Facilitating droplets detachment in microchannels via surface acoustic wave

Surface acoustic waves (SAW) emerge as an attractive approach for droplet detachment due to unique acoustic radiation force and acoustic streaming effects. The effect of SAW on droplet detachment primarily focused on open platform, where acoustic streaming serves as the principal driving force. However, when droplet is adhered within microchannels, the acoustic radiation force would be the primary actuation for the oil–water interface, also significantly enhanced by flow shear forces, leading to more complex detachment behaviors. To reveal the mechanisms of droplet detachment under these circumstances, we integrated SAW at the microchannel to investigate the detachment dynamics of sessile droplet. Our results indicated that: (1) with increasing capillary number under SAW actuation, droplets exhibit four distinct dynamic states: pinning, sliding, detachment, and pinch-off; (2) SAW induces pinning, and facilitates the earlier onset of detachment, with the effect intensifying at higher acoustic Weber numbers; and (3) SAW suppresses pinch-off, promoting a transition from pinch-off to detachment. This study advances the understanding of droplet detachment dynamics and provides new insights for addressing droplet adhesion challenges in microfluidic systems.