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PubMed2006

Behavior of rodlike polyelectrolytes near an oppositely charged surface.

The behavior of highly charged short rodlike polyelectrolytes near oppositely charged planar surfaces is investigated by means of Monte Carlo simulations. A detailed microstructural study, including monomer and fluid charge distributions and chain orientation, is provided. The influence of chain length, substrate's surface-charge density, and image forces is considered. Due to the lower chain entropy (compared to flexible chains), our simulation data show that rodlike polyelectrolytes can, in general, better adsorb than flexible ones do. Nonetheless, at low substrate-dielectric constant, it is found that repulsive image forces tend to significantly reduce this discrepancy.

Adsorption↗

PubMed2006

Computer simulations of diffusion and dynamics of short-chain polyelectrolytes.

Brownian dynamics simulations are conducted to investigate the diffusional and dynamic properties of polyelectrolytes in dilute salt-free solutions. The polyelectrolyte molecule is represented by a bead-spring chain in a primitive model. The long-range hydrodynamic and Coulomb interactions are both taken into consideration through the Ewald summations for the first time. The major finding of our simulations is that the dependence of the long-time chain diffusivity on the Coulomb interaction strength is very different from that of the Kirkwood short-time diffusivity, which simply shows a trend nearly opposite to the chain size. When ignoring the hydrodynamic interaction (HI), the coupling effect between the chain and its counterions gives rise to a noticeable increase in the long-time diffusivity at intermediate electrostatic interaction strengths. However, the incorporation of HI suppresses this effect to a degree that one can no longer discern it. Moreover, the rotational relaxation is found to show a dependence opposite to that of the gyration radius relaxation.

Computer Simulation↗

PubMed2006

Self-recognition and aggregation between diblock (charged/neutral) polyelectrolytes by Monte Carlo simulations.

The self-recognition between oppositely charged polyelectrolyte-neutral diblock copolymers and aggregate formation is investigated by Monte Carlo simulations. Both matched lengths and charge numbers are critical conditions for self-recognition. The optimum self-recognition occurs between oppositely charged chains with matched charged block lengths and charge numbers. The size of aggregates increases, as the total length and the ratio of charged to neutral beads become larger. Polyelectrolyte networks were observed in some cases containing unmatched chains. The molecular configurations of the entire chains and of the charged and neutral blocks as well as the radial distribution functions of the charged beads are also investigated.

Algorithms↗

PubMed2006

Stoichiometric polyelectrolyte complexes of ionic block copolymers and oppositely charged polyions.

Micellization in dilute solutions of diblock copolymers with a polyelectrolyte and a hydrophilic nonionic blocks and oppositely charged polyions is studied using mean-field theory. In aqueous solutions the micelle core consists of the polyelectrolyte complex (PEC) while the corona is formed by hydrophilic blocks of the block copolymers. Describing PEC as a globule in the framework of the Lifshitz [Zh. Eksp. Teor. Fiz. 55, 2408 (1968)] globule theory we calculate the surface tension of the micellar core/solvent interface as a function of the polyion degree of ionization, solvent quality, and concentration of low-molecular-mass salt. The equilibrium aggregation number of starlike micelles formed by block copolymers and homopolymers of opposite charge at stoichiometric mixture compositions is found as a function of the system parameters. It is shown that micelles disintegrate upon addition of salt.

Journal Article↗

PubMedDate not supplied

Plastic behaviour of polyelectrolyte microcapsules derived from colloid templates.

The deformability and osmotic properties of hollow microcapsules were studied by means of the micropipette video microscopic technique. The microcapsules were prepared by consecutive multiple adsorption of the polyanion, poly(styrene sulphonate), and the polycation, poly(allylamine hydrochloride), onto melamine formaldehyde resin latex of 5 microm diameter, which was decomposed after completing the coating by transferring to hydrochloric acid of pH 1.1. The polyelectrolyte microcapsules reacted to micropipette suction with plastic deformation. If lipids are added to the polyelectrolyte layers, the capsules cannot be visibly deformed by micropipette suction up to 10(4) N/m2. However, plastic shrinking was observed if the stress was generated by the osmotic pressure of a sucrose solution of 10(6) N/m2.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1993

Free energies calculated according to Manning's polyelectrolyte model compared with Poisson Boltzmann predictions.

The values of the different terms contributing to the free energy of a polyelectrolyte in ionic solution, calculated according to Manning's model are compared with those predicted by the Poisson-Boltzmann(P-B) equation solved for the cell model. On this ground, the limits of applicability of Manning's model and some of its features are discussed. The comparison confirms the usefulness of Manning's model for low charge density polyelectrolytes, while for higher charge densities some care should be used due to the breakdown of the approximations underlying the model.

Computer Simulation↗

PubMed2002

Application of the Poisson Boltzmann polyelectrolyte model for analysis of equilibria between single-, double-, and triple-stranded polynucleotides in the presence of K(+), Na(+), and Mg(2+) ions.

