Alexey A. Polotsky

• PhD
• Senior Researcher at Institute of Macromolecular Compounds, Russian Academy of Sciences

The adsorption of a single random copolymer chain containing correlations in a sequence on the chemically heterogeneous periodic surface with the alternating striped texture is studied theoretically. The problem is solved within the framework of a partially directed walk polymer model in three dimensions using the generating functions approach and...

Adsorption of a single AB random copolymer (RC) chain onto homogeneous and inhomogeneous ab surfaces with a regular periodic pattern is studied theoretically. For the averaging over disorder in the RC sequence, the constrained annealed approximation, known as the Morita approximation is employed. A general scheme for constructing the Morita approxi...

Compression and interpenetration of two opposing polymer brushes formed by end-grafted adsorption-active chains are studied by numerical self-consistent field approach and by analytical theory. For sufficiently strong polymer-surface attraction, a fraction of chains in the adsorption-active brush condenses into a near-surface layer, while the remai...

The adsorption of a single AB random copolymer (RC) chain onto an inhomogeneous ab surface with a regular periodic pattern is studied theoretically. The problem is considered within the simplest model of a partially directed random walk in two dimensions by using the method of generating functions and the annealed approximation for the averaging ov...

Adsorption of a single homopolymer chain with bending stiffness onto a heterogeneous regular stripe-patterned surface consisting of adsorbing and non-adsorbing stripes is studied theoretically in the framework of the lattice model and the generating functions approach. The stiffness is introduced by assigning a statistical weight to a trans-isomer...

Recently a novel class of responsive uncharged polymer brushes has been proposed [Klushin et al, J. Chem. Phys. 154, 074904 (2021)] where the brush-forming chains have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining ones form the outer brush wi...

Recently a novel class of responsive uncharged polymer brushes has been proposed [Klushin et al, J. Chem. Phys. 154, 074904 (2021)] where the brush-forming chains have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining ones form the outer brush wi...

We propose a novel class of responsive polymer brushes, where the effective grafting density can be controlled by external stimuli. This is achieved by using end-grafted polymer chains that have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining o...

We propose a novel class of responsive polymer brushes, where the effective grafting density can be controlled by external stimuli. This is achieved by using end-grafted polymer chains that have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining o...

Adsorption of a single homopolymer chain with bending stiffness on a homogeneous planar surface is studied theoretically in the framework of the lattice model and the generating functions approach. The stiffness is introduced by assigning a statistical weight to a trans-isomer (a straight segment) with respect to a gauche-isomer (a kink). This stat...

Using a combination of self-consistent field theory with coarse-grained Brownian dynamics simulations, we studied mechanical unfolding of an amphiphilic molecular brush in a solvent that was poor for the side chains but good for the main chain of the brush. In striking contrast to earlier theoretical predictions [O. V. Borisov and A. Halperin, Euro...

Adsorption of single macromolecules of random and regular heterpolymers was studied by the generating functions approach (or the method of grand canonical ensemble). Adsorption of random copolymers characterized by a sequence of monomer units set as a first order Markov chain was considered using the approximation of annealed disorder and constrain...

Recent fully atomistic molecular dynamics (MD) simulation of polymer nanocomposites based on polylactic acid (PLA) filled with cellulose nanocrystals (CNC) covalently modified by grafting of lactic acid oligomers (OLA) [A.D. Glova et al. Soft Matter 13 (2017) 6627] have revealed a non-trivial structure of the OLA brush. It was found that a segregat...

A numerical self-consistent field modeling approach was employed to study the mechanical unfolding of a globule made by comb-like polymers in a poor solvent with the aim of unraveling how the macromolecular architecture affects the shape of the single-molecule force–deformation curves. We demonstrate that the dependence of the restoring force on th...

Conformational transition in a single “minority” linear polymer chain inserted into a polymer brush made of arm-grafted chemically identical stars (star brush) is studied theoretically. It is shown that the chain can undergo a transition between conformations of the grafted coil and the “flower” consisting of a strongly stretched “stem” passing thr...

A planar polymer brush of arm-grafted polymer stars subjected to external deformation is studied theoretically by using a simple mean-field model of the star brush that takes into account segregation of the brushforming stars in two populations of weakly and strongly extended stars. The polymer density profile in the brush is assumed to have a “two...

The problem of a periodic heteropolymer adsorption onto a periodic heterogeneous surface is solved exactly in the framework of the twodimensional partly directed walk model and the generating functions approach. Analysis of the adsorption transition point dependence on polymer and surface block sizes reveals interesting “odd-even” and “recognition”...

