The pressure drop along rectangular microchannels containing bubbles.

This paper derives the difference in pressure between the beginning and the end of a rectangular microchannel through which a flowing liquid (water, with or without surfactant, and mixtures of water and glycerol) carries bubbles that contact all four walls of the channel. It uses an indirect method to derive the pressure in the channel. The pressure drop depends predominantly on the number of bubbles in the channel at both low and high concentrations of surfactant.

Coding/decoding and reversibility of droplet trains in microfluidic networks.

Droplets of one liquid suspended in a second, immiscible liquid move through a microfluidic device in which a channel splits into two branches that reconnect downstream. The droplets choose a path based on the number of droplets that occupy each branch. The interaction among droplets in the channels results in complex sequences of path selection.

Bifurcation of droplet flows within capillaries.

Flows of droplets through networks of microchannels differ significantly from the flow of simple fluids. Our report focuses on the paths of individual droplets through the simplest possible network: a channel that splits into two arms that subsequently recombine. This simple system exhibits complex patterns of flow: both periodic and irregular, depending on the frequency at which the drops are fed into the "loop.

Formation of droplets and bubbles in a microfluidic T-junction-scaling and mechanism of break-up.

This article describes the process of formation of droplets and bubbles in microfluidic T-junction geometries. At low capillary numbers break-up is not dominated by shear stresses: experimental results support the assertion that the dominant contribution to the dynamics of break-up arises from the pressure drop across the emerging droplet or bubble. This pressure drop results from the high resistance to flow of the continuous (carrier) fluid in the thin films that separate the droplet from the walls of the microchannel when the droplet fills almost the entire cross-section of the channel.

Mixing with bubbles: a practical technology for use with portable microfluidic devices.

This paper demonstrates a methodology for micromixing that is sufficiently simple that it can be used in portable microfluidic devices. It illustrates the use of the micromixer by incorporating it into an elementary, portable microfluidic system that includes sample introduction, sample filtration, and valving. This system has the following characteristics: (i) it is powered with a single hand-operated source of vacuum, (ii) it allows samples to be loaded easily by depositing them into prefabricated wells, (iii) the samples are filtered in situ to prevent clogging of the microchannels, (iv) the structure of the channels ensure mixing of the laminar streams by interaction with bubbles of gas introduced into the channels, (v) the device is prepared in a single-step soft-lithographic process, and (vi) the device can be prepared to be resistant to the adsorption of proteins, and can be used with or without surface-active agents.

Nonlinear dynamics of a flow-focusing bubble generator: an inverted dripping faucet.

We describe the rich dynamic behavior--including period-doubling and period-halving bifurcations, intermittency, and chaos--observed in the breakup of an inviscid fluid in a coflowing, viscous liquid, both confined in a microfabricated flow-focusing geometry. Experimental observations support inertia-dominated dynamics of the interface, and suggest the possible similarity to the dynamics of a topologically inverted counterpart of this system, that is, a dripping faucet.

Self-assembly of gears at a fluid/air interface.

This paper describes a dynamic system-a system that develops order only when dissipating energy-comprising millimeter to centimeter scale gears that self-assemble into a simple machine at a fluid/air interface. The gears are driven externally and indirectly by magnetic interactions; they are made of poly(dimethylsiloxane) (PDMS) or magnetically doped PDMS, and fabricated by soft lithography. Transfer of torque between gears can take place through three different mechanisms: mechanical interaction, hydrodynamic shear, and capillarity/overlap of menisci.