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. I know this sounds crazy and not logical, but the truth is to be observed. The system should not be too sophisticated.
Now that you have forced me to reflect on the model, I think it would be better not to interrupt the particle movement of the whole system after the sticky particles or the non-sticky particles touch. Summarizing:
1- There is a bulk of small particles that account for the Brownian system, the sticky particles and the non-sticky particles.
2- Particles have the same average kinetic energy.
3- There are no energy losses (heat).
4- When particles stick together, it could be due to a force that only acts when they interact.
5- This force is discrete, constant, originates in the point where they touch each other and points towards the centre of the particles; it would be interesting to make this force a variable as well.
6- When particles stick together they rotate, there is a angular moment around their centre of mass.
7- When the kinetic energy of the other colliding particles plus the centrifugal force caused by their rotation around the centre of mass allows, the sticking particles separate.
8- There is a counter for each time the sticky particles touch (and stick together). Another counter for each time the non-sticky particles touch.

Thank you very much for your constructive critics and for all the time spent on this model.