Polyelectrolyte chain collapse

Brilliantov NV, Kuznetsov DV, Klein R. Chain collapse and counterion condensation in dilute polyelectrolyte solution. Phys. Rev. Lett. 1998 81 1433-1436. 

Why does the collapse transition of a polyelectrolyte chain show the bead-string structure ... 

Finally, composition gradients from two different polymer chains have also been used to study wettability effects. A polystyrene poly(2-vinylpyridine) gradient allows a switchable wettability if submitted to a selective solvent treatment. In the selective solvent, one of the two chains collapses and the properties of the surface are determined by mainly the other component. The same effect can be exploited when submitting a polyelectrolyte gradient (poly(tert-butylacrylate) vs. poly(2-vinylpyridine)) to a pH change, Fig. 19. 

Note that the dependence of the number of monomers in a bead on the fraction of positively and negatively charged monomers and charge asymmetry (eqn [206]) has a similar functional form as a head size dependence on the fraction of the condensed counterions and charged monomers in the case of a polyelectrolyte chain when the chain collapse is caused by counterion condensation. ... 

As the water-ethanol mixture has lower permittivity ( = 50) than water (e 80), while the water-N-methylpropionamide mixture has higher permittivity (e 140), it is somewhat surprising that ESR spectra for FS counterions in an aqueous solution of PDADMAC are not consistent with the charged cylindrical cell model. The most likely cause for the failure of the model for pure water are differences in solvation of the polyelectrolyte chain compared to the mixed solvents. The organic components of both solvent mixtures feature ethyl groups that are better suited than water for solvating the hydrophobic parts of the PDADMAC chains. They may thus prevent a local hydrophobic collapse of the chain. 

The full self-consistent calculation is necessary if the chain changes its conformation significantly as the experimental conditions are varied. As an example, the polymer chain collects most of the counterions when it undergoes coil-to-globule transition (Kundagrami and Muthukumar 2010) as seen in experiments (Loh et al. 2008). The polyelectrolyte chain is essentially uncharged in its collapsed state. The role of multivalent counterions and salt... 

Loh, R, Been, R., Vollmer, D., Fischer, K., Schmidt, M., Kundagrami, A., and Muthukumar, M., 2008. Collapse of linear polyelectrolyte chains in a poor solvent When does a collapsing polyelectrol)de collect its counterions . 

Figure 6.22 Schematicofthe col lapse of a polyelectrolyte chain in a poor solvent. The chain collects all its counterions as it collapses.

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