Marián Sedlák

The ionic strength dependence of the structure and dynamics of polyelectrolyte solutions as seen by light scattering: The slow mode dilemma

The ionic strength dependence of the structure and dynamics of polyelectrolyte solutions was investigated by static and dynamic light scattering. Narrow molecular weight distribution sodium poly(styrenesulfonate) (NaPSS) standards in aqueous NaCl solutions were chosen as model systems. The study covers moderate polymer concentrations (∼0.5–50 g/L) where interparticle interactions rather than single‐polyion properties are dominant. Two diffusive modes characterized as fast and slow were detected in most cases. Scattering amplitudes of these modes were evaluated from light scattering data, which was not done in previous investigations. Amplitudes were normalized by the scattering of a benzene standard. Attention was paid mainly to the occurrence of the slow diffusive mode, which is interpreted as the dynamics of large multichain domains. Experimental results show that the occurrence of the slow mode is not connected with any kind of a sharp transition at some critical conditions. The amplitude of the slow m...

ON THE POSSIBLE ROLE OF NONELECTROSTATIC INTERACTIONS IN THE MECHANISM OF THE SLOW POLYELECTROLYTE MODE OBSERVED BY DYNAMIC LIGHT SCATTERING

The effect of a poor solvation of a polyelectrolyte chain backbone in a polar solvent was investigated as a possible origin of large multichain domains in polyelectrolyte solutions giving rise to the slow polyelectrolyte mode observed by dynamic light scattering. It was investigated if these domains could be interpreted as polymeric aggregates formed due to the poor backbone solvation. Static and dynamic light scattering experiments on polyions in solvents of different quality with respect to the polyelectrolyte chain backbone, and the temperature dependence of the slow mode, showed that this hypothesis is not realistic. Poor solvation of the polyelectrolyte chain backbone in polar solvents is therefore not the origin of domain formation in solutions of strongly charged polyelectrolytes. This conclusion was confirmed also by analysis of literature data in view of the investigated issue.

Real-time monitoring of the origination of multimacroion domains in a polyelectrolyte solution

First real-time monitoring of the origination of multimacroion domains in an initially homogeneous polyelectrolyte solution was performed. Domains were generated by pH-induced increase of macroion charge in solution of poly(methacrylic acid). Monitoring was performed by static and dynamic light scatterings, in which scattering contributions from individual polyions and growing multimacroion domains were separated, such that amplitudes of both modes were expressed in absolute units. Kinetic results also yield new information regarding the nature of multimacroion domains.

Influence of temperature on polyelectrolyte dynamics : partially neutralized solutions of poly (methacrylic acid)

The influence of temperature on the dynamics of partially neutralized solutions of poly(methacrylic acid) was investigated by photon correlation spectroscopy. A pronounced effect of aggregation above T ⋍ 70°C is observed. The aggregation process is accompanied by a rapid increase of the relative scattering amplitude of the slow diffusive mode occurring in strongly interacting polyelectrolyte systems, by a decrease of the corrected slow diffusion coefficient, and by an increase of the total scattered light intensity. The process is not fully reversible. The aggregation tendency strongly depends on the degree of neutralization α of the sample. In the interval α=0 to α=1 it reaches a maximum at α⋍0.4. An aggregation mechanism based on intermolecular hydrogen bonding between carboxyl groups is proposed.

Dynamic light scattering from binary mixtures of polyelectrolytes. II. Appearance of the medium polyelectrolyte mode upon mixing and comparison with experiments on binary mixtures of neutral polymers

Dynamic light scattering experiments were performed on salt-free aqueous binary mixtures of sodium poly(styrene sulfonate) (NaPSS) with different molecular weights. Three diffusive modes were observed and investigated as a function of the mixture composition, total polymer concentration, and molecular weights of the components of the mixture. In addition to the fast and slow polyelectrolyte modes, which are typical for binary polyelectrolyte solutions, a third new mode, named the “medium mode,” was observed. To investigate the role of electrostatic interactions in the mechanism of this mode, similar experiments were performed on analogical binary mixtures of neutral polystyrenes with different molecular weights in benzene. Polystyrene molecular weights were chosen to match the contour lengths of NaPSS samples used. No “medium mode” was observed in this system. Two diffusive modes corresponding to the cooperative diffusion of component 1 and the cooperative diffusion of component 2, respectively, were meas...

