Kyung-Hee Lim

Effect of temperature on critical micelle concentration and thermodynamic potentials of micellization of anionic ammonium dodecyl sulfate and cationic octadecyl trimethyl ammonium chloride

Abstract The critical micelle concentrations (CMCs) of anionic ammonium dodecyl sulfate (ADS) and cationic octadecyltrimethylammonium chloride (OTAC) were determined at various temperatures using a du Nouy ring tensiometer. The CMC decreased to a certain minimum and then increased with the temperature, displaying a U-shaped behavior. This behavior was analyzed using a power-law equation on the basis of reduced variables. The exponents of the power-law equation were found to be 1.05 for ADS and 1.12 for OTAC. These values were different from previous literature values of 1.74 for ionics, 3.54 for commercial ionics, and 5.80 for commercial amphoterics. Also, the U-shaped behavior is explained in terms of hydrophobic forces, as described by the thermodynamic potentials and parameters in the pseudo-phase separation model.

Morphologies of three-phase emulsions of the ternary nonionic amphiphile/oil/water systems and their determination by electrical method

Equations have been developed for the electrical and thermal conductivities of dispersions of two different phases of low conductivity in a third, conductive phase. These equations predict the conductivity of the dispersion from the volume fractions and conductivities of the constituent phases. Electrical conductivity measurements on dispersions of three liquid phases, i.e., three-phase emulsions, were made over a wide range of volume fractions of each dispersed phase and used to test the equations. The equations predict accurately dispersion conductivities from the measured volume fractions and conductivities of the constituent phases without any adjustable parameters. The predicted values are in excellent agreement with the measured conductivities of three-phase emulsions in the nonionic amphiphile/oil/water systems. This leads to the determination of three-phase emulsion morphologies. When the ratio Kd of the emulsion-drop conductivity to the continuous phase conductivity is O(10(-1)) <Kd <1, the electrical method yields the correct morphology. When Kd << 1, the equations predicted several morphologies, but the correct morphology can be chosen when the data are supplemented by another method such as microscopy. The electrical method, which is a combination of conductivity measurements and their fits to the equations, has been proven to be effective and reliable in determination of three-phase dispersion morphologies.

Effect of pre-cleaning treatment and contact wetting angle in the interface between P-doped Si surfaces and selective solar cell electrodes

Prior to electroless plating of the solar cell electrode, the sample was cleaned with a mixture of a sulfuric acid and peroxide solution and a H2NCH2CH2CH2Si(OC2H5) solution. We measured the de-wetting and contact angles of the solar cell thin film electrode. After SPM and APTES treatments, an excellent hydrophilic contact angle was observed. Our results show that it is more effective to remove oxidizer with SiO2 than HF mixed solutions. When comparing the efficiency, pre-treatment with a NH4F:HF mixed solution was more efficient than pre-treatment with a diluted HF solution. After NH4F:HF mixed solution cleaning, when the electrode was formed, the contact resistance that most directly affected the cleaning effect was 0.8194 ohm/sq, which had three times more improvement effect. It is expected that if an optimum cleaning time and process conditions for each cleaning chemical is developed, more improved contact resistance will be secured when each cleaning chemical is applied.