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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
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