Formation Pathways and Structural Diversity of Colloidal Tetramers in a Two-Dimensional System: A Brownian Dynamics Study

Abstract

The formation of colloidal crystals provides a valuable model system for understanding crystallization mechanisms, because their slow dynamics and large length scales allow direct observation of nucleation and growth processes. In our previous studies, we found that small clusters often adopt non-compact shapes, in contrast to the classical nucleation theory assumption that clusters remain compact during growth. Nevertheless, their size distribution is essentially the same as that of compact clusters. In this work, we perform Brownian dynamics simulations in four-particle systems to investigate the shape transitions of tetramers, the smallest clusters capable of exhibiting multiple geometries. Our results show that clusters do not adopt the most compact shapes under near-equilibrium conditions, particularly at low supersaturation. We also reveal in detail the process by which tetramers change their own shape.