Light-addressable liquid crystal polymer dispersed liquid crystal

Scattering-free liquid crystal polymer-dispersed liquid crystal polymer (LCPDLC) films are fabricated by combining a room temperature polymerizable liquid crystal (LC) monomer with a mesogenic photosensitive LC. The morphological and photosensitive properties of the system are analysed with polarized optical microscopy and high resolution scanning and transmission electron microscopy. A two-phase morphology comprised of oriented fibril-like polymeric structures interwoven with nanoscale domains of phase separated LC exists. The nanoscale of the structures enables an absence of scattering which allows imaging through the LCPDLC sample without optical distortion. The use of a mesogenic monomer enables much smaller phase separated domains as compared to nonmesogenic systems. All-optical experiments show that the transmitted intensity, measured through parallel polarizers, can be modulated by the low power density radiation (31 mW/cm2) of a suitable wavelength (532 nm). The reversible and repeatable transmission change is due to the photoinduced trans-cis photoisomerization process. The birefringence variation (0.01) obtained by optically pumping the LCPDLC films allow their use as an alloptical phase modulato

Interplay between dipole and quadrupole modes of field influence in liquid-crystalline suspensions of ferromagnetic particles

In the framework of continuum theory we study orientational transitions induced by electric and magnetic fields in ferronematics, i.e., in liquid-crystalline suspensions of ferromagnetic particles. We have shown that in a certain electric field range the magnetic field can induce a sequence of re-entrant orientational transitions in ferronematic layer: nonuniform phase --- uniform phase --- nonuniform phase. This phenomenon is caused by the interplay between the dipole (ferromagnetic) and quadrupole (dielectric and diamagnetic) mechanisms of the field influence on a ferronematic structure. We have found that these re-entrant Freedericksz transitions exhibit tricritical behavior, i.e., they can be of the first or the second order. The character of the transitions depends on a degree of redistribution of magnetic admixture in the sample exposed to uniform magnetic field (magnetic segregation). We demonstrate how electric and magnetic fields can change the order of orientational transitions in ferronematics. We show that electric Freedericksz transitions in ferronematics subjected to magnetic field have no re-entrant nature. Tricritical segregation parameters for the transitions induced by electric or magnetic fields are obtained analytically. We demonstrate the re-entrant behavior of ferronematic by numerical simulations of the magnetization and optical phase lag.Comment: 12 pages, 9 figures, to be published in Soft Matte

Effect of magnetic nanoparticles on the nematic-smectic-A phase transition

Recent experiments on mixed liquid crystals have highlighted the hugely significant role of ferromagnetic nanoparticle impurities in defining the nematic-smectic-A phase transition point. Structured around a Flory-Huggins free energy of isotropic mixing and Landau-de Gennes free energy, this article presents a phenomenological mean-field model that quantifies the role of such impurities in analyzing thermodynamic phases, in a mixture of thermotropic smectic liquid crystal and ferromagnetic nanoparticles. First we discuss the impact of ferromagnetic nanoparticles on the isotropic-ferronematic and ferronematic-ferrosmectic phase transitions and their transition temperatures. This is followed by plotting and discussing various topologies in the phase diagrams. Our model results indicate that there exists a critical concentration of nanoparticle impurities for which the second order N-SmA transition becomes first order at a tricritical point. Calculations based on this model show remarkable agreement with experiment

Algorithmes évolutionnaires et inspirés du quantique pour l'optimisation de systèmes de réfrigération magnétique

This thesis is carried out within the frame of the CoolMagEvo ANR project, which aims at developing of magneto cooling systems. In this context, we consider the two following simulation models as time-consuming optimization problems: a model of Magneto Caloric Materials (MCMs) and a model of an Active Magnetic Regenerator (AMR). According to the defined requirements of the problems, we develop three special optimization algorithms. Then, we develop the software tool based on the proposed algorithms for easily solving different problems of these simulation models. Next, using this tool, we present the new method based on optimization, for reproducing physical properties of different MCMs. Finally, we study the impact of the control and design parameters of the AMR model on its performance in two application modes.Cette thèse est réalisée dans le cadre du projet ANR CoolMagEvo, qui se donne comme objectif le développement de systèmes de réfrigération magnétique. Nous disposons de deux modèles de simulation dont on a assigné une fonction de problèmes d'optimisation: un modèle de Matériaux Magnetocaloriques (MMCs) et un modèle d'un Régénérateur Magnétique Actif (AMR). Selon les exigences des modèles, nous avons développé trois algorithmes d'optimisation. Par la suite, nous avons développé un outil basé sur les algorithmes proposés pour résoudre facilement et efficacement différents problèmes de ces modèles de simulation. Ensuite, à l'aide de cet outil, nous avons eu la possibilité d'ériger la nouvelle méthode basée sur l'optimisation, qui permet de reproduire les propriétés physiques de différents MMCs. Enfin, nous avons étudié l'impact des paramètres de contrôle et de désign du modèle de l'AMR sur ses performances pour deux modes d'application

Algorithmes évolutionnaires et inspirés du quantique pour l'optimisation de systèmes de réfrigération magnétique

Cette thèse est réalisée dans le cadre du projet ANR CoolMagEvo, qui se donne comme objectif le développement de systèmes de réfrigération magnétique. Nous disposons de deux modèles de simulation dont on a assigné une fonction de problèmes d'optimisation: un modèle de Matériaux Magnetocaloriques (MMCs) et un modèle d'un Régénérateur Magnétique Actif (AMR). Selon les exigences des modèles, nous avons développé trois algorithmes d'optimisation. Par la suite, nous avons développé un outil basé sur les algorithmes proposés pour résoudre facilement et efficacement différents problèmes de ces modèles de simulation. Ensuite, à l'aide de cet outil, nous avons eu la possibilité d'ériger la nouvelle méthode basée sur l'optimisation, qui permet de reproduire les propriétés physiques de différents MMCs. Enfin, nous avons étudié l'impact des paramètres de contrôle et de désign du modèle de l'AMR sur ses performances pour deux modes d'application.This thesis is carried out within the frame of the CoolMagEvo ANR project, which aims at developing of magneto cooling systems. In this context, we consider the two following simulation models as time-consuming optimization problems: a model of Magneto Caloric Materials (MCMs) and a model of an Active Magnetic Regenerator (AMR). According to the defined requirements of the problems, we develop three special optimization algorithms. Then, we develop the software tool based on the proposed algorithms for easily solving different problems of these simulation models. Next, using this tool, we present the new method based on optimization, for reproducing physical properties of different MCMs. Finally, we study the impact of the control and design parameters of the AMR model on its performance in two application modes