CONDUCTIVITY IN (HYBRID) MAGNETORHEOLOGICAL … · 2020. 7. 21. · v.2.2r20191120 *2020.6.24#d84f9fc9 MAGNETIC CONTROL OF LIGHT TRANSMISSION AND OF ELECTRICAL CONDUCTIVITY IN (HYBRID)

v.2.2r20191120 *2020.6.24#d84f9fc9

MAGNETIC CONTROL OF LIGHT TRANSMISSION AND OF ELECTRICALCONDUCTIVITY IN (HYBRID) MAGNETORHEOLOGICAL SUSPENSIONS

BASED ON BIOACTIVE COMPONENTS

I. BICA1, E. M. ANITAS2,3,a, L. M. E. AVERIS4

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

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

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

4University of Medicine and Pharmacy, Craiova, RomaniaE-mail:

Received March 18, 2020

Abstract. Bio-magnetic active suspensions and tissues are manufactured fromhoney, cotton fibers and various concentrations of carbonyl iron (ΦCI) microparticles.The obtained (h)MRSs composites are examined as magnetoactive materials for indus-trial and therapeutic applications. We propose a new experimental design, and showthat the light transmission through (h)MRSs and the electrical conductivity are sensi-bly influenced by the intensity H and gradient δ of an external magnetic field, as wellas by ΦCI. These effects make (h)MRSs versatile candidates in fabrication of techni-cal and medical devices and equipment which require a magnetic control of the lighttransmission and of the thermal transport of bioactive components. They can be usedfor various applications such as scaffolding biomaterials for tissue repair and regener-ation or in the quality control of honey crystallization and of its derivative products inindustrial processes.

Key words: Light transmittance, electrical conductivity, magnetorheologicalsuspensions, bioactive components.

1. INTRODUCTION

Bio-magnetic suspensions and tissues consist from a bioactive matrix in whichis dispersed a magnetizable phase and additives [1]. The matrix can be an organicliquid such as vegetable oil [2], honey (HB) [3, 4] etc., while the magnetizable phaseusually consists from carbonyl iron (CI) microparticles [2, 3]. Although there arenumerous applications of these types of materials such as in fabrication of structuredmagnetic circuits [5], electrical capacitors [6], magnetoresistors [7], in seismic pro-tection [8] or in adaptive tuned vibration absorbers [9], an important issue affectingthe physical performances of magnetorheological suspensions (MRSs) is the sedi-mentation of the magnetic phase.

Romanian Journal of Physics 65, 605 (2020)

Article no. 605 I. Bica, E. M. Anitas, L. M. E. Averis 2

In order to avoid this process, completely or partially, new research has shownthe possibility of using environmentally-friendly and low-costs additives, such asturmeric microparticles [3], cotton fabrics [4], cellulose fibers [10], γ-Fe2O3 or silse-quioxane nanoparticles [11, 12] etc. Thus, such materials can be used effectively invarious medical therapies by exploiting the healing properties of the matrix, of thedispersed phases together with an external magnetic and electric field.

The aim of this work is to synthesize a new class of bio-active magnetorhe-ological suspensions and to take advantage of a combined usage of the bioactivecomponents from bio-magnetic suspensions together with the usage of magnetic andelectric fields, so that to maximize the therapeutic effects of the obtained materials.Generally, improvements of these effects are achieved by eliminating the sedimen-tation process of the magnetizable phase, which leads to a more efficient selectiverelease of the required bio-active components. Here, we reveal key properties whichmakes the bio-suspensions useful for incorporation into various smart textiles withphase change materials [13], into soft robotics [14] or, generally, into various devicesfor increasing the overall comfort of human beings [3].

