1. FASCINATING FERROFLUIDS
R.V.Mehta
Ramanna Fellow,
Department of Physics,
Bhavnagar University, Bhavnagar

2. ACKNOWLEDGEMENT
Sponsors: Jyoti Ltd., UGC, British Council,DAE,DST, IFCPAR,CSIR and others
Collaborators: Profs. R.V.Upadhyay,S.P.Bhatnagar,Drs. P.S.Goyal,B.A.Dasanacharya, S.W.Charles,C.N.Ramchand,Prof. Kopkancky, Drs. K.Parekh,R.J.Patel,Rucha Desai,B.Chudasama and H.Desai N.Andhariya and many others

3. Magnetic Assemblies
Assemblies of colloidal magnetic particles play important role in soft condensed matter cf. Nature , 17,February issue of 2009.
Such materials are both scientifically interesting and technologically useful.
We shall describe here one such material- a ferrofluid also called magnetic fluid.

4. What is a Magnetic fluid?
A magnetic fluid/a ferrofluid is a stable colloidal dispersion of myriads of nanomagnetic particles in a suitable host liquid.
This material possess all the characteristics of (i) Soft matter (ii) a complex fluids and (iii) a smart material.
In zero magnetic field it behaves as a normal fluid

5. contd.
Under the influence of externally applied field several novel and intriguing phenomena are induced.
Consequently scientific as well as technological horizons are expanded.
In this talk some of these aspects especially work carried out by our team will be described. If time permits then a video film prepared under the sponsorship of DECU will be shown.

6. (I) Novel Phenomena
A ferrifluid appears and behaves like any normal black liquid. But as soon as one applies a magnetic field - particularly a gradient magnetic field, its fascinating properties are revealed.
(a) Liquid magnet
(b) Defying gravity
(C) Levitation of non magnetic object
(d) Self levitation
(e) Generation of fluid motion without mechanical means
(f) Ability to conduct magnetic flux
(g) Spontaneous formation of stable liquid spikes in presence of critical magnetic field.
These and several other properties are well explained on basis of Rosensweig model of Ferrohydrodynamics.
Certain additional properties like viscosity and asymmetric flow are better explained on Shliomis model which takes into account spin of the particles.[ R.E.Rosensweig,Ferrohydrodynamics,Cambrige U.P ]

7. Time span of invention from science to technology
Sr no
Invention
Invention year
Technological use and time span 1
Steam Engine
1801
1827 (26 yrs) 2
Telephone
1865
1875 (10 yrs) 3
Automobile
1885
1893 (8 yrs) 4
Television
1880
1936 (56 yrs) 5
E.M. Waves
(11 yrs ) 6
Nuclear fission
1930
(12 yrs) 7
Magnetic fluid
1965
(5 yrs)

8. Seals e.g. rotary shaft seals, exclusion seals
Engineering Applications
Seals e.g. rotary shaft seals, exclusion seals
Sensors e.g. inclination sensors
Dampers e.g. stepper motor dampers
Coolant e.g. loud speaker voice coil coolant
Lubricant e.g. magnetic bearing
Other uses like grinding and polishing,
separators, switches, NDT etc.

9. Market status in 2000 Sr no Device Total Number 1 Vacuum seals 200,000
Loud Speakers
450 million 3
Disk drives
500 million 4 5
Steppers
Dampers
50,000
Amount of MF used in material separation 100,000 liters
Total market US $ 120 million

10. Applications in biotechnology
Cell separation
Drug targeting
Hyperthermia
MRI contrast enhancement
Biosensing
Eye surgery
Tissue engineering

11. Our Contribution Engineering
Design & Development of
single stage rotary shaft seal (for Jyoti.ltd.)
multistage seal for high vacuum systems (DAE)
Synthetic Aperture Radar (SAC)
Inclination Sensor
Centrifugal Switch ( Patented)
Damper ( -do-
Synthesis of Temperature sensitive fluid (Exported)
Optical storage device (Patent pending)

12. Our Contribution Biotechnology
Direct binding of biomolecules like BSA,GOD,IG etc., on nanomagnetic particles
Synthesis of biocompatible nanomagnets for MTD,hyperhermia etc

