Dissertationen zum Thema „Antiferroelectric Liquid Crystal“

Com base em resultados de DSC, análise estrutural por difração de raios X e observações de textura, analisamos os efeitos da mistura do solvente apolar hexadecano com cristais líquidos formados pelas moléculas banana 1,3-fenilenobis[4-(4-tetradecilfeniliminometil)benzoato] (MB14) e 4-cloro-1,3-fenilenobis[4-(4-tetradecilfeniliminometil) benzoato] (MB14Cl). Propusemos um modelo estrutural para explicar as modificações causadas no arranjo molecular da fase B2 pelo acréscimo gradual do solvente. Observamos a diminuição da temperatura de transição entre esta fase e a fase isotrópica, porém a transição entre a fase B2 e a fase a temperaturas mais baixas não sofre alteração significativa. Para concentrações em massa de hexadecano de 45 % no MB14 e de 55 % no MB14Cl, a fase B2 já não é mais observada. Para o MB14Cl, resultados de difração de raios X revelaram que as moléculas de hexadecano penetram entre as camadas esméticas, aumentando a distância intercamada em torno de 3 Å. Acima de 5 % de concentração do solvente, o aumento da distância intercamada satura e ocorre segregação de fases em escala nanométrica. O comportamento da fase B2 sob a ação de um campo elétrico variável também foi analisado para o MB14 puro. Apresentamos um modelo para a linha de base do sinal de corrente de polarização, que leva em conta a não linearidade da condutividade para valores altos de campo aplicado, devido à movimentação iônica na amostra. Para o cálculo da viscosidade, consideramos a não linearidade da constante dielétrica com o campo aplicado, e adaptamos outro modelo, inicialmente utilizado para cristais líquidos ferroelétricos sob a ação de um campo quadrado, para o caso de um cristal líquido antiferroelétrico sob um campo triangular. Quanto aos dois tipos de arranjo molecular da fase B2, o arranjo homoquiral se mostrou bem mais estável que o racêmico, mesmo sob aplicação de campo triangular, quando este último é inicialmente favorecido. O arranjo racêmico se apresentou mais viscoso que o arranjo homoquiral, contrariando nossas previsões.
Based on DSC results, structural analysis by X-ray diffraction and texture observations, we observed the effects of mixing the nonpolar solvent hexadecane with the banana molecules liquid crystals ,3-phenilenebis[4-(4-tetradecilpheniliminometil)benzoate] (MB14) and 4-chloro-1,3-phenilenebis[4-(4-tetradecilpheniliminometil) benzoate] (MB14Cl). We propose a structural model to explain the changes in the molecular ordering of the B2 phase caused by the gradual increase of the solvent. We observed a decreasing of the transition temperature between B2 and isotropic phases, however the transition between B2 and lower temperature phases did not change significantly. For hexadecane concentrations above 45 wt% in MB14 and 55 wt% in MB14Cl, the B2 phase is no longer present. In MB14Cl, X-ray diffraction results showed that the hexadecane molecules penetrate between the smectic layers, increasing the interlayer spacing by about 3 Å. Above 5 wt% of solvent concentration, the increasing of the interlayer spacing saturates, and a phase segregation in nanometric scale occurs. The behavior of the B2 phase under variable electric field was also analysed for the pure MB14. We present a model for the baseline of the polarization current signal, which considers the non-linearity of the conductivity for high values of applied field, due to the presence of ions in the sample. In order to calculate the viscosity, we considered the non-linearity of the dielectric constant with the applied field, and adapted another model, initially used in ferroelectric liquid crystals under rectangular field, for the case of an antiferroelectric liquid crystal under triangular field. Concerning the two kind of molecular ordering in the B2 phase, the homoquiral ordering proved to be far more stable than the racemic, even under triangular field, when the latest is favored. Our measurements resulted in a racemic ordering more viscous than the homoquiral, going against our predictions.

