Fine droplet generation using tunable electrohydrodynamic pulsation

High-efficiency generation of fine droplets is significant for many microfluidic chips and sensor applications. To produce fine droplets, nozzles with small diameters are needed, which results in a high cost for nozzles and low efficiency of droplet generation. In this paper, a tunable electrohydrodynamic pulsation method which can generate fine droplets with high frequency and controllable size is presented using low conductivity liquids. The effects of flow rates and voltage parameters with respect to deposition frequency and droplet size are investigated. The influence of these parameters on Taylor cone formation time are also discussed and simple scaling laws are proposed to reveal and guide the droplet generation process. Experimental results show that single cycle deposition frequency decreases with increasing voltage frequency, but is only slightly influenced by the flow rates. The droplet size also decreases with voltage frequency, while large flow rates can make this decline gradual allowing better control. Moreover, the Taylor cone formation time may greatly affect the stability of the deposition frequency when the voltage frequency is larger than 30 Hz. Due to the short cycle time of high voltage frequencies, the hydrodynamic behavior in the emission process may be considerably affected by the increase of volume, which is also related to the flow rates. Tunable micropatterns consisting of fine droplets can be achieved by using this method in combination with motion stages.