Polyelectrolytes, molecular dynamics

The earliest fully atomistic molecular dynamic (MD) studies of a simplified Nation model using polyelectrolyte analogs showed the formation of a percolating structure of water-filled channels, which is consistent with the basic ideas of the cluster-network model of Hsu and Gierke. The first MD... 

Lin Y, Liao Q, Jin X. Molecular dynamics simulations of dendritic polyelectrolytes with flexible spacers in salt free solution. J Phys Chem B 2007 111 5819-5828. 

Recently, the stiff-chain polyelectrolytes termed PPP-1 (Schemel) and PPP-2 (Scheme2) have been the subject of a number of investigations that are reviewed in this chapter. The central question to be discussed here is the correlation of the counterions with the highly charged macroion. These correlations can be detected directly by experiments that probe the activity of the counterions and their spatial distribution around the macroion. Due to the cylindrical symmetry and the well-defined conformation these polyelectrolytes present the most simple system for which the correlation of the counterions to the macroion can be treated by analytical approaches. As a consequence, a comparison of theoretical predictions with experimental results obtained in solution will provide a stringent test of our current model of polyelectrolytes. Moreover, the results obtained on PPP-1 and PPP-2 allow a refined discussion of the concept of counterion condensation introduced more than thirty years ago by Manning and Oosawa [22, 23]. In particular, we can compare the predictions of the Poisson-Boltzmann mean-field theory applied to the cylindrical cell model and the results of Molecular dynamics (MD) simulations of the cell model obtained within the restricted primitive model (RPM) of electrolytes very accurately with experimental data. This allows an estimate when and in which frame this simple theory is applicable, and in which directions the theory needs to be improved. 

First of all, the comparison of the PB-theory and experiment shown in Fig. 8 proceeds virtually without adjustable parameters. The osmotic coefficient (j) is solely determined by the charge parameter polyelectrolyte concentration. The latter parameter determines the cell radius R0 (see the discussion in Sect. 2.1) Figure 8 summarizes the results. It shows the osmotic coefficient of an aqueous PPP-1 solution as a function of counterion concentration as predicted by Poisson-Boltzmann theory, the DHHC correlation-corrected treatment from Sect. 2.2, Molecular Dynamics simulations [29, 59] and experiment [58]. 

Deserno M, Holm C, Kremer K (2000) Molecular dynamics simulations of the cylindrical cell model. In Radeva T (ed) Physical Chemistry of Polyelectrolytes. Marcel Dekker,... 

A new area that has been examined is that of molecular dynamics in polyelectrolytes,106 where the molecular motions responsible for the glass transition have been identified. Another interesting study is the effect of molecular motion upon the ingress of solvent into polymer material, as a function of cross-linking density.107 In the particular case studied, of dioxane... 

We shall consider only some results of investigation of complex polymer systems by method of EPR-spectroscopy obtained recently (results obtained earlier were considered in details in works [2, 3]). We shall discuss possibilities of method of EPR-spectroscopy of spin marks and probes for determination of macromolecules conformation in solid state, and also the results of investigation of molecular dynamics and organization of micelle systems -complexes polyelectrolyte-SAS. We shall also discuss some results obtained with the use of method of EPR-spectroscopy and its modification - the method of EPR-tomography for revealing of particularities of spatial distribution of active sites resulted from process of thermo-oxidative destruction of solid polymers. 

Molecular Dynamics and Organization of Complexes Polyelectrolyte-Detergent... 

General regularities of molecular dynamics and local organization of micellar phase of polyelectrolytes complexes with ionic SAS [16-22, 26] were formulated for the solution of this problem spin probes were used. Formulas of some of the last ones are presented in Scheme 3. 

Stevens, M.J., and Kremer, K. The nature of flexible linear polyelectrolytes in salt-free solution - a molecular-dynamics study. Journal of Chemical Physics, 1995, 103, No. 4, p. 1669-1690. 

Liao, Q., Dobrynin, A.V., and Rubinstein, M. Molecular dynamics simulations of polyelectrolyte solutions Osmotic coefficient and counterion condensation. Macromolecules, 2003, 36, No. 9, p. 3399-3410. 

A number of reviews of interest have appeared of both a specific and general nature. These include photoresponslve polymers with the main emphasis on phase transitions, memory and shape retention 2 , the kinetics of polyelectrolyte formation , molecular modelling for excimer formation , luminescent probes and molecular dynamics . The uses of thermally stimulated emission for monitoring radical decay and chemiluminescence of polymers... 

Since the experimentally determined osmotic coefficient appears to be smaller even than the molecular dynamics results, this indicates effects to be relevant that go beyond the model used for simulation. Most obvious candidates for this are the neglect of additional chemical interactions between the ions and the polyelectrolyte as well as solvation effects, i.e., interactions between the ions or the polyelectrolyte with the water molecules from the solution. It is for instance demonstrated in Ref. 46 that the osmotic coefficient also depends on whether one uses chlorine or iodine counterions. While one could certainly account for the different radii of these ions when computing the distance of closest approach entering the PB equation, the implications of the different hydration energies is much less obvious to incorporate and in principle requires very expensive all-atom simulations. 

Micka U, Holm C, Kremer K. Strongly charged, flexible polyelectrolytes in poor solvents—a molecular dynamics study. Langmuir 1999 15 4033. 

Winkler RG, Gold M, Reineker P. Collapse of polyelectrolyte macromolecules by counterion condensation and ion pair formation a molecular dynamics simulation study. Phys. Rev. Lett. 1998 80 3731-3734. 

Abstract Aqueous solutions of star-like polyelectrolytes (PEs) exhibit distinctive features that originate from the topological complexity of branched macromolecules. In a salt-free solution of branched PEs, mobile counterions preferentially localize in the intramolecular volume of branched macroions. Counterion localization manifests itself in a dramatic reduction of the osmotic coefficient in solutions of branched polyions as compared with those of linear PEs. The intramolecular osmotic pressure, created by entrapped counterions, imposes stretched conformations of branches and this leads to dramatic intramolecular conformational transitions upon variations in environmental conditions. In this chapter, we overview the theory of conformations and stimuli-induced conformational transitions in star-like PEs in aqueous solutions and compare these to the data from experiments and Monte Carlo and molecular dynamics simulations. 

Molecular Dynamics Simulations of Annealed Polyelectrolyte Chains... 

Figure 31 Concentration dependence of the correlation length (in salt-free polyelectrolyte solutions. Filled symbols corresponds to the small-angle neutron scattering (SANS) data (circles) (Nierlich, M. etal. J. Phys. (Paris) 1979, 40, 701 ) and light scattering data (squares) (Drifford, M. Dalbiez, J. P. J. Phys. Chem. 1984, 88,5368 ) in solutions of NaPSS. Open symbols represent results of the molecular dynamics simulations. The lines with slope -1/2 are shown to guide the eye. Reproduced with permission from Dobrynin, A. V. Rubinstein, M. Prog. Polym. Sci. 2005, 30,1049-1118. Copyright 2005, Elsevier.

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