MOLECULAR DYNAMIC SIMULATION OF ADHESIONAL RELEASE OF PARTICLES FROM SURFACES

The generalized form of the Lennard-Jones soft-sphere pair potential i s used to examine the adhesional attachment and release behavior of pa rticles on surfaces for materials of varying ''ductility''. Using a tw o-dimensional simulation, with the repulsive term held constant at m = 12, the attractive term is varied from n = 2 to n = 10 at a constant binding energy to provide a controlled way of changing the effective r ange of interaction between atoms. Molecular dynamics simulates the pl acement of particles on a free surface and the subsequent removal of t hese particles by controlling the displacement of the center of mass. Simulations indicate that the longer-ranged removal forces literally t ear out a chunk of the surface by pulling out a tether-like strand con necting the ball and plate. As the forces become shorter range, the si ze of the region of disturbed material after separation decreases unti l, at the shortest range, only three atoms are transferred and there i s relatively little damage to the system on separation as indicated by the lack of slip steps in the plate. Results are discussed both mecha nistically and from the point of view of more traditional approaches t o surface force behavior, such as the JKR and DMT models.