Effect of thermal fluctuations on the average shape of a graphene nanosheet suspended in a shear flow

TL;DR

This study combines simulations to show that thermal fluctuations have a minor impact on the average shape and rheology of graphene nanosheets in shear flow, with the stable 'S' shape primarily driven by hydrodynamic traction.

Contribution

It demonstrates through combined simulations that thermal fluctuations minimally affect the average shape of graphene nanosheets in shear flow, emphasizing hydrodynamic traction's role.

Findings

Thermal fluctuations have a minor effect on the average shape.

The 'S' shape is mainly due to hydrodynamic traction.

Shape stability persists at moderate thermal fluctuations.

Abstract

Graphene nanosheets display large hydrodynamic slip lengths in most solvents, and because of this, adopt a stable orientation in a shear flow instead of rotating when thermal fluctuations are negligible [Kamal et al., Nature Comm., 11.1,2020]. In this paper, we combine molecular dynamics simulations and boundary integral simulations to demonstrate that the time-averaged 'S' shape adopted by a flexible graphene nanosheet subject to moderate thermal fluctuation is comparable to the shape predicted when neglecting thermal fluctuations. The stable 'S' shape adopted by the particle results primarily from the normal hydrodynamic traction, which is sensitive to the orientation of the particle with respect to the flow direction. Our results imply that thermally-induced shape fluctuations have a relatively minor effect on the time-averaged rheology of dilute suspensions of graphene nanosheets for relatively large but finite P\'eclet numbers.