201 research outputs found
Statics and kinetics at the nematic-isotropic interface: effects of biaxiality
We use the Landau-de Gennes theory of a nematic liquid crystal to investigate anew aspects of the properties of the interface between the isotropic and nematic liquid crystal phases of the same fluid. The equations of the static interface have been solved, both numerically and using asymptotic analysis, with an emphasis on the effect of inclusion of the order parameter biaxiality on the physical properties. We have compared the results of the exact solutions to the commonly used de Gennes ansatz, which assumes positive and uniform unixiality through the interface. Although the de Gennes ansatz in general gives good results, when bend and splay elastic constants dominate over the twist constants, it can lead to errors of up to 10% in the surface energy. The asymptotic analysis also shows that, by contrast with the de Gennes ansatz, the order parameter wings in the isotropic phase exhibit negative order parameter, with principal axis perpendicular to the surface. For moving interfaces, using an approximation which at this stage does not yet include hydrodynamic coupling, we have compared our results with the analogue of the de Gennes ansatz used by the present authors in an earlier paper. We find that including biaxiality leads to larger effects in the dynamic than in the static properties, and that whereas this is essentially a perturbation to the energy, the velocity of the moving interface can be significantly slowed down. The slowing down effects are strongly correlated with surface biaxiality, but both effects seem to be diminished when the isotropic phase is advancing
Binary Mixture Composed of Nematic Liquid Crystal and Carbon Nanotubes: A Theoretical Description
Based on the phenomenological model first presented by van der Schoot et al., which predicts the alignment of carbon nanotube (CNT) dispersions in thermotropic nematic liquid crystals, we present the extensive results concerning the phase diagram and the orientational properties of the mixture in this chapter
Voies de signalisation activées par les cristaux d'urate monosodique dans les neutrophiles humains
Les polymorphonucléaires neutrophiles sont les principales cellules effectrices du système immunitaire inné. Les cristaux d'urate monosodique sont l'agent étiologique de l'arthrite goutteuse. L'interaction directe entre les neutrophiles humains et les cristaux d'UMS est essentielle pour le déclenchement de la crise de goutte aiguë. Le principal objectif de ce projet de recherche est d'identifier les voies de signalisation activées par les cristaux d'UMS et de caractériser leurs fonctions dans les réponses des neutrophiles humains
The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior
We review the theoretical research on the influence of disorder on structure and phase behavior of condensed matter system exhibiting continuous symmetry breaking focusing on liquid crystal phase transitions. We discuss the main properties of liquid crystals as adequate systems in which several open questions with respect to the impact of disorder on universal phase and structural behavior could be explored. Main advantages of liquid crystalline materials and different experimental realizations of random field-type disorder imposed on liquid crystal phases are described
Stochastic resonance in soft matter systems: combined effects of static and dynamic disorder
We study the impact of static and dynamic disorder on the phenomenon of
stochastic resonance (SR) in a representative soft matter system. Due to their
extreme susceptibility to weak perturbations soft matter systems appear to be
excellent candidates for the observation of SR. Indeed, we derive generic SR
equations from a polymer stabilized ferroelectric liquid crystal (LC) cell,
which is a typical soft matter representative constituting one of the basic
components in several electro-optic applications. We generalize these equations
further in order to study an even broader class of qualitatively different
systems, especially disclosing the influence of different types of static
disorder and interaction ranges amongst LC molecules on the SR response. We
determine the required conditions for the observation of SR in the examined
system, and moreover, reveal that a random field type static disorder yields
qualitatively different responses with respect to random dilution, random bond
and spin glass universality classes. In particular, while the latter three
decrease the level of dynamic disorder (Gaussian noise) warranting the optimal
response, the former evokes exactly the opposite effect, hence increasing the
optimal noise level that is needed to resonantly fine-tune the system's
response in accordance with the weak deterministic electric field. These
observations are shown to be independent of the system size and range of
interactions, thus implying their general validity and potentially wide
applicability also within other similar settings. We argue that soft matter
systems might be particularly adequate as a base for different SR-based
sensitive detectors and thus potent candidates for additional theoretical as
well as experimental research in the presently outlined direction.Comment: 11 two-column pages, 6 figures; accepted for publication in Soft
Matte
Surface tension and capillary waves at the nematic-isotropic interface in ternary mixtures of liquid crystal, colloids, and impurities
In mixtures of thermotropic liquid crystals with spherical poly(methyl methacrylate) particles, self-supporting networklike structures are formed during slow cooling past the isotropic-to-nematic phase transition. Experimental results support the hypothesis that a third component, alkane remnants slowly liberated from the particles, plays a crucial role. A theoretical model, based on the phenomenological Landau-de Gennes, Carnahan-Starling, and hard-sphere crystal theories, is developed to describe the continuous phase separation in a ternary nematic-impurity-colloid mixture. The interfacial tension and the dispersion relation of the surface modes of the nematic-isotropic interface are determined. The colloids decrease the interfacial tension and the damping rate of surface waves, whereas impurities act in an opposite way. This should strongly influence the formation of abovementioned networklike structures and could help explain some of their rheological properties
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