共查询到20条相似文献,搜索用时 265 毫秒
1.
CB15/E9 mixtures submitted to an electric field exhibit a tetragonal phase BPX, having a D10 4(I4122) symmetry and two hexagonal phases BPH3d and BPH2d The Kossel diagram technique allows us (a) to confirm the hexagonal symmetry of BPH3d and to determine precisely its space group D2 6 (P6222) and (b) to study the field-induced phase transitions between BP II, BPX and BPH3d. We show that the BP II → BPH3d transition is a continuous deformation involving a dilatation in the field direction and a shear perpendicular to this direction. The BP II → BPX and BPX → BPH3d transitions are discontinuous. 相似文献
2.
The oriented superstructure of poly(vinylidene fluoride) is controlled by using a forced-quenching type of zone drawing apparatus. Systematic variation of the weight fraction χ(I) of form-I crystals and the orientation function fa of amorphous chains shows that the piezoelectricity increases with increasing χ(I) and fa. A change in the state of molecular aggregation during poling is also effective in increasing the piezoelectricity and the orientation of the crystal b axis along the poling direction. Equations relating piezoelectricity to the form-I crystallinity, the orientation of amorphous chains, and the orientation of the crystal b axis along the poling direction are derived. These are based on a mechanical model having regions of taut tie molecules in parallel with composite regions consisting of crystalline and amorphous blocks in series. 相似文献
3.
G. Pelosi C. Pelizzi M. Belicchi Ferrari M. C. Rodríguez‐Argüelles C. Vieito J. Sanmartín 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(10):o589-o592
The two title semicarbazones, namely 2,3‐dihydro‐1H‐indole‐2,3‐dione 3‐semicarbazone, C9H8N4O2, (I), and 1‐methyl‐2,3‐dihydro‐1H‐indole‐2,3‐dione 3‐semicarbazone, C10H10N4O2, (II), show the same configuration, viz. Z around the imine C=N bond and E around the C(O)—NH2 bond, stabilized by two intramolecular hydrogen bonds. The presence of a methyl group on the isatin N atom determines the difference in the packing; in (I), the molecules are linked into chains which lie in the crystallographic (102) plane and run perpendicular to the b axis, while in (II), the molecules are arranged to form helices running parallel to a crystallographic screw axis in the a direction. 相似文献
4.
Brian T. Holmes Clifford W. Padgett William T. Pennington 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(10):o602-o603
The title compound, C5H3I2N, crystallizes in the polar space group Fmm2, with crystallographic mm2 symmetry imposed on the molecule. Molecules are linked through C—H?N hydrogen bonding to form chains which are, in turn, joined through weak I?I halogen‐bonding interactions to form layers. The pyridine ring lies parallel to the polar z axis and has the N atom pointing in the +z direction. The layers stack in a polar fashion normal to the a axis and the absolute structure has been determined. 相似文献
5.
Takashi Nishino Kiyofumi Takano Katsuhiko Nakamae 《Journal of Polymer Science.Polymer Physics》1995,33(11):1647-1651
The elastic modulus El of the crystalline regions of cellulose polymorphs in the direction parallel to the chain axis was measured by x-ray diffraction. The El values of cellulose I, II, IIII, IIIII, and IVI were 138, 88, 87, 58, 75 GPa, respectively. This indicates that the skeletons of these polymorphs are completely different from each other in the mechanical point of view. The crystal transition induces a skeletal contraction accompanied by a change in intramolecular hydrogen bonds, which is considered to result in a drastic change in the El value of the cellulose polymorphs. © 1995 John Wiley & Sons, Inc. 相似文献
6.
