Modelling the Role of Interaction Heterogeneity in the Gelation of Micron-Scale Colloidal Systems

Abstract

Micron-scale colloids functionalized with supramolecular moieties represent a versatile platform for self-assembly. Single-stranded DNA functionalization, in particular, has been shown to be a highly tunable approach for inducing short-ranged attractive interparticle interactions that can be used to drive self-assembly into a wide range of crystalline structures. Recently, it has been noted that variability in the extent of surface functionalization across a population of colloids results in 'interaction heterogeneity', or IH, in which the binding strength between a pair of colloids varies according to the density of DNA strands on their surfaces. We have shown in previous work that IH strongly impacts colloidal crystal nucleation and growth but its impact on gelation further away from equilibrium conditions remains underexplored. In this study, we employ molecular simulations to systematically investigate the role of IH in colloidal gelation driven by thermal quenches. We consider four types of IH distributions: monodisperse (no IH), Gaussian, bidisperse, and uniform distributions, and analyze their effects on gel structure and gelation dynamics. Our results show that while IH minimally impacts macroscopic gel structure, it profoundly alters the local gel environment, as revealed by coordination number (CN) distributions. Principal component analysis of CN moments highlights distinct structural trends arising from the presence of IH, underscoring the sensitivity of local gel structure to IH. We also show that IH leads to a sequential aggregation of strong and weak binders, where strong binders first form a gel 'backbone' and weak binders subsequently decorate it. These findings highlight IH as a key parameter for modulating gel microstructure without significantly perturbing macroscopic organization.