US-Ireland R&D Partnership: Structure-property relationships of new polar liquid crystalline phases through synthesis and characterization using a range of analytical techniques

Nontechnical Explanation:

The well-known liquid crystal display is generally based on molecules that are rod-like and may be modeled as a pencil sharpened at both ends. In the past 10-15-years there has been significant scientific interest in liquid crystals formed from bent molecules, modeled as a hockey stick, which also coincide with their mirror image. The study of molecules with these two structural properties has led to the discovery of new liquid crystalline phases with unique properties that are largely unexplored.

The purpose of this research is to chemically synthesize new molecules that have these structures and exhibit these new phases and then study their physical properties with the dual goals of better understanding the relationships between molecular structure and liquid crystal properties and facilitating future applications of these materials as photonic, energy storage, and switching devices. These goals are accomplished by the pooling of the complementary expertise of a synthetic chemist, a physicist, and an engineer, from Northern Ireland, the US, and the Republic of Ireland respectively.

This provides students and post-doctoral fellows a unique multidisciplinary and multinational environment for scientific, professional, and cultural enrichment through collaboration, scientific residencies in other Principal Investigator’s laboratories and the acquisition of skills that are not obtainable by working in a single laboratory.

Technical Description:

Current liquid crystal technologies are almost exclusively based on rod-like (calamitic) molecules that form nematic, and/or smectic phases. However, over the past 10-15-years there has been great interest in non-chiral molecules that are not rod-like. This led to the discovery of new nematic phases and corresponding nematic-nematic phase transitions.

These new phases are called the twist-bend, the splay-bend, the splay, and the ferro nematic. These phases and their phase transitions and physical properties are a largely unexplored frontier. Molecules of this geometry sometimes form polar smectic phases, and should such phases be found; they too will be studied.

The goal of this research is to synthesize and study the physical properties of new liquid crystalline materials that form from “bent” molecules with the objective of better understanding and advancing the relationship between molecular structure, the resulting liquid crystalline phases, and the physical and chemical properties of the resulting polar nematic and smectic mesophases. This is achieved through systematic synthesis of new mesogens that form the desired phases from bent core, bimesogen, and twisted core moieties; determination of liquid crystal phases and their transition temperatures; use of electro-optical and complementary spectroscopic techniques (x-ray scattering, Raman scattering, infrared, birefringence, wideband dielectric spectroscopy, and second harmonic generation) to investigate the structure and physical properties of these phases.

Finally, test cells with well oriented liquid crystal molecules will be fabricated. These will be used to investigate the effect of various (electric, magnetic, surface anchoring, and flow) fields to investigate applications of these phases as well as to facilitate measurements of physical properties.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.