分子動力学法によるポリカーボネートのAFMナノインデンテーション

抄録

Atomic force microscopy (AFM) has been widely used to measure surface topography, friction force, adhesive force, and deformation response at nanoscale. In particularly, AFM nano indentation enables to measure deformation response at molecular level in polymer materials. This study aims to investigate the mechanism of elasto-plastic deformation by using AFM experiment and molecular dynamics (MD) simulation. To drastically improve computational efficiency, a new coarse-grained (CG) force field is first developed for Polycarbonate (PC) based on full-atom MD simulations. Using the newly developed force field and CG MD simulation, nano indentation loading on to PC is computed. During a loading process, reaction force (which comes from the interaction force between indenter probe and polymer surface) shows increasing with respected to the penetration depth. Energy variations associated with bond stretching, bending and torsion are further investigated to obtain useful insights of the deformation process. It is found that their potential energy significantly changes with respected to the penetration depth. Based on the variation of potential energy, we discussed mechanism of yielding onset and plastic deformation during AFM nano indentation test.