Rheological studies were performed with aqueous salt solutions of viscoelastic cationic surfactant erucyl bis(hydroxyethyl)methylammonium chloride (EHAC) and its mixtures with hydrophobically modified polyacrylamide. The solutions of surfactant itself above the concentration of crossover of wormlike micelles exhibit two regions of rheological response. In the first region, they behave like polymer solutions in semidilute regime characterized by viscoelastic behavior with a spectrum of relaxation times. In the second region, unlike polymer solutions their relaxation after shear is dominated by a single relaxation time. Being composed of "living" micelles, the EHAC solutions easily lose their viscosity at the variation of the external conditions. For instance, heating from 20 to 60 degrees C reduces viscosity by up to 2 orders of magnitude, while added hydrocarbons induce a sudden drop of viscosity by 3-6 orders of magnitude. Polymer profoundly affects the rheological properties of EHAC solutions. The polymer/surfactant system demonstrates a 10,000-fold increase in viscosity as compared to pure-component solutions, the effect being more pronounced for polymer with less blocky distribution of hydrophobic units. A synergistic enhancement of viscosity was attributed to the formation of common network, in which some subchains are made up of elongated surfactant micelles, while others are composed of polymer. At cross-links the hydrophobic side groups of polymer anchor EHAC micelles. In contrast to surfactant itself, the polymer/surfactant system retains high viscosity at elevated temperature; at the same time it keeps a high responsiveness to hydrocarbon medium inherent to EHAC.

Self-aggregation of rigid-rod poly(sodium p-phenylenesulfonate) in aqueous solution and inside water-swollen polyacrylamide gel was studied by small-angle neutron scattering. It was shown that both inside the hydrogel and in solution polyelectrolyte rods self-assemble into cylindrical aggregates having eight to nine single polymer chains in the cross-section, the chains being aligned parallel to the axis of the aggregate. The length of these aggregates is much higher than the contour length of a single chain. Gels with embedded rods were studied by contrast variation method in order to examine separately the scattering by the gel and by the rods. Two important observations were made. First, it was shown that the ordering of the rods in the gel resembles that in solution. Second, it was shown that the gel itself is more homogeneous in the presence of rods. Most probably, this effect is due to mobile counterions of rods, which counteract the formation of spatial inhomogeneities in the network during synthesis, because in an inhomogeneous network mobile counterions should be also distributed nonuniformly that is associated with significant translational entropy losses.

The swelling and mechanical behavior of polyelectrolyte gels with the degree of ionization varying from 7 to 100 mol % were studied in mixtures of a good solvent and a poor solvent. In a good solvent region for weakly charged gels the shear modulus decreases with the gel swelling, while for strongly charged gels swelling leads to the increase of the shear modulus. Also for strongly charged gels the elastic modulus can remain unchanged during the volume phase transition (for a weakly charged gel, a jump in the volume at the collapse transition is usually accompanied by a discontinuous upturn of the elastic modulus). Both of these features of strongly charged gels are attributed to a significant extension of the highly ionized subchains. At the same degree of swelling the modulus of the fully ionized gel was higher in the medium of lower polarity. This may be due to the formation of new effective cross-links between the subchains as a result of dipole−dipole attraction of ion pairs formed between charged groups of network and condensed counterions.