Blending nanomaterials with liquid crystal (LC) is considered to be a prospective method to enhance the electro-optical properties of the host. Threshold voltage, driving voltage, residual dc, response time and rotational viscosity etc. are found to decrease in nano doped LC system and in turn the anisotropic order of the liquid crystalline host imparts order in the nano-sized guest particles. Proper selection of size, shape and crystallographic phase of nanomaterial is important to achieve desired improvements of the host. This dissertation presents results of doping different type of nanomaterials in nematic, ferro- and antiferroelectric liquid crystal medium. Conducting polymer nanotubes in nematic LC exhibits remarkable reduction in the threshold and driving voltage which is good from application point of view. The residual dc is also reduced significantly in the doped cell and the reduction is even more than that observed in the carbon nanotube doped same LC system. The influence of multiferroic bismuth ferrite nanoparticles on the electro-optical and dielectric properties of an antiferroelectric LC mixture is investigated in planar cells. It is shown that dispersion of nanoparticles lead to modifications of response time, spontaneous polarization, rotational viscosity and voltage required for switching the molecules between two ferroelectric states in the antiferroelectric phase. The large electric field exerted by the nanoparticles on LC molecules and probable charge transfer among them, causes weakening of the interlayer and intermolecular interactions of LC molecules in the antiferroelectric and ferroelectric phases, respectively. In a ferroelectric LC/ conducting polymer nanotubes composite system electrooptic study reveals a lower electrical response time, rotational viscosity and spontaneous polarization. By fitting the capacitance with voltage in a Preisach model, four dipolar species in both pure and nanocomposite system have been obtained. The orientation of the four dipolar species in the composites system is such that the effective dipole moment in the transverse direction of the FLC molecule is less than that in FLC compound. Another aspect of this dissertation is to study a newly synthesized orthoconic antiferroelectric liquid crystal which provides an excellent dark state because of its high tilt. A detailed investigation of the dielectric, electro-optical properties and X-ray studies of the partially fluorinated high-tilt antiferroelectric LC material revealed that the SmA* phase of this material is of de Vries type. Double-peak polarization current response and tristable-optical-switching studies have revealed an antiferroelectric molecular ordering in the de Vries SmA* phase of this material. Two distinct dielectric relaxation peaks in the SmA* phase also complement the antiferroelectric-like ordering of the molecule in the SmA* phase.
The research was conducted under the supervision of Prof. Subir Kumar Roy of the Spectroscopy division under SPS [School of Physical Sciences]
The research was carried out under IACS fellowship and DST research grant

碩士
國立臺灣科技大學
高分子工程系
92
In this research, we used polymer dispersed antiferroelectric liquid crystal (PDAFLC) with pin photodiode of hydrogenated amorphous silicon (a-Si:H) to fabricate optically addressed spatial light modulator (OASLM) device. We measure that electro-optical conversion efficiency of pin photodiode and the electro-optical characteristic of PDAFLC. To investigate the influence of different thickness of a-Si:H and dose of ion-implantation of boron atom of this electro-optic device, Ar+ laser are used for excitation light source and He-Ne laser was used for a probe beam. We measure the properties of the threshold voltage and the driving voltage of device to estimate the electro-optical conversion efficiency. The results show that the photocurrent have direct ratio with writing light intensity and thickness of intrinsic layer. The dose of p-type doping in 11014/cm2 has well electro-optical conversion efficiency. When the dose of p-type doping over 11015/cm2, the electro-optical conversion efficiency will decreased. Different temperature and irradiating time will change the photocurrent. In the electro-optical characteristic of polymer dispersed antiferroelectric liquid crystal, the variables of liquid crystal doping ratio in 40% and UV intensity in 0.5mW/cm2 have good electro-optical effect. We could control the rotation state of liquid crystal molecule by change writing light intensity of OASLM. In addition, even slightly change of writing light wavelength, the modulation characteristic of OASLM will not be change. Therefore, we successful made an OASLM with stably and light modulation effect.

碩士
國立臺灣科技大學
高分子工程系
91
In this research we want to make liquid crystal cells and an antiferroelectricity liquid crystal（MHPOBC） doped with Azobenzene（methyl red）. To investigate what effects the properties photochromic dye have on liquid crystal molecules when Ar+ laser beams were irradiated at different temperatures and voltages, we measured the threshold voltage, the response time, and transparency of the device, and we also considered the applications of SLMs. Furthermore we will in the future compare the differences between our devices, doped MHPOBC cell and doped TN cell.

碩士
國立臺灣科技大學
高分子系
95
Using polymer dispersed antiferroelectric liquid crystal(PDAFLC) doped with Azo-Dye(DR1) to make optically addressed spatial light modulator (OASLM).Discuss the influence of Ar+ laser strength on OASLM’s the threshold voltage and the driving voltage. We found that the threshold voltage and driving voltage will decrease when we increase the percentage of Azo-Dye(DR1). Although the doped of azo-dye will decrease the penetration of liquid crystal, we can control the rotation state of liquid crystal by changing the intensity of Ar+ laser, and therefore we successful made an OASLM with stably and light modulation effect.