For this purpose we use HB as a matrix since it contains more that 300 bio-active components [15, 16] which can be used for various therapies, by a selectivetransport. In addition, in order to have a good response in the presence of an ex-ternal magnetic field as well as to avoid sedimentation processes, we use here CIas additives soaked in a cotton fiber tissue. Thus, by using a static magnetic fieldsuperimposed on an alternating electric field, specific bioactive components such asthose required to fight against various pathogens [17, 18] can be selected by using theabsorption characteristics of the alternating electric field [4]. To this aim, we makeuse of the ”optical window” effect of living tissues [19], by which light with wave-lengths between 650 and 1200 nm is allowed to penetrate enough deep through theskin so that, various useful photo-chemical reactions are initiated [20]. In this waythe mechanisms underlying the photocatalytic degradation of some antibiotics, suchas ciprofloxacin [21] or analgesics, such as antipyrine [22], from water systems byTiO2 photocatalysis, can be elucidated.

Here, the control of light transmission through the bio-suspensions and tissuesas well as the mass transport of the bioactive components is achieved by using apermanent magnet and a medium frequency electric field. In order to evaluate thetherapeutic properties of the synthesized bio-suspensions we investigate here twotypes of samples: suspensions based on HB and CI microparticles (MRSs), and ac-tive bio-magnetic tissues (hMRSs) consisting from MRSs soaked into a tissue ofcotton fibers. We show that very low volume fractions ΦCI of CI microparticles, thatis ΦCI = 1 vol.%, the transmission of white light increases up to 150 % in hMRSs,when the intensity of the external magnetic field increases up to Hmax = 46 kA/m.In addition, we show that the electrical conductivity for the same composition of

(c) RJP65(Nos. 5-6), ID 605-1 (2020) v.2.2r20191120 *2020.6.24#d84f9fc9

3 Magnetic control of light transmission and electrical conductivity in suspensions Article no. 605

hMRSs increases up to 20 %, at the same value of the magnetic field intensity. Thus,it is demonstrated that the light transmission and electrical conductivity of the synthe-sized bioactive materials can be controlled in an external magnetic field. We explainqualitatively the observed effects by using the theory of magnetic dipolar approxi-mation.

Generally, the obtained results can be used in fabrication of technical and med-ical devices and equipment aimed at the control quality of HB and its crystallizationin industrial processes, as well as for performing selective and targeted release ofvarious bioactive substances in the presence of a magnetic field. In the later case,it allows for performing specific photo-chemical reactions, useful for treatment ofvarious skin-related diseases, such as eczema, psoriasis, varicose, hives etc., withoutinvolving any chemically synthesized substance harmful for human body.

2. MATERIALS AND METHODS

The materials used for the synthesis of MRSs and hMRSs are the following:

• CI microparticles, in powder form, containing particles with diameters between4.5 and 5.4 µm. The Fe content is higher than 97 % and the mass density of CIis ρCI = 7.86 g/cm3;

• HB with density of 1.40 g/cm3 and viscosity η0 = 12 Pa×s at 297 K;

• Medical dressing (MD) consisting of cotton fiber, with granulation of 30 g/cm2.

The main steps followed in the fabrication of MRSs and hMRSs are the fol-lowing:

1. One prepares two different mixtures S1 and S2 of CI and HB at about 330 Kfor about 300 s until one obtains a dark coloured suspension. The volumes andvolume fractions of each component are listed in Tab. 1. Each mixture S1 and S2is used further to prepare MRSs and hMRSs.

2. Four disks are cut from a projector foil (TS) and respectively from MD, as shownin Fig. 1(a) and (b) with diameters of 40 mm, and respectively 30 mm. On eachof the TS disks are fixed two parallel copper electrodes with a diameter of de =0.28 mm and situated at a distance L = 5 mm, and are called support disks. Ontop of these support disks are superimposed MD disk, as shown in Fig. 1(c).

3. One pours into a mold a mixture of silicone rubber with catalyst. After polymer-ization one obtains the body shown in Fig. 2(a). The body is then mounted insidea toroidal coil together with the support disk, which is fixed at one opening.

4. From each sample S1 and S2 one extracts a volume of 0.70 cm3 with the help ofa syringe. This volume is then deposited on the support disk inside the silicone



Table 1

Composition of samples S1 and S2 used for synthesizing MRS and hMRS. VHP and VCI are the

volumes of HB and respectively of CI. ΦHB and ΦCI are the volume fractions of HB and respectively

of CI.

