Improved magneto-viscoelasticity of cross-linked PVA hydrogels using magnetic nanoparticles

Accepted Manuscript Title: Improved magneto-viscoelasticity of cross-linked PVA hydrogels using magnetic nanoparticles Authors: Noorjahan, Saurabh Pathak, Komal Jain, R.P. Pant PII: DOI: Reference:

S0927-7757(17)31099-3 https://doi.org/10.1016/j.colsurfa.2017.12.011 COLSUA 22135

To appear in:

Colloids and Surfaces A: Physicochem. Eng. Aspects

Received date: Revised date: Accepted date:

10-10-2017 3-12-2017 4-12-2017

Please cite this article as: Noorjahan, Saurabh Pathak, Komal Jain, R.P.Pant, Improved magneto-viscoelasticity of cross-linked PVA hydrogels using magnetic nanoparticles, Colloids and Surfaces A: Physicochemical and Engineering Aspects https://doi.org/10.1016/j.colsurfa.2017.12.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Improved magneto-viscoelasticity of cross-linked PVA hydrogels using magnetic nanoparticles Noorjahan1,2,#, Saurabh Pathak 1,2,# Komal Jain 1,2 and R. P. Pant1,2,* 1

Academy of Scientific and Innovative Research, CSIR-NPL Campus, New Delhi, India

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SAED, CSIR-National Physical Laboratory, New Delhi 110012, India

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# Equal contribution from Author, * Corresponding Author:[email protected]

Graphical abstract

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In this work, we report the effect of magnetic nanoparticles in cross-linked PVA matrix. The static and dynamic viscoelastic investigation confirms that the mechanical properties of the magnetic gel are improved. Tunable viscoelastic properties of magnetic gels make it very useful for the development of a device with enhanced performance.

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Abstract

Magnetic nanoparticle (MNP) incorporation in soft host media offers great possibilities to control its properties and flow dynamics via external magnetic field. In the present work we report, synthesis of stable homogeneous crosslinked PVA hydrogels with MNP and their detailed rheological investigations in static and dynamics modes. The measurement results were fitted with the theoretical model presented for nonlinear and transient static & dynamic flow behavior. 1

A good agreement has been observed with theoretical predictions confirming the high dispersivity and stability of these magnetic gels. MNP align themselves in the field direction, and field-induced structures produce hindrance to uniform stress flow which causes a nonlinear viscoelastic response. The substantial enhancement in viscoelastic properties in observed with incorporation of MNP. Static mode investigations show good yielding properties which increases

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with increase in MNP concentration whereas, dynamic mode storage/loss modulus response shows higher storage modulus than loss modulus. This enhancement indicates the dominance of solid-like nature of magnetic gel due to more significant field-induced structures over applied hydrodynamic forces. These magnetic gels show a quick response to the applied field which is established thru the transient viscosity response. The viscoelastic properties of these magnetic gels makes it effective and efficient solution for numerous applications in the field of

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engineering and biomedical.

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Keywords: Polymer, viscoelasticity, composite, yield, magnetic nanoparticles

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Introduction

Magnetopolymer composites (MPC) are hybrid materials containing micron-or nano-sized

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magnetic particles embedded in a polymer matrix[1, 2]. Stable MPC suspension is inveterate by

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choosing a suitable host medium which allows maximum diffusion of magnetic particles in a polymer gel. These systems constitute a fascinating class of materials for current technological

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applications as it possesses a combination of properties of both; magnetic fluid and polymer gels

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[3, 4]. These smart materials show unique physical, chemical and viscoelastic properties which can be controlled by an external magnetic field [5] and display significantly improved

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viscoelastic and magnetic properties. Tunable rheological and viscoelastic properties of magnetic gels via magnetic field allows them to be used for various applications such as magnetic air flow control valve, bushes in machines, vibration absorber, temperature sensing, vibration sensor, and actuator, etc. [6-9]

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The research in the area of MPC is mainly steadfast towards the optimization of its properties by using suitable polymer matrix, magnetic particles and surface modification of magnetic particles. These studies are mostly engrossed in the flow characteristic and mechanical behavior of

