Hyunaee Chun

Effects of trans-Polyoctylene Rubber (TOR) on the Properties of NR/EPDM Blends

trans-Polyoctylene rubber (TOR) was melt blended with an incompatible NR/EPDM (70/30) blend. Mixing torque and temperature were reduced as TOR was added to NR/EPDM blend. The curing characteristics of the blend were affected as TOR participated in vulcanization and became a part of network. A scanning electron micrograph demonstrated that addition of TOR improved the compatibility of the blend and thereby led to a finer phase morphology. The ozone resistance of the blends was determined in terms of a critical stress-strain parameter. The critical stored energy density for ozone cracking was significantly enhanced for the TOR containing rubber blend. It was believed that the improvement in ozone resistance arised from finely dispersed ozone-resistant EPDM particles in the blend. TOR caused an improvement in dynamic properties and an increase in tensile modulus, but a decrease in tensile stress and elongation at break of the rubber blend.

The effect of the molecular structure of the chromophore on the photorefractive properties of the polymer systems with low glass transition temperatures

Seven chromophores with different dipole moments and polarizability anisotropies were synthesized by varying conjugation bridges, such as polyene, thiophene, indole, and benzene combined with strong electron-donor and electron-acceptor groups. The birefringence of photorefractive materials containing 30 wt% of chromophore was observed to be in the range of 0.45 × 10−3 to 5.0 × 10−3 at an electric field of 70 V µm−1, depending on the chromophore structure. The photorefractive material containing a polyene-based chromophore exhibited the highest photorefractive property, followed by those containing thiophene-based, benzene-based and indole-based chromophores. It was observed that, within material systems used in this study, photorefractive properties of guest–host systems were linearly proportional to the orientational birefringence.

Determination of the space-charge field in polymeric photorefractive material

We proposed a method for measuring the magnitude of the space-charge field of the polymeric photorefractive materials. In the case of polymeric photorefractive material with low glass transition temperature, optically anisotropic chromophores are known to be reoriented under space-charge field. Simply by adding a pair of crossed polarizer units to a conventional degenerated four wave mixing setup, we could measure the birefringence of the photorefractive materials induced by a newly formed space-charge field. Since the birefringence of a given material is governed by the applied electric field, the space-charge field can be determined from the variation of birefringence using the oriented gas model.

Dependence of the Bragg condition on an external electric field for a polymeric photorefractive material

We investigated the effect of an applied electric field on the Bragg condition of degenerate four-wave mixing a polymeric photorefractive material with a low glass-transition temperatue. For a polymeric photorefractive material the application of an external electric field is necessary for photorefractivity leads to birefringence of the material by poling of the nonlinear optical chromophore. Because the propagation vectors of the pumping and reading beams inside the material are influenced by the refractive index of the material, the Bragg condition depends on the magnitude of the external field. Using an oriented gas model and the-coupled-mode theory, we numerically analyzed the Bragg-mismatch effect that causes a reduction in diffraction efficiency as a function of an external field. We present the boundary conditions for sample thickness and grating spacing for which the Bragg-mismatch effect must be taken into account.

The Highly Efficient Polymeric Photorefractive Materials: Influence of Alkyl End Group of Chromophore on Photorefractive Properties

Abstract Photorefractive composites based on carbazole-substituted polysiloxane, doped with a series of NLO chromophores and photo-sensitizer were presented. The alkyl end group of chromophore was observed to influence electro-optic and photoconductivity of composite, in addition to device stability. And the gain coefficient of composite containing 4-diethylaminobenzylidene malonitrile as a chromophore was over 100 cm −1 at 60 V/μm. And gain of composite was ca.2.0 at 90 V/μm, which indicates that the pump beam was almost transferred to the signal beam.