Dear Fatima

Here is a suggestion which may not be realistic, but think of it

Suppose that you prepare small spheres and you keep them non-agglomerated, and you can then anneal them while they are far away.

Heating will then smooth their surfaces based on surface tension of liquids. I would think of that.

This resembles your fingers which become smooth with time due to surface tension.

If a small particle is heated enough while being alone, it will have more spherical shape.

But it should not be heated while in contact with other particles (otherwise it will agglomarate).

Think of that

Thank-you for both your responses, much appreciated!

 @ Debmalya - For my small particles < 10 nm and larger particles > 90 nm, i have smooth surfaces and it is only the intermediary particles which are very rough presumably because of the nucleation and growth mechanism. 

I am using l-ascorbic acid as my reducing agent primarily because of its weak reducing power and sodium citrate as the stabilizer. I am not using oleyl amine, how will this in any way influence my surface roughness? 

It is very important for my experiments that the surface chemistry of my Pt-np remain homogeneous and non-functionalized, this is why I am not using any additional surfactants /ligands/capping agents etc 

@Hikmat - I have tried playing round with the heating rate but increasing it and allowing the nano-particles to cook for longer. However,  I think it is not possible for all my particles to stay non-agglomeration at one time (there will always be to a certain extent some agglomeration).