Showing papers by "Samo Kralj published in 2012"
TL;DR: In this paper, a tensor field Q vanishes whenever a defect occurs in the molecular order, and the concept of parallel transport on a manifold is adapted to define the topological charge m of a defect.
Abstract: Nematic shells are thin films of nematic liquid crystal deposited on the boundary of colloidal particles, where liquid crystal molecules may freely glide, while remaining tangent to the surface substrate. The surface nematic order is described here by an appropriate tensor field Q, which vanishes wherever a defect occurs in the molecular order. We show how the classical concept of parallel transport on a manifold introduced by Levi-Civita can be adapted to this setting to define the topological charge m of a defect. We arrive at a simple formula to compute m from a generic representation of Q. In a number of separate appendices, we revisit in a unified language several, apparently disparate applications of Levi-Civita’s parallel transport.
36 citations
TL;DR: In this paper, the structural and thermodynamic phase behavior of the thermotropic liquid crystal dodecylcyanobiphenyl (12CB) confined in controlled-pore glasses (CPGs) has been studied by means of high-resolution calorimetry and small-angle X-ray scattering.
Abstract: The structural and thermodynamic phase behavior of the thermotropic liquid crystal dodecylcyanobiphenyl (12CB) confined in controlled-pore glasses (CPGs) has been studied by means of high-resolution calorimetry and small-angle X-ray scattering. Non-treated CPG matrices have been used with a characteristic pore size R ranging from nanometre to micrometre scale. Even in the case of the strongest confinement the isotropic-to-smectic-A (I-SmA) transition was pronounced. Both the smectic pretransitional ordering and the broadening of the specific heat capacity anomaly were relatively weak. This signals the secondary importance of the surface interaction potential and of the disorder upon phase behavior. We claim that the surface interaction is dominated by the coupling between surface-frozen and volume liquid crystal molecules. This coupling is weak due to the flexible long alkyl chains which dominantly influence the phase behavior of 12CB. The depression of the phase transition temperature Tc is dominated by smectic elastic compressibility distortions. The observed anomalous Tc(R) dependence is explained by allowing surface rearrangement processes. In severely-confined samples the 1st order I-SmA phase transition tends to be replaced by a 2nd order one. This phenomenon is attributed to a dimensional-crossover which, in 12CB samples, is not masked by surface interactions as it is in case of similar liquid crystals with shorter alkyl chains. The observed behavior is explained using scaling and dimensional analysis within the Landau–Ginzburg–de Gennes mesoscopic approach.
24 citations
TL;DR: In this article, a mixture of Maghemite ferromagnetic nanoparticles and liquid crystal Felix 015/100 was experimentally analyzed in the vicinity of the ferroelectric smectic C* (SmC*) phase.
Abstract: A mixture of maghemite ferromagnetic nanoparticles and the ferroelectric liquid crystal Felix 015/100 was experimentally analysed in the vicinity of the ferroelectric smectic C* (SmC*) phase. In order to verify the existence of magnetoelectricity in prepared soft material, a SQUID-based magnetometer was used. It was shown that the orientation of magnetic nanoparticles is directly coupled to the liquid crystal molecular director field. Such coupling allows possibility of indirect coupling between the nanoparticle magnetization and liquid crystal polarization. This makes such mixtures potential for new soft magnetoelectrics.
14 citations
TL;DR: In this article, the concept of vibrational resonance was extended to a thermotropic bistable surface-stabilized ferroelectric liquid crystal cell and the impact of different origins of static disorder was investigated.
Abstract: Vibrational resonance manifests itself in certain nonlinear systems that are subject to the action of a biharmonic force with very different frequencies. A proper frequency and/or amplitude of the high-frequency harmonic signal can lead to a resonantly enhanced response of the system with respect to the low frequency signal. In the present study we extent the concept of vibrational resonance to a thermotropic bistable surface-stabilized ferroelectric liquid crystal cell. Furthermore, we systematically investigate the impact of different origins of static disorder and reveal that different kinds of static disorder affect the resonant response in a qualitative different way.
