Materials World Network: Structure, Dynamics and Critical Phenomena in Biaxial Liquid Crystals

Kent State University, Kent OH

Investigators

Abstract

This international collaboration, between scientists at the University of Hull, UK and Kent State University having complementary expertise, focuses on understanding phenomena associated with biaxiality - the spontaneous occurrence of two distinct optical axes - in the so-called nematic phase of liquid crystals (LCs). Although it was hypothesized about 38 years ago, biaxial nematics have, until recently, proven quite elusive in real materials - indeed, virtually all nematics are optically uniaxial and virtually all applications of LCs have been restricted to the manipulation of a single optical axis. The biaxial nematic phase is expected in LCs composed of molecules (or, molecular aggregates) that are intrinsically biaxial in shape, e.g., plank-like or bent-core (banana-shaped) molecules. Another important possibility for formation of a biaxial nematic, which has been the subject of several intense theoretical investigations, arises in mixtures of disk- and rod-shaped molecules. Depending on the aspect ratios of these component molecules and on the concentration, one can expect three nematic phases, two uniaxial and one biaxial, with a specific topology of the phase diagram and interesting evolution of the nature of phase transitions. The principal investigator in the UK, Professor Georg Mehl, and his team have pioneered the synthesis of compatible rod- and disk-like systems, which form stable solutions and exhibit distinct nematic phases (possibly including a biaxial phase). The US researchers will probe the structure, optical, and other physical properties, the dynamics, and critical behavior at several interesting phase transitions between different nematic phases, both in systems with biaxial-shaped molecules and in rod-disc mixtures. The results and the data acquired under this project will help test the validity of the current theories and provide important insight into the physics and chemistry of novel LC materials. The researchers will employ state-of-the-art techniques such as dynamic light scattering, synchrotron x-ray diffraction, confocal and atomic force microscopies, and electro-optical measurements in their investigations. The results of this project are likely to have transformative impact on the industry via the emergence of a new display technology and other applications of optically biaxial fluids. Undergraduate and graduate students and postdocs will be trained in an area that has the potential of impacting the fields of photonics, telecommunications, and cyber infrastructure. Junior researchers will have opportunities to interact and forge long-term professional contacts with members of the research group in the UK and other international scholars at the Advanced Photon Source. US graduate students and postdocs will be able to diversify their skills and scientific experience and begin their careers with a profound appreciation for materials development as well as physical characterization.