Electromechanical Effects of Ferroelectric Nematic Liquid Crystals

Kent State University, Kent OH

Investigators

Abstract

Non-Technical Description: This project focuses on investigating liquid crystals which exhibit a recently discovered special property called “ferroelectric nematic phase”. Ferroelectric nematic materials are remarkable in that even though they carry no net electric charge, they generate a spontaneous electric field, somewhat analogously to how certain materials such as iron become magnetic without the action of an external agent. Moreover, because ferroelectric nematics are fluid, the direction of their permanent electric orientation can be altered with a relatively small applied voltage. These properties make ferroelectric neumatic materials very attractive for new technological solutions for motion-control and energy conversion, which are important in applications ranging from soft robotics to green electricity generation. The project enables mentoring students at all levels in physics, chemistry and materials science, with a special focus on under-represented groups via the McNair Scholar and Research Experience for Undergraduates (REU) programs. It provides young scientists with interdisciplinary training that enable them to secure productive careers in cutting-edge STEM enterprise. An additional priority is the integration of highlights of the team’s research into hands-on, publicly accessible educational materials. Technical Description: Linear electromechanical coupling is an inherent property of ferroelectric materials, but has previously been explored only in crystals, polymers, and positionally ordered liquid crystals. The project’s research on ferroelectric nematic liquid crystals (FNLCs) explores the specific dependence of this coupling on both polarization and nanostructure. Complementary flexoelectricity studies illuminate the elastic and electric properties and reveal the role of ferroelectricity on flexoelectricity. The team’s materials’ synthesis effort furnishes an expanding library of FNLC compounds with optimized properties. Various experimental techniques are deployed to measure key material parameters, including ferroelectric polarization, dielectric constants, elastic constants, orientational viscosities, and intermolecular correlations that test current models predicting spatial modulation of the polarization orientation as an important feature of the ferroelectric phase. Detailed characterization of the collective molecular fluctuations elucidates the nature of phase transitions between different variants of polar nematic phases and explains variations of the electromechanical effects in antiferroelectric, ferroelectric, and modulated phases. The basic experimental results guide the way to new, comprehensive microscopic theories in addition to providing pathways to potential applications in emerging technologies such as soft robotics and clean electric energy generation. 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.