Liquid crystals (LCs) from particles and molecular aggregates: Self-organized films from disk-like LCs

Park Ji Hyun 서울대학교 융합과학기술대학원 2015 국내박사

Self-assembly is a powerful means of creation of molecular or particle organized structures without the intervention of external forces. Liquid crystals are an outstanding example of self-assembled systems exhibiting a large variety of assemblies and well known applications like flat panel displays. Liquid crystal is the phase that combines fluidity of isotropic liquids with macroscopic anisotropy in the properties like solid crystals due to the long-range orientational order. Materials forming liquid crystals phases are grouped into two main classes: thermotropic and lyotropic liquid crystals. Thermotropic liquid crystals are formed by single or multiple-component molecular systems that have liquid crystal phases within certain temperature range. Instead lyotropics can be formed by a variety of building blocks in aqueous solutions above a certain concentration threshold. For both classes, the building blocks are anisometric with typically rod- or disk-like shape and different nature, even formed by nanoparticles of graphene or cellulose. The self-assembly behavior of these systems is not trivial to understand but it is relevant for profiting from their properties, and find their use in various geometries with attractive optical or electrical properties. In the framework of exploring liquid crystals and nanoparticle systems, this work mainly deals with liquid crystal systems formed by disk-like building blocks, more precisely, hexapentyloxytriphenylene (HAT5) discotic liquid crystal molecules and graphene oxide or reduced graphene flakes. However, since the assembly of HAT5 goes through the formation of rod-like aggregates in solvents, also the self-assembly of elongated nanoparticles in solvent and during its evaporation has an attention here. Discotic liquid crystals (LCs) are formed by disk-like molecules that can form columnar hexagonal phases. They are attractive materials due to the 1-dimensional electrical conductivity along the columns as a result of π-π interaction between polycyclic aromatic cores. A key advantage of discotics is their self-organization into ordered molecular wires on macroscopic scale with the ability of annealing of defects by temperature. We investigate the formation of fiber-like structures of discotics deposited from solution, focusing on the factors that influence the wire assembly. In particular, the resulting molecular structures are strongly dependent on the evaporation rate of the solvent as well as the nature of the substrates. Moreover, the molecular structure of the solvent plays an important role in the structural formation influencing the morphology of the final assembly and presumably the molecular stacking. Aromatic solvents favor the formation of wires that in turn also self-organize assuming a common alignment direction. We argue that this process is driven by a lyonematic formation during the evaporation process. Our findings provide an attractive route for tailoring or changing the geometry of supramolecular assemblies not necessarily by changing the discotic molecular structure but by simply choosing a solvent with a desired structure. We use various deposition methods based on solution for the realization of molecular wire thin films and their morphology was investigated by atomic force microscopy (AFM) and polarized optical microscopy, for optically detectable films. Temperature can induce changes in of the structure even in very thin films, with thicknesses of few tents of nanometers, as monitored locally by AFM. Glazing incidence X-ray diffraction techniques confirmed that the alignment in our thin films is planar, which means that the discotic molecules have an edge-on position on the substrates, and columns with a lattice organization perpendicular to the substrates. Planar alignment was also confirmed by polarized Raman spectroscopy. We could also observe very strong anisotropic response, reflecting the much higher polarizability along the molecular wire axis compared to the perpendicular direction as a result of a good intra-columnar molecular overlap. The advantage of a structure formed by long and well aligned wires was confirmed by electrical measurements on isotropic versus macroscopically aligned samples, the latter showing a three time increase in electrical conductivity. The self-assembly ability and the promising conductive properties are attractive per se but also in view of the integration of these self-assembled structures with nanoparticles and nanowires in particular. The second liquid crystal system that was studied was based on graphene flakes in solvent. Graphene, a monolayer of graphite, is an attractive material for a variety of applications such as in electronic devices either as transparent and conductive electrodes or in sensors. Graphene can be produced with different methods such as mechanical exfoliation, chemical vapor deposition or chemical methods. The latter is interesting for the ease of processability and its versatility. This process goes through the formation of an oxidative form of graphene, called graphene oxide (GO). One of the greatest advantages of GO flakes is the dispersability in water due to the hydrophilic functional groups. In addition, GO can form spontaneously organized phases of discotic liquid crystal type, useful for creating long-range orientational order that is advantageous for optimizing charge paths in devices. The liquid crystal phase appears above a certain concentration of the GO flakes, and the threshold concentration is affected by several specific properties of graphene oxide sheets like their aspect ratio or flatness. Studying a series of GO suspensions from 1.0 mg/ml to 0.1 mg/ml, a clear nematic liquid crystal phase, phase exhibiting a certain degree of long-range orientational order but not positional, could be observed by polarized optical investigations at very low concentrations. The existence of a very low threshold, below 0.25 wt%, can be explained with the presence of ultra-large flakes of GO in our samples and to the relatively low amount of defects in the flakes which gives them flatness. We report the evaluation of GO concentration, especially the region of phase coexistence related to the size distribution of the flakes, using UV-visible spectroscopy, by taking advantage of the Lambert & Beer law. Unidirectional alignment of GO flakes can be induced by external electric fields from isotropic dispersions showing a very large Kerr coefficient. This behavior shows attraction to electro-optical switching devices such as a liquid crystal displays (LCDs). Since the electro-optic response is dependent on the particle polarizabiliy, the reduced GO having higher polarizability than GO is a very attractive system for improved electro-optic response. However, it is difficult to produce liquid crystalline phases with reduced GO (rGO) due to their poor dispersability in water and the consequent tendency to aggregate. Herein we induce suggest the LC phase in rGO by reducing directly GO suspension with L-ascorbic acid after pretreatment with surfactants. The samples were studied by dynamic light scattering and the birefringence of both GO and rGO suspensions was studied as a function of applied electric field.