Claudio Tavagnacco Gabriele Balducci Giacomo Costa Karl Tschler Wolfgang von Philipsborn 《Helvetica chimica acta》1990,73(5):1469-1480
In four series of strictly related organocobalt complexes, derived from cobaloximes by replacement of the O…H…O with O…-BF2…O and/or (CH2)3 groups, the trends of 59Co-NMR shielding and electrochemical data are discussed. A largely parallel behaviour of the plots of E1/2(I) values for the first Co(III)/Co(II) electron transfer vs. the 59Co chemical shifts reflects the similar sensitivity of the two parameters to a change in electron affinity of the central metal ion due to a variation of the organic group R. E1/2(II) values for the second Co(II)/CO(I) electron transfer are less sensitive to the change of R, but the trend of the plot vs. δ(59Co) is still parallel in the four series. Consistent deviations from a roughly linear dependence of E1/2(I) on pKa of the hydrocarbon acid corresponding to R, on Taft constant s?* and on 59Co shielding are noticed for the isopropyl derivatives and attributed to a steric effect. This was confirmed in a series of R? Co(DMG)pyridine complexes in which 59Co shielding decreases steadily with increasing steric parameter Es (Taft) of the alkyl group. There is experimental evidence from X-ray data that δ(59Co) decreases with an increase of the Co? C bond length, illustrating steric hindrance in alkyl coordination to be responsible for the decreased shielding of the 59Co nucleus. The relative displacements of the graphic displays for the different series reflect the effect of changes in electron affinity of the redox center, due to the equatorial ligand, which, in turn, is caused by variations in the electron-withdrawing power due to the introduction of the BF2 group and by the change from ?2 to ?1 valence of the (CH2)3-capped ligands. 相似文献
7.
Marcia Cristina Branciforti Carlos Amauri Oliveira Jose Alexandrino de Sousa 《先进技术聚合物》2010,21(5):322-330
In order to promote better understanding of the structure‐mechanical properties relationships of filled thermoplastic compounds, the molecular orientation and the degree of crystallinity of injection molded talc‐filled isotactic polypropylene (PP) composites were investigated by X‐ray pole figures and wide‐angle X‐ray diffraction (WAXD). The usual orientation of the filler particles, where the plate planes of talc particles are oriented parallel to the surface of injection molding and influence the orientation of the α‐PP crystallites was observed. The PP crystallites show bimodal orientation in which the c‐ and a*‐axes are mixed oriented to the longitudinal direction (LD) and the b‐axis is oriented to the normal direction (ND). It was found that the preferential b‐axis orientation of PP crystallites increases significantly in the presence of talc particles up to 20 wt% in the composites and then levels‐off at higher filler content. WAXD measurements of the degree of crystallinity through the thickness of injection molded PP/talc composites indicated an increasing gradient of PP matrix crystallinity content from the core to the skin layers of the molded plaques. Also, the bulk PP crystallinity content of the composites, as determined by DSC measurements, increased with talc filler concentration. The bulk crystallinity content of PP matrix and the orientation behavior of the matrix PP crystallites and that of the talc particles in composites are influenced by the presence of the filler content and these three composite's microstructure modification factors influence significantly the flexural moduli and the mechanical stiffness anisotropy data (ELD/ETD) of the analyzed PP/talc composites. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
8.
Guangrong Zheng Sean Parkin Linda P. Dwoskin Peter A. Crooks 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(1):o9-o11
The crystal structures of the title compounds, 2α,4α‐dibenzyl‐3α‐tropanol (2α,4α‐dibenzyl‐8‐methyl‐8‐azabicyclo[3.2.1]octan‐3α‐ol), C22H27NO, (I), and 2α,4α‐dibenzyl‐3β‐tropanol (2α,4α‐dibenzyl‐8‐methyl‐8‐azabicyclo[3.2.1]octan‐3β‐ol), C22H27NO, (II), show that both compounds have a piperidine ring in a chair conformation and a pyrrolidine ring in an envelope conformation. Isomer (I) is asymmetric, the benzyl groups having different orientations, whereas isomer (II) is mirror symmetric, and the N and O atoms, the C atom attached to the hydroxy group, and the methyl C atom attached to the N atom lie on the mirror plane. In the crystal structures of both (I) and (II), the molecules are linked together by intermolecular O—H⋯N hydrogen bonds to form chains that run parallel to the a direction in (I) and parallel to b in (II). 相似文献
9.
