Ferrofluids - Science topic

Hello

you can see the following articles:

(Ferrofluids can be synthesized using nanoparticles of ferromagnetic metals as well as magnetic compounds. The most frequently used ferromagnetic metal is the iron. In specific, iron oxide especially Fe2O3 is the most common oxide of iron)

Article Ferrofluid synthesis using oleic acid coated Fe3O4 nanoparti...

Mr. R. Sagayaraj has given good explanations.

Based on what I have understood, I will give you some suggestions, which is that first, by reading more articles similar to your work, make the desired magnetic nanoparticles with materials and conditions that achieve the desired magnetism, and then use these materials or Use the optimal parameters obtained in these methods, such as morphology, size, temperature, solvent, stabilizer, etc., in your desired method.

cis- oleic acid can be used for oil-based ferrofluids as a surfactant that produces steric repulsions

I think you can add volume force for magnetic fluid. The volumetric force can be expressed in terms of the magnetic field force on the magnetic fluid.

Dear all, may be this is due to a bad surface activation, i.e., the surface is to be activated first (surface full of OH groups, see attached ref.1). The quantification is done via various spectroscopic and chemical titration techniques. Please have a look at the following documents. My Regards

You are most welcome, Prof. Hossein Akhlaghi Garmejani

I noticed that the topic is actually being studied in some of the Russian literature. But of course, the language is a problem. Try Google Translate & check a few searches with the works you consider more important.

I saw in the past several monographies dedicated to ferrofluids in the former USSR since the problem is tractable theoretically.

Best Regards.

Do you have done Senthil Ram Nagapillai Durairaj ??

Zeinab Sadooghi

I offer you our method for the synthesis of cobalt ferrite nanoparticles in a system of straight micelles. Its advantage: stability of dispersion, the formation of self-organized uniformly distributed nanoparticles as a result of a quantum-thermal phase transition.

From the magnetic energy point of view, the peaks and valleys are energetically favorable. In the corrugated configuration, the magnetic field is concentrated in the peaks; since the fluid is more easily magnetized than the air, this lowers the magnetic energy. In consequence the spikes of fluid ride the field lines out into space until there is a balance of the forces involved.

Hemant Motiram Vishwasrao

If you perform decomposition of the complex in diphenyl ether, then your problem is not. 5 nm nanoparticles are formed.

Roca A.G., Morales M.P., Serna C.J. Synthesis of Monodispersed Magnetite Particles From Different Organometallic Precursors // IEEE Trans. Magn., V. 42. P. 3025 – 3029

Hence your problems arise from alcohol. The complex is chiral. It has in solution two optical isomers and a racemic mixture. Together with adsorption on nanoparticles during decomposition, it forms

complex mixture with high viscosity.

I see worth in the explanation of Dr S Kalaiselvan.

I think for such purpose we use electromagnetic field as a force required for ferrofluid movement.

I have a paper about this subject you can check it

It's always better to use AMR with varying the initial mesh sizes and then use the finner one to perform simulation. In some cases u cant find best solution when mesh size stops to effect the solution. In those cases u mention ur DOF solved for along with number of elements, maximum mesh size and time step in the paper to ensure reviewers that u have used enough discretization.

Dear Adnan,

You can apply the effect of a permanent magnet to the ferrofluid in your problem by adding additional sources in your governing equations. As you know, these magnetic sources appear in the governing equations to simulate ferrofluid behavior under the effect of a magnetic field.

Alan F Rawle Thank you very much for the information.

matrix magnetic filed

Dear Sir,

Thank you for the detailed response. I need a magnetizable liquid with high radiation length. When I said "magnetized up to 1 tesla", I meant that when a charged particle passes through such a liquid, it will feel the force due to 1 tesla magnetic field. So, this 1 T is not the "applied external field".

I am exploring such possibility and ferrofluid seemed to be an option. But if that is not a good option due to maintenance, what else can be done? Forcing water to be magnetized by putting coils around etc., seems to be inconvenient.

For information, this led to a fruitful collaboration ! Thanks Researchgate.

Here is the article:

Regards,

Emile

Naveen Joshi Use stoichiometric equation for calculation of dopant concentration

You can find reference from my thesis

and please find the sample calculation

Interesting..

Dear Yuri Mirgorod ：

appreciate for your helps.

