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Abstract

We discuss changes in the symmetry and physical properties of an isotropic phase which has initially tetrahedral symmetry characterized by four unit vectors. In its undeformed state, these four vectors are at the tetrahedral angle (109.47°) to each other. We find that this optically isotropic phase becomes uniaxial under the influence of an external electric field, E, resulting in a phase with C_3v symmetry. For an applied simple shear flow, the system becomes biaxial and a time-dependent state with C₁ symmetry arises. We discuss to what extent deformations induced by external forces and flows on this optically isotropic phase, which we call a "deformable tetrahedratic phase", are consistent with observations at the isotropic-B7 transition found recently in compounds composed of banana-shaped molecules and suggest a number of experiments to test the conclusions of this model.