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We investigate the complexation of long thin polyelectrolyte (PE) chains with oppositely charged spheres. In the limit of strong adsorption, when strongly charged PE chains adapt a definite wrapped conformation on the sphere surface, we analytically solve the linear Poisson-Boltzmann equation and calculate the electrostatic potential and the energy of the complex. We discuss some biological applications of the obtained results. For weak adsorption, when a flexible weakly charged PE chain is localized next to the sphere in solution, we solve the Edwards equation for PE conformations in the Hulthén potential, which is used as an approximation for the screened Debye-Hückel potential of the sphere. We predict the critical conditions for PE adsorption. We find that the critical sphere charge density exhibits a distinctively different dependence on the Debye screening length than for PE adsorption onto a flat surface. We compare our findings with experimental measurements on complexation of various PEs with oppositely charged colloidal particles. We also present some numerical results of the coupled Poisson-Boltzmann and self-consistent field equation for PE adsorption in an assembly of oppositely charged spheres. [ABSTRACT FROM AUTHOR]

We study the dynamics of flexible polymer chains in solution by combining multiparticle-collision dynamics (MPCD), a mesoscale simulation method, and molecular-dynamics simulations. Polymers with and without excluded-volume interactions are considered. With an appropriate choice of the collision time step for the MPCD solvent, hydrodynamic interactions build up properly. For the center-of-mass diffusion coefficient, scaling with respect to polymer length is found to hold already for rather short chains. The center-of-mass velocity autocorrelation function displays a long-time tail which decays algebraically as (Dt)-3/2 as a function of time t, where D is the diffusion coefficient. The analysis of the intramolecular dynamics in terms of Rouse modes yields excellent agreement between simulation data and results of the Zimm model for the mode-number dependence of the mode-amplitude correlation functions. [ABSTRACT FROM AUTHOR]

We investigate the influence of monovalent saltions on the structural properties of polyelectrolyte solutions using an integral equation theory. In this approach all species of the solution (polyions, counterions, and positively and negatively charged saltions) are treated explicitly leading to a four-component system. The polymer-reference-interaction-site model for this system, together with the reference-Laria-Wu-Chandler closure is solved numerically. We demonstrate that addition of salt leads to a screening of the Coulomb interaction, which is well captured by the Debye-Hückel potential with a salt density-dependent screening length, by discussing various correlation functions. Furthermore, we show that for an appropriate range of parameters, such as density or Bjerrum length, a shell of equally charged saltions exists in the vicinity of the polyion. The effective potential between two monomers reflects attraction among the equally charged polyions with a pronounced dependence on the salt concentration. [ABSTRACT FROM AUTHOR]

We investigate the structural and conformational properties of solutions containing semiflexible polyelectrolyte chains using a self-consistent integral equation theory approach. A one-component system is considered where the polyelectrolyte chains interact with each other via a Debye -- Hückel potential. Nonelectrostatic interactions among the polymers are taken into account by a self-consistently determined solvation potential. The conformational properties of the polymer chain are determined from a variational calculation with a semiflexible reference chain. The finite chain extensibility is taken into account by constraints for the bond lengths and bond angles using Lagrangian multipliers. The scaling relation for the size of an isolated semiflexible chain with respect to chain length exhibits a transition from rodlike to excluded volume type for a given Debye screening length. For flexible chains in solution, the theory provides conformational properties which are in excellent agreement with computer simulation results. The bare chain stiffness has a pronounced influence on the conformational and structural properties of the solution. In the semidilute regime a pronounced liquidlike order is obtained for flexible polyelectrolyte chains which diminishes with increasing bare persistence length. This process is accompanied by a shift of the structural peaks to smaller length scales. [ABSTRACT FROM AUTHOR]

The adsorption of a single polymer chain onto a solid surface is investigated by molecular dynamics simulations. The chain is composed of mass points interacting via a truncated Lennard-Jones potential, i.e., the excluded volume interaction is taken into account, and grafted to the surface with one end. The average adsorption degree is calculated for various chain lengths (N = 16, 32, 64, 128) and adsorption energies. In addition, the scaling behavior of the adsorption degree and the radius of gyration is investigated. The adsorption degree and the average length of loops and tails are obtained for chains of various stiffnesses. In this context, we find that stiffer chains adsorb more easily. Moreover, the distribution of the mass points perpendicular to the surface as well as the orientation of the bonds with respect to the surface is discussed for various adsorption energies and stiffnesses. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A general model for the description of the stress-strain behavior of polymer networks is introduced. We assume that the network consists of a gas of phantom chains. Its deformation is accounted for by macroscopic constraints, which allow nonaffine behavior on the microscopic scale. The advantage of the model lies in the fact that the number of assumptions is smaller than in other models and—at the same time—the main experimental features are reproduced. Comparison to mechanical deformation experiments shows good agreement with the model. [ABSTRACT FROM AUTHOR]

Stochastic dynamics simulations of polymethylene chains (CnH2n+2 for n=13, 28, 60) represented by united atom models have been carried out in order to investigate both the equilibrium and dynamic properties of polymer melts confined between flat solid surfaces. The packing manner of monomer segments, segment orientation and local conformations of chains are found to be independent of chain length, and agree very well with the results of the previous Monte Carlo simulations of C13H28 melts. The chains are extremely flattened close to the surface and many molecules assume essentially two-dimensional train configurations even in the case of C60H122 melts. However, the local chain conformations are only slightly affected by the surfaces. The apparent self diffusivities are found to be independent of the distance from the surface as the result of a reduced mobility normal to the surface and an enhanced mobility parallel to the surface. The absolute magnitudes of self-diffusion constants are larger than experimental values, most likely due to the application of united atom model. [ABSTRACT FROM AUTHOR]

Stochastic dynamics simulations of n-alkane melts (C13H28 and C28H58 ) have been performed in order to calculate their static properties. The system consists of linear chains of mass points, which are connected by fixed bond lengths. Each point of a chain is subjected to valence bond and torsional forces. Additionally, nonbonded interactions are taken into account by a truncated, Lennard-Jones potential. The mean-square end-to-end distance and the radius of gyration of the chains as well as the average fraction of trans conformations were calculated and compared with the results obtained by Monte Carlo simulations and by unperturbed rotational isomeric states model calculations. The comparison exhibits very good agreement between the results of the different approaches, and demonstrates the potential advantages of stochastic dynamics simulations for polymeric systems. An investigation of different torsional potentials exhibited the subtle effect of the curvature of the torsional potential on bulk structures. [ABSTRACT FROM AUTHOR]