In the synthesis of nanofluids, literature merely suggests the addition of surfactants, not much data is available regarding the activation conditions, optimization of surfactant concentration etc. Is there any specific activation temperature at which their adsorption on nanoparticles will commence? or will adsorption take place by mere storage time?
In my study I have observed that effectiveness of surfactants in promoting dispersion stability is better with prolonged storage of nanoparticles in it. Is this a true observation, or is there any other component in play?
Dear Binu: The process of stabilization of disperse systems depends on the type of disperse systems, the structure of the surfactant, temperature… Very slowly there are processes "aging": recrystallization, isothermal distillation, the changing nature of the adsorption of the surfactant. They are accompanied decrease in the surface energy. Disperse systems of the thermodynamic and kinetic unstable. Your case is an exception for a certain period of time. After a long period of time nanoparticles settle. For a detailed analysis is necessary to know the composition of your system.
Dear Prof. Mirgorod,
Thank you for the information. My objective is to maximize the colloidal stability. The colloid in question is TiO2 nanoparticles in engine oil. One of the surfactant I am using is Oleic acid. I have decided to go for zeta potential analysis on samples after particular periods of storage time of nanoparticles in surfactant, to understand the role of adsorption time. What are your thoughts on this?
Thank you for your time and suggestions.
Better in some vegetable oil. This is closer to the problem application bundle colors.
Regards.
why do you think you would have some charge on the surface of your particles? The oil is nonpolar and you produce STERIC stabilzation. I don't question your methods, I simly want to have some insights. What information can you get with the zeta potential in this case?
Dr Kubrin,
I am shooting in the dark here. I have got repeatable results which shows improvement in stability when I store processed nanoparticles in surfactants for more than 8 hours and then sonicate the samples. There is some change happening in the solution. I am guessing that adsorption of surfactant molecules on nanoparticles is altering surface charge and could be observed by monitoring the the zeta potential.
How do you measure the improvement in stabilty? Do you quantify it anyhow?
I am monitoring UV vis Spec peak absorbance of supernatant for stability... But the difference is visually apparent too.
Assume you use something like pyrogenic titania, which are highly aggregated and agglomerated primary nanoparticles. Therefore you may indeed have time effects. Would further assume that oleic acid does not only play a role in stabilizing the particles but also in the process of dispersion by breaking interparticle bounds (transforming Ti-O-Ti into Ti-O-Ac).
For characterization you may simply use change in transmission in visible range (smaller particle will give higher transmission on average) or turbidity ratio - ratio of extinctions at higher and lower wavelength (lower wavelength is more sensitive to smaller particles).
Dear Dr Sobisch,
Thanks a lot for the wonderful suggestions!!! I will work on it.
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