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Journal ArticleDOI

A thermotropic biaxial nematic liquid crystal

01 Dec 1988-Molecular Crystals and Liquid Crystals (Taylor & Francis Group)-Vol. 165, Iss: 1, pp 123-130
TL;DR: In this paper, optical studies have been carried out on a nematogenic copper complex, which incorporates the features of both rod-like and disk-like molecules, and conoscopic figures have been presented demonstrating the occurrence of a biaxial nematic phase in the pure complex, the uniaXial-biaxial (Na-Nb) transition in binary mixtures, and the temperature variation of the biaaxiality near this transition.
Abstract: Optical studies have been carried out on a nematogenic copper complex, which incorporates the features of both rod-like and disk-like molecules. Conoscopic figures are presented demonstrating (i) the occurrence of a biaxial nematic phase in the pure complex, (ii) the uniaxial-biaxial (Na-Nb) transition in binary mixtures, and (iii) the temperature variation of the biaxiality near this transition. The I-Na-Nb phase diagram has been studied for the binary system.
Citations
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Journal ArticleDOI
TL;DR: An overview on the recent developments in the field of liquid crystalline bent-core molecules (so-called banana liquid crystals) is given in this article, dealing with general aspects of the systematisation of the mesophases, development of polar order and chirality in this class of LC systems and explaining some general structure-property relationships.
Abstract: An overview on the recent developments in the field of liquid crystalline bent-core molecules (so-called banana liquid crystals) is given. After some basic issues, dealing with general aspects of the systematisation of the mesophases, development of polar order and chirality in this class of LC systems and explaining some general structure–property relationships, we focus on fascinating new developments in this field, such as modulated, undulated and columnar phases, so-called B7 phases, phase biaxiality, ferroelectric and antiferroelectric polar order in smectic and columnar phases, amplification and switching of chirality and the spontaneous formation of superstructural and supramolecular chirality.

753 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the field of coordination chemistry with transition metal liquid crystals is presented. But this review is limited to coordination chemistry who can use specific expertise of new transition metal liquids.

435 citations

Journal ArticleDOI
TL;DR: An overview of the current state of research in the field of biaxial nematic liquid crystalline materials is given in this paper, where the major theoretical concepts are outlined, including the classification to different symmetries, the importance of cooperativity and cluster formation for the development of BN order and the conditions for the establishment of field induced and spontaneous BN in nematic phases.
Abstract: An overview over the current state of research in the field of biaxial nematic liquid crystalline materials is given. After a short introduction, providing some general aspects and summarizing the classical approaches, the main part focuses on recent developments of new concepts for designing biaxial nematics. First, the major theoretical concepts are outlined, including the classification to different symmetries, the importance of cooperativity and cluster formation for the development of biaxial order and the conditions for the establishment of field induced and spontaneous biaxiality in nematic phases. These new concepts also require the re-evaluation of the tools used for the identification of phase biaxiality, which are discussed briefly. In the second part, recent progress in the design of potential biaxial nematic materials, especially focussing on bent-core molecules with nematic phases, is reported and, finally, comparisons with phase biaxiality as observed in smectic liquid crystals are made.

299 citations

Journal ArticleDOI
TL;DR: A review of the thermotropic materials for which a biaxial nematic has now been claimed can be found in this article, where it is suggested that deuterium NMR spectroscopy is a powerful method with which to determine this.

238 citations

Journal ArticleDOI
TL;DR: In this article, the detailed structures of the various discotic phases and some of their important physical properties are described. But they are classified into two distinct categories, the columnar and the nematic.
Abstract: Recent studies have established that many compounds composed of disc-shaped molecules exhibit stable thermotropic liquid crystalline phases. They are now referred to as discotic liquid crystals. Structurally, most of them fall into two distinct categories, the columnar and the nematic. The columnar phase, in its simplest form, has long-range translational periodicity in two dimensions and liquid-like disorder in the third, whereas the nematic phase is an orientationally ordered arrangement of discs without any long-range translational order. This review article describes the detailed structures of the various discotic phases and some of their important physical properties.

221 citations

References
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Journal ArticleDOI
N. D. Mermin1
TL;DR: Aspects of the theory of homotopy groups are described in a mathematical style closer to that of condensed matter physics than that of topology in this paper, where the focus is on mathematical pedagogy rather than on a systematic review of applications.
Abstract: Aspects of the theory of homotopy groups are described in a mathematical style closer to that of condensed matter physics than that of topology. The aim is to make more readily accessible to physicists the recent applications of homotopy theory to the study of defects in ordered media. Although many physical examples are woven into the development of the subject, the focus is on mathematical pedagogy rather than on a systematic review of applications.

1,612 citations

Journal ArticleDOI
TL;DR: In this article, the ternary system potassium laurate-1-decanol-D${2}\mathrm{O}$ was studied over concentration ranges where nematic phases are likely to occur.
Abstract: The phase diagram of the ternary system potassium laurate-1-decanol-D$_{2}\mathrm{O}$ was studied over concentration ranges where nematic phases are likely to occur. Two uniaxial nematic phases which are separated by a biaxial nematic phase are found. In limited concentration range the following phase sequence may be observed reversibly on heating and on cooling: isotropic-uniaxial nematic (positive optical anisotropy)-biaxial nematic-uniaxial nematic (negative optical anisotropy)-biaxial nematic-uniaxial nematic (positive optical anisotropy)-isotropic.

629 citations

Journal ArticleDOI
Marvin J. Freiser1

533 citations

Journal ArticleDOI
TL;DR: In this article, a simple model for an interacting liquid of particles lacking an axis of rotational symmetry is proposed, and the four order parameters necessary to describe an ordered phase are identified.
Abstract: A simple model for an interacting liquid of particles lacking an axis of rotational symmetry is proposed. The four order parameters necessary to describe an ordered phase are identified. An ensemble of such particles is described by a mean field theory. A phase diagram showing both uniaxial and biaxial phases results. The model predicts a phase diagram similar to that of the phenomenological model of Alben.

404 citations

Journal ArticleDOI
R. Alben1
TL;DR: In this paper, a model for a fluid of biaxial particles within a type of mean-field approximation was solved. And the results suggest that the phase diagram of such a fluid exhibits a special critical point where two second-order critical lines meet a first-order phase boundary in a sharp cusp.
Abstract: A model is solved for a fluid of biaxial particles within a type of mean-field approximation. The results suggest that the phase diagram of such a fluid exhibits a special critical point where two second-order critical lines meet a first-order phase boundary in a sharp cusp. The features of the phase diagram suggest a new way to look for critical phase transitions and biaxial phases in liquid crystals.

196 citations