Hi. I am also trying to isolate CTCs from dog. So what's the best way? Can you please share your experience?

To be specific my work will be more inclined towards wetting and spreading of droplet. I have chosen water based ferrofluids after going through existing literatures. Can you shed some more light in it?

Thanks in advance.

I am not familiar with FLUENT and CFX but I can confirm that COMSOL is one great solution - if not the best - to simulate multiple physics phenomenon such as electromagneto/fluidics.

Moreover, the community is big so a lot of questions and tutorials exists.

It is relatively simple to use: create your geometry, add your physics (electromagnetic and hydrodynamic in your case), add the conditions and launch the simulation.

Hope it helps choosing your solution.

Best,

Théo

Hello Keith Chua!

How nice that you found the answer to your problem. Any doubts are available, if it is within my reach I will be happy to respond.

Dear Ali, review these article,

The magnetic fluid consists of magnetite nanoparticles, kerosene, surfactant. If you determine the Curie temperature, the kerosene will begin to boil. If you refill the powder of magnetite nanoparticles with a size of 2 nm, the Curie temperature will be 600K, and with a size of 20 nm, 810K. If you determine the temperature of magnetite the size of a pea, then it will be also 810 nm. This is an example of dimensional effects for nanoparticles.

Dear All, 

Thank you all for your great feed back, and I am sorry for the late reply. I believe that one of the main holders of using nanofluids as heat transfer fluids is their rheological properties. My coauthor and I are proposing a new nanofluid named as Self-propelled nanofluids. In the Self-propelled nanofluids, the particles are swimming in a way similar to the Bacteria, and they can reduce the viscosity of the solvent significantly. Our paper is just been accepted in the Applied Thermal Engineering Journal. 

If you interested please let me know.

Hi Mekap

Can you please share more details about the synthesis itself? What is the coating you have initially straight after the synthesis? Are they superparamagnetic (or very very low coercivity)? 

Best

Superparamagnetic - single domain particles are achieved in the range of ferromagnetic particle diameter from 10 to 100 nm. Single domain particle formation depends on chemical and phase composition of the particles.

When u know the magnetic crystal structure than u can calculate the total magnetic moment and extend to the known single domain nano particle. This is simple approach for magnetic vector lies in 1D.

Use VSM or SQUID to determine the magnetic properties, in your cases: exchange length, anisotropy field, etc.

About SiC dispersions in aqueous media, you may possibly find useful to check the following discussion: https://www.researchgate.net/post/Which_is_the_suitable_binder_and_dispersant_for_making_SiC_slurry

Some ideas here too.

The aqueous solution of .0,1М FeCl3 is not mix with oil. Magnetic susceptibility 22x10^-7.

Name of some oil repellent ferrofluid (water loving ferrofluid):The aqueous solution of .0,1М FeCl3.

Best regards.

Thanks Mkhitar Hobosyan for the papers. I will certainly go through them and try out benzene and hexadecane. 

A ferrofluid is magnetically responsive fluid and in a moderate ( 100 Oe) field it's magnetzation changes significantly. If the fluid base( e.g.water) is unmixable with oil then oil drops will be dragged by externally applied magnetic field. The field acts like magnetic broom. 

 Dear Dr. Jaykumar, thank you for your informative comment. I was looking for something similar. 

Yes, any quality optic glass has little effect on image output. I've developed a technique where there are no air bubbles or debris within the cell and it maintains a sealed vacuum for at least 10 years (I have active cells from my first experiments).

My limited budget and health issues have prevented me from obtaining new equipment for a while, but we have 10 years of improvements and data to work with now.

Dear Zygimantas Gricius,

if available a four (Pt) electrode IS (Impedance Spectroscopy) measurement, it will show (in a Nyquist plot) a "magnetic" circle (1kHz<f<800kHz) with a diameter D, at a constant Temperature (near RT) . The plot of D with the concentration c (in DI water, or better quality) may uncover a critical concentration c₀ :  D(c<c₀)->0. This will show when (c=c₀) the superparamagnetic iron oxide nanoparticles lose their macroscopic magnetization in diliuted solutions. There are other magnetic measurements to find c0, also, but IS is quite sensitive.

Thanks a lot

There are so many ferrofluids available. However, suspension stabilty did not depend on the type of ferrofluids its mostly depend on various parameter like size of particles and so many other factors.

