The aim is to prepare a concentrated silica nanoparticle dispersion (si=70wt%) in a glycol medium with minimum water content.
Method A: I dispersed silica nanoparticles (diameter 450nm) in deionised water with a high shear mixer. Then I centrifuged the dispersion at 8,000 RCF (8000xG) for one hour and obtained a clear supernatant and silica particle pellet. After removing the supernatant, I transferred the silica pellet to a grinding jar of a ball mill. I added some ethylene glycol and ball-milled the silica pellet-EG mixture for an hour and obtained a seemingly homogeneous silica dispersion.
Method B: I added dry silica particles and EG in a grinding jar and ball-milled the mixture directly. I can obtain a relatively homogenous silica dispersion as well.
My question is: which method can prevent silica particles from forming micro-aggregates?
Please help. Thank you.
Eric Dickson
In method B, ethylene glycol does not participate in the unification of silica microparticles and prevent silica particles from forming micro-aggregates. In the first method, the hydroxyl particles of silica interact with the hydroxyl groups of ethylene glycol.
Dear all, please specify the area of this investigation. Is is for shear thickening fluids (nanofluids)? If so, VEROS and modified VEROS preparions techniques are exclusively followed, extreem and long lasting stabilities are attained. Other thing to specify, the word glycol applies to both low molecular weight compounds such as ethylene- and propylene- glycols and to polyethylene glycol polymers . My Regards
Yuri Mirgorod
Thank you for the answer.
Do you mean that method A is better than method B? Also, what are 'soft aggregates' and 'hard aggregates'? How can I know if my silica pellet after centrifugation is 'soft aggregate' or 'hard aggregate'?
Please help, thank you.
Abdelkader BOUAZIZ
Thanks for your answer. Yes, I am attempting to prepare a silica-based shear thickening fluid. I have identified the two methods (stated in the question above) but I do not know which method I should use to prepare a stable shear thickening fluid.
I don't particularly like method B because dried silica particles are difficult to be broken down into their individual diameters..That's why I think I should always disperse the dry silica particles in an invicid fluid and replacing the dispersing agent with another dispersing agent.
Thank you, Eric.
Dear Eric Dickson, first I think 450nm particle size is too high for shear thickening, second if you can use sonication in method A better results will be achieved. My Regards
Abdelkader BOUAZIZ Thank you for your answer. Do you mean I should re-disperse the silica pellet in ethylene glycol via sonication?
I am not sure if sonication works in this case, because I will mix 70wt% silica pellet and 30wt% ethylene glycol. The mixture will be too viscous to sonicate.
Eric.
Dear Eric Dickson, proceed by gradual addition (starve feeding) of silica. This purely experimental, try and see, hope it works. Have you documented the effects of milling on both silica and EG? My Regards
Abdelkader BOUAZIZ Thanks for your answer. No I haven't but I will in the near future.
OK, I'll try to add silica pellet gramwise in ethylene glycol and sonicate it with a probe sonicator for 10 mins for every gram of pellet added.
Regards, Eric.
Eric Dickson
When two particles interact (in the theory of two plates), their potential energy tends to 1. the first minimum upon contact. On the potential energy curve, depending on the distance between the particles, there is a second minimum at a distance of one solvent molecule or several. The first units are called rigid. The latter are called soft. The term "soft matter" also refers to all aggregates of surfactants, proteins, DNA ... These aggregates are due to the intermolecular interaction of water with each other. COVID (DNA and protein) exists because these molecules are surrounded by a thin layer of nano-sized water molecules. If the water disappears, COVID will disintegrate. COVID is soft matter.
Silica is obtained from silicon hydroxide. Despite the fact that hydroxyl groups almost disappear when heated, silica absorbs moisture well. The more hydroxyl groups remain on the surface during processing, the greater its interaction with ethylene glycol with the formation of soft matter.You can see the new theory of soft matter in the articles
Article Liquid Polyamorphous Transition and Self-Organization in Aqu...
Preprint Quantum entanglement in micellar solutions of ionic surfactants.
Preprint Quantum and thermal liquid -liquid phase transitions in aque...
Kindly check https://www.researchgate.net/publication/257629277_Shear-thickening_behavior_of_modified_silica_nanoparticles_in_polyethylene_glycol
Also check https://www.researchgate.net/publication/272613827_Preparation_of_SiO2PEG_Shear_Thickening_System_by_Centrifugal_Dispersion
Chinaza Godswill Awuchi , many thanks for recommending the references. The modification in the 1st reference is similar to what we have done in method A. We want to 'insert' water molecules in between two dry silica particles, so the silica pellet obtained from centrifugation can be relatively easily re-dispersed in ethylene glycol. By repeating the centrifugation and water-ethylene glycol exchanging processes, we hope to reduce the water content to the minimum.
We understand that the mechanical energy needed for dispersing dry silica particles in ethylene glycol, particularly at a high particle concentration, is very high. Not only because ethylene glycol is a relatively viscous fluid, but also because, when silica concentration gets above 60%, the silica-ethylene glycol mixture gets too viscous to stir.
Best wishes, Eric.
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