Elasticity and behaviour under magnetic fields of cubic lyomesophases and smectic D liquid crystals

We estimate the shear elastic constant in cubic liquid crystals such as D phases and cubic lyomesophases and find a value, which is about three orders of magnitude less than that of very soft atomic crystals ( 4 He) and three orders of magnitude higher when compared with colloidal crystals. The behaviour under an external magnetic field is discussed and the importance of coupling terms to the order parameter, especially for cubic lyomesophases, is pointed out Estimation de la constante d'elasticite de cisaillement pour ces phases: elle est de trois ordres de grandeur inferieure a celle des cristaux atomiques les plus mous (He) et de trois ordres de grandeur superieure a celle des cristaux colloidaux. Discussion du comportement sous champ magnetique, en particulier des termes de couplage au parametre d'ordre