RESUMEN
The effect of the simultaneous presence of mono- and divalent cations on the thermodynamics of polyelectrolyte solutions is not fully understood. In physiological conditions, combinations of these ions affect structure formation in biopolymer systems. It is known that divalent counterions form a tight sheath around the polymer backbone, while monovalent ions are distributed in a diffuse cloud. Dynamic light scattering measurements of the collective diffusion coefficient D and the osmotic compressibility of semi-dilute hyaluronan solutions containing different ratios of sodium and calcium ions are compared with simple polyelectrolyte models. Scaling relationships are derived in terms of polymer concentration and ionic strength J of the added salt. Differences in the effects of sodium and calcium ions are expressed only through J.
RESUMEN
Small angle neutron scattering is employed to estimate the interactions in complex multicomponent systems. The method is applied to describe a ternary system, poly(dimethyl siloxane) toluene with silica filler particles. Contrast variation by solvent deuteration is used to distinguish the three different partial structure factors of filled polymer samples, S(pp)(q), S(pf)(q), and S(ff)(q), where the subscripts p and f refer to polymer and filler. This procedure allows changes to be detected in the distribution of the polymer close to the solid surface. Independent dynamic light scattering measurements are used to validate the method. A comparison is made between the behavior of different filled poly(dimethyl siloxane) PDMS samples. It is found that the polymer distribution is perturbed in the vicinity of the solid surfaces. In the case of weak interactions, the solvent removes the polymer almost completely from the filler particles, while, when the interaction is strong, the surface remains covered.