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We present freeze-fracture transmission electron microscopy (FF-TEM), dielectric spectroscopy and electro-optic measurements on a dimeric liquid crystal mixture, which previously was proposed to form the twist-bend nematic (Ntb) phase. Our FF-TEM studies provide a direct image of a 10.5 nm periodic structure, consistent with the expected nanoscale, heliconical twist-bend modulation of the molecular orientation. Dielectric measurements in the 100 Hz to 10 MHz range reveal three nearly Debye-type dispersion processes in the nematic and the twist-bend phase. Low frequency 8 V/µm electric fields applied on planar cells cause the optical-scale stripe texture (another characteristic feature of the Ntb phase) to disappear. Higher (>16 V/µm) fields gradually realign the heliconical axis along the electric field; it relaxes back after the field removal. 相似文献
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We have extended photon correlation spectroscopy down to a one-nanosecond time scale, and applied it to a study of layer undulations in freestanding smectic-A films of two cyanobiphenyl liquid crystals. Temporal correlations in the intensity of scattered light reveal an interesting combination of under- and overdamped modes. The underdamped mode is accurately described by a recently calculated correlation function of the smectic layer displacement, although its frequency and damping rate exhibit stronger dispersion at large optical wave vectors than expected from current dynamical models for smectic films. 相似文献
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Polymer-stabilized liquid crystal microgratings are made using a focused Gaussian UV laser beam to photopolymerize 3 wt % reactive monomer in a cholesteric liquid crystal host. In a typical case, round gratings of 300 μm diameter and 10 μm pitch are produced. The microgratings highlight interesting differences between mesogenic and non-mesogenic monomers in the assembly and spatial distribution of polymer networks formed in a cholesteric host. We also observe a corresponding variation in the electro-optical properties of the stabilized gratings. In the mesogenic case, the grating state of the liquid crystal is faithfully captured even for relatively short UV exposures and over regions only a few pitch lengths in size. These findings are consistent with phase separation of the mesogenic monomer into regular domains templated by periodic, macroscopic variations in orientational order of the host. This templating effect is significantly reduced in the non-mesogenic case. 相似文献
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New measurements of the Raman spectrum of incommensurate BaMnF4 reveal that there is not a classically ‘soft’ amplitude mode as has hitherto been assumed. This finding questions the validity of predictions based on straightforward Landau theory. 相似文献
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A series of [1,2,3]-triazole-based liquid crystal compounds were synthesised via a fast and efficient microwave-mediated ‘Click Reaction’ and their phase behaviour is presented. Most of the 1,4-diaryl-[1,2,3]-triazole compounds exhibited a nematic phase with broad temperature ranges and relatively low transition temperatures compared to previously examined materials. Structural variations, involving regio-isomers and lateral halogenation, gave rise to different phase behaviour of the two families of triazole-based compounds. 相似文献
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本文利用KDV方程所对应的线性方程解所具有的光滑效应及压缩映像原理,得到了Hirota-Satsuma系统初值问题的局部和整体适定性结果. 相似文献
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The vibronic vapour phase photoacoustic spectrum of Br2 in the wavelength region 505–541 nm (19796–18480 cm−1) has been recorded using microphone as well as pump-probe method. Discrete vibronic bands superimposed on a monotonically
increasing continuum background towards the dissociation limit results from the overlapping B
3Π
0u
/+
← X
1Σ
g
/+
and 1Π1u
← X
1Σ
g
/+
electronic transitions. Vibronic bands originating from υ″=0 have been used to estimate the relative rate of non-radiative relaxation as a function of the excited state B
3Π0u
vibrational quantum number υ′. A comparison with the optical absorption spectroscopy of Br2 leads to the identification of three broad spectral regions between 505 and 541 nm (19796 and 18480 cm−1) on the basis of different non-radiative relaxation processes. 相似文献
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