Tuesday, 14 August 2012

Precise dielectric spectroscopy of a dual-frequency nematic mixture over a broad temperature range


Precise dielectric spectroscopy of a dual-frequency nematic mixture over a broad temperature range









P. Perkowskia*, M. Mrukiewicza, K. Garbata, M. Laskaa, U. Chodorowa, W. Pieceka, R. Dąbrowskia & J. Parkaa



DOI:
10.1080/02678292.2012.714483


Abstract

W1832A, a dual-frequency, multi-component nematic mixture prepared at the Military University of Technology, was investigated by means of dielectric spectroscopy over a wide frequency range (100 Hz–10 MHz) and over a wide temperature range (−60°C–100°C). At the temperature of−60°C it is still a nematic. The investigated mixture changes the sign of dielectric anisotropy at temperature and frequency domains. High-precision dielectric spectroscopy studies of molecular motions (around short (S) and long (L) molecular axes) were performed using cells of 5 μm thickness. Gold electrodes in measuring cells were spin-coated with agents for homogenous and homeotropic alignments. In the low-temperature region these motions are hindered enough to observe intra-molecular motions, which typically (at room temperature) are observed in THz frequency range of the measuring field. S molecular motion is eliminated from the measurement range at temperatures below−15°C, while L mode is still observed at−60°C. Dielectric spectroscopy results were compared with THz spectroscopy at room temperature.


.......we obtain n ∞O = 1.67 and n ∞E = 1.84. To verify these values we performed refractive indices measurements for the W1832A mixture via THz spectroscopy using a TDS spectrometer Teraview TPS 3000. .......




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