博士
大同大學
化學工程學系(所)
95
The primary of this research work was an attempt to elucidate the correlation between structure and property in the chiral smectic liquid crystals. Thus, two new chiral moieties, (S)-2-(metylsulfanyl)ethyl 2-hydroxypropanoate prepared by reacting (S)-lactic acid with 2-methylsulfanyl-1-ethanol, and (S)-[1-methyl-2-(2’-methylsulfanylethoxy)]ethanol prepared by reacting (S)-propylene oxide with 2-methylsulfanyl-1-ethanol under basic condition, were designed and synthesized, and three series of chiral liquid crystal compounds were subsequently prepared for the mesomorphic and physical studies. The target compounds were modified independently by (i) the non-chiral peripheral methylene chain length ‘m’ and (ii) the lateral substitution group in the core. In first series of chiral materials, MSEmBCPP(m=8-12), all materials displayed enantiotropic mesophases of the SmA*, and SmC* phases. The maximum magnitude of spontaneous polarization (Ps) for materials was around 85nC/cm2. The electro-optical response in the series of chiral materials in the SmC* phase displayed typical ferroelectric hysteresis loop or hysteresis-free, V-shaped switching property upon various applied frequencies and temperatures. In second series of chiral materials, MMSEEmCB(m=8-12), the formation of smectic phases are significantly depended of the achiral alkyl chain length. For example, material at m=7 displayed SmA*, SmCA* and SmX phases, while materials at m=8-12 display an additional SmC* phase but at m=10-12 the SmCA* phase and at m=11-12 the SmX* were suppressed. The maximum Ps value was observed to be 37.76 nC cm-2, and the maximum tilt angle reached 29.5o. In the third series of materials, the results obtained from MMSEEmBC2F(m=7–10) with lateral 2-fluoro substitution and MMSEEmBC2F(m=7–10) with 3-fluoro show that all materials display SmA* and SmC* phases. The antiferroelectric SmCA* phase only occurred in two materials, MMSEE7BC2F and MMSEE8BC3F. The results also indicate that lateral fluoro-substituent in the phenyl ring of the materials could depress the formation of higher ordered smectic phases, especially the SmCA* and SmX* phases, lowering the transition temperatures, melting points, clearing points. The measured Ps values, as compared fluoro-substituted materials to non-substtuted materials, have the order of MSEmBCPP > MMSEE7BC2F > MMSEE8BC3F, suggesting that fluoro-substituents depress the Ps values in which 3-fluoro-substituent has more effect than 2-fluoro-substituent. In conclusion, the results indicated that the chiral materials derived from (S)-2-(metylsulfanyl)ethyl 2-hydroxypropanoate are favorable for the formation of the wide temperature range of the ferroelectric phase, while that from (S)-1-methyl-2-(2’-methylsulphanylethoxy)ethanol are favorable for the formation of antiferroelectic phase. Fluoro-substituents could decrease the transition temperatures but suppress the formation of antiferroelectric phase.

博士
大同大學
化學工程學系(所)
95
ABSTRACT AFLCD display with such good characteristics as: wide screen, high resolution, excellent image quality and full color have been developed. However, so far, display manufacturers have been unable to commercialize AFLC display devices despite continuous efforts. It seems that the appearance of the SmCA* phase and structure-property relationship of AFLC materials are still understood well enough to optimize the material parameters. Thus, in order to ascertain the structure-property correlations and the practical application in electro-optical services, in this work, we attempt to elucidate the structure-property correlation in the chiral smectic liquid crystal. A homologous series of chiral materials derived from (S)-propylene oxide has been successfully synthesized and the structures-property relationship investigated in the chiral liquid crystal system. The target compounds were modified independently by the (i) the structure of the non-fluorunated, fluorinated alkoxy chain length and chiral swallow-tailed structure (ii) lateral halogen substituents in the core and (iii) different core structure of the molecules of the chiral molecules for the study. Chiral non-fluorinated materials, I(m, n; m=8-12, n=0-3) displayed enantiotropic mesophases of the SmA* and SmC* phases; however, chiral semi-fluorinated materials, II(m, n; m=8-12, n=1-3), exhibited SmA*, SmC* and SmCA* phases. These results demonstrate that the presence of the semi-fluorinated alkyl chain in the chiral tail of the material induces an antiferroelectric SmCA* phase. Chiral swallow-tailed materials, III(m, p; p=0, m=8-12), displayed enantiotropic mesophases of the SmA*, SmC* and SmCA* phases. The materials increasing methylene chain lengths n, III(m, p; m=8-12, p=1), the SmCA* was disappeared and only exhibited SmA* and SmC* phase. In addition, the antiferroelectric liquid crystal materials, II(m, n) and III(m, 0), have higher Ps and θ values than ferroelectric liquid crystal materials, I(m, n) and III(m, 1). The electro-optical response in the series of chiral materials, I(10, 2) and III(10, 1), in the SmC* phase displayed V-shaped switching property; however, in the series of chiral materials, II(10, 2) and III(10, 0), in the SmCA* phase displayed typical antiferroelectric tri-stable state of double hysteresis loop switching behavior . Chiral semi-fluorinated materials, IV(m, X, Y) and V(m, X, Y), were synthesized and investigating the influence of lateral halogen substituents in the core. The SmCA* phase was generally occurred in the alkyl chain length from m=8 to m=10 of the materials. The materials with lateral substitutents in the core could depress the formation of mesophase, lowering the transition temperature, melting point and Ps values but increasing θ values. Comparing with the materials of different atom substitution, it is seen that the materials with lateral chloro substituents in the core of molecular was most decreasing transition temperature and Ps values. The materials with halogens substuted at 2-position on the ring of the molecule were sterically shielded so that possessed higher transition temperature than that materials at 3-position; however, the materials with halogens substuted at 2-position on the ring of the molecules also enhanced Ps and θ values. In chiral semi-fluorinated materials, VI(m) and VII(m), the SmCA* phase was also occurred in the alkyl chain length from m=8 to m=10 of the materials. Comparing with different core structure of three series materials, II(m, 2), VI(m), VII(m), it can be found the materials, III(m, 2), with PhPhCOOPh as the core structure of the molecule were favorable for the formation of antiferroelectric SmCA* phase; however, the materials have highest Ps values in those materials. In chiral materials, VIII(m)-XIII(m) which derived firm cinnamatic acid can be found two ring core materials only exhibit ferroelectric SmC* phase; however, three ring core materials favor the formation of antiferroelectric SmCA* phase. Changing the core structure of molecule exhibited some sub-phases such as SmCα* and SmCγ* phases. Binary mixture study shows that the antiferroelectric mixtures with ambient temperature can be obtained by two antiferroelectric liquid crystals. The response of the optical transmission obtained from the antiferroelectric mixture of 80% V(8, H, Cl) and 20% XIV(10) in SSFLC cell by driving at 60Hz and 26V square wave at 25℃ show that the raise time is 586.7 μs and fall time is 109.5μs. In conclusion, the chiral swallow-tailed and semi-fluorinated alcohol groups can be prepared by the optically pure (S)-propylene oxide treating with semi-fluorinated or swallow-tailed alcohols. These chiral alcohols are then developed large amount of antiferroelectric liquid crystals, and subsequently, the structure-property correlation for the formation of antiferroelectric liquid crystals is established. The establishment of this correction will be beneficial for the future design and synthesis of more antiferroelectric liquid crystals. A large amount of antiferroelectric liquid crystals developed in the present work demonstrates that there is a potential for the preparation of suitable antiferroelectric mixtures for the display devices.

