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Smaller particles in a colloidal dispersion are less stable than larger ones due to their higher surface to volume ratio.

Therefore Ostwald ripening occurs, a process which promotes growth of larger particles at the expense of smaller ones (alternatively aggregation of smaller particles can occur).

In principle, this process goes on until one single particle is obtained.

Then, why are colloidal dispersions with lots of small particles stable? Or rather metastable? What makes the processes promoting further growth stop (ie dissolution of smaller particles in Ostwald ripening)? And do these processes really stop or just slow down tremendously?

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  • $\begingroup$ In colloidal dispersions all the colloidal particles possess the same charge and therefore this prevents their coagulation or aggregation to form larger particles that consequently settle down because of gravity. $\endgroup$ – Dibster7978 Feb 11 at 14:57
  • $\begingroup$ Your logic is strung up in the wrong way. ;) If a colloidal dispersion is stable, then the smaller particles are not measurably less stable than the biggest ones that occur in the same dispersion. Also the reason(ing) for Ostwald ripening is thermodynamic. I does not necessarily occur on your timescale, because the kinetics can just be too slow. $\endgroup$ – Karl Feb 11 at 19:08
  • $\begingroup$ Consider Brownian motion, as well as dispersants. $\endgroup$ – DrMoishe Pippik Feb 12 at 0:46