If polyelectrolyte chains are added to a system of charged macroions (i.e. an array of DNA molecules), an interesting phenomenon called the polyelectrolyte bridging might occur. The term bridging interactions is usually applied to the situation where a single polyelectrolyte chain can adsorb to two (or more) oppositely charged macroions (e.g. DNA molecule) thus establishing molecular bridges and via its connectivity mediate attractive interactions between them.
At small macroion separations, the chain is squeezed in between the macroions and electrostatic effects in the system are completely dominated by steric effects – the system is effectively discharged. As we increase the macroion separation, we simultaneously stretch the polyelectrolyte chain adsorbed to them. The stretching of the chain gives rise to the above mentioned attractive interactions due to chain's rubber elasticity.
Because of its connectivity the behaviour of the polyelectrolyte chain bears almost no resemblance to the case of confined unconnected ions.
Read more about this topic: Polyelectrolyte
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