碩士
國立臺灣科技大學
高分子工程系
91
This experimentation, synthesizing different structural Antiferroelectric-like liquid crystals: 2-ethylpentyl 4-(4’-decyloxybiphenyl-4-carboxyloxy)benzate, B1； 2-ethylpropyl 4-(4’-decyloxybiphenyl-4-carboxyloxy)benzate, B2； 2-ethylpentyl 4-(4’-decyloxybiphenyl-4-carboxyloxy)-3-fluorobenzate, F1； 2-ethylpropyl4-(4’-decyloxybiphenyl-4-carboxyloxy)-3-fluorobenzate, F2。 The study of binary mixtures were conducted by mixing B1, B2, F1, and F2 separately with (S)-MHPOBC((S)-(4-(1-methylheptyloxycarbonyl)phone 4’-octyloxybiphenyl-4-carboxylate), by various weight percentages to observed the influence of mesophases. We utilizied DSC and polarizing microscope to find out the phase variation temperature and determine mesophases. We measured the responses of the transmittance versus electrical field. The results showed that mixtures of B1 and (S)-MPHOBC have antiferroelectricity and ferroelectricity. The lateral fluorine substiuent in F1 and F2 can descend the phase variation temperature, but the mixtures have ferroelectricity, when F1 and F2 is more than (S)-MPHOBC. Mixtures of F1 60%, 40%, and 20% have antiferroelectricity, but the threshold voltage dependented of (S)-MHPOBC. wt%.