Programmable Alignment and Thermotropic Actuation in Liquid Crystal Elastomers with Smectogenic Moieties

이진형 부산대학교 대학원 2026 국내박사

TTF 기반 액정의 합성과 특성

왕뢰 전북대학교 대학원 2008 국내박사

Discotic liquid crystal (LC) materials have attracted a lot of attentions as promising charge-transfer organic candidates in optoelectronic devices. Due to the intermolecular π-orbital overlapping between discotic building blocks within ordered 2-dimensional (2D) columnar phases, electrical/photo conductivity can be significantly enhanced along the long axis of columns. Additionally, mesomorphic states of discotic columnar phases allow us to control the molecular alignment and minimize the defects, such as grain boundaries, which are inevitable drawbacks for the charge transportation in the crystal materials. Among the various candidates of organic materials for optoelectronic applications, tetrathiafulvalene (TTF) is one of the best candidates due to its excellent electron-donating properties. However, most researches about TTF and its derivatives have been focused on their crystal phases. In order to enhance their electron mobility, it is necessary to control their structures and morphologies to get rid of grain boundaries between the domains and to obtain the macroscopically oriented single domain. The question is: how can we obtain the defect-free single crystal-like TTF domain? One of the possible answers is the columnar LC phase. We synthesized four series of novel TTF derivatives. Two of them do not show any liquid crystal properties. The other two series including asymmetry and symmetry structure are liquid crystal TTF derivatives. Their chemical structures and purities were confirmed by 1H NMR, 13C NMR, Fourier-transform infrared spectroscopy, elemental analyses and high-resolution mass spectrometry. The phase structural evolutions of TTF derivatives were investigated by the combined techniques including differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM) and 1D wide angle X-ray diffraction (WAXD). Two asymmetric compounds are liquid crystal, one of which shows first room temperature columnar liquid crystal based on TTF, with a temperature window between 9 and 96 ℃. Four symmetric compounds all display columnar liquid crystal properties. We can get big domains up to mm grade in size on the bald glass by thermal treatment. We have measured cyclic voltammetry (CV) to evaluate electrochemical properties. For the asymmetry series, they all have two reversible single-electron oxidation peaks at~1.06 and 1.37 V, corresponding to the