Samo Kralj

Bio: Samo Kralj is an academic researcher from University of Maribor. The author has contributed to research in topics: Liquid crystal & Phase transition. The author has an hindex of 31, co-authored 198 publications receiving 3370 citations. Previous affiliations of Samo Kralj include University of Ljubljana & Eindhoven University of Technology.

Defects in Planar Cell Polarity of Epithelium: What Can We Learn from Liquid Crystals?

Abstract: Epithelial tissues are structured and highly organized monolayers of cells with many different tissue-specific functions. Ordering of epithelium cells in living tissues relies on spatially and temporally regulated cell behavior and is of vital importance for their functioning. The underlying mechanisms that govern the development of the tissue architecture and morphogenesis rely on planar cell polarity signaling pathways. Mutations and other disruptions of these pathways were found to cause developmental defects, leading to failures in lung branching or kidney development, for example, and are also involved in cancer cell migration. Here, we investigate how these defects affect the spatial arrangement and orientation of epithelium cells, giving special attention to tissue reorganization during development. For the characterization of the resulting polarized cytoarchitectures, we make use of methods developed in the field of liquid crystal (LC) research. In fact, epithelial tissues possess typical features of liquid crystalline systems albeit exhibiting a different local symmetry. Therefore, tools developed in the LC research community can be successfully applied for the description of the overall epithelial tissue topology and its orientational order. We additionally discuss and hypothesize the possibilities of using nanoparticles for structural defect stabilization and its application.

Confined liquid crystaline 5CB in 2D Thermodynamic Space - Preliminary Dielectric Relaxation Study

Abstract: Results of preliminary broadband dielectric spectroscopy studies in a wide range of temperatures and pressures range for a mixture of rod-like liquid crystalline 4–cyano–4–pentylalkylbiphenyl (5CB) and hydrophilic silica spheres (Aerosil 300) are shown. Pretransitional anomaly, observed previously in the bulk 5CB, has been found. Temperature dynamics of the mixture was investigated with via the DC conductivity σ, coupled to the reorientational relaxation. The derivative based analysis of electric conductivity showed a clear non-Arrhenius dynamics and indicated the anomalous increase of the fragility strength coefficient on approaching the isotropic-nematic transition. Pressure investigations of the solidification from the nematic phase showed the increase of the transition temperature on pressuring but with unusual increasing of dT NS /dP coefficient.

Random nematic structures in the absence of inherent frustrations

Abstract: We study the impact of anisotropic nanoparticles (NPs) on the nematic liquid crystal (LC) order. Within a mesoscopic Flory–Huggins-type approach we have estimated regimes where LC–NP mixtures are essentially homogenous. Using a lattice Lebwohl–Lasher type approach we have also studied the impact of anisotropic NPs on LC ordering. We analysed the cases where the orientations of NPs are either frozen-in or could be varied, to which we refer as random field mixtures and annealed mixtures, respectively. In the latter case we have demonstrated the existence of qualitatively different regimes. In particular, we determined the concentration regime, where LC configurations resembling a transparent nematic phase could be observed. Such domain patterns are stabilised by NPs hindering the annihilation of topological defects in LC order.

Orientational Order within Biological Membranes

Abstract: Recently developed approaches analyzing the degree of in-plane orientational ordering are compared. The first one originates from an intrinsic anisotropic shape of membrane constituents, based on which the mismatch curvature tensor M is introduced. The second one originates from the nematic tensor order parameter Q reflecting average local degree of orientational ordering. Based on these tensors free energy of systems are derived taking into account symmetry allowed combinations of tensors. From both approaches the degree of local orientational ordering is determined as a function of membrane shape. In the paper we discuss relevance of these approaches

Influence of polymer network in polymer-stabilized ferroelectric liquid crystals and its direct observation using a confocal microscope

Abstract: The paper presents the analysis of the three-dimensional polymer network distribution inside the polymer-stabilized ferroelectric liquid-crystal layer based on the laser scanning fluorescence confocal microscopy and a fluorescent dye tagging of the polymer. The studies of polymer-stabilized ferroelectric liquid-crystal structures described in this paper are focused on the comparison of the influence of polymer network in case that the polymerization is initiated in the chevron as well as in the quasibookshelf liquid-crystal molecular orientation. In the case of the chevron structure the regular distribution of the polymer network within the layer leads to the monostability of the chevron state. On the other hand the specific distribution of the polymer in the polymer-stabilized quasibookshelf stripe textures leads to the perfect bistability, improved multiplex driving, and analog gray scale capability.

Phase separation in confined systems

Abstract: We review the current state of knowledge of phase separation and phase equilibria in porous materials. Our emphasis is on fundamental studies of simple fluids (composed of small, neutral molecules) and well-characterized materials. While theoretical and molecular simulation studies are stressed, we also survey experimental investigations that are fundamental in nature. Following a brief survey of the most useful theoretical and simulation methods, we describe the nature of gas‐liquid (capillary condensation), layering, liquid‐liquid and freezing/melting transitions. In each case studies for simple pore geometries, and also more complex ones where available, are discussed. While a reasonably good understanding is available for phase equilibria of pure adsorbates in simple pore geometries, there is a need to extend the models to more complex pore geometries that include effects of chemical and geometrical heterogeneity and connectivity. In addition, with the exception of liquid‐liquid equilibria, little work has been done so far on phase separation for mixtures in porous media.

Effects of confinement on freezing and melting.

Abstract: We present a review of experimental, theoretical, and molecular simulation studies of confinement effects on freezing and melting We consider both simple and more complex adsorbates that are confined in various environments (slit or cylindrical pores and also disordered porous materials) The most commonly used molecular simulation, theoretical and experimental methods are first presented We also provide a brief description of the most widely used porous materials The current state of knowledge on the effects of confinement on structure and freezing temperature, and the appearance of new surface-driven and confinement-driven phases are then discussed We also address how confinement affects the glass transition

Liquid-crystal materials find a new order in biomedical applications.

Abstract: With the maturation of the information display field, liquid-crystal materials research is undergoing a modern-day renaissance. Devices and configurations based on liquid-crystal materials are being developed for spectroscopy, imaging and microscopy, leading to new techniques for optically probing biological systems. Biosensors fabricated with liquid-crystal materials can allow label-free observations of biological phenomena. Liquid-crystal polymers are starting to be used in biomimicking colour-producing structures, lenses and muscle-like actuators. New areas of application in the realms of biology and medicine are stimulating innovation in basic and applied research into these materials.