The arrangement of nanoscale building blocks into patterns with microscale periodicity is challenging to achieve via self-assembly processes. Here, we report on the phase-transition-driven collective assembly of gold nanoparticles in a thermotropic liquid crystal. A temperature-induced transition from the isotropic to the nematic phase under anchoring-driven planar alignment leads to the assembly of individual nanometer-sized particles into arrays of micrometer-sized agglomerates, whose size and characteristic spacing can be tuned by varying the cooling rate. Phase field simulations coupling the conserved and nonconserved order parameters exhibit a similar evolution of the morphology as the experimental observations. This fully reversible process offers control over structural order on the microscopic level and is an interesting model system for the programmable and reconfigurable patterning of nanocomposites with access to micrometer-sized periodicities.

Predictable and repeatable outcome is a major issue in nanoparticle synthesis. Traditionally, chemists rely on the one-factor-at-a-time method to investigate and optimise synthetic processes; however, this method is inefficient and often misleading. Design of Experiments (DoE), in contrast, can provide a greater amount of information in fewer experiments and lends itself to producing more reproducible results. Nevertheless, DoE techniques are only used by a relatively low number of practitioners in nanoparticle research. Here, we provide a case study on the synthesis of oleylamine-capped gold nanoparticles (AuNPs). Through the use of DoE, we achieved a marked reduction in dispersity and developed a model to carefully control the mean diameter of the nanoparticle populations.