Sample VHB (cm3) VCI (cm3) ΦHB (vol.%) ΦCI (vol.%)S1 99.0 1.0 99.0 1.0S2 99.9 0.1 99.9 0.1

(a) (b) (c)

Fig. 1 – Photos of: (a) Transparent disk; Cotton fabric disk with thickness of 0.48 mm; (c) Configurationof cotton fibers (1), copper electrodes (2), and support-disks (3).

rubber body (Fig. 2(b)). Thus one obtains two MRSs with a diameter of 30 mm,thickness of about 1 mm, and composition given by S1, and respectively by S2.

5. On each of the support disks is deposited another volume of 0.7 cm3 of S1 andrespectively S2, together with the MD disk. At the end of this procedure oneobtains two hMRSs with the same dimensions as of MRSs obtained in previousstep, and with the same composition given by S1, and respectively by S2.

A photo of the experimental setup used for investigating the light transmissionand electrical conductivity of MRSs and hMRSs in a magnetic field is shown inFig. 3(a), while the overall configuration is shown in Fig. 3(b).

The setup consists from a toroidal coil electrically connected to a power source.Inside the coil are fixed by turn the disks with MRSs, and respectively with hMRSsby means of the silicone rubber sleeves. Also, by using the same sleeves, a digitalmicroscope and a luxmeter probe are fixed to the coil. The electrical conductors ofthe disks with MRSs and hMRSs pass thorough the sleeves and are connected to anRLC bridge.

3. EXPERIMENTAL RESULTS AND DISCUSSION

The digital microscope generates white light which is incident to the (h)MRSsdisks. The microscope is connected to a computing unit with 4 GB of RAM, con-taining a preinstalled software with which (h)MRSs can be visualized and stored on



(a) (b)

Fig. 2 – (a) Silicone rubber body. (b) Silicone rubber body together with the magnetic field generatorcoil. 1 - toroidal coil, 2 - silicone rubber body (the same as in a), 3 - bioactive magnetic suspen-sion/tissue on a transparent support.

(a) (b)

Fig. 3 – (Color online). Experimental setup: (a) Photo, 1 - toroidal coil, 2 - digital microscope, 3 -probe, 4 - luxmeter, 5 - Gaussmeter, 6 - computing unit (CU); (b) Overall configuration: WLG - digitalmicroscope, CU - computing unit, TC - toroidal coil, DC - continuous current source, LX - luxmeter,LM - luxmeter probe, MT - (h)MRSs, R - inner radius of the toroidal coil, Br - RLC bridge, Oxy -Cartesian coordinate system, δ - magnetic field intensity gradient vector, H magnetic field intensityvector.

a magnetic disk. Figure 4 shows photos of hMRSs without and with an externalmagnetic field at H = 25 kA/m. It is clear that the light transmission is greatly de-termined whether the (h)MRSs is under the influence of a magnetic field. Without amagnetic field (Fig. 4(a)), CI microparticles are randomly distributed throughout the(h)MRSs, thus reducing from the illuminance passing through the disks. However,when a magnetic field is applied, CI microparticles form chain-like aggregates ori-ented along the magnetic field lines, thus allowing the illuminance to increase. Forthe investigated (h)MRSs, when the magnetic field is turned off, the CI return to theirinitial state characterized by a random distribution on the disk’s surface.



(a) 3 mm(b)

3 mm

Fig. 4 – (Color online). Digital microscopy of hMRSs without (a) and with (b) magnetic field (H =25 kA/m). Without a magnetic field, CI microparticles are randomly distributed, while in a magneticfield, they form chain-like aggregates oriented along the field lines. The semitransparent rectangulargrids with larger edge size of about 3 mm is the cotton fiber.

Investigations concerning the influence of magnetic field on the electrical con-ductivity and light transmission through (h)MRSs using white light is performed inthree main steps.

