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Zhulina E.B.,RAS Institute of Macromolecular Compounds | Leermakers F.A.M.,Wageningen University
Biophysical Journal | Year: 2010

Applying self-consistent field theory, we consider a coarse-grained model for the polymerlike projections of neurofilament (NF) proteins that form a brush structure around neurofilaments. We focus on effects of molecular composition, which is the relative occurrence of NF-H, NF-M, and NF-L proteins, on the organization of NF projection domains. We consider NF brushes with selectively truncated projections, and with a varied ratio L:H:M of constituent tails. Our conclusion is that the NF brush structure Is remarkably tolerant with respect to the variation In M and H chains. Results compare favorably with experimental data on model animals, provided that due attention is paid on the level of phosphorylation of the KSP repeats. © 2010 by the Biophysical Society.

Halperin A.,Joseph Fourier University | Zhulina E.B.,RAS Institute of Macromolecular Compounds
Langmuir | Year: 2010

Force versus distance profiles acquired by atomic force microscopy probe the structure and interactions of polymer brushes. An interpretation utilizing the Derjaguin approximation and assuming local compression of the brush is justified when colloidal probes are utilized. The assumptions underlying this approach are not satisfied for sharp tips, and deviations from this model were reported for experiments and simulations. The sharp-tip force law proposed assumes that the free energy penalty of insertion into the brush is due to the osmotic pressure of the unperturbed brush. This static force law is in semiquantitative agreement with the simulation results of Murat and Grest (Murat, M..; Grest, G. S. Macromolecules 1996, 29, 8282). © 2010 American Chemical Society.

Polotsky A.A.,RAS Institute of Macromolecular Compounds | Plamper F.A.,RWTH Aachen | Borisov O.V.,CNRS Institute of Analytical Sciences
Macromolecules | Year: 2013

We present a theory of a conformational collapse-to-swelling transition that occurs in aqueous dispersions of multiresponsive (pH- and thermoresponsive) microgels upon variation of ionic strength, temperature, or pH. Our theory is based on osmotic balance arguments and explicitly accounts for ionization equilibrium inside microgel partices. The theory predicts complex patterns in the dependence of the microgel particle dimensions on the control parameters: An increase in temperature leads to worsening of the solvent quality for the gel forming LCST-polymers and to concomitant decrease in the dimensions of the gel particles. This collapse of the gel particles provoked by an increase in temperature occurs either smoothly (at high or low ionic strength), or may exhibit a jump-wise character at intermediate ionic strength. The theory further predicts that the degree of swelling of microgel particles varies nonmonotonously and exhibits a maximum as a function of salt concentration at a pH close to the pK. This nonmonotonous variation of the particle dimensions occurs continuously at temperatures below or slightly above LCST (good or marginal poor solvent strength conditions, respectively), whereas at higher temperatures the jump-wise swelling of the gel particles is followed by either continuous or jump-wise collapse induced by progressive increase in the salt concentration. A decrease/increase in pH leads to deswelling of the weak polyacid/polybase gel particles, which occurs smoothly at temperatures below LCST, but may exhibit a discontinuity above LCST. These theoretical predictions can be used for design of smart stimuli-responsive microgels. © 2013 American Chemical Society.

Zhulina E.B.,RAS Institute of Macromolecular Compounds | Rubinstein M.,University of North Carolina at Chapel Hill
Soft Matter | Year: 2012

Intramolecular repulsion between charged monomers imposes intrinsic tension in a polyion, modifies its elasticity, and changes the dependence of polyelectrolyte brush thickness on salt concentration. We demonstrate that intrinsic polyion tension gives rise to a plateau of brush thickness in the middle of a salt dominated regime and to a subsequent steeper brush contraction with increasing salt concentration. This journal is © 2012 The Royal Society of Chemistry.

Polotsky A.A.,RAS Institute of Macromolecular Compounds
Journal of Physics A: Mathematical and Theoretical | Year: 2012

Adsorption of an (AB) random copolymer (RC) onto an (ab) random heterogeneous surface (RS), where both the RC and the RS have correlations, is studied using a two-dimensional partially directed walk model of the polymer. The problem is solved by using a combination of the annealed approximation for averaging over polymer and surface randomness with the generating functions (GFs) approach. A compact determinant equation for finding the smallest singularity of the GF of the adsorbed RC chain is derived. Dependences of inverse temperature of the adsorption transition on the RC and the RS correlation parameters are calculated for the chosen sets of monomer-site interaction parameters. We analyze the influence of interplay between correlations in the RC and the RS on the transition temperature, observe and discuss the effect of insensitivity of Bernoullian (uncorrelated) RC (or RS) to correlations in its adsorption partner. An exact solution for the regular alternating copolymer adsorption onto the regular alternating surface is obtained. © 2012 IOP Publishing Ltd.

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