Shape-induced phase transformation in nanoparticle assemblies

The role of interparticle interactions in a behavior of condensed phases of spherical objects is remaining in a focal point of diverse studies of micro- and nanoscale colloid systems. At the same time, recent advances in a fabrication of well-defined nanoscale materials allow for an exploration of geometrical effects in systems containing objects with non-spherical shapes. Herein, we report a phase evolution of 3D assemblies of ligand coated cube-like palladium nanoparticles. We observed a continuous phase transformation of particles assemblies from a simple cubic phase to a face-centered cubic rich phase with an increase of capping ligand thickness. The details of structural evolution were revealed using small angle x-ray scattering and electron microscopy methods. The observed phase transformation is attributed to an evolution of particle's shape from cube to quasi-sphere geometry, which was effectively regulated by amount of a ligand adsorbed on a particle surface.