共查询到20条相似文献,搜索用时 250 毫秒
1.
Monolithic silica gel with macropores was prepared in the solution of water glass and polyacrylic acid (HPAA) by freezing transitional structures of phase separation. In the system, phase separation proceeds between silica polymers and HPAA, so that the porous morphology varies from closed macropores to particle aggregates through bicontinuous morphology, where both macropores and silica skeleton are three-dimensionally interconnected, with increasing HPAA/silica ratio. In addition, we can control the macropore size in bicontinuous morphology by varying the concentration of both silica and HPAA, or by changing the molecular weight of HPAA. The pore size distribution is quite sharp indicating the presence of pores with the same size all through the monolithic samples. 相似文献
2.
Abstract The “marriage” between low molecular weight liquid crystals and polymers burgeoned in the 1980s with the idea of dispersing liquid crystal droplets in a rigid polymer matrix to create an electrically controllable light scattering medium. The orientation of the liquid crystal droplets, and hence the refractive index match and scattering, can be systematically controlled with an electric field. Today, dispersions of liquid crystals and polymers are found in many forms depending on the concentration of polymer, which can be as large as 70% or as small as 1%. The systems most understood are those of larger concentration where the liquid crystal is segregated out in the form of droplets randomly distributed throughout the surrounding polymer (see page 2). Dispersions of liquid crystals and polymers differ from macroscopic bulk liquid crystals because of the large surface-to-volume ratio and symmetry breaking non-planar geometry imposed by the polymer. Their composite nature profoundly affects the ordering of the liquid crystal, and their susceptibility to external fields makes them suitable for many new electro-optic applications, as well as intellectually challenging to study from the basic science perspective. 相似文献
3.
David Levy 《Liquid Crystals Today》2013,22(4):1-2
Abstract Liquid crystals can be trapped into inorganic (silica) substrates by sol-gel processes. The sol-gel process consists of hydrolysis and polycondensation reactions of metal organic monomers, i.e. organoalkoxy silanes, which allows the formation of a silica gel-glass. These processes have been used since 1984 for trapping organic molecules into inorganic oxides; usually, single molecules are trapped into isolated gel-glass (nm size) pores. However, it is possible, by chemical means, to induce larger (0.1–10 pm) cavities in the network of the gel-glass allowing the formation of embedded micron size droplets of low molecular weight nematic LC molecules. Surface variations in these cavities (e.g., providing a molecular oriented surface using Si-CH,CH, groups on the pore cage) may allow a lamellar structure and alignment of the nematogenic LC compounds at the surface. It was suggested that order arises as a consequence of the chemical affinity between the apolar character of the pore surface and the lipophilic groups of the LC. Therefore, the main concern has been to ascertain whether the sample manufacturing keeps the LC structure, thus giving gel-glass dispersed liquid crystals (GDLCs) with electrooptical response. 相似文献
4.
Abstract The properties of nematic and cholesteric Polymer Dispersed Liquid Crystal (PDLC) with ellipsoidal droplets are reported. The shape of the droplets are modified by a shear stress during the preparation. Different values of the shear stress were used which permit an ellipticity ratio modification by a factor 10. The electro-optical properties are measured for different types of samples and compared with theoretical previsions: transmission or reflection under voltage, threshold voltage, response times. We also describe the preparation of the sample, the experimental apparatus used for the shear stress, and the expected theoretical quantities like response times. When the liquid crystals are nematics, we obtain an increase of the threshold voltages, as predicted. The relaxation time decreases with increasing deformation but the diminution is not as great as predicted. When the liquid crystals are cholesterics, the high deformations induce polygonal fields, which strongly modify the electro-optical properties of the micro-composite. The threshold voltages and response time at applied voltage decrease whereas the relaxation time is increasing. 相似文献
5.
Polymorphic transformations in K0.975Rb0.025NO3 single crystals have been investigated by optical microscopy and X-ray diffraction. The equilibrium temperature between modifications
II and III has been determined. It is established that the crystal growth at II ↔ III polymorphic transitions is accompanied by the formation and growth of daughter-modification nuclei in the matrix crystal. 相似文献
6.