formation of radical cations and dications, respectively. All compounds displayed similar oxidation potentials, suggesting the lengths of alkyl chains do not appreciably influence the oxidation processes. For the symmetry series, due to the solubility, only 2 of them can be measured in chloroform and they show two irreversible single-electron oxidation peaks at ~ 1.20 and 1.49 V, corresponding to the formation of radical cations and dications, respectively. The others electrochemical properties are proposed to be almost same because the lengths of alkyl chains do not appreciably influence the oxidation processes. Two series of TTF derivatives of HOMO levels were estimated from the onset of oxidation potentials to be in the range of 4.9 and 5.5 eV, which are known typically HOMO levels of good p-type organic semiconductor. Low HOMO levels, in addition to the highly ordered liquid crystal property, suggest that all the compounds are promising hole transporting organic materials. 디스코틱 액정은 광전자 소자에 있어 우수한 유기 전하-이동체로서 많은 주목을 받아왔다. 2차원 정렬된 컬럼 내에서 디스코틱 분자간 π-오비탈 중첩으로 인하여 컬럼의 장축 방향으로 광전자적 전도도는 크게 향상된다. 또한 고체와 액체의 중간상인 디스코틱 액정상은 분자 배열을 가능하게 하며 결정성 유기재료에 있어 전하이동에 치명적으로 문제를 일으키는 grain boundary와 같은 결함을 극소화할 수 있게 해준다. 유기 광전자 응용을 위해 사용되는 다양한 화합물 중에서 테트라티아풀발렌 (TTF)은 우수한 전자-주게 특성으로 인해 가장 기대되는 물질 중 하나이다. 그러나, TTF 또는 그 유도체에 관한 대부분의 현재까지의 연구는 이들의 결정 형태에 대한 것이었다. TTF의 전하이동도를 증진시키기 위해서는 이들의 분자 구조와 모폴로지를 조절함으로써 결정 영역 간의 grain boundary를 없애 거시적으로 배향된 단일 영역이 되도록 하여야 한다. 문제는 어떻게 이와 같은 결함이 없는 단일 결정 구조의 TTF 영역을 만들 수 있을 것인가 하는 것이다. 이에 대한 한가지 가능한 해답이 컬럼형 액정상이다. 컬럼형 액정상을 갖는 새로운 TTF 유도체를 얻기 위하여 긴 알킬 곁사슬을 갖는 비대칭형과 대칭형을 포함하는 새로운 4 종류의 TTF 유도체를 합성하였다. 이들의 분자 구조와 순도는 1H NMR, 13C NMR, Fourier-transform 적외선분광기, 원소분석, 고분해능 질량분석 등을 이용하여 확인하였다. 이들 TTF 유도체들의 액정상 관찰은 주사열분석기, 편광현미경, 1차원 광각 X-선회절 등을 사용하여 실시하였다. 합성된 4 종류의 TTF 유도체 중에서 두개의 비대칭형 TTF 화합물에서 액정상이 관찰되었으며, 그 중 하나는 9 °C와 96 °C 사이에서 액정상을 보여 상온 액정 특성을 나타내었다. 대칭형 TTF 유도체는 모두 컬럼형 액정상을 가졌다. 특히 이 경우에는 유리 기판 위에서 자발적으로 넓은 면적의 단일 결정상을 형성하였다. 주사전압법 (cyclic voltammetry) 을 이용하여 이들 액정의 전기화학적 특성을 분석하였다. 비대칭형 TTF 유도체의 경우에는 라디칼 양이온과 2가 양이온에 해당하는 두 개의 가역적 산화-환원 반응을 각각 1.06V와 1.37 V에서 나타내었다. 모든 화합물이 비슷한 전기화학적 특성을 보여 알킬 사슬의 길이가 전기화학적 산화-환원 반응에 큰 영향을 미치지 않음을 확인할 수 있었다. 대칭형 TTF 유도체의 경우에는 알킬 사슬의 길이가 긴 두 개의 화합물에서 비가역적 단일-전자 산화-환원 반응을 각각 1.20V와 1.49V에서 나타내었다. 나머지 화합물은 용해도가 나빠서 전기화학적 특성을 확인할 수 없었다.각각의 산화-환원 전위로부터 HOMO 준위를 계산한 결과 -4.9 ~ -5.5 eV의 범위를 나타내었으며, 이는 좋은 p-형 유기 반도체가 가지는 전형적인 값에 해당하였다. 낮은 HOMO 준위, 액정성의 정렬된 분자 배열, TTF 분자 구조가 가지는 고유의 우수한 전하 이동 특성 등을 고려하면 본 실험을 통하여 합성된 TTF 구조를 갖는 액정 분자들은 정공 수송체로서 광전자 소자의 개발에 사용될 우수한 소재임을 알 수 있었다.

