Hanim Kim

Solvent‐Free Directed Patterning of a Highly Ordered Liquid Crystalline Organic Semiconductor via Template‐Assisted Self‐Assembly for Organic Transistors

Highly ordered organic semiconductor micropatterns of the liquid-crystalline small molecule 2,7-didecylbenzothienobenzothiophene (C10 -BTBT) are fabricated using a simple method based on template-assisted self-assembly (TASA). The liquid crystallinity of C10 -BTBT allows solvent-free fabrication of high-performance printed organic field-effect transistors (OFETs).

Multistep hierarchical self-assembly of chiral nanopore arrays

Significance 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. 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.

Alignment of helical nanofilaments on the surfaces of various self-assembled monolayers

We successfully prepared controlled layers of NOBOW molecules on a variety of self-assembled monolayers (SAMs) such that the layers formed oriented domain structures in which the complex chiral/polar crystalline helical nanofilaments (HNFs) were arranged to form a B4 bent-core liquid crystal (LC) phase. The alignment of the B2 phase, which formed at a higher temperature than the B4 phase, affected the direction of the HNFs. The HNFs formed on the B2 smectic layers and were aligned parallel or perpendicular, respectively, to the substrates with high or low surface energies (molecule-philic or -phobic SAM-treated substrates). The HNFs confined within rectangular microchannels modified by the SAMs were directly visualized by electron microscopy and X-ray diffraction studies. The orientations of the HNFs were found to be governed by the B2 smectic layer morphology.

Photomodulated Supramolecular Chirality in Achiral Photoresponsive Rodlike Compounds Nanosegregated from the Helical Nanofilaments of Achiral Bent-Core Molecules

We prepared a nonchiral mixture of achiral bent-core molecules and photoresponsive rodlike liquid crystalline (LC) molecules. With the help of the isothermal photochemical nematic (N)-isotropic (Iso) phase transition of the photoresponsive rodlike LC molecules, the corresponding phase transition from a dark conglomerate BX phase to another distinguishable dark conglomerate B4 phase took place in the mixture. A large circular dichroism (CD) signal originating from supramolecular chirality was detected in the initial BX phase. On the other hand, the detected CD signal was decreased in the B4 phase after UV irradiation. Interestingly, the decreased CD signal could be reverted to the initial CD signal with visible irradiation. This chiroptical process revealed in this work was stable and reversible and thus opens up the possibility of practical applications such as rewritable optical storage.

Orientation control over bent-core smectic liquid crystal phases

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.

Multidimensional Helical Nanostructures in Multiscale Nanochannels

We have investigated the various morphological changes of helical nanofilament (HNF; B4) phases in multiscale nanochannels made of porous anodic aluminum oxide (AAO) film. Single or multihelical structures could be manipulated depending on the AAO pore size and the higher-temperature phase of each molecule. Furthermore, the nanostructures of HNFs affected by the chemical affinity between the molecule and surface were drastically controlled in surface-modified nanochannels. These well-controlled hierarchical helical structures that have multidimensions can be a promising tool for the manipulation of chiral pores or the nonlinear optical applications.

Creation of a superhydrophobic surface from a sublimed smectic liquid crystal

Dual-scale structures showing superhydrophobic characteristics have been fabricated using sublimable smectic liquid crystals (LCs). Here, toric focal conic domains (TFCDs) of smectic LCs were prepared on micron-sized square pillar patterns. And the layer by layer reconstruction of TFCDs under a thermal sublimation process was followed to form nano-scale hemi-cylinders. Based on this dual-scale roughness, the superhydrophobic surface was successfully created with a water contact angle (CA) of ∼150° and a low CA hysteresis of ∼9°. The resulting superhydrophobic surface is the first application using sublimable LCs, suggesting a new approach for potential applications in LC science and engineering.

Structural transitions and guest/host complexing of liquid crystal helical nanofilaments induced by nanoconfinement

A perfectly aligned liquid crystal phase can be achieved by an interaction with helical nanofilament under nanoconfinement. A lamellar liquid crystal (LC) phase of certain bent-core mesogenic molecules can be grown in a manner that generates a single chiral helical nanofilament in each of the cylindrical nanopores of an anodic aluminum oxide (AAO) membrane. By introducing guest molecules into the resulting composite chiral nanochannels, we explore the structures and functionality of the ordered guest/host LC complex, verifying the smectic-like positional order of the fluidic nematic LC phase, which is obtained by the combination of the LC organization and the nanoporous AAO superstructure. The guest nematic LC 4′-n-pentyl-4-cyanobiphenyl is found to form a distinctive fluid layered ordered LC complex at the nanofilament/guest interface with the host 1,3-phenylene bis[4-(4-nonyloxyphenyliminomethyl)benzoate], where this interface contacts the AAO cylinder wall. Filament growth form is strongly influenced by mixture parameters and pore dimensions.

Nucleation and growth of a helical nanofilament (B4) liquid-crystal phase confined in nanobowls

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.

Airflow-aligned helical nanofilament (B4) phase in topographic confinement

We investigated a controlled helical nanofilament (HNF: B4) phase under topographic confinement with airflow that can induce a shear force and temperature gradient on the sample. The resulting orientation and ordering of the B4 phase in this combinational effort was directly investigated using microscopy. The structural freedom of the complex B7 phase, which is a higher temperature phase than the B4 phase, can result in relatively complex microscopic arrangements of HNFs compared with the B4 phase generated from the simple layer structure of the B2 phase. This interesting chiral/polar nanofilament behaviour offers new opportunities for further exploration of the exotic physical properties of the B4 phase.