Theoretical Seminar. Petr Zhilyaev

16.10.2019
12:00
Begin
16.10.2019
12:00
Place

Lomonosova 9, room 2530

Petr Zhilyaev, SkolTech

‘State of trapped matter inside graphene nanobubble’


Graphene nanobubbles consist of a substance that is trapped between a graphene sheet and atomically flat substrate. This substance is an example of confinement in which both the bulk and surface interactions and the tension of the graphene determine the mechanical and thermodynamic properties of the system. The van der Waals pressure build-up due to the graphene–substrate attraction and surface influence facilitates the advanced condensation of trapped substances. Different phases of the trapped substance are assumed to be found inside the graphene nanobubbles depending on their radii. Smaller radii are attributed to the crystal and liquid phases, and larger radii correspond to the gas phase. In this talk, the results of the theoretical investigation of graphene nanobubbles filled with argon and ethane on a graphite substrate will be presented.  In the first part of the talk recent results of molecular dynamics (MD) study of graphene nanobubbles of the radius of 7–34 nm with argon atoms inside will be shown.

In these computer simulations, graphene nanobubbles except for the smallest ones exhibit a universal shape, i.e., a constant ratio of a bubble height to its footprint radius, which is in an agreement with experimental studies and their interpretation using the elastic theory of membranes. MD simulations reveal that argon does exist in a solid close-packed phase, although the internal pressure in the nanobubble is not sufficiently high for the ordinary crystallization that would occur in a bulk system. In the second part of the talk continuum approach to model, graphene nanobubbles will be introduced. The energy minimization concept is used to calculate the equilibrium properties of the bubble at a constant temperature for a given mass of captured substance.  The total energy is considered as a sum of the elastic energy of the graphene sheet, the bulk energy of the inner substance and the energy of adhesion between this substance, the substrate, and graphene.

The developed model allows to reveal a correlation between the size of the bubble and the physical state of the substance inside it. A special case of a GNB that consists of argon trapped between a graphene sheet and a graphite substrate is considered. The ‘forbidden range’ of radii is predicted, within which no stable GNBs exist, that separates bubble sizes with liquid argon inside from bubble sizes with gaseous argon.