Nozzle size effects on the nanoelectrospraying of Au nanocolloid in a fully voltage-controlled form

Nozzle size effects on the nanoelectrospraying of Au nanocolloid were investigated in a pure voltage controlled form. The nanoelectrospraying system was set up in a nozzle-to-plate geometry and the spray current was monitored to evaluate the performance of the nozzles during the atomization of Au colloid. Current–voltage characteristic shows that nanoelectrospray properties strongly depend on the nozzle size. In the spraying of Au nanocolloid using nozzles sized from 4 to 30 μm in diameter, two well-distinguished regimes of pulsation and cone-jet were observed with an increasing of voltage. The onset voltages for entering both modes were found to increase with the nozzle size. In the pulsation mode, pulsating frequency ranged from several tens kHz up to hundred kHz was witnessed and current with low oscillation amplitude was detected in the case of small nozzles, indicating the rate of ejected charges decreases with a fine nozzle. Meanwhile, the DC equivalent resistance derived from the best-fit model was determined to be in the range of 0.89–3.16 GΩ. In cone-jet region the equivalent resistance, representing an electrical equivalence of the spray gap, was measured to be between 0.49 and 1.41 GΩ. The relatively low resistance at high field implies better efficiency of spray in cone-jet mode compared with in pulsating mode. In both modes the equivalent resistances fall with increasing nozzle size, reflecting large nozzles easier process high volume ejections.