碩士
國立清華大學
化學工程學系
88
Abstract The purpose of this research work was an attempt to elucidate the structure-property correlations in the chiral smectic liquid crystals, because the exciting results have been obtained the field of study. A homologous series of chiral materials MDn2Nx (n = 1, 2, 3; x = 1b, 2b, 2p, 3p) was designed for the synthesis and investigation of the structure-property relationship in the chiral liquid crystal system. The target compounds were independently modified by the length of the oligo(oxyethylene) chain (n) and terminal chiral alkyl chain (x) for the study. A chiral swallow-tailed compounds MDn2N3p (n = 2, 3) have the same phase sequence: Iso-Ch-SA-SCA*-Cr, suggesting that the extending the oxyethylene repeat unit from n=2 to n=3 oligo(oxyethylene) chain length has no remarkable effect on the formation of tilted smectic phases, compound with shorter oxyethylene chain length(n =1; MD12N3p) have the phase sequence: Iso-Ch-SA-SB-Cr. The thermal analysis shows that as n increases, the clearing point falls, and the SA-SCA* transition temperature decreases, resulting in a suppress of the SA phase stability, the temperature range of SCA* phase are generally increased as the n increased. In addition, The MD32N3p material SCA* phase range can be achieved about 50℃(including room temperature). The optical responses in the SCA* phases have been measured. The thresholdless phenomena are found and characterized in these phases. In addition, the maximal spontaneous polarization value (131 nC/cm2) and fast response time (140 μs) are found in MD22N3p, and also found MD32N3p material have maximal spontaneous polarization value (127 nC/cm2) and fast response time (270μs). The dielectric properties for the compounds MD22N3p and MD32N3p were also measured and two different relaxation processes were obtained and characterized as soft mode in the SA phase, and Goldstone mode in the SCA* phases. The results of dielectric investigations indicate that oligo(oxyethylene) chain length has no remarkably effect on the collective or non-collective molecular motions. On the other hand, the molecular modeling shows a similar result with the experimental X-ray diffraction of smectic liquid crystals to demonstrate the correct AFLC structures. Investigating the effect of terminal chiral alkyl chain (x) on the mesomorphic properties show that the stability of tilted smectic phases and the magnitudes of spontaneous polarization in the SC* phases are enhanced as the introduction of second anchiral methyl substitutent at chiral tail. In addition, the phase sequence for compounds MDn2Nx (n = 1, 2, 3; x = 1b, 2b, 2p) is depended on the oligo(oxyethylene) chain length n. A Iso-SA-SB-Cr sequence was obtained at shorter chain length (n = 1). A Iso-SA-SC*-Cr* sequence was obtained at longer chain length (n = 2 and 3).

博士
國立臺灣科技大學
材料科學與工程系
99
A series of novel liquid crystals containing different shapes and mesogenic groups was designed and synthesized by attaching different types of mesogenic units, terminal chiral and achiral segments to investigate the structure-property relation of liquid crystals and the electro-optical properties. The structures of the synthesized compounds were identified using 1H-NMR, MASS, and elemental analyses. The thermal properties of these compounds were analyzed using DSC, X-ray and POM. The electro-optical properties of the compounds, such as tilt angle, V-T curve, dielectric permittivity and switching behavior were also measured. The research work was carried out in two parts. In Part I, two series of rod shaped ferroelectric liquid crystals were synthesized. In the series I, the ferroelectric liquid crystals that have a 4'-hydroxybiphenyl-4-yl 4-hydroxybenzoate core 、a chiral butyl 2-hydroxypropanoate unit and an oligomeric siloxane end-group were synthesized, and the mesophases exhibited were compared. We examined the influence of the addition of a trisiloxane end-group on one side-chain of an achiral alkyl chain on the phase transition. In the series II, we report the synthesis and characterization of new ferroelectric liquid crystal material which have a 4-hydroxyphenyl 4'-hydroxybiphenyl-4-carboxylate core 、a chiral octan-2-ol unit and an oligomeric siloxane end-group. We examined the influence of the addition of different length of siloxane and achiral alkyl chain in the end-group on the phase transition. The target compounds with large tilt angle and wide temperature range of SmC* phase were also measured. In part II, two series of bend shaped antiferroelectric liquid crystals were synthesized. In series I, the series bent-core materials were based on a 3,4′-biphenyldiol central core containing salicylaldimine-based and two terminal tetradecyloxy tails. In addition, the effects of lateral substituents (R = F and Cl) at the biphenyl core into 3′-position were examined. These substituents have a strong influence in reducing the clearing temperatures and increasing temperature range of SmCP phase. In series II and III, the bent-shaped mesogens have been synthesised and their mesomorphic properties studied. We examined some novel series of bent-core compounds containing 3,4′-positions of a diphenol ring as the central unit with the side wings containing a cinnamoyloxy group and a methyl cinnamoyloxy group. We have to investigated the relation between the structure and the mesomorphic properties. Besides, we added the halogen (F and Cl) in 3′-position of the diphenol, and researched the effect in the mesomorphic properties. In conclusion, the molecules are then developed large amount of ferroelectric liquid crystals, and subsequently, the structure-property correlation for the formation of ferroelectric liquid crystals is established. The establishment of this correction will be beneficial for the future design and synthesis of more ferroelectric liquid crystals. A large amount of ferroelectric liquid crystals developed in the present work demonstrates that there is a potential for the preparation of suitable ferroelectric mixtures for the display devices.

