Hybrid magnetorheological elastomer: Influence of magnetic field and compression pressure on its electrical conductivity

G Model

JIEC-1832; No. of Pages 6 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec

Hybrid magnetorheological elastomer: Influence of magnetic field and compression pressure on its electrical conductivity Ioan Bica a,*, Eugen M. Anitas b,1, Madalin Bunoiu c, Boris Vatzulik d, Iulius Juganaru e a

West University of Timisoara, Bd. V. Parvan 4, 300223 Timisoara, Romania Joint Institute for Nuclear Research, Joliot Curie 6, Moscow Region, 141980 Dubna, Russia c West University of Timisoara, Bd. V. Parvan 4, 300223 Timisoara, Romania d West University of Timisoara, Bd. V. Parvan 4, 300223 Timisoara, Romania e West University of Timisoara, Bd. V. Parvan 4, 300223 Timisoara, Romania b

A R T I C L E I N F O

Article history: Received 18 September 2013 Accepted 29 December 2013 Available online xxx Keywords: Hybrid electro-conductive magnetorheological elastomer Magnetoresistive sensor Graphene nanoparticles Carbonyl iron Silicone rubber Electrical conductivity

A B S T R A C T

Graphene nanoparticles are used to produce a hybrid electro-conductive magnetorheological elastomer (MRE-hybrid). We fabricate a magnetoresistive sensor based on the obtained MRE-hybrid. We measure the electrical resistance of the MRE-hybrid in a transverse magnetic field of intensity 0  H (kA/m)  65, and separately, the electrical resistance under the influence of a compression pressure p  14.4 kPa. From the obtained results we determine the variation of electrical conductivity with H, and respectively with p. We develop a theoretical model which explains the effects of H and p on electrical conductivity of MRE-hybrid. The obtained results are presented and discussed. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

1. Introduction Magnetorheological elastomers (MREs), known also as magneto-sensitive elastomers, magneto-active or magneto-strictive polymers, are composite materials consisting of nano/micro-sized ferromagnetic particles dispersed in an elastic polymer matrix (rubber or rubber-like matrix) [1–4]. Their properties such as shear modulus, damping, magneto-striction, electrical conductivity, and so on, can be controlled by an external magnetic field, which is called magnetorheological effect (MR-effect) [5–7]. This feature of MREs is used for development of vibration dampers and mechanical shock attenuators in civil and industrial constructions, in bicycles and cars, in fabrication of passive and active elements of electric circuits etc. [8–10]. The processes and physical mechanisms that lead to MR-effect are important for various applications. Understanding of these mechanisms, together with determination of rheological properties and of elastic constants for MRE is an active research topic in

* Corresponding author. Tel.: +40256592203. E-mail addresses: [email protected] (I. Bica), [email protected] (E.M. Anitas), [email protected] (M. Bunoiu), [email protected] (B. Vatzulik), [email protected] (I. Juganaru). 1 Horia Hulubei National Institute of Physics and Nuclear Engineering, RO077125 Bucharest-Magurele Romania.

the last years. Recent investigations have shown that rheological properties, elastic constants, electrical conductivity, mechanical tensions and deformations of MREs depend on the volume fraction of the magnetizable phase, on the size, concentration, and type of the dispersed particles, and respectively on the intensity and direction of the applied magnetic field [4,6,7,10–12]. Graphene is a single two-dimensional layer of carbon atoms bound in a hexagonal lattice structure. It has been extensively studied in the last several years even though it was isolated for the first time in 2004 [13]. Preparation methods and physical properties of graphene are well known [13]. Their outstanding physical properties allow one to use graphene for fabrication of capacitors with giant capacitance, field-effect transistors, sensors etc. [3,13]. Recently, applied researches have been focused on producing stable magnetorheological suspensions. In Refs. [1,15] the group headed by Prof. Choi from Inha University has produced highly stable magnetorheological suspensions with remarkable rheological properties based on the hydrophilic property of graphene. They have found that using graphene oxide has the role to fill the interspaces of carbonyl iron (CI) particles and therefore to improve its agglomeration and resistance to sedimentation [15]. However, inside MREs magnetic micron-sized particles are frozen in the polymer matrix and graphene nano-sized particles have the role to provide the electro-conductive property of MREs.

1226-086X/$ – see front matter ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.12.102

Please cite this article in press as: I. Bica, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.102

G Model

JIEC-1832; No. of Pages 6 I. Bica et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

2

It is well known that in MREs based on silicone rubber and iron micro particles, the electrical conductibility is stabilized at relatively large time intervals Dt after a magnetic field or/and a compression pressure is applied, thus leading to undesired effects [7]. The aim of this work is to show that by using the graphenebased MRE-hybrid, we obtain MREs having the property Dt ! 0.

