Liquid crystal molecule-capped Ag−Pd bimetallic nanoparticles (atomic ratio = 1/9, 1/4, 1/1, 4/1, and 9/1) were prepared by photoirradiation of the tetrahydrofuran solution of silver perchlorate and palladium(II) acetate in the presence of liquid crystal molecule, 4′-pentylbiphenyl-4-carbonitrile. (5CB is often used for this compound based on conventional nomenclature 4′-pentyl-4-cyanobipenyl. Thus, 5CB is used in this paper.) The prepared bimetallic nanoparticles had an average diameter of 1.8−3.6 nm. Infrared spectra of carbon monoxide adsorbed on the bimetallic nanoparticles suggested that bimetallic nanoparticles had a random alloy structure. The nanoparticles were dispersed in liquid crystal 5CB to construct novel twisted nematic liquid crystal devices (TN-LCDs). The TN-LCDs containing Ag−Pd bimetallic nanoparticles revealed the electro-optic properties depending on the composition of nanoparticles, especially surface composition of nanoparticles, which was shown to be of importance to control not only the properties but also the stability of nanoparticle-doped LCDs by bimetallization.
TN-LCDs particularly doped with the metal nanoparticles of Ag-Pd composite, which are protected by chemical covering with nematic liquid crystal, 5CB (K-15, Merck) as a ligand, are shown to exhibit a long term stability in the electro-optical (EO) effect featured by a frequency modulation with short response times of ms or sub-ms order. This device is called FM-LCD. The unique electro-optical characteristics of the FM-LCD were clarified in terms of the Maxwell-Wagner effect of a heterogeneous dielectrics, where the analysis is done using an equivalent circuit model rather than the conventional potential theory; and we derived the formulae of the dielectric strength and the dielectric relaxation time. The former is used to explain the FM-LCD effect and also to evaluate the effective electrical conductivity of the metal nanoparticle that will be 4.4 Â 10 4 S=m, which is about 1 Â 10 À3 times smaller than that of metal Ag; and the latter is expressed to demonstrate that the relaxation time decreases with increasing the concentration of metal nanoparticle for the first time.
Herein, we report the dielectric properties of liquid crystal cells embedded with the nanoparticles of Pd, where each of which is covered with a diffusion cloud. It is shown that an amplification of the capacitors with these media occurs with the gain,Ac=12.5,when the concentration of nanoparticles is 0.3 wt% and in the frequency region below the dielectric relaxation frequency, 158.5 Hz. This phenomenon is explained by an equivalent circuit model together with a compatible explanation of the dielectric strength and the relaxation time. It is claimed that the occurrence of the capacitance amplification may be attributed to a special nature of the oscillating extra charges, which appear in the region between the host medium and inclusion, and produces an effective negative dielectric constant of the special nanoparticles. This explanation was made by formulating an independent auxiliary equivalent circuit equation that enables to determine the numerical condition of the production of the negativity in the dielectric constant of inclusions (nanoparticles), and, thus, we succeeded in getting the numerical value of this dielectric constant and that of the gain of the capacitance amplification.
We prepared 4 -pentylbiphenyl-4-carbonitrile (5CB)-stabilized rhodium (5CB-Rh) nanoparticles and poly(cyclodextrin) (PCyD)-stabilized rhodium (PCyD-Rh) nanoparticles. The average diameter of Rh nanoparticles stabilized by 5CB, P CyD, P CyD, and P CyD are 1.2, 5.4, 6.8, and 5.2 nm, respectively. The nanoparticles were dispersed in liquid crystal 5CB to construct novel twisted nematic liquid crystal device (TN-LCD). Voltage holding ratio was measured for TN-LCD fabricated by doping P CyD-Rh nanoparticles. The decrement of the voltage was very much reduced for that doped with P CyD-Rh. The response time of this TN-LCD in the presence of P CyD-Rh nanoparticles was faster than that in the absence.
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