No abstract

A large shift of the localized surface plasmon resonance (LSPR) spectrum of gold nanoparticles was attained by electrochemical oxidation of the nanoparticle surface. This oxidation occurred in the cell, which consisted of a pair of indium tin oxide (ITO) electrodes and water medium between the electrodes. On one side of the ITO electrode, the gold nanoparticles were adsorbed. With the application of a voltage of 5 V to the cell, a spectrum shift as large as 68 nm was obtained. Though the spectrum shift has already been observed by changing liquid crystal (LC) orientation surrounding gold nanoparticles, the size of the shift was not large (11 nm). That was because the variation of the effective refractive index of LC was rather small. Our large shift due to electrochemical oxidation resulted from the large refractive index of Au-O. The electrochemical oxidation was confirmed by XPS analysis of the gold nanoparticles with the LSPR spectrum shift. Other possible mechanisms of the shift such as charge localization, aggregation, and adsorption of charged materials proved to have no effect via SEM measurement and so on. This large shift of the resonance spectrum can be expected to lead to further development of spatial light modulators for next-generation optical communications and displays.

No abstract

The dynamic behavior of a polymer-dispersed liquid crystal (PDLC) under an electric field has been studied by static and two-dimensional infrared spectroscopy. The PDLC sample was prepared by polymerization-induced phase separation of a mixture of nematic liquid crystal E7 and acrylate. 2D IR correlation analysis indicates that the rigid core of the liquid crystal molecules reorients as a unit, and suggests that the polymer side chain existing in the interface between the polymer and the liquid crystals may reorient in phase with the liquid crystal reorientation by interaction with the liquid crystal molecules.

A two-dimensional infrared (2D IR) spectrometer has been modified by the following methods to solve several problems on the 2D IR spectroscopy of electric-field-induced reorientation dynamics of a mixed nematic liquid crystal: (1) The response of the liquid crystal (LC) to an electric field was stabilized by an amplitude-modulated ac electric field. (2) Formulation of an anti-reflection coating (ARC) has been proposed to suppress the interference caused by multiple reflections between IR liquid crystal cell windows. (3) The Fourier transform procedure has been modified to correct the phase of the dynamic difference interferograms without spectral anomalies. These modifications can provide a better signal-to-noise ratio and reproducible 2D IR spectrum of a mixed nematic liquid crystal.

We applied polarized infrared (IR) spectroscopy to the analysis of rubbed polyimide (PI) films and evaluated the PI orientation induced by rubbing by measuring the dichroic difference. The IR dichroic difference and liquid crystal (LC) alignment were analyzed for rubbed PI films that were immersed in various organic solvents. The solvents which reduced the dichroic difference and pretilt angle of LC molecules could be characterized in terms of their solubility parameters. When the dichroic difference of the PI films was greatly reduced by the immersion in the solvents, a correlation between the LC pretilt angle and the dichroic difference (i.e. the in-plane orientation of the PI molecules) was observed.

Abstract— A 9‐in. full‐color polymer‐stabilized OCB TFT‐LCD with stable bend alignment in the absence of an electric field was developed. The condition of the polymer stabilization, the characteristics of UV‐curable monomers, and their influence on the configurations of the polymer network in the cell were studied. Possible models of the configuration were proposed and their relationship to the electro‐optical properties was analyzed using a novel simulation method considering the distribution of anchoring effects from both alignment surfaces and the polymer network. It was suggested that a good performance such as high contrast ratio and fast response could be expected in the polymer network originating from newly developed monomers composed of multifunctional LC acrylates due to a relatively weak‐anchoring effect and presumably its localization near the alignment surfaces. By using the newly developed monomers under the optimized polymer‐stabilizing process, a high contrast ratio of 250:1 and fast response nearly equal to that of a conventional OCB cell were achieved.

To eliminate an initial transition from splay to bend alignment, polymer-stabilized OCB was developed. The influences of the monomer concentration and the applied voltage during UV irradiation were studied, and stable bend alignment in the absence of electric field was obtained. The large retardation change and the fast response were achieved by using a mixture of multifunctional LC acrylate monomers, and a 9-inch full-color polymer-stabilized OCB TFT-LCD with initial bend alignment and the contrast ratio of 250:1 was successfully developed.SID 07 DIGEST • 995 ISSN/007-0966X/07/3802-0995-$1.00 © 2007 SID