I know that by definition, van der Waals attraction presents a formidable problem in obtaining colloidal particles that are stable with respect to mutual agglomeration. To prevent agglomeration and keep colloid stable, particles are usually coated with surfactants such as oleic acid which produces steric repulsion. If you have iron oxide nanoparticles coated with oleic acid suspended in hexane, what chemical or physical reactions happen when you add ethanol to such colloid? Is it correct to say ethanol breaks the colloidal stability? I appreciate any explanation or reference to papers or studies on effects of polar solvent on non polar colloids.
Dear Rahman Mohtasebzadeh, at least one should consider the non-solvent (anti-solvent) effect of ethanol. Experimental try is the best witness. Can you tell why you are willing to add ethanol? Is it for destabilisation?. My Regards
The dispersed medium of the colloidal system hexane does not mix with water and therefore the dispersed system will be stable. If amyl alcohol is added, it will dissolve in hexane. The dispersed medium will be different (hexane + amyl alcohol) and the stability of the dispersed system will change.
Dear Rahman Mohtasebzadeh, you should specify whether it is just a simple addition or it is accompagnied with mixing. Ethanol is used to wash off nanoparticles from stabilizing agent, so obviously if addition with mixing the stability is eliminated and the result is setteling of the dispersed phase. My Regards
Thank you for the responses Mr.Mirgorod and Mr Bouaziz,
Mr. Bouaziz, it is a simple addition of small amount of ethanol in hexane colloid.
Dear Rahman Mohtasebzadeh, at least one should consider the non-solvent (anti-solvent) effect of ethanol. Experimental try is the best witness. Can you tell why you are willing to add ethanol? Is it for destabilisation?. My Regards
as stated by Yuri, addition of ethanol or any other solvent miscible with hexane means the continuous phase changes. Ethanol is not expected to change the coating with oleic acid in first place, so you can expect that destabilization will eventually happen due to worsening of compatibility with mixed solvent if ethanol content gets too high.
That's an excellent question, Rahman! I think in your scenario of oleate-capped iron oxide in hexane/ethanol, the short answer is that the key physical process is the solvation of ligands in hexane vs. ethanol (good in hexane, poor in ethanol, see this excellent recent paper for details and references therein: Article Entropy Can Bundle Nanowires in Good Solvents
), and a chemical process - stripping of oleate/oleic acid from the surface and replacement with ethanol/ethoxide species (can't recall reports for iron oxide at the moment, but such ligand stripping has been previously studied in semiconductor nanocrystals:Article Short-Chain Alcohols Strip X-Type Ligands and Quench the Lum...
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