Cholesteric liquid crystal (LC) microdroplet is applied in many areas, such as tunable laser, biosensor, information display and security identification, due to its unique optical properties. The topological structure, defects, and photonic crystallinity in the cholesteric liquid crystal (LC) microdroplet can be controlled through the chirality. Here we report an interesting phenomenon that chirality information can be shared among dispersed LC microdroplets in surfactant aqueous solution, which is driven by the transferring of chiral dopant molecules. As a result, we developed an artificial molecule transfer technology which could in situ vary the material composition within the isolated dispersed microdroplets. The molecular transfer is switchable and the transfer speed is controllable by tuning the molecular solubility in continuous phase. Based on this technique, we manipulated, forward and backward, the topological evolution and the photonic crystal band-gap of the dispersed LC droplet. This technique is an easy and powerful experimental tool, and it may be applicable to other fields in optical application, biology, chemistry and material science.
While a pixel in a color image has three colorimetric information of RGB, that in a spectral image contains full spectral
information, several tens times more information compared to the color image. Hence, the spectral image is widely
applicable in biology, material science, and environmental science. Although several methods for spectral image
acquisition have been suggested to date, those methods are expensive, bulky, or slow in actual device. In this work, we
designed a novel type of tunable narrow band-pass filter using rotatable polarizer, quarter-wave plate, and birefringence
films. Different from the conventional Lyot-Ohman type filter, we do not use a liquid crystal layer. The selection of
wavelength is made by rotating the polarizer in our filter set, and adopted a piezoelectric rotational actuator for that. We
simulated to find the optimal conditions of the filter set, and finally, fabricated a filter module. The minimum band width
was 5 nm, which is suitable for usual spectral imaging and can be reduced further if necessary, and the wavelength of
light passing through the filter set was continuously selectable. After setting the filter in a microscope, we obtained a
spectral image set for a bio sample that contained full spectrum information in each pixel. Using image processing, we
could demonstrate to read out the spectral information for any selected position.
Dielectrophoresis can provide a delicate tool to control electrically neutral particles in colloid. The dielectrophoresis is usually applied to solid particles or heterogeneous liquid droplet in continuous liquid, but we devised and investigated the dielectrophoresis of isotropic droplets within nematic phase or vice versa. Using multi-components liquid crystal mixtures that exhibit relatively wide temperature range of nematic-isotropic coexistence, we achieved a field-induced phase separation between isotropic and nematic. We also fabricated the isotropic-nematic filaments that was achieved using a biased surface preference for either isotropic or nematic phase of the alignment layer . The dielectrophoresis manipulations of isotropic and nematic droplets required much lower voltage compared to that for the electro wetting type devices. In addition, we observed the bi-directional actuation of isotropic droplets using anisotropic dielectric property of liquid crystal, which is not possible in usual dielectrophoresis. The bidirectional actuation was achieved by controlling the LC director within the cell so as to change the sign of the difference between the effective dielectric constant of nematic and isotropic liquid crystals. We simulated the bi-directional dielectrophoresis by performing the LC director calculation and the corresponding dielectrophoresis. The simulation results matched well with the experimental data. Thus, the bi-directional dielectrophoresis using isotropic and nematic droplets may open new possibility of electro- optical applications using liquid crystals.