Droplet charging

Since the current is proportional to the total droplet charge, this means that the addition of A+ to the solution leads only to a small increase in the droplet charge. However, in the charged droplets, the ions A+ compete with the ions B+ in the conversion process to gas-phase ions. A proportionality to concentrations of ions A+ and B+ in the droplets may be expected in this competition51 so that an increase of the concentration of A+ in the solution should lead to a decrease of production of gas-phase ions B+, i.e. to a decrease of /B. This is exactly what is observed in Figure 3. 

Significant charge loss also occurred when a nonradioactive microdroplet was injected in a C-contaminated balance. Figure 7 presents results obtained by Davis et al. for a droplet of dioctyl phthalate in a balance that had been contaminated by prior experiments. The voltage rapidly increased as the droplet charge was neutralized, and within two minutes the charge decreased from about 165,000 elementary charges to about 10,000. 

Fig. 7. Droplet charge and levitation voltage for radioactivity detection in a C-con-taminated electrodynamic balance, from Davis et al. (1988).

Field-proven methods for imparting charge qp to pesticide sprays are (a) ionlzed-field droplet charging of both conductive and... 

Figure 2. Conceptual representation of spray-droplet charging methods. (Reproduced with permission from Ref. 10. Copyright 1978, American Society of Agricultural Engineers.)...

Figure 3. Effect of spray-liquid dielectric constant upon charging-field concentration factor jj.+2(K-l)/(K+2Q associated with ionized-field droplet charging.

Table I summarizes the experimentally determined resistivity characteristics for the nine formulations investigated. On the basis of Equation 6 and these data, a high degree of spray charge-ability by the electrostatic induction process could be predicted for all the pesticide samples tested. For these particular pesticide formulations, laboratory spray tests confirmed excellent droplet charging to greater than 10 mC/kg. Similar electrical resistivity measurements will serve as a suitable predictor of the chargeability of other formulations of interest in the electrostatic pesticide-spraying process.

The droplets are produced with an commercial piezo-driven injector. Upon generation, they are charged weakly by influence of an electric field at the nozzle tip. This charge is needed for the electrodynamic levitation. By varying the charge to mass ratio between - -10 C/kg and —10 C/kg we were able to prove that in this range the nucleation rate is not influenced by the droplet charge. 

The electrospraying of biomaterials into cells is used in gene therapy and gene transfection. The biomaterial penetrates the cell by means of the intrinsic droplet charge that develops during electrospraying. ... 

In TSP, a solution of the sample and an auxiliary electrolyte (usually ammonium acetate) passes through a heated capillary to enter the pumped ion chamber (1-10 Torr). A supersonic beam of charged droplets emerges at the entrance of the chamber, which is heated to aid the desolvation of Ore droplets. TSP produces essentially equal numbers of positively and negatively charged droplets the droplet charge is determined by the electrolyte ion... 

Spraying capillaries for ESI (a) Nebulization and droplet charging by the electric field only, (b) Pneumatically assisted electrospray or ionspray and (c) Tri-coaxial probe with sheath flow. 

---