Showing papers by "Samo Kralj published in 2013"
TL;DR: In this article, it was shown that the twist-grain boundary phase in a chiral liquid crystal is driven by direct interactions between surface-functionalized CdSe quantum dots and screw dislocations.
Abstract: It is demonstrated that interactions between nanoparticles and topological defects induce a twist-grain boundary phase in a chiral liquid crystal. The occurrence of this phase, the analogue of the Shubnikov phase in type-II superconductors, is driven by direct interactions between surface-functionalized CdSe quantum dots and screw dislocations. It is shown that, within an adaptive-defect-core-targeting mechanism, nanoparticles of appropriate size and functionalization adapt to qualitatively different cores of topological defects such as disclination lines and screw dislocations. This mechanism enables the effective reduction of the energetically costly, singular defect core volume, while the surrounding phase ordering remains relatively weakly affected. The findings suggest new pathways towards the controlled assembly of superstructures in diverse, symmetry-broken, condensed-matter systems, ranging from nanoparticle-decorated liquid crystals to superconductors.
57 citations
TL;DR: In this article, the effect of surface functionalized graphene nanosheets on the blue phase range of a chiral liquid crystal was investigated and it was shown that the resulting soft nanocomposite exhibits an increased blue phase temperature stability range for a minute concentration of dispersed graphene.
Abstract: The stabilization of liquid-crystalline blue phases is recently attracting considerable interest because of the envisioned applications in fast optical displays and tunable photonic crystals. We report on the effect of surface-functionalized graphene nanosheets on the blue phase range of a chiral liquid crystal. Calorimetric and optical measurements, reproducible on heating and cooling, demonstrate that the resulting soft nanocomposite exhibits an increased blue phase temperature stability range for a minute concentration of dispersed graphene. The impact is stronger on the ordered, cubic structured blue phase I. These findings suggest that anisotropic nanoparticles may be of great usefulness for stabilizing blue phases.
37 citations
TL;DR: A brief theoretical model is presented accounting for the impact of anisotropic nanoparticles on the blue phase stability region and the addition of these nanoparticles effectively increases the temperature range of blue phases and especially the cubic structure of blue phase I.
Abstract: Liquid-crystalline blue phases are attracting significant interest due to their potential for applications related to tunable photonic crystals and fast optical displays. In this work a brief theoretical model is presented accounting for the impact of anisotropic nanoparticles on the blue phase stability region. This model is tested by means of high-resolution calorimetric and optical measurements of the effect of anisotropic, surface-functionalized MoS2 nanoparticles on the blue phase range of a chiral liquid crystal. The addition of these nanoparticles effectively increases the temperature range of blue phases and especially the cubic structure of blue phase I.
34 citations
TL;DR: In this paper, the authors present the results of a study conducted at the University of Ljubljana's Condensed Matter Physics Department, Jožef Stefan Institute.
Abstract: 1Condensed Matter Physics Department, Jožef Stefan Institute, Ljubljana, Slovenia; 2Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia; 3Department of Complex Systems and Chemical Processing of Information, Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland; 4Laboratory of Clinical Biophysics, Faculty of Health Studies, University of Ljubljana, Ljubljana, Slovenia; 5Laboratory of Clinical Biophysics, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia; 6Department of Physics, Faculty of Natural Sciences and Mathematics, University of Maribor, Maribor, Slovenia
19 citations
TL;DR: The impact of random-field-type disorder on a range of ordering in the (symmetry broken) nematic phase is studied, demonstrating that short-range order is observed even for a minute concentration of impurities, giving rise to disorder in line with the Imry-Ma theorem prediction.
Abstract: Universal behavior related to continuous symmetry breaking in nematic liquid crystals is studied using Brownian molecular dynamics. A three-dimensional lattice system of rod-like objects interacting via the Lebwohl‐Lasher interaction is considered. We test the applicability of predictions originally derived in cosmology and magnetism. In the first part we focus on coarsening dynamics following the temperature driven isotropic‐nematic phase transition for different quench rates. The behavior in the early coarsening regime supports predictions made originally by Kibble in cosmology. For fast enough quenches, symmetry breaking and causality give rise to a dense tangle of defects. When the degree of orientational ordering is large enough, well defined protodomains characterized by a single average domain length are formed. With time subcritical domains gradually vanish and supercritical domains grow with time, exhibiting a universal scaling law. In the second part of the paper we study the impact of random-field-type disorder on a range of ordering in the (symmetry broken) nematic phase. We demonstrate that short-range order is observed even for a minute concentration of impurities, giving rise to disorder in line with the Imry‐Ma theorem prediction only for the appropriate history of systems.
16 citations
TL;DR: In this article, the impact of severe spatial confinement on the phase transition behavior of smectic liquid crystals has been systematically studied by means of high-resolution ac calorimetry, and the results show that the carbon tails length of the liquid crystal molecules strongly influences the phase behavior.
