A Power-Free Single-Stripe-Guided Nanoliter Mixer for Micro-channels

A power-free method is explored to perform mixing in a microchannel without any external active mechanisms such as pumps, valves, or external energies like electrostatic, or magnetic fields. The proposed mixing device is power-free in the sense that the surface tension is the only force that transports, merges, mixes, and stops the liquid. It is cost-effective that the channel has no sidewalls with the liquid being confined to flow between a bottom hydrophilic stripe and a top-covered hydrophobic substrate. Moreover, asymmetric staggered cavities (Stroock et al., Science, 2002, 295, 647) are optimally arranged on the bottom substrate of the channel to help mixing two different liquid species. It is most crucial to this power-free mixing device that two liquid species must be well mixed before the liquids are transported to exit the channel by the surface tension. Here it is found with a strong physical background that this can be achieved if the microchannel has the physical dimensions: 3~5 mum in height, 1.5-2 cm in length with a fixed width 100 mum, and the cavities have a depth comparable to the channel height