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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.


Papers
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TL;DR: In this paper, a review of nanoparticle stabilized lattices of topological defects (TDs) in liquid crystals (LCs) is presented, focusing on conditions for which chiral liquid-crystalline blue phases and twist-grain boundary A phases might be stable in bulk LCs.
Abstract: We present a review of nanoparticle (NP) stabilized lattices of topological defects (TDs) in liquid crystals (LCs). We focus on conditions for which chiral liquid-crystalline blue phases and twist-grain boundary A phases might be stable in bulk LCs. These phases exhibit lattices of disclinations and dislocations corresponding to line TDs in orientational and translational LC order, respectively. NPs of appropriate size and surface coating can assemble in the cores of defects and stabilize metastable or increase the temperature range of already stable lattices of TDs. The stabilization is achieved by the universal defect core replacement and adaptive defect core targeting mechanisms. Representative experiments revealing these phenomena and potential applications are discussed.

16 citations

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TL;DR: In nontreated CPG samples the layers dilate significantly with respect to the bulk liquid crystal, and the layer thickness behavior on varying temperature and R has to take into account molecular details of the liquid crystalline samples as well as memory effects.
Abstract: A detailed x-ray scattering study has been performed in the temperature range of the smectic- A phase for the liquid crystal compounds dodecylcyanobiphenyl (12CB) and octylcyanobiphenyl (8CB) confined in different controlled-pore glasses (CPGs) characterized by their average void radius R . On decreasing the temperature in bulk samples the layer thickness is increasing for 12CB and decreasing for 8CB, respectively. In nontreated CPG samples the layers dilate significantly with respect to the bulk liquid crystal. In order to explain the layer thickness behavior on varying temperature and R , one has to take into account molecular details of the liquid crystalline samples as well as memory effects.

15 citations

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TL;DR: It is shown that the onset of orientational ordering increases the phase separation tendency, and the difference between the paranematic and speronematic ordering decreases, Consequently the structure of the phase-separated pattern can be much more complex in comparison to the Lambda=0 case.
Abstract: The influence of a random-anisotropy- (RA-) type disorder on the phase separation of the nematogen\char21{}non-nematogen mixture is studied. A combination of the phenomenological Landau\char21{}de Gennes and Flory-Huggins theories is used. We assume that the non-nematogen component (i.e., impurity) enforces the RA disorder to the enclosing thermotropic liquid-crystal (LC) phase. The Imry-Ma argument is used according to which the lower-temperature phase exhibits a domain-type pattern. The disorder strength is measured in terms of the dimensionless parameter $\ensuremath{\Lambda}$. We consider the case in which the LC molecules and impurities mix in the isotropic phase for $\ensuremath{\Lambda}=0$. The impurities enforce a finite degree of orientational ordering even in the high-temperature paranematic phase. In the low-temperature phase they give rise to a domain-type structure, resulting in the distorted nematic (speronematic) phase. We show that the onset of orientational ordering increases the phase separation tendency. The RA field, however, opposes this tendency. With increasing value of $\ensuremath{\Lambda}$ the difference between the paranematic and speronematic ordering decreases. Consequently the structure of the phase-separated pattern can be much more complex in comparison to the $\ensuremath{\Lambda}=0$ case.

15 citations

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TL;DR: A theory for surface modes at the nematic-isotropic interface in thermotropic nematogen-non-nematogen mixtures is developed, using the dynamical generalization of the Landau-de Gennes model for the orientational (nonconserved) order parameter, coupled with the Cahn-Hilliard equation for concentration (conserved parameter).
Abstract: We develop a theory for surface modes at the nematic-isotropic interface in thermotropic nematogen--non-nematogen mixtures. We employ the dynamical generalization of the Landau--de Gennes model for the orientational (nonconserved) order parameter, coupled with the Cahn-Hilliard equation for concentration (conserved parameter), and include hydrodynamic degrees of freedom. The theory uses a generalized form of the Landau--de Gennes free-energy density to include the coupling between the concentration of the non-nematogen fluid and the orientational order parameter. Two representative phase diagrams are shown. The method of matched asymptotic expansions is used to obtain a generalized dispersion relation. Further analysis is made in particular cases. Orientational order parameter relaxation dominates in the short-wavelength limit, while in the long-wavelength limit viscous damping processes become important. There is an intermediate region (depending on the temperature) in which the interaction between conserved parameter dynamics and hydrodynamics is important.

15 citations

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TL;DR: Hydrophilic and hydrophobic aerosil particles immersed in S-(+)-[4-(2-methylbutyl) phenyl 4-n-octylbiphenyl-4-carboxylate] or [p-(n-decyloxy) benzylidene-p-amino-( 2-methyl butyl) cinnamate] compound have been studied by employing x-ray diffraction.
Abstract: Hydrophilic and hydrophobic aerosil particles immersed in S-(+)-[4-(2-methylbutyl) phenyl 4-n-octylbiphenyl-4-carboxylate] or [p-(n-decyloxy) benzylidene-p-amino-(2-methylbutyl) cinnamate] compound have been studied by employing x-ray diffraction. The aerosil-induced relative layer compression Delta d has been measured in the smectic A phase as a function of aerosil concentration x. Delta d(x) is shown to sensitively monitor the intermediate-rigid transition of the adaptive aerosil network. The dominant mechanism leading to the Delta d(x) profiles is the global establishment of the aerosil-induced molecular tilt in the smectic A phase.

15 citations


Cited by
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TL;DR: A review of the current state of knowledge of phase separation and phase equilibria in porous materials can be found in this article, where the focus is on fundamental studies of simple fluids and well-characterized materials.
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.

1,436 citations

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TL;DR: Both simple and more complex adsorbates that are confined in various environments (slit or cylindrical pores and also disordered porous materials) are considered and how confinement affects the glass transition is addressed.
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

640 citations

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TL;DR: New areas of application in the realms of biology and medicine are stimulating innovation in basic and applied research into liquid-crystal materials, leading to new techniques for optically probing biological systems.
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.

636 citations