2019 
Klochko, L., Baschnagel, J., Wittmer, J. P., & Semenov, A. N. (2019). Relaxation dynamics in supercooled oligomer liquids: From shearstress fluctuations to shear modulus and structural correlations. Journal Of Chemical Physics, 151(5).
Abstract: Static and dynamical properties of a model glassforming oligomer liquid are analyzed using molecular dynamics simulations. The temperature and system size effects are assessed for the affine shear modulus mu(A), the quasistatic shear modulus mu(sf) (obtained using the stressfluctuation relation), and the shear relaxation modulus G(t). It is found that while both mu(A) and mu(sf) are nearly independent of the system size, their variances show significant system size dependence, in particular, below the glass transition temperature Tg. It is also shown that the standard deviation of the shear modulus, delta mu(sf)(T), exhibits a pronounced peak at T approximate to Tg whose position is nearly independent of the system volume V. Moreover, the whole function delta mu(sf)(T) is nearly the same for different system sizes above the glass transition. We propose a theory which quantitatively predicts delta mu(sf)(T) at T greater than or similar to Tg and explains both its independence of V and its peak near Tg. It is also established that below Tg the variance of the affine modulus follows the standard power law, delta mu A2 proportional to 1/V, while delta mu(sf) shows anomalously a slow decrease with V as >delta mu sf2 proportional to 1/V alpha with alpha < 1. On this basis, it is argued that the studied glassforming systems must show longrange structural correlations in the amorphous state.


2018 
Klochko, L., Baschnagel, J., Wittmer, J. P., & Semenov, A. N. (2018). Longrange stress correlations in viscoelastic and glassforming fluids. Soft Matter, 14(33), 6835–6848.
Abstract: A simple and rigorous approach to obtain stress correlations in viscoelastic liquids (including supercooled liquid and equilibrium amorphous systems) is proposed. The longrange dynamical correlations of local shear stress are calculated and analyzed in 2dimensional space. It is established how the longrange character of the stress correlations gradually emerges as the relevant dynamical correlation length ? grows in time. The correlation range ? is defined by momentum propagation due to acoustic waves and vorticity diffusion which are the basic mechanisms for transmission of shear stress perturbations. We obtain the general expression defining the time and distancedependent stress correlation tensor in terms of material functions (generalized relaxation moduli). The effect of liquid compressibility is quantitatively analyzed; it is shown to be important at large distances and/or short times. The revealed longrange stress correlation effect is shown to be dynamical in nature and unconnected with static structural correlations in liquids (correlation length (s)). Our approach is based on the assumption that (s) is small enough as reflected in weak wavenumber dependencies of the generalized relaxation moduli. We provide a simple physical picture connecting the elucidated longrange fluctuation effect with anisotropic correlations of the (transient) inherent stress field, and discuss its implications.


Nyrkova, I. A., & Semenov, A. N. (2018). Selfassembling helical structures in solutions of achiral diamideester gelator molecules. Polymer, 145, 202–231.
Abstract: Selfassembling structures of amphiphilic BHPBn gelator molecules are studied theoretically using a hierarchical approach involving both allatomic computer modelling and analytical consideration at the mesoscopic lengthscale (based on statistical mechanics of chain molecules and phenomenological models). We identify the main factors governing the thermodynamic stability of different self assembling structures and their geometric parameters. The physical mechanisms leading to spontaneous chirality (parity breaking in systems of achiral molecules) and curvature of the aggregated membrane structures are elucidated. The regions of stability of both monolayer and bilayer self assembling membranes giving rise to highaspect ratio morphologies including flat and helical ribbons, tubules and nanotubes are outlined and discussed. (C) 2018 Elsevier Ltd. All rights reserved.


Nyrkova, I. A., & Semenov, A. N. (2018). The concept of strongly interacting groups in self assembly of soft matter. European Physical Journal E, 41(9).
Abstract: Amphiphilic molecules in solution typically produce structures coming from cooperative interactions of many synergetically acting functional units. If all essential interactions are weak, the structure can be treated theoretically based on a free energy expansion for small interaction parameters. However, most selfassembling soft matter systems involve strong specific interactions of functional units leading to qualitatively new structures of highly soluble micellar or fibrillar aggregates. Here we focus on the systems with the socalled strongly interacting groups (SIGs) incorporated into unimer molecules and discuss the effects of packing frustrations and unimer chirality as well as the origins of spontaneous morphological chirality in the case of achiral unimers. We describe several theoretical approaches (overcoming the limitations of weak interaction models) including the concepts of superstrong segregation, geometrical mismatch and orientational frustration. We also review some recently developed phenomenological theories of surfactant membranes and multiscale hierarchical approaches based on allatomic modeling of packing structures of amphiphilic molecules with SIGs. In particular, we discuss selfassembling structures in systems possessing simultaneously several distinct types of SIGs: solutions of betasheet oligopeptides (showing different fibrillar morphologies), aromatic diamideester molecules (forming membranes, helical ribbons and tubules), and triarylamine amide derivatives (producing lightcontrolled supramolecular nanowires).


Subbotin, A. V., & Semenov, A. N. (2018). Microcones on a liquid interface in high electric field: Ionization effects. Physics Of Fluids, 30(2).
Abstract: We formulate and explore electrohydrodynamic equations for conductive liquids taking dissociation/recombination processes into account and discover a novel type of liquid cones which carry both surface and net bulk charge and can be formed on a liquid interface in an electric field. The bulk charge is generated by the corona discharge due to a high electric field at the cone apex. We establish correlation between the cone angle and physical parameters of the liquid on the one hand and the electric current passing through the cone on the other hand. It is shown that the current strongly increases when the cone angle tends to a critical value which is a function of the dielectric permittivity of the liquid. The cone stability with respect to axially symmetric perturbations is analyzed. It is shown that the cones with apex angles close to the critical angle are likely to be stable. The effect of the imposed flow on the cone apex stability is also discussed. Published by AIP Publishing.