13. Present Talk
Ferrofluid Seal
Synthesis
Direct Binding
Photonic effects

15. Advantages Zero leak No wear Self lubricating Self healing
Long shelf life

17. Burst pressure at 3000rpm Fluid DBM 0.19 0.11 0.04 LS 35 0.34 0.16
Lg=0.075mm
Lt=0.80mm
Lg=0.1mm
Lt=0.9mm
Lg=0.2mm
Lt=1.1mm
Lg=0.3mm
Lt=1.7mm
DBM
0.19
0.11
0.04
LS 35
0.34
0.16
0.08
DOB33
Synthesized
0.32
0.24
DOA
0.66
0.50
0.22
0.29

18. Synthesis (a) Ball milling (b) Co-precipitation
(c) Decomposition of metal carbonyl
(d) Reduction of metal salt
(e) Electrolytic process
(f) Evaporation technique

19. Synthesis contd.
Using the above techniques we have synthesized a large number FFS having different physical properties,
carrier liquid etc.
Notable amongst these are: temperature sensitive fluids using various mixed ferrites , FF with very high viscosity,biocompatible fluids etc.

20. Typical FF Particle

21. Biomagnetic Applications
1. Why Nanomagnetic particles ?
(i) Size is smaller than a cell, a gene & a protein
(ii) They can be coated with biomolecules.
2. What should be their characteristics.
(i) Low toxicity
(ii) High magnetization
(iii) Narrow size distribution
3. Surface Modification.
(i) For stability
(ii) Producing Functional groups for binding
(iii) Avoid immediate uptake by the
Reticulendothelial System (RES)

22. Physics behind the use of FF in BMA
1. Size of FF particle is 4-10 nm
Cell size : 10 to 100 m
Virus : 20 to 450 nm
Protein : nm
gene : 2 nm wide and 10 to 100 nm long
2. A fine magnetic particle can be coated with a biomolecule e.g. protein, silane, starch etc.
This facilitate to interact it with or bound to a biological entity. Thus a biomolecule of interest can be “tagged” or “labelled”.

23. 3. Due to Columbian interaction one can position or immobilize it with the help of an external magnetic field.
It should be remarked here that a magnetic field can penetrate a living tissue. Hence one can transport (i) an anticancer drug to a targetted region of a body – say a tumor by magnetic means.
Moreover nanomagnets can be made to resonantly respond to a time varying magnetic field. This may lead to transfer of energy from the exciting field to the nanoparticle resulting in the heating of the particle. This phenomenon can be used in cancer treatment by hyperthermia.

24. A human body contains biomagnetic materials which may be either diamagnetic or paramagnetic. While the nanomagnetic particle being ferro/ferri magnetic the Signal (magnetic response) due to it is far larger than biomaterials of the body.
Energy is required to overcome the barrier to domain wall motion imposed by the intrinsic anisotropy or impurities on grain boundaries in the materials. This energy is supplied by an external field. Under suitable conditions for a time varying magnetic field there will be continuous flow of energy from field to the material which may be transformed into heat. This is the physical basis of hyperthermia. NMP being SP energy transfer also arises due to the requirement of energy to coherently align the moments to achieve the saturation state.

25. Properties Size Size distribution Toxicity Surface charge
Opsonization and RES

26. They are single domain hence behave as tiny magnets
Size
Size of nanomagnetic particles is smaller than most of the biological entities like a cell (10-100µm) , a virus(20-450nm ), a protein (5-50nm) and a gene (2nm wide and nm long ).
Being nano size they are superparamagnetic and do not retain any magnetization after removal.
They are single domain hence behave as tiny magnets
In the present work we have used co-precipitation technique to synthesize nanomagnetic particles of magnetite , Mn-Zn ferrite. (Ref:Mehta et al Indian J. Pure & Apl. Phys.,44, ,2006 ) . Size by XRD technique was determined and was between 5-11nm.

27. Size Distribution
For even distribution within a system and to have a uniform interaction with the surrounding biological entities it is essential to have an almost monodispersed system i.e.σ < 0.1.
The present systems are polydispersed in this sense i.e.σ ~0.2.

28. Stability against RES
An opsonized particle i.e. a particle coated with plasma protein, is recognized by the body’s reticulo-endothelial system (RES) and thrown out from the system.
Coating by a hydrophilic polymer such as dextran helps to evade RES.
On such coating one can attach a layer of drug.

