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Lyulin S.V.,RAS Institute of Macromolecular Compounds
Chemical Physics Letters | Year: 2017

Using a simple freely-jointed polymer model and Debye-Hückel description of the electrostatic interactions, we showed that the peculiarities of the overcharging taking place in interpolyelectrolyte complexes (IPECs) formed by polymers of different topologies correlate with those of the IPECs solubility. It allows to assume that drastic disappearance of a turbidity in IPEC solutions observed in turbidimetric titration experiments may be related with the presence of phase transition in the conformation of a lyophilizing linear polyelectrolyte. © 2016 Elsevier B.V.


Tolmachev D.A.,RAS Institute of Macromolecular Compounds | Lukasheva N.V.,RAS Institute of Macromolecular Compounds
Langmuir | Year: 2012

The interactions responsible for the adhesion of calcium phosphate (CP) nanocrystals and bacterial cellulose (BC) nanofibrils in the composite material obtained by mixing aqueous suspensions of presynthesized CP and BC and the dependence of these interactions on the CP morphology and chemical structure have been elucidated by molecular mechanics calculations of the CP-BC interfacial structures. The interactions between the superficial CP and BC crystal layers have been simulated. Two crystalline CP structures (i.e., hydroxyapatite (HAP) and whitlockite) with two morphologies (plate-shaped and rod-shaped) were considered. Electrostatics has been found to be the major contributor to the adhesion of the CP crystallites and BC nanofibers, and the formation of interfacial hydrogen bonds makes a minor contribution to the interaction energy. It has also been found that, in general, the energy gain resulting from whitlockite-BC binding is greater than that for HAP-BC binding, and the binding of the rod-shaped crystallites of whitlockite with BC is the most profitable. The energy loss and entropy gain upon replacement of the BC-water and CP-water contacts by the BC-CP contacts have been estimated. © 2012 American Chemical Society.


Gurtovenko A.A.,RAS Institute of Macromolecular Compounds | Anwar J.,University of Bradford | Vattulainen I.,Tampere University of Technology | Vattulainen I.,Aalto University | Vattulainen I.,University of Southern Denmark
Chemical Reviews | Year: 2010

A study was conducted to demonstrate that in silico modeling provided significant information about defect-mediated trafficking across cell membranes. It was demonstrated that formation of transient defects in cell membranes and defect-mediated transport of solutes across membranes had clear biological relevance. Protein-free lipid membranes were considered for the investigations under the study and molecular dynamic (MD) simulations of lipid bilayers with embedded membrane proteins constituted a separate area of research of considerable interest. It was demonstrated that more coarse-grained models had the potential to provide valuable information about the formation of transient defects in lipid bilayers, along with the atomistic models. The force-field parameters of coarse-grained models were also calibrated against available experimental data and data from related atomistic simulations.


Zhulina E.B.,RAS Institute of Macromolecular Compounds | Borisov O.V.,RAS Institute of Macromolecular Compounds
Langmuir | Year: 2011

We present a self-consistent field analytical theory of a polymer brush formed by weakly charged pH-sensitive (annealing) polyelectrolytes tethered to a solid-liquid interface and immersed in buffer solution of low molecular weight salt. We use the Poisson-Boltzmann framework, applied by us previously to polyelectrolyte (PE) brushes with quenched charge (Zhulina, E. B.; Borisov, O. V. J. Chem. Phys.1997, 107, 5952). This approach allows for detailed analysis of the internal structure of annealing PE brush in terms of polymer density distribution, profiles of electrostatic potential and of local degree of chain ionization as a function of buffer ionic strength and pH without any assumptions on mobile ion distribution imposed in earlier scaling-type models. The presented analytical theory recovers all major asymptotic dependences for average brush properties predicted earlier. In particular, a nonmonotonic dependence of brush thickness on ionic strength and grafting density is confirmed and specified with accuracy of numerical coefficients including crossover regions. Moreover, the theory predicts qualitatively new effects, such as, e.g., disproportionation of tethered polyions into weakly charged concentrated proximal and strongly charged sparse distal brush domains at low salt and moderate grating densities. The presented results allow us to quantify responsive features of annealing PE brushes whose large-scale and local conformational properties can be manipulated by external stimuli. © 2011 American Chemical 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.


Zhulina E.B.,RAS Institute of Macromolecular Compounds | Borisov O.V.,RAS Institute of Macromolecular Compounds
ACS Macro Letters | Year: 2013

We predict how equilibrium morphology of self-assembled aggregates in dilute solution could be tuned by replacing a linear AB diblock copolymer by a heteroarm star-like or cyclic block copolymer. We demonstrate that in selective solvent AB miktoarm stars or diblock copolymers with cyclic associating block may give rise to cylindrical assemblies or vesicles, while linear diblock copolymers with same composition form only spherical micelles. The theoretical predictions are in line with experimental observations. © 2013 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.


Zhulina E.B.,RAS Institute of Macromolecular Compounds | Borisov O.V.,RAS Institute of Macromolecular Compounds
Macromolecules | Year: 2012

We present an overview of existing theories of block polymer micelles. We focus here on the equilibrium structure of nanoaggregates formed by solvophobic/solvophilic diblock copolymers in a dilute solution and briefly address the association behavior of triblock terpolymer. We outline recent advances in the field and some challenging problems for theoretical developments. © 2012 American Chemical Society.


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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