• Journal of the Korean Chemical Society
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• v.15 no.6
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• pp.293-303
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• 1971

The theological properties of aqueous suspensions of Black Hills bentonite were measured by using a Couette-type viscometer. Three kinds of flow units in aqueous bentonite suspension were postulated. Each has a different average relaxation time, one Newtonian. One of the non-Newtonian types is thixotropic, and the other is non-thixotropic. The thixotropic non-Newtonian unit is transformed to a Newtonian unit by shear stress. If the stress is relieved, the transformed unit returns to its original state. Two flow equations were derived by introducing chemical kinetics consideration for such a transition into the generalized theory of viscous flow. One equation describes the "upcurve," a diagram of rate of sheat versus shear stress, obtained by increasing the rate of shear, and the other relates to the "downcurve" obtained by decreasing the shear rate. The equations satisfactorilly describe the experimental thixotropic hysteresis of bentonite suspensions. The equations also were successfully applied to the flow curves of the suspensions containing various amounts of monovalent electrolyte (KCI).

• Proceedings of the Optical Society of Korea Conference
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• 1990.07a
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• pp.94-100
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• 1990

The rapid quenching dynamics of the F-center excitation by CN- defects in CsCl crystals were investigated by monitoring the ground state bleach recovery kinetics of F-centers, using a picosecond streak camera absorption spectrometer. The F-centers in CN- doped quenched samples show two bleach recovery components. Optical aggregation converts the slow component to the fast component. The slow one is due to the normal relaxation of the F*-centers as found in CN_ free crystals. The fast one is due to the energy transfer of the F-center electronic excitation to the vibrational energy levels of CN_ molecualr defects. The energy transfer occurs only in the F-center-CN_ defect pairs, FH(CN_)-centers.

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.18-18
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• 2002

Although it was suggested in 1962 that an efficient wavelength conversion could be achieved using ferroelectric crystals of periodic 180° domains, it was not until 1990's that quasi-phase-matching (QPM) became realized, as technology for periodic poling of LiNbO₃ crystals was readily available. Since ferroelectric domain inversion brings about change of the sign of second-order nonlinear susceptibility, periodically poled ferroelectric structures provide an ideal way of achieving QPM for second-harmonic generation and optical parametric oscillation. Periodically poled ferroelectric domains can also be utilized for optical devices, such as Brags electrooptic modulators. fabrication of stable periodic domain structures depends on a number of poling parameters of a ferroelectric crystal, such as coercive field, internal field and electrical conductivity. We present poling kinetics of KNbO₃ crystals, which involve domain nucleation and growth, backswitching, relaxation of internal field. Optimum poling conditions were established by designing a proper wave shape of external field. We demonstrate an efficient second-harmonic generation using QPM in a periodically poled KNbO₃ crystal.

• Bulletin of the Korean Chemical Society
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• v.12 no.6
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• pp.629-632
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• 1991

The rate constants for the formation and dissociation of nickel(II) and cobalt(II) complexes with mandelate have been determined by the pressure-jump relaxation study. The forward and reverse rate constants for the mandelate complex formation reactions were obtained to be $k_f=3.60{\times}10^4\;M^{-1}s^{-1}$ and $k_r=1.73{\times}10^2\;s^{-1}$ for the nickel(II), and $k_f=1.75{\times}10^5\;M^{-1}s{-1}$ and $2.33{\times}10^3\;s^{-1}$ for the cobalt(II) in aqueous solution of zero ionic strength ($(\mu{\to}0)\;at\;25^{\circ}C$. The results were interpreted by the use of the multistep complex formation mechanism. The rate constants evaluated for each individual steps in the multistep mechanism draw a conclusion that the rate of the reaction would be controlled by the chelate ring closure step in concert with the solvent exchange step in the nickel(II) complexation, while solely by the chelate ring closure step for the cobalt(II) complex.

• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.659-662
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• 1992

The pressure-jump relaxation method has been used to determine the rate constants for the formation and dissociation of maganese(Ⅱ), cobalt(Ⅱ), and nickel(Ⅱ) with some dicarboxylates in aqueous solution at zero ionic strength. The carboxylate ligands used are 3-nitrophthalate, 4-nitrophthalate, and phenylmalonate. The activation parameters have alse been obtained from the temperature dependence of the rate constants. A dissociative interchange mechanism with a chelate ring closure step as rate determining is employed to interpret the kinetic data of manganese(Ⅱ) and cobalt(Ⅱ) complexes. The rates of formation of nickel(Ⅱ) complexes are controlled by both the solvent exchange step and the chelate ring closure step.

• Membrane Journal
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• v.10 no.3
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• pp.139-147
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• 2000

Non-Fickian (or anomalous) diffusion was observed in transient sorption of aromatic solvents(such as benzene, toluene, and chlorobenzene) in fluoropolymers (such as ETFE, ECTFE and PVDF). In this study, five other transient sorption models (Crank, Long ＆ Richman, Berens ＆ Hopfenberg, Neogi, Li) based on Fick's law were employed to fit the anomalous sorption data for aromatic solvents. The adjustable parameters were determined by least square analysis of the measured and predicted fractional uptake. For ETFE sorption data slightly deviating from Fickian behavior, all the models exhibited satisfactory results in fitting the anomalous sorption data. In particular, Neogj model predicted intrinsic diffusivity (0.4～0.8$\times$10$^{-5}$ $\textrm{cm}^2$/day) and equilibrium diffusivity (0.13～0.31$\times$10$^{-4}$ $\textrm{cm}^2$/day) as well as relaxation kinetics related to non-Fickain diffusion. For a typical sigmoidal sorption behavior in PVDF, only Crank's model could give the reasonable evaluation on transport properties. The ratio of intial diffusivity (D$_{i}$) to final equilibrium diffusivity (D$_{\infty}$) was ranged from 80 to 200. For the final stage of uptake In ECTFE with drastic acceleration, all the models exhibited significant deviations from the sorption data. New diffusion models based on thermodynamics and continuum mechanics should be employed to get valuable information on transport properties as well as relaxation kinetics coupled with non-Fickian diffusion.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.139.2-139.2
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• 2016

