Should I add water after homogenization or after solvent evaporation???

I would say you may try both methods to see which works better for your nanoparticles, since both methods are not complicated and should be easy to give a try. Adding water after solvent evaporation probably better since the emulsified nanoparticles can be fixed after the solvent is removed from the systems, so adding water then may not dissociate your nanoparticles.

The purpose of addition of water, is to diffuse partially misciblity solvetn e.g. Ethylacetate to the external phase....therefore it should be added immediately after homogenization.

thank you everybody ;) i read another article and it should be after homogenization... that why the name "diffussion" :P