Orientation control over bent-core smectic liquid crystal phases

Abstract

Bent-core smectic liquid crystal (LC) phases (B phases) have been widely studied since their unusual polar and chiral properties were discovered in the 1990s. Relatively few studies have examined the mechanisms by which the orientation of the B phase may be controlled to produce the type of macroscopic domain that is essential for organic semiconductor, optical device and patterning applications. This review is intended to cover recent progress towards controlling the B phases upon layering, including anisotropic treatment methods and topographical confinement methods. Finally, this review closes with a discussion of B smectic phases that have been fabricated for use in certain applications.

Keywords:

• bent-core molecules
• liquid crystal phases
• orientation control
• external fields
• topographic confinement

Acknowledgements

This was supported by the National Research Foundation (NRF) Grant funded by the Korean Government (MSIP & MOE) (2012R1A1A1002486 and R31-10071), and the MRSEC Program funded by NSF DMR-0820579.

Additional information

Notes on contributors

Hanim Kim

Hanim Kim received her B.S. degree in applied chemistry and biological engineering from Ajou University in Korea in 2011. She is currently a graduate research assistant in Graduate School of Nanoscience and Technology (GSNT) at KAIST under the guidance of Professor Dong Ki Yoon in a Ph.D. program. Her research areas mainly focus on self-assembly and characterisation of novel liquid crystal phases including bent-core smectic liquid crystals, especially using porous anodic aluminium oxide, high-resolution scanning electron microscopy (SEM) and grazing-incidence X-ray diffraction (GIXD), which enables study of bent-core smectic liquid crystals in nanoscale.

Yun Ho Kim

Yun Ho Kim received his B.S., M.S. and Ph.D. degrees in chemical and biomolecular engineering from the KAIST in 2003, 2006 and 2010, respectively. His doctoral research was focused on the fabrication of large-area micro/nanopatterns by defect-assisted liquid crystalline structures. He then joined the Professor Xia’s group at Washington University in St Louis as a postdoctoral fellow from 2010 to 2011, working on the synthesis and self-assembly of novel metal nanostructures based on microfluidic system. After this, he joined Korea Research Institute of Chemical Technology as a senior researcher in Advanced Functional Materials Division. His current research focused on nanofabrication and optoelectronic applications based on functional materials such as liquid crystals, polymers and hybrid nanomaterials.

Sunhee Lee

Sunhee Lee received her B.S. degree in chemistry from Inha University in Korea in 2009. She is currently a graduate research assistant in GSNT at KAIST under the guidance of both Professor Sang Bok Lee and Professor Dong Ki Yoon in a Ph.D. program. Her research areas mainly focus on the synthesis of self-assembled nanoporous template and physical/chemical modification of nanochannel surface applying nanoconfinement system design, especially for characterisation of novel liquid crystal phases. SEM, transmission EM and GIXD analyses are powerful tools for studying of bent-core smectic liquid crystals in nanochannel confinement system.

David M. Walba

David M. Walba received his B.S. in chemistry from the University of California, Berkeley, in 1971 and Ph.D. in chemistry from the California Institute of Technology in 1975. After a 2-year postdoctoral (1975–77 and 1976–77 NIH fellowships) at the Univeristy of California, Los Angeles, he joined as an assistant professor in the Department of Chemistry (now Department of Chemistry and Biochemistry) at the University of Colorado, Boulder in 1977, where he has been Full Professor of Chemistry since 1987. He served as Chair of the Department (2006–2009) and founded the Materials and Nanoscience Program in the Department of Chemistry and Biochemistry during that time. He was also a co-founder and Vice President for Chemistry Research of Displaytech, Inc. (1984–1994) and served on the Dislaytech Board of Directors (1994–2001). He also serves as the Associate Director of the Liquid Crystal Materials Research Center headquartered on the University of Colorado Boulder campus (1998 to the present). He currently leads a group in the Department of Chemistry and Biochemistry working on the basic science and advanced applications of liquid crystals.

Noel A. Clark

Noel A. Clark received his Ph.D. in Physics from MIT in 1970. He subsequently held the positions of Research Fellow and Assistant Professor of Applied Physics at Harvard, before moving to the University of Colorado in 1977. Research in Professor Clark’s group is directed towards understanding and using the properties of condensed phases, ranging from experiments on the fundamental physics of phase transitions, such as melting, to the development of liquid crystal electrooptic light valves. The primary experimental tools are laser light scattering, electrooptics, video microscopy and high-resolution synchrotron X-ray scattering. Much of the research is on the physics of liquid crystals, colloids and suspensions that exhibit order on large length scales. These materials have become important testing grounds for modern theories of phase transitions, which is the principal focus of research. The group recently made a fundamental discovery about the nature of the melting transition, showing it to be a condensation of ‘broken bonds’. Applied research is in the area of liquid crystal electrooptics. Professor Clark’s group has pioneered a major new liquid crystal electrooptic technology, employing ferroelectric liquid crystals to make high-speed bistable light valves. These devices, which can be configured into linear and matrix arrays, are of particular use in optical computing and are one of the principal technologies to be developed in the Center for Optoelectronic Computing Systems at the University of Colorado. Recently the group has begun a new project on the fabrication of structures on a nanometer length scale. This work, which grew out of their research on biomembrane liquid crystals, is directed towards using two-dimensional protein crystals as fabrication masks and templates.

Sang Bok Lee

Sang Bok Lee is Professor in the Department of Chemistry and Biochemistry and the Deputy Director of the Nanostructure of Electrical Energy Storage (NEES) DOE-EFRC (Energy Frontier Research Center), University of Maryland, College Park, MD, USA, and also holds a WCU professorship at KAIST in Korea. He received his B.S., M.S. and Ph.D. degrees in chemistry from Seoul National University, Korea, in 1997. His research focuses on the fundamentals of synthesis and control of heterogeneous nanowire structures and fast electrochemistry of nanomaterials from high-power energy storage to electronics to nanomedicine.

Dong Ki Yoon

Dong Ki Yoon received his B.S. degree in chemical engineering from Yonsei University in 2001, and M.S. and Ph.D. degrees in chemical and biomolecular engineering from KAIST in 2003 and 2007, respectively. After working on the next-generation nanofabrication project in Samsung Electronics Co. for 2 years, he joined the Department of Physics at the University of Colorado, Boulder, for his postdoctoral research and focused on the study of the novel phenomena of liquid crystals in marginal space and laser-induced defects of liquid crystals. Following this, he joined KAIST as an assistant professor in the GSNT in 2011. Currently, he leads ‘Interesting Soft Matter group’ to pioneer the patterning applications based on soft matters such as liquid crystals, supramolecules and polymers.