Direct observation and characterization of the generation of organic solvent droplets with and without triglyceride oil by electrospraying

The primary aim of this study was to investigate the generation characteristics of organic solvent droplets with and without triglyceride oil by electrospraying using single-nozzle and nozzle-array devices. The liquids used were ethanol (10–99.5%), ethanol (99.5%) solutions containing a triacylglyceride oil, ethyl acetate, hexane, and heptane. The droplet generation behaviors from an electrode nozzle were observed using high-speed video cameras. Unstable micro-dripping mode was observed when using ethanol (<50%), hexane, and heptane. In contrast, the stable electrospraying by cone-jet mode was achieved when using ethanol (>66.7%) and ethyl acetate. The jet diameter values mostly ranged between 10 and 20 μm, which is similar to the estimated ones. High-speed photographic observation at a frame rate of 106 s−1 demonstrated the generation of ethanol droplets at very high frequencies of 3.0 × 105–5.0 × 105 s−1 by breaking up the jet. The ethanol jet diameter increased with increasing the flow rate (1–10 mL/h). The nozzle number per device did not affect the jet diameter when the flow rate per nozzle is the same. The stable cone-jet mode was also achieved when using ethanol solution containing 0.1% triacylglyceride oil. Triacylglyceride oil droplets with diameters of about 2 μm were collected after evaporating ethanol from the droplets generated by electrospraying.