Charge and Size Distributions of Electrospray Drops

• Published in: Journal of colloid and interface science Vol. 186; no. 2; pp. 280 - 293
• Main Authors: de Juan, L., de la Mora, J.Fernández
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 15.02.1997; Elsevier
• Subjects: Aerosols; charged drops; Chemistry; Colloidal state and disperse state; cone-jet; Exact sciences and technology; General and physical chemistry; liquid cone; Rayleigh limit; liquid cone; cone-jet; charged drops; Rayleigh limit; Particle size; Liquid particle; Charged particle; Aerosols; Experimental study; Electrospray; Drop
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1006/jcis.1996.4654

The distributions of chargeqand diameterdof drops emitted from electrified liquid cones in the cone-jet mode are investigated with two aerosol instruments. A differential mobility analyzer (DMA, Vienna type) first samples the spray drops, selects those with electrical mobilities within a narrow band, and either measures the associated current or passes them to a second instrument. The drops may also be individually counted optically and sized by sampling them into an aerodynamic size spectrometer (API's Aerosizer). For a given cone-jet, the distribution of chargeqfor the main electrospray drops is some 2.5 times broader than their distribution of diametersd, withqmax/qmin∼ 4. But mobility-selected drops have relative standard deviations of only 5% for bothdandq, showing that the support of the (q,d) distribution is a narrow band centered around a curveq(d). The approximate one-dimensionality of this support region is explained through the mechanism of jet breakup, which is a random process with only one degree of freedom: the wavelength of axial modulation of the jet. The observed near constancy of the charge over volume ratio (q ∼ d3) shows that the charge is frozen in the liquid surface at the time scale of the breakup process. The charge over volume ratio of the primary drops varies between 98 and 55% of the ratio of spray currentIover liquid flow rateQ, and decreases at increasingQ.I/Qis therefore an unreliable measure of the charge density of these drops.