Polyelectrolyte chain expansion

Borochov N, Eisenberg H. Stiff (DNA) and flexible (NaPSS) polyelectrolyte chain expansion at very low salt concentration. Macromolecules 1994 27 1440-1445. 

In the classical theories of polyelectrolytes, the chain expansion is characterized by the electrostatic excluded volume parameter, zel with ... 

Experimentally the expansion factor as of a polyelectrolyte chain in bulk solution is given as follows (17-19). The a is larger than at. s... 

This value of kn is actually low by an order of magnitude for dilute suspensions of charged spheres of radius Rg. This is due to the neglect of interchain correlations for c < c in the structure factor used in the derivation of Eqs. (295)-(298). If the repulsive interaction between polyelectrolyte chains dominates, as expected in salt-free solutions, the virial expansion for viscosity may be valid over considerable range of concentrations where the average distance between chains scales as. This virial series may be approxi-... 

The viscosity of a linear polyelectrolyte solution depends on the conformation of the molecules, which in turn is affected by intramolecular electrostatic interactions between charged segments located along the polymer backbone, but the interactions in systems of charged polyelectrolytes are still far from being understood. The study on the solution property of cyclic polyelectrolyte is of interest, since the chain expansion of a cyclic... 

Effects of Ionic Strength. Figure 13 illustrates the effect of NaCl concentration on intrinsic viscosity for each terpolymer. Of course, this experiment should demonstrate only the effects of added electrolyte on individual chain contraction or expansion. The chains with sufficient monomer pairs exhibit increases in viscosity as expected with addition of NaCl. The best chain expansion is seen for the 5-5 sample, which is rapidly solvated with increasing ionic strength. The 5-10 sample shows some typical polyelectrolyte behavior because it has an excess of macroanions at pH 7. 

A combination of the molecular polyelectrolyte theory with the methods of statistical mechanics can be used at least for the description of the chain expansion due to charges along the polysaccharide chain. The physical process of the proton dissociation of a (weak) polyacid is a good way to assess the conformational role of the poly electrolytic interactions, since it is possible of tuning poly electrolyte charge density on an otherwise constant chemical structure. An amylose chain, selectively oxidized on carbon 6 to produce a carboxylic (uronic) group, has proved to be a good example to test theoretical results. ... 

Viscosification with acrylamide based polymers depends not only on high molecular weight but also on chain expansion due to ionic charge repulsion or the polyelectrolyte effect. 

Many macromolecules in aqueous solution are polyelectrolytes. The remarkable changes in the conformation of linear polyelectrolytes as a function of concentration, ionic strength, and pH are discussed. The various theories of chain expansion are reviewed. The thermodynamic properties of polyelectrolyte solutions reveal dramatic behavior. The large increase in the reduced osmotic pressure, jr/c, as the solution is diluted is explained in terms of the entropy of the counterions. The strong dependence of the conformation of the chains with solution conditions also leads to large changes in the viscosity. The viscosity is also explained in terms of the coil size and the interactions of the chains. 

Poly(methacrylic acid) in the nonionized form in solution has a compact conformation and low intrinsic viscosity. Upon ionization to the polyelectrolyte form, chain expansion occurs and viscosity increases. Unlike PAA, PMAA shows inverse solubility-temperature behavior. The presence of chain-stiffening methyl groups and their added hydrophobicity are responsible for the phase and viscosity behavior. Tacticity also plays an important role. 

In addition to these high charge density ampholytes, low charge density ampholytes were prepared by copolymerization of acrylamide with styrene sulfonate and MPTMA [96,97]. These polymers were studied by viscosity measurements in various concentrations of salts and HCI. In general these species showed chain expansion with increases in the salt concentration (using NaCI and CeCl2 salts) as well as with hydrochloric acid concentration. Some polyelectrolyte behavior was seen due to the non-stoichiometric ratios of the ionic species present. 

The effect of intrachain, fixed-ion repulsions on polyelectrolyte expansion has been discussed extensively in the literature. The theory of Katchalsky and Lifson [33] has been used often (and with little justification) for describing fixed-ion repulsion effects on single-chain expansion [33], and on gel-swelling equilibria [26, 27]. In the hydrophilic limit, the simulation model of Figure 7 corresponds directly with the model used by Katchalsky and Lifson (K-L) in deriving their analytical theory for polyelectrolyte expansion. Thus, simulation results for this limit can be used to examine whether K-L theory truly represents the physical model on which it is based. 

---