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Chun-Fei Kung

2009-02-20
12:30:00 - 13:30:00

Investigation of Transport and Mixing in Microchannel Driven by Capillary Pumping

308 , Mathematics Research Center Building (ori. New Math. Bldg.)

In the present study, a power-free method is explored to perform mixing in a microchannel without any external active mechanisms such as pumps, valves or external energies like electrostatic or magnetic fields. Often a relatively large support is needed for the desired power, thus limiting the capability of system miniaturization and integration. The surface tension is the only mechanism for driving the fluids through the microchannel. The channel of this mixer is designed to have no sidewalls with the liquid being confined to flow between a bottom hydrophilic stripe and a fully covered hydrophobic substrate. This device has also been applied to whole blood to analyze the characteristics of blood in a microchannel at different sloping angles. It is observed that increasing the sloping angle from (downward flow) to (upward flow) increases the blood flow rate monotonically. The trend of the velocity of blood flow under various sloping angles is totally opposite to that of the DI water. These peculiar behaviors on the micro scale are explained by a dynamic model that establishes the balance among the inertial, surface tension, gravitational, and frictional forces. The frictional force is further related to the effective hematocrit. The model is used to calculate the frictional force from experimental data, and thus the corresponding hematocrit, which is smaller when the blood flows upward. In order to enhance the driven efficiency of this design, a superhydrophobic surface was considered to replace the original Teflon surface. We can find out the optimal fabrication parameters of utilizing induced couple plasma method, which can successfully generate compact silicon grass on the bottom. This structure can sustain DI water on the grass top and keep the contact angle around. And the average velocity is 1.21 times that of the original design from experimental results. To make a thorough investigation, when fluid flowing in the hydrophilic channel, it may contact with Teflon surface on both sides, thus produce friction force. Nevertheless, as for the superhydrophobic surface, it can form stable air cushion to isolate fluid; therefore, it will effectively reduce the friction force from both sides, and improve the driven efficiency.