Oligothiophenes with branched alkyl end groups show distinct aggregation in organic solvents. The process of supramolecular polymerization is assessed by three different methods (UV-vis absorption and fluorescence emission spectroscopy... more
Oligothiophenes with branched alkyl end groups show distinct aggregation in organic solvents. The process of supramolecular polymerization is assessed by three different methods (UV-vis absorption and fluorescence emission spectroscopy and...
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Using a fully atomistic model, we perform large-scale molecular dynamics simulations of sulfur-cured polybutadiene (PB) and nanosilica-filled PB composites. A well-integrated network without sol fraction is built dynamically by... more
Using a fully atomistic model, we perform large-scale molecular dynamics simulations of sulfur-cured polybutadiene (PB) and nanosilica-filled PB composites. A well-integrated network without sol fraction is built dynamically by cross-linking the coarse-grained precursor chains in the presence of embedded silica nanoparticles. Initial configurations for subsequent atomistic simulations are obtained by reverse mapping of the well-equilibrated coarse-grained systems. Based on the concept of "maximally inflated knot" introduced by Grosberg et al., we show that the networks simulated in this study behave as mechanically isotropic systems. Analysis of the network topology in terms of graph theory reveals that mechanically inactive tree-like structures are the dominant structural components of the weakly cross-linked elastomer, while cycles are mainly responsible for the transmission of mechanical forces through the network. We demonstrate that quantities such as the system densi...
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The structural and thermodynamic characteristics of highly charged rigid-chain polyelectrolytes with explicit incorporation of univalent counterions were studied using the Monte Carlo method and integral equation theory (in the PRISM... more
The structural and thermodynamic characteristics of highly charged rigid-chain polyelectrolytes with explicit incorporation of univalent counterions were studied using the Monte Carlo method and integral equation theory (in the PRISM approximation). Computations were performed for dilute and semidilute solutions over a wide temperature range. It was found that, at temperatures below the Manning threshold, the integral equation theory does not ensure exact quantitative agreement with the computer simulation results. On the basis of Monte Carlo calculations, it was shown that the reason for the lower accuracy of the PRISM approximation in the low-temperature region is the formation of locally anisotropic structures in the polymer subsystem. In a semidilute solution in a thermodynamically good solvent, aggregation processes due to the effective attraction of polyions can lead to LC ordering of short rodlike macromolecules.
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The concept of designing analogues of natural protein enzymes based on synthetic protein-like copolymers has been described. It is assumed that target globular nanostructures with a core–shell structure should form spontaneously in a... more
The concept of designing analogues of natural protein enzymes based on synthetic protein-like copolymers has been described. It is assumed that target globular nanostructures with a core–shell structure should form spontaneously in a selective solvent in the course of the polymerization reaction of monomers, which can be divided into two groups (hydrophobic and hydrophilic) according to their affinity for water. The hydrophilic monomers should contain catalytically active groups. α-Chymotrypsin was used as a natural prototype of an artificial catalyst. Computer-aided simulation of the radical copolymerization reaction confirms the efficiency of the formulated concept.
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A model based on the mesoscale simulation technique was developed for predicting the conditions for artificial enzyme formation from N-vinylcaprolactam (VCL) and N-vinylimidazole (NVI) by radical copolymerization of pre-synthesized... more
A model based on the mesoscale simulation technique was developed for predicting the conditions for artificial enzyme formation from N-vinylcaprolactam (VCL) and N-vinylimidazole (NVI) by radical copolymerization of pre-synthesized poly-VCL blocks of different molecular weight with VCL and NVI comonomers. This synthetic procedure gives model copolymer chains. Upon a change in the solvent nature, these chains are able to form compact two-layer globular nanostructures with core–shell type morphology if the fraction of the first poly-VCL block is 25–38% of the total copolymer and the fraction of NVI monomers in the reaction mixture (in the concentration range considered) is maximum.
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By means of computer simulation the association process of diphilic chains with strongly attractive head links (stickers) in the vicinity of critical point of the solvent is studied. The calculations were carried out by means of... more
By means of computer simulation the association process of diphilic chains with strongly attractive head links (stickers) in the vicinity of critical point of the solvent is studied. The calculations were carried out by means of Monte-Carlo simulation with bond-fluctuation model of polymer developed by us for the case of hexagonal-like lattice. It was found that the critical concentration of micelle formation and average aggregation number depend crucially not only on the attraction between stickers but on the quality and state of solvent.