S.M. Hamidi M.M. Tehranchi M. Ghanaatshoar M. Moradi S.M. Mohseni 《Journal of Non》2008,354(47-51):5178-5180
Amorphous magnetic thin films have been deposited onto BK-7 substrates using the pulsed laser deposition technique. The source material irradiated by the laser was a pack of amorphous ribbons of composition Fe78Si9B13. The structural properties of thin films were investigated and a large number of droplets were observed in the magnetic layers. Electric current passing through the films causes significant deformation of droplets and consequently changes the magnetic thin films characteristics. Magnetic properties evolution after electrical processing was investigated using magneto-optical Kerr effect. 相似文献
7.
A. E. Wróblewski W. T. Konieczko J. Skoweranda M. Bukowska-Strzyżewska 《Journal of chemical crystallography》1991,21(5):581-587
The title compound (4a) was synthesized from a phosphite compound obtained from 4-hydroxy-2-pentanone and dimethylphosphorochloridite, after addition of an equivalent of water. Thecis-configuration of the P=O and C3-OH groups was established based on31P NMR chemical shifts. In chloroform, as well as in benzene solution, the most favorable conformations of the title compound are
4
5
T,4
E, and
4
5
T. The crystal and molecular structure of4a has been determined by single-crystal X-ray diffraction data, and refined toR=0.056. The five-membered ring has an envelope4
E (C5) conformation, with the asymmetry parameter C
5(4)=3.5°. Both the C5-CH3 and the C3-CH3 groups are equatorial. In the solid state, the molecules form dimers with hydrogen bonding between the hydroxyl groups and the phosphoryl oxygen atom of an adjacent molecule. A quantitative comparison of the structure of 4a with the structure of the related 2-mcthoxy-3,5,5-trimethyl-2-oxo-1,2-oxaphosphospholan-3-ol is given. 相似文献
8.
L. V. Lutsenko L. P. Oleksenko O. P. Ripko G. V. Fedorenko 《Molecular Crystals and Liquid Crystals》2020,699(1):63-70
AbstractEffect of composition and morphology on the catalytic activity in CO oxidation of Co-, Cu-, Ce-containing oxide materials prepared by citrate method has been studied. It was shown that composites consist of well-dispersed oxides Со3O4, CuO and CeO2 with average crystallite sizes 13–24?nm, 14–26?nm and 3–7?nm, respectively. It was established that Co-, Cu-, Ce-oxide nanocomposites demonstrated higher catalytic activity in CO oxidation in comparison with individual oxides. The ternary oxide system Со3O4–CuO–СеO2 (Со:Cu:Се=10:1:1) was found to possess the highest catalytic activity due to formation finely dispersed particles of CuO and СеO2 oxides simultaneously with nanosized Со3O4 species and formation of large quantity of mobile oxygen at the interfaces between the oxide nanoparticles. 相似文献
9.
The growth mechanism of liquid phase epitaxial layers of Ga1?xAlxAs on preferentially etched GaAs substrates has been investigated. It has been found that enhanced diffusion of As atoms due to a local concentration gradient, which is set up by non-uniform growth at channels, plays a critical role in determining the growth morphology. The relation between growth morphology and growth conditions is discussed by using a simple growth model. 相似文献
10.
P. Gluziński S. Kasprzyk J. W. Krajewski P. Sałański T. Stankiewicz J. Jurczak 《Journal of chemical crystallography》1991,21(3):357-363
1,8-Diaza-11,14-dioxacyclohexadeca-2,7-dione (3) has been synthesized under high-pressure conditions, whereas 1,10-diaza-4,7-dioxacyclohexadeca-2,9-dione (6) has been obtained under thermal conditions. Both compounds have been investigated in the solid state and in solution by X-ray structural and NMR methods, respectively. The crystals of3 are orthorhombic, space groupPbca; the crystals of6 are triclinic, space groupP¯1. Both structures were solved by direct methods, and refined by a full-matrix, least-squares procedure giving for3
R=0.045 and for 6R=0.056 (R
w
=0.065). From the NMR investigations in solution a twofold symmetry of both molecules (probably in intermediate conformations) is suggested; no such symmetry was found in crystalline state. The structure of6 exhibits a positional disorder of one O-heteroatoms with the population ratio 0.510.49. The arrangement of the macroring with respect to the carbonyl groups was found to betransoid in3 andcisoid in6. 相似文献
11.