Self-alignment technique of liquid crystal using a novel thiol additive for LCD and smart window applications

Yoon, Hyunjin Sungkyunkwan University 2022 국내박사

LCD(Liquid Crystal Display)의 배향 막 공정이 필요 하지 않은 SA-VA(Self-Aligned Vertical Alignment) 기술은 비용 효율성과 LC 정렬 제어 및 LCD 제조의 유용성으로 인해 상당한 주목을 받아왔다. 그러나, 표면에 자가 배향 첨가제 부착이 균일하지 않아 LC 정렬 불량이 발생한다는 치명적인 단점이 있다. 결과적으로 이 기술은 아직 상용 어플리케이션에 채택되지 않았다. 본 연구에서 우리는 thiol 그룹을 포함하는 새로운 자가 배향 첨가제와 표면에 첨가제의 열 유도로 물리화학적 흡착을 사용하는 고급 SA-VA 기술을 제안한다. 새로운 재료와 방법을 사용하여 불 균일한 정렬 결함 없이 LC의 완벽한 수직 정렬을 성공적으로 입증했다. 또한, 테스트 셀의 전기광학 성능은 기존의 상용 소자와 대등함을 확인하였다. 따라서 우리의 방법은 기존 SA-VA 기술의 한계를 극복할 수 있으며 상용 SA-VA 모드 디스플레이에 적용할 수 있다. 또한 자체 정렬 기능을 통해 향후 초고해상도 디스플레이에 적용될 LC를 사용하는 비용 효율적인 스마트 윈도우와 같은 미래 디스플레이 응용 분야에 유용할 수 있다. Guest-Host Liquid Crystal(GHLC)으로 구성된 스마트 윈도우는 유망한 기술이지만 몇 가지 한계가 있다. 광 투과율의 상대적으로 좁은 조정 범위와 폴리이미드(Poly Imid) 배향 막 공정으로 인한 비용 효율적인 roll-to-roll 공정 채택의 어려움 등이다. 이 논문 3장에서는 GHLC에 티올기(thiol) 첨가제를 사용하는 SA(self-alignment) 기술을 소개하고 PI 층 코팅 단계를 건너뛰어 PI-less GHLC 장치를 성공적으로 소개하였다. SA 첨가제 분자는 소자의 내부 표면에 단단히 부착되어 자기조립 단층을 형성하고 액정의 우수한 수직 배향을 유도한다. 또한, SA 첨가제 부착 과정에서 세포 내 이온 농도가 증가하고 이온은 높은 인가 전압에서 유체역학적 불안정성 (hydrodynamic instability)을 유발하는 역할을 한다. 결과적으로 SA-GHLC 디바이스는 낮은 인가 전압에서 투과율 제어모드(Transmittance Control Mode)와 높은 인가 전압에서 헤이즈 제어모드(Haze Control Mode)의 이중 모드(Dural Mode)로 작동할 수 있다. 따라서 PI-less SA-GHLC는 고온의 PI 코팅 공정 없이 간단한 공정으로 제작할 수 있어 우수한 스마트 윈도우 특성을 나타낸다. 본 논문에서 소개하는 SA 기술은 roll-to-roll공정이 가능한 저렴한 비용으로 LCD 어플리케이션 뿐만 아니라 스마트 윈도우용으로도 적용 가능 하리라 기대된다. Self-aligned vertical alignment (SA-VA) technique in liquid crystal display (LCD), in which the alignment layer coating process is not necessary, has attracted significant attention owing to its cost-effectiveness and usefulness in the control of LC alignment and the fabrication of LCDs. However, it presents a critical drawback pertaining to the occurrence of LC alignment defects caused by non-uniform additive attachment on the surface; as a result, the technology has not yet been adopted for commercial applications. Here, we propose an advanced SA-VA technology using novel additives containing thiol groups and thermally induced physicochemical adsorption of additives on the surface. Using the new materials as well as method, we successfully demonstrate a perfect vertical alignment of LC without non-uniform alignment defects. In addition, it is confirmed that the electro-optical performance of the cell is comparable to that of a conventional commercial device. Thus, our method can overcome the limitation of existing SA-VA technology, and may be applied to commercial SA-VA mode displays. Further, with its self-alignment feature, the technology may be useful for the future display applications such as cost-effective smart window using LC to be applied to ultra-high-resolution displays in the future. A smart window composed of guest–host liquid crystals (GHLCs) is a promising technology but has several limitations, such as a relatively narrow tuning range of optical transmittance and the difficulty in adopting a cost-effective roll-to-roll process due to the polyimide (PI) alignment layer process. In this dissertation Chapter 3, we introduce a self-alignment (SA) technology that uses a thiol-group additive into GHLC and successfully demonstrate a PI-less GHLC device by skipping the PI layer coating step. The SA additive molecules attach firmly to the inner surfaces of the devices, forming a self-assembled monolayer, and induce an excellent vertical alignment of the liquid crystals. Additionally, during the SA additive attachment process, the ionic concentration increases within the cell, and the ions play a role in inducing hydrodynamic instability at high applied voltages. Consequently, the SA-GHLC device can be operated in dual modes: a transmittance control mode at low applied voltages and a haze control mode at high applied voltages. Thus, the PI-less SA-GHLC exhibits excellent smart-window properties as can be fabricated using a simple process without a high-temperature PI coating process. The SA technology introduced in this paper is expected to be applicable for not only LCD applications but also LC smart window applications at a low cost that allows roll-to-roll processes.