3.1. INFLUENCE OF MAGNETIC FIELD IN THE PROXIMITY OF (H)MRSS

By using the Gaussmeter probe one measures along Ox and Oy axis (see Fig. 3(b))the magnetic field intensity H generated by the toroidal coil, when the current inten-sity through the coil is I = 1.22 Adc. Along the coil diameter and the Oy axis, H isnot constant. At R = 15 nm from the coil center, H increases by about 9.09 %, andthus a gradient δ of magnetic field is established along Oy axis. Variation of δ withintensity I is shown in Fig. 5 (black dots). However, along the thickness d ' 1 mmof (h)MRSs (Ox axis in Fig. 3(b)), H is constant, and its values depend on intensityI , as shown in Fig. 5 (red dots).

3.2. ILLUMINANCE PRODUCED BY PASSING WHITE LIGHT THROUGH TS, MD ANDSUPPORT DISKS

The transparent disk TS from Fig. 1(a) plays the role of support for both MRSand hMRS. In order to reveal the influence of disks without (h)MRSs on the illu-minance, we proceed as follows: first, one measures the illuminance produced bythe microscope source of white light, without the presence of disks. The obtainedvalue is E0 = 782 lx. Second, the distances between light sources and disk, as wellas the distance between disk and luxmeter probe are fixed. Finally, we introduce byturn, inside the toroidal coil, first TS and then MD disks. The recorded values ofilluminances are E1 = 742 lx, and respectively E2 = 328 lx.



0.0 0.3 0.6 0.9 1.20

10

20

30

40

50

(kA/m2) H (kA/m)

I, (Adc)

Fig. 5 – (Color online). Variation of magnetic field intensity (H) and gradient δ with intensity I of theelectrical current through the toroidal coil.

3.3. ILLUMINANCE AND RESISTANCE OF (H)MRSS IN A MAGNETIC FIELD

The influence of magnetic field on light transmission and electrical conducti-vity of (h)MRSs is investigated as follows: first, one fixes by turn, transparent diskswith MRSs, and respectively with hMRSs in the center of the toroidal coil. For fixedvalues I of the electric current passing through the coil, one measures every secondthe illuminance E and resistanceR for a total time of 300 s.

The obtained values are presented in Figs. 6 and 7 (discrete dots), and show thatMRSs and hMRSs are translucent, and respectively, electrically conductive. Notethat in both figures, E, and respectively R are represented as a function of intensityI passing through the coil. In this way we include the effects of both magnetic fieldintensity H and its gradient δ, since they also depend on I , as shown in Fig. 5. Inparticular, for I = 0, i.e. H = 0 and δ = 0 in Fig. 5 one can observe that both thelight transmission and electrical conductivity of (h)MRSs are sensibly influenced bythe volume fraction ΦCI of CI microparticles.

While in the case of MRSs, E increases by a factor of about 1.25, when de-creasing ΦCI from 1 vol.% to 0.1 vol.%, in the case of hMRSs the increase is aboutten times larger. Note from Fig. 5 that at H 6= 0 and δ 6= 0, i.e. I 6= 0, the magneticfield has a more pronounced increase with I , as compared with the gradient. Thisshows that at I 6= 0, both H and δ contribute to E and respectively to R. However,their relative contribution changes with increasing I: while at I ' 0,E andR have anapproximate equal contribution, at I ' 1.2 Adc, H has a contribution about 4 timeslarger than that of δ. For fixed values of ΦCI, E of MRSs increases by a factor ofmaxim 1.32 when decreasing ΦCI from 1 vol.% to 0.1 vol.%, and which correspondsto I ' 1.2 Adc, while for hMRSs, E still increases by a factor of about 10.



0.0 0.2 0.4 0.6 0.8 1.0 1.20

100

200

300

400

MRS with S1; hMRS with S1; MRS with S2; hMRS with S2.

E, (l

x)

I, (Adc)

Fig. 6 – (Color online). Variation of illuminance E for MRSs and hMRSs with intensity I of theelectrical current through the toroidal coil. S1 contains ΦCI = 1. vol.% CI, and S2 contains ΦCI =0.1 vol.% CI (see Tab. 1). Dots - experimental data, continuous lines - theoretical fit using Eq. (17).Note that hMRSs allows less light to pass than MRSs due to the presence of the MD, which plays therole of an absorbent.

