Linear Flexible Polyelectrolytes Research Articles

Role of Charge Regulation and Fluctuations in the Conformational and Mechanical Properties of Weak Flexible Polyelectrolytes.

This work addresses the role of charge regulation (CR) and the associated fluctuations in the conformational and mechanical properties of weak polyelectrolytes. Due to CR, changes in the pH-value modifies the average macromolecular charge and conformational equilibria. A second effect is that, for a given average charge per site, fluctuations can alter the intensity of the interactions by means of correlation between binding sites. We investigate both effects by means of Monte Carlo simulations at constant pH-value, so that the charge is a fluctuating quantity. Once the average charge per site is available, we turn off the fluctuations by assigning the same average charge to every site. A constant charge MC simulation is then performed. We make use of a model which accounts for the main fundamental aspects of a linear flexible polyelectrolyte that is, proton binding, angle internal rotation, bond stretching and bending. Steric excluded volume and differentiated treatment for short-range and long-range interactions are also included. This model can be regarded as a kind of “minimal” in the sense that it contains a minimum number of parameters but still preserving the atomistic detail. It is shown that, if fluctuations are activated, gauche state bond probabilities increase and the persistence length decreases, so that the polymer becomes more folded. Macromolecular stretching is also analyzed in presence of CR (the charge depends on the applied force) and without CR (the charge is fixed to the value at zero force). The analysis of the low force scaling behavior concludes that Pincus exponent becomes pH-dependent. Both, with and without CR, a transition from 1/2 at high pH-values (phantom chain) to 3/5 at low pH-values (Pincus regime) is observed. Finally, the intermediate force stretching regime is investigated. It is found that CR induces a moderate influence in the force-extension curves and persistence length (which in this force regime becomes force-dependent). It is thus concluded that the effect of CR on the stretching curves is mainly due to the changes in the average charge at zero force. It is also found that, for the cases studied, the effect of steric excluded volume is almost irrelevant compared to electrostatic interactions.

Nanoassemblies with light‐responsive size and density from linear flexible polyelectrolytes

AbstractThis study presents electrostatically self‐assembled nanoparticles from linear flexible polyelectrolytes (poly(diallyldimethylammonium chloride or quarternized poly(4‐vinylpyridine)) and an ionic photo‐isomerizable azo dye (Acid Yellow 38) that can change their size upon UV‐light irradiation. Assemblies with narrow size distribution are stable in aqueous solution. For samples with under‐stoichiometric dye load, UV‐light exposure triggers a size decrease, e.g. from a hydrodynamic radius of Rh = 94 nm to Rh = 62 nm for an Ay38‐PDADMAC sample with a charge ratio of lcharge = 0.7. Size changes are caused by trans‐cis isomerization of the dye, accompanied by a change in hydrophilicity, binding enthalpy and entropy. Assemblies are characterized by static and dynamic light scattering, atomic force microscopy, UV–vis spectroscopy and isothermal titration calorimetry. Zeta potential measurements give insight into the electrostatic stabilization and size‐control of the ionic nano‐assemblies, revealing a master curve of effective surface charge density versus hydrodynamic radius. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys., 2013

Optical coherence tomography velocimetry in controlled shear flow

Doppler-shift optical coherence tomography with infrared light was used to probe the velocity profiles of concentrated solutions of complex fluids with samples experiencing steady-state shear flow. The apparatus is sensitive to a velocity range of 0.7-330 mm/s probing very small volumes of material (quasicylindrical volume elements of 9-μm length and 11-μm radius with 3.4-picoliter volumes) inside a plate-plate rheometer with a total sample volume of ~100-1000 μL. The technique can scan the flow in the plane perpendicular to the shear direction, building up a two-dimensional map of the velocity flow field. The use of a coherence gate with a broad-band infrared source (9-μm coherence length, 1300-nm wavelength) allows opaque specimens, such as concentrated colloidal suspensions (2% w/w) and margarine, to be probed. We observe the phenomena of wall slip (margarine) and shear banding (polyacrylamide, a linear flexible polyelectrolyte) using this technique.

