Formation of High-Viscosity Micro-Droplets in T-channels with Neck Structure Induced by Surface Acoustic Waves

In the fields of organ printing and drug preparation, high-precision and stable dispersion of high-viscosity biomaterials enable precise control of organ morphology and drug release rate. This paper proposes the use of an acoustic surface wave to overcome the problem of unstable interface breakup and weak size controllability when the traditional passive droplet microfluidics is applied to high-viscosity (higher than 0.4 Pa·s) dispersed phases. This paper studies the internal flow behavior of high-viscosity fluid under the influence of an acoustic field and realizes the accurate prediction of formation regime and droplet size. Experimental results show that with the increase in acoustic power, three unique droplet generation regimes (e.g., long jetting, transition, and dripping) exist. The transition regime is most suitable for high-throughput preparation of high-viscosity droplets, and its corresponding flow and acoustic conditions can be predicted by equation μd/μc = 4.8 × 10−8 (μc × vc/AP02 × w)−3.32. Affected by the regime transition, the droplet size increases with the increase in acoustic power. The droplet size prediction can be realized based on the capillary number Caf, which represents the intensity of the acoustic field.