R. Amaranatha Reddy

Bio: R. Amaranatha Reddy is an academic researcher from Martin Luther University of Halle-Wittenberg. The author has contributed to research in topics: Liquid crystal & Mesophase. The author has an hindex of 26, co-authored 36 publications receiving 2407 citations. Previous affiliations of R. Amaranatha Reddy include Raman Research Institute & University of Colorado Boulder.

Bent-core liquid crystals: polar order, superstructural chirality and spontaneous desymmetrisation in soft matter systems

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.

Spontaneous Ferroelectric Order in a Bent-Core Smectic Liquid Crystal of Fluid Orthorhombic Layers

Abstract: Macroscopic polarization density, characteristic of ferroelectric phases, is stabilized by dipolar intermolecular interactions. These are weakened as materials become more fluid and of higher symmetry, limiting ferroelectricity to crystals and to smectic liquid crystal stackings of fluid layers. We report the SmAP(F), the smectic of fluid polar orthorhombic layers that order into a three-dimensional ferroelectric state, the highest-symmetry layered ferroelectric possible and the highest-symmetry ferroelectric material found to date. Its bent-core molecular design employs a single flexible tail that stabilizes layers with untilted molecules and in-plane polar ordering, evident in monolayer-thick freely suspended films. Electro-optic response reveals the three-dimensional orthorhombic ferroelectric structure, stabilized by silane molecular terminations that promote parallel alignment of the molecular dipoles in adjacent layers.

Silicon-Containing Polyphilic Bent-Core Molecules: The Importance of Nanosegregation for the Development of Chirality and Polar Order in Liquid Crystalline Phases Formed by Achiral Molecules

Abstract: Polyphilic molecules composed of a bent aromatic core, oligo(siloxane) units, and alkyl segments were synthesized, and the self-organization of these molecules was investigated. Most materials organize into polar smectic liquid crystalline phases. The switching process of these mesophases changes from antiferroelectric for the nonsilylated compounds via superparaelectric to surface-stabilized ferroelectric with increasing segregation of the silylated segments. It is proposed that the siloxane sublayers stabilize a polar synclinic ferroelectric (SmCsPF) structure, and the escape from a macroscopic polar order as well as steric effects leads to a deformation of the layers with formation of disordered microdomains, giving rise to optical isotropy. Another striking feature is the spontaneous formation of chiral domains with opposite handedness. For two compounds, a temperature-dependent inversion of the optical rotation of these domains was found, and this is associated with an increase of the tilt angle of t...

Influence of fluorine substituent on the mesomorphic properties of five-ring ester banana-shaped molecules

Abstract: The synthesis and characterization of more than a hundred achiral compounds composed of banana-shaped molecules and belonging to eleven different homologous series are reported. All these symmetrical five-ring compounds are esters and are derived from resorcinol. The compounds have been systematically substituted by fluorine on the phenyl rings of the arms of these banana-shaped molecules. The mesophases exhibited by these compounds have been characterized using a combination of polarized light optical microscopy, differential scanning calorimetry and X-ray diffraction studies. Electro-optical investigations have been carried out on several compounds and both ferroelectric and antiferroelectric properties are observed. The influence of the position of the fluorine substituent on the nature of the mesophase obtained has been examined.

Direct transition from a nematic phase to a polar biaxial smectic A phase in a homologous series of unsymmetrically substituted bent-core compounds

Abstract: The synthesis and characterization of twenty seven new compounds belonging to three homologous series of compounds derived from 3-hydroxybenzoic acid are reported. One of the terminal positions of the constituent molecules of these compounds is substituted with a strongly polar cyano group while the other end contains an n-alkyl chain attached to a biphenyl moiety. Twenty two of these compounds show the polar partial bilayer biaxial smectic A phase which is antiferroelectric in nature. In addition, a direct transition from the nematic phase to the polar partial bilayer biaxial smectic A phase which has not been seen before is also reported. The mesophases have been characterized using polarized light optical microscopy, differential scanning calorimetry, X-ray diffraction studies and electro-optical experiments.

Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions

Abstract: In this review, we describe the recent advances in supramolecular helical assemblies formed from chiral and achiral small molecules, oligomers (foldamers), and helical and nonhelical polymers from the viewpoints of their formations with unique chiral phenomena, such as amplification of chirality during the dynamic helically assembled processes, properties, and specific functionalities, some of which have not been observed in or achieved by biological systems. In addition, a brief historical overview of the helical assemblies of small molecules and remarkable progress in the synthesis of single-stranded and multistranded helical foldamers and polymers, their properties, structures, and functions, mainly since 2009, will also be described.

PAMELA Measurements of Cosmic-Ray Proton and Helium Spectra

Abstract: Protons and helium nuclei are the most abundant components of the cosmic radiation Precise measurements of their fluxes are needed to understand the acceleration and subsequent propagation of cosmic rays in our Galaxy We report precision measurements of the proton and helium spectra in the rigidity range 1 gigavolt to 12 teravolts performed by the satellite-borne experiment PAMELA (payload for antimatter matter exploration and light-nuclei astrophysics) We find that the spectral shapes of these two species are different and cannot be described well by a single power law These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy More complex processes of acceleration and propagation of cosmic rays are required to explain the spectral structures observed in our data

Bent-core liquid crystals: polar order, superstructural chirality and spontaneous desymmetrisation in soft matter systems

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.

Bent-Core Liquid Crystals: Their Mysterious and Attractive World

Abstract: Structures and properties of liquid crystalline phases formed by bent-core molecules are reviewed. At least eight phases designated as B1–B8 have been found, being unambiguously distinguished from phases formed by usual calamitic molecules due to a number of remarkable peculiarities. In addition to B1–B8 phases, smectic A-like phases and biaxial nematic phases formed by bent-core molecules are also reviewed. The most attractive aspects of this new class of liquid crystals are in polarity and chirality, despite being formed from achiral molecules. The bent-core mesogens are the first ferroelectric and antiferroelectric liquid crystals realized without introducing chirality. Spontaneous chiral deracemization at microscopic and macroscopic levels occurs and is controllable. Moreover, achiral bent-core molecules enhance system chirality. The interplay between polarity and chirality provides chiral nonlinear optic effects. Further interesting phenomena related to polarity and chirality are also reviewed.