trigger animation on collision/spawn on collision

[theboykidney]

I feel like this is noob question, but it's got me stumped either way.

I have instanced geometry under a model, and the geometry has animation on it. How can I trigger the animation on collision with surface?

basically stylised rain drop colliding with object, and I need the main drop to disappear and a few small splashes to burst out of the collision.
The 2 approaches taken so far is animation on the instanced model, but can't get it triggering properly
and
doing it with the spawn on collision node, but unable to fine tune things like animation on size of new spawned particles etc. [may need to get into states here??]

Any ideas would be appreciated.

cheers.