Curvatures of smectic liquid crystals and their applications

김대석,윤동기 한국정보디스플레이학회 2018 Journal of information display Vol.19 No.1

Curvature is an important concept for understanding layering structures in soft matters, ranging from complex macromolecular self-assembled structures to simple lipid bilayers. Among the various kinds of soft matters, smectic liquid crystal (LC) phases have been widely studied because of their periodic featured curvatures under various external forces. Generally, their curvatures are on the micron-scale due to the bulk elasticity of smectic LC materials. In this review, a combination of sublimation and recondensation of smectic LC materials generates a variety of curvatures at the nanometer scale, which cannot be achieved by self-assembly under thermal equilibrium conditions. In particular, we have focused on the change of curvatures in focal conic domains under non-equilibrium conditions, in which negative and zero Gaussian curvatures in the micron-scale transform to positive Gaussian curvatures in the micron- and nanometer scales. Finally, the review closes with applications using such non-equilibrium self-assembly of smectics.

Curvatures of smectic liquid crystals and their applications

Kim, Dae Seok,Yoon, Dong Ki The Korean Infomation Display Society 2018 Journal of information display Vol.19 No.1

Curvature is an important concept for understanding layering structures in soft matters, ranging from complex macromolecular self-assembled structures to simple lipid bilayers. Among the various kinds of soft matters, smectic liquid crystal (LC) phases have been widely studied because of their periodic featured curvatures under various external forces. Generally, their curvatures are on the micron-scale due to the bulk elasticity of smectic LC materials. In this review, a combination of sublimation and recondensation of smectic LC materials generates a variety of curvatures at the nanometer scale, which cannot be achieved by self-assembly under thermal equilibrium conditions. In particular, we have focused on the change of curvatures in focal conic domains under non-equilibrium conditions, in which negative and zero Gaussian curvatures in the micron-scale transform to positive Gaussian curvatures in the micron- and nanometer scales. Finally, the review closes with applications using such non-equilibrium self-assembly of smectics.

Nuclear magnetic resonance study of the smectic-cholesteric phase transition in a dimesogenic liquid crystal

Han, J.H.,Kim, J.S.,Park, J.K.,Lee, K.W.,Jin, J.I.,Choi, E.H.,Lee, C.E. Elsevier 2014 Current Applied Physics Vol.14 No.10

Nuclear magnetic resonance (NMR) spectroscopy has provided a unique opportunity to study the characteristic smectic-A to chiral nematic phase transition in a dimesogenic liquid crystal (''KI-5S''). The order parameters in the liquid crystalline phases were obtained from the <SUP>2</SUP>H NMR quadrupole splitting and <SUP>13</SUP>C NMR chemical shift measurements, manifesting a first-order smectic-nematic phase transition.

Nuclear magnetic resonance study of the smectic-cholesteric phase transition in a dimesogenic liquid crystal

한준희,J.S. Kim,박준규,이규원,J.-I. Jin,최은하,이철의 한국물리학회 2014 Current Applied Physics Vol.14 No.10

Nuclear magnetic resonance (NMR) spectroscopy has provided a unique opportunity to study the characteristic smectic-A to chiral nematic phase transition in a dimesogenic liquid crystal (“KI-5S”). The order parameters in the liquid crystalline phases were obtained from the 2H NMR quadrupole splitting and 13C NMR chemical shift measurements, manifesting a first-order smectic-nematic phase transition.

The Physical Properties of Thermotropic Side-Chain Triblock Copolymers of n-Butyl Acrylate and a Comonomer with Azobenzene Group

단경식,한양규,김병철 한국고분자학회 2009 Macromolecular Research Vol.17 No.5

The side chain liquid crystal triblock copolymers (TBCs), which underwent phase transitions below their decomposition temperature, were prepared by copolymerization of poly(n-butyl acrylate) and a comonomer containing the mesogenic azobenzene group. The physical properties of TBCs in the distinctive transition temperature ranges were investigated in terms of the liquid crystal (LC) content in the copolymers. The phase transition temperatures traced optically, thermally and rheologically were well coincided one another and clearly exhibited the phase transition of smectic-nematic-isotropic with increasing temperature. In the smectic phase, increasing temperature made the liquid crystal system more elastic, but viscosity (η') remained almost constant. In the nematic phase, increasing temperature abruptly decreased η' and G', ultimately leading to isotropic phase. Both smectic and nematic phases exhibited Bingham viscosity behavior but the former gave much greater yield stress at the same LC content.

