Diffusion-limited aggregation
From Soft-Matter
Diffusion-limited aggregation is the process whereby particles undergoing a random walk due to Brownian motion cluster together to form aggregates of such particles [1]. This theory, proposed by Witten and Sander in 1981 [2], is applicable to aggregation in any system where diffusion is the primary means of transport in the system [1].
References
[1] http://en.wikipedia.org/wiki/Diffusion-limited_aggregation
[2] T. A. Witten Jr, L. M. Sander, Phys. Rev. Lett. 47, 1400 (1981)