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magnetic hydrogels. The magnetic gel is a network of constituted cross-linked polymer chains which are hydrophilic and able to dissolve significant amount of water and biological fluid [10]. Nature of cross-linking may differ in physical and chemical cross-linking. Physically crosslinked polymers are weaker and more reversible due to lower bond Vander wall forces, whereas physical cross-linked structure is strong and irreversible with covalent bonds[11, 12]. Various

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magnetic polymer gels are studied in the literature which is primarily based on incorporation of

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micron-nano sized particles in the polymer matrix[13]. This inclusion significantly affects the

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properties of magnetic hydrogel and behavior of magnetic particles mainly devices the

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performance these magnetic gel. Shape and size of particles are selected to achieve maximum diffusion of magnetic particles in the polymer matrix [14-16]. Soft magnetic particles show

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higher diffusion rate in the polymer matrix then hard magnetic material thus demonstrates higher

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improvement in viscoelastic properties.

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Homogeneity of the magnetic gel is essential as it governs the properties of magnetic gel and reduces the directional anisotropy. Gonzalez et al. investigated the superparamagnetic stable

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isotropic gel prepared by freezing-thawing one-pot synthesis of iron oxide in the presence of

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homogenous PVA [17]. M.E. Khosroshahi et al. synthesized stable magnetic gel containing welldispersed Fe3O4/PVA nanocomposites showing a fast magnetic response[18]. Viscoelastic properties of gel signify the Non –Newtonian behavior as it undergoes shear thinning/ thicking after a critical strain. Magnetic gel displays nonlinear macroscopic stress-strain behavior. Zuberev et al. modeled these nonlinear behaviors and theoretically explained the nonlinear 3

dependence of stress and strain. Magnetic particles forms chain in applied field direction and rapture of these chain with applied strain leads to lowering of stress[19]. Further, interparticle dipolar interaction tries to keep these particles in the chain, so instantaneously that small chain

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aggregates are formed. This behavior of magnetic gel was modeled by Zuberev et al. and this theoretical model fits well with the experimental results reported by various researchers [20]. The Mordina et al. studied the effect of varying particle concentration and observed an improvement in yield stress with addition of MNP [22] .Further, they observed that the particle alignment and anisotropy significant effect MPC gels which lead to improving magnetoeffect

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due to higher saturation magnetization [21]. Deformation properties of magnetic gels are

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considerably hindered with the application of magnetic field due to formation breaking of the

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chain in the field direction. Gollwitzer et al. measured the deformation characteristic of ferrogel

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by calculating dimensionless Poisson's ratio (𝜎). For this, they calculated the elongation parallel and perpendicular to the field and obtained a value 𝜎 = 0.5 which corrospondes to

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incompressible material [22]. Further Ning et al studied transient rheological response of

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magnetic nanocomposite system. They experimentally demonstrated enhancement in storage

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modulus of MR gel on applications of homogeneous magnetic field and compared the results of storage modulus of magnetic gel with equivalent MR fluid. The comparison shows enhanced

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viscoelastic properties due to strong rearrangement of inter-particles network under magnetic field [2]. Although, lots of research work has been carried out to understand the Non-linear

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transient behavior of magnetic gels but still various model presented lack in determining the exact mechanism for predication of the viscoelastic properties of the system. The present work aims to investigate thoroughly the effect of ferrofluid Fe3O4 concentration on the rheological properties of a magnetic gel prepared using water-soluble PVA. PVA is selected 4

for its biocompatible and reactive nature to a large number of functional groups due to the presence of hydroxyl group. The size of Fe3O4 nanoparticles was optimized to achieve maximum diffusion and homogeneity. Magnetic nanoparticles are attached to the cross-linked polymer

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chains; significantly altering the structural, mechanical, etc. properties of the polymer gel. The main focus is to understand the viscoelastic properties with the incorporation of magnetic nanoparticles. The strain controlled static and dynamic measurements are performed to investigate the effect on a viscoelastic parameter such as viscosity, shear stress, storage and loss modulus, etc. In static mode viscosity and shear stress response is taken at strain control mode;

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with and without applications of the magnetic field. Dynamic mode measurements were

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performed to take storage and loss modulus response at varying strain and frequency with and

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without field. Both static and dynamic mode results were fitted with theoretical models, and a

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good agreement with literature was observed. In this work, we extensively explain the mechanism for tunability of rheological properties of magnetic gel. Also effect of different

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particle concentration on properties of the magnetic gel has been studied. Optimized PVA

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magnetic hydrogels can serve as, an indispensable tool in biomedical and engineering

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applications. The biocompatibility and nontoxic nature of PVA magnetic gel and high chemical reactivity with a different functional group make there very useful for the development of a

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device with enhanced performance.

