A model of the interaction between a charged particle and a pore in a charged membrane surface

A model of the electrostatic and molecular interactions of a charged colloid particle with a charged membrane surface in an electrolyte solution has been developed. In Derjaguinʹs approximation, the force between a spherical colloid particle and a cylindrical membrane pore (with a rounded inlet) is calculated taking into account both electrostatic and van der Waals interactions. The force and energy are strongly dependent on the zeta-potential of both the particle and the membrane pore, the electrolyte concentration, and geometrical parameters. Conditions are found for which a potential barrier exists at the pore entrance. This barrier prevents a particle from entering the pore and, hence, gives an equilibrium position of the particle above the membrane surface. Therefore, there is a possibility in this case of removing the particle by a tangential flow, preventing pore blocking. The model was verified using a Finite Element Method (FEM) analysis developed earlier for colloidal interactions by two co-authors. It has been found that the accuracies of analytical formulae obtained for the interaction energy and force are within 10 and 20%, respectively, for practical application ranges of physico–chemical and geometrical parameters. Two major advantages of the model proposed compared to FEM calculations are: (1) the possibility of non-centerline calculations (when a particle is not moving along the axis of a membrane pore) without a three-dimensional solution; and (2) speed of calculations using the analytical formulae is much higher. Using a simplified expression for hydrodynamic force, critical values of pressure gradients across the membrane pore have been calculated analytically.