Analysis of the interaction energies between and within graphite particles during mechanical exfoliation

Abstract

A method for calculating the interaction energies between and within graphite particles is established by analyzing their thickness and lateral size distribution from AFM and SEM images of 300 particles during mechanical exfoliation at different times. The energy for exfoliating graphite sheets by breaking van der Waals (vdW) bonds, the energy for fracturing graphite sheets by breaking covalent bonds, the potential energies for restacking graphite sheets and the lateral aggregation of graphite particles are analyzed. Results show that the vdW interaction between graphite sheets is the key factor that leads to their restacking. Restacking and lateral aggregation become more active than exfoliation as exfoliation progresses. The energy for exfoliating graphite sheets by breaking vdW bonds is 4 times less than that the potential energy for restacking graphite sheets, and 2 orders of magnitude less than that the energy for fracturing graphite sheets by breaking covalent bonds. The increased number of exfoliated and fractured graphite sheets leads to a considerable increase in the restacking and lateral aggregation by vdW interaction. The coulombic energy is weak and can be ignored. The model has implications for the fabrication of aggregation-free graphite sheets with high aspect ratios.