Structure of Polyelectrolytes with Mixed of Monovalent and Divalent Counterions: Poisson-Boltzmann Analysis and SAXS Measurements

International audienceWe have studied by Small Angle X Ray Scattering (SAXS) the structure of salt free polyelectrolytes solutions containing monovalent and divalent counterions. We have considered mixtures of sulfonated polystyrene with monovalent (Na+) and divalent (Ca2+) counterions and measured the position of the scattering peak, q*, as a function of the monomer concentration cp and the monovalent / divalent content. The aim is to understand the variations observed in q* position when the valence of the counterions is gradually increased. This work is a continuation of a previous study in which first measurements were performed on a rather small number of sodium-PSS / calcium-PSS mixtures. In the present work, we used synchrotron radiation improved the quality of the data and varied the monovalent / divalent ratio with a much finer step. Indeed this gives new interesting results in the ranges of low and large divalent content. We analyzed SAXS results through the isotropic model and scaling approach description introduced by de Gennes et al. and developed by Dobrynin et al.. In this model, one key parameter is the chemical charge and / or the effective charge fraction feff of the polyions. Although the chemical charge fraction f of sodium-PSS and calcium-PSS polyelectrolyte is fixed by the synthesis, the effective charge fraction in mixtures varies with the monovalent / divalent ratio. This quantity has been calculated using the resolution of the Poisson-Boltzmann (PB) equation in the frame of the cell model for various monovalent / divalent contents and different concentrations. Severe deviations can be found in the effective charge values of mixtures at finite concentrations compared to the classical Manning-Oosawa prediction (infinite dilution limiting law). We demonstrate that the evolution of q* is still compatible with the isotropic model and the scaling approach in the low concentration range provided that the divalent content is not too high. In particular, a power law relation q * ~ f eff~ 0.3 can be found which looks very close to the one observed for weakly charged polyelectrolytes ( q*~ f 2 / 7 in good solvent or q*~ f 1/ 3 in theta solvent). Mixtures finally provide a way to adjust the effective charge fraction without changing the chemical nature of the polyions. However this procedure gives improvement of data prediction only in a limited range; it is still not able to fully explain the high concentration range, as well as the high divalent content mixtures. This is certainly due to the fact that the PB equations are not able to take into account the local interactions between monomers and divalent counterions, which goes beyond the mean field approach

In Situ Synthesis of Silver Nanoparticles in Linear and Branched Polymer Matrices

Silver nanoparticles were synthesized in linear and branched polymer matrices at different temperatures. The template role of the host linear Polyacrylamide and star-like copolymer Dextran-graft-Polyacrylamide for in situ synthesis of nanoparticles was studied by TEM, UV-Vis spectrophotometry and Dynamic light scattering. It was shown that the internal structure of polymers in solution drastically affects the process of Ag NPs formation. Branched polymer matrix allows to obtain a stable silver colloid even at high temperature when the linear PAA matrix is not efficient. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3484

SANS from Salt-Free Aqueous Solutions of Hydrophilic and Highly Charged Star-Branched Polyelectrolytes

International audienceScattering functions of sodium sulfonated polystyrene (NaPSS) star-branched polyelectrolytes with high sulfonation degrees were measured from their salt-free aqueous solutions, using the Small Angle Neutron Scattering (SANS) technique. Whatever the concentration c, they display two maxima. The first, of abscissa q 1 *, is related to a position order between star cores and scales as q 1 * 9 c 1/3. The second, of abscissa q 2 *, is also observed in the scattering function of a semi-dilute solution of NaPSS linear polyelectrolytes. In the dilute regime (c < c*, non-overlapping stars), peak abscissa does not depend on concentration c and is just an intramolecular characteristic associated with the electrostatic repulsion between arms of the same star. In the semi-dilute regime, due to the star interpenetration, the scattering function – through the peak position, reflects repulsion between arms of the same star or of different stars. The c threshold between these distinct c-dependencies of q 2 * in the dilute and semi-dilute regimes is estimated as c*. Just as simple is the measurement of the geometrical radius R of the star obtained from the q 1 * value at c* through the relation 2R = 2π/q 1 *. By considering NaPSS stars of the same functionality with different degrees of polymerization per arm N a , we find R scaling linearly with N a , suggesting an elongated average conformation of the arms. This is in agreement with theoretical predictions and simulations. Meanwhile the value of q 2 * measured in the dilute regime does not allow any inhomogeneous counterion distribution inside the stars to be revealed

