Molecular dynamic modeling of interfacial energy

Molecular dynamic modeling is used to calculate the changes in the energy between two surfaces when the surfaces are first allowed to approach one another and, subsequently, separated. The equations of motion of the atoms, which were assumed to interact via a Lennard-Jones potential, were integrated using Verlet's algorithm. They were implemented in an environment of periodic boundary conditions, feedback loop temperature and pressure controllers, with direct computation of the stress and strain tensors. This approach allows one to calculate the temperature dependence of the 'leap-to-contact' phenomenon, the thermodynamic work of adhesion, the work needed to separate the surfaces, and the forces of attraction and separation. Effects that occur during approach and separation, such as surface roughening and vacancy formation, were included in the energetics calculations. Sound waves and the resulting thermal transients were also modeled. The adhesion hysteresis and irreversible behaviors during approach and separation that arise from these calculations are discussed in detail.