Research projects of Vakhtang Rostiashvili

I. Polymer melt dynamics

shematic1 project1beschriftung
We have used the Marti-Siggia-Rose functional technique as well as the self-consistent Hartree approximation to investigate the dynamics of a chain in the melt of similar chains. The integration over the collective variables of the melt can be implemented in the framework of the dynamical random phase approximation. The resulting effective action functional of the test chain is treated by making use of the self-consistent Hartree approximation. As an outcome the generalized non-Markovian Rouse-Langevin equation of the test chain is derived and its static and dynamic properties are studied. It was found that the static upper critical dimension, d = 2, discriminates between Gaussian (or screened) and non-Gaussian regimes, whereas its dynamical counterpart, d = 4, distinguishes between the simple Rouse and renormalized Rouse behavior. We have found that the Rouse mode correlation function has a stretched exponential form. The subdiffusional exponents for this regime are calculated explicitly. The theoretical results are in good agreement with Monte-Carlo simulation.

Relevant publications:

  • V.G. Rostiashvili, M. Rehkopf and T.A. Vilgis: "The Hartree approximation in dynamics of polymeric manifolds in the melt", J. Chem. Phys. 110 (1999) 639-651. here
  • V.G. Rostiashvili, M. Rehkopf and T.A. Vilgis: "Langevin dynamics of the glass forming polymer melt: Fluctuation around the random phase approximation", Eur. Phys.J. B6 (1998) 233-243. here
  • V.G. Rostiashvili, M. Rehkopf and T.A. Vilgis: "Dynamics of polymeric manifolds in melts: the Hartree approximation", Eur. Phys.J. B6 (1998) 497-501. here
  • V.G. Rostiashvili, M. Rehkopf and T.A. Vilgis: "Langevin dynamics of polymeric manifolds in melts", J. Phys.: Condens. matter 11(1999) A307 - A315. here
  • M. Rehkopf, V.G. Rostiashvili and T.A. Vilgis: "Dynamics of a polymer test chain in a glass forming matrix", J.Phys. II (France) 7 (1997) 1469-1487. here
  • V.G. Rostiashvili, N-K. Lee and T.A. Vilgis: "Collapse or swelling dynamics of homopolymer rings: Self - consistent Hartree approach", J. Chem. Phys. 118, (2003), 937. here

II. Polymer chain in a quenched random medium

diff_scal project2beschriftung
  1. The Langevin dynamics of a self-interacting chain in a quenched random medium is investigated by the generating functional (Martin-Siggia-Rose) method in the one-loop (Hartree) approximation.
  2. We have found the anomalous diffusion regime of the chain center of mass and have calculated the corresponding subdiffusive exponent.
  3. It turns out that with increasing of the disorder strength the chain center of mass as well as other Rouse modes are getting frozen, i.e. the ergodicity breaks down.
  4. Our Monte Carlo simulation results agree well with these theoretical predictions.

Relevant publications:

  • G. Migliorini, V.G. Rostiashvili, T.A. Vilgis: "Polymer chain in a quenched random medium: slow dynamics and ergodicity breaking", Eur. Phys. J. B 33, 61 - 75 (2003). here
  • A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Dynamics of a polymer in a quenched random medium: A Monte Carlo investigation", Europhys. Lett. 68, 384 - 390 (2004). here
  • V.G. Rostiashvili, T.A. Vilgis: "Localization and freezing of a Gaussian chain in a quenched random potential", J. Chem. Phys. 120, 7194 - 7205 (2004). here

III. Globular structure of a helix-coil copolymers

composition project3beschriftung
  1. We have developed a self-consistent-field theory to study transitions in a helix-coil multiblock globule. The appropriate differential equations which determine the self-consistent fields were solved numerically with finite element method.
  2. Three different phase states are found: open chain, amorphous globule and nematic liquid-crystalline (LC) globule (see the picture).
  3. The suggested theory shows a clear interplay between secondary and tertiary structures in globular homopolypeptides. Moreover, it may give a simple explanation for the formation of helix bundles in certain globular proteins.

Relevant publications:

  • C. Nowak, V.G. Rostiashvili, T.A. Vilgis: "Rod-Coil Globular Structures - Simple Models for Proteins", Macromol. Chem. Phys. 206, 112-124 (2005). here
  • C. Nowak, V.G. Rostiashvili, T.A. Vilgis: "Entropically driven transition to a liquid - crystalline polymer globule", Europhys. Lett. 77, 76-82 (2006). here
  • C. Nowak, V.G. Rostiashvili, T.A. Vilgis: "Globular structures of a helix-coil copolymer: Self-consistent treatment", J. Chem. Phys. 126, 034902 (2007). here