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I. Experimental A two-step synthesis method is used for the preparation of magnetic hydrogel. First, Fe3O4 nanoparticles were prepared by chemical co-precipitation method and dispersed in water. Then a designated amount of polyvinyl alcohol (PVA) was mixed in water, and the solution was subjected to constant stirring (300rpm) for 15hrs at room temperature. Water soluble PVA is 5

selected as it is biocompatible hydrophilic nature and can accommodate a large number of functional groups. Now for the preparation of water-based ferrofluid, a salt solution of ferric chloride (FeCl3) and

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ferrous chloride (FeCl2) were mixed to maintain Fe3+/Fe2+ molar ratio 2:1. Oleic acid is used as a primary surfactant and added to the solution at the time of perception. Ammonia solution (25%) is used as a precipitating agent and added to the solution to maintain a pH 10 at temp 80oC. The solution is maintained at 80oC for half an hour at a constant stirring rate 600rpm. Temperature variation is monitored continuously and maintained in the range 80± 2C. Finally, the precipitate

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is washed 5-6 times to remove any trace of ammonia left and neutralized the pH. Thus obtained

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Fe3O4 particles were dispersed in sodium oleate aqueous solution, where sodium oleate works as

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a secondary surfactant to get FFW.

Afterward, three samples of ferrogel were prepared; ‘FF-10%’, ‘FF-20%’ and ‘FF-30%’ by

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mixing 10%, 20% and 30% v/v FFW in bubble-free PVA solution. The solution was made

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uniform by subjecting to constant stirring for 15 hours at 120 rpm at ambient temperature. Thus a

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uniform distribution of magnetic fluid in cross-likened polymer solution was obtained[23]. The structural characterization was performed with Rigaku XRG 2KW, Powder X-ray

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diffractometer (XRD). The diffraction pattern was recorded at 40kV, 30mA using CuKα (1.546A) radiation. Small angle X-ray (SAXS) scattering was used to determine the size

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distribution of the magnetite particles (Rigaku Ultima IV; standard transmission mode attachment). Measurements of magnetization were performed using Vibrating Sample Magnetometer (VSM, Lakeshore) for different magnetic samples. Magnetorheological measurements were performed using parallel plate magnet- rheometer (Physica MCR 301 Anton

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Paar, MRD-70 MR cell) in a strain-controlled mode with a magnetic field applied in a perpendicular direction to (1.2T). The diameter of the plate is 20 mm, and gap between parallel plates was kept constant 1 mm during the experiment. The measurement was carried out in static

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and dynamic mode. In static mode, the shear viscosity (𝜂) and shear stress (𝜏) was measured as a function of shear rate (γ) with and without external magnetic field and relaxation behavior with time. In order to study the mechanical properties of the material, the dynamic mode measurements were carried out, in which the frequency-dependent storage G’ (elastic) / loss G″ (viscous) modulus and damping properties were calculated.

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II. Result and discussion

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Fig 1(a) shows the x-ray diffractogram with peaks at 30.2, 35.4, 43.2, 57.5, 62.3 which

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corresponds to plane (220), (311) (400), (511),(440) of Fe3O4 (ASTM card No. 19-629) and peak position at 19.5 corresponds to the PVA. To calculate the structural strain more precisely a 𝜆

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Williamson-Hall equation 𝛽𝑐𝑜𝑠𝜃 = 4𝜖𝑠𝑖𝑛𝜃 + 𝐷 has been used. The average crystallite size D

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~ 9.5nm and the strain  = ~ 0.0006 [24] is shown inset of Fig 1(a). Fig 1(b) shows the size

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distribution of a FFW sample. The average diameter of the magnetite particles was found to be 12nm, size distribution 5-15nm, SAXS data are modeled assuming gamma distribution. The

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SAXS distribution signifies that the particles are

approximately spherical in shape. The

magnetization measurements of FFW and magnetic gel shows the particles saturate at low field

