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.

Orientational fluctuations and phase transitions in 8CB confined by cylindrical pores of the PET film

Abstract: Results of optical investigations of the isotropic-nematic and nematic-smectic A phase transitions in porous polyethyleneterephthalate (PET) films filled with octyl-cyanobihenyl (8CB) liquid crystal (LC) are reported. Samples of porous films of thickness 23 µm with normally oriented cylindrical pores of a radius R ranging from 10 nm to 1000 nm were prepared using the track-etched membrane technology. The dynamic light scattering method was used to probe the nematic orientational fluctuations of confined LC samples. The corresponding relaxation time τ was measured as a function of R and temperature T at slow enough cooling rates (0.3–0.6 K/h) to locate the phase transition temperatures. Changes in τ(T) dependencies relatively sensitivity fingerprint the LC phase transformations. Experimental results are analysed using the Landau-de Gennes-Ginzburg phenomenological approach.

Assembling of Topological Defects at Neck‐Shaped Membrane Parts

Abstract: The impact of intrinsic and extrinsic curvature on the distribution of topological defects (TDs) in neck-like regions of biological membranes is studied quantitatively. Biological membranes are modeled effectively at the mesoscopic level as two-dimensional films described in terms of the tensor nematic order parameter field and curvature fields. It is demonstrated that antidefects robustly form at the neck area and can promote a membrane fission. The assembling of antidefects near the catenoid’s equatorial ring, where catenoids roughly mimic neck shapes are analyzed in more detail. It is demonstrated that for sufficiently strong curvatures, the effective topological charge Δmeff within a strongly curved region equals zero, and the resulting structures are topologically neutral. Consequently, the total charge of antidefects within the region equals Δm1⁄4 ΔmV ΔmK. In most cases, the positions of antidefects are strongly influenced by the extrinsic curvature.

Influence of polar dopant on internal configuration of azoxybenzene nematic-in-water droplets

Abstract: We report the study of optical textures and director configurations within nematic-in-water microdroplets of the liquid-crystalline mixtures based on azoxybenzene and cyanobiphenyl (as a polar dopant). Both pure azoxybenzene and polar dopant materials exhibited bipolar configuration within liquid-crystalline droplets, whereas their mixtures at appropriate concentrations spontaneously formed radial droplets. It was found that increasing of the dopant’s concentration resulted in the forward tangential-homeotropic and reentrant homeotropic-tangential anchoring transitions. We also triggered bipolar-to-radial structural transition by UV irradiation providing trans-cis isomerisation of nematogens. Critical irradiation time needed for radial configuration formation was found to decrease with concentration of polar dopant. Mesoscoping modelling is proposed to explain main experimental results. The presented data are discussed for chemical and biological sensing applications.

Paranematic-Nematic Phase Transition of a Liquid Crystal Confined to a Controlled Porous Glass

Abstract: A deuteron NMR study of a pentylcyanobiphenil (5CB) liquid crystal confined in controlled pore glass (CPG) matrices of different pore diameters 2R between 7 nm and 400 nm has been performed. The paranematic-nematic (P-N) phase transition seems to be gradual in pores with 2R ≤ 24 nm and discontinuous in larger pores. Possible reasons for the observed temperature shift Δ and qualitative change of the phase transition are analyzed using a simple phenomenological approach. The theoretical analysis suggests that both surface interaction and elastic distortions significantly influence the ΔT= ΔT(R) dependence obtained in CPG samples.

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.