The influence of ionic strength and polymer charge density on the multilayer formation of strong polyelectrolytes is investigated by X-ray reflectivity. To a first approximation the adsorption behavior as a function of the degree of charge, f, is binary:  For f ≤ 50% the films are one order of magnitude thinner than those for f ≥ 75%. This is due to a threshold of charge overcompensation after each adsorption step which seems to be at f between 50% and 75%. Above the charge reversal limit the thickness and the surface roughness increase with decreasing polymer charge. Below a charge density of 50% the film thickness cannot be changed by salt additive whereas the film thickness increases with c NaCl 1/2 above a degree of charge of 75%. The density of all investigated films is quite similar.

Recent studies using a thin film balance of free-standing thin aqueous films (foam films) containing polyelectrolytes resulted in jump-like discontinuities in the film thickness with increasing outer pressure. These jumps in film thickness correspond to an oscillation of the disjoining pressure. The oscillation period of the disjoining pressure scales as c -0.5 with the polyelectrolyte concentration c. A mesoscopic ordering of the chains in the film similar to that found in aqueous semidilute polyelectrolyte solutions is assumed. In experiments presented in this work, the electrostatic effect is investigated by adding low molecular salt and varying the degree of charge of the polyelectrolyte chains. The studies reveal that the amplitudes of the disjoining pressure oscillations are reduced with increasing ionic strength and decreasing degree of charge. The results show that the jumps in film thickness and therefore the structuring are due to the electrostatic repulsions between the polyelectrolyte chains.

The utility of different polycarboxybetaines (PCB) as positively charged components of polyelectrolyte complexes was elucidated by potentiometry, turbidimetry, and fluorescence spectroscopy. PCB practically did not quench the fluorescence of either pyrenyl-tagged poly(methacrylic acid) or ethidium bromide intercalated in DNA. This indicates small, if any, interaction of PCB with the above polyanions due to formation of stable ion pairs between carboxylic and quaternary amino groups positioned in each repeated unit of PCB chains. Potentiometric titration curves of PCB solutions practically coincided with the curve of distilled water in the studied pH range 2-11. Addition of sodium poly(styrenesulfonate) (PSS) did not result in phase separation or noticeable change of the titration curve of PCB at pH > 7, whereas at pH < 7 phase separation occurred and the titration curve of the mixture significantly changed, being in close proximity with the curve of poly(acrylic acid). The pH value corresponding to the "cloud point" decreased gradually with the increase in PSS content, invariably of PSS molecular weight in the studied region M w ) 4000-100 000. These findings suggest that sulfonate groups of PSS are not able to compete with carboxylate groups of PCB for binding with the amino groups in neutral and alkaline media, whereas the competitive binding becomes pronounced at pH < 7. The revealed ability of PCB to interact efficiently with PSS forming polyelectrolyte complex with pH-controlled solubility can be important for development of bioseparation techniques.