Please can you explain details of application 

Did you consider that it is just red illumination and a standard black ferrofluid :-)

There is a paper by Chia-Hung Chen, Adam R. Abate,* Daeyeon Lee, Eugene M. Terentjev, and David A. Weitz titled "Microfluidic Assembly of Magnetic Hydrogel Particles with Uniformly Anisotropic Structure" Adv.Matr. . 2009, 21, 3201–3204 in which they have used Ferrotec ferrofluid.

Two simple ways ,so that a feerofluid may not wet a glass substrate:

(1) To use a non-wetting carrier

(2) To coat the substrate with an appropiate surfactant that may prevent wetting between the fluid and glass surface.

Within the context of magnetic hyperthermia, the SAR and SLP are the same magnitude. SLP was coined much later, because SAR is somewhat misleading because of two main reasons: 1) It was used in the context of high-frequency radiation (microwaves or higher) where the formulae and mechanisms for energy absorption by human tissues are different from the low-frequency magnetic mechanisms observed in magnetic hyperthermia; and 2) because "Absorption Rate" does not state what is that is being absorbed. Specific Loss Power is more accurate since it is mass-normalized (specific) and denotes the magnitude (Power) that is being absorbed/released.

Both are given in Watts/gram.

Hope this helps.

Interfacial shape of ferrofluids on a glass and other surfaces has been studied both thepretically and experimentally.[ for example:S. S. H. Tsai, I. M. Griffiths, Z. Li, P. Kim, and H. A. Stone, Soft Matter 9,8600 (2013),K.S. Khalil et al ,APL,, 105, 041604 (2014),Shahriar Afkhami  , Linda J. Cummings  , and Ian M. Griffiths ,Interfacial deformation and jetting of a magnetic fluid,arxiv.org/pdf/1501.01000,2015]. It has been shown that balance of magnetic body force and surface tenstion force depends on magnetic susceptibility which in turn can beshown to depend on size and applied magnetic field. I think you can workout from these references.

Dear Richard

If you can send me an email to james@liquidsresearch.co.uk detailing your specification for the particles then i will see what i can do.

James

My dear Amin,

You may be aware of several attempts to prepare electrically conducting fluids using nanoparticles of iron coated with tin and using mercury as liquid carrier. But it failed. One can using elctrolyte as liquid carrier. But so far I know it has not served any useful purpose.

Further, a wire carrying current generate magnetic field around it and this magnetic field affects the surrounding nanomagnetic particles of the ferrofluid. You may refer early paper of Rosensweig in which has given expressions about this.

Magnetic fluids are colloidal dispersions. The mechanism of electrical conductivity of disperse systems is determined by the material of the particles, the nature of the stabilizing layer and the properties of the dispersion medium. The magnetic liquids, as a rule, are polar or non-polar dielectrics with extremely low electrical conductivity. Ferromagnetic or ferrimagnetic particles (Fe, magnetite, maghemite, etc.) have a fairly high conductivity, but surrounded by a dense layer of dielectric phase: protective coating, surfactants (usually oleic acid) + the carrier base (water, kerosene and other hydrocarbon or organosilicon media). Therefore, the conductivity of the magnetic fluid is not caused by the conductivity of the magnetite particles and corresponds to the electrical properties of dilute electrolytes. The magnetic particles can have a marked effect on the electrical conductivity only at their high concentration in the system (suspension), when the conductive area form a continuous grid of clusters of such particles (above the percolation threshold).

It is believed that the charge carriers in magnetic fluids are ions of impurities.

Oleic acid is the most common choice.

Williamson-Hall (W-H) plot works well as long as the peak shape is purely Lorentzian or purely Gaussian.

W-H (for Lorentzian profile): {β_obs − β_inst}cosθ = λ/D + 4ε_str{sinθ}

W-H (for Gaussian profile): {β²_obs − β²_inst}cos²θ = λ²/D² + 16ε_str² {sin²θ}

(β_obs: integral breath of observed reflection, β_inst: instrumental broadening, D: volume averaged crystallite size and ε_str: strain)

In W-H method, depending upon the peak shape, we plot 1) {β_obs − β_inst}cosθ vs 4sinθ or 2) {β²_obs − β²_inst}cos²θ vs 16sin²θ. If the peak is a pure Lorentzian or Gaussian, either plot 1) or plot 2) will be linear and we will be able to extract the size and strain simply by measuring the y-intercept and slope of the straight line.

