Electrostatic interaction between a rod-like macromolecule and a circular orifice/disk in an electrolyte solution

We present the solutions of the interaction energy for a colloid system with a charged rod-like macromolecule immersed in a bulk electrolyte and moving along the axis of a circular orifice or disk （orifice/disk）. The calculation requires a numerical computation of the surface charge profiles, which result from a constant surface potential on the macromolecule and the orifice/disk. In the calculation, remarkable divergences of the surface charge emerge on the edges of the macromolecule and the orifice/disk, which are well-known edge effects. The anisotropic distribution of the surface charge （effective dipole） results in an attraction between these two charged objects. This attraction is enhanced with the increase of the screening length of the system for both the orifice and the disk systems. However, the sizes of the orifice and the disk reduce to different effects on the interaction energy.