29. Direct Binding method
A new method was developed by us called DBM.
It dispenses with coating of secondary antibody. Hence even with smaller magnetic field one can control the movement of the particle. Being nanosized particles their S/V high. This increases coating efficiency.
BSA , GOD, IG(g), dispase, and several other enzymes were bound by this technique. More than 90% binding and activity degradation maximum up to 20% was possible.
The method is recently tried by other groups also. ( Huang et al Biotechnol.Prog,19,1723,2003 ., Kouassi et al Biomedical Research and Tech. 2005,3:1. )

30. Experimental Materials and Methods:
GOD,BSA and IG were obtained from Bangalore gene. Carbodimide from Sigma and Coosmossie Brilliant Blue and 4-amino antipyrene from Fluka. Fe salts (AR-grade) and ammonium hydroxide from Merck were used.
2M of ferric chloride and 1M of ferrous sulphate solutions prepared by dissolving appropriate amount of iron salts in 100 ml of double distilled water were mixed and added to 8M NH4 OH with continuous stirring.
(2M) FeCl3,6H2 O +(1M)FeSO44H2 O +(8M )NH4OH →
Fe3O4 + NH4Cl + (NH4)2SO4 + H2O

31. Contd.
The black ppt were heated to 80 C for 30 min. pH was maintained at 10 by adding ammonia solution. Impurity ions were removed by repeated washes of hot distilled water. The particles ( φ = 10nm) were found to be strongly magnetic and were preserved in alkaline medium (pH =8.9). Stock solutions of biomolecules (1mg/ml) in O.003 M phosphate buffer (pH=6.3) were stored at 4 C while carbodiamide solutions in same buffer was prepared just before the reaction.
The % of binding was studied as functions of magnetic particles (x), carbodiamide (y) and biomolecules (z) as well as that of pH of buffer. The mixtures were shaken for 24 hrs. After 24 hrs the bound particles were removed with help of a magnet The supernatant was examined for unreacted portion by standard colorimetric technique. The strength of binding was ascertained by washing the sediments with the phosphate buffer and again checking the supernant for presence of biomolecules. (Ref:A. Dubey (1997) Ph. D. thesis Bhavnagar University)

32. Contd.
In case of GOD the activity was determined by measuring the initial rate of formation of H2 O2. The later is acted upon by peroxide to generate nascent oxygen which react with 4-AAP to form pink colored complex. The absorbance of the colored complex at 505 nm is compared with that of control.

33. Results Under the following conditions activity was ~75%
Bio-
molecule
x:y:z pH
Percentage
binding
GOD
3:1:0.5
4.6
>95
BSA
3:1:0.428
6.3 IG
3:1:1

34. Summary of some other systems
Particle
Coating
Properties
Applications
Ho-Fe3O4
Oleate
D = 11.7 nm
s = 0.3
MDT, contrast enhancement etc
Mn-Zn
Dextran
D= 11.3 nm
Ms= 51 emu/g
MHT
Zn0.5Fe0.5Fe2O4
Md= 200 emu/cc
D= 6 nm -
CdFe2O4
D= 50 nm
S= 0.3
Sensors & Biomedicine
Fe3O4
Silica
Phenolphthalein
D = 5 mm
Ms = 18 emu/g
MDT

35. Photonic Effects
A dispersion containing micron sized magnetic spheres in magnetite based magnetic fluid exhibits
Zero forward scattering
Enhanced coherent back scattering of light
Trapping and release of light
Ref.: 1. R V Mehta et al, Phy. Rev. Lett., 96, ( 2006)
2. R V Mehta et al, Phy. Rev. B,74,195127(2006)
3. R.V.Mehta et al, Current Sci. 93,1071(2007)

36. OBSERVATION OF SOME UNUSUAL
ELECTROMAGNETIC SCATTERING BY FERRO COLLOIDS
Diffraction pattern for electric vector perpendicular to the applied magnetic field in the case of 3m magnetic spheres dispersed in a ferrofluid (28% concentration); (b) H = 30 Gauss (c) H = 60 Gauss (d) H = 100 Gauss (e) H = 200 Gauss (f) H = 500 Gauss. Zero forward scattering is observed for H=100 Gauss (d)
PRL, 96, (2006)
Magnetically induced diffraction patterns by micron sized magnetic spheres dispersed in a ferrofluid disappears at a certain critical magnetic field, and upon increasing the magnetic field it reappears. This critical field is found to depend on the concentration of the ferrofluid and on the volume of the magnetic spheres.
INITIALLY
We attributed this effect to the zeroforward scattering by magnetic spheres as predicted by Kerkar et. al. [J. Opt. Soc. Am., 73, (1983)].

