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Liquid Crystals Beyond Displays: Chemistry, Physics, and Applications by Quan Li

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Chapter 13

Fact or Fiction: Cybotactic Groups in the Nematic Phase of Bent Core Mesogens

Bharat R. Acharya and Satyendra Kumar

Platypus Technologies, Madison, WI, USA

Satyendra Kumar

Department of Physics, Kent State University, Kent, OH, USA

13.1 Introduction

A defect-free crystalline solid possesses long-range bond-orientational and positional- order and, therefore, has low symmetry. Lattices of crystalline solids are invariant under symmetry operations corresponding to a specific space group and the basis of the crystal [1]. Isotropic liquids, on the other hand, exhibit positional–order correlations that extend over a very short distance, typically only up to few nearest neighbors. As a consequence, the isotropic (I) liquid is invariant under any (translational, rotational, or other) symmetry operation (Figure 13.1a). Some materials with non-spherical building blocks (e.g., rods, discs, parallelepipeds, and bent rods) exhibit a number of intermediate phases between the crystalline solid and isotropic liquid. These are collectively known as liquid crystals (LCs). The anisotropic shape of their building blocks effectively leads to anisotropic interaction potentials and to the development of long-range orientational order. Depending on specific molecular organization and the nature of interactions, a variety of LC phases with different (short or long) range of bond-orientational or positional order along different spatial directions have been predicted and observed [2].

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