The Poisson Boltzmann (PB) cell model of polyelectrolyte solution has been used for numerical calculations of the change in electrostatic free energy, DeltaG(el), for transformations between different structural forms (tri-, double-, and single-stranded) of the polyribonucleotides poly(rA).poly(rU)2, poly(rA).poly(rU), poly(rA), and poly(rU). In particular, the dependence on monovalent salt concentration, MCl (M = Na or K) in the absence and in the presence of MgCl(2) has been calculated. The results were obtained for conditions relevant to available experimental values of structural transition ("melting") temperatures (T(m)) and other thermodynamic quantities. Using the experimental T(m) values and theoretical electrostatic DeltaG(el), DeltaH(el), and DeltaS(el) functions, non-electrostatic contributions to the corresponding thermodynamic parameters of the poly(rA)/poly(rU) melting transitions were determined in MCl solutions in the absence of Mg(2+). Qualitative and to a large extent quantitative reproduction of the experimental calorimetry enthalpy, entropy and heat capacity values was found from the results of the PB theory. Furthermore, dependencies of T(m) on MCl concentration in the presence of MgCl(2) for the poly(rA)/poly(rU) transitions were also calculated. Compared to a model considering Mg(2+) as a fully-hydrated ion, much better agreement between experimental and PB theory was achieved by assuming the ion size of Mg(2+) to be given by that of a bare non-hydrated ion smaller than that of hydrated Na(+) or K(+). In agreement with data of experimental studies reported in literature, this result indicates that magnesium(II) can bind to RNA as a bare ion in a way that is different from that of DNA. Generally, we can conclude that the PB polyelectrolyte theory can provide an adequate description of thermally induced structural transitions in polydeoxy- and polyribonucleotides in different salt solutions in spite of the rather simplified model treating the solvent as dielectric continuum, the polyion as a uniformly charged cylinder, and the mobile ions as hard spheres in the absence of excluded volume effects.

DNA↗

PubMed2000

The influence of microwave heating on the characteristics of polyelectrolytes.

Results obtained by microwave (MW) and simultaneous microwave and electron beam (MW + EB) application in the chemistry of acrylamide and acrylic acid co-polymers (PA type polyelectrolytes) are presented. Comparative results concerning the molecular weight (Mw) and Huggins' constant for the acrylamide copolymers obtained by classical heating, MW heating, EB irradiation and simultaneous MW + EB treatment are reported. MW heating produces high PA water solubility but median Mw values; EB irradiation gives high Mw values but associated with a cross-linked structure (poor water solubility) while MW energy addition to EB energy gives simultaneously high Mw values and high PA water solubility. A MW installation of 2.45 GHz and 2.5 kW, designed to provide small-scale commercial production of PA polyelectrolytes, is described.

Journal Article↗

PubMed1999

Polyelectrolyte brushes: counterion distribution and complexation properties.

The structure of dense grafted polyelectrolyte layers has been studied with a combination of neutron reflectivity and infrared spectroscopy techniques. The polyelectrolyte brushes were made of poly(styrene sulfonate) neutralized by different counterions. Small counterions are distributed throughout the brush in order to ensure a highly local electroneutrality. In addition, they can be readily exchanged with other small ions. On the other hand, macromolecular counterions (as well as some proteins) are irreversibly trapped by the brush, but are located outside the grafted layer and cannot reach the surface.

Journal Article↗

PubMed2002

Persistence length of a polyelectrolyte in salty water: Monte Carlo study.

We address the long standing problem of the dependence of the electrostatic persistence length l(e) of a flexible polyelectrolyte (PE) on the screening length r(s) of the solution within the linear Debye-Hückel theory. The standard Odijk, Skolnick, and Fixman (OSF) theory suggests l(e) proportional, variant r(2)s, while some variational theories and some computer simulations suggest l(e) proportional, variant r(s). In this paper, we use Monte Carlo simulations to study the conformation of a simple polyelectrolyte. Using four times longer PEs than in previous simulations and refined methods for the treatment of the simulation data, we show that the results are consistent with the OSF dependence l(e) proportional, variant r(2)s. The linear charge density of the PE, which enters in the coefficient of this dependence is properly renormalized to take into account local fluctuations.

Journal Article↗

PubMed2002

Conformational instability of rodlike polyelectrolytes due to counterion fluctuations.

The effective elasticity of highly charged stiff polyelectrolytes is studied in the presence of counterions, with and without added salt. The rigid polymer conformations may become unstable due to an effective attraction induced by counterion density fluctuations. Instabilities at the longest, or intermediate length scales, may signal collapse to globule, or necklace states, respectively. In the presence of added salt, a generalized electrostatic persistence length is obtained, which has a nontrivial dependence on the Debye screening length. It is also found that the onset of conformational instability is a reentrant phenomenon as a function of polyelectrolyte length for the unscreened case, and the Debye length or salt concentration for the screened case. This may be relevant in understanding the experimentally observed reentrant condensation of DNA.