37. nano magnetic particles ~10nm
SAMPLE
Fe2+ / Fe3+=1:2
A - ferrofluid
Fe+2
nano magnetic particles
colloidally dispersed
Host liquid
= Surfactant
~10nm
Polar head
+ hydrocarbon chain
Fe+3 8M
NH4OH
B – micron size magnetite spheres
A + B
System contains small as well as large particles
Dilute ferrofluid matrix
Microscopic image of micron size magnetite coated with oleic acid

38. Effect of addition of different amount of the impurity (i. e
Effect of addition of different amount of the impurity (i.e. silica spheres ~3 m size) on the MPBG.
Variation of stop band as a function of size of magnetic scatterers in ferrofluid.
PRB 74, (2006)

39. After this unusual forward scattering effect we have studied
the backward scattering from the same system
Backward scattering patterns were recorded by tilting the cell by  10° to eliminate the directly reflected light from the cell surface.
At 100 Oe field propagation of light in both the direction is stopped. Then WHERE THE INCIDENT LIGHT IS GOING? However in the backward direction no stop band was observed and a slight increase in the field increases the backscattered intensity by a large amount, nearly 1.6 times the larger than the back scattered intensity at H = 0 Oe. This is similar to the enhancement of coherent backscattering observed in other photonic materials but here it is induced by the applied magnetic field
Forward & backward propagation of light is zero
Forward propagation remains zero
Enhancement in backscattered direction
LIGHT MAY BE MAGNETICALLY STORED INSIDE THE MEDIUM
PRB 74, (2006)

40. OPTICS LETTERS, 33, 1987, (2008)

41. How to verify the magnetically induced storage of light in the medium
At critical field
Incident green
laser beam A B C
Rhodamine die solution at critical field
Abs. wavelength of Rh dye l = 532 nm
Emission wavelength of Rh dye l ≈ 640 nm
(a) Initially when H =0 Oe the transmitted green laser light is observed. (b) at Hc the field of view is dark. (c) keeping the H = HC field on, the laser light is switched off and Rh dye is injected in the sample. An orange colored flash is observed. This confirms that even after switching off the light, captured photons remains inside the field induced structural cavity. When Rh dye is injected they interact with it and emits light of different frequency.
OPTICS LETTERS, 33, 1987, (2008)

42. Can we get back the stored light ???
RETRIEVAL OF LIGHT !!!
We believe that the critical combination of large magnetic particles in ferrofluid and the applied critical magnetic field is instrumental in magnetically induced storage of light.
Can we get back the stored light ???
Try……….
[a] first if we switch off the incident light……!!!
[b] and after switching of the light, in a very short time if we switch off the field…!!
WE OBSERVED A FLASH OF LIGHT
CURRENT SCIENCE, VOL. 93, NO. 8,

43. Photographic view of experimental setup at RRI13 2 3 8 1 10 9 11 4 12 5 6 7 15 14
1 He-Ne laser 2 Electromechanical chopper 3 Beam splitter 4 Reflector 5 Polaroid 6 Photo detector 7 CRO 8 Iris diaphragm 9 Gauss probe 10 Electromagnet Polaroid 12 Photo detector 13 Electromagnet power supply 14 Front view Glass cuvette
OPTICS LETTERS, 33, 1987, (2008)

44. Delay between switching events : 0 ms
Ref. beam
Magnetic field
Retrieved pulse
Magnetic field control
Retrieval time ≈ 550 ms

45. Possible explanation
The optical contrast is likely to be responsible for this effect. Hence, we measured the refractive index of all fluid samples. We also studied variations of the refractive index as a function of the fluid concentration. From the values of refractive indices, we calculated the average dielectric constant εav and compared it with the values obtained
from the Maxwell–Garnet theory
MAGNETOHYDRODYNAMICS Vol. 44 (2008), No. 1, pp. 69–74

46. Possible explanation……
This tunable contrast may induce magnetically controlled Mie resonance in large spheres. The light energy is stored in resonance mode and upon removal of field it may be retrieved.

47. Conclusion What we have here described is only a ‘tip-on-an iceberg’.
There may be many more magical as well as useful phenomena yet to be discovered.
THANK YOU