However, the difficulty would arise when the peak shape is more complex. For example, if the peak shape is a convolution of a Lorentzian and a Gaussian, the mathematical expressions given above will not apply. As a result, both plot 1) and plot 2) will start to deviate from a straight line and the W-H method will no longer be useful for extracting the size/ strain data.

Balzar has developed analytical models to describe such complex convoluted peak shapes. You might find his papers useful: http://mysite.du.edu/~balzar/lbap.htm.

you may get detailed information from the paper by Sato et al,Preparation and properties of ferromagnetic FePt dispersion, J. Mag.Mag. Matr.,289, March 2005,1-4.

If your original fluid is stable then it may be possible to redisperse the particles after drying them. For example if you have coprecipitated the ferrite nanoparticles by using ammonia solution and coated them with olic acid and disperse the particles in water. The ferrofluid will be stable. If you now remove water and prepare a cake. This cake can be again redispersed in water by adding a drop of ammonia solution.

I do not know exactly how you measured Ms. If you have a ferrofluid and measure M vs H. Then saturation reaches by super paramagnetic behaviour of liquid. From that you can get emu/cc. If you know density then you can get emu/gm

 While for dry powder

ferrimagnetic behaviour you have to consider

I think the dry powder is also of coated particles.

Another problem often found dealing with suspensions is that of finding the mass of solid powder (M_p) needed to obtain a known volume of suspension (V_s) of a given mass ratio (R= M_p / M_s). Considering mass balance for the mixing operation (M_p + M_d = M_s), where M_d stands for mass of dispersant, it follows that M_p = M_d / [(1/R) - 1].(*) Let the volume of the solid powder, of suspension, and of dispersant, be denoted as V_p, V_s, V_d; and the corresponding densities as ρ_P, ρ_s, ρ_d. Accepting volume additivity (i.e. volume balance holds) we may write V_d = V_s - V_p, and since M_d = V_d·ρ_d and V_p = M_p/ρ_P, we have M_d = (V_s - M_p/ρ_P)·ρ_d. Substitution of last equation at (*) yields, after some transformation M_p = V_s·[ρ_d / (1 - R·(1 - ρ_d/ρ_P))]·R, solving this problem.  

There are several theoretical approaches regarding the rheology of suspensions of spherical particles, which are the commonly used ferrofluids.  Einstein's theory is only sufficient for high diluted systems, Rosensweig gives a good analytic model which fits also for higher volume concentrations. For the general behaviour of colloidal suspension in dependency of the volume fraction and particle shape Mueller et al. (Proc. R. Soc. A 2010) gives a very good overview.

Actually i didn't succeed to disperse magnet nanopaticles. I changed nanoparticles  and used another  nanoparticles instead Fe3O4.

of course the volume of ferrrofluid that you want prepare ، ultrasonic device and concentration of nanoparticles are very important.

for example probe is better than ultrasonic bath for dispersing. but every probe have  sonicate ability of certain volume.the probe that we had was able to sonicate 250 cc ! for concentrated ferrofluid you should use dispersant for stability of ferrofluid.

since i wanted to prepare large volume of ferrofluid  , i didn't !

if your volume is small and your ferrofluid is dilute maybe you can disperse in water by probe or bath ultrasonic! 

Over and above discussion there is still at least one parameter which responsible for lowering saturation magnetization of ferrofluids and that is polydispersity. Usually a ferrofluid contains different sizes and often assumed to obey lognormal distribution. There are several papers which discussed this aspect. 

- Mr/Ms is Stoner-Wohlfarth value. It is important if you are synthesizing magnetic with nanorod shapes. Here is a reference for that value (E.C. Stoner and E.P. Wohlfarth, “A Mechanism of Magnetic Hysteresis in Heterogeneous Alloys”, The R. Soc. Lond. A, 1948, 240, 599-642.)

- If Mr/Ms value in M-H curve shows about 0.5, then it is an ideal Stoner-Wohlfarth value for randomly oriented uniaxial grains. Since the anisotropy symmetry of magnetite is cubic, this is showing that the M-H loop is governed by the shape anisotropy of the nanorods.

