Density fluctuations, polyelectrolyte solutions

Polyelectrolyte chains in a poor solvent for the polymer backbone adopt neddace-like conformations. There are three different length scales in the necklace globule the length of the string the bead size Db, and the thermal blob size fx determining the length scale of density fluctuations inside beads. Thus, all three different length scales will determine the properties of semidilute polyelectrolyte solutions in a poor solvent for the polymer backbone. 

This short summary of recent computer simulation results on the conformational properties of polyelectrolyte solutions showed that the classical pictures of screening and conformation changes for charged polymers need to be revised. At low concentrations the density fluctuations of the discrete counterions cause significant shape fluctuations, which go far beyond the short kink excitation driven by entropy. For increasing density with consequently increasing ionic strength, the chains dramatically shrink, before the classical overlapp concentration is reached. 

Fluctuations in ion density near a polyelectrolyte impose fluctuating electrostatic forces on the chain that can affect the chain s diffusion. As described by Sedl (207), polyelectrolyte diffusion in dilute solution is fast diffusion because coim-terions cause more rapid motion in a polyelectrolyte than would be noted in an equivalent neutral chain. Several investigators have modified equation 50 to include this Nernst-Hartley-type diffusion in a consistent manner (203,206). Tivant and co-workers suggested that in a monovalent electrolyte solution at large I the enhancement of Dm by polyelectrolyte-electrolyte coupling should be expressed as(208)... 

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