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A monolayer of comblike copolymers at an interface was studied by computer simulation. Macromolecules with a high grafting density of side chains (molecular brushes) placed in a Langmuir trough were considered. Upon lateral contraction of... more
A monolayer of comblike copolymers at an interface was studied by computer simulation. Macromolecules with a high grafting density of side chains (molecular brushes) placed in a Langmuir trough were considered. Upon lateral contraction of the monolayer, side chains first decreased to a size typical of single chains of the same length in solution and then began to desorb from the surface. With a further increase in the surface concentration of macromolecules, the side chains stretched into the subphase to form an oriented monolayer (Langmuir fencing). As the side-chain length increases, desorption becomes stronger; however, the complete desorption of side chains is never attained for steric reasons. The results of computer simulation are consistent with the available experimental data.
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We describe molecular dynamics computer simulations coupled with quantum chemical calculations of relevant geometries and interaction constants for studying the detailed behavior of solvent-containing Nafion® membranes. Our attention here... more
We describe molecular dynamics computer simulations coupled with quantum chemical calculations of relevant geometries and interaction constants for studying the detailed behavior of solvent-containing Nafion® membranes. Our attention here is focused on the effect of different solvent additives on the equilibrium structure of micellar aggregates. Taking into account the practical importance of methanol membrane fuel cells, methanol-containing systems are the subject of our primary interest. Also, we study mixed aggregates containing alcohols H(CH2)NOH with longer hydrocarbon chain, up to n = 7. In the case of the bicomponent solvent-containing aggregates we have suggested how events occurring at the molecular level produce polymorphic transitions in these mixed aggregates from spherical structures toward cylindrical and rather exotic toroidal micelle structures, stabilized by a more uniform compact packing of the hydrophobic groups in the micelle exterior. These transitions predicted in the present study illustrate how intermolecular forces such as solvation as well as solvent chain length can affect overall aggregate structure and result in polymorphism.
Molecular dynamics calculations are used to explore the structure of dense monolayers of long-chain molecules supported on a planar surface. As a model we consider ensembles of flexible chains consisting of N segments (N=32, 64 and 128)... more
Molecular dynamics calculations are used to explore the structure of dense monolayers of long-chain molecules supported on a planar surface. As a model we consider ensembles of flexible chains consisting of N segments (N=32, 64 and 128) in a box with lateral (x, y) periodicity conditions. The effect of surface coverage on the conformational properties of chains is studied. At high coverages, the results of the simulations show that each chain is strongly stretched along the normal to the surface and the mean layer thickness is linear in N. The segment density distribution along the normal is found to be an universal function A2/3 f (zA1/3 N), where A is the surface area per chain. The high-coverage distribution has a well defined broad plateau, in agreement with the so-called blob model. In contrast to the predictions of this model, however, we observe that the chains are strongly stretched at all space scales. Differences between the results of simulations and those predicted by the mean-field theory are also discussed.
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The effect of volume interactions on conformational characteristics has been investigated for polymethylene chains containing numbers of skeletal bonds n=20–600. The hindrance and pairwise correlation for internal rotation about skeletal... more
The effect of volume interactions on conformational characteristics has been investigated for polymethylene chains containing numbers of skeletal bonds n=20–600. The hindrance and pairwise correlation for internal rotation about skeletal bonds have been taken into account. A study has been made of the mean square end-to-end distance 〈r2〉 and the mean square radius of inertia 〈s2〉 in relation to n. It is shown that with n ⩾ 50 Domb's relationship bpν + a where ν=65 is satisfactory, and 〈s2〉〈r2〉 = 0·158 at n → ∞. Eleven closed equations relating the swelling coefficient α to the exclused volume parameter z have been analysed. It was found that for sufficiently long chains the best results are obtained using Flory's equation α5-α3 = 43z. Extrapolation relationships used to determine unperturbed dimensions of macromolecules have been analysed.
