Structural,magnetic and antibacterial properties of manganese-substituted magnetite ferrofluids

Manganese-substituted magnetite ferrofluids(FFs)Mnx Fe_(1-x)Fe_(2)O_(4)(x=0–0.8)were prepared in this work through a chemical coprecipitation reaction.The controlled growth of FF nanomaterials for antibacterial activities is challenging,and therefore,very few reports are available on the topic.This research focuses on stabilizing aqueous FFs with the tetramethylammonium hydroxide surfactant to achieve high homogeneity.Morphological characterization reveals nanoparticles of 5–11 nm formed by the chemical reaction and nanocrystalline nature,as evident from structural investigations.Mn-substituted magnetic FFs are analyzed for their structural,functional,and antibacterial performance according to the Mn-substituent content.Optical studies show a high blue shift for Mn^(2+)-substituted Mnx Fe_(1-x)Fe_(2)O_(4)with the theoretical correlation of optical band gaps with the Mn content.The superparamagnetic nature of substituted FFs causes zero coercivity and remanence,which consequently influence the particle size,cation distribution,and spin canting.The structural and functional performance of the FFs is correlated with the antibacterial activity,finally demonstrating the highest inhibition zone formation for Mnx Fe_(1-x)Fe_(2)O_(4)FFs.

Saturation Magnetization and Law of Approach to Saturation for Selfformed Ionic Ferrofluids Based on MnFe2O4 Nanoparticles

The magnetization curves of MnFe2O4 nanoparticles and self-formed ferrofluids based on these particles have been measured at room temperature. The median size of the particles is 13.67 nm. The specific saturation magnetization is less than the theoretical value for the ferrofluids. In the high field range from 5 kOe to 10 kOe, the higher the particle volume fraction is, the steeper the slope of the magnetization curves is when it approaches saturation. The behavior of the saturation magnetization and the law of approach to saturation are due to the presence of self-assembled aggregates of ring-like micelle structures which form in the absence of the magnetic field and field-induced aggregates, respectively. The field-induced aggregates have a dissipative structure, so that at high field, the law of approach to saturation magnetization is different from the one described using Langevin paramagnetism theory. The large particles in the ferrofluids result in apparent hysteresis.

Preparation of PMAA-coated Dysprosium Ferrite Ferrofluids and Study on the Superparamagnetism

The present paper covers the unprecedented preparation of stable aqueous Dy-ferrite ferrofluids, whereby colloidal Dy_ δ Fe_ 3- δ O_4 ultrafine particles were dispersed by using polymeric surfactant PMAA. The stabilities of the series of the ferrofluids were studied according to the stability indexes. The susceptibility measurements were made with a Farady-type magnetic balance at various temperatures and magnetic field intensities. In terms of Langevin function, the σ versus H/T curves showed that Dy-ferrite ferrofluids exhibited superparamagnetism behavior and the blocking temperatures were in the range from 160 to 200 K. Moreover, the ferrofluids were characterized by means of Infra-red spectroscopy, transmission electron microscopy, X-ray diffraction, and Mssbauer spectroscopy.

Polydispersity effects on the magnetization of diluted ferrofluids:a lognormal analysis

Based on a lognormal particle size distribution, this paper makes a model analysis on the polydispersity effects on the magnetization behaviour of diluted ferrofluids. Using a modified Langevin relationship for the lognormal dispersion, it first performs reduced calculations without material parameters. From the results, it is extrapolated that for the ferrofluid of lognormal polydispersion, in comparison with the corresponding monodispersion, the saturation magnetization is enhanced higher by the particle size distribution. It also indicates that in an equivalent magnetic field, the lognormally polydispersed ferrofluid is magnetically saturated faster than the corresponding monodispersion. Along the theoretical extrapolations, the polydispersity effects are evaluated for a typical ferrofluid of magnetite, with a dispersity of σ = 0.20. The results indicate that the lognormal polydispersity leads to a slight increase of the saturation magnetization, but a noticeable increase of the speed to reach the saturation value in an equivalent magnetic field.

