Kinetics of coagulation phenomena from a granular matter perspective

Abstract

Aggregation processes play a central role in systems ranging from aerosol coagulation and cloud formation to dust growth in protoplanetary disks and granular materials. These processes are traditionally described by Smoluchowski's coagulation equation, which provides a mean-field account of growth through binary collisions. However, incorporation of granular physics-dissipative interactions, spatial heterogeneity, and force transmission through contact networks-reveals important limitations of this framework. In this review, we show how such effects lead to the breakdown of mean-field assumptions and motivate a view of aggregation as a multi-scale process shaped by the interplay between interactions, structure, and collective dynamics. Phenomena such as segregation, jamming, and clogging further highlight the role of mechanical constraints and spatial organization in limiting or redirecting growth. By integrating insights from granular physics, aerosol science, and astrophysics, we outline a unified perspective on coagulation in non-equilibrium particulate systems. This paper is part of the thematic issue "Sand, silos and asteroids: clustering challenges in granular materials research".