Journal Article↗

PubMed2004

Effective electrostatic interactions in suspensions of polyelectrolyte brush-coated colloids.

Effective electrostatic interactions between colloidal particles, coated with polyelectrolyte brushes and suspended in an electrolyte solvent, are described via linear-response theory. The inner cores of the macroions are modeled as hard spheres, the outer brushes as spherical shells of continuously distributed charge, the microions (counterions and salt ions) as point charges, and the solvent as a dielectric continuum. The multicomponent mixture of macroions and microions is formally mapped onto an equivalent one-component suspension by integrating out from the partition function the microion degrees of freedom. Applying second-order perturbation theory and a random-phase approximation, analytical expressions are derived for the effective pair interaction and a one-body volume energy, which is a natural by-product of the one-component reduction. The combination of an inner core and an outer shell, respectively impenetrable and penetrable to microions, allows the interactions between macroions to be tuned by varying the core diameter and brush thickness. In the limiting cases of vanishing core diameter and vanishing shell thickness, the interactions reduce to those derived previously for star polyelectrolytes and charged colloids, respectively.

Journal Article↗

PubMed2004

Adsorption transition of a polyelectrolyte on a high-dielectric charged substrate.

The behavior of a polyelectrolyte adsorbed on a charged surface of high-dielectric constant is studied by both Monte Carlo simulation and analytical methods. It is found that in a low ionic strength medium, the transition is first-order with the repulsive charged surface. The surface monomer density, which is the order parameter of the adsorption transition, follows a linear relation with surface charge density. It indicates that the polyelectrolyte is compressed on the substrate without any conformational change before the desorption. Finally, a different scaling law for the layer thickness is derived and verified by simulation.

Journal Article↗

PubMed2001

Counterion phase transitions in dilute polyelectrolyte solutions.

In dilute solutions of rodlike polyelectrolytes some counterions are distributed far from polyions while others are located in their vicinity in the regions of cylindrical symmetry of the electrostatic potential. For these cylindrical regions around rodlike polyelectrolytes we find an exact solution of the nonlinear Poisson-Boltzmann equation for the case of nonzero net charge in these regions. This exact solution implies three qualitatively different phases of counterion distribution around the polyions with second order phase transitions between these phases.

Journal Article↗

PubMed2003

Monte Carlo simulation of a coarse-grained model of polyelectrolyte networks.

The structure and properties of a coarse-grained model of a polyelectrolyte network is studied by means of Monte Carlo simulations. Counterions are treated explicitly, and permanent tetrafunctional cross-linking sites are annealed. The resulting pressure-density relationships exhibit a strong dependence on the strength of electrostatic interactions. A discontinuous volume change is observed when electrostatic interactions are strong. The structure of the model networks is examined at various conditions, and it is found to be considerably different from that of noncross-linked polyelectrolytes.

Journal Article↗

PubMed2006

Density functional theory for polyelectrolytes near oppositely charged surfaces.

We report a nonlocal density functional theory of polyelectrolyte solutions that faithfully accounts for both short- and long-range correlations neglected in a typical mean-field method. It is shown that for systems with strong electrostatic interactions, the long-range correlations are subdued by direct Coulomb attractions, thereby manifesting strong local excluded-volume effects. The theory has also been used to describe the influence of the polyion chain length and small ion valence on charge inversion due to the adsorption of polyelectrolytes at an oppositely charged surface.

Electrolytes↗

PubMed2006

Optimal cell approach to osmotic properties of finite stiff-chain polyelectrolytes.

We propose a self-consistent geometry optimized cell model approach to study osmotic properties of stiff-chain polyelectrolyte solutions. In contrast with the usual monotonic Poisson-Boltzmann prediction, the cell model predicts the correct nonmonotonic dependence of the osmotic coefficient on concentration. A lower degree of polymerization is found to reduce significantly the counterion condensation in a typical dilute strong polyelectrolyte. The results agree quantitatively with simulations of a corresponding many-body bulk system up to a dense semidilute regime.

Electrolytes↗

PubMed2006

Frustrated polyelectrolyte bundles and T= 0 Josephson-junction arrays.

We establish a one-to-one mapping between a model for hexagonal polyelectrolyte bundles and a model for two-dimensional, frustrated Josephson-junction arrays. We find that the T = 0 insulator-to-superconductor transition of the quantum system corresponds to a continuous liquid-to-solid transition of the condensed charge in the finite-temperature classical system. We find that the role of the vector potential in the quantum system is played by elastic strain in the classical system. Exploiting this correspondence we show that the transition is accompanied by a spontaneous breaking of a discrete symmetry associated with the chiral patterning of the array and that at the transition the polyelectrolyte bundle adopts a universal response to shear.

Journal Article↗