arXiv subjects

Yu. A. Budkov

Publications and source records attributed to Yu. A. Budkov.

33 records · Page 2Linked to original sources

arXiv2019

Statistical theory of fluids with a complex electric structure: Application to solutions of soft-core dipolar particles

Based on the thermodynamic perturbation theory (TPT) and the Random phase approximation (RPA), we present a statistical theory of solutions of electrically neutral soft molecules, every of which is modelled as a set of sites that interact with each other through the potentials, presented as the sum of the Coulomb potential and arbitrary soft-core potential. As an application of our formalism, we formulate a general statistical theory of solution of the soft-core dipolar particles. For the latter, we obtain a new analytical relation for the screening function. As a special case, we apply this theory to describing the phase behavior of a solution of the dipolar particles interacting with each other in addition to the electrostatic potential through the repulsive Gaussian potential -- Gaussian core dipolar model (GCDM). Using the obtained analytic expression for the total free energy of the GCDM, we obtain the liquid-liquid phase separation with an upper critical point. The developed formalism could be used as a general framework for the coarse-grained description of thermodynamic properties of solutions of macromolecules, such as proteins, betaines, polypeptides, etc.

cond-mat.soft↗

arXiv2017

Statistical description of co-nonsolvency suppression at high pressures

We present an application of Flory-type self-consistent field theory of the flexible polymer chain dissolved in the binary mixture of solvents to theoretical description of co-nonsolvency. We show that our theoretical predictions are in good quantitative agreement with the recently published MD simulation results for the conformational behavior of a Lennard-Jones flexible chain in a binary mixture of the Lennard-Jones fluids. We show that our theory is able to describe co-nonsolvency suppression through pressure enhancement to extremely high values recently discovered in experiment and reproduced by full atomistic MD simulations. Analysing a co-solvent concentration in internal polymer volume at different pressure values, we speculate that this phenomenon is caused by the suppression of the co-solvent preferential solvation of the polymer backbone at rather high pressure imposed. We show that when the co-solvent-induced coil-globule transition takes place, the entropy and the enthalpy contributions to the solvation free energy abruptly decrease, while the solvation free energy remains continuous.

cond-mat.soft↗

arXiv2017

Polymer chain collapse induced by many-body dipole correlations

We present a simple analytical theory of flexible polymer chain dissolved in a good solvent, carrying permanent freely oriented dipoles on the monomers. We take into account the dipole correlations within the random phase approximation (RPA), as well as a dielectric heterogeneity in the internal polymer volume relative to the bulk solution. We demonstrate that the dipole correlations of monomers can be taken into account as pairwise ones only when the polymer chain is in a coil conformation. In this case the dipole correlations manifest themselves through the Keesom interactions of the permanent dipoles. On the other hand, the dielectric heterogeneity effect (dielectric mismatch effect) leads to effective interaction between the monomers of the polymeric coil. Both of these effects can be taken into account by the renormalizing the second virial coefficient of the volume interactions monomer-monomer. We establish that in the case when the solvent dielectric permittivity exceeds the dielectric permittivity of the polymeric material, the dielectric mismatch effect competes with the dipole attractive interactions, leading to polymer coil expansion. In the opposite case, both the dielectric mismatch effect and the dipole attractive interaction lead to the polymer coil collapse. We analyse the coil-globule transition caused by the dipole correlations of monomers within the many-body theory. We demonstrate that accounting for the dipole correlations higher than pairwise ones smooths this pure electrostatics driven coil-globule transition of the polymer chain.

cond-mat.soft↗

arXiv2016

Polarizable polymer chain under external electric field: Effects of many-body electrostatic dipole correlations

We present a new simple self-consistent field theory of the polarizable flexible polymer chain under the external constant electric field with account for the many-body electrostatic dipole correlations. We show the effect of electrostatic dipole correlations on the electric field-induced globule-coil transition. We demonstrate that only when the polymer chain is in the coil conformation, the electrostatic dipole correlations of monomers can be considered as pairwise. However, when the polymer chain is in collapsed state, the dipole correlations have to be considered at the many-body level.

cond-mat.soft↗

arXiv2016

Generation of mechanical force by grafted polyelectrolytes in an electric field. Application to polyelectrolyte-based nano-devices

We analyze theoretically and by means of molecular dynamics (MD) simulations the generation of mechanical force by a polyelectrolyte (PE) chain grafted to a plane. The PE is exposed to an external electric field that favors its adsorption on the plane. The free end of the chain is linked to a deformable target body. Varying the field one can alter the length of the non-adsorbed part of the chain. This entails variation of the deformation of the target body and hence variation of the arising in the body force. Our theoretical predictions for the generated force are in a very good agreement with the MD data. Using the developed theory for the generated force we study the effectiveness of possible PE-based nano-vices, comprised of two clenching planes connected by PEs and exposed to an external electric field. We exploit Cundall-Struck solid friction model to describe the friction between a particle and the clenching planes. We compute the self-diffusion coefficient of a clenched particle and show that it drastically decreases even in weak applied fields. This demonstrates the efficacy of the PE-based nano-vices, which may be a a possible alternative to the existing nano-tube nano-tweezers and optical tweezers.