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Abstract Using dissipative particle dynamics, we analyze the suitability of amphiphilic diblock copolymers as a material for high-performance proton conducting membranes of fuel cells. It is shown that the topology of water channel... more
Abstract Using dissipative particle dynamics, we analyze the suitability of amphiphilic diblock copolymers as a material for high-performance proton conducting membranes of fuel cells. It is shown that the topology of water channel network within hydrated block copolymer-based membranes can be controlled by varying the copolymer blocks length. In particular, our simulations predict the formation of bicontinuous cubic phases for hydrophilic, hydrophobic blocks, and water. The interfaces between microphase-separated subphases form triply periodic minimal surfaces.
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Abstract We present results from Monte Carlo simulations of the liquid-crystalline ordering in the athermal systems of partially flexible polymers in a two- and three-dimensional continuum. Any two non-bonded chain monomers interact via a... more
Abstract We present results from Monte Carlo simulations of the liquid-crystalline ordering in the athermal systems of partially flexible polymers in a two- and three-dimensional continuum. Any two non-bonded chain monomers interact via a hard spher potential. The chains are placed in a periodic box consistent with the number density C. It is observed that the mean dimensions of chains and the orientational order parameters increase sharply with increasing C. In other words, we observe elongation and stiffening of the chains. In contrast to semiflexible polymers, the mean dimensions of flexible chains are reduced as the density is increased.
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The Monte Carlo method has been used to study the concentration dependence of the mean dimensions R of non-selfintersecting non-lattice chains in a thermodynamically good solvent. Chains with the number of monomer units N = 31 and 61 and... more
The Monte Carlo method has been used to study the concentration dependence of the mean dimensions R of non-selfintersecting non-lattice chains in a thermodynamically good solvent. Chains with the number of monomer units N = 31 and 61 and their volumetric concentration c in the interval from 0 to 0·5 are considered. The mean square of the distance between the ends of the chains and the mean square radius of inertia are calculated. It has been established that for c ⩽ c∗∼N/R3 the value R does not depend on c. For c > c∗ fall in R is observed with rise in c, the dependence of R on c being well described by the relation R ∼ N12c−δ. Analysis of the results shows that the value δ does not exceed 0·073, i.e. is appreciably less than the theoretical value (δ≽0.125). In discussing the possible causes of such divergence the authors consider the role of chain length, the influence of the width of the concentration interval and the quality of the solvent. It is concluded that the behaviour of the non-lattice model of the chain in semi-dilute solution practically does not differ from that of chains arranged on the lattice.
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ABSTRACT We present a novel hierarchical multiscale methodology aimed at generating the atomistic structure of epoxy networks and predicting their properties and topology. Our approach combines several computational techniques and... more
ABSTRACT We present a novel hierarchical multiscale methodology aimed at generating the atomistic structure of epoxy networks and predicting their properties and topology. Our approach combines several computational techniques and consists of four separate procedures: (1) mapping of the polymerizing monomers onto a coarse-grained representation using the method of neural-gas networks, (2) cross-linking the coarse-grained monomers at mesoscale by applying dissipative particle dynamics and a probabilistic reaction scheme, (3) reverse mapping of the coarse-grained polymer network to a fully atomistic representation, and (4) simulation of the atomistic model by means of molecular dynamics technique. As a case study, we simulate DGEBA + DETDA epoxy network formation and analyze the thermal properties and the network topology. It was found that the parameters used for generating the atomistic structures (degree of coarse graining in our case) can significantly influence the network topology and properties. Moreover, we show that rather big simulation boxes are necessary to obtain the proper local structure of an epoxy resin. http://pubs.acs.org/doi/abs/10.1021/ma502220k
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A survey is given of theoretical and experimental methods as applied to the design of nontrivial sequences in synthetic copolymers aimed at achieving desired functional properties. We consider a recently developed approach, called... more
A survey is given of theoretical and experimental methods as applied to the design of nontrivial sequences in synthetic copolymers aimed at achieving desired functional properties. We consider a recently developed approach, called conformation-dependent sequence design, which is based on the assumption that a copolymer obtained under certain preparation conditions is able to ‘remember’ features of the original conformation in which it was built and to store the corresponding information in the resulting sequence. The emphasis is on copolymer sequences exhibiting large-scale compositional heterogeneities and long-range statistical correlations between monomer units. Several new synthetic strategies and polymerization processes that allow synthesis of copolymers with a broad variation of their sequence distributions are discussed.