5 rotations per minute. At temperature 330 K  5%, we add C (5%). After homogenization, the obtained product is poured in a layer of 2 mm thickness, on both sides of the system resistor body – coupling elements. At the end of polymerization process one obtains MREhybrid, which together with copper electrodes will be called magnetoresistor (MR) 2.2. Experimental device

2. Experimental 2.1. MRE-hybrid The magnetoresistor (MR) used for investigation of MRE-hybrid is shown in Fig. 1. Materials used for production of MRE-hybrid are:

The experimental device used for investigating the influence of the transverse magnetic field and separately of compression pressure, on electrical conductivity of MRE-hybrid is shown in Fig. 2. It contains a DC power-supply (A), electromagnet (E), Gaussmeter (G), ohmmeter (V), computing unit (PC) and the block ~ F. 3. Experimental results and discussions

 graphene nanoparticles (nG) from Sky Spring Nanomaterials Inc., with granulation between 6 nm and 8 nm;  CI powder, produced by Merck, with diameters between 4.5 mm and 5.4 mm and iron content minimum of 97%;  silicone rubber (SR) type RTV-3325, from Bluestar-Silicones;  catalyst (C) type 60R, from Rhone-Poulenc;  silicone oil (SO) with viscosity 250 mPa and with ignition temperature 733 K [14];  textile fabric having the shape of square openings with the edge length 0.5 mm containing linen 30% and polyester 70%. The fabric’s thickness is 0.28 mm. Along the length’s fabric (L = 0.095 m) one mounts two parallel copper electrodes (80 mm  3 mm  0.10 mm) separated by a distance 0.060 m. One prepares a mixture containing SO (92% mass) and nG (2% mass) which is homogenized at 400 K for about 1800 s. At the end of heating process, the resulted mixture is cooled at room temperature (300 K) thus obtaining a viscous electro-conductive solution (SnG). Then the mixture is deposited on both sides of the textile fabric in a layer of 0.07  0.005 mm. The system composed from the textile fabric with copper electrodes and SnG constitutes the resistor body (Fig. 1). On both sides of the resistor body one deposits a layer of a mixture containing SR (95% vol.) and C (5% vol.) with a thickness of 0.5  0.005 mm. At the end of polymerization process (24 h), one obtains the coupling elements shown in Fig. 1. Further, one prepares a mixture which contains SR (60% vol.) and CI (40% vol.). The homogenized mixture is thermally treated in a microwave oven (MM 820 CPB – Medeea). For about 600 s, the mixture is kept at 450  50 K. Then, the mixture is cooled down at room temperature and is continuously homogenized with a paddle, at

Fig. 1. Magnetoresistor (ensemble configuration): 1, resistor body (80 mm  36 mm  0.42 mm); 2, coupling element (30 mm  50 mm  0.5 mm); 3, magnetoactive element (35 mm  60 mm  1.80 mm).

MR is fixed between the polar pieces 3 and 4 as shown in Fig. 2. At room temperature (300 K) and without applying a compression, we measure using the multimeter V, the resistance R of MR as a function of time t, for various values of intensity of the applied magnetic field H. The measured values for R, taken at time intervals of one second after applying H are shown in Fig. 3. We observe that DR=Dt has the following values:  0.022 V s–1, for H = 0 kA/m;  0.011 V s–1, for H = 15 kA/m; and  0, for H > 15 kA/m. In addition we can observe that the values of R are clearly separated with increasing of H. Thus, at t = 1 s, one obtains:       

R = 85.9V, R = 83.9V, R = 81.5V, R = 78.3V, R = 75.8V, R = 73.1V, R = 72.9V,

for H = 0kA/m; for H = 15kA/m; for H = 25kA/m; for H = 35kA/m; for H = 45kA/m; for H = 55kA/m; for H = 65kA/m.

With increasing the magnetic field intensity H in steps of 10 kA/ m, at t = 1 s, R decreases in steps from 2 to 2.7 V. However, increasing H from 55 kA/m to 65 kA/m, resistance R decreases only by 0.2 V. Further increase of H leads to a constant value of R and this is the range in which the conductivity of MRE-hybrid reaches a maximum value. For t = 1 s and 0  H(kA/m), from Fig. 3 one obtains R = R(H) as shown in Fig. 4 and one can observe that R decreases quasilinear for H  45 kA/m, while for H > 45 kA/m tends to constant values.

