Temperature- and Pressure-Induced Ligand Anisotropy Drives Structural Reorganization of Dendronized Gold Nanoparticle Monolayers

Self-assembly at the air/water interface provides a versatile platform for organizing organic ligand-functionalized inorganic nanoparticles (NPs) into two-dimensional monolayers. However, how ligand behavior under interfacial confinement governs collective structural organization of NP assemblies remains poorly understood. Here, we demonstrate that ligand redistribution on Au NPs induces emergent NP shape anisotropy, which in turn drives directional reorganization of interfacial monolayers. A monolayer of Au NPs dual-functionalized with a liquid-crystalline dendron and dodecanethiol reorganizes from island-like arrays to network-like structures upon heating. X-ray reflectometry and grazing-incidence small-angle X-ray scattering further reveal correlated variations in out-of-plane ligand-shell thickness and in-plane lattice constants. Integrating these X-ray results with local structural insights from electron microscopy clarifies that adaptive redistribution of the two coexisting ligands on the NP surface was the key factor that changes the NP shape anisotropy. This ligand-driven anisotropy directly induced directional anisotropy of the macroscopic monolayer structure. Such dynamic ligand redistribution is enabled by a precisely engineered NP surface, dual-functionalized with liquid-crystalline dendrons and simple alkanethiols. Altogether, this work establishes a strategy for designing thermoresponsive NP monolayers with tunable topology at liquid interfaces and highlights how interfacial confinement fundamentally alters ligand-mediated assembly behavior.