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
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. .......