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Giustiniano Tiberio Dr. Luca Muccioli Dr. Roberto Berardi Dr. Claudio Zannoni Prof. 《Chemphyschem》2009,10(1):125-136
We study the important n‐cyanobiphenyl (with n= 4–8) series of mesogens, using modelling and molecular dynamics simulations. We are able to obtain spontaneously ordered nematics upon cooling isotropic samples of 250 molecules. By using the united‐atom force field developed herein, we show that the experimental isotropic–nematic transition temperatures are reproduced within 4 K, allowing a molecular‐level interpretation of the odd–even effect along the series. Other properties, like densities, orientational order parameters and NMR residual dipolar couplings are also reproduced well, demonstrating the feasibility of predictive in silico modelling of nematics from the molecular structure. 相似文献
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Witold Brostow Antnio M. Cunha John Quintanilla Ricardo Simes 《Macromolecular theory and simulations》2002,11(3):308-314
In recent papers we have used statistical mechanics to predict multiple phase formation in polymer liquid crystals (PLCs).[1, 2] Now we have performed molecular dynamics simulations of PLC copolymers as materials consisting of LC islands in flexible matrices. A method for creating such materials on a computer is described. The overall concentration of the LC units, island size, and spatial distribution of the islands (random, in rows, and evenly distributed throughout the material) were varied. Crack formation and propagation as a function of these parameters were investigated. The local concentration of LC units in each chain has been defined. We found that the probability of a crack initiation site goes symbiotically with the local LC concentration. The first small crack is sometimes a part of the path through which the material breaks, however, although several small cracks may evolve at first, some of these never evolve into larger cracks since crack arrest occurs. The results can be used for creation of real materials with improved mechanical properties. 相似文献
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Stablen-hexadecane/water andn-tetradecane/water macroemulsions containing monolayers of natural (egg yolk lecithin, EY) and synthetic (dimyristoylphosphatidylcholine,
DMPC) phospholipids at liquid-liquid interfaces were prepared. The existence of the monolayers was proved by studying the
reduction kinetics of a surface-active spin probe with ascorbate anions. Spin labeled derivatives of stearic acid in which
the nitroxide group is locared at different distances from the polar head (5-, 12-, and 16-doxylstearic acids) were used to
study the temperature dependences of the molecular ordering, rotational mobility, and local polarity in the monolayers in
emulsions and also in bilayers in liposomes obtained from the same lipids. In the EY monolayers, the degree of spin probe
solubilization is higher, while the order parameters (S) and rotational correlation times (τ) are lower than those in EY bilayers. The differences between these parameters for mono-
and bilayers increase with an increase in the distance of the reporter group from the aqueous phase. In the DMPC monolayers,
a first-order phase transition was detected by measuring the temperature dependences ofS and τ. The temperature region of the phase transition in monolayers is shifted to lower temperatures with respect to that
for bilayers and depends on the nature of the oil phase. It was concluded that the phospholipid monolayers in emulsions incorporate
hydrocarbon molecules, whose concentration in the DMPC monolayers increases on going from the low-temperature (gel) to the
high-temperature (liquid crystal) phase.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 418–425, March, 1998. 相似文献
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Jingjing Guan Mingzhi Zhang Birong Li Prof. Huai Yang Prof. Guojie Wang 《Chemphyschem》2012,13(17):3812-3818
