Elena Govorun
Lomonosov Moscow State University, Faculty of Physics, Faculty Member
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Interchain interactions affect both reactivity and mobility of macromolecules and hence influence such processes as interdiffusion and phase separation. Three types of reactions in polymer blends proceeding without participation of low... more
Interchain interactions affect both reactivity and mobility of macromolecules and hence influence such processes as interdiffusion and phase separation. Three types of reactions in polymer blends proceeding without participation of low molecular reagents and leading to different kinds of copolymers are considered. For polymeranalogous reaction leading to statistical copolymers, the evolution of the blend structure under concerted action of the
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Thermoresponsive polymers are usually characterized by a locally amphiphilic chain structure and their self-assembly in solution is controlled, in particular, by the surface activity of the monomer units or side chains. We theoretically... more
Thermoresponsive polymers are usually characterized by a locally amphiphilic chain structure and their self-assembly in solution is controlled, in particular, by the surface activity of the monomer units or side chains. We theoretically study the condensed state of a single diblock copolymer molecule consisting of a hydrophobic block and amphiphilic block with hydrophobic groups in the backbone and pendant polar groups. The equilibrium parameters of the polymer globules of different shapes are determined using the mean-field approach to determine the most favorable structure. Morphological diagrams of condensed macromolecules are presented depending on the chain length, amphiphilic block fraction, interaction parameters, and pendant volume and length. The diagrams are compared with those of a copolymer molecule with the same fraction of amphiphilic monomer units which are regularly distributed along the chain. The diblock copolymer molecule is found to form a single spherical or fla...
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Conformation-dependent design of polymer sequences can be considered as a tool to control macromolecular self-assembly. We consider the monomer unit sequences created via the modification of polymers in a homogeneous melt in accordance... more
Conformation-dependent design of polymer sequences can be considered as a tool to control macromolecular self-assembly. We consider the monomer unit sequences created via the modification of polymers in a homogeneous melt in accordance with the spatial positions of the monomer units. The geometrical patterns of lamellae, hexagonally packed cylinders, and balls arranged in a body-centered cubic lattice are considered as typical microphase-separated morphologies of block copolymers. Random trajectories of polymer chains are described by the diffusion-type equations and, in parallel, simulated in the computer modeling, the probability distributions of block length k being calculated. The problem is similar to that of gambler’s ruin and first passage time in probability theory but the consideration is generalized to 3D and the domains of different shapes are considered. In any domain, the probability distribution can be described by the asymptote ∼k −3/2 at moderate values of k if the s...
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Amphiphilic polymer blocks can envelop the domains of major non-amphiphilic blocks in diblock copolymer melts: a theoretical study.
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Research Interests: Algorithms, Thermodynamics, Protein Folding, Molecular Evolution, Polymers, and 11 moreEntropy, Computer Simulation, Mathematical Sciences, Physical sciences, Molecular Phylogenetics and Evolution, Proteins, Theoretical Models, Protein Conformation, Coarse Grained Soil, Ligands, and Monte Carlo Method
The compositional relaxation in random copolymer systems on a macroscopic scale is considered in theory. A set of diffusion equations is derived that describes the motion of chains of different composition and then converted into coupled... more
The compositional relaxation in random copolymer systems on a macroscopic scale is considered in theory. A set of diffusion equations is derived that describes the motion of chains of different composition and then converted into coupled equations for statistical moments of the compositional distribution. Several ways to solve the closure problem for these equations are discussed. The simplest is the situation when the shape of the transient compositional distribution can be predicted a priori, for example, a bimodal distribution is kept during interdiffusion of two copolymers that are not very close in composition. For a general case, it is shown that the cumulant-neglect closure based on the truncation of high-order cumulants is an effective method to get an approximate solution in terms of the time-dependent local mean composition and its dispersion. This method is applied to non-homogeneous compatible polymer systems, such as a random copolymer AB of a composition varying in space, a bilayer of Bernoullian copolymers AB of different composition, and a bilayer of homopolymers A and B, in which an autocatalytic polymer-analogous reaction A → B takes place, with possibility of the neighbor group effect. It is found that the interdiffusion can lead to a substantial broadening of the local compositional distribution, which, in turn, accelerates the system dynamics and promotes chemical reactions.
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ABSTRACT
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A new approach was developed to the theory of polymer-analogous transformations in a compositionally inhomogeneous polymer blend. Diffusion equations describing the evolution of blend composition were derived for an arbitrary distribution... more
A new approach was developed to the theory of polymer-analogous transformations in a compositionally inhomogeneous polymer blend. Diffusion equations describing the evolution of blend composition were derived for an arbitrary distribution of units in the chains of a copolymer produced in the course of reaction. The calculation of the free energy of the blend was shown to be much simplified by using information entropy. As an example, an expression for the free energy was obtained in terms of variables describing a distribution of triads of various types in the reacting chains.