가시광 감응 아조계 폴리이미드를 이용한 네마틱 액정의 이중파장 광배향 및 안정화

Kumar, Vineet 전북대학교 일반대학원 2019 국내박사

Application of liquid crystals has been enabled by controlling its alignment properties on the different substrates surfaces. Among several other alignment methods proposed and available today, photoalignment technique has the key to the solution of all the rubbing limitations. As photoalignment is a noncontact technique, enables the alignment of LCs on small pixel dimensions and can be performed easily with cost-effective manner. Azobenzene based photoalignment possess some superiority among the other photoresponsive materials as it results in quick alignment with strong anchoring, fast response time and high contrast ratio. The major problem associated with azobenzene based photoalignment system is its stability against heat and unpolarized light treatment. Since azobenzene goes under continuous isomerization process can easily deteriorate the LC device alignment property in a long span of time at the ambient condition or faster at elevated temperature and high-intensity unpolarized light treatment. Several reports were published addressing the issue of stability, where co-system of reactive mesogens (RMs) and photoresponsive materials were employed resulting in stable and strong alignment conditions. In most of the reports, RM and chromophores were treated with the same wavelength range of UV light for inducing LC alignment and RM polymerization. Both processes of alignment and polymerization can interfere with each other and result in poor or inefficient alignment quality. To address this issue I have proposed, dual wavelength photoalignment approach, where selective wavelength range of light can be used for inducing LC alignment and different wavelength range for RM polymerization to stabilize the alignment state. I have designed and synthesized visible light sensitive polyimides and employed them for attaining different LC alignment mode and further stabilizing the alignment. In chapter 3, visible light sensitive polyimides PI-MR and PI-DR were used to perform in situ photoalignmnet of LCs. The polyimides with azo-chromophores covalently attached to its side chain result in anisotropic surface upon LPVL irradiation in the isotropic phase of LCs. Obtained aligned state was reversible in nature at this stage, so RM polymerization was done at room temperature with unpolarized UV light. RM layer formed on top of polyimide coating layer results in pacifying the photochromic effect of azo-dyes beneath that layer and now acts as new active alignment layer with irreversible nature. The success of the dual wavelength approach was confirmed by performing stability tests and detailed analysis of surface morphology after polymerization under FESEM and AFM. A similar approach was used for the stabilization of pretilt state in a VA cell discussed in chapter 4. Polyimides with a different molar ratio of modified disperse yellow 7 azo-dye attached in their side chain were shown resulting in planar and vertical alignment (VA) of LCs after coating and backing on ITO substrates. In situ photoalignment process was performed to obtain uniform planar alignment by treating the electro-optic cell in the isotropic phase with linearly polarized visible light. Polymer-stabilized vertical alignment states were reported recently and possess great significance for enhancing viewing angle of LCDs. So far mainly slit-patterned electrodes have been used to stabilize the PS-VA, whereas photoalignment can be an ideal candidate. Photoalignment can produce multidomain patterned alignments and using RM stabilization, PS-VA could be achieved. In an effort to stabilize the pretilt homeotropic alignment, the dual wavelength approach was employed. Vertically aligned cells were treated with oblique linearly polarized visible light (LPVL) in the isotropic phase, results in 0.5 degree pretilt. Further stabilization with UV light in second step yields in higher pretilt of 1 degree with irreversible alignment state. Stability test and surface analysis using FESEM and AFM were performed. Apart from PI based LC alignment using visible light sensitive chromophore using dual wavelength approach, we tried to employ it in PI-less alignment procedure. We have used a host-guest system containing modified azo-dye with hydrophilic end group and alkyl tail along with polymerizable RMs. Hydrophilic end interaction with ITO interface spontaneously results in vertical alignment of LCs and in situ photoalignment using oblique LPVL results in pretilt state. Further polymerization of RM with UV at room temperature results in the stabilized planar state. The details of surface analysis and stability of the cell were discussed in chapter 5. The dual wavelength approach possesses significant potential for further exploration and can enhance the quality of LC-based devices.

Synthesis of Perovskite Nanocrystal Using Liquid Crystal and Application to Optoelectronic Device

한명근 포항공과대학교 일반대학원 2024 국내박사

This dissertation investigates the innovative utilization of liquid crystals in the synthesis of perovskite nanocrystals, exploring their potential to enhance the control of nanocrystal morphology, stability, and the optoelectronic properties. This research is motivated by the need for precise morphological control and enhanced stability in perovskite nanocrystals, which are critical for advancing their application in optoelectronic devices. The primary objective of this study is to elucidate the uniform synthesis and growth mechanisms of rod-shaped perovskite nanocrystals using liquid crystals as a template and to assess their impact on the optical properties of nanocrystals post-ligand exchange processes. Liquid crystals offer a strategic approach due to their elasticity and orientation, acting as templates during the synthesis of nanocrystals. This allows for the uniform synthesis of nanocrystals with targeted morphologies. The presence of liquid crystals during the synthesis process enables advanced analytical and quantitative analysis through their optical polarization phenomena. The methodology adopted involves the liquid crystal-assisted synthesis of perovskite nanocrystals, focusing on rod-shaped morphologies. Utilizing liquid crystals as a template not only aids in achieving the desired morphology, but also improves the stability of nanocrystals during ligand exchange processes. This research introduces a novel chemical transformation approach using liquid crystal templates to develop precise synthesis methodologies. The influence of liquid crystals on the surface of nanocrystals during post-ligand exchange processes is critically evaluated to understand their impact on optical and optoelectronic properties of the nanocrystals. The final chapters discuss the successful synthesis of bismuth-based perovskite nanocrystals using the liquid crystal method and a machine learning optimization approach to overcome the lead toxicity challenge. These techniques enhance predictive modeling for achieving desired outcomes and developing lead-free perovskite nanocrystals. This research contributes to the field of materials science by offering viable solutions for the commercialization of perovskite nanocrystals in optoelectronic applications and highlights innovative methods to address environmental and stability concerns associated with these materials.

