[quote]
I want to study if particles that have some sort of affinity for each other (they stick together when they touch) collide more often than particles that don't have any affinity.[/quote]

Are you trying to compare two different cases: in different system?
1. system A: particles which stick together when they touch.
2. system B: particles which collide with each other when they touch.

If there are two different kinds of particles A and B, then they are three different cases
1. A and A touch
2. B and B touch
3. A and B touch
It is more than two cases.

Model for the following simulation : There are two kind of particles A,B
When same kind of particle touch, they will stick together and become a bigger particle (momentum is conserved but energy is not conserved).
Elastic collision occurs when different kind of particle touch each other (energy and momentum are conserved).

The energy is not conserved if two particles stick together.

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