Dynamic behaviour of poly(methacrylic acid) in methanolic solutions

Abstract Methanolic solutions of poly(methacrylic acid) adjusted to various degrees of neutralization with lithium methoxide were investigated by photon correlation spectroscopy. The results obtained are compared with the dynamic behaviour of aqueous solutions. The influence of the solvent dielectric permittivity e on the polyelectrolyte dynamics is discussed (e = 31.4 and 78.5 for methanol and water, respectively). While two diffusive modes corresponding to the dynamics of individual chains and of multi-chain domains can be observed in aqueous solutions, no domains are present in methanolic solutions. The only observable mode (Nernst-Hartley coupled diffusion of polyions and counterions) depends anomalously on the degree of neutralization, indicating the existence of ‘excess counterion counterion condensation’. Both phenomena cannot be explained by the classical polyelectrolyte theory, which takes into account only the change of the dielectric permittivity. The role of counterions in these effects is stressed. They influence the solvent quality and cause a chain collapse reflected in excess counterion condensation. The absence of domains in methanol is ascribed to the relatively low osmotic activity of counterions.

Dynamic light scattering from binary mixtures of polyelectrolytes. I. Influence of mixing on the fast and slow polyelectrolyte mode behavior

Dynamic light scattering experiments were performed on salt-free aqueous binary mixtures of sodium poly(styrene sulfonate) with different molecular weights. Three diffusive modes were observed and investigated as a function of the mixture composition, total polymer concentration, and molecular weights of the components of the mixture. The fast and slow polyelectrolyte modes, which are typical for binary polyelectrolyte solutions, are observed also in binary mixtures and maintain their basic characteristics. The fast diffusive mode is independent of the total polymer concentration, mixture composition, and molecular weights of the two components, in agreement with results obtained on binary solutions. Only one slow diffusive mode is observed in binary mixtures, in spite of the fact that polyions with appreciably different molecular weights in binary solutions give slow modes on appreciably different time scales. Therefore, the slow polyelectrolyte mode cannot be identified with any single-chain property. O...

A novel approach to controlled self-assembly of pH-responsive thermosensitive homopolymer polyelectrolytes into stable nanoparticles

This review addresses the recent research progress in introducing and elaborating a novel approach to controlled polymer self-assembly into stable nanoparticles using pH-responsive thermosensitive homopolymer polyelectrolytes. Interesting aspect of this approach is that stable polymeric nanoparticles are formed from homopolymers of one type only and without any assembly-triggering additives. The process of their formation can be monitored online e.g. by light scattering and particle size can be finely custom tuned. Obtained nanoparticles have interesting properties and are very stable over long periods of time and over a broad range of salt concentrations including physiological conditions. Much effort was devoted not only to finding optimum experimental protocols and to characterizing resulting nanoparticles in detail, but also to understanding physical processes behind these successful protocols.

Poly(alkylacrylic acid)s: solution behavior and self-assembly

This review addresses solution behavior and self-assembly of poly(alkylacrylic acid)s including the unsubstituted poly(acrylic acid). It includes solubility limits, hydrogen ion equilibria, counterion condensation, pH-induced conformational transitions, chain expansion due to charge repulsions, specific effects in solutions of charged poly(alkylacrylic acid)s in organic solvent, thermoresponsivity of poly(alkylacrylic acid)s including its practical use for the preparation of nanoparticles by controlled self-assembly process, hydrogen-bonded block copolymer micelles, and potential for using poly(alkylacrylic acid)s in intracellular drug delivery via endocytosis followed by endosomal escape due to the disruption of the endosomal membrane by poly(alkylacrylic acid)s and release of important biomolecular drugs inside cells.