The layer-by-layer deposition method to prepare multilayers of polyelectrolytes of alternating charge has been followed in situ by means of optical reflectometry experiments. It turns out that in solutions containing both polyelectrolyte and appropriate salts up to a certain concentration, the regular build up of multilayers is modified and becomes an adsorption/redissolution process. We explain this by taking into account (i) that during the regular multilayer formation process the macromolecules cannot equilibrate, (ii) that the added salt plasticizes the multilayer to a state where the molecules are sufficiently mobile to enable them to equilibrate between the layer and the surrounding solution, and (iii) that the presence of excess polyelectrolyte brings the system to a one-phase region of the polyelectrolyte complex phase diagram, implying that polyelectrolyte complexes must dissolve under these conditions.

The layer-by-layer deposition method to prepare multilayers of polyelectrolytes of alternating charge has been followed in situ by means of optical reflectometry. It has been shown previously that in solutions containing both weak polyelectrolytes and appropriate salt the buildup of multilayers is modified and becomes an adsorption/dissolution process. The influence of different salts (phosphates, chlorides, and nitrates) and polyelectrolyte molecular weight on formation and erosion of multilayers on silica surfaces was investigated. In all experiments, the anionic polyelectrolyte was poly(acrylic acid). As the cationic polyelectrolyte, poly-(dimethylaminoethyl methacrylate), poly(allylamine hydrochloride), and poly(2-vinyl-N-methylpyridinium iodide) were used. It has been shown that at very low ionic strength (1 mM) regular buildup of multilayers is observed independent of the salt used. However, at higher ionic strength, dissolution also takes place, and the critical "glass-transition ionic strength" needed for the multilayer to be dissolved depends on the salt used, as well as on the polycation/polyanion pair studied.

Abstract. This article summarizes methods for determining proton surface charge at mineral/water interfaces. It covers conventional experimental procedures and discusses problems with the techniques. Also it involves recommendations for obtaining reasonable and comparable results. The term "comparable results" refers to comparison between results for the same solid as obtained in different laboratories. The most important parameters for the surface titrations are discussed. We also propose a reference titration procedure that would allow direct, unbiased comparisons of experimental data. The article finally includes a check-list for researchers and reviewers which should allow limiting the amount of titration data that are not useful for future uses. (doi: 10.5562/cca2062)

Electrostatically driven coassembly of poly(acrylic acid)-block-poly(acrylamide), PAA-b-PAAm, and poly(2-methylvinylpyridinium iodide), P2MVP, leads to formation of micelles in aqueous solutions. Light scattering and small angle neutron scattering experiments have been performed to study the effect of concentration and length of the corona block (N PAAm ) 97, 208, and 417) on micellar characteristics. Small angle neutron scattering curves were analyzed by generalized indirect Fourier transformation and model fitting. All scattering curves could be well described with a combination of a form factor for polydisperse spheres in combination with a hard sphere structure factor for the highest concentrations. Micellar aggregation numbers, shape, and internal structure are relatively independent of concentration for C p < 23.12 g L -1 . The Guinier radius, average micellar radius, hydrodynamic radius, and polydispersity were found to increase with increasing N PAAm . Micellar mass and aggregation number were found to decrease with increasing N PAAm.

Complexation between poly­(acrylate) (PA) and poly­(allylammonium) (PAH) macroions at pH = 7.0 was studied by means of electrokinetics, microcalorimetry, and DLS. At low polyelectrolyte concentrations and no electrolyte present strong overcharging of primary nanocomplexes occurred. In contrast, the increase in polyelectrolyte concentration led to flocculation taking place near the equivalence. The nanocomplex charge reversal was also achieved in the high polymer concentration regime by the abrupt instead of stepwise titrant addition. The procedure was successfully used in the case of several other polyion pairs. The presence of electrolyte affected the PAH–PA interpolyelectrolyte neutralization considerably, leading to ion-specific aggregation and extrinsic charge compensation. The complexation energetics was weakly influenced by ionic conditions. To the best of our knowledge, the reported results are the first direct evidence for primary complex overcharging. Their rationalization explains why interpolyelectrolyte neutralization in solution and at surfaces usually results in formation of neutral and charged products, respectively.

Complexation between polyallylammonium cations and polystyrenesulfonate anions was investigated in aqueous solutions of binary 1 : 1 sodium electrolytes (NaX, X = F, Cl, Br, I, NO3, ClO4) by means of microcalorimetry, dynamic light scattering, electrokinetics and spectrophotometry. At lower molar ratios of monomer units charged polyelectrolyte complexes were formed. At molar ratios close to equivalence and at lower salt concentrations (c(NAX)/mol dm(-3) ≤ 0.1) flocculation occurred. The obtained precipitates contained approximately equimolar amounts of oppositely charged monomer units. At c(NAX)/mol dm(-3) ≥ 0.5 (X = NO3, ClO4) and in the case when the polycation was present in excess, the amount of positively charged monomer units in the precipitate was higher than that of negatively charged monomers (asymmetric neutralisation). In addition, the aggregation of positively charged complexes in concentrated solutions of all investigated electrolytes was noticed. The onset of aggregation was strongly anion specific. However, the aggregation of negatively charged complexes did not occur even at c(NaX) = 3 mol dm(-3). The composition of the insoluble products at equimolar ratio of monomer units and higher concentrations of NaNO3 and NaClO4 was dependent on the order of addition, indicating non-equilibrium interpolyelectrolyte neutralisation under all ionic conditions. At 25 °C and c(NaClO4) = 1 mol dm(-3) equilibrium was not reached after two months. In contrast, the supernatants showed no traces of free polyanion chains after being heated for a week at 60 °C. The pairing of monomer units was predominantly entropically driven, irrespective of the type of reaction products formed (polyelectrolyte complexes, precipitates) and the electrolyte type. The results obtained indicate that the overcharging is not an enthalpically demanding process. The calorimetric measurements also suggest that the strong influence of counteranions on the composition of the reaction product must be related to differences in ion distribution around polycations. However, despite rather similar energetics for complex and precipitate formation in the presence of various sodium salts a clear correlation of formation enthalpies with corresponding anion hydration enthalpies (Hofmeister series) was observed. Somewhat surprisingly, the titration calorimetry experiments have also revealed that the increase in electrolyte concentration affects the enthalpy of interpolyelectrolyte neutralisation negligibly.

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Bacterial adhesion can be controlled by different material surface properties, such as surface charge, on which we concentrate in our study. We use a silica surface on which poly(allylamine hydrochloride)/sodium poly(4-styrenesulfonate) (PAH/PSS) polyelectrolyte multilayers were formed. The corresponding surface roughness and hydrophobicity were determined by atomic force microscopy and tensiometry. The surface charge was examined by the zeta potential measurements of silica particles covered with polyelectrolyte multilayers, whereby ionic strength and polyelectrolyte concentrations significantly influenced the build-up process. For adhesion experiments, we used the bacterium Pseudomonas aeruginosa. The extent of adhered bacteria on the surface was determined by scanning electron microscopy. The results showed that the extent of adhered bacteria mostly depends on the type of terminating polyelectrolyte layer, since relatively low differences in surface roughness and hydrophobicity were obtained. In the case of polyelectrolyte multilayers terminating with a positively charged layer, bacterial adhesion was more pronounced than in the case when the polyelectrolyte layer was negatively charged.