Counter-ion release and electrostatic adsorption
  The effective charge of a rigid polyelectrolyte (PE) approaching an oppositely charged surface is studied. The cases of a weak (annealed) and strongly charged PE with condensed counterions (such as DNA) are discussed. In the most interesting case of the adsorption onto a substrate of low dielectric constant (such as a lipid membrane or a mica sheet) the condensed counterions are not always released as the PE approaches the substrate, because of the major importance of the image charge effect. For the adsorption onto a surface with freely moving charges, the image charge effect becomes less important and full release is often expected. 
Pierre Sens & Jean-Francois Joanny