Subbotin, A. V., & Semenov, A. N. (2018). VolumeCharged Cones on a Liquid Interface in an Electric Field. Jetp Letters, 107(3), 186–191.
Abstract: In this study, we explore a novel type of slender conical liquid meniscus arisen in high electric field, which carries surface charge and net bulk charge of opposite sign. Stability of such dissipative structure is ensured by the balance between capillary and electrostatic forces and competition between the surface and bulk electric currents. The bulk charge is governed by the applied voltage being generated by the electric field of the cone due to dissociation/associations reactions at its apex. The effect of the physical parameters of the liquid on the microcone structure is elucidated. It is shown that the cone angle cannot exceed a critical value, which is a function of dielectric permittivity of the liquid. The electric current through the cone is found to be proportional to the square of the applied voltage. The obtained results can be applied for analysis of atomization processes of various liquids.


2017 
Armao, J. J., Nyrkova, I., Fuks, G., Osypenko, A., Maaloum, M., Moulin, E., et al. (2017). Anisotropic SelfAssembly of Supramolecular Polymers and Plasmonic Nanoparticles at the Liquid Liquid Interface. Journal Of The American Chemical Society, 139(6), 2345–2350.
Abstract: The study of supramolecular polymers in the bulk, in diluted solution, and at the solid liquid interface has recently become a major topic of interest, going from fundamental aspects to applications in materials science. However, examples of supramolecular polymers at the liquid liquid interface are mostly unexplored. Here, we describe the supramolecular polymerization of triarylamine molecules and their lighttriggered organization at a chloroform water interface. The resulting interfacial nematic layer of these 1D supramolecular polymers is further used as a template for the precise alignment of spherical gold nanoparticles coming from the water phase. These hybrid thin films are spontaneously formed in a single process, without chemical prefunctionalization of the metallic nanoparticles, and their ordering is improved by centrifugation. The resulting polymer chains and strings of nanoparticles can be coaligned with high anisotropy over very large distances. By using a combination of experimental and theoretical investigations, we decipher the full sequence of this oriented selfassembly process. In such a highly anisotropic configuration, electron energy loss spectroscopy reveals that the selfassembled nanoparticles behave as plasmonic waveguides.


Chandran, S., Handa, R., Kchaou, M., Al Akhrass, S., Semenov, A. N., & Reiter, G. (2017). Time Allowed for Equilibration Quantifies the Preparation Induced Nonequilibrium Behavior of Polymer Films. Acs Macro Letters, 6(11), 1296–1300.
Abstract: Performance and properties of materials may strongly depend on processing conditions. This is particularly so for polymers, which often have relaxation times much longer than the processing times and therefore may adopt preparation dependent nonequilibrated molecular conformations that potentially cause novel properties. However, so far it was not possible to predictably and quantitatively relate processing steps and resulting properties of polymer films. Here, we demonstrate that the behavior of polymer films, probed through dewetting, can be tuned by controlling preparation pathways, defined through a dimensionless parameter p, which is the appropriate preparation time normalized with the characteristic relaxation time of the polymer. We revealed scaling relations between p and the amount of preparationinduced residual stresses, the corresponding relaxation time, and the probability of film rupture. Intriguingly, films of the same thickness exhibited hole nucleation densities and subsequent dewetting kinetics differing by up to an order of magnitude, indicating possibilities to adjust the desired properties of polymer films by preparing them in appropriate ways.


Malkin, A. Y., Semakov, A. V., Skvortsov, I. Y., Zatonskikh, P., Kulichikhin, V. G., Subbotin, A. V., et al. (2017). Spinnability of Dilute Polymer Solutions. Macromolecules, 50(20), 8231–8244.
Abstract: Expeiments carried out on a series of seven different polymers with molecular weights varying over a wide range have allowed us to confirm that stable jets can be obtained at concentrations much below the crossover point. A jet was considered as stable if its lifetime exceeds the PlateauRayleigh time by several orders of Magnitude.,The systematic study carried out for polyethylene oxide) solutions in a wide range of high molecular weight showed that the lowest concentration at which a stable fiber can still be formed is scaled by η(2.14 +/ 0.3) or m(1:63 +/ 1.0.29). However, for the domain of not so high M, the spinnability Concentration corresponds to the onset of entanglements and scales as M0.70 +/ 0.14 with is the same as the dependence of the crossover concentration On molecular weight. The difference in the scaling exponents reflects two possible regimes of stable fiber formation in fiber spinning. These exponents are close to those obtained by Palangetic et al. [Polymer 2014, 55, 4920] for other polymer solutions in the electrospinning experiments. Several examples of spinnability at very low concentrations for other polymer solutions are demonstrated. A possibility of the formation of stable jets from dilute solutions is explained by an increase of the intermolecular interactions of extended macromolecular chains, resulting in the phase separation and leading to the formation of fibers created by oriented macromolecules. The theoretical considerations show that there are two sources of jet stabilization at low concentrations (high M), namely, the coilstretch transition and demixing of the polymer solution.


Ruscher, C., Semenov, A. N., Baschnagel, J., & Farago, J. (2017). Anomalous sound attenuation in Voronoi liquid. Journal Of Chemical Physics, 146(14).
Abstract: The physics of simple fluids in the hydrodynamic limit and notably the connection between the proper microscopic scales and the macroscopic hydrodynamical description are nowadays well understood. In particular, the three peak shape of the dynamical structure factor S(k, omega) is a universal feature, as well as the kdependence of the peak position (proportional to/k) and width proportional to k(2), the latter accounting for the sound attenuation rate. In this paper, we present a theoretical model of monodisperse fluid, whose interactions are defined via the Voronoi tessellations of the configurations [called the Voronoi liquid and first studied in Ruscher et al., Europhys. Lett. 112, 66003 (2015)], which displays at low temperatures a marked violation of the universal features of S(k,omega) with a sound attenuation rate only proportional to k. This anomalous behaviour, which apparently violates the basic symmetries of the liquid state, is traced back to the existence of a time scale which is both short enough for the viscoelastic features of the liquid to impact the relaxational dynamics and however long enough for the momentum diffusion to be substantially slower than the sound propagation on that characteristic time. Published by AIP Publishing.


