solution, the dispersion became dark-brown indicating that magnetite has been formed in the system. After 30 min, formed PSAAEM-magnetite (SAM) composite particles were removed from the reaction vessel and cleaned by precipitation to remove all by-products [14]. To prepare the MR fluid, these composite particles and carbonyl iron (CI, BASF, Germany, CM grade, spherical shape with a density of 7.86 g/ml) particles were dispersed in mineral oil. MR characterizations were performed at 20 1C via a rotational rheometer (Physica MCR 300, Stuttgart, Germany) equipped with a magnetorheological device (MRD 180). A parallel-plate measuring system was made of nonmagnetic metal to prevent the occurrence of radial magnetic force components on the shaft of the measuring system. The magnetic field direction was set to be perpendicular to the flow direction.
0
-2
-4 -10000
-5000
0
5000
10000
H (Oe) Fig. 2. Magnetization curve of SAM as a function of magnetic field strength.
nanoparticles of the PS-AAEM are uniform and regular in both size and shape. Fig. 2 shows the magnetization curves of the SAM composite powder. Magnetic saturation value of the SAM was about 5 emu/g. Based on these properties, we applied these magnetic nanoparticles as additives. Note that recently, there have been a lot of studies on additives for MR application [15,16]. Previous works have been mainly focused on the non magnetic additives. Fig. 3 represents the flow curves of shear stress as a function of shear rate for both CI (closed symbol) based and SAM filled CI (CI/SAM, open symbol) based MR fluids under four different external magnetic field strengthes ranging from 0 to 343 kA/m. The concentration of CI was fixed at 20 v/v% in both systems, and that of subsized filler (SAM) was adjusted to 3 wt% with respect to the suspending medium. With the increase in magnetic field strength, the shear stresses leveled off for the entire shear
ARTICLE IN PRESS B.J. Park et al. / Journal of Magnetism and Magnetic Materials 303 (2006) e290–e293
e292
1.0 CI CI-SAM
Sedimentation ratio
Shear stress (Pa)
104
86 kA/m 171 kA/m 343 kA/m
103
10-1
100
101
102
Shear viscosity (Pa.s)
105
0.8 0
Shear rate (1/s)
200
400 Time [hr]
600
800
Fig. 4. Sedimenation test of both CI/SAM and CI in mineral oil.
86 kA/m 171 kA/m 343 kA/m
we could confirm the effect of nanosized magnetic particles on MR fluid.
104
4. Conclusions
103
102
10-1
0.9
100
101
102
Shear rate (1/s) Fig. 3. Flow behavior of CI (closed symbol) and CI/SAM (open symbol) in MR fluids.
rate region. The yield stresses at 343 kA/m are 15.5 kPa for the CI suspension and 12.3 kPa for the CI/SAM suspension, respectively. This decrease in yield stress comes from more weak magnetic property of SAM. That is, the chain consisting of the magnetic suspension particle under applied magnetic field were broken in more weak point consisting of SAM in shear flow (Fig. 3). Drastic drop-off in yield stress was not observed for plenty of CI contents but smaller value of yield stress is shown through the all magnetic ranges. In a zero magnetic field, both magnetic fluids represent similar behavior [17]. Fig. 4 shows the sedimentation ratio as a function of time for both the CI and the CI/SAM in mineral oil media, in which the settling of the macroscopic phase boundary between the concentrated suspension and the supernatant liquid was observed. The MR fluids with and without the SAM were set in a static condition until it reached asymptotic values. The decreased sedimentation ratio clearly demonstrated the role of CI/SAM in sedimentation phenomenon, showing that the CI/SAM suspension has a better dispersion stability than the CI suspension. Thereby,
CI and CI/SAM based MR fluids were prepared, and their MR characterization and sedimentation characteristics were examined. Since the SAM added MR fluid enhanced sedimentation behavior but with slightly lower yield behaviors of constant shear stresses in a broad range of shear rate, we mixed CI particles having high ferromagnetic properties with SAM composite. MR property of this bimodal MR fluid not only improved sedimentation behavior but also maintained proper yield stresses in a broad range of shear rates for application in MR fluids. Acknowledgments This work was supported by research grants from KOSEF through the Applied Rheology Center, Korea. References [1] J.D. Carlson, D.M. Catenzarite, K.A.St. Clair, Int. J. Modern Phys. B 10 (1996) 2857. [2] G. Bossis, P. Khuzir, S. Lacis, O. Volkova, J. Magn. Magn. Mater 258–259 (2003) 456. [3] M.S. Cho, S.T. Lim, I.B. Jang, H.J. Choi, IEEE Trans. Magn 40 (2004) 3036. [4] T. Ukai, T. Maekawa, Phys. Rev. E 69 (2005) 032501. [5] G. Bossis, E. Lemaire, J. Rheol. 35 (1991) 1345. [6] H.J. Choi, M.S. Cho, J.W. Kim, C.A. Kim, M.S. Jhon, Appl. Phys. Lett 78 (2001) 3806. [7] J.W. Kim, L.W. Jang, H.J. Choi, M.S. Jhon, J. Appl. Polym. Sci 89 (2003) 821. [8] J.W. Kim, S.G. Kim, H.J. Choi, M.S. Jhon, Macromol. Rapid Commun. 20 (1999) 450. [9] J. Claracq, J. Sarrazin, J.P. Montfort, Rheol. Acta. 43 (2004) 38.
