These data validate our proposed working mechanism, that being, in our system the density of the PDMS and speed of sound leads to the refraction of MHz-generated SAWs into the PDMS layer, thereby developing heat. The diminished displacement coupled to loss of acoustic energy as heat in the MHz frequency domain prevents SAWs from destabilizing the surfactant shell of water-in-oil droplets as they pass the injection nozzle and therefore no acoustoinjection occurs. On the other hand, the acoustic pressure wave triggered when operating our device in the kHz frequency domain actuates acoustoinjection. This acoustic pressure field maintains most of the acoustic energy, enables transmission of acoustic energy into the droplets, and thereby causes the surfactant layer at the water-oil interface of the passing