I would like to receive comments on the alignment of ferrofluid droplet with an effect of magnetic field [ kindly check the attachment ] . For same quantity and same magnetic field , distance the ferrofluid droplet of different particle size exhibits different pattern , smaller particle size tends to accumulate more closer [ Fig.a ] , with increase in particle size , it tends to spread out [ Fig. b ] , with an effect of surfactant for smaller particles , it tends to spread in larger area [ Fig.c ] and if the magnetic field is moved then accumulation is towards one point leaving behind some particles away from magnetic field [ Fig.d ] , can somebody explain the relation between the effect of magnetic field on various pattern for particles with different size . need clarification on accumulation , spread out w.r.t particle size and magnetic field.
I would like to add few more information , it is aqueous based ferrofluid , surfactant used is citric acid which is very polar , strong permanent magnetic field is used and electromagnetic is not used. droplet quantity , magnetic field , distance between magnetic and point of interest were kept constant , only difference is particle size and [ with / without surfactant ] , in case of Fig.D the magnetic is slightly moved towards right eventually more accumulation on that area then lest side. In Fig.a ,particle size less than 50 nm and in FIg.c , particles were around 150 nm with surfactant and in Fig.b,d same ssytem without surfactant . I was interested in finding the behavior of these droplet pattern with a relation between particle size and effect of magnetic field
Magnetic fluid should be attracted to places with gradient of the magnetic field. The a) situation should be present when pernament magnet is far. As the magnet comes closer, the fluid is more attracted to the bottom and you shoud get situation b (I think it is a bit exegerated). Then because the fluid polarizes itself, due to dipole-dipole interaction inside ferrofluid you will get symmetry breaking (c and d pictures). I suppose you shoud get with the same probaility situation d) and mirroring situation d by vertical mirror.
Jaroslav , can you relate something with nanoparticle size and the pattern exhibited due to the magnetic field ?? any view on the effect of different particle size and FF pattern [ accumulate or diffuse ]
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 Prof.Mehta , thanks for the references , especially APL paper ; all the references describe the variation in droplet shape w.r.t distance from the magnetic field , but i would like to know more about the effect of particle size and surfactant on the inter facial shape of ferrofluid under the presence of magnetic field [ any distance] , any suggestion / references on this topic will be highly supportive , thanks .
You may try to seprate out magnetic size of your particles and size of surfactant molecues. Each surfactant (assuming monolayer) coated on bare magnetic particle will increase its hydrodynamic size.
It has to be added citric acid is no surfactant at all, i.e. it does reduce surface tension at higher solute concentration only by a few mN/m. It is a polar solute of low molecular mass.
Dear Vikram ,
I do not insist on the correctness of my explanation, but I like it for its simplicity.
Fa and Fb: If the size of the nanoparticle increased 2 times, its weight increased by 8 times. It seems that the drop spreads out under its own weight.
Fc: Better surfactant, greater area that it occupies.
Fd: The drop becomes so shaped as it has friction of rest.
Dr.Shur,
Thanks for your comments , can you please more on Fc , with effect of citric acid why it occupies more area , can i assume that the repulsive forces between particles due to citric acid is the reason behind this behavior ? , while compared to Fa which does not have citric acid , any proper literature for this part , I was studying these behavior under hydrodynamics and expecting similar behavior ; i was keen on knowing the behavior especially in Fc , thanks.
Dear Vikram,
I will not explain here how a drop on a variety of materials is formed. Why is gasoline spreads on the water in a monatomic layer. This is all described in detail in the books, and I will not do it better.
It is not hydrodynamics. These are: the surface tension; wettability.
I have to admit that the forces between the particles are not repulsive but attracting!
Do not hesitate to ask me questions. I'll be glad to answer.
Yours sincerely
Dear Vikram,
Sorry, not all of your questions, I answered.
I do not think that the forces of interaction between the particles depend on the concentration of acid. Acid is not ferromagnetic, therefore does not shield the magnetic field.
Yours sincerely
not sure about composition of your ferrofluid - is A simple hydrosol?
This is usually poorly stabilized, i.e. contains larger agglomerates. So maybe this is the origin of difference between A and C.
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