magnetic fluids is smart fluid. viscosity can be controlled by providing external magnetic field

1. MAGNETIC FLUIDS
RAKESH K V
3rd Semester M.sc PHYSICS
CUSAT
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2. INTRODUCTION
Smart 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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3. Classification of the smart materials and their response
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4. 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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5. 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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6. Components of a magnetic fluid
Base 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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7. Classification of Ferrofluids
Surfacted Ferrofluid
 Formed by magnetic particles(usually magnetite)
 Suitable surfactants are used ( Amphiphilic molecules such as oleic acid )
to prevent agglomeration
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8. Ionic Ferrofluid
Magnetic nanoparticles are electrically charged to keep the colloidal
system stable
Generally used magnetic particles are ferrites MFe2O4 (M=Mn,Zn,Cu )
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9. Stbility of colloids
D ≤ (72KBT/∏µ0M2)1/3
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10. 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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11. Normal field Instability
When a ferrofluid is subjected to a strong vertical magnetic field the
surface forms regular patterns of peaks and valleys
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12. Magneto Rheological Fluids
MR fluids are non colloidal suspensions of micro sized magnetisable
particles in an inert base fluid along with some addditives
In the absence of external magnetic field it behave like normal
Newtonian fluid
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13. Working modes of MR fluids
I. Valve mode
II. Shear mode
III. Squeeze mode
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14. Applications
Electronic devices
Medical fields
Seat suspensions
Robotics
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15. References
www.popsci.com/diy/article/2009-09/making-ferrofluids-work-you
https://www.teachengineering.org/.../uoh_nano_lesson02_activity2
https://en.wikipedia.org/wiki/Ferrofluid
https://science.nasa.gov/science-news/science-at.../23aug_mrfluids
www.intechopen.com/download/pdf/39980
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16. Thank You
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