Institute of Biochemical Physics

Moscow, Russia

Institute of Biochemical Physics

Moscow, Russia
SEARCH FILTERS
Time filter
Source Type

News Article | May 3, 2017
Site: www.materialstoday.com

Russian researchers believe that they have solved the mystery of why fullerite nanocomposites are so ultrahard [Kvashnina et al., Carbon 115 (2017) 546]. Nearly 20 years ago, a team of scientists at the Technological Institute for Superhard and Novel Carbon Materials led by Vladimir Blank synthesized a material based on polymerized fullerite with outstanding stiffness and hardness called ‘tisnumit’. Fullerite is a molecular crystal lattice made up of fullerene molecules – hollow spheres of carbon atoms. But the atomic structure of fullerite and the origin of its exceptional mechanical properties remained a mystery. Now a team of researchers from the same institute, along with colleagues from Moscow Institute of Physics and Technology, Skolkovo Institute of Science and Technology, Emanuel Institute of Biochemical Physics, and the National University of Science and Technology, has come up with a new model of fullerite, which closely matches experimental data. The researchers suggest that when the fullerite is compressed at high temperature, some of the fullerenes transform into polycrystalline diamond while the rest remains in a compressed state (SH-phase). “The amorphous structure of ultrahard fullerite led us to assume that the compressed polymerized fullerite is surrounded by an amorphous shell made of carbon atoms with diamond-like sp3 bonds, which does not allow the structure to expand,” explains researcher Alexander G. Kvashnin. In other words, fullerite could be considered as a grain of nanocomposite with a shell of diamond. The fullerite grains are arranged in a period pattern in single crystal diamond like raisins in a cake, says Kvashnin. “It is known from the experiments and theory, that a material in a compressed state will display greater mechanical properties compared to relaxed state,” he explains. “In this nanocomposite with nanoparticles in the SH-phase clamped in a diamond-like amorphous matrix, the improved mechanical properties remain preserved.” Those mechanical properties include ultrahigh mechanical stiffness, higher even than that of diamond. If such outstanding properties could be realized in materials that could be readily synthesized, it could lead to mechanical parts with reduced wear and longer lifetimes in many industries. But such ultrahigh hard materials, which are likely to require high pressures to produce, could be difficult to handle. Kvashnin believes the next step forward is to try to synthesize the new material under different high pressure and temperature conditions and investigate its properties. Researchers around the world are looking anew at ultrahard carbon and Kvashnin hopes their new model will help understand these exceptional materials.


Aliev M.A.,Institute of Biochemical Physics | Kuzminyh N.Y.,Institute of Biochemical Physics
Physica A: Statistical Mechanics and its Applications | Year: 2011

A two or more chemically different homopolymers attached to a single junction point form a macromolecule of miktoarm star copolymer. The model of such copolymer composed of an arbitrary number of types of homopolymer arms is considered. The lengths distributions of arms are assumed to be arbitrary, provided that average length of an each arm is long enough. The algorithm is suggested to find the contributions into the Landau free energy of this copolymer melt which are necessary to obtain a phase diagram in weak segregation regime. Using this algorithm the contributions are found up to the fourth order. The phase diagrams have been constructed for the simple model of AB 2 copolymer melt whose macromolecules consist of polydisperse A-block and two monodisperse B-blocks. © 2011 Elsevier B.V. All rights reserved.


Aliev M.A.,Institute of Biochemical Physics
Modern Physics Letters B | Year: 2015

The analytical expressions have been obtained to describe the dependence of spinodal curve at which isotropic state of polydisperse melt of semiflexible diblock copolymer becomes unstable with respect to formation of nematic state on the polydispersity indices of the blocks, parameters of anisotropic interactions, and flexibility of blocks. The flexibility of blocks is taken into account within discrete worm-like chain model, lengths of blocks are assumed to be distributed by the Schulz-Zimm distribution. It is shown that increase of degree of polydispersity of blocks yields the increase of nematic spinodal temperature. © 2015 World Scientific Publishing Company.


Zabrodin A.,Institute of Biochemical Physics
Journal of Geometry and Physics | Year: 2011

Intertwining operators for infinite-dimensional representations of the Sklyanin algebra with spins ℓ and -ℓ-1 are constructed using the technique of intertwining vectors for elliptic L-operator. They are expressed in terms of elliptic hypergeometric series with operator argument. The intertwining operators obtained (W-operators) serve as building blocks for the elliptic R-matrix which intertwines tensor product of two L-operators taken in infinite-dimensional representations of the Sklyanin algebra with arbitrary spin. The Yang-Baxter equation for this R-matrix follows from simpler equations of the star-triangle type for the W-operators. A natural graphic representation of the objects and equations involved in the construction is used. © 2011 Elsevier B.V.


