講演題目：　LC PHASES FORMED BY BANANA-SHAPED MOLECULES
                  POSSIBLE CONSEQUENCES OF TETRAHEDRATIC ORDER

講　師　：　Prof. Helmut R. Brand
　　　　　　     (Theoretische Physik III, Universitat Bayreuth,
                                                 95440 Bayreuth, Germany)

日　時　：　平成15年10月14日（火）　11:00-
場　所　：　北海道大学大学院理学研究科物理学専攻　大学院講義室
　　　　　　　理学部　2号館（2−11号室）

要　旨　：
　 　Some of the most interesting developments in liquid crystals over the last few years are related to the physical properties of the liquid crystalline phases exhibited by banana-shaped (bent-core) molecules.
    Experimental evidence to date suggests that this is indeed a new sub-field of thermotropic liquid crystals. The biggest challenge is the condensed state known as B7 that grows into the isotropic liquid with many different growth patterns including spirals with both hands. Neither the symmetry nor the physical properties of B7 are understood. A tetrahedratic phase, T, is described by four unit vectors, n¹ to n⁴, oriented along the four tetrahedral corners of a cube. It has the symmetry:

T (- n^a) = - T ( n^a)       (a = 1,2,3,4);

that is odd under parity.
As tetrahedra are not space-filling objects, they can be viewed equally well as precursors of condensed lamellar and/or columnar mesophases. Tetrahedratics are thus a model for studying frustrated lamellar and columnar liquid crystalline phases with many different condensed states that are energetically very close together. In a first step we analyzed the coupling of flow to electric fields and temperature gradients assuming that the symmetry of the tetrahedratic phase is unchanged by the external forces. We also discuss what happens when the tetrahedral angle is allowed to change under the influence of external forces and fields. We also analyze how an external electric field applied to an isotropic tetrahedratic phase can induce orientational order Qij as well as smectic layering. The relation of our analysis to recent experimental observations by Weissflog et al. will be discussed. Work done in collaboration withP.E. Cladis and Harald Pleiner

世話人　　　北　孝文 （北海道大学大学院理学研究科）
　　　　　　　　　　　　（Tel: 011-706-2687, kita@phys.sci.hokudai.ac.jp）