Electrons and phonons in chalcogenide-based materials play are important factors in the performance of an optical data storage media and thermoelectric devices. However, the fundamental kinetics of carriers in chalcogenide materials remains controversial, and active debate continues over the mechanism responsible for carrier relaxation. In this study, we investigated ultrafast carrier dynamics in an multilayered $\{Sb(3{\AA})/Te(9{\AA})\}n$ thin film during the transition from the amorphous to the crystalline phase using optical pump terahertz probe spectroscopy (OPTP), which permits the relationship between structural phase transition and optical property transitions to be examined. Using THz-TDS, we demonstrated that optical conductance and carrier concentration change as a function of annealing temperature with a contact-free optical technique. Moreover, we observed that the topological surface state (TSS) affects the degree of enhancement of carrier lifetime, which is closely related to the degree of spin-orbit coupling (SOC). The combination of an optical technique and a proposed carrier relaxation mechanism provides a powerful tool for monitoring TSS and SOC. Consequently, the response of the amorphous phase is dominated by an electron-phonon coupling effect, while that of the crystalline structure is controlled by a Dirac surface state and SOC effects. These results are important for understanding the fundamental physics of phase change materials and for optimizing and designing materials with better performance in optoelectronic devices.

• Polymer(Korea)
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• v.31 no.4
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• pp.335-342
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• 2007

The goal of this study is to investigate the effect of molecular structure modifications on the kinetics of physical aging of thin films formed from 6FDA-based polyimides with time. The permeability for 6FDA-based polyimide thin films containing carboxyl acid groups commonly decreased 20-50% after the isothermal aging and the selectivity gained anywhere from 10% to 30% while the rate of permeability loss on the change of polymer structure showed different reciprocal relationship between 6FDA-6FpDA based polyimides and 6FDA-DAM based polyimides. The Lorenz-Lorentz equation was used to relate changes in refractive index to densification and volume relaxation with aging time. The permeability as a function of aging time fits the expected form $P=Ae^{(-B/f)}$. The results matched well with the data for different polymer membranes.

• Journal of Plant Biology
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• v.36 no.2
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• pp.133-140
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• 1993

The photosynthetic activities in relation to oxygen evolution rates, quantum yield, CO2 uptake rates and room temperature chlorophyll fluorescence were investigated in cotyledons of cucumber seedlings exposed to low temperature (at 4$^{\circ}C$) for 24 h. Light-chilling caused more inhibition on light-saturated maximum oxygen evolution rates, quantum yield, and CO2 uptake rates than dark-chilling did in the cucumber plant. Light-chilling induced more marked increase in Fo and decrease in (Fv)m/Fm than dark-chilling did in the room temperature chlorophyll induction kinetics. The above results affected by chilling in the light are considered to be associated with the partial damage of the reaction center of PS II and the decreased photosynthetic activities. There occurred a large decrease in qQ with little change in qNP in the light-chilling plant. When light- and dark-chilled plants were recovered at room temperature for 24 h and their chlorophyll fluorescences were induced with light doubling technique, light-chilled plants showed more smaller magnitude and rate of fluorescence relaxation than dark-chilled plants. These suggest that light-chilling might cause some alterations in transthylakoid pH formation, and that photosynthetic apparatus of cucumber cotyledons is more susceptible to light-chilling. In the fast fluorescence induction kinetics, FR was decreased by 60% in the light-chilled plants with reference to $25^{\circ}C$ light-grown plants, while the dark-chilled plants showed a decreased rate of only 20% with reference to $25^{\circ}C$ dark-treated plants for 24 h, indicating that cucumber seedling is very sensitive to chilling stress. So, it is certain that chilling injury to the photosynthetic apparatus is strongly dependent on the presence of light in cucumber seedlings.

• Journal of the Korean Vacuum Society
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• v.21 no.4
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• pp.219-224
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• 2012

We study for long-term performance of amorphous silicon solar cells under light exposure. The performance is predicted with a kinetic model in which the carrier lifetimes are determined by the defect density. In particular, the kinetic model is described by the stretched-exponential relaxation of defects to reach equilibrium. In this report, we simulate the light-induced degradation of the amorphous silicon solar cells with the kinetic model and AMPS-1D computer program. And data measured for outdoor performances of various solar cells are compared with the simulated results. This study focuses on examining the light-induced degradation for the following amorphous silicon pin solar cells: thickness${\approx}$300 nm, built-in potential${\approx}$1.05 V, defect density (at t=0)${\approx}5{\times}10^{15}cm^{-3}$, short-circuit current density (at t=0)${\approx}15.8mA/cm^2$, fill factor (at t=0)${\approx}0.691$, open-circuit voltage (at t=0)${\approx}0.865V$, conversion efficiency (at t=0)${\approx}9.50%$.