On the features of breaking a microjet of dilute polymer solution into main and satellite microdroplets under external vibration perturbation

An experimental study of the morphology of the laminar microjet flow of diluted aqueous solutions of sodium alginate without and with the addition of hydroxyethyl cellulose after a nozzle subject to external vibration stimulation by the action of the reverse piezoelectric effect was carried out. We studied the influence of the polymer concentration in the solution (0.5-5 mg/ml), the flow rate of the liquid (4-26 ml/min), and the frequency of the current of external perturbation (0-1.2 kHz) on the capillary crushing of the microjet with a diameter of about 210 um in the range of Ohnesorge numbers from 0.046 to 1.88 and Reynolds numbers 0.7 to 470. The modes of microjet flow and crushing on microdroplets with indication of boundaries of transitions between them are selected, and a general map of modes is built. Taking into account the polymer concentration in the solution, the dependence of the microjet fracture length on its velocity is shown. The conditions of monodisperse microjet destruction with equidistant arrangement of the main microdroplets in the flow are determined, which are related to an optimal balance between the molecular mass of the polymer in the solution, the intensity of external disturbance and the time of stress relaxation in polymer viscoelastic microjets. The role of formation of structures such as “beads-on-filament” in capillary destruction of microjet with identification of cases of absence of occurrence of “satellite” microdroplets from liquid threads between the main microdroplets has been studied. The results are applied to technologies based on in-air microfluidics (bioengineering and additive technologies), dealing with heterogeneous fluids with viscoelastic properties.