I am preparing alloy nanoparticles by ball milling. But, the alloy nanoparticles have neutral surface. How can I make the surface positive or negative charged so that I can add some anionic or cationic surfactants to it???
You need to determine the particle size. In accordance with the size of the surfactant added so that they formed a dense monolayer first. Then add the desired portion of the second surfactant to form a second layer with your desired charge.
Best regards.
Generally you have to coat nanoparticles with some kind of coupling agent. For example, an extremely dilute solution of 3-aminopropyltrimethoxysilane or tetraethoxysilane in volatile solvent like ethanol with continuous ultrasonication will help. You can spray dry such coated nanparticles to achieve the desired particle flow characteristic. Later, you may use any cation/anionic surface as desired for the suspension.
Dear @Dr Yuri, should the first surfactant be any charged or chargeless surfactant???
If your nanoparticle is some kind of ferrite add a acid like HNO3 and use a negatively charged surfactant. Especially for oxides the point of zero charge can be determined quite easily and is often well-known.
The first surfactant is adsorbed on the surface of the charged group. The second surfactant tail to tail.
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