Semenov, A. N., & Subbotin, A. V. (2017). Phase Separation Kinetics in Unentangled Polymer Solutions Under HighRate Extension. Journal Of Polymer Science Part BPolymer Physics, 55(7), 623–637.
Abstract: Phase separation processes following highrate extension in unentangled polymer solutions are studied theoretically. The flowinduced demixing is associated with the coilstretch transition predicted in highmolecularweight polymer solutions at highenough Weissenberg numbers. The developed meanfield theory is valid in the dilute/semidilute solution regime, where the stretched coils overlap strongly. We elucidate and discuss the main kinetic stages of the polymer/solvent separation process including (i) growth of concentration fluctuations and formation of oriented protofibrils by anisotropic spinodal decomposition; (ii) development of welldefined highly oriented and stiff fibrils forming an anisotropic network (crosslinked fiber); (iii) microphase separation and lateral collapse of the network yielding dense oriented fiber. These novel predictions are in qualitative agreement with the experimental data. (C) 2017 Wiley Periodicals, Inc.


2016 
Subbotin, A. V., & Semenov, A. N. (2016). Adsorption of flexible polyelectrolytes on charged surfaces. Soft Matter, 12(32), 6771–6787.
Abstract: Adsorption of weakly charged polyelectrolyte (PE) chains from dilute solution on an oppositely charged surface is studied using the selfconsistent meanfield approach. The structure of the adsorbed polymer layer and its excess charge are analyzed in the most important asymptotic and intermediate regimes both analytically and numerically. Different regimes of surface charge compensation by PE chains including partial and full charge inversion are identified and discussed in terms of physical parameters like the magnitude of specific shortrange interactions of PE segments with the surface, solvent quality and ionic strength. The effect of excludedvolume monomer interactions is considered quantitatively both in the marginally good and poor solvent regimes.


Subbotin, A. V., & Semenov, A. N. (2016). Phase separation in dilute polymer solutions at highrate extension. Journal Of Polymer Science Part BPolymer Physics, 54(11), 1066–1073.
Abstract: In this article the demixing instability and phase segregation in unentangled polymer solutions of semiflexible chains at highrate uniaxial extension above the coil to stretched coil transition was studied. Orientation of the stretched chains was described in terms of an effective potential field. Based on the free energy analysis it was shown that the flowinduced orientation of polymer segments could drastically reduce the energy of their steric repulsion. As a result attraction between the chains gain more importance, and this effect lead to the demixing process and eventual segregation of polymer from the solvent if the strain rate exceeds some critical value. A meanfield theory was developed to study this flowinduced phase separation effect. The phase diagrams of the system showing the spinodal and binodal transitions at different extension rates were calculated and discussed. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 10661073


2015 
Semenov, A. N. (2015). Thermodynamic nature of vitrification in a 1D model of a structural glass former. Journal Of Chemical Physics, 143(4).
Abstract: We propose a new spinglass model with no positional quenched disorder which is regarded as a coarsegrained model of a structural glassformer. The model is analyzed in the 1D case when the number N of states of a primary cell is large. For N. 8, the model exhibits a sharp freezing transition of the thermodynamic origin. It is shown both analytically and numerically that the glass transition is accompanied by a significant growth of a static length scale. pointing to the structural (equilibrium) nature of dynamical slowdown effects in supercooled liquids. (C) 2015 AIP Publishing LLC.


Semenov, A. N., & Shvets, A. A. (2015). Theory of colloid depletion stabilization by unattached and adsorbed polymers. Soft Matter, 11(45), 8863–8878.
Abstract: The polymerinduced forces between colloidal particles in a semidilute or concentrated polymer solution are considered theoretically. This study is focussed on the case of partially adsorbing colloidal surfaces involving some attractive centers able to trap polymer segments. In the presence of free polymers the particles are covered by selfassembled fluffy layers whose structure is elucidated. It is shown that the freepolymerinduced interaction between the particles is repulsive at distances exceeding the polymer correlation length, and that this depletion repulsion can be strongly enhanced due to the presence of fluffy layers. This enhanced depletion stabilization mechanism (which works in tandem with a more shortrange steric repulsion of fluffy layers) can serve on its own to stabilize colloidal dispersions. More generally, we identify three main polymerinduced interaction mechanisms: depletion repulsion, depletion attraction, and steric repulsion. Their competition is analyzed both numerically and analytically based on an asymptotically rigorous meanfield theory. It is shown that colloid stabilization can be achieved by simply increasing the molecular weight of polymer additives, or by changing their concentration.


Subbotin, A. V., & Semenov, A. N. (2015). Electrohydrodynamics of a ConeJet Flow at a High Relative Permittivity. Jetp Letters, 102(12), 815–820.
Abstract: We have proposed a new solution of the electrohydrodynamic equations describing a novel conejet flow structure formed at a conductive liquid meniscus in an electric field. Focusing on the liquids characterized by a high relative permittivity and using the slender body approximation, the conejet transition profiles and their characteristic radii are predicted in relation to the material parameters. The stable value of the cone angle is obtained using the Onsagerâs principle of maximum entropy production. Three different regimes of the conejet flow behavior are identified depending on the relative importance of capillary, viscous and inertial stress contributions. The presented complete analytical solutions for the conejet transition zone and the far jet region yield several different laws of algebraic decrease for the radius, surface charge, and electric field of the jet.


Subbotin, A. V., & Semenov, A. N. (2015). Electrohydrodynamics of stationary conejet streaming. Proceedings Of The Royal Society AMathematical Physical And Engineering Sciences, 471(2182).
Abstract: We discover novel types of stationary conejet steams emitting from a nozzle of a syringe loaded with a conductive liquid. The predicted conejetflow geometries are based on the analysis of the electrohydrodynamic equations including the surface current. The electric field and the flow velocity field inside the cone are calculated. It is shown that the electric current along the conical stream depends on the cone angle. The stable values of this angle are obtained based on the Onsagerâs principle of maximum entropy production. The characteristics of the jet that emits from the conical tip are also studied. The obtained results are relevant both for the electrospraying and electrospinning processes.


2014 
Farago, J., Semenov, A., Frey, S., & Baschnagel, J. (2014). New conserved structural fields for supercooled liquids. European Physical Journal E, 37(6).
Abstract: By considering Voronoi tessellations of the configurations of a fluid, we propose two new conserved fields, which provide structural information not fully accounted for by the usual 2point density correlation functions. One of these fields is scalar and associated with the volume of the Voronoi cell, whereas the other one, termed the âgeometric polarisationâ, is vectorial and related to the local anisotropy of the configurations. We study the static and dynamical properties of these fields in the supercooled regime of a model glassforming liquid. We show that the geometric polarisation is statically correlated to the force field, but contrary to it develops a plateau regime when the temperature is lowered. This different relaxation is related to the cage effect in glassforming liquids, which prevents a complete relaxation of the shape of the cage around particle on intermediate time scales.


