Abstract
Twisted nematic liquid crystal displays (TN-LCDs), doped
with the nanoparticles of metal, such as Pd, Ag, or Ag-Pd, which are
protected with ligand molecules, such as nematic liquid crystal, exhibit a
frequency modulation (FM) electro-optical (EO) response with short response
time of milliseconds (ms) or sub-ms order together with the ordinary rms voltage
response. These devices are called FM/AM-TN-LCDs; they are distinct from the
ordinary LCDs featured by the amplitude modulation (AM) response. The phenomena
of the FM/AM LCDs may be attributed to the dielectric dispersion of a heterogeneous
dielectric medium known as the Maxwell-Wagner effect. It is experimentally
shown that the frequency range spreads from several tens hertz to several
tens kilohertz and the spectrum is more or less centered about the dielectric
relaxation frequency. We formulated a theory based on an equivalent circuit
model to evaluate the dielectric relaxation frequency and the dielectric strengths;
and we succeeded in explaining the dependence of the dielectric relaxation
frequency on the concentration of nanoparticles and the their dielectric and
electrical properties, whereas conventional theories based on electromagnetic
theory are unable to explain this concentration dependence. This paper reports
on the experimental results of the EO effects and the dielectric spectroscopy
including the dielectric relaxation times and the dielectric strengths of
nematic liquid crystal, 5CB (4-pentyl-4'-cyanobiphenyl), doped with the metal nanoparticles of Pd alone
and Ag-Pd composite; and discusses how the observed dielectric relaxation
frequency or dielectric relaxation time depend on the concentration of the
doped nanoparticles and also their electrical and dielectric properties.
© 2006 IEEE
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