14 citations
TL;DR: This paper attempts to elucidate the subtle interplay between the stabilizing and destabilizing processes in the fusion neck and indicates that topologically driven defects of the in-plane orientational membrane ordering in the region of the fusion pore may disrupt the fusion.
14 citations
TL;DR: In this article, the impact of surface-functionalised CdSe nanoparticles on various phase transitions of the two liquid crystals, 8CB and CE8, has been examined by means of high-resolution calorimetry.
Abstract: The impact of the surface–functionalised CdSe nanoparticles on various phase transitions of the two liquid crystals, 8CB and CE8, has been examined by means of high-resolution calorimetry. The addition of nanoparticles results in suppression of phase transitions and change in heat capacity anomalies. In contrast to silica aerosils CdSe nanoparticles do not form a rigid network. As a consequence, the impact of CdSe impurities on phase transitions resembles so called floppy phase regime, which exists at low concentrations of aerosils mixtures.
8 citations
TL;DR: In this article, the influence of defect core replacement mechanism on phase stability of a structure possessing topological defect is demonstrated under which conditions topological defects could be exploited as trapping centers for nanoparticles.
Abstract: We study theoretically mixtures of liquid crystals (LCs) and nanoparticles (NPs) at a mesoscopic level. Orientational LC ordering is given in terms of a tensor order parameter. We estimate conditions which favor or disfavor phase separation. We show under which conditions topological defect could be exploited as trapping centers for nanoparticles. Influence of Defect Core Replacement mechanism on phase stability of a structure possessing topological defect is demonstrated.
3 citations
TL;DR: Recently developed approaches analyzing the degree of in-plane orientational orientational ordering are compared and relevance of these approaches is discussed.
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
2 citations
TL;DR: In this article, the authors demonstrate basic physics of topological defects in orientational ordering and demonstrate equilibrium (or relatively stable) nematic structures possessing 2 to 8 defects pairs with the winding number |M|=1/2, where the sum of all defects corresponds to Mtot = 2.
Abstract: In this pedagogical presentation we demonstrate basic physics of topological defects in orientational ordering. We limit to two dimensional (2D) films. Different defect structures and pairs defect-antidefect are visualized in the applet presentation, which shows also the corresponding interference textures simulating typical polarizing microscopy experiment. The conservation of topological defect is shown on the case of 2D films on curved surfaces. In different geometrical shapes with the same Euler characteristics we demonstrate equilibrium (or at least relatively stable) nematic structures possessing 2 to 8 defects pairs with the winding number |M|=1/2, where the sum of all defects corresponds to Mtot = 2.
1 citations
09 Jul 2012
TL;DR: In this article, the existence of indirect magnetoelectricity in a soft composite material prepared as a mixture of a ferroelectric liquid crystal (FLC) and magnetic nanoparticles (MNPs) was verified.
Abstract: By using the SQUID susceptometer the existence of an indirect magnetoelectricity in a soft composite material prepared as a mixture of a ferroelectric liquid crystal (FLC) and magnetic nanoparticles (MNPs) was verified. It is shown that the orientation of MNPs is directly coupled to the FLC molecular director field. Such coupling allows the possibility of indirect coupling between the MNP's magnetization and FLC's polarization. This demonstrates the possibility to engineer the soft magnetoelectrics from mixtures of magnetic nanoparticles and ferroelectric liquid crystals.
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03 Oct 2012TL;DR: In this paper, the authors demonstrate an example of pattern recognition type of lecturing modern physics. By using already absorbed knowledge and analogies, they exploit their innate pattern recognition brain capabilities for more effective learning of new concepts in physics.
Abstract: It is now well accepted that we all have amazing capabilities in recognizing faces in a fraction of a second. This specific pattern recognition ability could be by appropriate training transferred to some other field of expertise. At the same time pattern recognition skills are becoming increasingly important survival strategy in the modern competitive world which faces information overload. In the paper we demonstrate an example of pattern-recognition type of lecturing modern physics. By using already absorbed knowledge and analogies we exploit our innate pattern recognition brain capabilities for more effective learning of new concepts in physics.