Nyrkova, I., Moulin, E., Armao, J. J., Maaloum, M., Heinrich, B., Rawiso, M., et al. (2014). Supramolecular SelfAssembly and Radical Kinetics in Conducting SelfReplicating Nanowires. Acs Nano, 8(10), 10111–10124.
Abstract: By using a combination of experimental and theoretical tools, we elucidate unique physical characteristics of supramolecular triarylamine nanowires (STANWs), their packed structure, as well as the entire kinetics of the associated radicalcontrolled supramolecular polymerization process. AFM, smallangle Xray scattering, and allatomic computer modeling reveal the twocolumnar âsnowflakeâ internal structure of the fibers involving the pstacking of triarylamines with alternating handedness. The polymerization process and the kinetics of triarylammonium radicals formation and decay are studied by UVvis spectroscopy, nuclear magnetic resonance and electronic paramagnetic resonance. We fully describe these experimental data with theoretical models demonstrating that the supramolecular selfassembly starts by the production of radicals that are required for nucleation of doublecolumnar fibrils followed by their growth in doublestrand filaments. We also elucidate nontrivial kinetics of this selfassembly process revealing sigmoid time dependency and complex selfreplicating behavior. The hierarchical approach and other ideas proposed here provide a general tool to study kinetics in a large number of selfassembling fibrillar systems.


Semenov, A. N. (2014). Longrange correlation effects in directional living polymers. Soft Matter, 10(47), 9534–9561.
Abstract: The statistics of (equilibrium) living polymers including both linear chains and rings are considered theoretically. Particular attention is addressed to directional polymers characterized by an arrow along the backbone defined by its chemical structure. Thermodynamic and correlation properties of living polymers are studied both in the meanfield and in the critical scaling regimes. It is shown that living polymers with no rings, classical living polymers with rings, and directional living polymers with rings form three distinct classes characterized by different critical exponents and qualitatively different longrange correlation functions.


2013 
Semenov, A. N., & Meyer, H. (2013). Anomalous diffusion in polymer monolayers. Soft Matter, 9(16), 4249–4272.
Abstract: The tagged chain dynamics in strictly twodimensional (2D) polymer melts (where the chains are collapsed to dense spots) is considered both theoretically and by computer simulations. It is shown that the chain relaxation time in such systems scales as t(m) proportional to Nalpha with alpha approximate to 1.73 (N is the number of monomer units per chain). An extended transient regime of anomalous subdiffusion is identified at t less than or similar to t(m) where the chain centreofmass (CM) velocity autocorrelation function (VAF) scales as C(t) proportional to N(0)t(1.42). This anomalous dynamics is accounted for by the effect of the viscoelastic hydrodynamic interactions (VHI). The developed quantitative theory of the VHIcontrolled chain dynamics is in good agreement, with no parameter adjustment, with the extensive simulation data. The dynamics of polymer monolayers with frictional contact to the supporting surface is considered as well. It is shown that an external (Langevin) friction gamma leads to the asymptotic regime C(t) f proportional to (N gamma)(1.37)t(0.84) that crosses over to N(0)t(1.42) at longer t. We also present a detailed analysis of other important factors controlling the 2D chain diffusion: finite boxsize, inertial and finite compressibility effects.


Shvets, A. A., & Semenov, A. N. (2013). Effective interactions between solid particles mediated by free polymer in solution. Journal Of Chemical Physics, 139(5).
Abstract: Effective potentials of interaction between solid nonadsorbing surfaces in semidilute or concentrated polymer solutions are calculated using two approaches: the numerical selfconsistentfield theory (SCFT) and the analytical theory generalizing the groundstate dominance approximation by taking into account the finite chainlength (chainend) effects (GSDE). A good agreement between the two approaches is demonstrated within the natural region of validity of the asymptotically exact GSDE theory. It is shown that in most cases the interaction potentials involve the shortrange depletion attraction which is replaced by the polymermediated repulsion at longer separations ranging from roughly 10 xi to 3R(g) (xi is the concentration correlation length and Rg is the polymer coil gyration radius). For a given polymer concentration and molecular weight the highest repulsion energy barrier, Um, is predicted for xi/Rg similar to 0.2 and in the thetasolvent conditions. The fluctuationinduced (antiCasimir) polymermediated repulsion forces are analyzed as well. It is shown that the overall polymermediated repulsion energy between naked spherical particles of radius Rc = 200 nm is typically not enough for their kinetic stabilization. There are, however, a few special cases where colloidal stability can be imparted by free polymers only. (C) 2013 AIP Publishing LLC.


2012 
Farago, J., Meyer, H., Baschnagel, J., & Semenov, A. N. (2012). Hydrodynamic and viscoelastic effects in polymer diffusion. Journal Of PhysicsCondensed Matter, 24(28).
Abstract: We develop a fluctuating hydrodynamics approach to study the impact of the hydrodynamic and viscoelastic interactions on the motion of the center of mass of a polymer as well as on the relaxation of Rouse modes, either in a Theta solvent or in a melt of identical unentangled chains. We show that this method allows us to describe the effect of hydrodynamic interactions beyond the Zimm (for a single chain in a Theta solvent) or the Rouse models (for an unentangled melt). In the latter case, we recover the same important effect of the viscoelastic hydrodynamic interactions on the centerofmass diffusion, first described in Farago et al (2011 Phys. Rev. Lett. 107 178301).