Liquid crystal/Liquid basd adaptive photonic devices : 액정/액체 기반의 적응 광소자

서묘 Chonbuk National University 2013 국내석사

적응 광자 장치는 널리 광 스위치, 빔 조향, 영상, 편광 변환기 및 디스플레이에 사용되었다. 다양한 접근 방법이 개발되었다. 액정 (LC)와 액체 기반 장치 때문에 직접 전압 작동의 많은 매력이 있다. 이 논문에서는 LC 또는 액체를 사용하여 네 가지 광자 장치가 개발되었다. 이 장치는 이전 장치에 비해 몇 가지 독특한 공연을 갖추고 있다. LC의 양극화 변환기: 정렬 레이어로 원형 - buffed 폴리스티렌을 사용은 편광 변환기를 준비했다. 이 변환기는 축 방향 또는 반경 방향으로 편광 빛에 선형 편광 빛을 변환 할 수 있다. 우리 장치의 장점은 쉽게 제조, 스케일 크기, 무료 온도 처리한다. 2. 폴리머 네트워크 LC microlens 배열: 패턴의 photomask를 통해 액정 / 단량체 혼합물을 포함하는 균일 한 셀을 노출하는 UV 빛을 사용하여, 우리는 폴리머 네트워크 액정 (PNLC) microlens 배열을 준비했다. 셀에 외부 전압을 적용하여, LC의 굴절률의 기울기가 변경됩니다. 그 결과, microlens의 초점 길이를 조정 할 수 있다. 이러한 microlens 배열은 낮은 운전 전압의 장점, 적절한 응답 시간, 좋은 안정성을 소유하고 있다. 3. 자기 조립 microlens 배열: dielectrophoretic 효과에 따라, 나는 액체 단량체에 액정 (LC)의 위상 분리 형태를 조작하기 위해 fringing 필드를 사용하여보고한다. LC / 단량체 혼합물에 fringing 필드를 적용, 무작위로 분산 LC 방울은 격자 모양의 줄무늬에 조립 될 수있다. 필드가 제거되면, LC 줄무늬가 다시 작은 방울에 침입. 이러한 microlens 배열은 3D 디스플레이 및 이미징 처리에서 응용 프로그램을 약속했다. 4. 광 스위치: dielectrophoretic 효과에 따라, 나는 모양 변형 액체 물방울을 사용하여 광 스위치를보고한다. 장치의이 종류의 광 스위치, 광 셔터, 그리고 적응 아이리스의 매력적인 응용 프로그램이 있다. Adaptive photonic devices have been widely used in optical switch, beam steering, imaging, polarization converters, and displays. Various approaches were developed. Liquid crystal (LC) and liquid based devices are much attractive because of direct voltage actuation. In this thesis, four different photonic devices using either LC or liquid were developed. These devices have some unique performances in comparison to previous devices. 1. LC polarization converter: Using circular-buffed polystyrene as the alignment layer, a polarization converter was prepared. This converter can convert a linear polarization light to axially or radially polarization light. The advantages of our device are the easy fabrication, scale size, and free temperature treatment. 2. Polymer network LC microlens array: Using UV light to expose a homogeneous cell containing liquid crystal/monomer mixture through a patterned photomask, we prepared a polymer network liquid crystal (PNLC) microlens array. By applying an external voltage to the cell, the gradient of the LC refractive index is changed. As a result, the focal length of the microlens can be tuned. Such a microlens array owns the advantages of low driving voltage, reasonable response time, and good stability. 3. Self-assembled microlens array: Based on dielectrophoretic effect, I report to use a fringing field to manipulate the phase separation morphology of liquid crystal (LC) in a liquid monomer. Applying the fringing field to the LC/monomer mixture, the randomly dispersed LC droplets can be assembled to grating-like stripes. When the field is removed, the LC stripes break into tiny droplets again. Such a microlens array has promising applications in 3D displays and imaging processing. 4. Based on dielectrophoretic effect, I report an optical switch using a shape-deformable liquid droplet. This kind of device has attractive applications in optical switch, light shutters, and adaptive iris.