Z. Mencik 《Journal of Polymer Science.Polymer Physics》1975,13(11):2173-2181
The unit cell of poly(tetramethylene terephthalate) is triclinic with parameters a = 5.96 Å, b = 4.83 Å, c (fiber axis) = 11.62 Å, α = 115.2. β = 99.9, and γ = 111.3°; space group P1 , calculated crystalline density 1.41 g/cc. The plane of the benzene ring is found to be inclined by about 15° from the fiber axis, contributing to a shortening of the fiber period as compared to the period expected on the basis of analogy with other members of the terephthalate ester series. The remaining shortening of the fiber period occurs in the ? O? °CH2? °CH2? segment of the chain. No abnormally short distances among neighboring chain atoms were observed. A typical texture pattern was found in specimens of this polymer that were cold rolled and subsequently annealed. In this texture the c axis of the unit cell is highly oriented in the rolling direction; the a and b axes of the unit cell are oriented preferentially so that the terephthalate residue lies as close as possible to the plane of rolling. 相似文献
10.
Digna Varghese V. Arun P. P. Robinson Manju Sebastian P. Leeju G. Varsha K. K. M. Yusuff 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(12):o612-o614
The Schiff base compounds N,N′‐bis[(E)‐quinoxalin‐2‐ylmethylidene]propane‐1,3‐diamine, C21H18N6, (I), and N,N′‐bis[(E)‐quinoxalin‐2‐ylmethylidene]butane‐1,4‐diamine, C22H20N6, (II), crystallize in the monoclinic crystal system. These molecules have crystallographically imposed symmetry. Compound (I) is located on a crystallographic twofold axis and (II) is located on an inversion centre. The molecular conformations of these crystal structures are stabilized by aromatic π–π stacking interactions. 相似文献
11.
《Journal of Structural Chemistry》2001,41(4):640-645
The crystal structures of new dyes: 4-[[3-[[2,6-bis-(tert-butyl)-4H-pyran-4-ylidene]methyl]-2-oxido-4-oxo2-cyclobuten-]-ylidene]methyl]2,6-bis(tert-butyl)pyrylium
(I) and its thio analog (II) were determined. Crystal data: space group P1 (I), P21/n (II); a = 5.960(9) ? (I), 10.400(4) ? (II); b = 9.366(3) ? (I), 12.242(4) ? (II); c = 13.948(3) ? (I), 14.482(6) ? (II);
α = 70.43(2)° (I), 90.0° (II); ? = 84.82(9)° (I), 94.65(3)° (II); γ = 79.10(9)° (I), 90.0° (II); V = 720.0 ?3 (I), 1837.7 ?3 (II); Z = I (I), 2 (II); dcalc = 1.131 g/cm3 (I), 086 g/cm3 (II); R1(F) 0.049 (I), 0.045 (II). The substituents are trans-oriented relative to the planar 4-membered ring. Bond length
distribution points to a considerable electron density delocalization over the whole molecule except the But groups. The pyrane rings are oriented differently relative to the central group; in II the rings lie in the same plane which
is rotated through 7.7° with respect to the central fragment, whereas in I they lie in parallel planes which are 1.38 ? apart
and deviate from the central fragment to opposite sides, forming with it dihedral angles of 12.8°. These conformational differences
are possibly the result of the action of crystal field forces. In I molecules are arranged as overlapping stacks, whereas
in II the pairwise parallel dye molecules are oriented in such a way that their long molecular axes are perpendicular to the
long axes of the neighboring pair, resulting in a herringbone packing.
Translated fromZhurnal Strukturnoi Khimii, Vol. 41, No. 4, pp. 781-787, July-August, 2000 相似文献
12.