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itself with saturation magnetization (Ms) = 1emu g-1 as shown in Fig 1 (c). So we can conclude that within the experimental accuracy M-H loop shows no hysteresis, which confirm the supperparamagnetic nature of magnetic gel. Figure 1 7

III. Magnetorheological study Effect of shear rate on viscosity The strain-controlled rheological measurement was performed for all the samples at room temperature

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(25oC) with varying magnetic field. Shear viscosity (η) response as a function of shear rate (0.01-1000 s-1) at different magnetic field (H = 0 to 0.5T) was recorded to investigate the viscoelastic nature of the samples (Fig.2 (a-c)), and it can be divided into four regimes: 1) low shear regime (𝛾̇ = 0.01 −5 s-1): A sharp decrease in viscosity is observed with increase in shear rate due to breaking of chainlike structures formed in the magnetic field direction. MNP-PVA together forms cross-linked entangled structures which

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comes in the influence of interplay between magnetic forces (FM) and hydrodynamic forces(FH) with

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application of shear. Higher viscosity is observed for the greater MNP concentration and decreases

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significantly even with small change in shear rate. Homogeneity of PVA hydrogel samples can be

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conferred with the viscosity-shear rate response as a sharp steady decrease is observed for all the samples and all the results are showing highly repeatable set of measurement results. Further, the increase in

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applied field, the strength of these columnar chain structure increase; which leads to higher viscosity of

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the sample. In Fig 2 (a-c) all the samples showing a greater viscosity with increase in magnetic field strength. 2) Intermediate shear regime (𝛾̇ = 5-500 s-1): In this region, a linearly constant behavior is

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observed and viscosity is mainly arises due to chemical cross-linked PVA structures with entangled MNP. Also increase in viscosity is observed with increasing FF particle concentration due to smooth flow of

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stress is hindered. 3) Critical shear regime (𝛾̇ = 500-700 s-1): This region shows the transition behavior, where field induced structures completely breaks which leads to a sharp decrease in viscosity [Fig 2 (a-

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c)].Columnar structure behaves as an elastic solid but after a critical strain value, these structures behaves inelastic as shear induced breakup dominates the field induced structures. With increase in magnetic field, strength of columnar structure increase thus critical strain value shift towards the higher strain value. Also, for higher MNP concentration strength of MNP-PVA structures are higher thus the critical strain for transition, shifts towards higher strain value.[25]. 4) Higher shear rate (𝛾̇ = 700-1000 s-1), In this 8

region columnar structure breaks completely and barely any structures forms due to dominance of hydrodynamic forces over magnetic. Due to this, it shows shear thinning and saturation behavior in the sample is observed with increase in shear rate. Small chain aggregates forms column structure, but due to the domination of hydrodynamic forces, these structure brakes instantaneously and liquid-like behavior

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was observed.

Further, with an increase in particle volume concentration of FF, viscosity increase as ferrofluid particles get embedded in the polymer matrix and in the presence of magnetic field they align in the direction of the field. Fig 4 shows the schematic of the ferrofluid particles embedded in the polymer matrix. FF particles randomly occupy the space in the polymer matrix when a magnetic field is applied; particles

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start to align themselves in the field direction and consequently polymer matrix. Therefore we can control

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the magnetic gel flow characteristics with the application of the field.

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Figure 2

Effect of shear rate on shear stress. The influence of FF concentration on rheological

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properties of the magnetic gel has been studied to measure its steady state characteristic as a

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function of shear rate (𝛾̇ = 0.01-1000 s-1) at different magnetic field (H = 0 to 0.5T). Yield stress

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is calculated using earlier reported theoretical models for polymer [26]. From Fig 3, we observed a nonlinear behavior of stress strain, in which up to a critical value, magnetic gel shows a linear

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response and after crtical point material exhibit a nonlinear response. This point is known as elastic point, up to which magnetic gel shows linear-stress strain response. Further, increase in

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strain value causes non-linearity in the samples and after a critical strain value magnetic gel does not regains its original position. This point is defined as the yield point of the magnetic gel samples. From the flow curve we can define the three different yield stress point: elastic–limit yield stress; the static yield stress and dynamic yield stress[27]. With increase in shear rate shear

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stress shows a linear behavior at low shear rate and after, a critical shear rate, material shows incomplete recovery when applied stress is detached. This critical point is known as elastic limit yield stress, and up to this point, material shows

