THROUGH MAGNETORHEOLOGICAL SUSPENSIONS ...THROUGH MAGNETORHEOLOGICAL SUSPENSIONS BASED FILMS I....

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EFFECTS OF MAGNETIC FIELD ON THE LIGHT TRANSMITTANCETHROUGH MAGNETORHEOLOGICAL SUSPENSIONS BASED FILMS

I. BICA1, E. M. ANITAS2,3,∗

1West University of Timisoara, Timisoara, Romania,E-mail:

2“Horia Hulubei” National R&D Institute for Physics and Nuclear Engineering,RO-077125, Magurele-Bucharest, Romania

3Joint Institute for Nuclear Research, Dubna 141980, Russian FederationCorresponding author∗:

Received January 19, 2019

Abstract. Magnetorheological suspensions (MRS) are prepared using siliconeoil and various volume concentrations of carbonyl iron (CI) microparticles. The ob-tained MRS are deposited on a non-magnetic transparent thin film support. We buildan experimental setup and show that light transmission through films is sensibly influ-enced by the concentration of the magnetizable phase and by the intensity of an externalmagnetic field. This property can be used in designing various clutches, dampers, sen-sors and electronic circuit elements, or in fabrication of magnetically controlled opticaldevices which require low values of magnetic field intensity.

Key words: Transmittance, illuminance, magnetorheological suspension,carbonyl iron, silicone oil.

1. INTRODUCTION

Magnetorheological suspensions (MRS) consist from a liquid matrix in whichare dispersed ferro/ferri-microparticles. Various studies, such as optical microscopyshow that in the presence of a magnetic field the magnetizable phase form aggregateswhose strength depend on the type of particles and on magnetic field intensity [1–3].Therefore, their physical characteristics can be drastically changed, and this propertyis widely used for various technical and industrial applications, such as in fabricationof magnetically controlled clutches [3], vibration dampers and seismic shocks [4, 5],magnetic field sensors [6], passive circuit elements [7], etc.

Investigations concerning particle aggregation in MRS, of the defects whichappear inside magnetic dipole chains, of the dipole-dipole interactions, and of mag-netic interactions between dipole chains are mainly performed by using optical me-thods [8–26]. The average length of magnetic-dipole chains, the shape of the par-ticle forming the dipole or aggregation processes are often investigated by opticalvideo-microscopy, scattering dichroism [8] or small-angle light scattering [15]. Otherwidely employed methods to study the formation of dipole structures aligned along

Romanian Journal of Physics 64, 604 (2019)

Article no. 604 I. Bica, E. M. Anitas 2

magnetic field lines inside the liquid matrix, their stability and kinematics in a rotat-ing and pulsed magnetic field include optical anisotropy, birefringence, dichroism orlaser video-microscopy.

Light transmission is a very suitable method also for investigating the structuralproperties of magnetic fluids, and cluster formation of nanoparticles can be studiedby changing the transmittance of monochromatic radiation through a liquid film inthe presence of a magnetic field. Generally, small-angle scattering techniques (light,X-rays or neutrons), are very suitable to study the shape and size of clusters, as wellas to determine the fractal dimensions and the shape of basic units composing theclusters [27]. Structural modifications of the clusters formed in the liquid matrix areused for fabrication of various devices such as optical switches and modulators [19–21] or thermal sensors [24].

Experimental setups which use optical methods to study the properties of fluidactive magnetic materials requires a monochromatic light incident to the measuringcell and are mainly specialized on studies concerning the statistics of MRS particlesor on magnetic fluids. For such purposes, the studied cells consist from a magneticfluids situated between two transparent plates, and a light transducer [8, 9, 15, 18,19, 28, 29]. However, the advantage of using MRS over magnetic fluids in variousapplications, relies on the ability of MRS to display remarkable magnetic propertiesat small values of magnetic field intensities [30].

In this work we study the transmission of white light through MRS films basedon silicone oil (SO) and various volume concentrations of carbonyl iron (CI) mi-croparticles. We manufacture an experimental setup which allows us to reveal thephysical mechanisms leading to modification of light transmission through MRSfilms. The setup consists of a digital microscope, a generator of low-intensity mag-netic fields and a luxmeter, used as a transducer. It generates white light and a mag-netic field of constant flux, it measures the illuminance produced by the light passingthrough the MRS film, photographs and records the movements of the dipoles. Weshow that the transmission of white light through MRS films is sensibly influencedby the magnetic field intensity and by the volume fraction of CI microparticles.

