Dear Dr Rawle

Could you kindly clarify the mixing process from you point view in details.

Regards

Dear Dr Chaichan

I think using ultrasonic shaker for a period of time will help you in mixing nanomaterials with water.

Regards

I'm agree with Mr. Khalil, about ultrasonic shaker  for a time until all the sedimentation is disappear. Thanks

Kind Regards 

It is possible to control it by adding heat sinks  materials 

Dear Dr Khaleel and Dr Mahdy

Thank you for your contribution. I have used this technique several times and failed to keep the nano-particles mixed with the water for hours.

Regards 

Dear Dr Sanaa

Thank you for your suggestion. Can you give me examples of these heat sink materials.

Regards

Nanoparticles invariably will not be stable in DI water.  The attractive van der Waals forces will mean that aggregation and agglomeration of the particles will follow as certain as night follows day.  Nanoparticles need to be stabilized either with appropriate charges (charge or electrostatic stabilization) or with attached polymers shielding the core particle (steric stabilization).  You can see some illustrations of this from slide 44 onwards in:

Nov 11th, 2008. Dispersion and nanotechnology  http://tinyurl.com/hpywsge

Functionalize of nonmaterial with groups contain O, S, or N may  enhances dispersion in distilled water 

Dear Dr Rawle

Thank you very much. You are a great help to me. Could I contact you if I need more from your wonderful experience.

Regards

Dear Dr Al-Shamsi

Could you help me by clarifying the functionalize process.

Regards

Functionalize with amine ,thiol,hydroxyl and carboxyl groups is successful in case of CNTs,rGO,GO,fullerene ,carbon nanoparticles,soot ,..etc. In case of metals and metals oxides nonmaterials ,surfactant assisted sonication may be useful. Surfactant such as DEG,PEG,DBS,CTAB..etc

Dear Dr Alshamsi

Thank you very much for your wonderful clarification.

Regards

I would agree with Hassan and Alan, 

to prepare stable nanofluids for a long period of time is still not been accomplished. 

Three main methods are used to prepare nanofluids:

1. By changing the ph level of the basefluid, trying to have the nanomaterials dispersed in the basefluid with either negative or positive zeta potential value, the value abour the isoelectric point. 

2. By adding surfactants such as arabic gum, SDS, PEG, PVP, or anything polymer that completes the chains or keeps the nanomaterials dispersed in the basefluid. 

3. Researchers have also used COOH and OH functionalized nanomaterials which show better stability compared to normal nanomaterials in water. 

Time of sonication and amplitude also effects the stability and a high pressure homogenizer is better for stability compared to sonicator. 

Dear Dr Said

Thank you very much for your wonderful clarification.

Regards

@ Zafar Only one comment on 1. above as I suspect a typo in your text (as well as ph for pH)  The zeta potential must be well away from the isoelectric point for stability.  The IEP is the place where instability is greatest and the most statistical likelihood of precipitation, agglomeration, settling etc  For nanomaterials (< 100 nm) a zeta potential of magnitude 30 mV (as reported in the literature) is definitely insufficient to confer stability. Even for 350 nm TiO2, then - 50 mV is needed for stability.  For 10 nm material probably nearer to 100 mV in magnitude.

For any ionic additive (be it citrate or phosphate, or anionic surfactant) there's always an optimum level.  Too much destroys the double layer and caused salting out.

I agree with Alan F Rawle. Mostly in preparing stable dispersions, one should look at the surface charge of their nanomaterials and try to add suitably oppositely charged surfactant and mix with bath sonicator. Choosing a right surfactant with suitable concentrations is the key in preparing stable dispersions.

Dear Gunda

I  used this technique of mixing, the water bath shaker device for hours but failed, and the nanomaterials was sediment. Thanks

Kind Regards.

Dear Aedah,

Do you use any surfactant?

dear dr miqdam

I agree with Hassan and Alan and Zafar Said, so i think that Three main methods are used to prepare nanofluids.

Dear Dr Rawle

Could you kindly clarify the mixing process from you point view in details.

Regards

Dear Dr Mahdi

I have passed through the same experiment.

Regards

@Alan

as always there are exemptions of the rule. Nanosilica dispersions are highly stable against agglomeration at IEP without any stabilizer.

Therefore Miqdam, you may build your nanofluid system by using commercially available silica suspensions like Ludox, ...

@Titus  Yes, you are right with certain specific situations.  However, it is best in many situations to answer in generalities on ResearchGate - my answers are trying to provide a general framework of charge and steric stabilization..  Again there are exceptions to your comment!  Nanosilicas are not stable at pH's > 12 (they dissolve).  At the iep there is the statistical highest probability of agglomeration - doesn't mean it will happen.

it seems agglomeration is prevented by high sterical (self) stabilization. In general? highly solvated particles are stable against agglomeration, i.e. zero probability if they like community with solvent more than community with each other.

@ Titus - you make a good point. The shield of solvated molecules around such entities can also confer stability.  However, in the nano field from the 1860's (Faraday's gold sols) onwards we find a lot of witchcraft and pseudo-science in terms of nanoparticle stabilization - gums and organic materials.  Sometimes they work; sometimes they don't.  From a personal perspective, I'm trying to get more science into this area - I spent a whole Ph.D working on the stabilization of small metal and metal alloy systems and there are generalities that can be employed and some easy empirical jar or beaker tests to gage (or gauge as it was in my day) stabilization.

Dear Dr Sobisch and Dr. Rawle

Thank you for your valuable discussion. Is not it wonderful that we can cross-communicate by RG to find a scientific and practical solutions to research topics with the help of leading scientists such as yourselves.

Best regards

Dear Dr. Miqdam

Thank you: but I want to ask about the normal water, so

What is the best way to mixing nanomaterials with physical water in large quantities without   allowing him sedimentation?

usually it does not make to just mix nanomaterials with water if you do not succeed in keeping them sufficiently dispersed/stabilized. Nevertheless, you find the answer to Your 'pure' question in Stokes law minimize density difference, ideally to zero and/or increase viscosity.

Dear Dr  Sobisch 

Thank you for your scientific advice.

Regards