Computational analysis of the effect of interaction heterogeneity on fluid–crystal coexistence in micron-scale colloidal systems

Micron-scale colloidal particles with short-ranged attractions, e.g., colloids functionalized with single-stranded DNA oligomers, have emerged as a powerful platform for studying colloidal self-assembly phenomena with the long-term goal of identifying routes for metamaterial fabrication. Although these systems have been investigated extensively both experimentally and computationally, the role of "real world" features that may impact self-assembly in unexpected ways has been largely ignored. One such example of an important, yet underappreciated, feature is interaction heterogeneity (IH), i.e., variations in interparticle interaction strengths, which can arise from variability in the DNA strand areal density on particle surfaces during fabrication. A previous study demonstrated that IH can modulate nucleation and gelation kinetics under non-equilibrium conditions. Here, we investigate in detail the dependence of bulk fluid-crystal coexistence on IH. Using a multicomponent coexistence tracing approach, we compute phase diagrams for both Gaussian and bidisperse IH distributions, revealing that IH shifts the fluid-side coexistence boundaries outward, promoting crystallization at lower particle volume fractions while also resulting in crystals that are enhanced in the stronger binding species. Our results demonstrate that IH significantly influences crystallization behavior even under equilibrium conditions and provide a new perspective on tuning IH as a controllable parameter for optimizing colloidal self-assembly.