(353g) Multilayer Microfluidic Flows of Suspensions

Many analytical operations at the microfluidic scale, such as cell sorting, involve flows containing particles. There are also many microfluidic applications that involve networks of converging and diverging channels. However, only a limited amount of work to date covers the fundamentals of particle behavior during flow in microchannels, especially those with complex geometries. A microfluidic system is attractive as a tool for fundamental studies of particulate flows for two main reasons, specifically, the ease of fabricating and testing multiple flow geometries and the accessibility of certain flow conditions that are difficult to achieve in macroscopic systems.

This experimental study quantified the spreading of parallel streams with viscosity contrast in multilayer microfluidic flows. Three streams converged into one where a test fluid was sheathed between two layers of a Newtonian reference fluid. The different test fluids were Newtonian fluids with a range of viscosities (from 1.1 to 48.2 cP) and suspensions of 10 micron diameter PMMA particles (volume fractions from 0.16 to 0.30). The reference and test fluids were dyed with different concentrations of a fluorescent dye. The intensity differences were visualized by fluorescence microscopy and image analysis was used to identify the position of the interface between the fluids. The flow cells were fabricated by standard lithography and replica molding techniques in poly(dimethylsiloxane). In general, the extent of spreading of the test fluid layer increased with the viscosity ratio of the test and reference fluids. Additional results from the microfluidic multilayer flow will be presented.