Interfacial instability of ferrofluid flow under the influence of a vacuum magnetic field

This study is to numerically test the interfacial instability of ferrofluid flow under the presence of a vacuum magnetic field.The ferrofluid parabolized stability equations(PSEs)are derived from the ferrofluid stability equations and the Rosensweig equations,and the characteristic values of the ferrofluid PSEs are given to describe the ellipticity of ferrofluid flow.Three numerical models representing specific cases considering with/without a vacuum magnetic field or viscosity are created to mathematically examine the interfacial instability by the computation of characteristic values.Numerical investigation shows strong dependence of the basic characteristic of ferrofluid Rayleigh-Taylor instability(RTI)on viscosity of ferrofluid and independence of the vacuum magnetic field.For the shock wave striking helium bubble,the magnetic field is not able to trigger the symmetry breaking of bubble but change the speed of the bubble movement.In the process of droplet formation from a submerged orifice,the collision between the droplet and the liquid surface causes symmetry breaking.Both the viscosity and the magnetic field exacerbate symmetry breaking.The computational results agree with the published experimental results.

Splitting Regularities of Thin Ferrofluid Layer Manipulated by Vertical Magnetic Field

The regular distribution of micro-droplets splitting from thin ferrofluid layer is systematic experimentally investigated, as the layer is placed in a vertical magnetic field. In this work, the field is applied in an instant manner and a slow manner, respectively; the field strength is linear increased. With instantly raising the field, it is observed that the ferrofluid layer is split into several regularly distributed micro-droplets, and that the number of micro-droplets is linear to the magnetic field strength and the thickness of the liquid layers. When the field is slowly increased, a liquid ring together with several micro-droplets appears from the ferrofluid layer splitting. A spatial drift of the micro-droplets is also observed in the process of increasing the magnetic field. Our results are useful for manipulating the splitting regularities of ferrofluid layers by magnetic field, which may be used in non-contact segmentation, and magnetically manipulated drug carriers for targeting the therapy, etc.

FERROFLUID CONTAINING SOLUBLE CONDUCTIVE POLYANILINE AND ITS FREESTANDING FILMS

Ferrofluid containing highly conductive polyaniline (PANI) was prepared, in which soluble PANI solutions dopedwith 10-camphorsulfonic acid (CSA) and dodecyl benzenesulfonic acid (DBSA) were used as the basic solution and Fe_3O_4nanoparticles (d = 10 nm) as the magnetic material. Moreover, the freestanding films of the resulting ferrofluid can beobtained by an evaporation method. The electrical and magnetic properties of the ferrofluid or its films can be adjustedthrough changing the content of PANI and Fe_3O_4. High saturated magnetization (≈ 30 emu/g) and high conductivity(≈ 250 S/cm) of the composite films can be achieved when the composite film contains 26.6 wt% of Fe_3O_4. In particular, itwas found that the composite films exhibit a super-paramagnetic behavior (Hc = 0) attributed to the size of Fe_3O_4 particles on the nanometer scale.

Control of Magnetic Particle Size in Ferrofluid and Its Effect on Rheological Properties

Rheological properties are the theoretical basis and the key to common problems in ferrofluid applications,therefore they are expected to be adjustable to satisfy different technical requirements through altering the microstructure of ferrofluid during the process of preparation.In this paper,Four ferrofluid samples with different magnetic particle size were prepared by controlling the concentration of precursor solution during co-precipitation process and the rheological properties of these samples were investigated.These samples exhibited field-controlled rheological properties.Eternal magnetic field would enhance the formation of microstructures,resulting in an increase of viscosity.While with the increase of shear rate,microstructures tended to be destroyed,causing viscosity to decrease.There were two opposing mechanisms of the influence of precursor solution concentration.On one hand,the reduction of the precursor solution concentration would produce primary magnetic particles of smaller size.But on the other hand,the surfactant became insufficient to completely coat the magnetic particles because of an increased specific surface area,causing the magnetic particles to aggregate and form secondary clustering structures which strongly enhanced the magnetoviscous effect and weakened the viscoelastic effect.