We report a computational model to simulate vapour growth morphology of urea crystal by considering molecular anisotropy and surface relaxation of different crystal faces. It has been argued that the faces' growth occurs through the adsorption of molecular layers rather than a slice of thickness dhkl. The molecular layer is a 2-D periodic arrangement of molecules in which each molecule has same the orientation. The molecular orientations in a slice of thickness dhkl may differ from each other and depend on crystallographic orientation of the slice. The discussed approach has been employed to simulate vapour growth shape of crystalline urea by calculating attachment energy of molecular layers using Hartee–Fock and density functional theories. The calculated growth morphology is in good agreement with the vapour grown shape of urea crystal. The role of thermal and growth kinetics affecting the vapour growth morphology has been discussed. The observed polar growth morphology of urea crystal has also been discussed particularly in the context of different atomic environments of (111) and (?1?1?1) faces. 相似文献
12.
Gia Petriashvili Mauro D. L. Bruno Erica Fuoco Riccardo Barberi 《Molecular Crystals and Liquid Crystals》2019,684(1):82-88
AbstractIn the last decade, the possibility to use liquid crystal droplets as optical micro-cavities and lasers has attracted much attention since it paves the way for many applications in the field of sensors or tunable photonics. Several techniques can be used to obtain small micro-resonators as, for example, dispersing a cholesteric liquid crystal inside an immiscible isotropic fluid to create an emulsion. Since liquid crystals are extremely sensitive to external factors as temperature or external fields, laser tuning can be easily achieved. Here, we report on the possibility to tune the laser emission from dye doped cholesteric liquid crystals microdroplets dispersed in a glycerol matrix in presence of nitric acid molecules in the emulsion. Using a fluorescent dye with pH dependent optical properties, the emitted laser wavelength can be tuned in a range of 60?nm. This effect could find applications for the development of spectroscopy based sensors. 相似文献
13.
Balawant S. Joshi Taikyun Rho Peter L. Rinaldi Weixia Liu Todd A. Wagler M. Gary Newton Doowon Lee S. William Pelletier 《Journal of chemical crystallography》1991,27(9):553-559
The structure of the π-molecular complex (10) was assigned on the basis of the solid state13C-nmr spectrum. The solid state13C-nmr spectrum of quinhydrone (12) has also been determined. Accurate1H and13C chemical shift assignments have been made for the compounds3,5,6,7,8, and10 on the basis of HMQC and HMBC spectral data. The π-molecular complex10 crystallizes in the space groupP21
In with cell parameters:a=4.052 (1) ?,b=6.477 (1) ?,c=19.093 (2) ?, β=90.17 (1)o,z=1,D
c
=1.400 g mc−32. Crystal and molecular structure of the title compound, C28H22O4, has been determined by an X-ray analysis of10 by direct methods from diffractometer data and refined by full-matrix least-squares 相似文献
14.
AbstractZeolitic materials were synthesized from coal fly ash (CFA) using the fusion/hydrothermal method. The effect of NaOH/CFA ratio and particle size on the morphological structure of the zeolitic material crystals prepared was investigated by analyzing crystals morphology and crystallinity. The chemical composition, morphology, and crystallinity of the synthesized materials were characterized by SEM, XRD, and XRF. It was possible to synthesize chamfered-edged cubic crystals at NaOH/CFA ratio of 0.9. The particle size of the zeolite crystals tended to decrease with increasing the alkali content of NaOH/CFA from 0.9 to 1.8. The morphological structure of the crystalline particles was similar to that of zeolite A synthesized from the CFA. This study has shown that the fusion/hydrothermal method is a very effective technique for synthesizing the zeolitic materials from the CFA and provides a potential application for obtaining commercial products. 相似文献
15.
CdSe hierarchical microspheres have been successfully synthesized by a hydrothermal route at 120 °C for 16 h via a reaction between CdCl2 and Na2SeSO3 in ionic liquid (1‐butyl‐3‐methylimidazolium bromide)‐water mixed medium. The structure and morphology of the as‐prepared products have been investigated by XRD and SEM, and the results indicate that the CdSe hierarchical microspheres have wurtzite structures and are self‐assembled by nanorods. It has been found that ionic liquid, reaction temperature, and reaction time have influence on the morphology of the products. The possible growth mechanism of CdSe with special morphology has been discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
16.