cond-mat.soft↗

arXiv2016

On a new application of the path integrals in polymer statistical physics

We propose a new approach based on the path integral formalism to the calculation of the probability distribution functions of quadratic quantities of the Gaussian polymer chain in d-dimensional space, such as the radius of gyration and potential energy in the parabolic well. In both cases we obtain the exact relations for the characteristic function and cumulants. Using the standard steepest-descent method, we evaluate the probability distribution functions in two limiting cases of the large and small values of corresponding variables.

cond-mat.soft↗

arXiv2016

A statistical theory of coil-to-globule-to-coil transition of a polymer chain in the mixture of good solvents

We present an off-lattice statistical model of a single polymer chain in mixed solvent media. Taking into account a polymer conformational entropy, renormalization of solvent composition near the polymer backbone, the universal intermolecular excluded volume and Van-der-Waals interactions within the self-consistent field theory the reentrant coil-to-globule-to-coil transition (co-nonsolvency) has been described in this paper. For convenience we split the system volume in two parts: the volume occupied by the polymer chain and the volume of bulk solution. Considering the equilibrium between two sub-volumes, the polymer solvation free energy as a function of radius of gyration and co-solvent mole fraction within internal polymer volume has been obtained. Minimizing the free energy of solvation with respect to its arguments, we show two qulitatively different regimes of co-nonsolvency. Namely, at sufficiently high temperature a reentrant coil-to-globule-to-coil transition proceeds smoothly. On the contrary, when the temperature drops below a certain threshold value a coil-globule transition occurs in the regime of first-order phase transition, i.e., discontinuous changes of the radius of gyration and the local co-solvent mole fraction near the polymer backbone. We show that, when the collapse of polymer chain takes place, the entropy and enthalpy contributions to the solvation free energy of globule strongly grow. From the first principles of statistical thermodynamics we confirm earlier speculations based on the MD simulations results that the co-nonsolvency is the essentially enthalpic-entropic effect and caused by enthalpy-entropy compensation. We show that the temperature dependences of solution heat capacity change due to the solvation of polymer chain are in qualitative agreement with the Differential scanning calorimetry data for PNIPAM in aqueous methanol.

cond-mat.soft↗

arXiv2016

On the theory of electric double layer with explicit account of a polarizable co-solvent

We present a continuation of our theoretical research into the influence of co-solvent polarizability on a differential capacitance of the electric double layer [EPL 111, 28002 (2015)]. We formulate a modified Poisson-Boltzmann theory, using the formalism of density functional approach on the level of local density approximation taking into account the electrostatic interactions of ions and co-solvent molecules as well as their excluded volume. We derive the modified Poisson-Boltzmann equation, considering the three-component symmetric lattice gas model as a reference system and minimizing the grand thermodynamic potential with respect to the electrostatic potential. We apply present modified Poisson-Boltzmann equation to the electric double layer theory.

cond-mat.soft↗

arXiv2016

Generation of mechanical force by grafted polyelectrolytes in an electric field

We study theoretically and by means of molecular dynamics (MD) simulations the generation of mechanical force by grafted polyelectrolytes in an external electric field, which favors its adsorption on the grafting plane. The force arises in deformable bodies linked to the free end of the chain. Varying the field, one controls the length of the non-adsorbed part of the chain and hence the deformation of the target body, i.e., the arising force too. We consider target bodies with a linear force-deformation relation and with a Hertzian one. While the first relation models a coiled Gaussian chain, the second one describes the force response of a squeezed colloidal particle. The theoretical dependencies of generated force and compression of the target body on applied field agree very well with the results of MD simulations. The analyzed phenomenon may play an important role in a future nano-machinery, e.g. it may be used to design nano-vices to fix nano-sized objects.

cond-mat.soft↗

arXiv2015

Polarizable polymer chain under external electric field in a dilute polymer solution

We study the conformational behavior of polarizable polymer chain under an external homogeneous electric field within the Flory type self-consistent field theory. We consider the influence of electric field on the polymer coil as well as on the polymer globule. We show that when the polymer chain conformation is a coil, application of external electric field leads to its additional swelling. However, when the polymer conformation is a globule, a sufficiently strong field can induce a globule-coil transition. We show that such $"$field-induced$"$ globule-coil transition at the sufficiently small monomer polarizabilities goes quite smoothly. On the contrary, when the monomer polarizability exceeds a certain threshold value, the globule-coil transition occurs as a dramatic expansion in the regime of first-order phase transition. The developed theoretical model can be applied to predicting polymer globule density change under external electric field in order to provide more efficient processes of polymer functionalization, such as sorption, dyeing, chemical modification, etc.