Adsorption of a homopolymer chain onto a heterogeneous stripe-patterned surface is studied in the framework of the three-dimensional partially directed walk model of the polymer by using the generating function approach. Both annealed random and quenched regular (periodic) stripe-patterned surfaces are considered. For random surfaces the adsorption...

Adsorption of a symmetric (AB) random copolymer (RC) onto a symmetric (ab) random heterogeneous surface (RS) is studied in the annealed approximation by using a two-dimensional partially directed walk model of the polymer. We show that in the symmetric case, the expected a posteriori compositions of the RC and the RS have correct values (correspond...

Using a combination of analytical theory, Monte Carlo simulations, and three dimensional self-consistent field calculations, we study the equilibrium properties and the switching behavior of adsorption-active polymer chains included in a homopolymer brush. The switching transition is driven by a conformational change of a small fraction of minority...

The structure of a mixed brush made of arm-grafted polymer stars and grafted linear chains is investigated using the Scheutjens-Fleer self-consistent field method. It is shown that the mixing of stars and chains is thermodynamically favorable with respect to their lateral segregation in the brush. On the other hand, a segregation of linear and star...

A planar polymer brush of arm-grafted polymer stars subjected to external deformation is studied theoretically We propose a simple mean-field model of the star brush that takes into account segregation of the brush-forming stars in two populations: (i) those with weakly extended arms and (ii) those with a very strongly stretched grafting arm (stem)...

By using the Scheutjens-Fleer self-consistent field approach, structure of the fourth-generation dendrimer with attached terminal chemically different oligomeric segments is studied theoretically. It is demonstrated that an incompatibility of terminal segments with inner dendrimer units leads to formation of a "hollow" core with reduced polymer den...

Polymer molecules densely tethered to surfaces (polymer brushes) can improve the colloidal stability of dispersion by protecting particles against aggregation. We use mean field and self-consistent field theoretical models to consider repulsive interactions between brushes of branched (dendritic) macromolecules tethered to planar and spherical surf...

We develop approximate analytical (AA) model to describe the structure of a brush made of starlike polymers (regularly branched dendrons of the first generation) grafted by one arm onto a planar surface. It is demonstrated that introduction of two sub-layers with distinct populations of strongly and weakly stretched dendrons allows for adequate sem...

We propose a design for polymer-based sensors and switches with sharp switching transition and fast response time. The switching mechanism involves a radical change in the conformations of adsorption-active minority chains in a brush. Such transitions can be induced by a temperature change of only about ten degrees, and the characteristic time of t...

The adsorption of a periodic heteropolymer onto a periodic heterogeneous surface is studied using the two-dimensional partially directed walk model of the polymer. We show how the generating function approach developed by Polotsky (2012 J. Phys A: Math. Theor. 45 425004) for the adsorption of a random copolymer onto a random surface can be extended...

The coil-bridge transition in a self-avoiding lattice chain with one end fixed at height H above the attractive planar surface is investigated by theory and Monte Carlo simulation. We focus on the details of the first-order phase transition between the coil state at large height H ⩾ Htr and a bridge state at H ⩽ Htr, where Htr corresponds to the co...

Dendron brushes are molecular structures built up of treelike macromolecules, with multiple generations of branches, grafted with a root segment to a surface (particle) or to a backbone chain (dendronized polymer) with a sufficiently high grafting density so that the dendrons interact laterally. Recent advances in the theory of dendron brushes are...

Full adsorption of flexible chains onto typical solid substrates occurs at a surface interaction energy of (5-10) kBT. The corresponding detachment force is in the range 10-50 pN. In contrast to “bare” solid substrates common to non-living materials, surfaces coated with brush-like polymer layers are very common in biological soft matter. We employ...

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 the...

Equilibrium structural properties of polymer brushes formed by dendrons grafted via the root segment onto spherical surfaces (dendritic spherical polymer brushes, DSPB) are studied by means of the Scheutjens–Fleer self-consistent field (SF-SCF) numerical approach and scaling analysis. In particular, we focus on the effects of the variable curvature...

We investigate the effects of the range of adsorption potential on the equilibrium behavior of a single polymer chain end-attached to a solid surface. The exact analytical theory for ideal lattice chains interacting with a planar surface via a box potential of depth U and width W is presented and compared to continuum model results and to Monte Car...

