“Counter-Intuitive Flows of Bubbles and Droplets in
Microfluidic Channel Networks”
Dr. Wonjae Choi, Harvard University
Networks – which can be represented abstractly by sets of nodes, joined by edges – are ubiquitous. It is thus important to understand the mechanisms by which autonomous components (e.g., blood cells in capillary beds) navigate natural networks and to use this understanding to develop strategies for the design of synthetic networks. This talk will discuss our recent study on the flows of bubbles in microfluidic networks, a system that we developed to model blood streams in capillary vessels. Single-phase continuum fluids, when infused into fluidic networks, allocate continuously among all possible paths connecting the inlet and outlet based on the global structure of the network. In contrast, each of the bubbles used in this work is discrete and traverses networks by making a sequence of binary choices based only on the local pressure gradients at branching intersections. Such local interactions often lead the bubble to display counter-intuitive flow patterns; for example, the path a bubble takes in a given network is not necessarily the quickest or least resistive route from the entrance of the network to the exit. The systems described here illustrate how difficult it is to navigate throughout a complex network when the choices among the paths are based only on local information about individual junctions. This work, however, also illustrates that an ensemble of discrete components can overcome such challenges by mutually interacting with one another and sharing the local information probed by each of them. A brief summary of the potential projects based on the observed phenomena will also be discussed.
Wonjae Choi holds a PhD in mechanical engineering from MIT. His doctoral research topic was the omniphobicity, i.e., repellency against all liquids, of textured solid surfaces. He is now a research fellow in the Department of Chemistry and Chemical Biology at Harvard, where he is working on the behavior of two-phase complex fluids (one fluid dispersed in the other) in confined geometries.