Stopping Microfluidic Flow.

A cross-comparison of three stop-flow configurations-such as low-pressure (LSF), high-pressure open-circuit (OC-HSF), and high-pressure short-circuit (SC-HSF) stop-flow-is presented to rapidly bring a high velocity flow O(m s -1 ) within a microchannel to a standstill O(µm s -1 ). The performance of three stop-flow configurations is assessed by measuring residual flow velocities within microchannels having three orders of magnitude different flow resistances. The LSF configuration outperforms the OC-HSF and SC-HSF configurations within a high flow resistance microchannel and results in a residual velocity of <10 µm s -1 . The OC-HSF configuration results in a residual velocity of <150 µm s -1 within a low flow resistance microchannel. The SC-HSF configuration results in a residual velocity of <200 µm s -1 across the three orders-of-magnitude different flow resistance microchannels, and <100 µm s -1 for the low flow resistance channel. It is hypothesized that residual velocity results from compliance in fluidic circuits, which is further investigated by varying the elasticity of microchannel walls and connecting tubing. A numerical model is developed to estimate the expanded volumes of the compliant microchannel and connecting tubings under a pressure gradient and to calculate the distance traveled by the sample fluid. A comparison of the numerically and experimentally obtained traveling distances confirms the hypothesis that the residual velocities are an outcome of the compliance in the fluidic circuit.