Streaming potential measurements were carried out on a family of polyacrylamide-co-sodium acrylate gels cross-linked with N,N'-methylenebisacrylamide in a homemade electrokinetic cell. Measurements of the ionic conductivity within thin films of these gels allowed the equilibrium Donnan potential difference between the bulk gel and the bulk electrolyte environments to be estimated at various ionic strengths. The resulting Donnan potential data were combined with the directly measurable streaming potential data and used to evaluate the diffuse soft interface model of electrokinetics (Langmuir 2004, 20, 10324). The model introduces the concept of a gradual decay of polymer density and fixed charge density within a narrow inter-phase at the gel/solution interface. The nature of the decay at the interface has a dramatic effect on the magnitude of the streaming potential as predicted by the diffuse soft interface model. In this investigation, the gradual decay of polymer density within the inter-phase is described with a hyperbolic tangent function. For the gels mentioned, the characteristic length scale of the decay, alpha, as calculated from the fit to the model, increases significantly with decreasing ionic strength, suggesting an osmotically driven swelling of the loosely cross-linked polymer chains at the interface. The experimental data and the results of the fitting are discussed in terms of the physical picture of the interface and compared to fitting results for a model which assumes a simple step function at the gel-solution interface.

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The dynamics of hairy spherical nanoparticles in a melt of linear polymer chains has been investigated by mechanical spectroscopy as a function of particle topology and concentration. Using a simple free volume approach for the data analysis of the structural relaxation time vs concentration and the well-known hard-sphere result as a reference, a semiquantitative measure for the interparticle interactions, that is particle deformability/softness, and the effective particle size compared to the size of a nonswollen spherical brush has been determined. For these studies, model particles of hairy nanoparticles differing in either hair length or grafting density have been prepared. In contrast to our previous studies of copolymer micelles, for the new graft particles at very high grafting densities our free volume approach led to nonphysical results:  the effective particle size is increasing with increasing concentration. Therefore, it has been concluded that densely grafted hairy particles in a matrix of linear polymer chains cannot be mapped onto a hard-sphere reference system, indicating that the interaction potential is not simply soft repulsive.

The steady-state diffusion of metals ions through thin films with fixed charged groups was investigated using diffusive gradients in thin films (DGT) measurements. Copolymers of acrylamide and sodium acrylate cross-linked with N,N'-methylenebisacrylamide were used as diffusive gels. The rate of diffusion of cadmium ions through the gels was measured by determining the mass of cadmium bound to a backing chelex resin after a known deployment time. Variation of the ionic strength as well as the fixed charge density and the thickness of the gel layer allowed evaluation of the impact of the Donnan partitioning and the diffusion layer in solution on the observed steady-state flux of ions through the layer. The results underscore that, as the Donnan partitioning increases, the impact of the diffusion layer in solution becomes more significant. At modest Donnan potentials, Donnan partitioning controls the net flux of metal ions, whereas at conditions of increasing Donnan potential, i.e., at decreasing ionic strength, the flux is increasingly limited by diffusion in solution. An analytical expression is developed to describe the influence of Donnan partitioning on the observed steady-state flux of metal ions.

This paper presents a spin-coating layer-by-layer assembly process to prepare multilayered polyelectrolyte-clay nanocomposites. This method allows for the fast production of films with controlled layered structure. The preparation of a 100-bilayer film with a thickness of about 330 nm needs less than 1 h, which is 20 times faster than conventional dip-coating processes maintaining the same hardness and modulus values. For validation of this technique, nanocomposite films with thicknesses up to 0.5 m have been created with the common dip self-assembly and with the spin coating layer-by-layer assembly technique from a poly(diallyldimethylammonium)chloride (PDDA) solution and a suspension of a smectite clay mineral (Laponite). Geometrical characteristics (thickness, roughness, and texture) as well as mechanical characteristics (hardness and modulus) of the clay-polyelectrolyte films have been studied. The spin-coated nanocomposite films exhibit clearly improved mechanical properties (hardness 0.4 GPa, elastic modulus 7 GPa) compared to the "pure" polymer film, namely a sixfold increase in hardness and a 17-fold increase in Young's modulus.