Farago, J., Meyer, H., Baschnagel, J., & Semenov, A. N. (2012). Modecoupling approach to polymer diffusion in an unentangled melt. II. The effect of viscoelastic hydrodynamic interactions. Physical Review E, 85(5, 1).
Abstract: A modecoupling theory (MCT) version (called hMCT thereafter) of a recently presented theory [Farago, Meyer, and Semenov, Phys. Rev. Lett. 107, 178301 (2011)] is developed to describe the diffusional properties of a tagged polymer in a melt. The hMCT accounts for the effect of viscoelastic hydrodynamic interactions (VHIs), that is, a physical mechanism distinct from the densitybased MCT (dMCT) described in the first paper of this series. The two versions of the MCT yield two different contributions to the asymptotic behavior of the centerofmass velocity autocorrelation function (c.m. VAF). We show that in most cases the VHI mechanism is dominant; for long chains and prediffusive times it yields a negative tail alphaN(1/2)t(3/2) for the c. m. VAF. The case of nonmomentumconserving dynamics (Langevin or Monte Carlo) is discussed as well. It generally displays a distinctive behavior with two successive relaxation stages: first N(1)t(5/4) (as in the dMCT approach), then N(1/2)t(3/2). Both the amplitude and the duration of the first t(5/4) stage crucially depend on the Langevin friction parameter gamma. All results are also relevant for the early time regime of entangled melts. These slow relaxations of the c.m. VAF, thus account for the anomalous subdiffusive regime of the c. m. mean square displacement widely observed in numerical and experimental works.


Farago, J., Semenov, A. N., Meyer, H., Wittmer, J. P., Johner, A., & Baschnagel, J. (2012). Modecoupling approach to polymer diffusion in an unentangled melt. I. The effect of density fluctuations. Physical Review E, 85(5, 1).
Abstract: We quantitatively assess the effect of density fluctuation modes on the dynamics of a tagged polymer in an unentangled melt. To this end, we develop a densitybased modecoupling theory (dMCT) using the MoriZwanzig approach and projecting the fluctuating force onto pairdensity fluctuation modes. The effect of dynamical density fluctuations on the centerofmass (c.m.) dynamics is also analyzed based on a perturbative approach and we show that dMCT and perturbation techniques yield identical results. The c. m. velocity autocorrelation function (c. m. VAF) exhibits a slow power law relaxation in the time range between the monomer time t(1) and the Rouse relaxation time t(N). We obtain an analytical expression for the c. m. VAF in terms of molecular parameters. In particular, the c. m. VAF scales as N(1)t(5/4) (where N is the number of monomer units per chain) in the relevant time regime. The results are qualitatively accounted for by the dynamical correlation hole effect. The predicted t(5/4) dependence of the c. m. VAF is supported by data of nonmomentumconserving computer simulations. However, the comparison shows that the theory significantly underestimates the amplitude of the effect. This issue is discussed and an alternative approach is addressed in the second part of this series [Farago et al., Phys. Rev. E 85, 051807 (2012), the following paper].


Lazutin, A. A., Semenov, A. N., & Vasilevskaya, V. V. (2012). Polyelectrolyte Complexes Consisting of Macromolecules With Varied Stiffness: Computer Simulation. Macromolecular Theory And Simulations, 21(5), 328–339.
Abstract: Monte Carlo simulations are employed in order to analyze the structure of polyelectrolyte complexes consisting of two identical but oppositely charged macroions with varying chain stiffness. It is shown that two complex structures can arise depending on the stiffness of the constituent chains. Stiff chains are organized into a ladder structure in which chains are located parallel to each other and monomeric units are arranged into ionic pairs according to their position in the chain. Flexible chains form a globular scrambledegg structure with a disordered position of monomer units. The conformational transition between the two structures proceeds as a phase transition.


Meyer, H., & Semenov, A. N. (2012). Anomalous Dynamics in 2D Polymer Melts. Physical Review Letters, 109(24).
Abstract: The dynamics in polymer monolayers where chains are strongly confined and adopt 2D conformations are drastically different to those in the bulk. It is shown that viscoelastic hydrodynamic interactions play a major role defining the anomalous chain diffusion properties in such systems where chains cannot cross each other. We developed a quantitative analytical theory of polymer subdiffusion in 2D systems revealing a complex behavior controlled by a delicate interplay of inertial, viscoelastic hydrodynamic interactions, finiteboxsize and frictional effects. The theory is fully supported by extensive momentumconserving and Langevin moleculardynamics simulation data explaining the highly cooperative character of 2D polymer motions. DOI: 10.1103/PhysRevLett.109.248304


Semenov, A. N., Farago, J., & Meyer, H. (2012). Lengthscale dependent relaxation shear modulus and viscoelastic hydrodynamic interactions in polymer liquids. Journal Of Chemical Physics, 136(24).
Abstract: A quantitative theory of hydrodynamic interactions in unentangled polymer melts and concentrated solutions is presented. The study is focussed on the preRouse transient time regimes (t < tau(R), the Rouse relaxation time) where the hydrodynamic response is governed mainly by the viscoelastic effects. It is shown that transient viscoelastic hydrodynamic interactions are not suppressed (screened) at large distances and are virtually independent of polymer molecular mass. A number of transient regimes of unusual and qualitatively different behavior of isotropic and anisotropic hydrodynamic response functions are elucidated. The regimes are characterized in terms of two main lengthscale dependent characteristic times: momentum spreading time tau(i) proportional to r(4/3) and viscoelastic time tau* proportional to r(4). It is shown that for t > tau(i) the viscoelastic hydrodynamic interactions can be described in terms of the time or length scale dependent effective viscosity which, for t < tau(R) and/or for r < Rcoil, turns out to be much lower than the macroscopic âpolymerâ viscosity eta(m). The theory also involves a quantitative analysis of the lengthscale dependent stress relaxation in polymer melts. The general predictions for hydrodynamic interactions in thermostated systems with Langevin friction are obtained as well. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730166]


2011 
Farago, J., Meyer, H., & Semenov, A. N. (2011). Anomalous Diffusion of a Polymer Chain in an Unentangled Melt. Physical Review Letters, 107(17).
Abstract: Contrary to common belief, hydrodynamic interactions in polymer melts are not screened beyond the monomer length and are important in transient regimes. We show that viscoelastic hydrodynamic interactions (VHIs) lead to anomalous dynamics of a tagged chain in an unentangled melt at t < t(N), the Rouse time. The centerofmass (c.m.) meansquare displacement is enhanced by a large factor increasing with chain length. We develop a theory of VHIcontrolled chain dynamics yielding a negative c.m. velocity autocorrelation function which agrees with our molecular dynamics simulations without any fitting parameter. It is also shown that Langevin friction strongly affects the shortt c.m. dynamics, also captured by our theory. The transient VHI effects thus provide the dominant contribution to the subdiffusive c.m. motion universally observed in simulations and experiments.


