Making Liquid particles: two joining into one?

Hi guys, i know i’ve seen this before, maybe on that flash experimental math site that was all black and white and had a picture of a kid swatting at some molecular looking flies? anyone remember the name of that/

well anyway, what i’m trying to pull off here is like a circle of some sort, all of sudden growing a small little circle and then both of them dividing, or possibly, a two circles(modules, atoms, particles) join to be one.

any ideas?