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complete recovery when applied shear is removed. Further, increases the shear rate beyond this critical point, material exhibit Non-linear inelastic characteristic as cross-linked bond between FF particles in a polymer matrix, starts to break. The minimum stress required to cause fluid flow is defined as static yield stress. After this point, further, increase in shear rate cause decrease in shear rate due to slip of particle aggregates plates in the applied forces direction. From Fig 3(a-

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c); increase in shear rate from (𝛾̇ = 463-600 s-1) causes a decrease in stress. This nonlinear

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characteristic can be well understood as shear induced breakup of plate shaped aggregates, takes

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place after a critical stress value. The inelastic nature of this deformations leads to a decrease in

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shear stress due to relaxation of particles aggregation which leads to lowering of stress hindrance in the flow direction. Furthermore, the dynamic yield is defined as the saturation point of the

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macroscopic stress-strain curve. After this value curve shows a saturation behavior, as particles

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chain aggregates disappear instantaneously. From Fig 3(a-c) it is very clear that, with increase

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in particle concentration the yield stress of the material is improved significantly (approximately 2 times). This is due to the entangled magnetic nanoparticles forms a chain aggregates in the

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field direction which resist the smooth stress flow. This hindrance increases the yield stress of the material. Also with increase in magnetic field, strength of this structures increase; thus shear

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stress also increases.

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IV. Magnetoviscous effect

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Figure 5 shows magnetic sweep test of all the magnetic gel samples with varying magnetic field (0 to 1 T) at a constant shear rate (𝛾̇ = 100 𝑠 −1 ). All the samples show an increase in viscosity with increase in magnetic field, as magnetic nanoparticles aligns themselves due to magnetic interaction. These particles are embedded in polymer matrix and moves together, with matrix thus caused restriction to the magnetic gel motion. After a critical magnetic field, structures

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formed due to magnetic interactions do not affected by the shear force and shows a saturation

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behavior. Further, increasing particle volume concentration of FF particles leads to higher

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viscosity due to increase in magnetic interactions and causes a greater influence in the fluid flow.

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Also saturation critical magnetic field shift towards higher field value with increase in particle concentrations. From these observations, we can conclude the increase in viscosity with

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application of field gives direct indication of the strong bonding between polymer matrix and FF

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particles. Also optimum value of magnetic particle concentration allows maximum stability and

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enhanced magnetic properties. Also for higher concentration of magnetic particle the gels shows lower stability due to loosely bonded magnetic particles. Adding a optimum concentration of FF

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allows a maximum effectiveness of the magnetic gel.

V Oscillation mode The dynamic behavior of Fe3O4-PVA magnetic gels was studied to investigate their strain amplitude and angular frequency response at room temperature. The strain amplitude test was

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performed to examine the viscoelastic response of magnetic gel with varying shear rate and test was conducted in the different magnetic field. This test signifies the energy storing capacity of the magnetic gel samples. Further angular frequency sweep test was performed to investigate

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loss modulus, and storage modulus G’ and G” response are recorded at constant strain amplitude 1% with varying frequency range 1-600rad/sec.

Strain Amplitude sweep test. The G’ and G” response with varying shear rate 0.01 to 100% at the different magnetic field (H= 0.1-0.5T) is shown in Figure 6. The flow response shows a constant linear response for both G’ and G” with varying the shear rate and storage modulus is

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greater than loss modulus. Figure 6 signifies the domination of solid like nature of the magnetic

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gel sample over liquid nature. This can be well understood as FF particle embedded crosslinked

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polymer matrix forms an overriding structure and these structures behave as incompressible

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elastic materials. Thus they have ability to store a significant amount of energy due to field-

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induced structures as compared to applied strain. The constant linear response can be well

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observed as a test performed up to a strain value 600s-1 and till this amplitude of strain, fieldinduced structure showing a reversible response. Further, increasing the strain over critical value

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tends to decrease in storage modulus and increase in loss modulus as field-induced structure is hindered and does not show reversible characteristics. With increase in FF particle concentration,

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both storage and loss modulus increases due to the increase in crosslinking of magnetic particles. The significant increase from 10 to 20 volume % shows a critical behavior at 20 volume %. This