Semenov, A. N., & Nyrkova, I. A. (2011). Endgrowth/evaporation living polymerization kinetics revisited. Journal Of Chemical Physics, 134(11).
Abstract: Endgrowth/evaporation kinetics in living polymer systems with âassociationreadyâ free unimers (no initiator) is considered theoretically. The study is focused on the systems with long chains (typical aggregation number N >> 1) at long times. A closed system of continuous equations is derived and is applied to study the kinetics of the chain length distribution (CLD) following a jump of a parameter (Tjump) inducing a change of the equilibrium mean chain length from N(0) to N. The continuous approach is asymptotically exact for t >> t(1), where t(1) is the dimer dissociation time. It yields a number of essentially new analytical results concerning the CLD kinetics in some representative regimes. In particular, we obtained the asymptotically exact CLD response (for N >> 1) to a weak Tjump (epsilon = N(0)/N – 1 << 1). For arbitrary Tjumps we found that the longest relaxation time t(max) = 1/gamma is always quadratic in N (gamma is the relaxation rate of the slowest normal mode). More precisely t(max) proportional to 4N(2) for N(0) < 2N and t(max) proportional to NN(0)/(1 – N/N(0)) for N(0) > 2N. The mean chain length N(n) is shown to change significantly during the intermediate slow relaxation stage t(1) << t << t(max). We predict that N(n)(t) – N(n)(0) proportional to root t in the intermediate regime for weak (or moderate) Tjumps. For a deep Tquench inducing strong increase of the equilibrium N(n) (N >> N(0) >> 1), the mean chain length follows a similar law, N(n)(t) proportional to root t, while an opposite Tjump (inducing chain shortening, N(0) >> N >> 1) leads to a powerlaw decrease of N(n): N(n)(t) proportional to t(1/3). It is also shown that a living polymer system gets strongly polydisperse in the latter regime, the maximum polydispersity index r = N(w) /N(n) being r* approximate to 0.77N(0)/N >> 1. The concentration of free unimers relaxes mainly during the fast process with the characteristic time t(f) similar to t(1)N(0)/N(2). A nonexponential CLD dominated by short chains develops as a result of the fast stage in the case of N(0) = 1 and N >> 1. The obtained analytical results are supported, in part, by comparison with numerical results found both previously and in the present paper. (C) 2011 American Institute of Physics. [doi:10.1063/1.3560661]


2010 
Nyrkova, I. A., & Semenov, A. N. (2010). Twisted surfactant structures: an advanced theoretical model. Soft Matter, 6(3), 501–516.
Abstract: We analyze twisted membrane structures of chiral surfactants in the framework of the equilibrium theoretical approach based on a continuous elastic model. It is shown that both the surfactant ribbon width and its twist pitch can be defined by equilibrium factors, including the chiral elastic energy. We show however that the theoretically predicted dependencies of the ribbon geometrical parameters on the enantiomeric excess (ee) obtained for the unilamellar liquid membrane model are in partial, but qualitative disagreement with experimental data. The surfactant membrane model is then generalized in two directions: (i) we consider also multilamellar ribbons (of many bilayers), (ii) we allowed for the crystalline (Lbeta) state of the bilayers. The multibilayer crystalline structure of selfassembling twisted ribbons is consistent with recent results of Xray and other experimental studies on gemini surfactants, and, simultaneously, the theory developed for such ribbons yields the eedependencies of the twisted ribbon width and pitch that are in reasonable agreement with the data based on TEM images.


Semenov, A. N. (2010). BondVector Correlation Functions in Dense Polymer Systems. Macromolecules, 43(21), 9139–9154.
Abstract: It is wellknown that homopolymer chains do not exactly follow the Gaussian statistics even in the melt state. In particular, orientations of two bonds l(1) and of the same chain in a concentrated polymer system are always correlated even when they are separated by a long segment of s >> 1 units: <(l) under bar (1) . (l) under bar (2)>(s) = C(s) similar to l/s(3/2). It is important to know how these orientational correlations are distributed in space, i.e. how <(l) under bar (1) . (l) under bar (2)> depends on the distance (r) under bar between the bonds.(1) An unexpected feature is revealed in the present paper: it is shown that the distancedependent bondvector correlation function K(r) = <(l) under bar (1) . (l) under bar (2)>(r) is extremely sensitive to the definition of r. Depending on the definition, K(r) for r >> b (b is the monomer size) can be either significantly lower, or significantly higher than the positionaveraged correlator C(s) with s similar to r(2)/b(2) corresponding to a given distance r. We propose an âinvariantâ definition of the intrachain orientational correlation function and show that it is related to the formfactor of a single chain. A quantitative link between the orientational and positional correlations in polymer melts is thus discovered. We also have found a quantitative relationship between the intrachain and interchain correlation functions. It is shown that the interchain orientational correlation function (for bonds of different chains) is longrange and follows the l/r(4) scaling law in the case of infinite chains.


Semenov, A. N., & Subbotin, A. V. (2010). Theory of SelfAssembling Structures of Model Oligopeptides. Macromolecules, 43(7), 3487–3501.
Abstract: Aggregation and micelle formation in dilute solutions of amphiphilic oligopeptides (Ala(nH) Asp(nP)) is considered theoretically. It is shown that the peptides can selfassemble forming micelles of different morphologies in the regime where Asp units are negatively charged. The micelles are stable thermodynamically if a sufficient amount of monovalent salt is added (the âsalting inâ effect). The thermodynamic stability of the micelles also strongly depends on pH and on the size delta of added cations. The micelles get destabilized as their surface charge (due to Asp units) decreases at low pH or low ionic strength I(infinity). A larger cation size delta also results in aggregation (precipitation) of the micelles. The aggregation process can be kinetically arrested clue to electrostatic repulsion even in the regime of weakly charged Asp units. The kinetically defined size R of the aggregates strongly depends on the effective peptide/water interfacial tension gamma and on the Debye length r(D): R decreases as either gamma or r(D) is increased.


