van der Waals dispersion power laws for cleavage, exfoliation and stretching in multi-scale, layered systems

TL;DR

This paper investigates the unique van der Waals power laws in layered systems, revealing differences between cleavage and exfoliation, and how scale affects these laws, impacting the interpretation of experimental results.

Contribution

It provides a detailed analysis of vdW power laws in layered systems, distinguishing cleavage from exfoliation, and explores scale effects on these laws in multi-scale systems.

Findings

Cleavage obeys a $C_2 D^{-2}$ vdW power law.

Exfoliation follows a $C_3 ext{log}(D/D_0) D^{-3}$ or $C_{5/2} D^{-5/2}$ law.

Scale changes can simplify complex power laws to standard ones.

Abstract

Layered and nanotubular systems that are metallic or graphitic are known to exhibit unusual dispersive van der Waals (vdW) power laws under some circumstances. In this letter we investigate the vdW power laws of bulk and finite layered systems and their interactions with other layered systems and atoms in the electromagnetically non-retarded case. The investigation reveals substantial difference between `cleavage' and `exfoliation' of graphite and metals where cleavage obeys a $C_2 D^{-2}$ vdW power law while exfoliation obeys a $C_3 \log(D/D_0) D^{-3}$ law for graphitics and a $C_{5/2} D^{-5/2}$ law for layered metals. This leads to questions of relevance in the interpretation of experimental results for these systems which have previously assumed more trival differences. Furthermore we gather further insight into the effect of scale on the vdW power laws of systems that simultaneously exhibit macroscopic and nanoscopic dimensions. We show that, for metallic and graphitic layered systems, the known "unusual" power laws can be reduced to standard or near standard power laws when the effective scale of one or more dimension is changed. This allows better identification of the systems for which the commonly employed `sum of $C_6 D^{-6}$' type vdW methods might be valid such as layered bulk to layered bulk and layered bulk to atom.