Abstract
The large-scale processing of nanomaterials such as graphene and MoS2 relies on understanding the flow behaviour of nanometrically-thin platelets suspended in liquids. Here we show, by combining non-equilibrium molecular dynamics and continuum simulations, that rigid nanoplatelets can attain a stable orientation for sufficiently strong flows. Such a stable orientation is in contradiction with the rotational motion predicted by classical colloidal hydrodynamics. This surprising effect is due to hydrodynamic slip at the liquid-solid interface and occurs when the slip length is larger than the platelet thickness; a slip length of a few nanometers may be sufficient to observe alignment. The predictions we developed by examining pure and surface-modified graphene is applicable to different solvent/2D material combinations. The emergence of a fixed orientation in a direction nearly parallel to the flow implies a slip-dependent change in several macroscopic transport properties, with potential impact on applications ranging from functional inks to nanocomposites.
Highlights
The large-scale processing of nanomaterials such as graphene and MoS2 relies on understanding the flow behaviour of nanometrically-thin platelets suspended in liquids
Note that the analysis of such quasi-2D configuration is not restrictive, and the results are valid for geometries that vary in the ^ez direction up to a numerical prefactor
We have demonstrated that in the presence of hydrodynamic slip effects, there exists a regime in which a rigid nanoplatelet suspended in a liquid does not rotate when subject to a shearing flow
Summary
The large-scale processing of nanomaterials such as graphene and MoS2 relies on understanding the flow behaviour of nanometrically-thin platelets suspended in liquids. By combining non-equilibrium molecular dynamics and continuum simulations, that rigid nanoplatelets can attain a stable orientation for sufficiently strong flows Such a stable orientation is in contradiction with the rotational motion predicted by classical colloidal hydrodynamics. The rotational dynamics of the suspended particles and the ensuing orientational microstructure affects the value of the suspension viscosity[16,17], and impacts other effective two-phase transport properties, such as thermal and electrical conductivities[18]. Controlling these macroscopic properties is paramount to delivering the promise of two-dimensional materials in market applications. It is currently unclear what effects may arise in suspensions due to slip
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