CO₂ Microbubbles in Silicone Oil (Part I: Study of the Frequency of Formation)

The objective of this work is the study of gas microbubble dissolution in a carrier liquid. To achieve this, we will analyze, using microfluidic techniques, the formation and evolution of carbon dioxide (CO₂) gas microbubbles in silicone oil, monitoring the size, position, and distance between the formed bubbles as they advance through a microchannel. This work consists of two parts (Part I and Part II): in Part I, we analyze the mechanisms determining the variation in the spatial frequency of bubbles as they move through the microchannel, while Part II examines the evolution of their size and demonstrates the utility of the device for obtaining diffusion coefficients and Henry's constant for the gases used. The microchip containing the microchannels has a serpentine shape, allowing extensive bubble trajectories to be captured in a single image. Regarding the study of bubble spatial frequency (Part I), it was found to exhibit three regimes during its displacement through the microchannel. Initially, the frequency increases because the bubbles block the microchannel, preventing liquid transfer through the residual film formed between the channel wall and the gas. Then, there is a transition stage during which the liquid manages to penetrate the residual film due to a local increase in pressure gradient. The pressure gradient overcomes the reduction in film thickness due to the decrease in carrier phase flow rate, which is affected by gas dissolution in the liquid. Therefore, the frequency begins to stabilize until the bubbles lose contact with the microchannel wall and assume a spherical shape, being transported at the carrier liquid velocity. These studies contribute to the understanding of transport phenomena and interfaces in CO₂ foams in oils, which are of great interest in industries such as oil recovery and refrigerants.