0.0 0.2 0.4 0.6 0.8 1.0 1.20.0

0.8

1.6

2.4

MRSs with S1; MRSs with S2; hMRSs with S1; hMRSs with S2.

I, (Adc)

R, (

M)

Fig. 7 – (Color online). Variation of resistance R for MRSs and hMRSs with intensity I of the electricalcurrent through the toroidal coil. Dots - experimental data, continuous lines - theoretical fit usingEq. (16).

A similar behaviour can be seen also for the resistance of MRSs and hMRSsshown in Fig. 7, where at I = 0 a decrease of ΦCI from 1 vol.% to 0.1 vol.% leadsto a decrease of resistance by a factor of about 1.54 for MRSs, and by a factor of 2.1for hMRSs. At constant ΦCI, R has a quasi-constant behaviour up to I ' 0.85 Adc

for both MRSs and hMRSs. At higher values, R starts to decrease more pronounced.This behaviour can be explained also through the interplay between various contri-butions of H and δ, when increasing the current intensity I through the coil.



0.0 0.2 0.4 0.6 0.8 1.0 1.20

2

4

6

8

10

12, (

%)

S1

S2

(a) I, (Adc)0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

25

50

75

100

125

150

, (%

)

(b)

S1

S2

I, (Adc)

Fig. 8 – (Color online). Variation of relative illuminance α (Eq. (1)) for MRSs (a) and hMRSs (b) withintensity I of the electrical current through the toroidal coil.

3.4. DATA ANALYSIS AND INTERPRETATION

The results obtained in Fig. 6 clearly shows that the light emitted by the trans-mitter, and recorded by the luxmeter probe, depends on the structure of the (h)MRSs,through the value of volume fraction ΦCI, as well as on the external magnetic field.For a quantitative characterization of the translucence of (h)MRSs, we introduce therelative illuminance through:

α(%) =

(E

E0−1

)×100, (1)

whereE0 is the illuminance in the absence of magnetic field, andE is the illuminancein the presence of a magnetic field. By using the values of illuminances from Fig. 6(a)and (b) in Eq. (1) one obtains the relative illuminance α(%) as a function of intensityI for MRSs and hMRSs, as shown in Fig. 8(a) and (b). The results show that therelative illuminance depends on ΦCI, and is sensibly influence by the composition ofthe biomaterial. The same figure shows that α also increases with intensity I . ForMRSs, α decreases by a factor of about 1.4 when ΦCI is increased from 0.1 vol.% to1 vol.%. However, in the case of hMRSs (Fig. 8(b)), α increases by a factor of about10 at I = 1.2 Adc. This effect arise since for hMRSs,E0' 182 lx at ΦCI = 0.1 vol.%,which is much higher as compared to E0 ' 17 lx at ΦCI = 1 vol.%.

As in the case of illuminance, in order to compare the variation of R withintensity I for MRSs and hMRSs, we introduce the relative resistance, defined by:

β(%) =

(RR0−1

)×100, (2)

where R0 is the resistance without a magnetic field, and R is the resistance in thepresence of the magnetic field.

The quantitiesR andR0 from Fig. 7 are introduced in Eq. (2), and one obtains



0.0 0.2 0.4 0.6 0.8 1.0 1.2-30

-20

-10

0, (

%)

(a)

S1

S2

I, (Adc)0.0 0.2 0.4 0.6 0.8 1.0 1.2

-20

-15

-10

-5

0

, (%

) S1

S2

(b) I, (Adc)

Fig. 9 – (Color online). Variation of relative resistance β (Eq. (2)) for MRSs (a) and hMRSs (b) withintensity I of the electrical current through the toroidal coil.

the variation of relative resistance β with intensity I of the electric current throughthe coil, as shown in Fig. 9. The results show that the electrical resistance of bioma-terials decreases in the magnetic field produced by the coil. The quantity β increasesin absolute value with increasing the volume fraction ΦCI, and respectively, withincreasing the intensity I .

