The cheapest and most common nanoparticles are oxides, such as SiO_2 and Al_2O_3. They can be obtained as powders or solutions. SiO_2 particles are typically symmetrical in shape and have a relatively narrow size distribution; Alumina particles are often irregular in shape and have a wider size distribution. Both are relatively easy to dissolve in water (control the zeta potential by controlling ph).

In addition to the above suggestion I also suggest the use of a surfactant to encourage homogeneity.

Thanks Tapio and Kettner for your suggestions.

Nitin

Surfactants can be great help but controlling the zeta potential is the most important thing, We've taken a lot of DLS spectra and TEM pictures of (frozen) samples of nanofluids recently and the results show that you cannot trust that what you buy is what you get...

I think its better to go with Tapio's suggestion of using SiO_2 before trying use a surfactant.

An example of nano suspended particles in water is milk. What kind of Nano materials do you have in mind?

Milk is a complicated colloidal liquid, not a nanofluid. One of the main challenges in the field is to be able to prepare nanofluids with a well-controlled size distribution of the particle phase.

Thank you for the comment. Now what is the definition of nanofluid.

Citrate capped nanoparticles are easy to make, and cheap enough to buy. I've had these stay in solution for weeks/months. If you order these from a company, you can talk to their reps and they will give you particles with a capping agent that will preserve their stability for a long time.

Oops, should mention these are GOLD nanoparticles in particular.

Definition: Nanofluid is a composite liquid-solid material, comprising a solvent (e.g. water) and a solid phase of nanoparticles, i.e. particles whose size is less than about 100 nm. Nanofluids are a limit of colloidal systems, where gravity (sedimentation) can be neglected. Typically, theories of the Maxwell-Garnett type to describe the physical properties of nanofluids fail due to large fluctuation effects.

How surfactants help in maintaining the homogeneity of size of particles?

Sal, could you please rephrase your question more clearly?

Make sense. But any scientific reason for 100 nm limit. I need to think about this some more.

By definition: A colloid is a substance microscopically dispersed evenly throughout another substance.The dispersed-phase particles have a diameter of between approximately 1 and 1000 nano-meters.

I think Prof. Krishna means to say that the surfactant prevents particles agglomerations and thus keeps homogenous size distribution.

The (approximately) 100 nm limit is set by sedimentation (in water), i.e. the Peclet number is small enough such that Brownian motion dominates.

Can we say that the particles (i.e the ones which are enclosed in micelle) are of uniform size ? Do the surfactant molecules form micelle of uniform size ? Can we expect any particular range of sizes of micelle ?

I am asking these questions to get a more accurate information.

Thank you

Dear Sai Krishna, please look on the article "Surfactant-Assisted Sol-Gel Synthesis of TiO2 with Uniform Particle Size Distribution" available here http://downloads.hindawi.com/journals/ijic/2011/108087.pdf

As mentioned the particle size is important, one experiment I would suggest would be to study the difference between a nonmoving and a very slowly moving fluid (i.e. strongly laminar) with nanoparticulate. This is because the B-field component of your EM field can obviously do no work on the particles while the fluid is still. However with a moving fluid, the B-field can potentially polarize the particulate to a degree, as the flow combined with the B-field presents the opportunity to do work on the particles due to the Lorentz force, assuming the particles develop a charge in the E-field. By varying the flow with Reynolds numbers between zero and about 1000, you should be able to build up a profile of how the particles move in the EM field. Your measurement might include the voltage perpendicular to flow direction, which indicates the potential in the charge separation. If you have any questions, please feel free to contact me.