HYDRODYNAMICS AND ELECTROKINETICS OF FERROELECTRIC NEMATIC

Kent State University, Kent OH

Investigators

Abstract

Non-technical abstract: Nematic liquid crystals are fluids formed by orientationally ordered rod-like molecules. The combination of fluidity and orientational order makes them highly responsive to external electromagnetic fields, a property that revolutionized the industry of informational displays. For more than 100 years, research and applications focused on nematics with a nonpolar orientational order that does not distinguish between the heads and tails of the molecules. It was established that the fluid properties of these non-polar nematics are incredibly complex, with five different viscosity coefficients and a variety of flow regimes, such as flow-aligning, tumbling, logrolling, kayaking, back-flowing, etc. Prior studies uncovered how one can control the flows to enable useful functionalities, such as optical contrast switching in liquid crystal displays or production of highly ordered Kevlar polymers with a high tensile strength. The project explores flows in newly discovered ferroelectric nematic liquid crystals, in which the orientational order is polar, with all the molecules pointing in the same direction, thus building a macroscopic electric polarization. The activity’s broader significance and importance in research and education is that it establishes how the hydrodynamic flows of ferroelectric nematic fluids are triggered by externally applied shear and by the application of electric field. Understanding flows of ferroelectric fluids has the potential for enormous societal benefits in the technologies of the future, which exploit the unique sensitivity of the ferroelectric nematics to weak electric fields. The data form an important background for the development of miniature machines and actuators. The research provides an excellent platform to educate students in materials science, out-of-equilibrium phenomena, hydrodynamics, electrokinetics, and advanced microscopy. The activity educates a new generation of scientists with fundamental and technological expertise in advanced soft materials. The research involves high schoolers, undergraduate students, and graduate students. Technical abstract: Exploration of ferroelectric nematic fluids, which started only a few years ago, is an explosively growing fascinating area. The project answers fundamental questions of how the electric polarization of ferroelectric nematic behaves under shear, how surface anchoring patterning shapes electro-osmotic flows, and what are the mechanisms of electrophoresis of colloids in the ferroelectric fluid environment and ferroelectric droplets in isotropic electrolytes. The intellectual merit is in unveiling new physics of fluid ferroelectrics and advancing the knowledge of mechanisms by which the uniform and spatially varying predesigned polarization field can command the dynamics in response to the external electric field. The research unveils the remarkable potential of ferroelectric nematics to convert the energy of the environment into systematic and controlled directional movement at the microscale. The dynamics of ferroelectric nematics is an important part of the science of out-of-equilibrium phenomena. The experiments combine precision shear-producing and shear-characterizing rheometers with state-of-the-art modern optics techniques such as polarizing microscopy, second harmonic generation microscopy, fluorescence confocal polarizing microscopy. 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.