- You can simply determine to see if your magnetic phase is superparagmagnetic, ferromagnetic or.... by M-H loop.

The ideal experiment would be to do dc magnetization measurements using magnetic fields of the order usually used for ac magnetization (say few Oe)..if the system is really magnetic, you can pick it up..otherwise the choice of fields, anything below 100 Oe should be ideal in most of the cases..

Hi Ms. Zahra,

If you are interested to characterize properties of Fe3O4 of the ferrofluid then one of the way is to use powder XRD.

As you have mentioned you have used magnetite particles. If you are getting good/moderate magnetic response of ferrofluid then the magnetite particles must be crystalline. Now, to determine crystallinity of the particles, you may take small amount of fluid (say 2-5 ml, depending on the magnetic fraction) add any solvent (say acetone) in the ferrofluid, mix it gently and decant acetone. You may keep the glass vessel on the magnet(s), so the magnetic particles will be settled and you can easily remove the solvent. Repeat this steps 2-3 times. Now spread the slurry on the walls of the beaker.  You may keep this beaker on the hot air Owen (T ~ 80-100 C). Within 30-40 mins, you can collect the dried particles and take XRD.

By the way, properties of crystallize Fe3O4 does not change upto 100-120 C.

When subjected to an external magnetic filed a ferrofluid performs like an uniaxial crystal with its optic axis (easy axis) parallel to the field. The propagation along the field direction is refered as extraordinary ray while in perpendicular directions it behaves as ordinary ray. This gives rise to birefringence.

Spike formation in a ferrofluid occurs due to the ferrohydrodynamic phenomenon called Normal field instability. When a ferrofluid is subjected to a normal magnetic field then on  its surface three forces acts (i)  Gravity force normal to the surface working in downward direction (ii) Surface tension-tangential to the surface (iii) magnetic body force working upwards. At a certain critical field the fluid shoots up at points and sharp pikes forms. Balance of the three forces depend on magnetization of the fluid, surface tenstion, permeability  and density of the fluid. So  unless the criteria given in the following eqn. is satisfied, spikes will not be formed.

                         (  Mc)<2> =( 2/ µo )[ 1+ µo/µ ](ρgσ)1/2

Where symbols have usual meaning.

The stronger the field larger will be spikes.

Thanks a lot Dr Rasbindu I will definitely read them.

RESEARCH I N THE SYNTHESIS AND CHARACTERIZATION

OF MAGNETIC FLUIDS (Phase II), great paper on the design considerations of ferrofluids. Also in my experience vegetable oils don't form so stable ferrofluids, the nanoparticles aggregate quickly. The best carriers I have found are the short to middle length hydrocarbon chains. Octane, Decane, Dodecane, Tetradecane and Hexadecane.

I don't think it is so easy to replace oleic acid, there was another paper which compared it with stearic acid for ferrofluids and the stearic coated particles proved to be far less stable: Resolving the Puzzle of Ferrofluid Dispersants

Rafael Tadmor, Ronald E. Rosensweig, Joseph Frey, and Jacob Klein, Langmuir 2000,16, 9117-9120

Yes, you can. For quick and good result use liquid carrier like hexane or other liquids which evaporate rapidly. Use spin drying technique to prepare ferrofluid films. You can apply external field while drying. This will orient particles to form chains.

In any colloid when number concentration of the dispersed phase is large then there will be always attraction between particles due to van der Walls force. Iron oxide particles synthesized in any way is no exception. Moreover ,if the nano- particles are magnetic as in a ferrofluid they performs like a tiny magnets and there will be magnetic attraction between particles.Both these attractions will lead to aggregation. Hence to counteract these attraction one has provide either steric or Coulomb attraction. For a water base ferrofluid the later one can be used and is called ionic ferrofluid. The former one requires a suitable surfactant. The choice of surfactant depends on end application. For biological application water base is more suitable and one has to select surfactants to provide hydrophilic environment.

We have used Pluronic F-127 to prepare hydrophilic oleic acid stabilized magnetite particles. The particles were subsequently functionalised with doxorubucin. The details of the method and limitations of other methods are described in the following paper.

J Nanopart Res (2011) 13:1677–1688

DOI 10.1007/s11051-010-9921-6