2009 
Nyrkova, I. A., & Semenov, A. N. (2009). Theory of chiral recognition in DNA condensation. Soft Matter, 5(5), 979–989.
Abstract: Collapse of long chiral Amacromolecules assisted by a chiral Badditive (where B associates with A) is considered theoretically. Based on a simple model we demonstrate that the compaction activity of B molecules can strongly depend on the sense of their chirality. The theory is applied to the DNA compaction in the presence of conformationally rigid divalent enantiomeric cations (SS and RR enantiomers).(1) It is shown that both chiral isomers of the dications adsorb well on the DNA surface, but the SS and RRbinding energies are different, reflecting their unequal stereocomplementarities (the âboltandnutâ effect). Unexpectedly, we find that the compaction activity of less strongly bound SS dication is significantly higher than that of its RR enantiomer. Moreover, the RR molecules tend to replace the SS enantiomers adsorbed on the DNA, so that SS compaction ability is significantly reduced in the presence of RR isomers. The theory thus provides a basis for explanation of recently observed dramatic stereoisomeric selectivity and antagonistic effects in DNA compaction.(1) The revealed chiral discrimination effects may serve as selection mechanisms leading to natural homochirality.


Semenov, A. N. (2009). Theory of Cluster Formation in Homopolymer Melts. Macromolecules, 42(17), 6761–6776.
Abstract: A physical mechanism of micelle formation in homopolymer systems is elucidated. The mechanism is applicable in particular to melts of stereoisomeric polymers, for example, polystyrene. It is hinged on aggregation and crystallization of occasional atypical stereoregular fragments of mostly irregular (atactic) polymer chains. Phase diagrams involving the regimes of lamellar, tapelike, and disklike semicrystalline micelles are obtained and discussed. The possible relevance of the theory to the puzzling anomalous cluster phenomena observed in homopolymer melts (lowfrequency solidlike rheological behavior; lowq excess light scatteringFischer cluster modes) is discussed as well.


2008 
Maresov, E. A., & Semenov, A. N. (2008). Mesoglobule Morphologies of Amphiphilic Polymers. Macromolecules, 41(23), 9439–9457.
Abstract: A statistical theory of finitesized aggregates and domain structures in dilute solutions of amphiphilic macromolecules (homopolymers or copolymers) is developed. A minimalist model involving, essentially, two types of chemical groups (insoluble H and soluble P) is studied in the regime where polymer tends to phase separate, forming rather dense amorphous particles with low Surface energy. The surface tension and the elastic bending moduli of the polymer/solvent interface are obtained and are related to the molecular parameters. The Gaussian modulus kappa(G) is predicted to be negative; typically vertical bar kappa(G)vertical bar is smaller than the mean bending modulus kappa(2). It is shown that the condensed polymer phase can remain dense, homogeneous, and stable with respect to microphase separation even as the surface tension decreases down to zero (or below it). Stable large aggregates of welldefined size are predicted in this regime. The size of aggregates and their shape depend on surface tension gamma, the spontaneous bending modulus kappa(1), and the ratio kappa(G)/kappa(2). We show that bicontinuous morphologies (rather than colloidally stable polymer mesoglobules) are thermodynamically favorable for small vertical bar kappa(G vertical bar). We present a quantitative argument showing that the gyroid structure is more favorable than other bicontinuous morphologies (primitive cubic and double diamond). The gammakappa(1) phase diagrams showing the regions of stability of different morphologies are obtained. Two types of spherical rnesoglobules are predicted, namely equilibrium and metastable globules whose sizes are shown to be essentially different: they depend on kappa(1) in qualitatively different ways. Recent experimental data on mesoglobule formation in solutions of thermosensitive amphiphilic polymers are discussed in the theoretical light.


Nunez, E., Clark, J. C. G., Cheng, W., Best, A., Floudas, G., Semenov, A. N., et al. (2008). Thermodynamic, structural, and nanomechanical properties of a fluorous biphasic material. Journal Of Physical Chemistry B, 112(21), 6542–6549.
Abstract: The dynamics of the amphiphilic semifluorinated F(CF2)(12)(CH2)(12)H (F12H12) alkane that undergoes two condensed phase transitions have been investigated by Brillouin light spectroscopy, shear rheometry, small(SAXS) and wideangle (WAXS) Xray scattering, and thermodynamic PVT measurements. The solid (I)solid (II) transition (T,) is marked by a stronger temperature dependence of the sound velocity in phase II and by a 2 orders of magnitude drop of the shear modulus. Between the T, and the melting transition (Tm), the presence of two phonons implies a coexistence of solid (II) and amorphous (liquid) regions in the submicrometer range at thermal equilibrium as revealed by the SAXS pattern of a single reflection superimposed on a very broad amorphous halo. This intriguing finding of a transient, very slow (over 10 h) solid/liquid coexistence within phase II is rationalized by a twostage mechanism for melting of the smectic phase (II) of F12H12. A refinement of the known packing motifs for the two solidstate structures is proposed.


2004 
Abramchuk, S. S., Semenov, A. N., & Khokhlov, A. R. (2004). Binary polymer mixtures in selective solvents: Interfacial structure. Macromolecular Theory And Simulations, 13(1), 64–72.
Abstract: The interaction of a large polymer droplet (formed by a poorly soluble polymer A) with a soluble polymer additive (polymer B) is investigated in the framework of a meanfield approach. We found that polymer B may tend to adsorb on the surface of the droplet even when it is immiscible with polymer A in the droplet and is soluble in the solvent surrounding the droplet. We calculated the concentration profiles of both polymers A and B near the interface and established conditions for polymer B accumulation at the interface. The dependencies of the surface tension and the interfacial excess of polymer B on its bulk concentration are also calculated. We found that even a very small amount of homopolymer B additive may result in a significant reduction of the interfacial tension (by a factor of 2). The effect is stronger if the additive is more flexible than the insoluble polymer.