The photocontrolled phase transitions and reflection behaviors of a smectic liquid crystal, 4‐octyl‐4′‐cyanobiphenyl (8CB), tuned by a chiral azobenzene, are systematically investigated. For the smectic 8CB doped with the chiral azobenzene (1R)‐(?)‐4‐n‐hexyl‐4′‐menthylazobenzene (ABE), the initial smectic phase can be switched to cholesteric and then to isotropic upon UV irradiation due to the trans‐to‐cis photoisomerization of ABE; however, no reflection band is observed. For the smectic 8CB doped with ABE and the chiral agent (S)‐(?)‐1,1′‐binaphthyl‐2,2′‐diol (BN), a reflection band located in the short‐wavelength infrared region is observed, which disappears after further UV irradiation. For the smectic 8CB doped with ABE and a chiral agent with higher helical twisting power, (S)‐2,2′‐methylendioxy‐1,1′‐binaphthalene (DBN), a phototunable system with cholesteric pitch short enough to reflect visible light is demonstrated. With a given concentration of the chiral dopant DBN, a reversible reflection color transition is realized tuned by the isomerization of azobenzene. The reverse phase transition from isotropic to cholesteric and then to smectic can be recovered upon visible irradiation. The photocontrolled phase transitions in smectic liquid crystals and the corresponding changes in reflection band switched by photoisomerization of azobenzene may provide impetus for their practical application in optical memories, displays, and switches. 相似文献
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Kazuma Hamaguchi Dr. Huanjun Lu Shota Okamura Dr. Satoshi Kajiyama Dr. Junya Uchida Shunsuke Sato Dr. Go Watanabe Dr. Yoshiki Ishii Prof. Dr. Hitoshi Washizu Prof. Dr. Goran Ungar Prof. Dr. Takashi Kato 《Chemphyschem》2023,24(8):e202200927
Reentrant phenomena in soft matter and biosystems have attracted considerable attention because their properties are closely related to high functionality. Here, we report a combined experimental and computational study on the self-assembly and reentrant behavior of a single-component thermotropic smectic liquid crystal toward the realization of dynamically functional materials. We have designed and synthesized a mesogenic molecule consisting of an alicyclic trans,trans-bicyclohexyl mesogen and a polar cyclic carbonate group connected by a flexible tetra(oxyethylene) spacer. The molecule exhibits an unprecedented sequence of layered smectic phases, in the order: smectic A-smectic B-reentrant smectic A. Electron density profiles and large-scale molecular dynamics simulations indicate that competition between the stacking of bicyclohexyl mesogens and the conformational flexibility of tetra(oxyethylene) chains induces this unusual reentrant behavior. Ion-conductive reentrant liquid-crystalline materials have been developed, which undergo the multistep conductivity changes in response to temperature. The reentrant liquid crystals have potential as new mesogenic materials exhibiting switching functions. 相似文献
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Molecular Dynamics,Phase Transition and Frequency‐Tuned Dielectric Switch of an Ionic Co‐Crystal 下载免费PDF全文
Jing‐Yan Liu Shi‐Yong Zhang Ying Zeng Xia Shu Prof. Dr. Zi‐Yi Du Dr. Chun‐Ting He Prof. Dr. Wei‐Xiong Zhang Prof. Dr. Xiao‐Ming Chen 《Angewandte Chemie (International ed. in English)》2018,57(27):8032-8036
Dielectric switches that can be converted between high and low dielectric states by thermal stimuli have attracted much interest owing to their many potential applications. Currently one main drawback for practical application lies in the non‐tunability of their switch temperatures (TS). We report here an ionic co‐crystal (Me3NH)4[Ni(NCS)6] that contains a multiply rotatable Me3NH+ ion and a solely rotatable one due to a more spacious supramolecular cage for the former one. This compound undergoes an isostructural order–disorder phase transition and it can function as a frequency‐tuned dielectric switch with highly adjustable TS, which is further revealed by the variable‐temperature structure analyses and molecular dynamics simulations. In addition, the distinct arrangements and molecular dynamics of two coexisting Me3NH+ ions confined in different lattice spaces as well as the notable offset effect on the promoting/hindering of dipolar reorientation after dielectric transition provide a rarely observed but fairly good model for understanding and modulating the dipole motion in crystalline environment. 相似文献
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液晶基本上可分为3类:向列型液晶、近晶型液晶和胆甾型液晶[1].液晶材料的相转变温度的预测对选择和设计液晶材料具有非常重要的作用.本文用分子动力学模拟法对聚[ω-(4′-甲氧基联苯-4-氧基)己基]甲基丙烯酸酯(PM6MPP)单链分子进行了研究,模拟... 相似文献
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Dr. Eugénie Fournier Dr. Sybille Tachon Dr. Nicholas J. Fowler Dr. Guillaume Gerbaud Dr. Pascal Mansuelle Dr. Pierre Dorlet Dr. Sam P. de Visser Prof. Valérie Belle Dr. A. Jalila Simaan Dr. Marlène Martinho 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(60):13766-13776