ARTICLE IN PRESS B.J. Park et al. / Journal of Magnetism and Magnetic Materials 303 (2006) e290–e293 [10] P.J. Rankin, A.T. Horvath, D.J. Klingenberg, Rheol. Acta. 38 (1991) 471. [11] Z. Huang, F. Tang, J. Colloid Interf. Sci. 275 (2004) 142. [12] F. Caruso, R.A. Caruso, H.M. Hwald, Science 282 (1998) 1111. [13] A. Imhof, Langmuir 17 (2001) 3579. [14] A. Pich, S. Bhattacharya, A. Ghosh, H.J. Alder, Polymer 46 (2005) 4596.
e293
[15] S.T. Lim, M.S. Cho, H.J. Choi, M.S. Jhon, Int. J. Modern Phys. B 19 (2005) 1142. [16] S.T. Lim, M.S. Cho, I.B. Jang, H.J. Choi, J. Magn. Magn. Mater. 282 (2004) 170. [17] I.B. Jang, H.B. Kim, J.Y. Lee, J.Y. You, H.J. Choi, M.S. Jhon, J. Appl. Phys. 97 (2005) 10Q912.
Journal of Magnetism and Magnetic Materials 303 (2006) e290–e293 www.elsevier.com/locate/jmmm
Magnetorheological characteristics of nanoparticle-added carbonyl iron system B.J. Parka, I.B. Janga, H.J. Choia,, A. Pichb, S. Bhattacharyab, H.-J. Adlerb a
b
Department of Polymer Science and Engineering, Inha University, Incheon 402-751, Korea Institute of Macromolecular Chemistry and Textile Chemistry, Dresden University of Technology, D-01062 Dresden, Germany Available online 20 February 2006
Abstract Magnetorheological (MR) fluid, suspension of magnetic carbonyl iron (CI) and magnetic additives in mineral oil, were prepared. The novel core–shell structured additives, comprising monodisperse polystyrene (PS) spheres as cores and magnetite as shells, were fabricated by surfactant-free emulsion polymerization. This MR fluid with bimodal particles was suspended in mineral oil and their MR characteristics were examined via a rotational rheometer in a parallel plate geometry equipped with a magnetic field supplier. MR properties of the bimodal MR fluid with magnetic additive exhibit similar magnetic and MR properties compared to MR fluid consisting of pristine CI, but with much improved dispersion stability. r 2006 Elsevier B.V. All rights reserved. PACS: 81.05.Ni; 82.70-y; 81.07.Pr; 75.50.-y Keywords: Magnetorheology; Carbonyl Iron; Core/shell; Additive
1. Introduction Magnetorheological (MR) fluids are regarded as one of the smartest materials, since they exhibit remarkable characteristics of changing their flow properties under the application of an external magnetic field [1–3]. When MR fluid is subjected to a magnetic field, MR fluids can be reversibly transformed from a fluid-like to a solid-like state within milliseconds because of the forming chain cluster of the magnetic particles [4]. Since its first discovery, there have been a large number of studies on MR characteristics and its potential applications including active controllable dampers, torque transducers, and position controllers [5,6] along with its electrical counterpart [7,8]. Despite these potential applications, there are only few commercially available devices due to the lack of suitable fluids. MR fluid must have certain features including noncorrosive, active over a broad temperature range, stable against settling, irreversible flocculation, chemical stability, and high magnetic saturation [9]. Furthermore, it should Corresponding author. Tel.: +82 32 860 7486; fax: +82 32 865 5178.
