You can use infiltraton instead of centrifuge. I think you must change your drying process. I think you are compacting your powder before you add toluene. And when you compact, it becomes dificult to capillary infiltration to disperse the powder.

Dear Inacio Regiani, Thank you very much for your answer. Yes, I also think that something is wrong with the compacting and drying process. After receiving particles in compacted form after washing with Acetone, I make solution in Toluene and a trace amount of Oleic acid and then I evaporate Toluene using Rotary evaporator for better capping/wetting effect of particles by Oleic acid and then re-add toluene for final dispersion.

Can you please explain little more about infiltration process so that I can use it without any loss of the TiO2 solution?

Dear Dr. James H Adair, Thank you very much for your useful advice. I dont have pyrrollidone silane agent so I tried the second general approach which you mentioned with 5 different silane coupling agents but results were not good. I think either it is due to the presence of water molecules on the particles' surface or may be particles clustered together. 

Now I am again synthesizing TiO2 particles with more high aspect ratio so that it will be easy to separate them and disperse them.