I am wondering if adding nanoparticles to liquids can reduce the viscosity? And is there a certain type of nanoparticles having this ability?
Thank you in advance.
No, it is not possible. Einstein showed that adding particles of any size to liquids always increases the viscosity.
Many thanks to you, Alan. But recently, I got results from a rheometer which shows that' adding copper nanoparticles to a mixture of DI water, Gum-Arabic and sodium citrate reduces the viscosity of this mixture. Copper nanoparticles concentration increases, viscosity decreases'.
I would be grateful if you have an interpretation to this.
Yes, it can happen for Shear thinning (or pseudoplastic) fluids!
It happens in this kind of fluids because at the applied shear rate the particles are in the stream direction and lead to a decrease in the viscosity. For more information please refer to the following text book:
Non-Newtonian Flow and Applied Rheology: Engineering Applications. By R. P. Chhabra, J.F. Richardson
Dear Ali Nematollahzadeh, I've read the section '1.3.1 Shear-thinning or pseudoplastic fluids' as you suggested me and I could not find a relation between the reduction of the viscosity and the nanoparticle concentration. There is no mention of nanoparticles in this book!
I would be grateful if you can give more details (explanation) about your first answer.
Aimen - you did say "liquids", which I interpreted as "simple liquids". A solution of gum Arabic is something different :-). I can imagine in this case that adsorption of gum Arabic onto the nanoparticles will change the conformation of the gum Arabic molecules - making them more compact, so that the viscosity is reduced by the addition of nanoparticles.
Thank you very much Alan Parker. Yes, it is my mistake. So I have to say sorry. This is because I am a mechanical engineer not a chemical engineer and I have a shortage in the chemical engineering.
Can I imagine from your answer that the viscosity of the solution is related to the size of the gum Arabic molecules- molecule size increases, viscosity increases?
No problem. Here's the key idea: the polymer (gum Arabic) molecules in solution have a very open structure, so the fill a large volume & leading to high viscosity. They are surface active so they adsorb (stick) to the nanoparticles. When on the surface their structure is less open, more "crowded" close to the surface, so they will have a lower volume and will not be so good at viscosifying. I hope that's clear.
Dear Aimen Zeiny,
I basically agree with Alan Parker, but let me go further. It is not excluded that gum Arabic (adsorbing on Cu-nano-particles) will connect several nano-particles, which finally form such a big aggregate that can settle down due gravity. If this happens, the role of your nano-partcles is a "cleaning agen", so it reduces the concentration of gum Arabic in the solutiion, and so viscosity reduces. But: do you observe any sediment at the bottom of your solution?
Let me also add, that basically it is not possible (viscosity reduction), if there is no side effect. So, you can explain your observation only by a side effect. One of the possible side effect is what Alan explained and I developed further.
George
there may be also an interaction of the copper nanoparticles with the citrate changing the interaction between citrate and polymer. In a complex system there are many interactions leading to first hand surprising results.
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