Self-Organized Colloidal Assemblies in Confined Spaces: Formation Mechanism, Internal Structure, and Resulting Optical Properties

Spontaneous organization of matter is a remarkable natural process, observed across length scales, from the crystalline architectures of minerals via nanostructured features within biological materials to the complex hierarchical organization of tissues. Understanding the interplay between individual nanoscale building blocks and the emergent structures they self-organize into is of general importance for resolving fundamental processes of structure formation. In addition, self-assembled materials find technological applications as photonic materials exhibiting structural color, phononic crystals to control acoustic properties or heat conduction, or as nanoporous materials to tailor adsorption or catalytic processes. This research proposal focuses on structure formation by colloidal self-assembly in confining elements, especially within spherical emulsion droplets – mimicking, e.g. the formation of minerals, such as framboidal pyrite. In the first funding period, we established thermodynamic and kinetic frameworks for the self-organization of colloidal particles into clusters with unique symmetries and surface geometries, notably icosahedral and decahedral. These configurations demonstrate enhanced thermodynamic stability and are influenced by factors like confinement shape and constituent particle volume fraction. Building on these findings, we propose three strategies for the second funding period to direct colloidal cluster formation actively. First, we aim to tailor the confinement interface to control cluster symmetry, hypothesizing that interface shape alterations can steer the assembly towards specific crystal structures. Second, we plan to exploit thermodynamic principles to manage the order and structure, directing defects within clusters to minimize free energy loss. Third, we intend to manipulate the kinetic formation pathway to guide the structural organization, leveraging an understanding of phase transition processes to preferentially form certain cluster symmetries. Following these strategies will not only provide tools for the self-assembly of complex materials but generate a fundamental understanding of structure formation in confinement. Building on our successful collaboration in the first funding period, we will pursue these goals by close interconnection between experimental observations and event-driven molecular dynamics simulations.