Collaborative Research: Field-Induced Mesophases

Old Dominion University Research Foundation, Norfolk VA

Investigators

Abstract

Liquid crystals are widely known for their use in display technology, where rod-like molecules are aligned and reoriented via electric fields. Most of the available displays operate close to physical limits, and the constant demand for faster and more efficient devices has made the search for new materials the focus of the industry. Bent-core liquid crystals differ from the standard materials used in flat panels and portable displays in that the special shape of their molecules allows for ferroelectric behavior and intrinsic bistability at a lower manufacturing cost. That is, they have potential for superior operational speed, resolution, and efficiency at a competitive production cost as well as a wider spectrum of commercial applications which include spatial light modulators (SLMs), optical memories, optical computers and high-resolution microdisplays. To date, a clear description of the configurations (mesophases) of the devices based on bent-core materials has not been established, and many technical difficulties need to be overcome. This project is concerned with the numerical and theoretical modelling of these application-intensive materials and will fill an existing gap between theory and experiments. Its outcome will contribute to the validation and extension of the available models and will add to the understanding of the nature of phase transitions, and of electrical and optical properties, ultimately contributing to the manufacturing of superior liquid crystals-based devices. The graduate students involved will be trained in the interdisciplinary areas of applied mathematics, computational mathematics, and materials science. The main research objective will be in the analysis of electro/magneto optic effects, which will involve the study of materials' defects and their interactions; the refinement of existing models for ferroelectric liquid crystals with layered structures; and the study of a newly discovered phase, where the bent molecules arrange themselves in an heliconical structure, winding about a helical axis with nanoscale pitches. The investigators will examine the response to applied fields exhibited by a liquid crystal based on the materials' anisotropic optical properties. The main focus will be on the modelling and analysis of electro-optic interactions in bent-core molecule liquid crystals with an emphasis on bistable/ferroelectric properties and on the newly discovered twist-bend nematic phase. The effects of boundary conditions on the morphology of bulk and confined samples in Smectic A phases will also be considered. The studies will be based on generalized unit vectors and smectic order parameter energy models. The investigators will use and advance a diverse collection of mathematical tools for nonlinear problems, including variational methods, asymptotic analysis, and bifurcation and regularity theories for nonlinear partial differential equations. An essential component of the project will be to select, refine, and propose models that contains the relevant physical features of the examined phenomena. Numerical simulations of gradient flows and comparison with available experiments will play an important role in the research approach. Specific issues that will be addressed include a description of defects introduced in the polarization modulated smectic A phase by the bistable response to an applied field, understanding the electric self-interaction terms for bent-core materials, and exploring phase transitions and magnetic field effects in twist-bend bent-core materials. 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.