IV. Multiblock copolymers at selective liquid - liquid interfaces

co128n_new co128_new
Snapshots of typical configurations of a copolymer in a weak (left) and strong (right) localization limit.
  1. The consideration of the localization of a hydrophobic-polar (HP) multiblock copolymer at a selective interface is based on the mapping of the problem at hand onto a homopolymer adsorption problem. The theoretically predicted scaling behavior for chain gyration radii (parallel and perpendicular to the interface) is compared with results of Monte Carlo simulations. Our prediction are manly concerned with chain length and block length dependences.
  2. We have studied the localization kinetics. The questions which we have tried to answer: How the characteristic relaxation times in perpendicular and parallel directions are scaled with the chain and block lengths?
  3. The field-driven translocation of a HP - copolymer through the interface has been comprehensively studied. We have found (theoretically and by making use the Monte Carlo simulation) that the "capture" time of a HP - block-copolymer strongly depends on the block length and degree of the interface selectivity. This fact suggests a possible application as a new type of chromatography designed to separate complex mixtures with different block sizes of individual macromolecules.

Relevant publications:

  • A. Corsi, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Localization of a multiblock copolymer at a selective interface: Scaling predictions and Monte Carlo verification", J. Chem. Phys. 122, 094907 (2005). here
  • A. Corsi, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Copolymer adsorption kinetics at a selective liquid-liquid interface: Scaling theory and computer experiment", Europhys. Lett. 73, 204-210 (2006). here
  • A. Corsi, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Kinetics of copolymer localization at selective liquid-liquid interface", Macromolecules 39, 1234- 1244 (2006). here
  • A. Corsi, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Field-driven translocation of regular block-copolymers through a selective liquid-liquid interface", Macromolecules 39, 7117 - 7124 (2006). here
  • A. Corsi, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Multiblock copolymers at selective liquid-liquid interfaces: toward a block size chromatography", J. Polym. Sci. B 44, 2572 - 2588 (2006). here
  • A. Corsi, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Interface stability and copolymers: application to food systems", Food Hydrocolloids 21, 870 - 878 (2007). here

V. Polymer chain translocation through a nanopore

picture projekt5beschriftung
projekt5Beschreibung

Relevant publications:

  • J. L. A. Dubbeldam, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Polymer translocation through a nanopore - a showcase of anomalous diffusion", Phys. Rev. E 76, 010801(R) (2007). here
  • J. L. A. Dubbeldam, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Driven polymer translocation through a nanopore: a manifestation of anomalous diffusion", Europhys. Lett. 79, 18002 (2007). here
  • J. L. A. Dubbeldam, V.G. Rostiashvili, A. Milchev, T.A. Vilgis: "Fractional Brownian motion approach to polymer translocation: The governing equation of motion", Phys. Rev. E 83, 011802 (2011). here
  • J. L. A. Dubbeldam, V.G. Rostiashvili, A. Milchev, T.A. Vilgis: "Forced translocation of a polymer: dynamical scaling vs. MD-simulation", Phys. Rev. E (submitted). here

VI. Polymer desorption under pulling: a dichotomic phase transition

pull2 projekt6beschriftung
projekt6Beschreibung

Relevant publications:

  • S. Bhattacharya, V.G. Rostiashvili, A. Milchev, T.A. Vilgis: "Force-induced desorption of a polymer chain adsorbed on a attractive surface: Theory and Computer experiment", Macromolecules, 42, 2236 (2009). here
  • S. Bhattacharya, V.G. Rostiashvili, A. Milchev, T.A. Vilgis: "Pulling an adsorbed polymer chain off a solid surface", Eur. Phys. J, E 29, 285 (2009). here
  • S. Bhattacharya, V.G. Rostiashvili, A. Milchev, T.A. Vilgis: "Single chain adsorption under pulling: a novel dichotomic phase transition", Phys. Rev. E 79, 030802(R) (2009). here

VII. Thermal breakage of a single polymer chain

3D_big_2_zero_force slopes_and_1D
projekt7beschriftung
projekt7Beschreibung

Relevant publications:

  • A. Ghosh, D.I. Dimitrov, V.G. Rostiashvili, A. Milchev, T.A. Vilgis: "Thermal Breakage and Self-Healing of a Polymer Chain under Tensile Stress", J. Chem. Phys. 132, 204902 (2010). here
  • J. Paturej, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Polymer Chain Scission at Constant Tension- an Example of Force-Induced Collective Behavior", Europys. Lett. 94, 48003 (2011). here
  • J. Paturej, A. Milchev, V.G. Rostiashvili, T.A. Vilgis: "Thermal Degradation of Unstrained Single Polymer Chain: Non-linear Effects at Work", J. Chem. Phys. 134, 224901 (2011). here
  • A. Milchev, J. Paturej, V.G. Rostiashvili, T.A. Vilgis: "Thermal Degradation of Adsorbed Bottle-Brash Macromolecules: Molecular Dynamics Symulation", Macromolecules, 44, 3981 (2011). here
Home Research interests Research projects Publications Photo Gallery Impressum