8 citations
TL;DR: In this paper, the authors study the properties of a randomly perturbed nematic liquid crystal (LC) phase and show that for a weak enough interaction between the LC molecules and impurities, qualitatively different history-dependent states could be obtained.
Abstract: We study the characteristics of nematic structures in a randomly perturbed nematic liquid crystal (LC) phase. We focus on the impact of the samples history on the universal behavior. The obtained results are of interest for every randomly perturbed system exhibiting a continuous symmetry-breaking phase transition. A semimicroscopic lattice simulation is used where the LC molecules are treated as cylindrically symmetric, rod-like objects interacting via a Lebwohl-Lasher (LL) interaction. Pure LC systems exhibit a first order phase transition into the orientationally ordered nematic phase at on lowering the temperature . The orientational ordering of LC molecules is perturbed by the quenched, randomly distributed rod-like impurities of concentration . Their orientation is randomly distributed, and they are coupled with the LC molecules via an LL-type interaction. Only concentrations below the percolation threshold are considered. The key macroscopic characteristics of perturbed LC structures in the symmetry-broken nematic phase are analyzed for two qualitatively different histories at . We demonstrate that, for a weak enough interaction among the LC molecules and impurities, qualitatively different history-dependent states could be obtained. These states could exhibit either short-range, quasi-long-range, or even long-range order.
6 citations
TL;DR: In this paper, the existence of indirect magnetoelectricity in a soft composite material prepared as a mixture of magnetite ferromagnetic nanoparticles (NPs) and the ferroelectric liquid crystal (FLC) Felix 015/100 was verified by using a SQUID-based magnetometer.
Abstract: The existence of an indirect magnetoelectricity in a soft composite material prepared as a mixture of magnetite ferromagnetic nanoparticles (NPs) and the ferroelectric liquid crystal (FLC) Felix 015/100 was verified by using a SQUID-based magnetometer. It was observed that the orientation of nanoparticles is directly coupled to the liquid crystal director field. Such a coupling allows the possibility of indirect coupling between the magnetic and ferroelectric order. This gifts the mixtures of FLC and magnetic nanoparticles (MNPs) with a great potential for soft indirect magnetoelectrics.
3 citations
TL;DR: The classical methods of solid mechanics assume that the homeomorphism of deformation sometimes does not provide an adequate description of the behavior and fracture of real materials, while irreversible macro deformation and the fracture of solids are predetermined by material behaviour in nanoscale as discussed by the authors.
Abstract: The classical methods of solid mechanics assume that the homeomorphism of deformation sometimes does not provide an adequate description of the theological behaviour and fracture of real materials, while irreversible macro deformation and the fracture of solids are predetermined by material behaviour in nanoscale. When we talk about crack propagation, we must talk at least about four phenomena, namely about crack incubation, initiation, and crack propagation must be sleeted in two parts, to growth of short crack and to growth of linear elastic or long crack.
2 citations
09 May 2013
TL;DR: In this paper, the authors studied mixtures of various soft materials and nanoparticles and found combinations where each component introduces a qualitatively different behavior into the system such systems are expected to play an important role in the emerging field of nanotechnology and also in composites with extraordinary material properties.
Abstract: The past decade has witnessed an increased interest in the study of mixtures [1–3] of various soft materials and nanoparticles A characteristic feature of a nanoparticle is that at least one of its dimensions is limited to between 1 and 100 nm It is of interest to find combinations where each component introduces a qualitatively different behavior into the system Such systems are expected to play an important role in the emerging field of nanotechnology and also in composites with extraordinary material properties
1 citations
Journal Article•
22 Mar 2013-World Academy of Science, Engineering and Technology, International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering
TL;DR: In this paper, the typical domain size and configuration character of a randomly perturbed system exhibiting continuous symmetry breaking was studied, where rod-like objects within a cubic lattice interacting via a Lebwohl-Lasher-type interaction.
Abstract: We study the typical domain size and configuration character of a randomly perturbed system exhibiting continuous symmetry breaking. As a model system we use rod-like objects within a cubic lattice interacting via a Lebwohl–Lasher-type interaction. We describe their local direction with a headless unit director field. An example of such systems represents nematic LC or nanotubes. We further introduce impurities of concentration p, which impose the random anisotropy field-type disorder to directors. We study the domain-type pattern of molecules as a function of p, anchoring strength w between a neighboring director and impurity, temperature, history of samples. In simulations we quenched the directors either from the random or homogeneous initial configuration. Our results show that a history of system strongly influences: i) the average domain coherence length; and ii) the range of ordering in the system. In the random case the obtained order is always short ranged (SR). On the contrary, in the homogeneous case, SR is obtained only for strong enough anchoring and large enough concentration p. In other cases, the ordering is either of quasi long range (QLR) or of long range (LR). We further studied memory effects for the random initial configuration. With increasing external ordering field B either QLR or LR is realized. Keywords—Lebwohl-Lasher model, liquid crystals, disorder, memory effect, orientational order.