3.5. THEORETICAL MODELS FOR RESISTANCE AND ILLUMINANCE

The results presented in Figs. 8 and 9 suggest that important correlations arisebetween the optical and electrical phenomena occurring in these materials. In orderto characterize them quantitatively, we make several assumptions: first, CI micropar-ticles are identical, second, and their size is equal to the average diameter dm = 5 µm,and third, in the presence of a magnetic field, CI microparticles are transformed intomagnetic dipoles. Therefore the magnetic moment of the microparticles, projectedalong Or-axis attached to the radiusR (see Fig. 8) can be calculated according to [23]:

m≡ π

6χd3mH = 0.5πd3mH, (3)

where χ is the initial magnetic susceptibility, and H is the magnetic field intensity.The quantity χ can be obtained from [23]:

χ= 3µCI−µHB

µCI +µHB' 3, (4)

when µCI µHB. Here, µCI and µHB are the magnetic permeabilities of CI mi-croparticles, and respectively of HB, or HB soaked with cotton fibers.

On the surface of (h)MRSs, the magnetic field gradient vector δ has a radialdistribution, as shown in Fig. 10. In the presence of a magnetic field gradient arisemagnetic interactions between two neighboring magnetic dipoles. Their intensity



Fig. 10 – (Color online). A model of (h)MRSs in a magnetic field: (a) Front view. (b) Cross-section. R- radius, δ - magnetic field gradient vector. H - magnetic field intensity vector.

along the radius R, is given by:

Fm ≡−µ0µHBmδ =−0.5πµ0µHBd3mHδ, (5)

where µ0 is the vacuum magnetic permeability. The resistance force arising from theembedding matrix is given by [23]:

Fη = 3πηdmv, (6)

where η is the apparent viscosity of (h)MRSs, and v is the velocity vector. In amagnetic field, when the two forces are at equilibrium, inside the matrix are formedmagnetic dipole chains, as shown in Fig. 4. The ends of these chains are attached tothe copper electrodes used in the second step of Sec. II. B for preparation of activebiosuspensions and tissues (see also Fig. 1c).

Therefore, a contact electrical resistance is established between the dipolesfrom the chain. In order to obtain a mathematical expression of this resistance weassimilate the resistor to a linear one. Thus, by using the formula which gives the ex-pression for the contact electrical resistance between two magnetic dipoles, we canwrite, the well know expression:

Rr =4r

σ0d2m, (7)

where r is the distances between the center of masses of dipoles, and σ0 is the elec-trical conductivity of MRS/hMRSs without magnetic field.

By using the equilibrium condition for the forces Fm and Fη, projected on



Or-axis (see Fig. 10) one obtains the equation of motion of the dipoles, that is:

3πηdr

dt+ 0.5πµ0µHBd

2mHδ = 0. (8)

At the initial moment when the magnetic field is applied, the distance between thecenter of masses of the magnetic dipoles is [24]:

r = r0 =dm

3√

ΦCI=

23.02 µm for S1

50.00 µm for S2.(9)

However, at t > 0, for both S1 and S2, the distance between the center-of-masses ofthe dipoles is r, and therefore Eq. (8) can be rewritten as:

r = r0

(1− µ0µHBd

2mHδt

6ηr0

). (10)

Along ”Or” direction the maximum number of contact electrical resistances is:

nr =R

2dm,when nr 1. (11)

Therefore, the resistance of a dipole chain of lengthR, is obtained from Eqs. (7), (10)and (11), and it has the expression:

Rr ≡ nrRr =2R

σ0d3m

(1− µ0µHBd

2mHδt

6ηr0

). (12)

Along the thickness d of (h)MRSs, the number of magnetic dipoles can beapproximated by:

n≡ ΦCIV

Vp=

6ΦCIR2d

πd3m, (13)

where V is the volume of (h)MRSs, and Vp is the volume of the average dipole. Then,the number of dipole chains from the (h)MRSs volume can be approximated by:

nl =n

nr=

6ΦCIRd

πd2m, (14)

and therefore the electrical resistance along R is:

R≡ RRnl

=R0

(1− µ0µHBd

2mHδt

6ηr0

), (15)

whereR0 = πr0/(3σ0dmΦCId) is the electrical resistance in the absence of the mag-netic field (see also Eq. (2)).

