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Electrostatic Correlations fold Polyelectrolytes

Highly charged polyelectrolytes (PE) normally take on a stretched conformation due to the repulsion between the monomers. This is the case for a PE with monovalent counterions in a water solution. When increasing the valancy of the counterions, computer simulations show that the size of the polyelectrolytes decrease, even to dimensions smaller than for a neutral polymer. This effective attraction between the like-charged monomers is thought to be due to ion-ion correlations. That the electrostatics are governing the compaction is further emphasized by mixing in organic solvent and lowering the dielectric constant. This way of increasing the direct Coulomb interaction also leads to an effective attractive interaction between like-charged monomers. Comparisons are made with fluorescence microscopy experiments of DNA which show much the same trends. Lastly, we discuss the effect of adding salt to the compacted chains which then unfold, in contrary to normal screening theory.

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