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MAGNETIC FLUIDS

RAKESH K V 3rd Semester M.sc PHYSICS

CUSAT

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INTRODUCTIONSmart material

Smart materials are materials that have multiple propertiess (chemical, electrical, magnetic, mechanical and thermal)

The properties of these materials can be significantly changed in a controlled fashion by external stimuli

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Classification of the smart materials and their response

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Magnetic nanomaterials

At the nanolevel there is drastic change of properties for magnetic materials

They exhibit single domain characteristics, superparamagnetism etc.

Dependence of coercivity on particle size is important as they can be used to distinguish whether the material are in single domain or multidomain.

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Magnetic Colloids A Magnetic colloid also known as Ferrofluid is a colloidal suspensions

of single domain magnetic particles with a typical dimensions about 10nm dispersed in a carrier liquid

Properties can be controlled by external magnetic field

Ferrofluids are optically isotropic but in presence of an external magnetic field exhibit induced birefringes

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Components of a magnetic fluidBase fluid:It needed a base fluid,the choice of base fluid is based on

the field of application.eg; Water, Organic liquids

Single domain magnetic particles

Surfactants: It is used to prevent agglomeration.Common surfactants are Oleic acid,Citric acid,tetramethylammonium hydroxide etc.

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Classification of FerrofluidsSurfacted Ferrofluid

Formed by magnetic particles(usually magnetite) Suitable surfactants are used ( Amphiphilic molecules such as oleic acid ) to prevent agglomeration

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Ionic FerrofluidMagnetic nanoparticles are electrically charged to keep the colloidal

system stableGenerally used magnetic particles are ferrites MFe2O4 (M=Mn,Zn,Cu )

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Stbility of colloids

D ≤ (72KBT/∏µ0M2)1/3

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Mechanisms of Rotation of magnetic moments

Ferromagnetic single domains in suspension can relax by one of two methods

Brownian Relaxation with relaxation time

TB=3Vή/KBT

N´eel relaxation is caused by thermal fluctuations in the magnetocrystalline anisotropy energy

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Normal field InstabilityWhen a ferrofluid is subjected to a strong vertical magnetic field the

surface forms regular patterns of peaks and valleys

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Magneto Rheological FluidsMR fluids are non colloidal suspensions of micro sized magnetisable

particles in an inert base fluid along with some addditivesIn the absence of external magnetic field it behave like normal

Newtonian fluid

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Working modes of MR fluids

I. Valve mode

II. Shear mode

III. Squeeze mode

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ApplicationsElectronic devicesMedical fieldsSeat suspensionsRobotics

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Referenceswww.popsci.com/diy/article/2009-09/making-ferrofluids-work-youhttps://www.teachengineering.org/.../uoh_nano_lesson02_activity2https://en.wikipedia.org/wiki/Ferrofluidhttps://science.nasa.gov/science-news/science-at.../23aug_mrfluidswww.intechopen.com/download/pdf/39980

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Thank You