Complexes between High Charge Density Cationic Polyelectrolytes and Anionic Single- and Double-Tail Surfactants

Polyelectrolyte/surfactant complexes formed between well-defined linear flexible polyelectrolytes, namely, quaternized poly[3,5-bis(dimethylaminomethylene)hydroxystyrene] (Q-N-PHOS), bearing two cationic sites on each repeating unit, and two different anionic surfactants, namely, sodium dodecyl sulfate (SDS) with one hydrocarbon tail and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) with two hydrocarbon chains, are studied by means of fluorescence spectroscopy, electrophoretic, dynamic and static light scattering, and atomic force microscopy. Depending on the surfactant state in initial solutions (i.e., below or above nominal critical micelle concentration, cmc) and final (-/+) charge ratio, self-assembly in nanoparticles of variable size, stability, and effective charge is possible. Spherical, rather polydispserse complexes are formed in all cases. Critical aggregation concentrations (cac) depend on the surfactant type, while hydrophobicity of the main polyelectrolyte chain plays a role in colloidal stability of the complex nanoparticles.

Effect of Dendrimer Generation on the Assembly and Mechanical Properties of DNA/Phosphorus Dendrimer Multilayer Microcapsules

We report the preparation, characterization and mechanical properties of DNA/phosphorus dendrimer multilayer microcapsules. The shells of these microcapsules are composed by alternating DNA and positively charged dendrimer Gn(NH+Et2Cl-)m (n = 1, 2, 3, 4; m = 12, 24, 48, 96). The same multilayers were constructed on planar support to examine their layer-by-layer growth and to determine the multilayer thickness. Surface plasmon resonance spectroscopy (SPR) showed regular linear growth of the multilayer film after the first dendrimer layer. We probe the mechanical properties of these DNA/dendrimer microcapsules by measuring force−deformation curves with the atomic force microscope (AFM). The experiment suggests that they are softer than microcapsules assembled from linear flexible polyelectrolytes (PE) studied before. The stiffness of the capsules increases with the generation of used dendrimer. This reflects the change in the multilayer thickness, but not the changes in structure of surface DNA/dendrimer complexes, which almost likely remains similar for all dendrimer generations.

The microrheology of polystyrene sulfonate combs in aqueous solution

Video particle tracking (VPT) and diffusing wave spectroscopy were used to characterize the microrheology of polystyrene sulfonate combs in aqueous solutions. At low frequencies VPT demonstrated predominantly viscous behavior. The manner in which the viscosity scaled as a function of monomer concentration was a sensitive function of the comb architecture. Densely branched combs or combs with long side chains demonstrated entangled polyelectrolyte scaling above the overlap concentration, whereas sparsely branched combs had unentangled polyelectrolyte scaling. A dynamic scaling model was developed for the viscosity of unentangled semidilute solutions of comb polyelectrolytes. Diffusing wave spectroscopy demonstrated Rouse modes (G' approximately G" approximately omega12) for the high-frequency dynamics of the semidilute comb solutions. The form of the high-frequency viscoelasticity was independent of the chain architecture and the modulus scaled as expected for linear flexible polyelectrolytes.

Polyelectrolyte–macroion complexation. I. Effect of linear charge density, chain length, and macroion charge

The complexation between a linear flexible polyelectrolyte and one or several oppositely charged macroions was examined by employing a simple model system with focus on the electrostatic interactions. The composition and the structure of the complex as well as conformational data of the polyelectrolyte were obtained by using Monte Carlo simulations. These properties were investigated at different linear charge densities of the polyelectrolyte, different chain lengths of the polyelectrolyte, and different macroion charges, all at different numbers of macroions at constant volume. The binding isotherms obtained are Langmuir type, and in excess of macroions the polyelectrolyte–macroion complex displays a charge reversal. Upon complexation, the polyelectrolyte extension first reduces and thereafter increases as the number of complexed macroions increases, the minimal extension appearing for a neutral complex. Macroions prefer to complex to central polyelectrolyte segments, but for a neutral or an overcharged complex the entire polyelectrolyte chain is involved. In the complex, the macroions are able to come into direct contact with each other, despite their mutual electrostatic repulsion. The distribution of the small ions is also presented.