1-Aminocyclopropane-1-carboxylic oxidase (ACCO) is a non-heme iron(II)-containing enzyme involved in the biosynthesis of the phytohormone ethylene, which regulates fruit ripening and flowering in plants. The active conformation of ACCO, and in particular that of the C-terminal part, remains unclear and open and closed conformations have been proposed. In this work, a combined experimental and computational study to understand the conformation and dynamics of the C-terminal part is reported. Site-directed spin-labeling coupled to electron paramagnetic resonance (SDSL-EPR) spectroscopy was used. Mutagenesis experiments were performed to generate active enzymes bearing two paramagnetic labels (nitroxide radicals) anchored on cysteine residues, one in the main core and one in the C-terminal part. Inter-spin distance distributions were measured by pulsed EPR spectroscopy and compared with the results of molecular dynamics simulations. The results reveal the existence of a flexibility of the C-terminal part. This flexibility generates several conformations of the C-terminal part of ACCO that correspond neither to the existing crystal structures nor to the modelled structures. This highly dynamic region of ACCO raises questions on its exact function during enzymatic activity. 相似文献
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Łukasz Kolek Maria Massalska-Arodź Marian Paluch Karolina Adrjanowicz Tomasz Rozwadowski Dorota Majda 《Liquid crystals》2013,40(8):1082-1088
For 1-[3-fluoro-4-(1-methylheptyloxycarbonyl)phenyl]-2-[4-2,2,3,3,4,4,4-heptafluorobutoxybutoxy)biphenyl-4-yl]ethane (1F7), built of chiral molecules, results of dielectric measurements of liquid-crystalline and solid phases are presented. Rich polymorphism of liquid-crystalline (SmC*, SmC*A and SmI*A) phases as well as of solid (Cr1 and Cr2) phases were observed down to –130°C. At a frequency range from 0.1 Hz to 3 MHz, the relaxation processes were detected in ferroelectric SmC*, antiferroelectric SmC*A and highly ordered SmI*A smectic phases. The mechanism of complex dynamics (moleculear and collective) was identified with the help of the bias field. Vitrification of conformationally disordered crystal phase Cr2 was found in accordance with calorimetric observations. 相似文献
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Gnatyuk I. I. Puchkovskaya G. A. Goltsov Yu. G. Matkovskaya L. A. Drozd M. 《Journal of Thermal Analysis and Calorimetry》2000,62(2):365-371
The results of nematic liquid crystal - isotropic liquid phase transition study by the method of differential scanning calorimetry
for inclusion compounds - mesoporous aluminosilicate molecular sieves of MCM-41 type (including Cu-exchanged samples) with
encapsulated in inner-crystalline space nematic liquid crystal (5CB), as well as IR spectroscopic data for such compounds
were represented. It was shown, that the 5CB molecules are able to interact with the active centers in the MCM-41 channels
forming strong enough bonds of -C≡N⋅⋅⋅H-O- type. The relative amount of 5CB molecules interacting with the walls of channels
and those retaining ‘liquid crystalline’ state in binary systems of molecular sieves MCM-41 and CuMCM-41 was estimated. This
conclusion was confirmed by the data obtained from differential scanning calorimetry measurements.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Kim Jinsoo Jamil Muhammad Jung Jae Eun Jang Jae Eun Farzana Ahmad Jin Woo Lee Sang Woo Park Woo Min-Kyung Kwak Ji Yeon Jeon Young-Jae 《中国化学》2011,29(1):48-52
Molecular dynamics (MD) computer simulation techniques, as a powerful tool commonly utilized by the liquid crystal display (LCD) community, usually are employed for computing the equilibrium and transport properties of a classical many body system, since they are very similar to real experiments in many respects. In this paper we present molecular dynamics computer simulation results taken for a mixture of the two different kinds of nematic liquid crystals (LCs). We calculated rotational viscosity from Brownian behavior with friction of the mean director of the mixture comprising pentylcyanobiphenol (5CB) and decylcyanobiphenol (10CB) by using molecular dynamics computer simulation, where intermolecular potential parameter is Generalized AMBER force field (GAFF). Our computed results show a good agreement with the experimental results. 相似文献