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is observed to be the most optimum volume % of FF and further increase does not cause the significant effect on the performance of the magnetic gel. Figure 6

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Angular Frequency Sweep Test. Storage and loss modulus in the sample originates mainly due to crosslinked polymer structure and their interaction with emended nanoparticles. From Fig 7(ac), we can clearly observe that all the samples were showing a similar behavior as a response

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with a frequency sweep. Storage modulus (G’) and loss modulus (G”) was recorded as a response with varying frequency from 1-600rad/sec. A linearly increasing behavior of G’ is observed in the sample with an increase in frequency whereas a consistent linearly incresing behavior is observed for loss modulus. This is due to the applied energy is stored in the sample thus with an increase in frequency, thus storage modulus also increased but not much affected by an increase

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in the FF particles concentration. Storage modulus increase with an increase in frequency as the

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applied energy is captivated by the FF particles and PVA cross-linked structure, which rearrange

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themselves to minimum energy state. In this state magnetic gel attain minimum energy state and

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shows a constant linear behavior as solid-like nature dominates and applied frequency is not

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sufficient to hinder its viscous behavior

VI Time-dependent relaxation response

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The stability and relaxation behavior is observed in magnetic gel samples with transient viscosity measurement at a fixed shear rate (𝛾̇ = 100s-1). The transient behavior is studied in three

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different regions: (i) H=0T, (viscosity response in steady state constant shear without application of field). In this region almost linear viscosity response is observed in the sample which signifies

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the Newtonian behavior of the sample. (ii) H = 0.18T, in this region at magnetic field of 0.18T is switched on while shear rate remain the same. A significant increase in viscosity is observed due to formation of field induced structure formed in field direction due to chain formation. A straight line between region (i) and (ii) shows a quick transient and efficient response of

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magnetic gel.(iii) H=0T, In this region magnetic field is switched off thus viscosity is decrease . Although the viscosity is slightly higher than initial due to the formation of smaller chain aggregates present in the sample. So form Fig 8 , we can conclude that all the magnetic gels

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shows an efficient and quick magnetic response. Figure 8 VII Conclusion

The results of experimental study indicate that the PVA magnetic gel samples show improved

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magneto-viscoelastic properties. Structural, morphological and magnetic characterization of the

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magnetic gel samples is performed to ensure the samples quality and anisotropy. Tunable

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rheological properties were studied using parallel plate magneto-rheometer. Strain-controlled

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static mode measurements confirm the enhanced viscoelastic properties of magnetic gel samples with increasing the nanoparticle concentration. The effect of chain formation and magneto-

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deformation with varying magnetic field and shear rate is discussed together. Frequency & strain

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controlled storage and loss modulus response of the PVA magnetic gel was recorded. This investigation gives a direct evidence of the dominance of solid-like nature of the magnetic gels

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over liquid behavior due to the dominance of magnetic force over hydrodynamic forces. Also,

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transient viscosity response is also plotted which indicate an approximate reversible transition of viscosity when magnetic of field ON/OFF. The response time of viscosity transition is very sharp

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but magnetic particles from small aggregates even after removing the field, which slightly gives rise to viscosity after switching magnetic field off. These static and dynamic viscoelastic results are significant as it correlates the theoretical predictions with experimental measurement data. The effect of chain aggregation concentration of magnetic particles, shape & size of particles and distribution, etc. are modeled from literature, and produced results show a good fit with these 14

theoretical models. PVA hydrogel is very important for numerous application and improvement in its mechanical properties makes it even more useful to perform efficiently. VIII Acknowledgments

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This work was supported by Department of Science and Technology (DST), Ministry of Science and Technology, Government of India, (Project no.GAP123532). Noorjahan thanks, Council of Scientific & Industrial Research (CSIR), India, for providing Senior Research Fellowship (SRF)

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to carry out the research work.