Integral equation theory of flexible polyelectrolytes. II. Primitive model approach

The multicomponent Polymer Reference Interaction Site Model is solved numerically for solutions of linear flexible polyelectrolytes in the Primitive Model approach with an explicit description of the counterions and salt ions. All the ionic species interact via bare Coulomb and hard sphere potentials. The wormlike chains modeled as connected interacting charged sites are characterized by their persistence length. The hypernetted chain integral equation is used as the closure relation. The structural and thermodynamic properties of semidiluted polyelectrolyte solutions are presented. The model gives the pair correlation functions for monomer–monomer, monomer–ion, and ion–ion pairs. From the monomer–counterion correlations information on the ionic condensation around flexible chains is deduced. The ion-averaged monomer–monomer potential obtained from the monomer–monomer correlations presents a classical screened Coulomb behavior at low coupling and reveals an attractive character at high electrostatic coupling.

What Can Be Seen by Static and Dynamic Light Scattering in Polyelectrolyte Solutions and Mixtures?

The aim of this paper is to give a summary, classification, and interpretation of the dynamic modes observed by dynamic light scattering in polyelectrolyte solutions and mixtures under various experimental conditions. Dynamic data are analyzed together with data from static light scattering. The system under consideration is a solution of linear flexible polyelectrolytes, with and without added low molecular weight salt.

Quasi Elastic Light Scattering Study on Solutions of Linear Flexible Polyelectrolytes at Low Ionic Strengths

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTQuasi Elastic Light Scattering Study on Solutions of Linear Flexible Polyelectrolytes at Low Ionic StrengthsRoy G. Smits, Maxim E. Kuil, and Michel MandelCite this: Macromolecules 1994, 27, 20, 5599–5608Publication Date (Print):September 1, 1994Publication History Published online1 May 2002Published inissue 1 September 1994https://doi.org/10.1021/ma00098a013RIGHTS & PERMISSIONSArticle Views125Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Sodium ion and solvent nuclear relaxation results in aqueous solutions of DNA.

AbstractThe field‐dependent 23Na nuclear relaxation in aqueous DNA solutions has been obtained for a range of temperatures, including the DNA melting region. At least two correlation times are needed to characterize the spectral density function for the 23Na relaxation. For the slow process (with the largest correlation time), the temperature dependence of the coupling constant and the correlation time were determined, and important premelting effects were observed. Possible origins of the slow process are discussed. The last process is shown to be correlated with the properties of the hydration water of DNA as reflected by the 17O relaxation rates in these solutions. The influence of the polyelectrolyte and NaCl concentrations on the 23Na relaxation rate is compared with previous results from solutions of linear flexible polyelectrolytes.

Stereoselective hydrolysis of amino acid esters by modified polyethylenimines: Effects of quaternization of polymer and of added surfactants

AbstractQuaternized polyethylenimines exhibit viscosity behavior very similar to that of linear flexible polyelectrolytes and thus evidently swell in dilute salt solutions. This swelling is manifested also in the rate constants for the hydrolysis of chiral or achiral nitrophenyl esters catalyzed by these polymers. Stereoselective preference is exhibited in hydrolyses catalyzed by the quaternized polymers containing covalently linked l‐histidine moieties. Maximum stereoselectivity is manifested at polymer concentrations corresponding to nonswollen conformations. With added cetyltrimethylammonium bromide, the stereoselective preference of the catalyzing polymer can be reversed. A comparison of the effects of added anionic, nonionic, and cationic detergents shows decreases in rate for the first, no significant effect for the second, and substantial changes for the third, depending on the polymer and detergent concentrations. Cationic detergents of different chain lengths and structures show different effects reflecting largely their extent of binding by the polymer.

Relaxation and electrophoretic effects in polyelectrolyte solutions. I. Salt‐free solutions

AbstractRelations between relaxation and electrophoretic effects in salt‐free polyelectrolyte solutions are studied in terms of nonequilibrium thermodynamics and of binary friction coefficients. The significance and the method of determining these coefficients are explained. Consideration of experimental results and of long‐ and short‐range interactions suggests that the concept of “ion condensation” is needed to provide a consistent desciption of transport processes for linear flexible polyelectrolytes. Empirical relations previously used are shown to have only limited validity.