Ferrofluid Actuated Thermal Overload Relay

Thermal overload relays are economic electromechanical protection devices which offers reliable protection for electric motors in the event of overload or phase failure. Presently there are two types of overload relays which depend on the temperature characteristics of metals to provide protection by tripping the circuit. These relays lack accuracy as they do not activate the trip circuit at any exact specified temperature. In this paper we introduce a new form of thermal over-load relay actuated by ferrofluid. The ferrofluid has a very accurate transition temperature known as curie temperature. It acts as a ferromagnetic material below the curie temperature and loses the property of ferromagnetism above this temperature. By using this property of the fluid we propose an alternative method for more accurate op-eration under overload condition. This relay finds application in the protection system of electrical machines. Thus, in this paper we present a novel and simple technique for protection against thermal overloading using ferrofluid.

Ferrofluid nucleus phase transitions in an external uniform magnetic field

The phase transition between a massive dense phase and a diluted superparamagnetic phase has been studied by means of a direct molecular dynamics simulation. The equilibrium structures of the ferrofluid aggregate nucleus are obtained for different values of a temperature and an external magnetic field magnitude. An approximate match of experiment and simulation has been shown for the ferrofluid phase diagram coordinates ＂field-temperature＂. The provided phase coexistence curve has an opposite trend comparing to some of known theoretical results. This contradiction has been discussed. For given experimental parameters, it has been concluded that the present results describe more precisely the transition from linear chains to a dense globes phase. The theoretical concepts which provide the opposite binodal curve dependency trend match other experimental conditions： a diluted ferrofluid, a high particle coating rate, a high temperature,and/or a less particles coupling constant value.

Process Modeling of Ferrofluids Flow for Magnetic Targeting Drug Delivery

Among the proposed techniques for delivering drugs to specific sites within the human body, magnetic targeting drug delivery surpasses due to its non-invasive character and its high targeting efficiency. Although there have been some analyses theoretically for magnetic drug targeting, very few researchers have addressed the hydrodynamic models of magnetic fluids in the blood vessel of human body. This paper presents a mathematical model to describe the hydrodynamics of ferrofluids as drug carriers flowing in a blood vessel under the applied magnetic field. A 3D flow field of magnetic particles in a blood vessel model is numerically simulated in order to further understand clinical application of magnetic targeting drug delivery. Simulation results show that magnetic nanoparticles can be enriched in a target region depending on the applied magnetic field intensity. Magnetic resonance imaging confirms the enrichment of ferrofluids in a desired body tissue of Sprague-Dawley rats. The simulation results coincide with those animal experiments. Results of the analysis provide the important information and can suggest strategies for improving delivery in favor of the clinical application.

Hydrodynamic modeling of ferrofluid flow in magnetic targeting drug delivery

Among the proposed techniques for delivering drugs to specific locations within human body, magnetic drug targeting prevails due to its non-invasive character and its high targeting efficiency. Magnetic targeting drug delivery is a method of carrying drug-loaded magnetic nanoparticles to a target tissue target under the applied magnetic field. This method increases the drug concentration in the target while reducing the adverse side-effects. Although there have been some theoretical analyses for magnetic drug targeting, very few researchers have addressed the hydrodynamic models of magnetic fluids in the blood vessel. A mathematical model is presented to describe the hydrodynamics of ferrofiuids as drug carriers flowing in a blood vessel under the applied magnetic field. In this model, magnetic force and asymmetrical force are added, and an angular momentum equation of magnetic nanoparticles in the applied magnetic field is modeled. Engineering approximations are achieved by retaining the physically most significant items in the model due to the mathematical complexity of the motion equations. Numerical simulations are performed to obtain better insight into the theoretical model with computational fluid dynamics. Simulation results demonstrate the important parameters leading to adequate drug delivery to the target site depending on the magnetic field intensity, which coincident with those of animal experiments. Results of the analysis provide important information and suggest strategies for improving delivery in clinical application.