Fig. 2. Experimental device (ensemble configuration): A, DC power-supply (LabEc 3010); E, electromagnet (1, coil; 2, core); N and S magnetic poles; 3 and 4, polar pieces; M, magnetoresistor MR; 5, turntable; 6, Hall probe; G, Gauss meter (G-04); ~ magnetic field intensity vector; V, multimeter (UT 70B); ~ F, compression force; H, PC, computing unit with software for UT 70B.

Please cite this article in press as: I. Bica, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.102

G Model

JIEC-1832; No. of Pages 6 I. Bica et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

where F is the volume fraction of magnetizable phase, L, l, h, and V are the length, width, thickness, and respectively, the volume of MRE-hybrid, and Vp is the average volume of iron nanoparticles. Along the thickness h, the maximum number of dipoles in the chain is

86 84 82 80

R(Ω )

3

nd ¼

78

h 2n

(3)

Using Eqs. (2) and (3) one obtains the number of magnetic dipole chains

76 74

n 3F Ll ¼ nd 2p a2

nl ¼

72 70

H = 0 kA/m;

H = 15 kA/m;

H = 25 kA/m;

H = 35 kA/m;

H = 45 kA/m;

H = 55 kA/m;

Let’s consider that H is oriented along the Oz axis and the distance between the dipoles (z) inside the same chain, at a given ! moment t, is kept constant after applying H. If rm is the resistivity of MRE-hybrid at H = 0, then the electrical resistance of a single dipole chain is:

H = 65 kA/m.

68 0

1

2

3

4

5

6

7

8

(4) !

9 10

t(s) Fig. 3. Resistance R versus time t, for various values of magnetic field intensity H.

Therefore, the saturation effect of electrical conductivity in MREhybrid can be observed in the range 45 < H (kA/m) 65. Graphene nanoparticles have hydrophilic property and therefore they stick on the surface of iron particles, forming a nanometric layer [1] and forming also chains between them. In this way the electrical conductivity is instantaneously established and, during application of the magnetic field, its value remains constant. In magnetic field, iron particles instantaneously become magnetic dipoles, they follow the direction of magnetic field lines, therefore forming a network of parallel chains inside MRE-hybrid. Between two identical and neighboring dipoles a magnetic interaction arises, given by

Rl ¼ rm

nd  1 z 2pa2

(5)

Knowing Rl and nl, one obtains the electrical resistance of MREhybrid for n  1 R¼

Rl rm n z ¼ nl 6pFLl d

(6) !

When applying the magnetic field H, the thickness of MREHybrid is given by h ¼ nd z

(7)

and the resistance becomes R¼

rm 6pFLl

h

(8)

The magnetic force exerted in each chain is obtained from 0

Fm ¼ 2m0 M s a2 H

(1)

F ml ¼ nd F 0m ¼ m0 Ms ahH

(9) !

where ðm0 M s ÞFe ¼ 2:1T and a is the mean radius of particles. The distance between magnetic dipoles decreases under the influence of F 0m [7,11]. The number of magnetic dipoles is given by n¼F

V 3FLlh ¼ Vp 4pa3

(2)

and therefore, the magnetic force generated by H inside MREhybrid, is given by (10)

The elastic matrix exerts an opposite force to Fm, given by F el ¼ kðh  h0 Þ

(11)

where k is the elasticity constant, h and h0 are the thicknesses of MRE-hybrid for H 6¼ 0 and H = 0 respectively. At equilibrium, using Eqs. (10) and (11) one obtains

86 84

h¼

82

R(Ω)

3F Llh m Ms H 2p a 0

F m ¼ nl F ml ¼

h0 1 þ 23pFk

Ll a

m0 Ms H

(12)

80

Introducing Eq. (12) into Eq. (8) one obtains the electrical resistance in the following form:

78

R¼

76

where:

74

R0 1 þ 23pFk

R0 ¼

72 0

5 10 15 20 25 30 35 40 45 50 55 60 65

H(kA/m) Fig. 4. Resistance R versus magnetic field intensity H.