Study of New Liquid Crystal System for Sustained Release Injection

임종래 성균관대학교 일반대학원 2015 국내박사

Chapter 1 A new injectable liquid crystal system for one month delivery of leuprolide 원An injectable liquid crystal-forming system (LCFS) was prepared by using sorbitan monooleate (SMO) as a new liquid crystal-forming material for injections, and its potential use of clinically available sustained-release formulation was evaluated. LCFS was prepared using SMO mixed with phosphatidyl choline and tocopherol acetate, and contained 3.75 mg of leuprolide acetate as a monthly dose in 90 µl of a liquid form. The semi-solid mesophase was formed from the liquid LCFS when it contacted water. The mesophase showed typical characteristics of the liquid crystalline phase, which was classified as the hexagonal phase. The safety of the LCFS was studied by an in vitro extraction colony assay and by examining the injection site in rats and white rabbits after an autopsy. Both in vitro release test and in vivo pharmacokinetic and pharmacodynamic studies showed a sustained release of leuprolide. When compared with a commercial depot formulation of leuprolide, the LCFS showed a similar AUClast value and significantly reduced initial burst with the sufficient suppression of testosterone after subcutaneous injections in rats and dogs. The LCFS can serve as a new type of sustained-release injection formulations for its safety, ease of preparation, and sustained release properties. Chapter 2 An injectable liquid crystal system for sustained release of entecavir Liquid crystal (LC) technology has attracted much interest for new injectable sustained-release (SR) formulations. In this study, an injectable liquid crystal-forming system (LCFS) including entecavir was prepared for the treatment of hepatitis B. In particular, an anchoring effect was introduced because LCFSs are relatively hydrophobic while entecavir is a slightly charged drug. The physicochemical properties of LCFSs were investigated by cryo-transmission electron microscopy (cryo-TEM), polarized optical microscopy, and small-angle X-ray scattering (SAXS), showing typical characteristics of the liquid crystalline phase, which was classified as the hexagonal phase. A pharmacokinetic study in rats showed sustained release of entecavir for 3–5 days with a basic LCFS formulation composed of sorbitan monooleate (SMO), phosphatidyl choline (PC), and tocopherol acetate (TA) as the main LC components. 1,2-dipalmitoyl-sn- glycero-3-phosphatidic acid (DPPA), an anionic phospholipid, was added to increase the anchoring effect between the cationic entecavir and the anionic DPPA, which resulted in a 1.5-times increase in half-life in rats. In addition, anchoring was strengthened by optimizing the pH to 2.5-4.5, increasing the half-life in the rat and dog. Also, due to the increasing terminal half-life from rat to dog resulting from species differences, LCFS produced one week delivery of entecavir in rat and two weeks delivery in dog. Therefore, LCFS injection using the anchoring effect for entecavir can potentially be used to deliver the drug over more than 2 weeks or even 1 month for the treatment of hepatitis B.

(The)high speed response liquid crystal materials for TFT-LCD

허일국 建國大學校 2002 국내박사

Liquid crystals play an important role in fabricating of liquid crystal display (LCD) and they are model materials for organic chemists to investigate the connection between chemical structures and physical properties. For their applications, a complete understanding of the matter, the design and synthesis of liquid crystal, and the corresponding necessary general physical properties is required on the basis of some knowledge of the particulars of display technology. The first part of this thesis includes synthesized liquid crystal compounds with core structures as follows; (1) CCP (bicyclohexylphenyl), (2) CPP (cyclohexylbiphenyl), (3) CECP or CCEP with ethylene linkage group and (4) CeP (cyclohexylbenzoate) with ester linkage group, where C stands for cyclohexane ring, P for benzene sing, E for ethylene linkage groups and e for ester linkage groups and e for ester linkage group. As a certain set of physicochemical requirements related to the optimal performance of AM-LCD measured in order to investigate relationship with structure-physical~properties. These specifications include the nematic phase range, dielectric anisotropy(Δε ) birefringence(Δn), kinematic viscosity(η) and elastic constatns(K_(1),K_3). Also the thesis includes the calculations of not only the configuration and geometrical anisotropy of the molecule, but also the polarity and polarizability of the molecule using the MOPAC 5.0 package program in Chem 3D 5.0 POR version as empirical methods for the molecular design of high speed response liquid crystal material. The final goal of the thesis work is aimed for the performance which was required in fast response display technology for TV/Monitor applications, via the electro-optic response exhibited by liquid crystals, to form a moving image on the screen at the time interval between two video frames (at 6OHz). We have investigated how a certain chemical structure can be produced towards improved electro optical and viscoelastic properties of liquid crystal mixtures; on the other hand, for the increasing performance of TFT-LCDs be considered extremely stringent reliability demands on the liquid crystals. This work empirical trends concerning the relations between molecular structure and electro-optic response of thermotropic liquid crystals. This involves the following aspects (1) factors increasing the polarizability and polarity of a molecular structure, (2) factors leading to higher optical anisotropy, (3) factors favoring the formation of high-clearing liquid crystal materials and (4) factors influencing the packing density of the mesophase. These factors are not only related to the configuration, conformation, and geometrical anisotropy of the molecule, but also to the polarity and polarizability of the molecule. The mutual effect of the electronic and the stereochemical factors are also discussed, ending up with suggestions for the molecular design of high-speed response liquid crystal materials with high birefringence and dielectric anisotropy, and high clearing temperatures. This work has been a major part of the thesis and resulted in an advanced mixture with distinctly superior performance in comparison with the commercially available LC mixtures and ideally successful for research on TV/Monitor application for the addressing of AM-LCDs