PREPARATION OF FERROFLUID FOR MINERAL PROCESSING AND ITS PROPERTIES

１ＩＮＴＲＯＤＵＣＴＩＯＮＢｅｃａｕｓｅｏｆｉｔｓｅｓｐｅｃｉａｌｙｈｉｇｈｓｅｐａｒａｔｉｎｇｄｅｎｓｉｔｙａｎｄｓｅｐａｒａｔｉｎｇｐｒｅｃｉｓｉｏｎ，ｔｈｅｆｅｒｏｆｌｕｉｄｉｃｓｅｐａｒａｔｉｏｎｈａｓａｔａｃｔｅｄｓｃｉｅｎｔｉｓｔ’ｓｇｒ...

All-optical modulator based on a ferrofluid core metal cladding waveguide chip

We propose a novel optical intensity modulator based on the combination of a symmetrical metal cladding optical waveguide （SMCW） and ferrofluid, where the ferrofluid is sealed in the waveguide to act as a guiding layer. The light matter interaction in the ferrofluid film leads to the formation of a regular nanoparticle pattern, which changes the phase match condition of the ultrahigh order modes in return. When two lasers are incident on the same spot of the waveguide chip, experiments illustrate all-optical modulation of one laser beam by adjusting the intensity of the other laser. A possible theoretical explanation may be due to the optical trapping and Soret effect since the phenomenon is considerable only when the control laser is effectively coupled into the waveguide.

Effect of temperature dependent viscosity on revolving axi-symmetric ferrofluid flow with heat transfer

The prime objective of the present study is to examine the effect of tempera- ture dependent viscosity/z（T） on the revolving axi-symmetric laminar boundary layer flow of an incompressible, electrically non-conducting ferrofiuid in the presence of a stationary plate subjected to a magnetic field and maintained at a uniform temperature. To serve this purpose, the non-linear coupled partial differential equations are firstly converted into the ordinary differential equations using well-known similarity transformations. The popular finite difference method is employed to discretize the non-linear coupled differ- ential equations. These discretized equations are then solved using the Newton method in MATLAB, for which an initial guess is made with the help of the Flex PDE Solver. Along with the velocity profiles, the effects of temperature dependent viscosity are also examined on the skin friction, the heat transfer, and the boundary layer displacement thickness. The obtained results are presented numerically as well as graphically.

Preparation and Acute Toxicology of Nano-Magnetic Ferrofluid

The nano-magnetic ferrofluid was prepared by chemical coprecipitation and its acute toxicology was investigated. The effective diameter (Eff. Diam.) of the magnetic particles was about 19.9 nm, and the concentration of the ferrofluid was 17.54 mg/ml. The acute toxic reaction and the main viscera pathological morphology of mice were evaluated after oral, intravenous and intraperitoneal administration of the nano-magnetic ferrofluid of different doses respectively. Half lethal dose (LD 50)>2104.8 mg/kg,maximum non-effect dose (ED 0)=320.10mg/kg with oral; LD 50>438.50 mg/kg, ED 0=160.05 mg/kg with intravenous route; and LD 50>1578.6 mg/kg, ED 0=320.10 mg/kg with intraperitoneal administration. Degeneration and necrosis of viscera were not found. So the nano-magnetic ferrofluid, of which toxicity is very low, may be used as a drug carrier.

