The Effect of Surface Treatment on Rising Air Bubbles in a Hele-Shaw Cell
John Vigorita 
Faculty Advisor: M. Wu

     My summer research focused on the two-dimensional fluid dynamics problem of a single air bubble traveling through a viscous fluid between two parallel plates, separated by a uniform spacing, namely a Hele-Shaw cell.
     Several factors affect the behavior of the rising bubble: the gap size, the fluid, the angle of elevation, and the surface properties of the plates. Recent development in microfluidic devices ask questions regarding how micro and nano-sized bubbles travel through a Hele-Shaw cell. Thus, we extend our work from previous summers to smaller sized bubbles. One of the challenging questions is how the surface properties of the plates affect the traveling bubbles. 
     A new apparatus was designed and created to deal with the smaller sized bubbles. In order to define the surface properties of the plates, we first found the contact angle that clean water droplets made on different plates. We then measured the velocities of varying sized bubbles at varying angles of elevation. Graphs of velocity versus the sin of the angle were used for analysis.
     We confirmed that air bubble velocities increase as the angle of elevation increases. We found the lower the viscosity of a fluid, the higher the velocity of the air bubble. Finally, when using a more hydrophobic surface compared to glass, such as plexi-glass, air bubble velocities decrease considerably in clean water – to the point of not rising.

Support provided by: The National Science Foundation