Diversifying Composition Leads to Hierarchical Composites with Design Flexibility and Structural Fidelity

Abstract

In a blend of four or more components, the mixing entropy diversifies the chemical compositions of each phase. This reduces interfacial interactions, enhances inter-phase miscibility, weakens the dependence on specific pair interactions for self-assembly, and removes diffusion barriers to forming large-scale structures. When this design principle is applied to blends containing nanoparticles, colloidal particles, small molecules, and supramolecules, hierarchically-structured composites can be obtained with enhanced formulation flexibility in the filler selection and blend composition. Here, detailed characterization and simulations confirm entropy-driven phase behavior, where each component is distributed to locally mediate unfavorable interactions, and nanostructures form near or in a miscible state. Kinetically, this facilitates molecular diffusion across microdomains and through different phases, and ultimately leads to the facile fabrication of photonic crystals in minutes and nanocomposites with tunable microstructures. Besides advancing capabilities to engineer functional materials, the present study provides molecular insights into how entropy-driven complex blends navigate variations and uncertainties without compromising structural fidelity, as commonly seen in high-entropy alloys and biological blends.

Using Machine Learning to Predict and Understand Complex Self‐Assembly Behaviors of a Multicomponent Nanocomposite

“…The system's ability to redistribute PDP results in formulation flexibility across the nanocomposite system and allows orderly incorporation of NPs with a range of sizes, shapes, and core chemistries. [ 17 ] Unbonded PDP also accelerates assembly kinetics and provides a route for controlling the microdomain morphology and orientation independent of the substrate chemistry. [ 16 ] The system's ability to self‐regulate has proven useful in scalable fabrication of optical devices, and we expect the same principle could be applied to manufacture electronic, dielectric, and thermal transport devices.…”

“…This is consistent with recent experimental studies of this nanocomposite system, which uncovered something surprising: the free (unbonded) small molecules redistribute to relieve entropic strain on the BCP. [ 17 ] Despite being less miscible in the PS microdomains, free PDP will leave the P4VP(PDP)‐rich areas as needed, making room for incorporated NPs. From the ( r D )* prediction trend plotted in Figure 3B, we estimate that 30–40% of free PDP is incorporated into the PS microdomains in a typical sample (Figure S4, Supporting Information).…”

“…Due to its compositional flexibility and rich phase behaviors, this nanocomposite system has been the subject of research efforts spanning nearly two decades and thousands of samples. [10][11][12][13][14][15][16][17][18][19] In addition to scientific insights, these efforts have produced an ideal dataset for testing current ML capabilities on complex blends. Ordered assembly can be achieved across a wide range of PS-b-P4VP(PDP) + NP compositions and processing conditions.…”

“…[15,16] Within the last decade, it has been established that adding organic small molecules to a BCP-NP blend facilitates the incorporation of large or anisotropic particles, accelerates assembly, and produces new nanostructures. [17][18][19] These are exciting milestones in the development of functional nanocomposites but, with the addition of small molecules, the parameter space of nanocomposite compositions has grown even larger.The challenges of working with large parameter spaces are not unique to self-assembly. Humans are excellent at finding patterns in low-dimensional data but struggle to understand trends in high-dimensional systems.…”

“…[15,16] Within the last decade, it has been established that adding organic small molecules to a BCP-NP blend facilitates the incorporation of large or anisotropic particles, accelerates assembly, and produces new nanostructures. [17][18][19] These are exciting milestones in the development of functional nanocomposites but, with the addition of small molecules, the parameter space of nanocomposite compositions has grown even larger.…”