BS in Materials Engineering
Materials Engineering Department
Trevor Harding, Richard Savage
The goal of this research is to compare electro-kinetic and pressure driven flow rates and velocity profiles (near wall vs. middle) in a microfluidic chip made of PDMS using particle imaging velocimetry (PIV) of an aqueous solution of fluorescent polystyrene (PS) particles using a laser confocal microscope (LCM). Microfluidic channels were fabricated out of PDMS using a SU-8 mold to be 25mm long and 180um by 1000um. Pressure-driven data did not show the expected parabolic profile because of the large width to depth ratio. In addition, data showed a calculated average significantly higher than the projected particle velocity through the channel. Unexpected results were hypothesized to be caused by inaccuracies with the syringe pump or interactions with the tubing. The accuracy of the syringe pump was tested and found to be 20% lower for 0.5uL of flow and 4% lower for 0.75uL of flow, making the data even stranger. However, at the low pump rates the syringe pump was pulsing instead of having a consistent flow. This could have led to the inconsistencies seen. Other issues occurred when measuring electro-kinetic flow. Often flow would switch directions at random intervals, possibly due to some kind of charge build up. In addition, bubbles, possibly introduced into the system when connecting tubing or when moving the channel, were very problematic. Changes in temperature, pressure, surface properties of the channel, and properties of the fluid within the channel can cause bubbles to grow. Research suggested a bubble trapping method for temporary relief of keeping bubbles out of the channel. This research will be continued as my master’s thesis next year.