I am trying to make a coating of Al2O3 .But for that I need to disperse the al2o3 particle. So how can I do that?
if you do not want commercial surfactants you can just use organic acids e.g. citric acid or acetic acid, stability in the acid range is very good at pH ~ 4.5 - 5.
Atasi,
I suggest you to use an specific dispersant: Dolapix PC 67 (from Zschimmer & Schwarz), and you can start with round 0,4% (% of solid content).
During synthesis, cap the nanoparticles with some capping ligands, which will help to make them disperse in organic solvents. Then after the coating, heat it in furnace at high temperatures to remove the capping ligands...
if you do not want commercial surfactants you can just use organic acids e.g. citric acid or acetic acid, stability in the acid range is very good at pH ~ 4.5 - 5.
In the pH range 6-11 you can use polyacrylic acid Mw from 2 000 to 15 000 depending on particle size, with ratio of about 0,5-0,6 mg/m2
to understand this look at the zetapotential curve of alumina in water (see article zetapotential in wikipedia) zetapotetial is 0 at pH ~ 9, this means there is no surface charge on alumina at this pH and the dispersion is completely unstable, to obtain stable dispersions you have to go either into the alkaline range (alumina will be close to dissolving at high pH before becoming stable) or to lower pH, maximum stability is reached at pH ~ 5. Is does not matter much by which acid addition you come to this pH value. This is the principle of electrostatic stabilisation, i.e. the particles are charged with the same (positive or negative) charge and their electrostatic repulsion prevents flocculation.
Other methods proposed are based on steric stabilization or electrosteric stabilization here molecules acting like tensides are applied which keep the alumina particles at a distance.
Could we call this type stabilization electro-steric as citric acid adsorb on particles surface as well?
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