• Bulletin of the Korean Chemical Society
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• v.21 no.6
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• pp.577-582
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• 2000

Interdiffusion process at interfaces of chemically identical polymers (e.g., deuterated-nondeuterated pairs) with different molecular weights or polymers with similar physical properties, is studied here by varying the diffusion time. Considering the vacancy flux ($J_v$) and adopting the Cahn-Hilliard interracial energy in describing this system, we can see that the variation of the interfacial composition profile with time is asymetric and the interface moves towards the polymer with the lower molecular weight as interdiffusion progresses. Furthermore, interface shift $\Delta\chi$, which characterizes the interdiffusion between polymers, agrees well with the behaviors of the existing experimental data. We can also obtain the interface shift factor C, which can be converted into values of $D_s$ (self-diffusion coefficient of the smaller molecules), from the slopes of the linear fits to the data of the interface shift.

• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.613-620
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• 1992

The solvent-dependent photophysical properties of 2-biphenylcarboxylic acid (2BPCA) and 4-biphenylcarboxylic acid(4BPCA), which have a pre-twisted conformation in the ground state, have been investigated. The fluorescence spectra of 4BPCA show vibrational structure with a non-mirror image to the absorption spectra in nonpolar solvent while those of 2BPCA show no structure even in nonpolar solvents. As the solvent polarity increases, the fluorescence spectra become diffuse and broad with a strong red shift resulting in the large Stokes shift. The large fluorescence Stokes shift of BPCA's in polar solvent is also partially due to an intramolecular charge transfer (ICT) interaction in the excited state, as demonstrated by the large dipole moment in the excited state (7.6-10.6 D). The fluorescence decay behaviors of BPCA's (decay-times and their pre-exponential factors) also depend on solvent polarity in agreement with the solvent-dependent properties of the steady-state fluorecence. The data have been discussed in terms of change in the excited-state potential energy surface with respect to change of the dihedral angle of biphenyl moiety.

• Bulletin of the Korean Chemical Society
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• v.11 no.3
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• pp.241-244
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• 1990

The photochemistry of 1-Methyl-2-cyclohexenyl aryl ketones (phenyl ketone 7a, p-toluyl ketone 7b, biphenyl ketone 7c and -naphthyl ketone 7d) is reported. The aryl ketone 7a, 7b and 7c undergo photo-racemization with efficiencies of 0.75, 0.79 and 0.76 respectively on direct irradiation. Direct irradiation of the ketone 7d, however, undergoes 1,3-shift with an efficiency of 0.02. Triplet states are responsible for the racemizations and singlet state is responsible for 1,3-shift as in general. The ketone 7a, 7b and 7c are good example of a few ${\beta},{\gamma}$-unsaturated ketones which undergo efficient intersystem crossing on direct irradiation.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1767-1772
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• 2008

A microcantilever is a well-known MEMS structure for sensing bio-chemical molecules. When bio-chemical molecules are adsorbed on the microcantilever's surface, resonance frequency shift is generated. There are two issues in this phenomena. The first one is which one between mass change and surface stress change effects is more dominant on the resonance frequency shift. The second one is what will be the performance change when the boundary condition is changed from cantilevers to double clamped beams. We have studied the effect of surface stress change and compared it with that of mass change by using FEM analysis. Furthermore, for microstructures having different boundary conditions, we have studied Q-factor, which determines the detection limit of micro/nano mechanical sensors.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3265-3268
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• 2013

The multi-hydrogen bonded systems with the solvated electrons are investigated at the B3LYP/6-311++$G^{**}$ basis set level. The symmetrical linear geometrical characteristic is common for the dimer systems, while for the tetramer system, the tetrahedron configuration is generated. The NBO charge analyses demonstrate that the multi-hydrogen-multi-electron (mH-ne) coupling exist in these anion systems, as is supported by the electrostatic potential and the molecular orbital analyses. The positive chemical shift value of the central hydrogen ($H_c$) and the negative chemical shift value of the terminal hydrogen ($H_t$) indicate that the $H_c$ is electronegative while the $H_t$ is electropositive, respectively. Strong coupling between two central hydrogen atoms is demonstrated by the large spin-spin coupling constants. The solvated electron donates significant contributions for the stability of these systems.

• Journal of the Korean Chemical Society
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• v.6 no.1
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• pp.54-60
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• 1962

The water gas shift conversion catalyst prepared by the American Cyanamide Co. was subjected to fluidization in a 2-in. Pyrex glass tube to obtain the basic fluidization characteristic data. The size of the catalyst charged ranged from 70 to 120 meshes and it was supported on a single layer 300-mesh wire gauze through which the fluidizing medium, the air, was passed. Following are some data and facts found by the authors: (1) The catalyst particles were porous, and their surfaces were trough and irregular. (2) The average effective particle density and the average shape factor of these particles were 152.2 lb/$ft^3$ and 0.865 respectively. (3) As the particle diameter of the catalyst increased, the minimum fluid voidage of the bed decreased slightly. (4) Just before the incipient fluidization, pressure drop suddenly fell and the bed expanded simultaneously. (5) After fluidization set in, the expansion characteristics of the catalyst bed were similar to those of sand and glass beads except intense bubbling in the catalyst bed.

• Bulletin of the Korean Chemical Society
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• v.30 no.7
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• pp.1559-1562
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• 2009

The influence of hot pressing on the pore structures of Nafion membranes was investigated by observing the Nafion before and after hot pressing with $^1H$ nuclear magnetic resonance (NMR) spectroscopy. The freezing point depression and chemical shift data of water in the Nafion indicated the presence of two different pore size ranges in Nafion. Hot pressing mainly reduced the sizes and number of the big pores. The reduction of water uptake and proton conductivity after hot pressing was explained by this variation of pore size and number. We demonstrated the potential application of chemical shift data and NMR cryoporometry experiments to measure the relative pore sizes, on a nano scale, and numbers.

• Bulletin of the Korean Chemical Society
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• v.7 no.4
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• pp.299-304
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• 1986

Master formulas for overlap integrals and the dipole moments involving |4p > atomic orbitals have been derived by the expansion method for spherical harmonics. The radial integrals for the hyperfine interaction have also been derived for |4p > atomic orbitals. The calculated values of the overlap integrals and dipole moment matrix elements by the expansion method for spherical harmonics for a hypothetical NO molecule are exactly in agreement with those of Mulliken's method. The radial integrals for the hyperfine interaction may be used to calculate the chemical shift for |4p > atomic orbitals.

• Journal of the Korean Chemical Society
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• v.41 no.5
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• pp.271-276
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• 1997

• Bulletin of the Korean Chemical Society
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• v.23 no.11
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• pp.1507-1508
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• 2002