Christoph Elschenbroich Fabian Gerson Hiroaki Ohya-Nishiguchi Christoph Wydler Axel Nissen 《Helvetica chimica acta》1977,60(8):2530-2538
Proton hyperfine data are reported for the radical anions of 1,8-di (propyn-1-yl)-naphthalene (I), 7,8,12,13-tetradehydro-10,11-dihydro-9H-cyclodeca[d,e]naphthalene (II) and 2,2′-di(propyn-1-yl)-biphenyl (III), as well as of 5,6,11,12-tetradehydro-7,8,9,10-tetrahydro-dibenzo[a,c]cyclodecene (IV) and its 8,8,9,9-tetradeuterio-derivative (IV-d4). The triple bonds in I and II can be regarded as roughly parallel, while those in IV (and IV-d4) may be considered as crossed. The π-spin distributions in I? to IV? are discussed in terms of simple MO models which suggest a weekly bonding interaction between the acetylenic fragments in IV?, in contrast to III? where such an effect appears to be negligible. The importance of an analogous interaction in I? and II? is difficult to deduce, since its inclusion into a MO model does not substantially affect the π-spin distribution in these radical anions. 相似文献
13.
Joanna Meszko Artur Sikorski Olexyj M. Huta Antoni Konitz Jerzy Baejowski 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):o669-o671
The title compounds, C14H12N+·CH3O4S?, (I), and C15H14N+·CH3O4S?, (II), respectively, crystallize with the planar 10‐methylacridinium or 9,10‐dimethylacridinium cations arranged in layers, parallel to the twofold axis in (I) and perpendicular to the 21 axis in (II). Adjacent cations in both compounds are packed in a `head‐to‐tail' manner. The methyl sulfate anion only exhibits planar symmetry in (II). The cations and anions are linked through C—H?O interactions involving three O atoms of the anion, six acridine H atoms and the CH3 group on the N atom in (I), and the four O atoms of the anion, three acridine H atoms and the carbon‐bound CH3 group in (II). The methyl sulfate anions are oriented differently in the two compounds relative to the cations, being nearly perpendicular in (I) but parallel in (II). Electrostatic interaction between the ions and the network of C—H?O interactions leads to relatively compact crystal lattices in both structures. 相似文献
14.
Daniel E. Lynch Ian McClenaghan 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):e537-e537
The structure of the title compound, C14H12ClNO3, (I), comprises essentially planar molecules stacked parallel to the a axis. C—H?O hydrogen‐bonding interactions exist to both naphthoquinone O atoms and the Cl atom, but not to the morpholine O atom. 相似文献
15.
Takashi Nishino Ryousuke Matsui Katsuhiko Nakamae 《Journal of Polymer Science.Polymer Physics》1999,37(11):1191-1196
The elastic moduli El of the crystalline regions of α‐chitin and chitosan in the direction parallel to the chain axis were measured by X‐ray diffraction. The El values were 41 GPa for α‐chitin, and 65 GPa for chitosan, respectively, at 20°C. The contracted skeletons of α‐chitin and chitosan are the key factor for the low El values compared with that (138 GPa) of cellulose I. The El value of α‐chitin was constant at 41 GPa both at −190°C and 150°C, which indicates that the molecular chain of α‐chitin is stable against heat within the temperature and stress range studied. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1191–1196, 1999 相似文献
16.
Artur Sikorski Karol Krzymiski Antoni Konitz Jerzy Baejowski 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(4):o227-o230
The title compounds, C21H14Cl2NO2+·CF3O3S−, (I), and C20H11Cl2NO2, (II), form triclinic crystals. Adjacent cations of (I) are oriented either parallel or antiparallel; in the latter case, they are related by a centre of symmetry. Together with the CF3SO3− anions, the antiparallel‐oriented cations of (I) form layers in which the molecules are linked via a network of C—H·O and π–π interactions (between the benzene rings). These layers, in turn, are linked via a network of multidirectional π–π interactions between the acridine rings, and the whole lattice is stabilized by electrostatic interactions between ions. Adjacent molecules of (II) are oriented either parallel or antiparallel; in the latter case, they are related by a centre of symmetry. Parallel‐oriented molecules are arranged in chains stabilized via C—H·Cl interactions. These chains are oriented either parallel or antiparallel and are stabilized, in the latter case, via multidirectional π–π interactions and more generally via dispersive interactions. Acridine and independent benzene moieties lie parallel in the lattices of (I) and (II), and are mutually oriented at an angle of 33.4 (2)° in (I) and 9.3 (2)° in (II). 相似文献
17.