碩士
大同大學
化學工程研究所
90
Abstract The purpose of this research work was an attempt to elucidate the structure-property correlation in the chiral amide smectic liquid crystals, because the exciting results have been obtained this field of chiral system　in our laboratory. Therefore, two series of chiral materials DPmPBNPA(m=9~13) and DEmPBNPA(m=10~15) were designed for the synthesis and investigation of the stricture-property relationship in the chiral amide liquid crystal system. The target compounds was modified independently by the length of the alkyl chain length (m) and swallow-tailed length (n) for the study. Chiral amide liquid crystals were derived by using chiral (S)-2-(6-methoxy-2-naphthyl)propionic acid with N,N’-dialky amines. Mesophases and their corresponding transition temperatures of the materials were identified by the polarizing microscopic textures, DSC carlorimetry and electro-optical measurements. The results showed that most of the chiral amide materials exhibited phase : chiral smectic A (SmA*), antiferroelectric (SmCA*) phases. SmCA* phase was further characterized by the schlieren textures, switching behaviors, dielectric constants and eletro-optical response. Compounds DPmPBNPA(m=9~11) exhibited monotropic mesophases of the SmA* and SmCA* phases in cooling process. The variation of alkyl chain length (m) showed that the temperature range of SmA* phase became smaller, but the temperature range of SmCA* phase became larger as the number of alkyl chain length increased. Compounds DPmPBNPA with higher alkyl chain length m=12,13 had no mesophase observed either in heating or cooling process, therefore, they are not mesomorphic compounds. Compounds DEmPBNPA(m=10~15), with the exception of compounds DEmPBNPA(m=12,13) exhibited enantiotropic SmA* and SmCA* phases, while the rest of compounds displayed monotropic SmA* and SmCA* phases. The temperature range of the SmCA* phase decreased as the alkyl chain of compounds DEmPBNPA increased. Physical properties of these two series of chiral amide materials in SmCA* phase were characterized by spontaneous polarization, dielectric constant, switching current and electro-optical responses. The maximum magnitudes of spontaneous polarization (Ps values) for the chiral amide materials were obtained in the range of 80~115 nC cm-2. The electro-optical response demonstrated that material DEmPBNPA (m=12) displayed thresholdless V-shaped switching in antiferroelectric(SmCA*) phase while other compounds of these two series of materials displayed typical characteristic of double hysteresis in antiferroelectric(SmCA*) phase. It is strongly demonstrated that V-shaped switching properties for these materials are critically dependent on the alkyl chain length; the effect of nonchiral alkyl chain length. The analogous V-shaped switching was reported by Inui et al. in some antiferroelectric liquid crystal mixtures. Thus, binary mixtures of two chiral materials; compound DEmPBNPA(m=12) and chiral swallow-tailed ester material EP10PBNP possessing V-shaped switching property were studied in order to investigate the miscibility of these two compounds, more particularly, the effect of mixtures on the electro-optical responses; the thresholdless, V-shaped switching properties. The different between two materials DEmPBNPA(m=12) and EP10PBNP is that the former appeared monotropic SmCA* phase and the later has enantiotropic SmCA* phase in heating and cooling processes. EP10PBNP displayed a phase sequence of BPII-N*-TGBA*-SmA*-SmCA*, but as the component ratio of DEmPBNPA(m=12) greater than 9wt%, the BPII phase was disappeared and as the component ratio of DEmPBNPA(m=12) greater than 75wt%, the TGBA* phase was disappeared. The temperature range of SmCA* phase in component ratio D50/E50 was the largest. The eletro-optical responses in the SmCA* phase of the binary mixtures exhibited V-shaped switching in the cell with 5μm thickness. Ours results demonstrate two materials with V-shaped switching responses are mixable. In particular, we like to emphasize that the magnitudes of spontaneous polarization have no any effect on the appearance of thresholdless, V-shaped switching property.

碩士
淡江大學
化學學系
90
This study empolyed stilbene as a core to construct rod-like chiral mesogens and banana shaped mesogens.The mesophase behaviors were studied by optical polarizing microscopy and differential scanning calorimetry.The rod-like chiral mesogens were obtained by esterification of 4-alkoxy—3—fluoro -(4’-hydroxy)stilbene with mono ester of terephthalic acid having (1) S-2-methylbutanol, and (2) L—ethyl lactate as the chiral moieties, CnFSTMBT and CnFSTLET, respectively.(1)CnFSTMBT, where n = 6, 7, 8, 9, 10, 12, exhibited enantiotropic I-BP-N*- TGBA-SA-Sc*-K phase sequence with temperature range of 130℃. As compared to those of the non-fluoro homologues, the clearing point and melting point are slightly lower and the mesophase temperature range is slightly narrower. However, the frustrated (BP and TGBA) persisted although with narrower ranges.(2)CnFSTLET, where n = 6, 7, 8, 9, 12, exhibited enantiotropic I-N*-TGB- SCA*-K phase sequence with temperature range of 110℃. Compare to the CnFSTMBT homologues, the disappearance of Blue Phase and appearance of SCA* are attributed to the dipole moment and twisting power of the lactate moiety. The TGB phase occurs between the N* and SCA* is tentatively assigned to be TGBc on the basis of microscopic observation. Further study is necessary to identify this phase.The banana shaped mesogens were obtained with three different bent cerntral cores.(1)3,4’-bis((4-alkoxybenzoyloxy)-benzoyloxy)stilbene (3-4’-(CnOBB)2ST, where n = 8, 10, 12, 14, 16)exhibited enantiotropic banana phases, B1 phase for n = 8, 10, and B2 phase for n = 12, 14, and 16. The mesophases temperature ranges are about 100℃, much wider than those reported in the literature.(2)1,3-bis(2-(4-alkoxybenzoyloxyphenyl)ethenyl)benzene(1,3-(CnOBST)2B, where n = 8, 10, 12, 14, 16), monotropic B2 phase for n = 12, and enantiotrpic B2 phase for n = 14, 16. The rather short mesophase temperature ranges is attributed to the coplanarity of distyrenyl benzene, which would result in a stronger π-π stacking. (3)1,3-bis(2-(4-(4-alkoxybenzoyloxy)phenoxycarbonyl)ethenyl)benzene(1,3-(CnOBBAc)2B, where n = 12,16)exihibited peculiar enantiotropic smectic phases, banana leaf-like texture for n = 12, fractal and focal conic for n = 16. These phases require further studies for characterization.

