Some articles have discussed the dispersion of nanoparticles in "pure ethanol" in which the pure ethanol by forming a gelatin-like layer around the nanoparticles causes the stabilization of nanoparticles without surfactant for a while (3-4 hours- Al2O3 nanoparticle).
I used the pure ethanol (99.5%) for dispersing of Al2O3 nanoparticles, but their stabilization did not last for more than an hour.
In your opinion, is it possible that the application of 99.9% ethanol causes an increase in the stabilization of nanofluid for 2-3 hours without surfactant?
Can you show these articles which you are referring to? (make a scan and attach as pdf, or if fully published on the web, send a link)
2- http://www.nanoscalereslett.com/content/7/1/226
article's name : Surface tension of Nanofluid-type fuels containing suspended nanomaterials
thanks, in article 1, Ref 22 is mentioned, did you get that one as well, can you send a scan as attachment?
For article 2, I can already say the following: I do not believe that they had stable dispersions / stable colloids; it is absolutely impossible to have such high (up to 10%) nanoparticles in a stable colloidal system, already at around 1%, if really dispersed in nano size, the dispersion will become a gel / a soft solid.
Or maybe they got some suspensions with bigger sized agglomerates.
The problem is they did not report about a) particle size for the time when they measured the surface tension b) how long these dispersions had been stable. That article 2 is fuzzy superficial work.
For article 1, they claim to have a 0.1% dispersion (and stable), but although the particle size they mentioned is well within nano scale, both dispersions are not clear transparent, but one is milky, the other one non-transparent black.
This already tells you: they did not have well dispersed colloidal systems.
for the purpose of their studies, this does not matter, they wanted to see the effect of radiation onto droplet evaporation, but for the question of how long such dispersions are "stable" (anyway, these are never really stable, see below) this matters a lot.
About "stability of colloidal dispersions": frankly spoken, I do not see a real difference between around 1 hour and 3 - 4 hours. Anyway, these are unstable, they are already not reall colloidal dispersions! if really colloidal, they must be transparent clear (maybe coloured, but transparent!), then the effective particle size is well below 1 µm.
As the "dispersions" mentioned in both articles are not transparent, the particle size is well above 1 µm, such dispersions will not be stable without surfactants.
Finally, the "stability" you are talking about is probably only determined visually, right? in reality, one should measure the development of particle size over time, but that makes only sense if you start with particle size well below 100 nm. Also, the nanomaterial source is critical: as you will not have the same material as the authors of the articles you mentioned, you can not get the identical results, even if you were using exactly same dispersion methods (which also will be different, I assume).
You should consider that dispersions are non-equilibrium systems, that means, the results of a preparation process are very much dependant upon the starting conditions and the exact process history which you can never exactly reproduce.
(non-equilibrium systems are chaotic systems, like "weather": when do you have the exactly same weather as you measured at a certain day / time? never, it is always changing)
also Ref 14 is a key reference, as it describes the preparation technique, did you check it?
Dear Dr.Bernhard Wessling , thanks for your answers. would you please give me your email address for further explanations about the case?
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