Effect of Small Particle Interactions on Assembly of Binary Colloidal Clusters
A central challenge in colloidal self-assembly is understanding how interaction strength influences the competition between structural optimization and kinetic arrest during the formation of hierarchical structures. Here, we investigate the assembly process of a binary mixture of differently sized silica colloids dispersed in a near-critical water/2,6-lutidine solvent, where critical Casimir forces provide reversible and temperature tunable attractions. By systematically tuning the effective interactions between large-large (L-L), large-small (L-S), and small-small (S-S) particle pairs, we directly observe how the nucleation and growth of the binary colloid assemblies evolve in a wall-confined quasi-two-dimensional geometry when multiple pair-interactions are present. Confocal laser scanning microscopy imaging shows that combined L-L interactions and L-S interactions lead to compact L-S core-shell clusters with high shell occupancy, while the additional presence of S-S interactions suppress the shell formation and lead to extended, branched binary networks. Particle-resolved analyses of cluster growth and bond dynamics reveal that these structural transitions are governed by the motion of the small particles in the clusters changing from highly dynamic leading to structural reorganization to frozen dynamics resulting kinetic trapping. Our findings demonstrate how the interaction-governed mobility and kinetic arrest of small particles influence the growth of finite binary clusters and offers microscopic insight into the formation of binary crystals and kinetically trapped space-spanning binary colloidal networks and gels.