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Nanometer‐sized anions (nano‐ions) like polyoxometalates and boron clusters exhibit so‐called superchaotropic behavior, which describes their strong binding to hydrated non‐ionic matter in water. We show here that nano‐ions, at millimolar concentrations, dramatically enhance the viscosity and induce gelation of aqueous solutions of non‐ionic cellulose ethers (CEs), a class of widely utilized polymers known for their thickening and gel‐forming ability. These phenomena arise from an interplay of attractive forces and repulsive electrostatic forces between CE‐chains upon nano‐ion binding. The attractive forces manifest themselves as aggregation of CE‐chains into a physically crosslinked polymer network (gel). In turn, the electrostatic repulsions hamper the viscosity increase and gelation. Superchaotropic nano‐ion binding emerges as a novel and general physical crosslinking motif for CE‐solutions and exceeds by far the conventional thickening effects of classical salts and ionic surfactants. [ABSTRACT FROM AUTHOR]

Sodium polyacrylate (NaPA) in dilute aqueous solution at an ionic strength of [NaNO3] = 0.01M establishes a rich phase behavior in the presence of low amounts of silver cations, which were introduced at a few millimoles or less by replacing the corresponding amount of Na+ cations. Beyond an extremely low level of Ag+ cations, anionic PA chains aggregate. By increasing the concentration of Ag+, the aggregates become denser and keep on growing without limit. Once a certain range of [Ag+] is reached, the instantaneously formed dense aggregates remain stable. Irradiation of the PA aggregate solutions with UV-light induces formation of silver nanoparticles (Ag-Nps). Based on a combination of UV-vis spectroscopy, light scattering, transmission electron microscopy, and small angle neutron scattering, the mechanism of this NaPA assisted formation of Ag-Nps is studied. One focus of the study is lying on the effect of the two different solution states of dense aggregates, corresponding to the unstable growing AgPA aggregates and to the stable AgPA aggregates and another focus is aiming at the characterisation of the morphology of the generated hybrid particles composed of Ag-Nps and hosting PA chains. [ABSTRACT FROM AUTHOR]

We present steady shear rheology data for sodium polystyrene sulfonate (NaPSS) in semidilute unentangled salt-free aqueous solution as a function of polymer concentration (c) and degree of polymerisation (N). The measured terminal modulus (G) agrees with the scaling prediction of G ≃ kBTc/N. The specific viscosity varies with the degree of polymerisation as ηsp ∝ N1.24±0.08. The observed dependence differs with the linear relation expected from the Rouse model for ideal chains as predicted by de Gennes’ scaling model and subsequent theories. Together with the diffusion data of Oostwal et al., our results suggest that chains may follow non-Gaussian statistics beyond the correlation length (ξ). Small angle neutron scattering data on salt-free semidilute solutions at low polymer concentrations partially support this hypothesis but do not confirm it. The electrostatic Kuhn length of NaPSS salt-free solutions is found to be proportional and slightly larger than the correlation length (LK,e ≃ 1.3ξ). This result agrees well with the scaling model of Dobrynin et al. Radii of gyration (Rg) data as a function of polymer concentration reveal that a concentrated regime (Rg ∝ c0) does not occur for NaPSS in the concentration range considered (c ≲ 4M). We conclude by comparing the predictions of the scaling model of Dobrynin et al. and Muthukumar’s double screening theory with viscosity data for different polyelectrolyte-solvent systems. Dobrynin’s model provides a better description of experimental observations. Our findings confirm several aspects of current models for polyelectrolyte solutions but some deviations from theory remain. [ABSTRACT FROM AUTHOR]