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气液界面上阴离子表面活性剂单层膜的分子动力学模拟 总被引:2,自引:0,他引:2
用分子动力学方法研究了阴离子表面活性剂十二烷基硫酸钠(SDS)在气液界面上的结构和动力学性质. 选择单分子占有面积分别为0.45和0.68 nm2的两个模拟体系, 通过径向分布函数表征了单层膜的厚度, 并根据疏水链中碳原子与极性头中硫原子之间组成的矢量分布和取向函数, 对比了不同界面单层膜的有序排列情况. 结果表明在分子占有面积较小达到饱和吸附的情况下, 界面上的SDS具有较好的有序性. 通过计算气液界面附近水分子的扩散系数发现: 由于氢键和静电作用的影响, 界面区域内的水分子较本体溶液中的水分子有较弱的迁移能力. 相似文献
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Prof. Dr. Tomoyuki Mochida Dr. Yusuke Funasako Mai Ishida Shingo Saruta Dr. Takashi Kosone Prof. Dr. Takafumi Kitazawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15725-15732
Sandwich compounds often exhibit various phase transitions, including those to plastic phases. To elucidate the general features of the phase transitions in metallocenium salts, the thermal properties and crystal structures of [Fe(C5Me5)2]X ([ 1 ]X), [Co(C5Me5)2]X ([ 2 ]X), and [Fe(C5Me4H)2]X ([ 3 ]X) have been investigated, where the counter anions (X) are Tf2N (=(CF3SO2)2N?), OTf (=CF3SO3?), PF6, and BF4. The Tf2N salts commonly undergo phase transitions from an ordered phase at low temperatures to an anion‐disordered phase, followed by a plastic phase and finally melt at high temperatures. All these salts exhibit a phase transition to a plastic phase, and the transition temperature generally decreases with decreasing cation size and increasing anion size. The crystal structures of these salts comprise an alternating arrangement of cations and anions. About half of these salts exhibit phase transitions at low temperatures, which are mostly correlated with the order–disorder of the anion. 相似文献
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Richard J. Mandle John W. Goodby 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(63):14454-14459
The NTB phase phases possess a local helical structure with a pitch length of a few nanometers and is typically exhibited by materials consisting of two rigid mesogenic units linked by a flexible oligomethylene spacer of odd parity, giving a bent shape. We report the synthesis and characterisation of two novel dimeric liquid crystals, and perform a computational study on 10 cyanobiphenyl dimers with varying linking groups, generating a large library of conformers for each compound; this allows us to present molecular bend angles as probability weighted averages of many conformers, rather than use a single conformer. We validate conformer libraries by comparison of interproton distances with those obtained from solution-based 1D 1H NOESY NMR, finding good agreement between experiment and computational work. Conversely, we find that using any single conformer fails to reproduce experimental interproton distances. We find the use of a single conformer significantly overestimates the molecular bend angle while also ignoring flexibility; in addition, we show that the average bend angle and flexibility are both linked to the relative stability of the NTB phase. 相似文献
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Shiwei Chen Jinliang Zhang Huilong Liu Tongyue Qiu Haoxiang Tang Zunmin Zhang 《Molecules (Basel, Switzerland)》2022,27(21)
Rational design of thermotropic liquid crystal (LC)-based sensors utilizing different mesophases holds great promise to open up novel detection modalities for various chemical and biological applications. In this context, we present a dissipative particle dynamics study to explore the unique anchoring behavior of nematic and smectic LCs at amphiphile-laden aqueous-LC interface. By increasing the surface coverage of amphiphiles, two distinct anchoring sequences, a continuous planar-tilted-homeotropic transition and a discontinuous planar-to-homeotropic transition, can be observed for the nematic and smectic LCs, respectively. More importantly, the latter occurs at a much lower surface coverage of amphiphiles, demonstrating an outstanding sensitivity for the smectic-based sensors. The dynamics of reorientation further reveals that the formation of homeotropic smectic anchoring is mainly governed by the synchronous growth of smectic layers through the LCs, which is significantly different from the mechanism of interface-to-bulk ordering propagation in nematic anchoring. Furthermore, the smectic LCs have also been proven to possess a potential selectivity in response to a subtle change in the chain rigidity of amphiphiles. These simulation findings are promising and would be valuable for the development of novel smectic-based sensors. 相似文献