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The competition of spinodal decomposition and interchain exchange reaction in a melt of a Markov multiblock AB copolymer is theoretically studied. The stability region of the homogeneous system state is determined depending on the... more
The competition of spinodal decomposition and interchain exchange reaction in a melt of a Markov multiblock AB copolymer is theoretically studied. The stability region of the homogeneous system state is determined depending on the blockiness parameter, which changes in the course of the reaction. Within the random phase approximation, equations for the structural factor are derived; they describe the linear stage of the spinodal decomposition. The compatibilizing effect of the exchange reaction is studied via numerical solution of these equations. The region of unstable fluctuations is found to be narrowed during the reaction as (const − t)^1/2, whereas the characteristic inhomogeneity size increases as ~ exp(const t). As is shown, the polydispersity of the chain length significantly delays phase separation in the polymer blend even in the absence of a chemical reaction.
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The interchain exchange and interdiffusion in blends of poly(ethylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) are investigated with reprecipitated commercial samples (M η ∼ 104) and samples containing no... more
The interchain exchange and interdiffusion in blends of poly(ethylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) are investigated with reprecipitated commercial samples (M η ∼ 104) and samples containing no polycondensation catalyst (M η ∼ 103) synthesized in the course of this study. The kinetics of multiblock copolymer formation and gradual reduction of the mean block length in quasi-homogeneous blends were shown to
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ABSTRACT Microstructuring in the bulk of a polymer globule in a solution that contains dimeric amphiphilic molecules, in particular, surfactants, is studied in terms of the weak-segregation theory. An inhomogeneous structure can result... more
ABSTRACT Microstructuring in the bulk of a polymer globule in a solution that contains dimeric amphiphilic molecules, in particular, surfactants, is studied in terms of the weak-segregation theory. An inhomogeneous structure can result from a decrease in free energy with the orientation of amphiphilic molecules in the region of inhomogeneity owing to the interaction of hydrophobic and polar parts of the molecules with the solvent. For the sake of simplicity, we discuss the case of identical second virial coefficients of the interaction of monomer units and amphiphilic molecules with different energies of interaction of the hydrophobic and polar parts of the molecule with the solvent. By comparing the free energy for different types of microstructures, we predict that, with deterioration in the quality of the solvent, there is an initial formation of a homogeneous globule followed by formation of a body-centered cubic structure; a hexagonal cylindrical structure; and, finally, a lamellar structure. For a low degree of amphiphilicity, the transition from a homogeneous globule to only a lamellar structure occurs. An increase in the concentration of the amphiphilic substance in the surrounding solution hinders the formation of a globule but facilitates its microstructuring, which is also promoted by an increase in the volume of the amphiphilic molecule and the difference in the interaction energies of its hydrophobic and polar parts with the solvent. Phase diagrams of a globule’s state at different values of model parameters are plotted.
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ABSTRACT We consider lamellar morphologies in the mixtures of AC diblock and ABC triblock copolymers and show that a proper functionalization of the end blocks of the triblock and diblock copolymer chains by donor and acceptor functional... more
ABSTRACT We consider lamellar morphologies in the mixtures of AC diblock and ABC triblock copolymers and show that a proper functionalization of the end blocks of the triblock and diblock copolymer chains by donor and acceptor functional groups, respectively, could result in occurrence of the thermodynamically stable noncentrosymmetric lamellar structures in such mixtures. Depending on the chemical nature of the donor-acceptor bond (i.e., the values of the effective entropy Sbond and energy E per one bond), the typical phase diagrams could contain the upper and lower triple points where the pure diblock, pure triblock and noncentrosymmetric lamellae of a finite composition coexist. With increase of the association strength the triple points merge and the noncentrosymmetric lamellae become thermodynamically favorable at all temperatures. The boundary on the (Sbond ,E)-plane, which separates the regions corresponding to different types of the phase behavior, is found. The influence of the architecture of the system and the chemical nature of the donor-acceptor bond on the stability of the noncentrosymmetric lamellae is analyzed and typical phase diagrams are presented.
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Research Interests: Engineering, Biophysics, Thermodynamics, Polymers, Sequence Analysis, and 11 moreComputer Simulation, Mathematical Sciences, Physical sciences, Protein Secondary Structure Prediction, Statistical Properties, Water soluble polymers, Molecular Conformation, Protein Conformation, Levy Flight, Poisson Distribution, and Monte Carlo Method
ABSTRACT The globular state of the homopolymer macromolecule in a blend composed of a poor solvent and an amphiphilic solvent (substrate), whose molecules tend to be aligned with the solvent concentration gradient in the inhomogeneity... more
ABSTRACT The globular state of the homopolymer macromolecule in a blend composed of a poor solvent and an amphiphilic solvent (substrate), whose molecules tend to be aligned with the solvent concentration gradient in the inhomogeneity region, was theoretically studied. The size of a homogeneous globule and the substrate concentration in its volume were calculated in terms of a bulk approximation. After the transition of the macromolecule from the coil to the globule state, its volume first decreases with a decrease in temperature and then begins to grow due to substrate molecules penetrating the globule. The substrate concentration in the globule insignificantly exceeds that outside the globule at identical second virial coefficients of interaction between monomer units and between substrate molecules. The expression for the free energy functional depending on the volume fractions of the components and on the orientation of substrate molecules was examined in the ground-state approximation. The orientation effect leads to narrowing of the surface layer and to a decrease in the surface tension of the homogeneous globule, thereby increasing its stability with respect to the transition to the unfolded-coil state.