Ll a

m0 Ms H

rm h0 6pFLl

(13)

(14)

is the electrical resistance of MR at H = 0. From Eq. (13) one can observe that for H 6¼ 0 one obtains R < R0, in agreement with experimental data from Fig. 3. From the relation describing the resistance of linear resistor, and using the numerical values L = 0.095 m, l = 0.060 m, and

Please cite this article in press as: I. Bica, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.102

G Model

JIEC-1832; No. of Pages 6 I. Bica et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

4

88

h = 0.005 m one obtains electrical conductivity of MRE-hybrid according to

s¼

0:87 RðVÞ

84 80

(15)

76

R(Ω )

Using the form R = R(H) from Fig. 4 and introducing it in Eq. (15) one obtains the dependence s = s(H), as shown in Fig. 5. The curve s = s(H) in Fig. 5 shows three distinct regions, with different points where the conductivity s increases as a function of the magnetic field intensity H, namely:

72 68 64 60

 for 0  HðkA=mÞ  17 one obtains

56

Ds 1 ¼ 0:064ðVkAÞ ; DH

0

p = 0 kPa; p = 0.50 kPa; p = 5.17 kPa; p = 8.21 kPa; p = 14.57 kPa.

p = 2.50 kPa; p = 11.57 kPa;

1

8

2

3

4




7

9

10

Fig. 6. Resistance R versus time t, for various values of the compression pressure p of MR.

Ds 1 ¼ 0:17ðVkAÞ ; DH kA m

6

t(s)

 for 17  HðkA=mÞ  45:8 one obtains

 for 45:8  H

5

 65 one obtains

Ds 1 ¼ 0:052ðVkAÞ : DH Next, the magnetic field intensity is brought to zero and magnetoresistor MR is compressed. Using the ohmmeter V, one measures the resistance R of MR, at Dt = 1s after applying the compression force ~ F. Fig. 6 shows the measured values. One observes that the shape of R = R(t) in Fig. 6 is similar to that of R ¼ RðHÞ from Fig. 3. This suggests that the shape of R ¼ RðHÞ is due to the pressure induced by H in MRE-hybrid. For t = 1s, from R ¼ RðHÞ one obtains the function R ¼ Rð pÞ, as shown in Fig. 7. Considering MR as a linear resistor, using the equation for linear resistor and data from Fig. 7 one obtains the dependence s = s(p) as shown in Fig. 8 and which is characterized by the presence of three slopes. They correspond to three regions where the compression pressure of MRE-hybrid increases, namely Ds = 1.33 (VmkPa)1;  for 0  pðkPaÞ  3:6 one obtainsD p Ds = 0.91 (VmkPa)1;  for 3:6  pðkPaÞ  8:4 one obtainsD p Ds = 0.33 (VmkPa)1.  for 8:4  pðkPaÞ  14:4 one obtainsD p

By comparing Figs. 5 and 8 one observes that the shape of s = s(H) and s = s(p) are different. The difference is due to the effect which leads to modification of the conductivity s of

MRE-hybrid. Under application of force ~ F (Fig. 2), the thickness of MRE-hybrid decreases. When the force ~ F is applied, MRE-hybrid reacts with the elastic force F el ¼ kðh  h0 Þ or p ¼ 

k ðh  h0 Þ Ll

(16)

From Eq. (16) one obtains:   p Ll h ¼ h0 1  k h0 Inserting Eq. obtains:  rh0 Ll 1 R¼ h0 Ll

(17)

(10) into the equation of linear resistor R, one  p k

(18)

Eqs. (13) and (18) have the same meaning, therefore from their equality one obtains the elasticity constant k k¼

Ll p 4

(19)

which for L = 0.09m, l = 0.03m,and h = 0.05m, becomes: 10

3

kðN=mÞ ¼ 1:14 pðkPaÞ

(20)

87 84

36

81

35

78

R(Ω)

σ (1/Ω m)

37

34

75 72

33

69

32

66 63

31 0

5 10 15 20 25 30 35 40 45 50 55 60 65

H(kA/m) Fig. 5. Conductivity s versus magnetic field intensity H.

0

2

4

6

8

10

12

p(kPa) Fig. 7. Resistance R versus compression pressure p.

Please cite this article in press as: I. Bica, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.102

14

G Model

JIEC-1832; No. of Pages 6 I. Bica et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

5

44

4

3 10- x k(N/m)

42

σ (1/Ω m)

40 38 36 34

3 2 1 0

32 0

2

4

6

8

10

12

14

0

10

20

3

H(k 40 A/m )

p(kPa)

2

30

50

1 60

0

4

5

a) P k p(

Fig. 8. Conductivity s versus compression pressure p. Fig. 10. Elasticity constant k versus magnetic field intensity H and compression pressure p.

The values of H and p for which the resistance R of MR has the same values are shown in Fig. 9, from which one observes that for      

When L = 0.095 m, l = 0.05 m, and h0 = 0.005 m, for H and p corresponding to the same R in Fig. 9 and from Eq. (19) one obtains k = k(H, p), as shown in Fig. 10. One can observe from Fig. 10 that the value of elasticity constant can be fixed magnetically, by choosing an appropriate value for magnetic field intensity H, corresponding to compression pressure p.

