Lyotropic chromonic liquid crystals (LCLCs) form a columnar discotic liquid crystalline (LC) phase in aqueous solution
due to the disc-like or plank-like molecular shape of chromonic dyes and their ionic peripheries. Such columnar
structures in the chromonic columnar N phase can be coated on a glass substrate, and aligned in one direction by
applying external forces. The resulting thin crystalline film (TCF) can absorb a polarized light parallel to the molecular
axis while transmitting a polarized light parallel to the columnar axis, which constructs an E-polarizer. Although the
concept of the coatable polarizer known, it has not been commercially successful due to numerous problems mainly
originated from the use of aqueous solution. It is extremely difficult to coat the aqueous solution on most of substrates,
especially on plastic substrates. Large volume shrinkage occurs during the crystallization process generating unfavorable
defects. Also, weak adhesion becomes an important issue when a TCF is applied to a flexible substrate.
In this presentation, we demonstrate a novel preparation method of coatable polarizer from a photo-curable organicbased
LCLC solution. Lyotropic LC solutions were prepared by dissolving amino-functional chromonic dye in acrylic
acid containing photoinitiator and crosslinking agents. The solution was shear-coated with subsequent UV irradiation to
provide a thin film polarizer. The coating processibility of this organic-based solution was outstanding, particularly on a
plastic substrate. The maximum polarization efficiency was measured to be > 98 %. The resulting thin film polarizer
showed excellent film characteristics, such as good adhesion strength to various substrates, superior surface hardness,
good solvent resistance and decent thermal stability.
To explore novel photoresponsive liquid crystalline polymer actuator, a new difunctional photosensitive nematic liquid
crystalline monomer was synthesized synthesized in high yield (>60% overall), and polymerized via acyclic diene
metathesis polymerization (ADMET) method. Nematic monomer, 4-butoxy-2'-(4-hex-5-enyloxy)-4'-(4-hex-5-
enyloxybenzyloxy)-azobenzene, exhibited crystalline to nematic and nematic to isotropic transitions at 85.6 and 98.3 °C,
respectively. ADMET polymerization of the monomer using Grubbs catalyst (Gen II) was performed to obtain a high
molecular weight polymer. Brown colored free-standing polymer film and fiber were prepared from casting chloroform
solution or from drawing polymer melt, respectively. The polymer film showed nematic liquid crystalline property with
photosensitive phase transition behavior as observed by polarized microscope and differential scanning calorimetry. The
photomechanical deformation of the film and fiber induced by polarized UV irradiation was investigated.
Novel photosensitive fluorinated poly(arylene ether) containing chalcone unit (F-PAECh) in the main chain was synthesized from decafluorinated chalcone and fluorinated bisphenol at low temperature for polymer optical waveguide application. Upon UV irradiation on the resulting polymer film, [2+2] cycloaddition of chalocone moiety induced the anisotropic decrease of the refractive indices (nTE and nTM) accompanied with crosslinking of polymer film. The decrease was more significant in in-plane direction than out-of-plane direction, and consequently, zero birefringence was obtained with 4.5 min of exposure. Zero-birefringence as well as its excellent optical properties of F-PAECh makes it a promising candidate material for use in high-performance wavelength division multiplexing components such as polarization-independent arrayed waveguide gratings and Bragg wavelength filters.
A novel zero birefringent and photosensitive polyimide was synthesized. The polymer is soluble in solvents and contains a chalcone group for photo-crosslinking by UV exposure. The glass transition and decomposition temperature of the polymer were 254°C and 430°C before cross-linking. Evolution of the absorption spectra upon UV exposure indicated that the cross-linking reaction is related to the cycloaddition of the double bonds in the chalcone group to form cyclobutane. The photo-crosslinking reaction not only increased the thermal stability, but also induced a refractive index change of the films. The refractive index of the film was reduced upon UV exposure from 1.5862 to 1.5697 for TE mode and from 1.5807 to 1.5697 for TM mode, respectively, resulting in zero birefringence after curing. Loss of p-conjugation in the chalcone group by the crosslinking reaction is supposed to induce the reduction of the refractive indices and orbital change from sp2 to sp3 makes the polymer chain be kinked, resulting in decrease of birefringence. The polymer film showed optical loss of 0.41 dB/cm at 1.3 mm and 0.54 dB/cm at 1.55 mm. Zero birefringence and low optical loss combined with photo-processibility of the material are making it an excellent candidate for the high performance waveguide materials.