碩士
大同大學
化學工程學系(所)
96
The purpose of this research work was an attempt to elucidate the structure-property correlation in the chiral smectic liquid crystals. Optically active (S)-1-propyloxy-2-propanol and (S)-1-(2,2,3,3,3-pentafluoropropyloxy)-2-propanol were designed and prepared by the treatment of (S)-propylene oxide with corresponding alcohols under basic condition. Three homologous series of chiral compounds derived from these alcohols were synthesized, and their mesophases and electro-optical properties were investigated. The effects of changing (1) the linking group in the core structure of the molecule changing from carboxylate group to methyleneoxy group, (2) the chiral group varied from non-fluorinated to semi-fluorinated alkoxy chain length and, (3) the linking groups modified from -CH2O- to deuterated –CD2O- core structure of the molecule were compared and discussed. The mesomorphic phases and their corresponding transition temperatures were primarily characterized by the microscopic textures and DSC thermograms, and the ferroelectric and antiferroelectric phases were further identified by the measurements of electric switching behavior and dielectric constant ε'. Compounds I(m=8-11) exhibited the SmA*, SmC* and SmCγ* phases, while compound (m=12) with longer alkyl chain exhibited the SmA*-SmC* phases. Compounds II(m=8,10) with even number of alkyl chain length displayed ferroelectric SmC*, antiferroelectric SmCA* and ferroelectric SmX* (SmI* or SmF*) phases, and compounds II(m=9,11,12) with odd number of alkyl chain length displayed exclusively SmC* phase. It is interesting to found that the deuterated compounds III(m=8-12) suppressed the formation of SmCγ* and resulted in the formation of SmA* and SmC* phases as compared to the non-deuterated compounds I(m=8-11). These results demonstrated that the semi-fluorinated compounds II(m=8-12) facilitate the formation of antiferroelectric phase, and suppressed the formation of SmA* phase. When the linking group changes from -CH2O- to deuterated –CD2O- core structure of the molecules, the temperature range of the SmA* phase and the SmC* phase increase. Comparing structurally similar non-fluorinated compounds PPmPPB(m=8-12) to I(m=8-12), it can be found that when the linking group changes from –COO- to -CH2O-, the temperature range of the SmA* phase and the SmC* phase decrease. Comparing structurally similar compounds II(m=8-12) to MPFPECPmBC(m=8-12), it can be found that compounds with -CH2O- linking group, suppresses the formation of SmA* phase and decreases the temperature range of the SmCA* phase, but increases the temperature range of the SmC* phase. The physical properties of the chiral compounds in ferroelectric SmC*, SmCγ*, SmX* (SmI* or SmF*) and antiferroelectric SmCA* phases were also measured. The maximum magnitudes of the spontaneous polarization for compounds I(m=8-12), II(m=8-12) and III(m=8-12) are approximately in a range of 17.7-30.9nC/cm2, 80-120.4nC/cm2 and 8-20nC/cm2, respectively, demonstrating that the compounds with semi-fluorinated chiral group have larger Ps values. When the linking group of the chiral compounds changes from -CH2O- to deuterated –CD2O- in the core of the molecule, the maximum Ps values slightly decreases. Comparing I(m=8-12) to PPmPPB(m=8-12), and II(m=8-12) to MPFPECPmBC(m=8-12) indicate that the maximum Ps values are greater in the structurally similar compounds with methyleneoxy linking group than carboxylate group in the core of the molecules. The maximum apparent tilt angles of series I(m=8-12), II(m=8-12) and III(m=8-12) are approximately in a range of 18°-22°, 23°-34.5° and 21°-27.5°. The results showed that the compounds with semi-fluorinated chiral group have larger apparent tilt angles. When the linking group changes from -CH2O- to deuterated –CD2O- in the core structure of the molecule, the optical tilt angles increase. Comparing I(m=8-12) to PPmPPB(m=8-12), and II(m=8-12) to MPFPECPmBC(m=8-12), it can be found that there has no any signification correlation of the maximum apparent tilt angles. In conclusion, the chiral compounds with -COO- or -CD2O- linking group on the main core structure of the molecule suppress the formation of the SmCγ* phase. And when the chiral compounds with –CH2O- linking group on the main core structure of the molecule having semi-fluorinated alkyl chain in chiral tail facilitate the formation of SmCA* phase but suppress the formation of the SmA* phase. Regardless of the compounds with -COO- or -CH2O- linking group on the main core structure of the molecule, the results show that the compounds with semi-fluorinated alkyl chain in chiral tail largely enhance the maximum Ps value.

