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S. Fuller J. Hopwood A. Rahman N. Shinde G. J. Tiddy G. S. Attard 《Liquid crystals》2013,40(3):521-529
Abstract We have studied the lyotropic liquid-crystalline behaviour of cationic surfactants containing a potentially thermotropic moiety, a terminal cyanobiphenyloxy group. Both mono-alkyl and mid-chain substituted dialkyl surfactants have been examined using optical microscopy and NMR spectroscopy. Incorporation of the cyanobiphenyloxy group destabilizes the hexagonal and bicontinuous cubic phases, with only an extensive lamellar region being observed. For the dialkyl surfactant there is a range of compositions where two lamellar phases co-exist, one water-rich and the second surfactant-rich. 相似文献
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In the first part of this paper an experimental setup using Fourier-transform infrared spectroscopy (FTIR) in combination with a photoelastic modulator (PEM) for linear dichroism measurements is described. The second part shows the influence of PEM-amplitude and scan-velocity on the sensitivity of the instrument. The third part deals with the fringe-problem in the baselines of absorbance spectra and its influence on the determination of the linear dichroic ratio. 相似文献
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We have measured the electrical resistivity of NbSe3 samples which have been radiation damaged with 2.5 MeV protons up to a defect concentration of 0.5%. We find that, unlike substitutional impurities, the defects do not destroy the charge density wave (CDW) transitions and the samples do not go superconducting. The defects become more effective scatterers below the CDW transitions so that the defect resistivity is temperature dependent. The defects pin the CDWs randomly so that carriers in the unnested regions can be scattered by the CDW. This leads to an enhancement of the defect resistivity. The resistivity of the highly damaged samples is still increasing with decreasing temperatures to below 1 K. 相似文献
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Concentrated polystyrene solutions were investigated on the inception and cessation of simple shear flow by means of the technique of two-color flow birefringence. Both monodisperse solutions of various molecular weights and bimodal mixtures were studied. The molecular weight affected both the amount of overshoot in the birefringence and the response time on the inception of shear flow. Large overshoots in birefringence, up to 250%, and undershoot in the orientation angle were observed. The shear stress and the first normal stress difference were calculated by using the stress–optical rule. The amount of strain at the peaks in the stress growth curves are presented along with the steady-state viscosity and primary normal stress coefficient. The experimental results are compared qualitatively with theoretical predictions of various molecular models. 相似文献