Tomoki Gunjima

Phase diagram and phase separation in LC/prepolymer mixture

A new method to obtain liquid crystal and polymer composite(LCPC) material is reported. This material is a new electro-optic material which can control scattering and transparent states in an electric field. e obtained this material by the photo-polymerization-induced phase separation from liquid crystal and prepolymer mixture where both monomer and oligonier are used as prepolymer. We have found new type of phase diagram in this mixture which has a nematicisotropic line in addition to binodal and spinodal lines. Electro-optic properties of this material are strongly affected by the point on the phase diagram at which the polymerization-induced phase separation starts. This method enables us to control these properties such as voltage-transmittance characteristics. Typical devices using these materials are also shown. They have high contrast ratio and high transmittance in ON state and are suitable for display devices. Drive voltage can be reduced by optimizing this material and the device with high contrast ratio about 200:1 in low drive voltage below 6Vrms was obtained.

Grating Polarizing Beam-Splitter Using Polymerized Liquid Crystal

A grating polarizing beam-splitter was developed using a newly synthesized UV curable liquid crystal. The fabricated device shows high diffraction efficiency (+1st order: 35.5%, -1st order: 31.9%) and transmittance (83.8%). The temperature dependence of diffraction efficiency variation was suppressed by about 5% within temperature range from 20 to 80°C because these device parameters become less sensitive to temperature variation as a result of photopolymerization.

Morphology and ordering control in LCPC

A phase separation under an applied electric field (PSUF treatment) in LCPC relaxes the energetic stress for dynamic operation of its device. Both higher dynamic response time and less hysteresis in dark gray scales which are significant issues in LCPC are achieved, since its treatment can control the interface between liquid crystal and matrix polymer without the damage to scattering in off state and contrast ratio. It is based on the morphological characteristic which is caused by the first step: a segregation of liquid crystal and ordering process of the liquid crystal under an applied field, and the second step: polymer/pre-polymer precipitation to maintain the early ordering of segregated liquid crystal. The essential structure of LCPC caused by the characteristic phase separation process, is characterized with confocal fluorescence microcopy, which also supports its process mechanism.