Sonication leads to de-aggregate particles. So, when we coated Fe core with PEI we use the sonicator for this purpose to get a small size, but when we coated it with Au we avoid using the sonicator because it breaks our particles and distorts their shape.

By definition, sonication will disrupt agglomerates, but not aggregates. For a general use of sonication, see this webinar:

Ultrasound, cavitation, and the singing kettle

https://www.brainshark.com/malvern/vu?pi=501349995&text=M021507

http://tinyurl.com/olueohz

I have also experienced cases where after sonication the particles get agglomerated. I think there is no general rule. It varies from particle to particle.

Sonication increases the collision frequency between particles. If there is inadequate zeta potential or some steric factors to stabilize the system, then agglomeration will result when sonication is applied.

Thank you all for your useful discussion. Also, I found this article covers all the basics in detail.

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