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ABSTRACT Mesoscopic simulation in the framework of the mesoscopic dynamics method (a version of the dynamic density functional method) was performed for a proton conducting membrane based on sulfonated aromatic poly(ether ether ketone) in... more
ABSTRACT Mesoscopic simulation in the framework of the mesoscopic dynamics method (a version of the dynamic density functional method) was performed for a proton conducting membrane based on sulfonated aromatic poly(ether ether ketone) in a wide range of water content in the system. For the selected parametric field, the model demonstrates microphase separation of hydrophilic and hydrophobic segments of the polymer. In the bulk of the membrane, a spatial network of water channels forms, whose walls consist of polar (sulfonated) units of the macromolecule. Independent molecular dynamics simulation for one set of parameters gives close values of the structural characteristics of the membrane, which confirms the correctness of the mesoscopic model.
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Dense planar brushes of diblock copolymers physically attached to the substrate by end groups are studied by the dissipative particle dynamics simulation technique. We predict stability of spatially ordered perpendicularly oriented... more
Dense planar brushes of diblock copolymers physically attached to the substrate by end groups are studied by the dissipative particle dynamics simulation technique. We predict stability of spatially ordered perpendicularly oriented domains which are separated from the substrate and the free surface of the film by homogeneous layers of different type. Depending on composition of the copolymer, various structures including hexagonally ordered “golf holes”, parallel “gullies” and “ridges”, and “stalactites” ordered with the symmetry of hexagonal lattice can be stable. We analyze regimes of good and poor solvents for both blocks (nonselective solvents). Physical reasons for perpendicular domain orientation are discussed. In the case of low “grafting” density, our results coincide with those reported in the literature.
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The method of atomistic molecular dynamics simulations is used to investigate the static properties of the organic–inorganic interface in a polymer nanocomposite consisting of polyimide and silica nanoparticles with modified surface.... more
The method of atomistic molecular dynamics simulations is used to investigate the static properties of the organic–inorganic interface in a polymer nanocomposite consisting of polyimide and silica nanoparticles with modified surface. Alkylsilane chains are used as the surface modifiers. The surface density and chains length of the modifier are the main parameters of the simulations. For simplicity, the model of the composite has been constructed as a polymer layer sandwiched between two solid surfaces. Our results show that one can change the properties of the interface between the polymer matrix and the inorganic filler by choosing the molecular weight and surface density of the modifier.
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Research Interests: Engineering, Materials Science, Molecular Biology, Polymer science, Polyelectrolytes, and 15 moreMonte Carlo Simulation, Modeling and Simulation, Chemical Physics, Medicine, Metal Nanoparticles, DNA, Computer Simulation, Gold, Physical sciences, CHEMICAL SCIENCES, Particle Size, Surface Properties, Monte Carlo Method, Biomacromolecules, and Static Electricity
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We have designed, for the first time, a functional analog of chymotrypsin from synthetic monomers imitating protein amino acid residues.
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... with a special adsorption-tuned primary structure Ekaterina A. Zheligovskaya Institute of Physical Chemistry, Russian Academy of Sciences, Moscow 117915, Russia Pavel G. Khalatur ... 30 S. Kamtekar, JM Schiffer, H. Xiong, JM Babik,... more
... with a special adsorption-tuned primary structure Ekaterina A. Zheligovskaya Institute of Physical Chemistry, Russian Academy of Sciences, Moscow 117915, Russia Pavel G. Khalatur ... 30 S. Kamtekar, JM Schiffer, H. Xiong, JM Babik, and MH Hecht, Science 262, 1680 1993 . ...
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Atomistic and first-principles molecular dynamics simulations are employed to investigate the structure formation in a hydrated Nafion membrane and the solvation and transport of protons in the water channel of the membrane. For the... more
Atomistic and first-principles molecular dynamics simulations are employed to investigate the structure formation in a hydrated Nafion membrane and the solvation and transport of protons in the water channel of the membrane. For the water/Nafion systems containing more than 4 million atoms, it is found that the observed microphase-segregated morphology can be classified as bicontinuous: both majority (hydrophobic) and minority (hydrophilic) subphases are 3D continuous and organized in an irregular ordered pattern, which is largely similar to that known for a bicontinuous double-diamond structure. The characteristic size of the connected hydrophilic channels is about 25-50 Å, depending on the water content. A thermodynamic decomposition of the potential of mean force and the calculated spectral densities of the hindered translational motions of cations reveal that ion association observed with decreasing temperature is largely an entropic effect related to the loss of low-frequency m...