The Physical Properties of Thermotropic Side-Chain Triblock Copolymers of n-Butyl Acrylate and a Comonomer with Azobenzene Group

Dan, Kyung-Sik,Kim, Byoung-Chul,Han, Yang-Kyoo The Polymer Society of Korea 2009 Macromolecular Research Vol.17 No.5

The side chain liquid crystal triblock copolymers (TBCs), which underwent phase transitions below their decomposition temperature, were prepared by copolymerization of poly(n-butyl acrylate) and a comonomer containing the mesogenic azobenzene group. The physical properties of TBCs in the distinctive transition temperature ranges were investigated in terms of the liquid crystal (LC) content in the copolymers. The phase transition temperatures traced optically, thermally and rheologically were well coincided one another and clearly exhibited the phase transition of smectic-nematic-isotropic with increasing temperature. In the smectic phase, increasing temperature made the liquid crystal system more elastic, but viscosity (${\eta}'$) remained almost constant. In the nematic phase, increasing temperature abruptly decreased ${\eta}'$ and G', ultimately leading to isotropic phase. Both smectic and nematic phases exhibited Bingham viscosity behavior but the former gave much greater yield stress at the same LC content.

Syntheses and Properties of New Smectic Reactive Mesogens and Their Application in Guest-Host Polarizer

Yang Ye,Rui He,오은채,강신웅,이승희,Xiang-Dan Li,이명훈 한국고분자학회 2020 Macromolecular Research Vol.28 No.10

We designed and synthesized new smectic liquid crystalline monomers containing photopolymerizable acrylate groups and a mesogenic core unit composed of two benzene rings, one pyrimidine-based heteroaromatic ring and an acetylene linking group. The structures of monomers were characterized by 1H nuclear magnetic resonance spectroscopy, and their mesomorphic behaviors were investigated by differential scanning calorimetry and polarized optical microscopy. Both of monomers showed an enantiotropic phase transition behavior with exhibiting both nematic phase and highly ordered smectic phase. Both of monomers showed smectic phases during the cooling process in the temperature range of 144.2-94.0oC and 154.0-85.8oC, respectively. Neither of these compounds showed a homogeneous alignment even at various temperatures, and therefore, their 50:50 mixture was chosen for the preparation of guest-host mixture because of its lowest crystallization point, wide smectic phase temperature range and superior aligning property. Polymerizable “host-guest” mixture formulated from the host liquid crystalline monomer mixture, dichroic dye and additives was injected into the sandwiched glass substrates having rubbed alignment layers at the isotropic temperature. Subsequent in-situ photopolymerization by UV irradiation at room temperature successfully resulted in a thin film polarizer with good polarizing properties. The fabricated guest-host polarizer showed a dichroic ratio (DR) of 13.1 and a degree of polarization (DOP) of 95.5% with the thickness of 5 μm.

Investigation on Induced Non-Tilted Smectic A* and Thermochromic Eect in Tilted Smectic C Phase of Linear Double Hydrogen Bonded Ferroelectric Liquid Crystals

P. Subhasri,T. Vasanthi,V. N. Vijayakumar,R. Jayaprakasam 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.4

Linear double hydrogen bonded ferroelectric liquid crystal (HBFLC) complexes are derived from non-mesogenic (R)-(+)-methylsuccinic acid and mesogenic 4-n-alkyloxybenzoic acids. Fourier transform infrared (FT-IR), polarizing optical microscope (POM), dierential scanning calorimetry (DSC) and X-ray diraction (XRD) studies are used to verify the existence of intermolecular hy- drogen bonds in the synthesized HBFLC complexes. An induced orthogonal non-tilted smectic A phase and a noteworthy observation of a thermally tuned thermochromic phenomenon are analyzed by using textural and thermal studies. Due to increasing elastic viscous force, the induced hexago- nal higher- order smectic G phase is reported in the lower alkyloxy carbon mesogens whereas the same is not observed in the individual compounds. Based on the temperature and change in the alkyloxy chain length, the induced thermochromic eect is discussed. Quenching of the nematic phase by an induced orthogonal phase is observed. Other liquid crystal parameters, such as the melting point, the phase transition temperature, the texture and the enthalpy, are reported.

