Entropic Bonding-Not Quite So Simple Behaviors from Simple Hard Particles

Advances in experimental synthesis and computer simulations have led to the proliferation of anisotropy and particle geometry as popular handles for directed self-assembly. This paradigm employs entropy to direct building block organization into desired spatial and orientational orderings. Yet, how does a metric associated primarily with disorder give rise to ordered assemblies? We first explain the governing principles behind entropic crystallization and entropy maximization processes. We then show how entropic forces can produce emergent, attractive, and bond-like interactions between otherwise sterically repulsive particles. Building on these ideas, we establish entropy as a mediator of interparticle attraction in hard particle systems that relies on extrinsic, systems-level behaviors as opposed to intrinsic, particle-level properties. Finally, we present a theory of entropic bonding that formalizes the phenomena discussed into a rigorous mathematical framework and discuss relevant next steps for its development and applications of entropic crystallization in materials design.