碩士
大同大學
化學工程學系(所)
94
The primary of this research work was an attempt to elucidate the correlation between structure and property in the chiral smectic liquid crystal. A homologous series of chiral materials derived from optically active (S)-1-methyl-2-[(2’-methoxy) ethoxy]ethanol has been successfully synthesized and the structures-property relationship investigated in the chiral liquid crystal system. The target compounds were modified independently by (i) the achiral peripheral methylene chain length ‘m’ and (ii) the lateral fluoro substituents in the phenyl ring of the core. The results showed that compounds I(m=8-12) exhibited the phases sequence of SmA*-SmC*-SmX*, compounds II(m=8-12) exhibited the phases sequence of SmA*-SmC*, while the compound II(m=9) posesses an additional SmX*. In the compounds III(m=8-12), compounds III (m=8, 9) with shorter alkyl chain displayed an enantiotropic phase sequence of SmA*-SmCA* while compounds III(m=10-12) with longer alkyl chain exhibited enantiotropic phase sequence of SmA*-SmC*. Extending achiral alkyl chain length in compounds I(m=8-12) and III(m=8-12) stabilizes the temperature ranges of SmC* phase, but suppresses the formation of SmA* phase. In compounds II(m=8-12), as the achiral alkyl chains are extended, the transition temperatures of SmC*-Cr are increased but the temperatures ranges of SmC* phase are decreased. The compounds with lateral fluoro substituents in the phenyl ring of core could affect the formation of the mesophase, lower the transition temperatures, melting points and clearing points. Moreover, the phenyl ring with 2-fluoro substituent possesses higher transition temperature than that with 3-fluoro substituent, suggesting that molecular broadening minimized due to the sterically shielded of 2-flueoro substituent. The electro-optical responses of chiral compound II(m=11) in the SmC* phase displayed V-shaped switching behavior, chiral compound III(m=9) in the SmCA* phase displayed U-shaped and double hysteresis loop switching behavior. Comparison of compounds I,II, III(m=8~12) clearly show that the compounds I(m=8-12) have higher Ps values than the compounds II, III(m=8-12), suggesting that compounds with the lateral fluoro substituents could suppress the polarity of the transverse dipole. The maximum Ps values of I, II, III(m=9-12) are about 6-16 nC/cm2. The compounds III(m=8-12) with 3-fluoro substituent have higher tilt angle than the compounds I, II(m=8-12). The maximum optical tilt angle values of the compounds I, II, III (m=8-12) were between 20-30o.

碩士
大同大學
化學工程學系(所)
94
Research this prove optical rotation layer arrange looks relation between the his structure and nature of liquid crystal mainly, Israel (S) -[1-methyl-2-(2' -methylsulfanylethoxy) ]Ethanol formates a series of optical rotation liquid crystal materials for the initial thing, probe into and does not fasten all end length ' m ' of alkane chain it to the looks of the liquid crystal and influence of the photoelectric characteristic of physics, in order to establish molecular structure and relation of fastenning the looks of all liquid crystal. The experimental result shows: The first serial of liquid crystal material I (m=8-12) only shows SmA* phase. In the second serial II (m=8-10) shows SmA*, SmC* and SmCA* three kinds of liquid crystal phases. Change and does not fasten all end length ' m ' of alkane chain, find it with not fastenning the increase of all end length ' m ' of alkane chain, the reducing thereupon of temperature range of the looks of the liquid crystal, namely clarify some temperature with rising with reducing, crystalline temperature temperature The second serial liquid crystal chemical compound shows when SmC* liquid crystal carries on the photoelectricity amount to examine that can get the V type and change the behavior under changing the temperature and frequency, electric current change quantity of behavior examine result can is it fasten all end alkane chain length ' m ' is it have heavy difference too to change to receive. Second series of spontaneity polarization values maximum lie between 93 nC/cm2 and angle of inclination maximum lie between 31o- 35o.