Optical Materials based on Polymer/Liquid Crystalline Hybrid System

배재현 경희대학교 일반대학원 2018 국내석사

Liquid crystals have their own alignment depending on temperature and concentration, and they can form self-assembled nanostructures. In addition, because of its dielectric and optical anisotropy, liquid crystal is a promising material for optical devices. However, its fluidity and instability have hindered its application. To overcome this problem, we constructed a hybrid system that mixes low molecular weight liquid crystals and polymers. By utilizing the hybrid systems, stabilizing the defect of liquid crystals or peculiarizing unique characteristics so that make functional films. Blue Phase II is a photonic crystal with a three-dimensional structure that appears in a chiral nematic liquid crystal. It exhibits Bragg reflection and can easily align the domains through surface treatment. It also has low hysteresis and fast response speed, which shows excellent electro-optic performance. Despite these advantages, BPII’s very narrow temperature range makes it difficult for commercialization. In this study, BPII was stabilized using polymers to attain a wide temperature range, which includes the room temperature. Unlike polymer stabilized blue phase I, analysis of the transmittance and spectral change through the electric field in the polymer-stabilized BPII revealed that it has stable selective reflection without changing the wavelength when an external force such as temperature and electric field is applied. Haze is an expression of how frequent and significant the path changes within a material as light passes through it. In energy conversion technology, there have been many efforts to increase the efficiency by light scattering. Herein, we fabricate micro-segregated liquid crystal films with high haze and transmittance using liquid crystals and polymers in a simple process. The liquid crystal was dispersed in the polymer and exist in the form of droplets. When the light passes through the polymer, it comes into contact with the droplet causing a change in refractive index. This change scatters the light at various angles. Mixtures of liquid crystal and polymer were injected into the cell and cured under UV light at the required temperature to obtain a stable film. The haze value of the obtained film was high. It was also confirmed that the energy conversion efficiency increased by simply attaching the film to a solar cell. Liquid crystals are electrically and optically anisotropic and can form photonic crystals by spontaneously aligning them. Improving these materials with the use of polymers makes it more promising for optical devices. 액정은 그 스스로 열이나 농도에 따라 고유한 정렬을 가지며 몇몇 상태에서는 자가조립으로 나노 구조물을 형성하기도 한다. 또한 전기적, 광학적으로 이방성을 가지고 있어 여러 광학 장비의 재료로서 많은 가능성을 가지고 있다. 그러나 액정이 가지는 유동성과 불안정성에 의해 이러한 광학 장비의 응용에 문제가 되고 있다. 이를 보완하기 위해, 이 연구를 통해 저 분자량 물질인 액정과고분자를 혼합하는 하이브리드 시스템을 구성하였다. 고분자와 액정의 자발적인 상 분리 현상을 이용하여, 액정의 불안정한 결함을 안정화 하거나 전체 혼합물에 특정한 물리적 특징을 부여하여 기능성 필름을 제작하였다. 본 논문에서는 먼저 온도 안정성이 매우 낮아 상온에서 유지되기 어려운 블루페이즈Ⅱ를 고분자를 통해 안정화 시켰다. 블루페이즈Ⅱ는 카이랄 네마틱액정에서 확인 할 수 있는 물질로 3 차원 구조를 가지는 광결정이다. 브래그회절을 통해 빛을 선택 반사 시키며, 표면 처리를 통해 도메인을 쉽게 정렬시킬 수 있다. 또한 낮은 히스테리시스와 빠른 응답속도를 가지고 있어 우수한 전기광학성능을 보여준다. 이러한 장점에도 불구하고 매우 좁은 온도 범위를 가지고 있어 상용화에 큰 어려움이 있었다. 이번 연구에서는 고분자를 통해 블루페이즈Ⅱ를 실온을 포함한 넓은 범위에서 유지될 수 있도록 안정화 하였다.또한 안정화된 블루페이즈에 전기장을 통한 투과율 및 스펙트럼 변화를 분석하여 고분자 안정화 된 블루페이즈Ⅱ가 블루페이즈Ⅰ과 다르게 온도, 전기장 등의 외부 힘을 받아서 파장의 변화 없이 안정적인 선택반사를 보여준다는 것은 확인할 수 있었다. 헤이즈란 빛이 물질을 통과할 때 물질 내부에서 경로가 얼마나 빈번히, 그리고 크게 변화하는 가를 나타내는 표현이다. 에너지 변환 기술에 있어서 빛의 산란을 이용하여 그 효율을 증가시키고자 하는 많은 노력들이 있었다. 여기서 우리는 액정과 고분자를 이용하여 높은 헤이즈와 투과율을 가지고 있는 필름은 간단한 공정으로 제작하였다. 투과율이 매우 높은 고분자속에 잘 분산된 액정은 방울의 형태로 존재한다. 입사된 빛이 고분자를 투과할 때 이 방울에 닿으며, 굴절률의 변화에 의해서 빛은 다양한 각도로 산란된다. 잘 섞은 두개의 혼합물을 셀에 넣고 경화 온도에서 UV 로 경화함으로서 단단하고 안정적인 필름을 얻을 수 있었다. 또한 얻어진 필름의 헤이즈 성능을 분석하여 높은 헤이즈값을 가지고 있음을 확인하였고, 이 필름을 단순히 태양전지 위해 부착하는 것으로 에너지변환 효율이 증가하는 것을 확인 할 수 있었다.액정은 전기적, 광학적으로 이방성을 지니고 있으며, chirality 를 유도함으로서 나노구조에서 자발적으로 정렬하여 광 결정을 형성할 수 있다. 또한, 고분자와 혼합함으로서 불안정하고 유동적인 액정을 안정적이고 고정적인 상태로 바꿔줌으로서 다양한 광학 장비로의 응용을 기대 할 수 있다.