E-mail address: [email protected] (H.J. Choi). 0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.01.084
have a large field-induced yield stress with small apparent viscosities in the absence of an applied magnetic field [10]. However, main drawback is the sedimentation in the equipment due to high density mismatch, because MR fluids in general contain high-density particles (e.g., iron, ferrites) dispersed in a liquid carrier with a low density. In order to resolve these problems, we synthesized magnetic nanoparticles, the composite particles with polymeric core particles covered by Fe3O4 (magnetite) shell, as additive. These core–shell particles were prepared by controlled precipitation of inorganic precursors onto the core particles [11]. Several studies have been conducted on the preparation of composite particles consisting of cores covered with shell of different chemical composition. Such materials may exhibit a few unique magnetic, optical, catalytic, chemical, electric, adsorptive properties and therefore have aroused extensive scientific and technological interest [12]. Composites with magnetic property were prepared by twostep procedure. At first, highly monodisperse polystyrene (PS)-acetoacetoxyethyl methacrylate (AAEM) microspheres were synthesized by surfactant-free emulsion polymerization [13] and then magnetite nanoparticles have been deposited onto the preformed polymeric cores
ARTICLE IN PRESS B.J. Park et al. / Journal of Magnetism and Magnetic Materials 303 (2006) e290–e293
e291
providing formation of magnetic shell. After all, since lower particle density of the nanoparticles could be accomplished, sedimentation stability in MR fluids was found to be enhanced with addition of certain amounts of the nanoparticles. 2. Experimental
3. Results and discussion Fig. 1 shows the surface morphology of both PS-AAEM particles and SAM composite particles (inset). Average particle size of the spherical PS-AAEM nanoparticles was observed to be about 200 nm. Surface of the SAM composite shows rough morphologies with many tiny particles compared with the smooth surface morphologies of typical polymer particle. It can be seen that the
Fig. 1. SEM images of PS-AAEM. Inset is the SAM image.
4
2 M (emu/g)
Both styrene (ST) (Fluka, USA) and AAEM (Aldrich, USA) were purified by vacuum distillation prior to use. Sodium peroxydisulfate (SPDS) and 2,20 -azobis (2-methylpropyonamidine) dihydrochloride (AMPA), iron (III) chloride (FeCl3), and iron (II) chloride (FeCl2) (Aldrich, USA) were used as received. Aqueous ammonium hydroxide (NH4OH) (40%) (Fluka, USA) was also used. Double-wall glass reactor equipped with stirrer and reflux condenser was purged with nitrogen. Distilled water (170 g) and appropriate amounts of ST (19 g) and AAEM (1 g, 5% to ST) were added into a reactor and stirred at room temperature. After 10 min, the temperature was increased to 70 1C and aqueous solution of initiator (0.3 g SPDS in 10 g water) was added to initiate the PS-AAEM copolymerization process. The PS-AAEM latexes were prepared at ca.10% solid content. Diluted PS-AAEM dispersions were placed into stirred reactor and mixture was stirred for 15 min under nitrogen flow at 25 1C. Solutions of FeCl2 and FeCl3 were prepared in separate flasks and added to stirred dispersion under nitrogen blanket (molar ratio FeCl3:FeCl2 was kept constant at 2:1). Aqueous NH4OH solution was added dropwise to initiate the magnetite formation process. Immediately after the addition of base solution, the dispersion became dark-brown indicating that magnetite has been formed in the system. After 30 min, formed PSAAEM-magnetite (SAM) composite particles were removed from the reaction vessel and cleaned by precipitation to remove all by-products [14]. To prepare the MR fluid, these composite particles and carbonyl iron (CI, BASF, Germany, CM grade, spherical shape with a density of 7.86 g/ml) particles were dispersed in mineral oil. MR characterizations were performed at 20 1C via a rotational rheometer (Physica MCR 300, Stuttgart, Germany) equipped with a magnetorheological device (MRD 180). A parallel-plate measuring system was made of nonmagnetic metal to prevent the occurrence of radial magnetic force components on the shaft of the measuring system. The magnetic field direction was set to be perpendicular to the flow direction.
0
-2
-4 -10000
-5000
0
5000
10000
H (Oe) Fig. 2. Magnetization curve of SAM as a function of magnetic field strength.
nanoparticles of the PS-AAEM are uniform and regular in both size and shape. Fig. 2 shows the magnetization curves of the SAM composite powder. Magnetic saturation value of the SAM was about 5 emu/g. Based on these properties, we applied these magnetic nanoparticles as additives. Note that recently, there have been a lot of studies on additives for MR application [15,16]. Previous works have been mainly focused on the non magnetic additives. Fig. 3 represents the flow curves of shear stress as a function of shear rate for both CI (closed symbol) based and SAM filled CI (CI/SAM, open symbol) based MR fluids under four different external magnetic field strengthes ranging from 0 to 343 kA/m. The concentration of CI was fixed at 20 v/v% in both systems, and that of subsized filler (SAM) was adjusted to 3 wt% with respect to the suspending medium. With the increase in magnetic field strength, the shear stresses leveled off for the entire shear
ARTICLE IN PRESS B.J. Park et al. / Journal of Magnetism and Magnetic Materials 303 (2006) e290–e293
e292
1.0 CI CI-SAM
Sedimentation ratio
Shear stress (Pa)
104
86 kA/m 171 kA/m 343 kA/m
103
10-1
100
101
102
Shear viscosity (Pa.s)
105
0.8 0
Shear rate (1/s)
200
400 Time [hr]
600
800
Fig. 4. Sedimenation test of both CI/SAM and CI in mineral oil.
