1,721,082 research outputs found
Some Remarks on the Impedance Variations of a Homeotropic Nematic Cell Subjected to Ultrasounds
No full textOrientazione di un cristallo liquido nematico indotta da un substrato: effetto dell'energia di adesione
No full textOn the surface-type elastic constant K24 in nematics
No full textIn the present paper a novel method is presented, allowing us to measure the saddle-splay elastic constant K24 and consequently the mixed splay-bend elasticity K12, in the frame of the continuum-theory. On a weakly anchored nematic cell with a pure bend distortion a twist deformation is superimposed, due to a magnetic field greater than Freedericksz' threshold. The free energy term of the K13-type is rigorously zero, whereas the term affected by K24 is different from zero, and is dependent only on the twist angles at the walls, and not on their first derivatives. Such a situation allows us to solve the variational problem and to evaluate K24, by measuring the shift of the critical field, provided the anchoring strengths at both walls are suitably chosen
A New Method for Measuring the Mixed Splay-Bend Elasticity and the Anchoring Strength in a Nematic Film
No full textSecond order elasticity and critical thickness of hybrid aligned nematics strongly anchored on the planar side
No full textThe second order bulk elastic constants, characterizing the squares of second order derivatives of the director, deeply influence the behavior of weakly anchored nematics. Here the critical thickness of a Hybrid Aligned Nematic cell, strongly anchored on the planar side, is calculated as a function of the anchoring strength at the homeotropic side, of the mixed splay-bend, and of the second order bulk elasticity
On the Critical Thickness of a Twisted Nematic Cell
No full textThe critical thickness of a twisted nematic cell is predicted in the framework of the continuum theory, and its dependence on the twist elastic constant and on the twist anchoring conditions is deduced in the absence of pretilt Moreover, the presence of a pretilt identical on both substrates is considered, but with the restriction of a single elastic constant Furthermore, the rigorous independence of the critical thickness of the surface-like volume elasticities is shown and the twist angles at the walls are analytically obtained for the cell thickness close to the critical one. The particular case of equal anchoring on both sides is also discussed.Dans le cadre de la théorie du continuum nous avons calculé l'épaisseur critique d'une cellule nématique en présence de déformation de torsion, et obtenu sa variation en fonction de la constante élastique de torsion et des conditions d'ancrage pour une inclination nulle. En outre, le cas d'inclinations identiques aux deux parois a été étudié dans l'hypothèse d'une constante élastique unique. Nous avons montré que l'épaisseur critique ne dépend pas des constantes élastiques en volume de type surface, et nous avons calculé analytiquement l'angle de torsion aux parois pour une cellule mince d'épaisseur voisine de l'épaisseur critique. Nous avons également analysé le cas particulier d'une cellule avec des conditions d'ancrage identiques sur les deux parois
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