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[12] G.M. Kavanagh, S.B. Ross-Murphy, Rheological characterisation of polymer gels, Progress in Polymer Science, 23 (1998) 533-562. [13] T. Yadav, C. Kostelecky, E. Franke, B. Miremadi, M. Au, Nanostructured fillers and carriers, Google Patents, 2001. [14] N. Dishovsky, K. Ruskova, I. Radulov, “In situ” magnetic modification of polar elastomers, Materials research bulletin, 36 (2001) 35-45. [15] Y. Wang, Y. Hu, H. Deng, X. Gong, P. Zhang, W. Jiang, Z. Chen, Magnetorheological elastomers based on isobutylene–isoprene rubber, Polymer Engineering & Science, 46 (2006) 264-268. [16] G. Stepanov, A. Chertovich, E.Y. Kramarenko, Magnetorheological and deformation properties of magnetically controlled elastomers with hard magnetic filler, Journal of Magnetism and Magnetic Materials, 324 (2012) 3448-3451. [17] J.S. Gonzalez, C.E. Hoppe, P. Mendoza Zélis, L. Arciniegas, G.A. Pasquevich, F.H. Sánchez, V.A. Alvarez, Simple and efficient procedure for the synthesis of ferrogels based on physically cross-linked PVA, Industrial & Engineering Chemistry Research, 53 (2013) 214-221. [18] G.R. Mahdavinia, S. Mousanezhad, H. Hosseinzadeh, F. Darvishi, M. Sabzi, Magnetic hydrogel beads based on PVA/sodium alginate/laponite RD and studying their BSA adsorption, Carbohydrate polymers, 147 (2016) 379-391. [19] A.Y. Zubarev, L.Y. Iskakova, M.T. Lopez-Lopez, Towards a theory of mechanical properties of ferrogels. Effect of chain-like aggregates, Physica A: Statistical Mechanics and its Applications, 455 (2016) 98-103. [20] A.Y. Zubarev, Effect of chain-like aggregates on ferrogel magnetodeformation, Soft Matter, 9 (2013) 4985-4992. [21] N. Jahan, S. Pathak, K. Jain, R. Pant, Enchancment in Viscoelastic Properties of Flake-Shaped Iron Based Magnetorheological Fluid Using Ferrofluid, Colloids and Surfaces A: Physicochemical and Engineering Aspects, (2017). [22] C. Gollwitzer, A. Turanov, M. Krekhova, G. Lattermann, I. Rehberg, R. Richter, Measuring the deformation of a ferrogel sphere in a homogeneous magnetic field, The Journal of chemical physics, 128 (2008) 164709. [23] K. Jain, S. Pathak, R. Pant, Enhanced magnetic properties in ordered oriented ferrofibres, RSC Advances, 6 (2016) 70943-70946. [24] A. Shankar, M. Chand, G.A. Basheed, S. Thakur, R.P. Pant, Low temperature FMR investigations on double surfactant water based ferrofluid, Journal of Magnetism and Magnetic Materials, 374 (2015) 696-702. [25] L.J. Felicia, J. Philip, Effect of Hydrophilic Silica Nanoparticles on the Magnetorheological Properties of Ferrofluids: A Study Using Opto-magnetorheometer, Langmuir, 31 (2015) 3343-3353. [26] H. Chemmi, D. Petit, V. Tariel, J. Korb, R. Denoyel, R. Bouchet, P. Levitz, A comprehensive multiscale moisture transport analysis: From porous reference silicates to cement-based materials, The European Physical Journal Special Topics, 224 (2015) 1749-1768. [27] J. de Vicente, D.J. Klingenberg, R. Hidalgo-Alvarez, Magnetorheological fluids: a review, Soft Matter, 7 (2011) 3701-3710.

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Figure.1 (a) X-ray diffraction curve of PVA/ Fe3O4 composite. (b) Small-angle x-ray scattering

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size distribution plot of Fe3O4 nanoparticles. (c) M-H curve of magnetic gel samples.

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Figure.2 Show the viscosity plot of sample as a function of shear rate at different field

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Figure.3 Shear stress response as a function of shear rate at the different magnetic field divided into three regions

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Figure.4 The schematic of the PVA-FF system, where entangled green shapes represent the PVA gel structure, and small spherical spheres represent Fe3O4 nanoparticles

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Figure.5 Magneto sweep test of different volume fraction samples

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Figure.6 Strain sweep test for F-PVA samples at different magnetic field (H= 0, 0.5T) with

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Figure.7 Frequency sweep test for F- PVA samples at different magnetic field (H= 0, 0.5T) with volume fraction samples.

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Figure.8 Transient viscosity response of PVA magnetic gel samples: 100 s , region I: H = 0, region II: H = 0.18T and region III: H = 0

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