86 kA/m 171 kA/m 343 kA/m
we could confirm the effect of nanosized magnetic particles on MR fluid.
104
4. Conclusions
103
102
10-1
0.9
100
101
102
Shear rate (1/s) Fig. 3. Flow behavior of CI (closed symbol) and CI/SAM (open symbol) in MR fluids.
rate region. The yield stresses at 343 kA/m are 15.5 kPa for the CI suspension and 12.3 kPa for the CI/SAM suspension, respectively. This decrease in yield stress comes from more weak magnetic property of SAM. That is, the chain consisting of the magnetic suspension particle under applied magnetic field were broken in more weak point consisting of SAM in shear flow (Fig. 3). Drastic drop-off in yield stress was not observed for plenty of CI contents but smaller value of yield stress is shown through the all magnetic ranges. In a zero magnetic field, both magnetic fluids represent similar behavior [17]. Fig. 4 shows the sedimentation ratio as a function of time for both the CI and the CI/SAM in mineral oil media, in which the settling of the macroscopic phase boundary between the concentrated suspension and the supernatant liquid was observed. The MR fluids with and without the SAM were set in a static condition until it reached asymptotic values. The decreased sedimentation ratio clearly demonstrated the role of CI/SAM in sedimentation phenomenon, showing that the CI/SAM suspension has a better dispersion stability than the CI suspension. Thereby,
CI and CI/SAM based MR fluids were prepared, and their MR characterization and sedimentation characteristics were examined. Since the SAM added MR fluid enhanced sedimentation behavior but with slightly lower yield behaviors of constant shear stresses in a broad range of shear rate, we mixed CI particles having high ferromagnetic properties with SAM composite. MR property of this bimodal MR fluid not only improved sedimentation behavior but also maintained proper yield stresses in a broad range of shear rates for application in MR fluids. Acknowledgments This work was supported by research grants from KOSEF through the Applied Rheology Center, Korea. References [1] J.D. Carlson, D.M. Catenzarite, K.A.St. Clair, Int. J. Modern Phys. B 10 (1996) 2857. [2] G. Bossis, P. Khuzir, S. Lacis, O. Volkova, J. Magn. Magn. Mater 258–259 (2003) 456. [3] M.S. Cho, S.T. Lim, I.B. Jang, H.J. Choi, IEEE Trans. Magn 40 (2004) 3036. [4] T. Ukai, T. Maekawa, Phys. Rev. E 69 (2005) 032501. [5] G. Bossis, E. Lemaire, J. Rheol. 35 (1991) 1345. [6] H.J. Choi, M.S. Cho, J.W. Kim, C.A. Kim, M.S. Jhon, Appl. Phys. Lett 78 (2001) 3806. [7] J.W. Kim, L.W. Jang, H.J. Choi, M.S. Jhon, J. Appl. Polym. Sci 89 (2003) 821. [8] J.W. Kim, S.G. Kim, H.J. Choi, M.S. Jhon, Macromol. Rapid Commun. 20 (1999) 450. [9] J. Claracq, J. Sarrazin, J.P. Montfort, Rheol. Acta. 43 (2004) 38.
ARTICLE IN PRESS B.J. Park et al. / Journal of Magnetism and Magnetic Materials 303 (2006) e290–e293 [10] P.J. Rankin, A.T. Horvath, D.J. Klingenberg, Rheol. Acta. 38 (1991) 471. [11] Z. Huang, F. Tang, J. Colloid Interf. Sci. 275 (2004) 142. [12] F. Caruso, R.A. Caruso, H.M. Hwald, Science 282 (1998) 1111. [13] A. Imhof, Langmuir 17 (2001) 3579. [14] A. Pich, S. Bhattacharya, A. Ghosh, H.J. Alder, Polymer 46 (2005) 4596.
e293
[15] S.T. Lim, M.S. Cho, H.J. Choi, M.S. Jhon, Int. J. Modern Phys. B 19 (2005) 1142. [16] S.T. Lim, M.S. Cho, I.B. Jang, H.J. Choi, J. Magn. Magn. Mater. 282 (2004) 170. [17] I.B. Jang, H.B. Kim, J.Y. Lee, J.Y. You, H.J. Choi, M.S. Jhon, J. Appl. Phys. 97 (2005) 10Q912.