Self-regulated Mixing Leads to Hierarchical Composites with Design Flexibility

The modernization toward nanocomposites has been stalled due to the inability to modulate their structures over all length scales albeit of surging developments in colloidal synthesis and self-assembly. Realization of large scale assembles requires long-range diffusivity, a fundamental challenge in nanoscopically ordered systems. This is due to the competition between the enthalpic forces to form assemblies and the kinetic barriers to diffuse through ordered domains. We hypothesize that forming nanostructures in dilute, miscible solution will overcome these fundamental challenges and experimentally realized this by leveraging entropy-driven phase behavior upon increasing composition diversity, akin to that seen in high entropy alloys. The complex blends, composed of nanoparticles/block copolymers/small molecules, self-regulate the spatial distribution of each component to enhance miscibility and, thus, minimize the enthalpic effects. The resultant entropy-driven phase behavior enables NP ordering unachievable before, even in dilute solutions, with unparalleled design flexibility. This makes it kinetically feasible to realize nanoscopic ordering-induced macrophase separation with tunable microstructures. In addition to opening all-new pathways to modulate nanocomposites, these energetic insights may be applicable to understand behavior in other complex blends such as liquid-liquid phase separation.