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Investigations of dual-frequency nematic liquid crystals doped with dichroic dye
摘要： In this work, we studied and analysed a particular variety of liquid crystals, the so-called dual-frequency nematic liquid crystals (DFNLCs). The interest was to perform dielectric spectroscopy and optical characterisation with two pure and doped mixtures of DFNLCs. By means the dielectric spectroscopy we observed a low value of crossover frequency at room temperature for one dye doped mixture. Additionally, in the spectra studies, a scattering of light at cross-frequency, and a stable and unstable focal conical state was observed, respectively, for the investigated mixtures.
关键词： relaxation frequency,crossover frequency,dielectric spectroscopy,optical characterisation,Dual-frequency liquid crystal
更新于2025-09-10 09:29:36
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Frequency-Modulated Wave Dielectrophoresis of Vesicles And Cells: Periodic U-Turns at the Crossover Frequency
摘要： We have formulated the dielectrophoretic force exerted on micro/nanoparticles upon the application of frequency-modulated (FM) electric fields. By adjusting the frequency range of an FM wave to cover the crossover frequency fX in the real part of the Clausius-Mossotti factor, our theory predicts the reversal of the dielectrophoretic force each time the instantaneous frequency periodically traverses fX. In fact, we observed periodic U-turns of vesicles, leukemia cells, and red blood cells that undergo FM wave dielectrophoresis (FM-DEP). It is also suggested by our theory that the video tracking of the U-turns due to FM-DEP is available for the agile and accurate measurement of fX. The FM-DEP method requires a short duration, less than 30 s, while applying the FM wave to observe several U-turns, and the agility in measuring fX is of much use for not only salty cell suspensions but also nanoparticles because the electric-field-induced solvent flow is suppressed as much as possible. The accuracy of fX has been verified using two types of experiment. First, we measured the attractive force exerted on a single vesicle experiencing alternating-current dielectrophoresis (AC-DEP) at various frequencies of sinusoidal electric fields. The frequency dependence of the dielectrophoretic force yields fX as a characteristic frequency at which the force vanishes. Comparing the AC-DEP result of fX with that obtained from the FM-DEP method, both results of fX were found to coincide with each other. Second, we investigated the conductivity dependencies of fX for three kinds of cell by changing the surrounding electrolytes. From the experimental results, we evaluated simultaneously both of the cytoplasmic conductivities and the membrane capacitances using an elaborate theory on the single-shell model of biological cells. While the cytoplasmic conductivities, similar for these cells, were slightly lower than the range of previous reports, the membrane capacitances obtained were in good agreement with those previously reported in the literature.
关键词： Cell,Frequency-modulated wave,Crossover frequency,The Clausius-Mossotti factor,Spectroscopy,Dielectrophoresis,Vesicle
更新于2025-09-04 15:30:14