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A proton conducting hydrated membrane on the basis of sulfonated aromatic poly(ether-ether-ketone) was modeled for the first time using dynamic density functional theory (the ``mesoscopic dynamics'' method). The model... more
A proton conducting hydrated membrane on the basis of sulfonated aromatic poly(ether-ether-ketone) was modeled for the first time using dynamic density functional theory (the ``mesoscopic dynamics'' method). The model constructed was used to demonstrate the microphase separation of hydrophilic and hydrophobic polymer chain units in the selected region of parameters. A spatial network of water domains formed in the membrane volume. The domain walls consisted of polar (sulfonated) macromolecule units. A comparison with the well-studied Nafion-1100 membrane showed that the cross sections of water channels in the two systems had similar values. This must ensure approximately equal ionic conductivity characteristics.
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A statistical model is developed for radical graft copolymerization in a solution of monomers A and B in the vicinity of a surface selectively absorbing the monomers of type A and corresponding copolymer sections. The influence of the... more
A statistical model is developed for radical graft copolymerization in a solution of monomers A and B in the vicinity of a surface selectively absorbing the monomers of type A and corresponding copolymer sections. The influence of the monomer concentrations and the short-range monomer A−surface attraction on the copolymer sequence is investigated. It is shown that under certain conditions, the adsorption copolymerization can yield gradient copolymers. We find three copolymerization regimes corresponding to different values of dimensionless adsorption energy u. When the growing macroradical is weakly or nonadsorbed, u < uc (uc is the critical adsorption energy), the statistical properties of graft copolymers approach asymptotically, in the long-chain limit, to those of a random copolymer. If u ≳ uc, the statistics of designed and random copolymers is very different. In the vicinity of uc, the adsorption copolymerization leads to copolymers with the largest compositional nonuniformity and well-pronounced gr...
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... by molecular dynamics simulations. In the constant pressure (NPT) MD simulations, it is straightforward to construct the OPLS/AA model for the CAER system based on the work by Jorgensen and co-workers. 88-91 The total ...
Research Interests: Engineering, Polymer science, Molecular Dynamics Simulation, Multiscale Modelling, Modeling and Simulation, and 10 moreDensity, Polymer networks, Macromolecules, CHEMICAL SCIENCES, Epoxy Resins, Glass Transition Temperature, Epoxy Resin, Molecular Dynamic Simulation, Linear Coefficient of Thermal Expansion, and Monte Carlo Method
We present the results of molecular dynamics simulations of micelle organization as well as the formation of micellar aggregates in the solutions of semiflexible telechelic chains with strongly attracting end-groups (sticker sites).... more
We present the results of molecular dynamics simulations of micelle organization as well as the formation of micellar aggregates in the solutions of semiflexible telechelic chains with strongly attracting end-groups (sticker sites). Using the cluster size distribution function, we study ...
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Research Interests: Engineering, Thermodynamics, Chemistry, Polymer Chemistry, Polymer science, and 11 morePolyelectrolytes, Monte Carlo Simulation, Modeling and Simulation, Chemical Physics, Medicine, Physical sciences, CHEMICAL SCIENCES, Self Organization, Chemical Structure, Polyelectrolyte-Surfactant Complexes, and Electrostatic interaction
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Abstract We discuss advances that have recently been achieved in the computer simulation and theoretical understanding of solutions of hydrophobic polyelectrolytes. The focus is on bioinspired ‘proteinlike’ copolymers with specific... more
Abstract We discuss advances that have recently been achieved in the computer simulation and theoretical understanding of solutions of hydrophobic polyelectrolytes. The focus is on bioinspired ‘proteinlike’ copolymers with specific chemical sequences resembling those known for soluble proteins. Due to a complex interplay between hydrophobic attraction and Coulomb interactions, ‘proteinlike’ polyelectrolytes can readily adopt stable spherical-shaped globular conformations and can be protected against large-scale intermolecular aggregation in selective (poor) solvents. The concept of conformation-dependent sequence design, which takes into account a strong coupling between the conformation and primary structure of copolymers during their synthesis, is also discussed.