Semenov, A. N. (2004). Core/shell structures of proteinlike copolymers: Are finite aggregates thermodynamically stable? Macromolecules, 37(1), 226–237.
Abstract: We propose a theory of aggregation in solutions of amphiphilic copolymers consisting mostly of insoluble H (hydrophobic) units with a small fraction of soluble (P, polar) monomer units. When P units are arranged along the sequence in a periodic (regular) fashion, the resultant HP copolymers are essentially insoluble: they precipitate. The main result is that finite aggregates of HP copolymers can be made stable by an appropriate smart arrangement of the same number of soluble P units in the chemical sequence. An analytical approach yielding the thermodynamic quantities of Hcore/Pshell copolymer structures in the weak stretch limit is developed. We show that different types of copolymer aggregates and microdomain structures can be thermodynamically stable depending on the copolymer chemical sequence. The relationship between the blocklength distribution and copolymer aggregation is illustrated by a few phase diagrams. Copolymers that can form stable finite aggregates with Hcore/Pshell structure (including singlechain globules) are often referred to as the proteinlike copolymers. Thus, the present theory sheds a new light as to the essential features of proteinlike copolymer sequences.


Wittmer, J. P., Meyer, H., Baschnagel, J., Johner, A., Obukhov, S., Mattioni, L., et al. (2004). Long range bondbond correlations in dense polymer solutions. Physical Review Letters, 93(14).
Abstract: The scaling of the bondbond correlation function P1(s) along linear polymer chains is investigated with respect to the curvilinear distance s along the flexible chain and the monomer density rho via Monte Carlo and molecular dynamics simulations. Surprisingly, the correlations in dense threedimensional solutions are found to decay with a power law P1(s)similar tos(omega) with omega=3/2 and the exponential behavior commonly assumed is clearly ruled out for long chains. In semidilute solutions, the density dependent scaling of P1(s)approximate tog(0)(omega)(s/g)(omega) with omega(0)=22nu=0.824 (nu=0.588 being Floryâs exponent) is set by the number of monomers g(rho) in an excluded volume blob. Our computational findings compare well with simple scaling arguments and perturbation calculation. The powerlaw behavior is due to selfinteractions of chains caused by the chain connectivity and the incompressibility of the melt.


2003 
Govorun, E. N., Khokhlov, A. R., & Semenov, A. N. (2003). Stability of dense hydrophobicpolar copolymer globules: Regular, random and designed sequences. European Physical Journal E, 12(2), 255–264.
Abstract: Stability of dense globular structures formed by amphiphilic copolymers consisting of hydrophobic (insoluble) units and a small fraction of single polar (soluble) monomer units is considered in the meanfield approximation for different types of unit distributions along the chain. Polar (P) units are located in a relatively thin surface layer due to their strong repulsion from hydrophobic (H) monomer units. We compared globules formed by different copolymer sequences with the same gross numbers of P and Hunits: regular HPsequences (Punits separated by equal Hblocks), random copolymers (uncorrelated positions of Punits, i.e. Flory distribution of Hblock lengths), proteinlike (PL) sequences (designed sequences involving both long Hblocks dominating by total mass, and short blocks dominating by number). We showed that PLglobules are more stable (lower free energy) and are characterized by a higher temperature of the coiltoglobule transition when compared with the other sequences mentioned above. We also considered HPHcopolymers consisting of one long and many short hydrophobic blocks; we showed that it is these sequences that yield the dense globules corresponding to the lowest free energy.


Semenov, A. N., & Johner, A. (2003). Theoretical notes on dense polymers in two dimensions. European Physical Journal E, 12(3), 469–480.
Abstract: Two models of dense twodimensional (2d) polymers are considered: (1) when chain intersections in 2d are totally forbidden, and (2) when they are allowed to some extent. It is shown that both polymer chain statistics and dynamics are entirely different for the two models. In the first case studied by Duplantier in 1986 polymer chains are essentially segregated and are characterized by nonclassical gamma exponents. The contact line between segregated chains is fractal which leads to an unusual demixing behavior in 2d blends. In the second case (crossings are allowed) polymer coils are overlapping and show meanfield statistics with logarithmic corrections. The correlation function of concentration fluctuations in this system is predicted to exhibit a universal long range power tail (1/r(4)) which is due to nonmeanfield effects. The dynamical behavior of the two models is even more drastically different: The first model is characterized by a relatively fast dynamics with conformational relaxation time t(N)proportional toN(15/18) (i.e. t(N) is slightly shorter than the Rouse time proportional to N2). On the other hand an exponentially slow dynamics is predicted for model 2 (with 3d entanglements).


2002 
Semenov, A. N. (2002). Adsorption of a semiflexible wormlike chain. European Physical Journal E, 9(4), 353–363.
Abstract: Adsorption of ideal polymers with stiff backbone onto a flat surface is considered theoretically. Both scaling approach and quantitative theory are developed. We predict a selfsimilar monomer concentration profile c(x) similar to x(4/3) near the surface (when the distance to the surface x is much smaller than the chain persistence length l/2). The typical conformation of a weakly adsorbed chain can be viewed as a sequence of alternating flat (2dimensional) trains of wormlike short loops (flat blobs) and coillike (3dimensional) loops forming a triplelayer structure: contact layer (x < Delta) of adsorbed fragments virtually laid on the surface, proximal layer (Delta < x < l) of flat blobs, and more dilute distal corona layer (x > l). Here Delta defines the range of monomer/surface attraction, Delta much less than l. The adsorption transition is continuous. However, its relative width DeltaT/T* is small (T* is the adsorption temperature, DeltaT is the relevant temperature interval): DeltaT/T* similar to (Delta/l)(4/3), i.e. a discontinuous transition in the limit Delta/l Â> 0.


2000 
Clement, F., Johner, A., Joanny, J. F., & Semenov, A. N. (2000). Stress relaxation in telechelic gels. 1. Sticker extraction. Macromolecules, 33(16), 6148–6158.
Abstract: We discuss the nonlinear rheology of telechelic gels formed by triblock copolymers with short hydrophobic end blocks (the stickers). In this first paper, we merely study the variation of the extraction time of a sticker from a hydrophobic aggregate with the chain tension. Using a model potential that binds the sticker/chain junction point to the aggregate/water interface, we explicitly show that the extraction time only depends on the chain tension at the junction point. The results are extended to more realistic potentials by heuristic arguments. At this level of description various effects (curvature of the aggregate, sticker flexibility, impenetrable aggregate constraint) can also be accounted for.