Aliev M.A.,Institute of Biochemical Physics
Molecular Physics | Year: 2016

The isotropic-to-nematic phase transition in a melt of semi-flexible homopolymers with length polydispersity have been considered within the Landau–de Gennes approach. The number of monomer units in chain is assumed to be a random variable distributed by the Schulz–Zimm distribution; the stiffness of macromolecules has been taken into account within discrete worm-like chain model. It was found that increase of polydispersity yields the increase of the temperature of the isotropic–nematic transition. © 2016 Taylor & Francis


Aliev M.A.,Institute of Biochemical Physics | Kuzminyh N.Y.,Institute of Biochemical Physics
Journal of Chemical Physics | Year: 2015

The stability limits of the isotropic state of melt of rod-rod AB polydisperse diblock copolymer have been studied within weak segregation theory. The number of units in A block is assumed to be a random variable distributed by the Schulz-Zimm distribution. Inspection of the spinodal curves shows that the copolymer melt with polydisperse rigid blocks is less stable with respect to formation of the nematic and microphase separated states than the monodisperse melt. The values of ratios between strengths of isotropic and anisotropic interactions in the system strongly influences the forms of isotropic-nematic boundary curves. © 2015 AIP Publishing LLC.


Zabrodin A.,Institute of Biochemical Physics
Complex Analysis and Operator Theory | Year: 2010

The partition function for a canonical ensemble of 2D Coulomb charges in a background potential (the Dyson gas) is realized as a vacuum expectation value of a group-like element constructed in terms of free fermionic operators. This representation provides an explicit identification of the partition function with a tau-function of the 2D Toda lattice hierarchy. Its dispersionless (quasiclassical) limit yields the tau-function for analytic curves encoding the integrable structure of the inverse potential problem and parametric conformal maps. A similar fermionic realization of partition functions for grand canonical ensembles of 2D Coulomb charges in the presence of an ideal conductor is also suggested. Their representation as Fredholm determinants is given and their relation to integrable hierarchies, growth problems and conformal maps is discussed. © 2010 Birkhäuser / Springer Basel AG.


Aliev M.A.,Institute of Biochemical Physics | Kuzminyh N.Yu.,Institute of Biochemical Physics | Ugolkova E.A.,RAS Institute of Chemistry
Physica A: Statistical Mechanics and its Applications | Year: 2013

The stability limits of the homogeneous state of melts of rod-coil RC, RC2, and CRC polydisperse block copolymers have been investigated in the framework of the weak segregation theory. It was assumed that the number of units in either the rod-like R or the flexible C block is a random variable distributed by the Schulz-Zimm distribution. Inspection of the spinodal curves shows that the copolymer melts with polydisperse rigid blocks are less stable with respect to formation of the nematic state than melts with the monodisperse ones. If flexible C blocks are polydisperse the homogeneous state of a rod-coil melt is less stable against microphase separation than the homogeneous state of monodisperse melt of the same architecture. © 2013 Elsevier B.V. All rights reserved.


Tsvetkov N.A.,Korea Advanced Institute of Science and Technology | Larina L.L.,Korea Advanced Institute of Science and Technology | Shevaleevskiy O.,Institute of Biochemical Physics | Al-Ammar E.A.,King Saud University | Ahn B.T.,Korea Advanced Institute of Science and Technology
Progress in Photovoltaics: Research and Applications | Year: 2012

A barrier layer of undoped TiO 2 was deposited on the Nb-doped TiO 2 electrode to suppress the recombination at the Nb-doped TiO 2/dye-electrolyte interface for highly efficient dye-sensitized solar cells (DSCs). The Nb content in TiO 2 was varied in a range of 0.7-3.5 mol% to modify the TiO 2 energy-band structure. Nb-doped TiO 2/dye interfaces were characterized by a combination of ultraviolet photoemission spectroscopy and optical absorption spectroscopy measurements, allowing the determination of the conduction band minimum (CBM) of the TiO 2 electrode and the lowest unoccupied molecular orbital of the N719 dye. The lowering of TiO 2 CBM by Nb doping induced the increase in short-circuit current of DSCs. However, open-circuit voltage and fill factor are decreased, and this result was ascribed to the enhanced recombination at the Nb-doped TiO 2/dye-electrolyte interface. The effect of doping on charge transport in DSCs was analyzed using electrochemical impedance spectroscopy. We have shown that by introducing of TiO 2 barrier layer, the Nb doping content, which results in DSC highest efficiency, can be increased because of the suppression of the dopant-induced recombination. The energy conversion efficiency of the solar cells increased from 7.8% to 9.0% when undoped TiO 2 electrode is replaced with electrode doped with 2.7 mol% of Nb because of the improvement of the electron injection and collection efficiencies. The correlation between the electronic structure of the TiO 2 electrode, charge transfer characteristics, and photovoltaic parameters of DSCs is discussed. Copyright © 2012 John Wiley & Sons, Ltd.


PubMed | Institute of Biochemical Physics and RAS Institute of Chemistry
Type: Journal Article | Journal: The Journal of chemical physics | Year: 2016

The phase behavior of a monodisperse melt of polymer molecules consisting of two rod-like segments joined at an angle has been inspected within the Landau theory of phase transitions. The interactions between monomer units were assumed to be of the Maier-Saupe form. The Landau-de Gennes expansion of the free energy of the melt has been obtained up to the sixth order in powers of the nematic order parameter, the coefficients of this expansion have been calculated from the microscopic model of polymer molecule. The phase diagram contains the regions of stability of isotropic, prolate uniaxial, oblate uniaxial, and biaxial nematic phases. The isotropic-uniaxial nematic and uniaxial-biaxial nematic transitions are of the first and second order, respectively. We found two Landau points in the phase diagram at which continuous transition from biaxial nematic state to isotropic phase occurs.

Loading Institute of Biochemical Physics collaborators
Loading Institute of Biochemical Physics collaborators