Research / Annual reports / Main research results of the Institute for Condensed Matter Physics of NAS of Ukraine in 2014

# Main research results of the Institute for Condensed Matter Physics of NAS of Ukraine in 2014

### а) Main fundamental results

In order to describe the effect of the porous medium on the phase behavior and percolation properties of patchy colloids a statistical approach is developed. The proposed approach combines the ideas of the associative theory of liquids, the scaled particle theory and the percolation Flory-Stockmayer theory. It is shown that with decreasing of porosity the critical point of liquid-gas transition is shifted to the region of lower density and the temperature region of liquid-gas coexistence decreases. The percolation threshold is also shifted into the region of lower density in this case. It was observed that the results obtained from the theory and computer simulations are in a good agreement (M.Holovko, Yu.Kalyuzhnyj, T. Patsahan ).

Using the coarse-grained molecular dynamics simulation, the defects of the nematic director around the spherical colloid particle are studied. Two models for the colloid are considered, namely: the “soft colloid”, which mimics the liquid crystalline dendrimer, and “decorated colloid”, which represents a nanoparticle with its surface decorated by the liquid crystalline groups. To match the properties of the nematic phase to the experiments, the Frank elastic constants are evaluated, as well as the coherence length for the surface anchoring. Both models lead to the same defects, namely: the Saturn ring for the homeotropic anchoring and the “boojum” defect for the tangential anchoring. The new defect – the biaxial boojum is also predicted, which is observed for the case of the longitudinal planar anchoring (J.Ilnytskyi, A.Trokhymchuk, M.Schoen).

The conformational properties of ring polymers in solutions in presence of structural impurities, correlated on large distances according to a power law, are analyzed. Applying the direct polymer renormalization scheme, we evaluate the analytical estimates for averaged gyration radius and asphericity of typical ring polymer conformation. The results quantitatively reveal an extent of the effective size and anisotropy of closed ring macromolecules in disordered environments (V. Blavatska).

The effect of competition between Coulomb and dispersion forces on the gas-liquid phase behaviour is studied within the framework of a charge-asymmetric model of ionic fluids. Both the critical parameters and the coexistence envelope are calculated in a one-loop approximation as a function of the parameter measuring the relative strength of the Coulomb to short-range interactions. We found the very narrow region of the parameter bounded from the both sides by tricritical points which separates the models with “nonionic” and “Coulombic” phase behaviour (O.V. Patsahan).

The energy spectrum for a finite one-dimensional ionic quantum conductor with periodic boundary conditions has been calculated using exact diagonalization technique. The ionic conductor is described with the lattice model where particles are treated in frames of 'mixed' Pauli statistics. The model involves the ion transfer, interaction between neighbor ions and modulating field. One-particle spectral densities are calculated, and phase diagrams are plotted for various temperatures, magnitudes of interaction between particles, and modulating field strengths. Conditions for the transition from the charge-density-wave (CDW) phase to the superfluid (SF) phase with Bose-Einstein condensate (it can be analog of the superionic phase) and to Mott-insulator type (MI) phase are investigated. (R.Ya. Stetsiv, I.V. Stasyuk, O. Vorobyov)

Ground states of a spin-1/2 Ising-Heisenberg model on the Shastry-Sutherland lattice with Heisenberg intra-dimer and Ising inter-dimer couplings are found rigorously. It is shown that the model exhibits a zero-temperature magnetization curve with just two intermediate plateaus at one-third and one-half of the saturation magnetization. The nature of the remarkable stripe order relevant to the one-third plateau is thoroughly investigated. The rigorous results for the spin-1/2 Ising-Heisenberg model on the Shastry-Sutherland lattice are compared with the analogous results for the purely classical Ising and fully quantum Heisenberg models. Finally, we discuss to what extent the critical fields of SrCu2(BO3)2 and (CuCl)Ca2Nb3O10 can be described within the suggested Ising-Heisenberg model. (T.M.Verkholyak in collaboration with J.Strecka , F. Mila, K.P.Schmidt)

Lattice gas model of catalytically-activated reactions on the Bethe lattice with catalytic sites is considered. The phase diagram of adsorbate with ordered phase is obtained. For the fraction of catalytic sites above a critical value the second order phase transition from disordered phase to ordered phase is observed with increasing of activity. It is established, that further increasing of activity leads to reentrant phase transition from ordered phase to disordered phase. It was shown that order of reentrant transition is either of second order or of first order depending on fraction of catalytic sites. (M. Dudka)

### b) Main applied results

In development of the previously proposed new information technology for separations of complex images ICaS-ColorPrint® a package of specialized software for industrial purposes including fundamentally new computer program ICaS ColorSyntesis was developed. With this software it was guaranteed the implementation process of the synthesis of the original color image and the full cycle manufacturing operations prepress printing digital files for direct output to the printing plate and the paper. The program automatically provides comparison of synthesized image with the original for assessment of quality color reproduction in accordance with the requirements of modern technology color printing. Herewith it was achieved a high quality of image reproduction and the exceptional contrast in areas of dark tones. According to the research, partner company "Univest PrePress" (Kyiv) has prepared for publication illustrated album of art photos. This package is completely ukrainian product and can commonly compete with imported graphic editors (M.V.Shovhenyuk).