engleski

Interpolyelectrolyte neutralization in solution and at surfaces

Complexation of several linear vinylic polyions with complementary charge density in aqueous solutions of binary 1:1 salts was investigated by means of microcalorimetry, dynamic light scattering, electrokinetics and spectrophotometry. The build-up of corresponding multilayers was monitored using quartz crystal microbalance. Charged primary and secondary polyelectrolyte complexes were formed upon stepwise titrant to titrand addition. At csalt / mol dm–3 ≤ 0.1 their flocculation near the equivalence occurred, resulting with precipitates containing approximately equal amounts of oppositely charged monomers [1–3]. However, in the case of abrupt (instead of stepwise) titrant addition in excess, the primary complex charge reversal was achieved [3]. The counterion specific aggregation and more pronounced overcharging of primary complexes were noticed at higher electrolyte concentrations [1–3]. This resulted with asymmetric interpolyelectrolyte neutralization. The monomer-counterion preferences were correlated with standard Gibbs energies and enthalpies of counterion hydration. The reactions of investigated polyelectrolytes were predominantly (or entirely) entropically driven, irrespectively of the type of reaction products formed (nano- complexes, precipitates) and the concentration of electrolyte present [1–3]. The equilibrium establishment proceeded slowly and solely in the presence of simple salt. The influence of electrolyte type and concentration on the multilayer build-up was essentially the same as in the case of corresponding reactions in solution. These results, and the fact that sequential nano- complex overcharging in solution can be achieved simply by manipulating with the amounts of monomers introduced, suggest that no fundamental differences between the processes of complex and multilayer formation exist.

overcharging, polyelectrolyte complexes, poly(acrylate) anion, poly(allylammonium) cation, electrokinetics, dynamic light scattering, microcalorimetry

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