On the signature of tensile blobs in the scattering function of a stretched polymer

We present Monte Carlo data for a linear chain with excluded volume subjected to a uniform stretching. Simulation of long chains (up to 6000 beads) at high stretching allows us to observe the signature of tensile blobs as a crossover in the scaling behavior of the chain scattering function for wave vectors perpendicular to stretching. These results and corresponding ones in the stretching direction allow us to verify for the first time Pincus prediction on scaling inside blobs. Outside blobs, the scattering function is well described by the Debye function for a stretched ideal chain.Comment: 4 pages, 4 figures, to appear in Physical Review Letter

Stabilization and Controlled Association of Inorganic Nanoparticles using Block Copolymers

We report on the structural properties of mixed aggregates made from rare-earth inorganic nanoparticles (radius 20 Angstroms) and polyelectrolyte-neutral block copolymers in aqueous solutions. Using scattering experiments and Monte Carlo simulations, we show that these mixed aggregates have a hierarchical core-shell microstructure. The core is made of densely packed nanoparticles and it is surrounded by a corona of neutral chains. This microstructure results from a process of controlled association and confers to the hybrid aggregates a remarkable colloidal stability.Comment: 14 pages, 5 figure

Scale-free static and dynamical correlations in melts of monodisperse and Flory-distributed homopolymers: A review of recent bond-fluctuation model studies

It has been assumed until very recently that all long-range correlations are screened in three-dimensional melts of linear homopolymers on distances beyond the correlation length $\xi$ characterizing the decay of the density fluctuations. Summarizing simulation results obtained by means of a variant of the bond-fluctuation model with finite monomer excluded volume interactions and topology violating local and global Monte Carlo moves, we show that due to an interplay of the chain connectivity and the incompressibility constraint, both static and dynamical correlations arise on distances $r \gg \xi$. These correlations are scale-free and, surprisingly, do not depend explicitly on the compressibility of the solution. Both monodisperse and (essentially) Flory-distributed equilibrium polymers are considered.Comment: 60 pages, 49 figure

Polyelectrolytes and ionic liquids

Cette thèse présente une étude de la structure de solutions de polyélectrolytes (PEs) dans les liquides ioniques (LIs) et de la structure locale des LIs en présence de PEs. Les techniques de diffusion de rayons X et de neutrons ont été principalement utilisées pour cette étude. Dans une première partie, la capacité des LIs à former des clusters à l échelle nanoscopique est démontrée. Dans une seconde partie, l influence de la nature des contreions et du solvant sur le comportement du polystyrène sulfonate (PSS) en solution est abordée. La conformation moyenne du PSS et son état de dispersion dans les milieux aqueux et organiques sont alors explorés dans une troisième partie. Une étude similaire pour le cas spécifique des milieux LIs est présentée dans une quatrième partie. Finalement, d autres polymères, chargés ou neutres, en solution dans les LIs, sont considérés dans une cinquième et dernière partie.In this thesis the structure of polyelectrolyte (PE) solutions in ionic liquids (ILs) and mutual influence of bothcomponentsthe local structure of the latter in the presence of PEs are studied. X-ray and neutron scatteringtechniques have been mainly used for the present investigation. In a first part, the ability of considered ILs toform clusters at nanoscale is demonstrated. In a second part, the influence of the nature of counterions andthe solvent on the polystyrene sulfonate (PSS) behavior in solution is tackled. PSS average conformation anddispersion state in aqueous and organic media are then explored in a third part. A similar investigation, carriedout on the specific case of PSS in IL media, is described in a fourth part. Finally, other polymers, both chargedand neutral, in IL solutions are considered in a fifth and last part.STRASBOURG-Bib.electronique 063 (674829902) / SudocSudocFranceF