Micro-channel is made of PDMS (polydimethylsiloxane) using soft lithography. But native PDMS micro-channel could not generate electroosmotic flow because it has no charge on its surface. Therefore, surface treatments were needed. In this research, two methods - HCl treatment and PVA coating - were used to change surface charge of native PDMS. Both HCl-treated micro-channel and PVA-coated micro-channel can generate stable electroosmotic flow for 3 days. As pH of buffer solution increases, the magnitude of ζ-potential becomes larger. As pH of buffer solution decreases, hydrogen ion can block the surface of micro-channel and electroosmotic effects becomes decreased. When concentration of salt is small, electroosmotic flows also decrease.
PS (polystyrene) particles of different sizes have different mobilities because their surface charge is proportional to their sizes. Big particles can have more SDS on its surface. They feel more electrophoretic effects than small particles. In this research, ζ-potential of PS was measured. From that, we can predict electrophoretic velocity of PS and the results of electrophoretic separations. PS particles, which are different in their size, are separated in HCl-treated micro-channels. Their separation tendency is similar to calculated result. But separation efficiency is not good. This is mainly because reflow of buffer solution and unexpected bubble formation in micro-channels.
