Acoustic-counterflow microfluidics by surface acoustic waves

In this letter, we demonstrate an unexpected surface-acoustic-wave (SAW)-driven pumping effect in hydrophobic polydimethilsiloxane (PDMS)-lithium niobate (LiNbO3) microchannels. Atomization within the fluidic channel followed by SAW-assisted coalescence leads to liquid counterflow with respect to the SAW propagation direction. This physical mechanism is contrasted with the acoustic-streaming process driving isolated drop displacement on piezoelectric substrates. This principle is shown not to be readily applicable to the present microchannel case. The proposed device geometry can be exploited to integrate micropumps into complex microfluidic chips, improving the portability of micro-total-analysis systems.