magnetic fluids
TRANSCRIPT
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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