By using the model of a randomly coiled chain, a relation is derived describing the equilibrium stress–strain behavior of variously ionized polyelectrolyte gels swollen in solutions of a uni–univalent salt. The effect of the concentration of bound counterions calculated on the basis of the cylindrical model and the effect of the change of length of the statistical chain segment with the change in ionization of the gel on stress–strain, swelling, and potentiometric equilibria is discussed.

The deformational, swelling, and potentiometric behavior of poly(methacrylic acid) gels was measured as a function of the degree of crosslinking, ionic strength, and degree of ionization. The comparison of the stress–strain behavior with theoretical relations derived in the preceding part has shown that the relations are valid only if an increase is assumed in the number of monomeric units in the statistical chain segment with increasing degree of neutralization of the gel. This dependence is affected by the salt content in the swelling solution and is also dependent on the activity coefficient of counterions. The pK0 values for an undissociated gel approach pK0 = 5.0 and increase somewhat with degree of neutralization. The swelling equilibria are in qualitative agreement with theoretical assumptions; their quantitative agreement depends on the activity coefficient of counterions.

A colloidal system able to act as a miniature reactor for on-demand release of reactive payloads has been demonstrated. The system is based on submicrometer aggregates consisting of anionic liposomes that act as storage reservoirs for the reactants, superparamagnetic iron oxide nanoparticles (SPIONs) that enable magnetic positioning in space and controlled release of reactants from the liposomes by radiofrequency stimulation, and an oppositely charged polyelectrolyte (poly-l-lysine) that keeps the constituent elements within the aggregates at a defined ratio. The kinetics of liposome-PLL-SPION heteroaggregation was systematically mapped and a suitable composition of the liposome bilayer was found such that the system exhibits stability at ambient conditions and radiofrequency triggered release at physiological temperature. The functionality of the system was demonstrated using a reaction between resazurin and ascorbic acid. The ability to release the reactants on-demand at defined time points was demonstrated. The system opens up opportunities for the controlled local delivery of unstable of highly bioactive molecules produced in situ and on demand from stable precursors.

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synopsisMooney's version of the molecular theory of polymer networks has been generalized to the case when the external strain applied in the isotropic state is different from that at network formation. As in the theory of equilibrium behavior of the polymer networks, this generalization allows inclusion in the viscoelastic functions of effects connected with the temperature dependence of internal energy of the chains and with the strain effect of the solvent. From viscoelastic functions thus generalized, it is possible to derive a relation for calculation of the monomeric friction coefficient. It also suggests the possibility of superposing data obtained at various temperatures, degrees of swelling, and condition of network formation.