2. MATERIALS AND METHODS

The materials used for fabrication of MRS-based films (Fig. 1) are: (a) Car-bonyl iron (CI) powder, C-3518-type, with diameters between 4.5 and 5.4 µm andiron content of min. 97 %, and a density of 7.86 g/mL at 298 K. Elemental ironis produced by reduction of pentacarbonyl; (b) Silicone oil (SO), MS100 type withviscosity η0 = 100 cSt × s, density 0.97 g/cm3 at 298 K and flash point tp > 583 K;(c) Circular transparent cassette lid with a diameter of 40 mm.

The fabrication process of MRS-based films is based on two main steps. First,

(c) RJP64(Nos. 7-8), ID 604-1 (2019) v.2.2r20190928 *2019.10.2#3caf435a

3 Transmittance through MRS-based films Article no. 604

Fig. 1 – Left side - Circular transparent cassette lids. Right side - Thin film of MRS (ΦCI = 10 %)with a thickness h = 312 µm deposited on the cassette lid.

three samples of MRS are prepared with various volume fractions of CI microparti-cles ΦCI (1 %, 5 % and 10 %) and homogenized at 420 K for about 300 s, until thetemperature of the mixture reaches 297 K. Second, a volume of 0.4 cm3 is depositedon the 40 mm diameter circular transparent cassette lid (Fig. 1). The height of theMRS is fixed at 312 µm.

Figure 2 shows the overall configuration of the experimental setup used to studythe influence of magnetic field on the transmittance of white light through the MRSfilms. The setup consists from a toroidal coil connected to a source of continuouscurrent, a digital microscope connected to a computing unit, and a luxmeter. Theheight of the toroidal coil is 40 mm, inner and outer diameters are 50 mm, and res-pectively 140 mm. The MRS-based film is fixed inside the coil on the silicone rubbersheath as shown in Fig. 3. The digital microscope and luxmeter probe are fixed on thecoil. The microscope comes with a white light source. The accompanying softwareallows to take photos of MRS, view and store them in the computing unit to whichit is connected. The software also allows recording of the kinematics of particle ag-glomeration in the presence of a magnetic field. The luxmeter allows measurementsin the range 0.1 ÷ 50000 lx, with a precision of ±5 %, and is optically isolated fromthe environment. The hall probe of the gaussmeter allows monitoring of the mag-netic field intensity applied on the MRS film. The silicone rubber sheaths fixes thedistances between the microscope and the film, and respectively between the filmand the luxmeter probe.

3. EXPERIMENTAL RESULTS AND DISCUSSIONS

The influence of magnetic field and of the volume concentration of magneticphase on the transmittance of light through the MRS films is studied by using the ex-



Fig. 2 – Experimental setup. Left side: overall configuration, with 1 - MRS film, 2 - digital microscope,3 - computing unit, 4 - luxmeter, ~H - magnetic field intensity vector, h - MRS film thickness. Rightside: A - source of continuous current, B - measurement block, 1 - digital microscope, 2 - silicone

rubber sheath, 3 - toroidal coil, 4 - luxmeter probe, 5 - luxmeter, 6 - gaussmeter, C - computing unit.

Fig. 3 – Toroidal coil. Left side: 1 - body coil, 2 - silicone rubber sheath, 3 - MRS film, 4 - terminals forconnecting the coil to the DC source. Right side: ensemble view of the coil, with 1 - digital microscope,

2 - coil, 3 - silicone rubber sheath, 4 - luxmeter probe.



perimental setup shown in Fig. 2 (right). To this aim, three main steps are performed:First step concerns investigation of the distribution of magnetic field on the in-

ner radius of the toroidal coil. Figure 3 (left) shows that the radius of the investigatedfilm is R = 15 mm. The intensity of magnetic field is measured along the radius R,starting from the center of the film, in steps of 5 mm. The results are presented inFig. 4(a) and show that the differences between intensities H at various values of R,are negligible. Thus, we may consider that inside the toroidal coil, the variation ofmagnetic field intensity with the electric field intensity can be obtained by averagingthe values obtained in Fig. 4(a). The results are shown in Fig. 4(b), and further weshall refer to Hm as the magnetic field intensity inside the toroidal coil.

Second, visual effects inside MRS films in a magnetic field are investigated. Avolume of 0.4 cm3 of MRS is deposited on the transparent lid fixed in the center ofthe toroidal coil. The images captured by the digital microscope are then visualizedon the monitor of the computing unit, with and without magnetic field. The mostrepresentative images are presented in Fig. 5, and show that in the magnetic field areformed regions containing aggregates as well as transparent regions. By increasingthe magnetic field intensity, the height of the aggregates increases as well, and as aconsequence, the surface they cover on the support lid decreases. The incident whitelight, generated by the digital microscope, has a constant luminous flux. However,the emergent flux after light passes through the lid increases proportionally to theavailable area on the lid. Therefore the luxmeter situated behind the support lid,records the values of illuminance E, as a function of magnetic field intensity H .