Susan C. Gross 《Journal of polymer science. Part A, Polymer chemistry》1971,9(11):3327-3335
Rotational mobility of nitroxyl radicals in polyester films was investigated at temperatures from ?180 to +240°C by ESR spin-probe techniques. Evidence obtained indicated that mobility of radicals was related to polymer structure and reflected increased volume made available to the probe molecule by the polymer matrix. A single correlation time, which followed the form τC = τ0 exp {Ea/RT}, was calculated for the temperature range of rapid reorientation (~109 Hz) of nitroxyl radicals. Ea ranged from 5 to 25 kcal/mole for various systems. Uniaxially oriented semicrystalline polymer matrix restricted radical mobility to a greater extent than a semicrystalline biaxially oriented sample. Effective local viscosity encountered by a nitroxyl radical in several polymers was calculated as 9–13 poise. 相似文献
18.
Jesus Bueno Manuel Melguizo M. Luisa Quijano John Nicolson Low 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(7):o363-o366
The supramolecular structures of the isomeric compounds 5,7‐dimethoxyimidazo[1,2‐c]pyrimidine, C8H9N3O2, (I), and 7‐methoxy‐1‐methylimidazo[1,2‐a]pyrimidin‐5(1H)‐one, C8H9N3O2, (II), are determined by weak C—H⃛N and C—H⃛O hydrogen bonds in (I), which generate alternating linked centrosymmetric R(8) and R(10) rings that form a ribbon running parallel to the c axis, and by C—H⃛O bonds in (II), which link the molecules into sheets comprising centrosymmetric R(10) and R(22) rings. 相似文献
19.
William W. Fleming R. E. Fornes J. D. Memory 《Journal of Polymer Science.Polymer Physics》1979,17(2):199-211
Broad-line NMR measurements were made on water in cellulosic samples. The spectra for oriented rayon at 65% relative humidity and room temperature consisted of a visually apparent doublet (SD) and a narrow singlet (SN) which was shifted upfield about 7 ppm from the center of the doublet. The doublet separation varied as A(3 cos2θ—1), where θ is the angle between the fiber axis and the magnetic field; the maximum doublet separation was 350 mG at both 15.1 and 56.4 MHz, indicating the doublet is dipolar in origin. The peak-to-peak linewidth of the narrow singlet was orientation and field dependent. The upfield shift of the narrow singlet from the doublet center was field dependent. Spectra for vacuum-treated rayon consisted of only the narrow singlet, which was orientation dependent. The doublet separation decreases with increasing moisture content and is essentially zero for oriented rayon samples at 100% relative humidity; the resulting spectra due to the collapsed doublet and SN singlet was an asymmetric line. Temperature-dependent measurements were made on oriented rayon at 65% relative humidity with the fiber axis parallel to the magnetic field; when the temperature was increased from about 0° the peak-to-peak linewidth of the doublet halves and the doublet separation decreased. As the temperature was increased from about 30 to about 65°C, a previously unobserved singlet (SE) became visible. The relative amplitudes of the three lines varied with temperature as follows: The SE singlet increased, the SD doublet decreased, and the amplitude of the SN singlet remained constant. Measurements using oriented cotton samples and randomly packed rayon samples indicated that the NMR line shape of the water spectra depends upon the physical properties of the macromolecular substrate. The doublet component of the spectra is attributed to a water species (SD) which is highly bonded to the macromolecular substrate. The SE singlet is attributed to an energetic water species (SE) which is rapidly tumbling in the macromolecular environment. The SN singlet is not due to free water. 相似文献
20.
V. E. Dmitrienko 《Liquid crystals》2013,40(3):847-851
Abstract A theory of electro-optic and elasto-optic effects in the blue phases of cholesteric liquid crystals is developed. The case of small structure deformations and a weak field is considered: |E| ? E c, where E e is the critical field for the cholesteric-nematic transition. The theory explains all of the main experimental facts: the field-induced birefringence and biaxiality, the distortion of the cubic structure (electrostriction) and the orientation of the blue phase monocrystals in an electric field. 相似文献