Equation (15) shows that for fixed values of time t, the resistance R dependson the product between magnetic field intensity H and its gradients δ. We also sawin Fig. 5 that both H and δ depend on the intensity I of the electric current passing



through the coil. These observations suggest us that Eq. (15) can be rewritten as:

R=R0

(1−kI2

), (16)

where k is a coupling constant, with units of A−2. Thus, we can use this relation tofit the experimental data for the resistance R. Figure 7 shows the corresponding fitsas continuous lines for (h)MRSs, with S1 and S2. The values of the parameters R0,E0 and k are listed in Tab. 2, and respectively in Tab. 3. The same figure shows thatthe approximation between the theoretical model and experimental data is very good.This suggests that the proposed model describes well the underlying current flow in(h)MRSs.

In the presence of a magnetic field, the ordering of the magnetisable phasein the form of chain-like aggregates, and their displacements towards the edges ofthe toroidal coil (Fig. 10), together with the results form Figs. 6 and 7 suggest thatthe relationship between the emergent light from (h)MRSs and the magnetic field issimilar to the one characterizing the electrical resistance. Thus, we can write:

E = E0 +(1 +kI2

), (17)

where E0 is the illuminance produced without the presence of magnetic field. Thecorresponding fits are shown also by continuous lines in Fig. 6, where we can seethat, as in the case of resistance, the agreement between the experimental data and thetheoretical model is very good. This suggests that the proposed model can adequatelycharacterize the light-diffusion processes occurring in (h)MRSs.

Table 2

The parameters used in Eqs. (16) and (17) to fit experimental data in Fig. 7, and respectively in Fig. 6

for MRSs.

Sample R0 ( MΩ ) E0 (lx) k (A−2)S1 0.86 325 0.052S2 0.56 410 0.075

Table 3

The parameters used in Eqs. (16) and (17) to fit experimental data in Fig. 7, and respectively in Fig. 6

for hMRSs.

Sample R0 ( MΩ ) E0 (lx) k (A−2)S1 2.30 30 0.145S2 1.10 189 0.080



4. CONCLUSIONS

In this work we have successfully synthesized two types of bioactive mem-branes. First type is based on MRSs consisting of HB and CI microparticles, and thesecond one is based on hMRSs consisting of HB and CI microparticles soaked intoa cotton fabric tissue. The obtained membranes have a thickness of about 1 mm andlateral dimensions of about 30 mm, and are used as magnetoactive materials betweenthe poles of an electromagnet.

We build and describe an experimental setup for measuring the effect of anexternal magnetic field generated by the toroidal coil of the electromagnet, on theresistance and illuminance of (h)MRSs at various concentrations of CI microparticlesΦCI.

The results show the formation inside (h)MRSs of magnetic dipoles in the pre-sence of the magnetic field, which are arranged in the form of chain-like aggregates.The effect of the magnetic field on the electrical resistance and light transmissionthrough (h)MRSs in white-light is explained by the decrease of the distance betweenmagnetic dipoles with increasing magnetic field intensity. This, in turn, leads to adecrease of the electrical resistance (Fig. 7) and to an increase of light transmission(Fig. 6). We explain the results in the framework of dipolar approximation and showthat they can be successfully applied in fabrication of various bio-medical and in-dustrial equipment devices where a selective and targeted release of bio-active com-ponents is required, in the presence of an external magnetic field, or for the qualitycontrol and crystallization of HB and of its derivatives in industrial processes.

Acknowledgements. The paper is a result of the collaboration between JINR (Dubna, Russia)and the partner Universities/Institutes from Romania. Financial support from PN-III-P1-1.2-PCCDI-2017-0871 (CNDI-UEFISCDI) project is acknowledged.

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