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 structure of a brush made of arm-grafted polymer stars is investigated using the Scheutjens–Fleer self-consistent field method. By using the “probe macromolecule” approach, conditional distributions of end- and branching points were obtained, which allowed for a detailed analysis of intramolecular correlations in the brush. Results strongly sup...

We present a theory of intramolecular collapse transition in a weak (pH sensitive) polyelectrolyte (PE) star induced by a decrease in the solvent strength and/or variation in the ionic strength in the solution. Our system mimics conformational coil-to-globule transitions in individual star-shaped thermo- and pH-sensitive (e.g. poly(dimethylaminoeth...

Equilibrium mechanical unfolding of a globule formed by long flexible homopolymer chain collapsed in a poor solvent and subjected to an extensional force f (force-clamp mode) or extensional deformation D (position-clamp mode) is studied theoretically. Our analysis, like all previous analysis of this problem, shows that the globule behaves essential...

We propose the quantitative mean-field theory of mechanical unfolding of a globule formed by long flexible homopolymer chain collapsed in poor solvent and subjected to extensional deformation. We demonstrate that depending on the degree of polymerization and solvent quality (quantified by the Flory-Huggins $\chi$ parameter) the mechanical unfolding...

We consider conformations and intra-molecular conformational transitions in amphiphilic starlike polymers formed by diblock copolymer arms with inner hydrophobic and outer polyelectrolyte blocks. A combination of an analytical mean-field theory with the assumption-free numerical self-consistent field (SCF) modeling approach is applied. It is demons...

The phase transition occurring when a single polymer chain adsorbed at a planar solid surface is mechanically desorbed is analyzed in two statistical ensembles. In the force ensemble, a constant force applied to the nongrafted end of the chain (that is grafted at its other end) is used as a given external control variable. In the z-ensemble, the di...

Equilibrium structural properties of polymer brushes formed by dendritic polymer chains (dendrons) are studied by means of Scheutjens−Fleer self-consistent field (SF-SCF) modeling and scaling analysis. Limiting cases of minimal and maximal possible losses of conformational entropy corresponding to different assumptions concerning distribution of el...

We propose the quantitative mean-field theory of mechanical unfolding of a globule formed by long flexible homopolymer chain collapsed in poor solvent and subjected to an extensional force We show that with an increase in the applied force the globule unfolds as a whole without formation of an intermediate state. The value of the threshold force an...

We study the adsorption of ideal random lattice copolymers with correlations in the sequences on homogeneous substrates with two different methods: An analytical solution of the problem based on the constrained annealed approximation introduced by Morita in 1964 and the generating function technique, and direct numerical simulations of lattice chai...

We present results of numerical self-consistent field (SCF) calculations for the equilibrium mechanical unfolding of a globule formed by a single flexible polymer chain collapsed in a poor solvent. In accordance with earlier scaling theory and stochastic dynamics simulations findings we have identified three regimes of extensional deformation: (i)...

We study the adsorption of ideal random lattice copolymers with correlations in the sequences on homogeneous substrates with two different methods: An analytical solution of the problem based on the constrained annealed approximation introduced by Morita in 1964 and the generating functional (GF) technique, and direct numerical simulations of latti...

We present an analytical theory describing intramolecular conformational transition in a star-shaped polyelectrolyte (PE) molecule induced by a decrease in the solvent strength or/and increase in the ionic strength in the solution. We apply a mean-field Flory-type analysis in a box-like approximation, that is we assume fairly uniform distribution o...

Cover: The 6‐th International Symposium “Molecular Order and Mobility in Polymer Systems” was held in Saint‐Petersburg, Russia, 2–6 of June 2008. It was a continuation of the series of Symposia organized by the Institute of Macromolecular Compounds of RAS. The cover is taken from the manuscript by A. Polotsky et. al. p. 24 and shows a polyelectroly...

We present theoretical arguments and experimental evidence for a longitudinal instability in core-shell cylindrical polymer brushes with a solvophobic inner (core) block and a solvophilic outer (shell) block in selective solvents. The two-gradient self-consistent field Scheutjens-Fleer (SCF-SF) approach and Monte Carlo (MC) simulations are employed...

We study equilibrium aspects of molecular recognition of two biomolecules using idealized model systems and methods from statistical physics. Starting from the basic experimental findings we demonstrate exemplarily how an idealized coarse-grained model for the investigation of molecular recognition of two biomolecules can be developed. In addition...

