Low Interfacial Free Energy Describes the Bulk Ordering Transition in Colloidal Cubes

Area of Science:

• Materials Science
• Physical Chemistry
• Nanotechnology

Background:

• Hard faceted nanoparticles typically transition from disordered to ordered states via classical nucleation and growth.
• Previous studies revealed hard cubes exhibit a nonclassical, bulk-phase transition, not dependent on nuclei.
• An unexpectedly high fraction of ordered particles was observed in the metastable disordered phase, even at low supersaturation.

Purpose of the Study:

• To investigate the hypothesis that hard cubes' unique phase transition properties stem from low interfacial free energy between disordered and ordered phases.
• To quantify the interfacial free energy for hard cubes and compare it with other hard particle systems.
• To explore the implications of low interfacial tension on ordering mechanisms in nanoparticle systems.

Main Methods:

• Employed the cleaving wall method to directly measure the interfacial free energy of hard cubes.
• Utilized a theoretical nucleation model to analyze the impact of interfacial tension on phase transitions.
• Compared interfacial free energy values for cubes with those of hard spheres.

Main Results:

• Direct measurements confirmed that hard cubes possess a significantly low interfacial free energy between disordered and ordered phases.
• At phase coexistence, the interfacial free energy for cubes was found to be approximately one-fifth of that for hard spheres.
• The study provides evidence supporting the link between low interfacial tension and a bulk ordering mechanism.

Conclusions:

• The unusually high fraction of ordered particles and bulk ordering in hard cubes are attributed to their low interfacial free energy.
• The findings challenge classical nucleation theories for certain nanoparticle systems.
• This research offers new insights into the phase transition mechanisms of geometrically constrained particles.