Fig. 4 – (a) Magnetic field intensity as a function of electric field intensity, for the radial distancesRi, i = 0,1,2,3 from the center of the toroidal coil. (b) Average intensity of the magnetic field as a

function of electric field intensity.

Third, the illuminance E of the white light which passes through the transpar-ent lid with 0.4 cm3 of SO is measured, and the recorded values are shown graphi-cally (see Fig. 6). Then, on the support lid are deposited in turn 0.4 cm3 of MRS at



different concentrations Φ of the magnetizable phase. The illuminance is measuredfor the same values of the magnetic field intensity H (see also Fig. 6), and one cansee that it depends both on the magnetic field intensity and on the volume concentra-tion of magnetizable phase. The results show that in the absence of a magnetic field,addition of magnetic phase leads to a significant decrease of the illuminance, fromE0 = 660 lx at Φ = 0 %, to E0 = 48 lx at Φ = 10 %.

We consider that the illuminance measured by the luxmeter increases with mag-netic field intensity according to:

E(H) = αE0 +ηH, (1)

where E0 is the illuminance at H = 0, α is a dimensionless parameter whose valuedepends on the volume concentration ΦCI of CI microparticles, η is the slope of thefunctions E = E(H)ΦCI

(Fig. 6 - left side) and is a measure of the surface area oc-cupied by CI microparticles and the total area of the transparent support lid. Table 1summarizes the obtained values for α and η.

(a) H = 0 kA/m (E = 48 lx) (b)H = 12 kA/m (E = 104 lx) (c)H = 24 kA/m (E = 130 lx)

Fig. 5 – Microscopy images of MRS films for increasing magnetic field intensities.

Table 1Variation of parameters α and η with volume concentration ΦCI of CI microparticles, from Eq. (1).

ΦCI (%) α η (lx ·m/kA)0 1.000 0.001 0.661 2.605 0.121 4.0010 0.073 3.20

The data clearly show that both α and η are significantly influenced by thevolume fraction of the magnetizable phase.

For each MRS film one defines the transmission coefficient of white light, by:

β(%) =E(H)−E0

E0·100, (2)



where E(H) is the transmittance in the presence of the magnetic field. By usingEq. (2) together with experimental data from Fig. 6 - left side, one obtains the vari-ation β = β(H)ΦCI

(Fig. 6 - right side). As seen previously for the case of illumi-nance, the coefficient β is also significantly influenced by both H and Φ.

Fig. 6 – Left side - variation of illuminance E produced by the white light of the digital microscopeas a function of the intensity H of magnetic field, for fixed values of ΦCI . Dots - experimental data;Continuous line: theoretical model given by Eq. (1). Right side: Transmission coefficient of white lightas a function of magnetic field intensity for fixed values of ΦCI . Dots - experimental data; Continuous

line: theoretical model given by Eq. (2).

4. CONCLUSIONS

In this work we have obtained MRS base on SO and CI microparticles. Bydepositing a volume of 0.4 cm3 of MRS on a transparent support lid with a diameterof 40 mm one obtains MRS films with a thickness of 312 µm. In a constant mag-netic field are formed aggregates on the surface lid. As a consequence, the MRS filmthickness decreases, thus leading to an increased illuminance throughout the film.The same effect holds also when the magnetic field intensity is increased, since thethickness of the film decreases, and the luminous flux increases. Shortly after themagnetic field is removed, the MRS film return to its initial position and the illumi-nance tends to the initial values, before the magnetic field was applied.

By increasing the volume concentration of CI, the illuminance decreases at agiven value of magnetic field intensity. However, the transmission coefficient β ofwhite light through the film increases with magnetic field intensity as well as withvolume concentration of magnetic phase.

The obtained results can be used for fabrication of switches and optical mod-ulators. Also, the magnetostriction effect and addition of additives such as lead,gadolinium, aluminum or silica particles can be used for fabrication of compositeMRS films, with applications in the controlled transmission of various types of par-ticles beams, such as X-rays or neutrons in a magnetic field.



Acknowledgements. The results presented in this paper have been obtained in the framework ofa cooperation protocol between JINR-Russia and various universities and research institutes from Ro-mania and respectively from Romanian National Authority for Scientific Research, CNDI-UEFISCDI,project number PN-III-P1-1.2-PCCDI-2017-0871.

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