Casimir Effect in Optoelectronic Devices Using Ferrofluids

Some of the modern electronic and optoelectronic devices exploit ferrofluids contained in narrow gaps between two material plates. When the width of the gap becomes below a micrometer, the boundary plates are subjected to the Casimir force arising from the zero-point and thermal fluctuations of the electromagnetic field. These forces should be taken into account in microdevices with the dimensions decreased to below a micrometer. In this paper, we review recently performed calculations of the attractive Casimir pressure in three-layer systems containing a ferrofluid. We also find the ferrofluidic system where the Casimir pressure is repulsive. This result is obtained in the framework of the fundamental Lifshitz theory of van der Waals and Casimir forces. The conclusion is made that enhanced repulsion due to the presence of a ferrofluid may prevent from sticking of closely spaced elements of a microdevice.

Penetrative Bénard-Marangoni Convection in a Micropolar Ferrofluid Layer via Internal Heating and Submitted to a Robin Thermal Boundary Conditions

Penetrative Bénard-Maranagoni convection in micropolar ferromagnetic fluid layer in the presence of a uniform vertical magnetic field has been investigated via internal heating model. The lower boundary is considered to be rigid at constant temperature, while the upper boundary free open to the atmosphere is flat and subject to a convective surface boundary condition. The resulting eigenvalue problem is solved numerically by Galerkin method. The stability of the system is found to be dependent on the dimensionless internal heat source strength Ns, magnetic parameter M1, the non-linearity of magnetization parameter M3, coupling parameter N1, spin diffusion parameter N3 and micropolar heat conduction parameter N5. The results show that the onset of ferroconvection is delayed with an increase in N1 and N5 but hastens the onset of ferroconvection with an increase in M1, M3, N3 and Ns. The dimension of ferroconvection cells increases when there is an increase in M3, N1, N5 and Ns and decrease in M1 and N3.

Effects of Velocity and Thermal Slip Conditions with Radiation on Heat Transfer Flow of Ferrofluids

To analyze the thermal convection of ferrofluid along a flat plate is the persistence of this study. The two-dimensional laminar, steady, incompressible flow past a flat plate subject to convective surface boundary condition, slip velocity in the presence of radiation has been studied where the magnetic field is applied in the transverse direction to the plate. Two different kinds of magnetic nanoparticles, magnetite Fe3O4 and cobalt ferrite CoFe2O4 are amalgamated within the base fluids water and kerosene. The effects of various physical aspects such as magnetic field, volume fraction, radiation and slip conditions on the flow and heat transfer characteristics are presented graphically and discussed. The effect of various dimensionless parameters on the skin friction coefficient and heat transfer rate are also tabulated. To investigate this particular problem, numerical computations are done using the implicit finite difference method based Keller-Box Method.

Biomimetically Synthesized Aqueous Ferrofluids Having Antibacterial and Anticancer Properties

Synthesis of functional iron oxide nanoparticles, well dispersed in aqueous fluids still remains a challenge as its stability requires a delicate balance between electrostatic and magnetic interactions. Templated synthesis using biomolecules is useful because the biomolecules have their unique arrangement in aqueous systems that enhance stability, commonly called “biomimetic synthesis”. We have developed a one-pot in-situ, low energy process for the synthesis of highly monodispersed, Collagen Functionalized Ferrofluids (CFF) as a templating agent in an aqueous medium. The nanoparticles so obtained were characterized by X-ray diffraction (XRD), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR). The antibacterial activity in terms of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and growth inhibition has been assessed against gram positive, Staphylococcus aureus, ATCC 13709 (native strain) and in Escherichia coli, DH5α gram negative bacteria. The cytotoxicity of the CFFs on cancer cell lines human embryonic kidney (HEK), breast adenocarcinoma (MCF-7) and Ehrlich ascitic carcinoma (EAC) have also been investigated. CFFs indicated variable MIC and MBC values against S. aureus and E. coli being minimum for 1.5% CFF (MIC:23.43 μg/ml and 93.75 μg/ml and MBC: 46.87 μg/ml and 187.5 μg/ml). The observed cytotoxicity in mammalian cells indicated the susceptibility of MCF-7 breast cancer cells when compared to HEK cells.