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Ryu, Seong Ho,Shin, Tae Joo,Gong, Tao,Shen, Yongqiang,Korblova, Eva,Shao, Renfan,Walba, David M,Clark, Noel A,Yoon, Dong Ki Published by the American Physical Society through 2014 Physical review. E, Statistical, nonlinear, and so Vol.89 No.3
<P>We have identified a metastable liquid-crystal (LC) structure in the de Vries smectic-A* phase (de Vries Sm-A*) formed by silicon-containing molecules under certain boundary conditions. The phase transition with the metastable structure was observed in a LC droplet placed on a planar aligned substrate and LCs confined in the groove of a silicon microchannel. During the rapid cooling step, a batonnet structure was generated as an intermediate and metastable state prior to the transition that yielded the thermodynamically stable toric focal conic domains. This distinctive behavior was characterized using depolarized reflection light microscopy and grazing incidence x-ray diffraction techniques. We concluded that the silicon groups in the molecules that formed the de Vries phase induced the formation of layered clusters called cybotactic structures. This observation is relevant to an exploration of the physical properties of cybotactic de Vries phases and gives a hint as to their optoelectronic applications.</P>
Highly Oriented Liquid Crystal Semiconductor for Organic Field-Effect Transistors
Han, Moon Jong,Wei, Dayan,Kim, Yun Ho,Ahn, Hyungju,Shin, Tae Joo,Clark, Noel A.,Walba, David M.,Yoon, Dong Ki American Chemical Society 2018 ACS central science Vol.4 No.11
<▼1><P/><P>We report a mesogenic compound which introduces nematic liquid crystal (LC) ordering into the benzothienobenzothiophene (BTBT) family of LCs, creating a new class of LC semiconducting materials which respond in a facile way to anisotropic surfaces, and can, thereby, be effectively processed into highly oriented monodomains. Measurement on these domains of the electrical conductivity, with in situ monitoring of domain quality and orientation using LC birefringence textures in electroded cells, brings a new era of precision and reliability to the determination of anisotropic carrier mobility in LC semiconductors.</P></▼1><▼2><P>The synthetic LC OSC is uniaxial planar aligned on the rubbed polymer substrate due to the long-range ordering characteristic of the nematic phase directly observed by polarized optical microscopy.</P></▼2>
Nucleation and growth of a helical nanofilament (B4) liquid-crystal phase confined in nanobowls
Ryu, Seong Ho,Kim, Hanim,Lee, Sunhee,Cha, Yun Jeong,Shin, Tae Joo,Ahn, Hyungju,Korblova, Eva,Walba, David M.,Clark, Noel A.,Lee, Sang Bok,Yoon, Dong Ki The Royal Society of Chemistry 2015 SOFT MATTER Vol.11 No.39
<P>The B4 helical nanofilament (HNF) liquid crystal (LC) phase is a three-dimensional (3D) helical structure composed of 2D smectic layers. Because of the complex shape of the HNF phase, it is difficult to understand the generation mechanism of HNFs in the bulk as well as in the thin-film condition. Here, we directly investigated the nucleation and growth of HNFs in nanobowls. A combination of electron microscopy and X-ray diffraction was used to reveal the transitional surface structures, in which barrel-like structures as well as short HNFs with random handedness were observed, depending on the LC film thickness. These results will be useful in achieving a better understanding of thin film structures of complex chiral structures in soft matter.</P> <P>Graphic Abstract</P><P>We investigated the confined B4, helical nanofilament LC phase in nanobowls as a function of LC film thickness. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5sm01783a'> </P>
Self-assembled hydrophobic surface generated from a helical nanofilament (B4) liquid crystal phase
Kim, Hanim,Yi, Youngwoo,Chen, Dong,Korblova, Eva,Walba, David M.,Clark, Noel A.,Yoon, Dong Ki The Royal Society of Chemistry 2013 Soft matter Vol.9 No.10
<P>Hydrophobic air/liquid crystal (LC) surfaces exhibiting self-assembled dual scale roughness have been made by simple cooling of a bent-core mesogen from its high temperature isotropic melt through two liquid crystal phases. The transition to the fluid smectic B2 phase generates micron-scale toric focal conic domains (TFCDs) at the surface. Upon further cooling into the hexatic smectic B4 phase these TFCD structures are preserved and become textured by the nanometer-sized helical nanofilaments (HNFs) of the B4. The resulting TFCD/HNF surface is hydrophobic and shows clear evidence for surface tension reduction characteristic of dual-scale roughness, suggesting a simple self-assembly-based approach to low surface tension surfaces using LC morphology.</P> <P>Graphic Abstract</P><P>Hydrophobic air/liquid crystal (LC) surfaces exhibiting self-assembled dual scale roughness have been made by simple cooling of a bent-core mesogen from its high temperature isotropic melt through two liquid crystal phases. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3sm27221d'> </P>
Three-dimensional textures and defects of soft material layering revealed by thermal sublimation
Yoon, Dong Ki,Kim, Yun Ho,Kim, Dae Seok,Oh, Seong Dae,Smalyukh, Ivan I.,Clark, Noel A.,Jung, Hee-Tae National Academy of Sciences 2013 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.110 No.48
<P>Layering is found and exploited in a variety of soft material systems, ranging from complex macromolecular self-assemblies to block copolymer and small-molecule liquid crystals. Because the control of layer structure is required for applications and characterization, and because defects reveal key features of the symmetries of layered phases, a variety of techniques have been developed for the study of soft-layer structure and defects, including X-ray diffraction and visualization using optical transmission and fluorescence confocal polarizing microscopy, atomic force microscopy, and SEM and transmission electron microscopy, including freeze-fracture transmission electron microscopy. Here, it is shown that thermal sublimation can be usefully combined with such techniques to enable visualization of the 3D structure of soft materials. Sequential sublimation removes material in a stepwise fashion, leaving a remnant layer structure largely unchanged and viewable using SEM, as demonstrated here using a lamellar smectic liquid crystal.</P>
Multistep hierarchical self-assembly of chiral nanopore arrays
Kim, Hanim,Lee, Sunhee,Shin, Tae Joo,Korblova, Eva,Walba, David M.,Clark, Noel A.,Lee, Sang Bok,Yoon, Dong Ki National Academy of Sciences 2014 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.111 No.40
<P><B>Significance</B></P><P>Bent-core mesogenic molecules form smectic liquid crystal phases in which the molecular layers are locally polar and chiral, and have a built-in tendency for saddle splay curvature, a combination that fills bulk neat bent-core smectics with self-assembled helical nanofilament bundles of twisted layers. This observation led us to explore the growth mode of such smectics under conditions of nanoconfinement and the remarkable observation reported here that single nanofilaments readily grow in linear nanoscale pores, generating a new motif of hierarchically self-assembled hybrid organic/inorganic structures for applications in chiral synthesis and separation.</P><P>A series of simple hierarchical self-assembly steps achieve self-organization from the centimeter to the subnanometer-length scales in the form of square-centimeter arrays of linear nanopores, each one having a single chiral helical nanofilament of large internal surface area and interfacial interactions based on chiral crystalline molecular arrangements.</P>