Emergence of dynamical disorder and phase metastability in carbon nanobowls

Mattia Gaboardi, Ian Silverwood, Balthasar Braunewell, Jay Siegel, and Félix Fernández-Alonso.
Carbon 183, 196 (2021)

The curved “nanobowl” corannulene is a fascinating molecule, topologically corresponding to one-third of the celebrated Buckminsterfullerene C60. Emerging applications of this seemingly simple molecular system in its condensed solid and fluid phases include the storage of chemical and thermal energy.

In this particular work, the authors have used radiation-scattering techniques (neutron and synchrotron X-rays) in combination with thermophysical measurements to unveil the microscopic mechanisms underpinning its phase behavior within the solid and liquid phases at ambient pressure. For the first time, Gaboardi et al identify the presence of a well-defined solid-to-solid transition well below the melting point. Contrary to naïve expectation, detailed analysis of the neutron-spectroscopy data below and above this pre-melting transition signals the emergence of correlated relaxational dynamics in the picosecond domain within both thermodynamically stable solid phases of the material. The researchers also find that these are progressively responsible for the suppression of molecular and supramolecular order over mesoscopic length scales, and are associated with the formation of high-symmetry rotor-like states exhibiting localized stochastic motions. Corannulene is certainly not a canonical solid, but rather exhibits a rich phenomenology linked to this viscoelastic response. Upon cooling from the melt, a robust hysteresis has also been discovered, associated with the existence of hitherto-unknown metastable liquid (deep-supercooled) and disordered-solid phases. BThis behavior is markedly different from that observed in the quintessential buckminsterfullerene C60 or other chemically substituted fullerene adducts studied to date at this level of detail. These results evince new and yet-to-tapped opportunities for the use of the stable and metastable phases of corannulene in novel applications exploiting the emergence of dynamical disorder at the nanoscale.

State-of-the-art radiation-scattering techniques (neutron & synchrotron X-rays) unveil the emergence of dynamical disorder in carbon nanobowls.

Figure: Cartoon highlighting the emergence of dynamical disorder in corannulene, well within its low-temperature phase.