The critical adsorption point (CAP) of self-avoiding walks (SAW) interacting with a planar surface with surface disorder or sequence disorder has been studied. We present theoretical equations, based on ones previously developed by Soteros and Whittington (J. Phys. A.: Math. Gen. 2004, 37, R279-R325), that describe the dependence of CAP on the diso...

The two-gradient self-consistent field Scheutjens-Fleer (SCF-SF) approach is employed for study of conformational transition occurring in molecular bottle brushes upon decrease in the solvent strength for grafted chains. In particular, the solvent strength was varied from theta to poor solvent conditions. It was found that at moderately poor solven...

Planar polymer brush formed by semirigid chains of freely jointed rigid segments and immersed into a solvent is considered. Brush collapse induced by deterioration of the solvent quality and its deformation by external normal or lateral force is studied. It is demonstrated that these three different situations can be described in the framework of t...

Using a reference system approach, we develop an analytical theory for the adsorption of random heteropolymers with exponentially decaying and/or oscillating sequence correlations on planar homogeneous surfaces. We obtain a simple equation for the adsorption-desorption transition line. This result as well as the validity of the reference system app...

We study the adsorption of homogeneous or heterogeneous polymers onto heterogeneous planar surfaces with exponentially decaying site-site correlations, using a variational reference system approach. As a main result, we derive simple equations for the adsorption-desorption transition line. We show that the adsorption threshold is the same for syste...

We study the adsorption of homogeneous or heterogeneous polymers onto heterogeneous planar surfaces with exponentially decaying site-site correlations, using a variational reference system approach. As a main result, we derive simple equations for the adsorption-desorption transition line. We show that it is preferable to have a small amount of str...

The theory of lamellar superstructures of an ABC 3‐miktoarm star terpolymer in the conditions corresponding to the strong segregation limit for linear ABC triblock terpolymer has been developed. According to the particular molecular topology (namely, the common junction point for all three blocks), the system cannot avoid volume interactions betwee...

An analytical theory for the adsorption of random heteropolymers on planar homogeneous surfaces was investigated using a reference system approach. A simple equation for the adsorption-desorption transition line was obtained. A mapping procedure which adjusts the monomer profiles for adsorbed homopolymers was also tested. The results show that in t...

A collapse of polymeric brushes in a solvent can be induced by a change in external conditions, for example, solvent quality or its temperature. The systems with following specific interactions are considered in this paper, namely, polyelectrolyte brushes, amphiphilic brushes in a mixture of incompatible solvents, and brushes with possibility of li...

The lyotropic LC transition in a polymer brush, the layer of grafted polymer chains composed of freely jointed rigid segments, was considered. It was shown that such a transition can be due to deterioration of the quality of the solvent in which the brush is placed. Depending on the segment length and grafting density, the transition can occur eith...

The theory of supercrystalline structures with lamellar and cylindrical morphologies is developed for mixtures of linear ABC triblock and ab diblock copolymers in the strong segregation limit. It was established that the behaviour of these mixtures ranges from complete immiscibility to the formation of mixed superstructures with different morpholog...

The theory of lamellar superstructures in ternary mixtures of ab and bc diblock and linear ABC triblock copolymers under the condition of strong segregation between chemically different blocks is developed. This system is considered using Alexander-de Gennes (box) and self-consistent field (SCF) models. The theory predicts the possibility of phase...

Theoretical analysis of the ability of forming mixed supercrystalline structures in the mixtures of ABC triblock copolymer with ab, bc, and ac diblock copolymers in the strong segregation limit is carried out. Effects of combined phase and microphase segregation are analysed. The possibility of changing the initial superstructure is demonstrated.

The theory of lamellar superstructures in binary mixtures of AB diblock and linear ABC triblock copolymers under the condition of strong segregation between chemically different blocks is developed. This system is considered using Alexander-de Gennes (box-model) and self-consistent field (SCF) models. The formation of a mixed lamellar superstructur...

A statistical theory of the structure and thermodynamics of a planar brush (‘accordion’) formed by bridged polymer chains containing mesogenic segments and immersed in a solvent is developed. It is shown that deformation of an accordion can lead to the formation of a two-phase structure with coexisting liquid-crystalline (LC) and swollen microphase...

The mean-field theory of liquid crystalline (LC) ordering is developed for a polymer brush immersed in a solvent. Additional attraction between neighbouring parallel mesogenic segments of the grafted chains is taken into account. It is shown that LC ordering in this brush is connected with the loss of solubility and occurs as a discrete first-order...