H = 0 kA/m and p = 0 kPa one obtains R = 85.7 V; H = 19 kA/m and p = 0.6 kPa one obtains R = 83 V; H = 30 kA/m and p = 1.25 kPa one obtains R = 80 V; H = 38kA/m and p = 1.8 kPa one obtains R = 78 V; H = 47kA/m and p = 2.80 kPa one obtains R = 76 V; H = 60kA/m and p = 3.8 kPa one obtains R = 73 V.

From these data we conclude that for fixed R it is necessary either an applied magnetic field of intensity H, either a compression pressure p. Therefore, using data from Fig. 9, one can obtains information regarding magnetic pressure (pmag), induced by H inside MRE-hybrid. For example,  R = 74V corresponds to H = 48kA/m and to p = pmag = 2.8kPa;  R = 80V corresponds to H = 30kA/m and to p = pmag = 1.2kPa;  R = 84V corresponds to H = 14kA/m and to p = pmag = 0.3kPa.

86 84

R(Ω)

82 80 78 76 74

We have fabricated an electro-conductive MRE-hybrid and measured separately the electrical resistance of the MRE-hybrid in a transverse magnetic field ð0  HðkA=mÞ  65Þ and respectively, under the influence of the compression pressure (p  14.4 kPa). The electrical conductivity of MRE-hybrid depends on the intensity of the applied magnetic field and respectively on the compression pressure. It increases with increasing magnetic field intensity or compression pressure and it is constant in time. Using the dipolar approximation and considering a perfectly elastic MRE-hybrid, we have developed a theoretical model which explains the effects of the applied magnetic field and of compression pressure on the electrical conductivity of MREhybrid, respectively. We have shown that to an applied magnetic field corresponds a compression pressure. For the same values of the electrical conductivity of MRE-hybrid we determine the dependence between resistance, magnetic field intensity and compression pressure, and accordingly between elasticity constant, magnetic field intensity and compression pressure. Knowing these types of dependences one can use MRE-hybrid for various applications in civil and industrial constructions or in industry, such as vibration dampers or mechanical shock attenuators.

3 0 10 20 30

p( kP a)

72

4

4. Conclusions

2 40

H( k A/m

1 50

60

70

0

Fig. 9. Resistance R versus compression pressure p and magnetic field intensity H.

References [1] [2] [3] [4] [5] [6] [7]

Y.D. Liu, H.J. Choi, Polymer Intern. 62 (2013) 147–151. G. Liao, X. Gong, S. Xuan, Ind. Eng. Chem. Res. 52 (2013) 8445–8453. X. Gong, G. Liao, S. Xuan, Appl. Phys. Lett. 100 (2012) 211909–211911. I. Bica, M. Balasoiu, A.I. Kuklin, Solid State Phenom. 190 (2012) 645–648. O.V. Stolbov, Y.L. Raikher, M. Balasoiu, Soft Matter 7 (2011) 8484–8487. I. Bica, Y.D. Liu, H.J. Choi, Colloid Polym. Sci. 290 (2012) 1115–1122. I. Bica, J. Ind. Eng. Chem. 18 (2012) 483–486.

Please cite this article in press as: I. Bica, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.102

G Model

JIEC-1832; No. of Pages 6 6

I. Bica et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx

[8] G.J. Liao, X.L. Gong, S.H. Xuan, C.J. Kang, L.H. Zong, J. Intell. Matter. Syst. Struct. 23 (2012) 25–33. [9] W. Li, X. Zhang, H. Du, J. Intell. Mater. Syst. Struct. 23 (2012) 1041–1048. [10] I. Bica, Mater. Sci. Eng. B 166 (2010) 94–98. [11] I. Bica, J. Ind. Eng. Chem. 17 (2011) 83–89. [12] I. Bica, J. Ind. Eng. Chem. 15 (2009) 773–776.

[13] D.R. Cooper, B. D’Anjou, N. Ghattamanemi, B. Harack, M. Hilke, A. Horth, N. Majlis, M. Massicotte, L. Vandsburger, E. Whiteway, V. Yu, ISRN Condens. Matter Phys. (2012) 501686–501742. [14] Silicone Oil: Chemical and Physical data, Merck Chemicals, 2012, Web address: www.powerchemical.net. [15] W.L. Zhang, H.L. Choi, J. Appl. Phys. 111 (2012), 07E724-1-L 07E724-3.

Please cite this article in press as: I. Bica, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.102