cond-mat.soft↗

arXiv2015

A new equation of state of a flexible-chain polyelectrolyte solution: Phase equilibria and osmotic pressure in the salt-free case

We develop a first-principle equation of state of salt-free polyelectrolyte solution in the limit of infinitely long flexible polymer chains in the framework of a field-theoretical formalism beyond the linear Debye-Hueckel theory and predict a liquid-liquid phase separation induced by a strong correlation attraction. As a reference system we choose a set of two subsystems - charged macromolecules immersed in a structureless oppositely charged background created by counterions (polymer one component plasma) and counterions immersed in oppositely charged background created by polymer chains (hard-core one component plasma). We calculate the excess free energy of polymer one component plasma in the framework of Modified Random Phase Approximation, whereas a contribution of charge densities fluctuations of neutralizing backgrounds we evaluate at the level of Gaussian approximation. We show that our theory is in a very good agreement with the results of Monte-Carlo and MD simulations for critical parameters of liquid-liquid phase separation and osmotic pressure in a wide range of monomer concentration above the critical point, respectively.

cond-mat.soft↗

arXiv2015

The Equation of State for Solution of Semiflexible Polymer Chains

We formulate a self-consistent procedure for calculation of thermodynamic and structural properties of polymer solutions based on the Gaussian equivalent representation method (GER) for functional integrals calculation beyond the mean-field approximaton. We show that an equation of state, potential of mean force of interaction monomer-monomer, and persistent length should be defined self-consistently by solving of some system of coupled equation.

cond-mat.stat-mech↗

arXiv2015

A flexible polymer chain in a critical solvent: Coil or globule?

We study the behavior of a flexible polymer chain in the presence of a low-molecular weight solvent in the vicinity of a liquid-gas critical point within the framework of a self-consistent field theory. The total free energy of the dilute polymer solution is expressed as a function of the radius of gyration of the polymer and the average solvent number density within the gyration volume at the level of the mean-field approximation. Varying the strength of attraction between polymer and solvent we show that two qualitatively different regimes occur at the liquid-gas critical point. In case of weak polymer-solvent interactions the polymer chain is in a globular state. On the contrary, in case of strong polymer-solvent interactions the polymer chain attains an expanded conformation. We discuss the influence of the critical solvent density fluctuations on the polymer conformation. The reported effect could be used to excert control on the polymer conformation by changing the thermodynamic state of the solvent. It could also be helpful to estimate the solvent density within the gyration volume of the polymer for drug delivery and molecular imprinting applications.

cond-mat.stat-mech↗

arXiv2014

A Statistical Theory of cosolvent-induced coil-globule transitions in dilute polymer solution

We present a statistical model of a dilute polymer solution in good solvent in the presence of low-molecular weight cosolvent. We investigate the conformational changes of the polymer induced by a change of the cosolvent concentration and the type of interaction between the cosolvent and the polymer. We describe the polymer in solution by the Edwards model, where the partition function of the polymer chain with a fixed radius of gyration is described in the framework of the mean-field approximation. The contributions of polymer-cosolvent and the cosolvent-cosolvent interactions in the total Helmholtz free energy are treated also within the mean-field approximation. For convenience we separate the system volume on two parts: the volume occupied by the polymer chain expressed through its gyration volume and the bulk solution. Considering the equilibrium between the two subvolumes we obtain the total Helmholtz free energy of the solution as a function of radius of gyration and the cosolvent concentration within gyration volume. After minimization of the total Helmholtz free energy with respect to its arguments we obtain a system of coupled equations with respect to the radius of gyration of the polymer chain and the cosolvent concentration within the gyration volume. Varying the interaction strength between polymer and cosolvent we show that the polymer collapse occurs in two cases - either when the interaction between polymer and cosolvent is repulsive or when the interaction is attractive. The reported effects could be relevant for different disciplines where conformational transitions of macromolecules in the presence of a cosolvent are of interest, in particular in biology, chemistry and material science.

cond-mat.stat-mech↗

arXiv2014

The local phase transitions of the solvent in the neighborhood of a solvophobic polymer at high pressures

We investigate local phase transitions of the solvent in the neighborhood of a solvophobic polymer chain which is induced by a change of the polymer-solvent repulsion and the solvent pressure in the bulk solution. We describe the polymer in solution by the Edwards model, where the conditional partition function of the polymer chain at a fixed radius of gyration is described by a mean-field theory. The contributions of the polymer-solvent and the solvent-solvent interactions to the total free energy are described within the mean-field approximation. We obtain the total free energy of the solution as a function of the radius of gyration and the average solvent number density within the gyration volume. The resulting system of coupled equations is solved varying the polymer-solvent repulsion strength at high solvent pressure in the bulk. We show that the coil-globule (globule-coil) transition occurs accompanied by a local solvent evaporation (condensation) within the gyration volume

cond-mat.stat-mech↗