Counterion condensation to cationic polyelectrolytes in methanol/water mixtures
- Universidad de Chile, Casilla (Chile)
Manning`s theory states that counterion condensation phenomenon is basically governed by two factors: the average distance between charges on the polyion framework and the {open_quotes}bulk{close_quotes} dielectric constant. In this work, the effect of macroscopic dielectric constant on solutions of chloride, bromide and nitrate of poly-[N,N-dimethyl-N-(2-hydroxypropyl)ammonium], using mixtures of methanol/water as solvent, was investigated. Results are analyzed as compared with those reported in water for the same system. The equivalent electrical conductivity at infinite dilution, {Lambda}{degrees}, of their solutions agrees well with both the viscosity and the dielectric constant behavior of pure mixtures in all the composition range. However, the behavior of the counterion-polyion interaction parameter, referred to that calculated according to Manning`s definition, shows a maximum in the same range where {Lambda}{degrees} abruptly decreases at about 0.2 mole fraction of methanol. This apparently anomalous behavior involves an increase in the average distance between charges without ionic dissociation and it can be explained in terms of a polyion conformational change. Accordingly, viscosity measurements showed a maximum in the same composition range. The preferential adsorption coefficient, {lambda}{sup *}, measured by dialysis equilibrium and differential refractometry, shows that water is the component more adsorbed to the polyelectrolyte, at least in the range from 0.05 to 0.3 mole fraction of methanol. Consequently, if one of the components of the mixture is preferentially adsorbed to the polyelectrolyte, then the parameter on which depends the counterion condensation is the dielectric constant in the association microdomain.
- OSTI ID:
- 182228
- Report Number(s):
- CONF-950140--
- Country of Publication:
- United States
- Language:
- English
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