Stepan M. Yayloyan Liana S. Bezhanova Ashot M. Yayloyan 《Molecular Crystals and Liquid Crystals》2013,570(1):747-754
Abstract A theoretical investigation of molecular ordering of smectic C liquuid crystals C8H17O-C6H4-C6H 4-COO-C6H4-OC8H17 { A }, C9H19O-C6H4-COO- C6H4-COO-C6H4-NO2 { B } and its binary mixtures { A+B } has been carried out by the method based on the Rayleigth-Schrodinger perturbation theory. The mutual arrangement of two molecules corresponding to the minimum of the total interaction energy between them Upair has been established. The curves of the dependence of Upair and its various contributions on displacement of molecules from each other along the molecular long X-axis and angle θ between molecules' long axes has been also computed in the minimum point vicinity. The obtained results make it possible to determine the peculiarities of the structural organization of molecules, as well as to construct a model of the structure of A and B compounds in different phases taking into account the most probable packing of molecules. 相似文献
17.
Hatsumi Nakazawa Shinobu Fujinami Miho Motoyama Takao Ohta Takeaki Araki Hajime Tanaka 《Molecular Crystals and Liquid Crystals》2013,570(1):871-878
Abstract Polymerization-induced phase separation in polymer-dispersed liquid crystal is studied by computer simulations in two dimensions. The domain morphology resulting from phase separation is investigated by solving the couple set of equations for the local volume fraction and the nematic order parameter, taking into account the viscoelastic effects and gelation due to polymerization. Comparing the morphology of phase separation by temperature quench, it is shown that the viscoelastic effects and gelation enable the polymer-rich phase to form a stable interconnected domain even when the polymer component is minority. 相似文献
18.
Somnath Bhattacharyya Thomas Hche Nicols Hemono María J. Pascual Peter A. van Aken 《Journal of Crystal Growth》2009,311(18):4350-4355
Aiming at tailoring optical properties, the precipitation of LaF3 nano-crystals in LaF3–Na2O–Al2O3–SiO2 glass-ceramics is studied thoroughly on the nano-scale using advanced transmission electron microscopic techniques. Nano-sized phase-separation droplets enriched in lanthanum and silicon are formed already in the base glass. Within these less than 20 nm large droplets, LaF3 crystallizes upon heat treatment. The nano-crystallization mechanism revealed is self-limited since growth is restricted by the size of the droplets. An average crystallite size of around 12 nm is achieved with a narrow size distribution since the phase-separation droplets also contain silicon not incorporated into the growing crystal. Instead, excess silicon relocated to the periphery of the pre-existing phase-separation droplets forms a diffusion barrier around the LaF3 nano-crystals preventing further crystal growth and/or ripening. 相似文献
19.
Hassan Hadadzadeh Ali Reza Rezvani Mahmood Karimi Abdolmaleki Khaled Ghasemi Hadi Esfandiari Marzieh Daryanavard 《Journal of chemical crystallography》2010,40(1):48-57
Abstract
Pyridine-2,6-dicarboxylic acid (dipic) was used for the synthesis of a co-crystal with 1,10-phenanthroline-5,6-dione (phen-dione) and a nickel(II) complex. The co-crystal dipic·phen-dione·4H2O (1) has been synthesized and studied by X-ray crystallography. The structure is stabilized with hydrogen bonds between dipic, H2O and phen-dione. It is surprising that there is no direct hydrogen bonding between phen-dione and dipic and yet the molecules co-crystallize in aqueous solution. A new complex of nickel(II), [Ni(phen)(dipic)(H2O)]·4H2O (2), (where phen = 1,10-phenanthroline) has been synthesized and characterized by elemental and thermogravimetric analyses, FT-IR, UV–Vis and 1H-NMR spectroscopy. The structure of (2) has been studied by X-ray crystallography. The coordination around Ni(II) is a distorted octahedron. The crystal packing shows that the dimensionality of (2) is enlarged to 3D, through hydrogen bonds and π–π interactions. Cyclic voltammetry of (2) shows that the Ni(II/I) couple is irreversible. 相似文献20.
P. Sagan G. Wisz B. Tsizh I. Virt I. Rudy 《Molecular Crystals and Liquid Crystals》2018,671(1):148-155
AbstractThe structure, morphology and optical transmittance spectra of pentacene films on the (glass/ITO) surface were studied. The films were grown by two methods - the thermal vacuum deposition (TVD) and pulsed laser deposition (PLD). The electron diffraction pattern from thermally deposited pentacene films confirms their polycrystalline structure while the diffraction pattern of PLD-coated layers has a diffusion character. The results obtained showed that layers deposited by the TVD method has an optical spectrum that is characteristic for the pentacene film in contrary to the layers deposited by the PLD method. It is found a sensitivity of the optical transmittance of pentacene films to the ammonia action, which may be used for development the optical gas sensor. 相似文献