| Miniaturization of (bio)analytical processes has become a significant research area in the past decade. Factors driving the development of microanalytical devices include the need for a reduction in samples and reagents consumption, cost and waste production, and analysis time. The development of integrated microfluidic technology (lab-on-a-chip) requires local control of fluid flow. Conventional approaches involve moving parts and complex fabrication techniques, which makes them unreliable and prevents their integration in large microanalytical systems.; This research presents a reliable and inexpensive way to electrically regulate the fluid flow through the microchannels via a structure that is simple to fabricate and eliminates the need for moving parts. An electrical signal is used to deposit silver on a thin solid electrolyte layer in a small region of a microchannel (valve area). By reversing the polarity of the voltage applied, the electrodeposits dissolve returning the valve area to its original condition.; The electrodeposited silver, which has a high fractal dimension and can have features as high as 0.6 mum, changes the fluid-surface interaction. It is shown that the electrodeposition increases the contact angle of water, methanol, and 40 weight% methanol in water, by 20°, 27°, and 19°, respectively. The increase in contact angle is representative of a decrease in surface energy or an increase in surface hydrophobicity. Since fluid flow in a microchannel is dominated by the nature of the channel surface, this increase in effective hydrophobicity can be used to control the movement of the fluid.; The electrodeposited silver can act as a control element by adding roughness and heterogeneity to the surface. The surface roughness and heterogeneity are able to control the fluid flow through the microchannels by pinning the liquid at the surface defects and by trapping air under the liquid at the surface roughness.; The characteristics of the fluid control system are shown by comparing the flow rate of water through a channel with an open valve versus a channel with an inhibited valve, where a micropump is used for fluid actuation.{09}It is shown that it takes the water only 6 seconds to pass through an open valve area versus 1 minute and 4 seconds to pass through an inhibited valve area. Moreover, the flow rate of 40 weight% methanol in water through a channel with an open valve is compared to the rate through a channel with a closed valve. In this case, where only capillary pressure is used for fluid propagation through the microchannels, it can be seen that the electrodeposited silver is able to completely stop the flow. |
