Electrospraying of liquid in the cone-jet mode has recently generated a great deal of interest in several technological applications. The purpose of the paper is to evaluate the electrospray characteristics of multi-nozzle system. The stable cone-jet voltage range, droplet size, droplet velocity, spray angle and spray current are selected as the main characteristics of electrospray. In addition, performance of coating with 200nm PSL (ethanol solution) using electrospray is evaluated by counting number of particles.
At the standard condition, the cone-jet mode is generated by supplying ethanol at a various liquid flow rate $(5~40μl/min)$ through the syringe pump and applying a high positive voltage to a stainless-steel capillary’s tip (0.5 mm i.d., 0.9 mm o.d.). The range of the stable cone-jet mode is measured. If applied voltage is 2.5kV, the stable cone-jet mode is made at all of the range. The spray current is measured by nano electrometer. In the stable cone-jet mode and fixed flow rate, the spray current is nearly constant except 0kV of $2^{nd}$ applied voltage. But the spray current increases as the flow rate increases.
The spray at the cone-jet mode is visualized using a CCD camera, a telephoto lens and argon ion laser. The spray angle including satellites is determined by the image processing. When the input voltage of guard plate is 1, 2, 3, 4, 5kV, the spray angle is about 50˚, 27˚, 20˚, 17˚, 13˚ at height 25mm. In addition, the spray angle isn’t affected by the flow rate, but the spray angle becomes smaller with the guard plate.
The size distributions of electrospray droplets from the Taylor cone in cone-jet mode are measured by a laser diffraction system. At fixed flow rate (Q), the droplets produced by electrospray have fairly monodisperse size distribution. As the flow rate increases, the droplet size increases. When the flow rates are 10, 20, 30, 40μl/min, the droplet size (SMD) is about 7.5, 12.0, 15.0. 17.0 μl/min. When $2^{nd}$ applied voltage is changed, the droplet size is similar. In electrospray of multi-nozzle, the droplet size is equal to that of single-nozzle. Therefore, the effect of the guard plate and multi-nozzle on the droplet size can be ignored. The droplet velocity of electrospray is measured by LDV (Laser Doppler Velocimetry). The droplet velocity increases as $2^{nd}$ applied voltage increases. The droplet velocity is in the range of 1.5 ~ 11m/s by $2^{nd}$ applied voltage.
Using electrospray, nanoparticles of PSL is coated at slide glass. Coating quality is investigated by counting number of particle. Nanoparticle is observed to be homogenous with a particle size of 200nm. The electrospray of multi-nozzle can be possible to coat nonoparticles on the wide range.
