Surfaces, Chirality, and Liquid Crystals

Case Western Reserve University, Cleveland OH

Investigators

Abstract

NON-TECHNICAL ABSTRACT Surfaces play an important role in aligning the liquid crystals (LC) that are the core of LC displays. Currently, only simple forms of alignment have been used and these have been adequate for today's displays. However, future devices with even greater capabilities will depend on developing more complex surface alignments. One possibility is to use surfaces patterned at the microscopic level to introduce chirality, or handedness, into the ordering of the liquid crystals. Chirality - the fact that your right hand is not a mirror image of the left - plays an important role in many areas such as biology and chemistry. In fact, many pharmaceuticals must be prepared with a specific chirality (either right or left handed) to be effective. In this project the principal investigator and his team will explore ways of introducing chirality into liquid crystals by patterning the surface they are in contact with. They will then study these systems to determine what new patterns develop, what are the forces introduced by these new patterns and how they can be used to more effectively separate molecules with different chirality, such as pharmaceuticals. The students involved in these studies, from high school to graduate school, will be trained in state-of-the-art techniques and will work with collaborators from around the world. TECHNICAL ABSTRACT Surfaces play a defining role in myriad systems; this is especially true of liquid crystals. By mechanically tailoring the surface structure on nanoscopic length scales, the PI manipulates the behavior and symmetry of the adjacent liquid crystal, facilitating new phenomena, applications, and a more profound understanding of fundamental physical and chemical properties. This project focuses on imposed chirality at the surface, induced chirality in the achiral liquid crystal, and forces associated with chirality. In recent years the PI has developed powerful techniques both to establish controlled chirality at surfaces using inherently achiral materials and to image liquid crystal orientation on nanoscopic length scales. He is ratcheting up these techniques and addressing the most seminal issues in which chirality originates at an interface. The work has several objectives, including: optimization of mechanically-generated chiral surfaces; understanding the influence of surface chirality on liquid crystal symmetry and anchoring; spatially-controlling enantiomeric segregation at scales as small as 2-3 micrometers; examining forces associated with chiral "dipoles"; creating chiral topological defects, including chiral defects, at the 2-3 micrometer scale and using them as traps for chiral nanoparticles; and the Holy Grail: understanding chiral induction, both the strength and penetration depth. The PI?s team exploits a battery of experimental tools, including - but not limited to - optical microscopy and optical nanotomography (the PI's modification of near field scanning optical microscopy), atomic force microscopy, AFM and electron beam nanolithography, and ellipsometry. By exploiting the PI's ability to create exquisitely tailored chiral substrates from achiral materials and to image liquid crystal orientation down to x,y,z dimensions of 60 x 60 x 1 nm, this work is transforming our conceptions about - and methodology toward - surface chirality and its effects on anisotropic fluids. In particular, it is leading to vastly improved methods to create spatially-controlled chirality at surfaces, the quantification and understanding of surface-induced chirality in otherwise achiral molecules, and its manifestation in other physical phenomena. These issues cut across multiple disciplines, as consequences of chirality appear throughout biology, chemistry, physics, medicine, and pharmacology. The research is giving rise to a host of novel phenomena, and establishing new scientific paradigms for surface chirality and liquid crystals.