Observing pH changes in electroosmotic flow

• Main Author: Adin Sucipto
• Other Authors: Lam Yee Cheong
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/64030
• Institution: Nanyang Technological University

There are many research papers stating that pH change occurs in the reservoirs during electroosmotic flow (EOF). However, no studies have been conducted to determine the characteristics of pH change in microchannel specifically at the electrical double layer (EDL). pH change is not ideal because it causes the zeta potential and EOF velocity to fluctuate. Therefore, the aim of this project is to investigate and understand the characteristics, and conditions for the variation of pH to occur during EOF at the EDL. Potassium chloride (KCl) was mixed with disodium fluorescein to serve as pH indicator for the experiments. Total internal reflection fluorescence microscopy (TIRFM) was employed to detect changes in fluorescent dye intensity at the channel wall (fixed position near the inlet of microchannel) during EOF. Investigations of the effects of different parameters such as the position of electrodes, volume of electrolyte solution in reservoirs and voltage applied, on the time taken for the dye intensity to decrease drastically (indicating pH drop) were carried out. The experimental data show a general trend whereby the fluorescent dye intensity increases sharply (intensity peak formation) after long period of EOF, and followed by an immediate drop in intensity. The abrupt drop in dye intensity after the peak observation is believed to be caused by the state change of fluorescein, due to pH change of the electrolyte solution, as a result of electrolysis at the electrodes in the reservoirs. The time taken for the drastic drop in pH can be controlled by adjusting different experimental parameters. The optimal conditions that can effectively delay the time for the pH to change drastically during EOF are: placing the electrode far away from the inlet and outlet, filling the reservoirs with sufficient amount of solution and supplying moderate voltage.