So if we have an ion, say Cl- in solution, and we have a membrane immersed into the solution. Apparently there is a method in which any ion, of any charge is inhibited from crossing the membrane because it induces the same charge as itself on the membrane. This is called dielectric exclusion. However I'm not sure how the ion induces the same charge as itself onto the membrane. The Cl- will attract polarized water molecules toward itself. So the negative side of the water dipole will be facing outward. This negative side would induce a positive charge on the membrane. So its still the opposite polarity as that of Cl-. The paper in which I was reading about this says its supposed to be a very obvious application of electrostatics...I guess I'm just missing it.