Nikhil Mane No such thing as a 'nanopowder'... There are no free, independent, discrete particles < 100 nm in any powder. It's a collection (at best) of a group of post- and sub-micron aggregates and agglomerates.

As two metal oxide nanoparticles may not only differ in particle size but also property profile which would reflect upon the stability of nanofluids when mixed metal oxides are suspended in a suitable solvent. Stability of nanofluids is very vital property under the given conditions when used for one or the other purpose like heat exchange or lubricant etc.

Alan F Rawle You are right and not right. The term nanopowders is often used by manufacturers of nanoproducts.

Nikhil Mane The term nanofluid does not apply. Instead, there is the scientific term dispersed system. The dispersed system does not have the properties of a liquid. Physicists have historically used the term magnetic fluid for the dispersed system of magnetite in kerosene.

The term nanohybrid is used for core / shell nanoparticles. If two varieties of nanoparticles are present in the dispersion, then it is better to call such a dispersion a mixed dispersed system.

The answer to your question. I see no reason for refusing to use a mixture of two types of oxides to solve scientific and technical problems. Usually mixtures give a synergistic effect in some cases.

Nikhil Mane

You will find satisfactory answers to your question(s) by looking into the "colloidal dispersion" literature rather than the "nanofluid" literature, which is often the case with me.

But generally speaking, the colloidal stability of dispersions with (nano)particles of different materials/sizes/morphologies (such as hybrid/blended/composite nanofluids; these terms are really blurry in the literature and seem to change every other day) is often more challenging to attain compared to the case of dispersions with similar, monodisperse (nano)particles.

The former case results in hetero-clustering, while the latter results in homo-clustering.

To name a few of the anticipated challenges I can think of when attempting to impart electrostatic or steric stabilization on hybrid/blended/composite nanofluids:

1. Nanoparticles of different materials can have different surface charges (in sign and magnitude) when immersed in an ionic solution. This leads to difficulties in electrostatically protecting particles against hetero-clustering. In fact, you could end up with a situation where vdW attraction is aided by the attraction of oppositely charged surfaces over some of the pH range.

2. Nanoparticles of different materials can have different affinities towards polymer stabilizers and base-fluid molecules. This leads to difficulties in sterically protecting particles against hetero-clustering.

3. Nanoparticles of different materials can have different effective Hamaker constants when interacting with each other.

A special case of hetero-clustering, which I believe is of relevance to your question, is the deposition of (nano)particles on a collector of different material.