(371i) Characterization of Bubble Breakup in a Rectangular Microchannel

The production and manipulation of calibrant bubbles is crucial to the operation of some types of self-calibrating biosensors. Interactions between the bubble, liquid, and channel surface plays a critical role in the behavior of the bubbles during manipulation. Channel roughness is directly related to the frictional resistance imparted on the bubbles by the channel surface. This affects the mobility and can lead to undesired bubble breakup. In addition, the degree of hydrophobicity of the channel surface impacts the meniscus shape and movement of the bubble through the channel, which can also contribute to bubble breakup.

In the present study, we characterized the surface roughness of several rectangular PDMS microchannels to determine the relationship between channel roughness and bubble breakup patterns. Profilometry was used to measure the roughness of the bottom surface of the channel, and Scanning Electron Microscopy (SEM) was used to view the side walls and the sharpness of the corners, as they contribute to the overall roughness. Subsequently, the pressure drop across the channel was experimentally measured over a range of fluid velocities and compared to the theoretical pressure drop across the channel. These results have been used to map various bubble breakup patterns and predict the fluid velocities and surface roughnesses that lead to bubble breakup.