Investigation on charge deterioration of electrically charged filter media using electric force microscopy

by 1973- Kim, Jooyoun

KIM, JOOYOUN. Investigation on charge deterioration of electrically charged filter media using Electric Force Microscopy. (Under the direction of Dr. Roger L. Barker and Dr. Juan Hinestroza) Electret filter media is widely used in filtration application as the presence of embedded electrostatic charges allows for better particle capture efficiency with lower pressure drop. The effect of exposure to organic solvents on filtration performance of electret filter media was investigated using several different organic solvents and electret filter media. The exposure of electret filter media to liquid organic solvents caused a decrease in filtration performance without significant changes in resistance. It is hypothesized that the lowered performance of the electret filter media is due to the changes in electric field caused by the liquid organic solvents or to morphological changes. Scanning Electron Microscopy (SEM) was used to examine any observable morphological changes in the fibers after exposure to liquid organic solvents. There were no observable changes in morphology of fibers, suggesting the performance deterioration by chemical exposure was not caused by morphological changes in fibers. Electric Force Microscopy (EFM) was used to analyze the electric field of electret filter media prior to and after exposure to organic liquid solvents. Changes in the electric field were detected and quantified. Electric field gradient imaging (EFGI) by phase and frequency detection was shown to be a feasible method for the analysis of charge deterioration in electret filtration media. Two mathematical models based on electrostatics fundamentals were used to explain the behavior of EFM experimental data. Model I accounted for both a coulombic force and induced polarization phenomena. Model II incorporates a capacitance term. Both models exhibited good quantitative agreement with the experimental data hence the performance deterioration of the electret filter media after chemical immersion was proven to be directly related to changes in the electric field of the sample.