Search results for "Excluded volume"
showing 10 items of 33 documents
Semiflexible polymer brushes and the brush-mushroom crossover.
2015
Semiflexible polymers end-grafted to a repulsive planar substrate under good solvent conditions are studied by scaling arguments, computer simulations, and self-consistent field theory. Varying the chain length N, persistence length lp, and grafting density σg, the chain linear dimensions and distribution functions of all monomers and of the free chain ends are studied. Particular attention is paid to the limit of very small σg, where the grafted chains behave as "mushrooms" no longer interacting with each other. Unlike a flexible mushroom, which has a self-similar structure from the size (a) of an effective monomer up to the mushroom height (h/a ∝ N(v), ν ≈ 3/5), a semiflexible mushroom (l…
How does stiffness of polymer chains affect their adsorption transition?
2020
The adsorption transition and the structure of semiflexible adsorbed macromolecules are studied by a molecular dynamics simulation of a coarse-grained, bead-spring type model. Varying chain length N and stiffness κ (which is proportional to the persistence length lp in d = 3 dimensions) as well as the strength ϵwall of the adsorption potential, the adsorbed monomer fraction, orientational bond order parameter, and chain linear dimensions are studied. In the simulations, excluded volume interactions normally are included but can be “switched off,” and thus, the influence of excluded volume (leading to deviations from predictions of the wormlike chain model) can be identified. It is shown tha…
The Electrostatic Expansion of Linear Polyelectrolytes: Effects of Gegenions, Co-ions, and Hydrophobicity
1997
The molar mass and ionic strength dependence of the dimensions of hydrophobically modified poly(vinylpyridinium) cations are demonstrated to be almost perfectly described by a theoretical expression derived on the basis of only excluded volume considerations. Generally, the effective charge density of the polyions decreases significantly with increasing hydrophobicity and with increasing polarizability of the gegenions. Unexpectedly, the intrinsic excluded volume effect which becomes dominating at high ionic strength not only depends on the hydrophobicity of the polyion but also significantly increases with decreasing polarizability of the gegenions (i.e., if the iodide gegenions are replac…
Dynamics of single semiflexible polymers in dilute solution
2016
We study the dynamics of a single semiflexible chain in solution using computer simulations, where we systematically investigate the effect of excluded volume, chain stiffness, and hydrodynamic interactions. We achieve excellent agreement with previous theoretical considerations, but find that the crossover from the time τb, up to which free ballistic motion of the monomers describes the chain dynamics, to the times W−1 or τ0, where anomalous monomer diffusion described by Rouse-type and Zimm-type models sets in, requires two decades of time. While in the limit of fully flexible chains the visibility of the anomalous diffusion behavior is thus rather restricted, the t3/4 power law predicted…
Scale-free static and dynamical correlations in melts of monodisperse and Flory-distributed homopolymers: A review of recent bond-fluctuation model s…
2011
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 compres…
Nonlinear effects in charge stabilized colloidal suspensions
2006
Molecular Dynamics simulations are used to study the effective interactions in charged stabilized colloidal suspensions. For not too high macroion charges and sufficiently large screening, the concept of the potential of mean force is known to work well. In the present work, we focus on highly charged macroions in the limit of low salt concentrations. Within this regime, nonlinear corrections to the celebrated DLVO theory [B. Derjaguin and L. Landau, Acta Physicochem. USSR {\bf 14}, 633 (1941); E.J.W. Verwey and J.T.G. Overbeck, {\em Theory of the Stability of Lyotropic Colloids} (Elsevier, Amsterdam, 1948)] have to be considered. For non--bulklike systems, such as isolated pairs or triples…
Modified Mode Coupling Theory of Glassy Dynamics Generated by Entanglement
2004
Increasing the density in systems with strong excluded volume interactions leads simultaneously to an increase of static correlations and a slowing down of the relaxational dynamics. Mode coupling theory in its present form describes this mechanism, satisfactorily. In contrast, for systems where entanglement is dominant, e.g. infinitely thin hard rods on a lattice, glassy dynamics is not driven by increasing static correlations but by entanglement. We show how mode coupling approximation can be modified such that non-vanishing vertices occur which might account for such pure entanglement effects.
Dynamics of Polymer Chains Confined in Slit-Like Pores
1996
Monte Carlo simulations of an off-lattice bead spring model of polymer chains are presented, confining the chains between two repulsive parallel planes a distance D apart. Varying the chain length N from N = 16 to N = 128, we show that under good solvent conditions the chains behave like two-dimensional self-avoiding walks, their mean square gyration radius scales as (R g 2 ) N 2v with v = 3/4. The density profile across the slit is independent of N and maximal in the center of the slit. The dynamical properties of the chains are found to be in full agreement with the Rouse model with excluded volume in d = 2 dimensions, the relaxation times vary like τ N Z with z = 2v +1 = 5/2, the diffusi…
Dynamics of star polymers in a good solvent: A Kramers potential treatment
1994
The ‘‘effective’’ relaxation time τ of isolated star polymers with excluded volume interactions in the Rouse model limit (i.e., disregarding hydrodynamic interactions present in real solvents) is studied varying both the number of arms f and the number of monomers per arm l. Here τ is defined from the response of the gyration radius of the star polymer to a Kramers potential that describes the effect of shear flow in lowest order in the shear rate. Monte Carlo simulations are performed with two different techniques (simple sampling with enrichment or dynamic Monte Carlo, respectively) for two different models (simple self‐avoiding walks with an extended core or the bond fluctuation model, r…
Linear Dimensions of Adsorbed Semiflexible Polymers: What can be learned about their persistence length?
2019
Conformations of partially or fully adsorbed semiflexible polymer chains are studied varying both contour length $L$, chain stiffness, $\ensuremath{\kappa}$, and the strength of the adsorption potential over a wide range. Molecular dynamics simulations show that partially adsorbed chains (with ``tails,'' surface attached ``trains,'' and ``loops'') are not described by the Kratky-Porod wormlike chain model. The crossover of the persistence length from its three-dimensional value (${\ensuremath{\ell}}_{p}$) to the enhanced value in two dimensions ($2{\ensuremath{\ell}}_{p}$) is analyzed, and excluded volume effects are identified for $L\ensuremath{\gg}{\ensuremath{\ell}}_{p}$. Consequences fo…