Fabrication of highly efficient coatable polarizer from tolane-based smectic reactive mesogen

He, Rui,Oh, Enche,Ye, Yang,Wen, Pushan,Jeong, Kwang-Un,Lee, Seung Hee,Li, Xiang-Dan,Lee, Myong-Hoon Elsevier 2019 Polymer Vol.176 No.-

<P><B>Abstract</B></P> <P>This work is aimed to fabricate ultra-thin coatable polarizers on a single substrate based on “host-guest” effect between highly ordered smectic reactive mesogen (RM) and dichroic dye. We designed and synthesized a new tolane-based RM with a highly ordered smectic A phase at room temperature. Polymerizable “host-guest” mixture was formulated from the host RM, dichroic dye and additives, then spin-coated on a single substrate having an alignment layer. Subsequent in-situ photopolymerization by UV irradiation successfully resulted in a coatable polarizer with good polarizing properties. The fabricated coatable polarizer showed a dichroic ratio (DR) of 16.4 and a degree of polarization (DOP) of 99.3% with the thickness of 4 μm. The resulting coatable polarizer possessed a considerable solvent resistance, good thermal stability and robust mechanical properties. Moreover, we prepared a TN-mode LC cell by using the prepared coatable polarizers inside the cell (in-cell), in which the coatable polarizers acted as a polarizer and an alignment layer, simultaneously. The resulting TN cell with in-cell polarizers exhibited a decent electro-optical behavior. We believe that the coatable polarizer proposed in this study possesses practical application potential in ultra-thin LCDs or flexible OLEDs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Reactive mesogen with smectic A phase was synthesized for coatable polarizer. </LI> <LI> Coatable polarizer was fabricated on a single substrate by “host-guest” method. </LI> <LI> Coatable polarizer exhibits considerable optical property and excellent stability. </LI> <LI> LCD with in-cell structure was demonstrated by using the prepared coatable polarizer. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

새로운 스멕틱 액정 단량체의 합성 및 특성 연구

( Yang Ye ),김병국 ( Byeong Guk Kim ),안희영 ( Huiyeong Ahn ),이명훈 ( Myong-hoon Lee ) 한국화상학회 2021 한국화상학회지 Vol.27 No.1

분자 중심에 두 가지 다른 형태의 길고 강직한 core 구조를 함유하고 양 말단에 적당한 길이의 스페이서와 중합이 가능한 아크릴기를 포함하도록 설계된 두 종류의 액정단량체를 설계, 합성하였으며, 분자구조를 ¹H-NMR을 통해 확인 하였다. 합성된 액정단량체의 액정 특성을 DSC와 편광현미경을 사용하여 조사한 결과 각각 냉각 온도를 기준으로 84.6~74.0 ℃와 133.5~91.6 ℃ 사이에서 스멕틱 상을 나타냄을 확인하였다. 특히 경직된 선형의 아세틸렌기를 포함하는 액정단량체(PRM-2)의 경우에는 보다 스멕틱 액정상의 발현 온도 범위가 넓을 뿐 아니라 좀 더 정렬도(order parameter)가 높은 스멕틱 A상을 나타냄을 확인 할 수 있었다. Two reactive mesogens having two different type of rigid core with spacers and polymerizable acryl moieties at both ends were firstly designed and synthesized. Molecular structures of the compounds were characterized by ¹H-NMR spectroscopy, and their liquid crystalline properties at various temperature were investigated by DSC and a polarized optical microscopy. These compounds showed smectic liquid crystalline phase at 84.6~74.0 ℃ and 133.5~91.6 ℃, respectively. Especially, one of the synthyesized reactive mesogens containing a rigid linear acetylene unit exhibited a wide smectic temperature range showing a smectic A phase with a higher order parameter.