In the solution phase reduction for the nanoparticles preparation methods we are using surfactant to stabilize of the nano solution or dispersion. In case we centrifuge and dried the sample to get the solid sample, if we disperse it again in the solvent, whether we will get the same stable dispersion or the stability will decrease? What happened to the surfactant or stabilizing agent after centrifugation?.
Are the surfactants chemically bond to the particles? If not, the adsorption of the surfactant molecules to the particle surface is in equilibrium to free surfactant in the solution. Changing the surfactant concentration in the bulk (e.g. diluting) might have an effect on the stability of the dispersion.
Well, by centifugation one can separate HEAVY WATER D2O from the bulk of largely H2O. All you need is a High RPM and TIME.
Bou, in the case dispersion of solid particles is stabilized by surfactants, the fraction of surfactants adsorbed on solid surfaces will be centrifuged out along with solids.
In general, if you centrifuge many times (over 5x) than it is possible that your surfactant comes of your nanoparticles, even if the surfactants are strongly bond to you particles. So, if your sample is purified after 3 centrifugation & wash cycles, than it is better to stop. If you really want to make sure that your mixture is purified, you can 'play' with different kind of nonsolvents, to precipitate your particles.
I also would not recommend to dry your sample if you want to redispers you particles. This can cause a decrease in stability of your suspension. Hence, after centrifugation and removal of the supernatant, you can already add your solvent to your precipitated particles.
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