We report on the infrared emission of aqueous bridges under the application of high dc voltage (‘floating water bridge’) over the range between 400 and 2500 cm−1 (4.0–10.3 µm). Comparison with bulk water of the same temperature reveals an additional broad peak at ∼2200 cm−1 as well as water vapour emission lines. Two complementary explanations are presented for the broad peak: first, a cooperative proton transfer comprising an orientational motion along the direction of conduction is suggested. Second, the electrolysis-less current flow is explained by a proton/defect-proton band mechanism, which is in line with the cooperative proton transfer. The water vapour emissions occur due to collision ionization of space charges with micro- and nano-droplets which are electrosprayed from the liquid/gas interface.

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Experiments were conducted in order to study and characterize electrohydrodynamic atomization in the simple-jet mode for inviscid liquids. The operational window of this mode regarding the electric potential and liquid flow rate is presented. From the data it could be concluded that this mode can be divided by the characteristics of its breakup mechanism and that these characteristics are a function of the liquid Weber number and the electric Bond number for a given setup. Additionally we were also able to calculate the average charge per droplet and define the average size of primary and satellite droplets. The dispersion of the spray was also studied regarding its relation to the liquid Weber number and to the electric Bond number. We conclude that simple-jet mode electrosprays are a good option for applications which require monodisperse micrometer droplets with high throughput.

Experiments were conducted in order to investigate the influences of flow rate, applied voltage, and electric conductivity on droplet size and size distribution of water electrosprays in the simple-jet mode. The results show that the electric potential decreases significantly the relative standard deviation (RSD) of the spray size distribution, with the best result obtained for Weber number, We ¼ 3.3 (240 ml/h) when the RSD decreases from 0.50 at 0 kV to 0.18 at 5 kV. We conclude that simple-jet mode electrosprays are a good option for applications which require monodisperse micrometer droplets with high throughput. V C 2012 American Institute of Physics.[http://dx.doi.org/10.1063/1.4729021]The generation of monodisperse sprays is crucial for many industrial and medical applications. [1][2][3][4][5][6][7] Among others, such sprays can be used to control droplet deposition in inkjet printing, 8 to improve lung targeting in drug inhalation technology 9,10 and they are known to enhance the evaporation rate in combustion systems. 11 Commonly, the droplets generated in these processes are formed from the breakup of a liquid ligament. The process is named after the mechanism used to create the filament, e.g., pressure gradients (pressure atomizers), gas streams (air assisted atomizers), centrifugal forces (rotary atomizers), and electrostatic forces (electrohydrodynamic atomizers). 1,12,13 Empirical and theoretical investigations have been done to understand the mechanism responsible for the formation of such sprays. Among them, the most famous one is the study done by Rayleigh 14 who found that noncompressible inviscid liquid jets are unstable regarding axisymmetric disturbances of wave number (k) less than a certain cut-off wave number, i.e., the critical wave number (k c ) and calculated that the diameter of the formed droplet (d) is related to the jet diameter (D) as d % 1.89 Â D. From nonlinear theory, we know nowadays that for each disturbance forming a main droplet one or more usually smaller droplets (satellite or secondary droplets) can be formed. 1 However, it is possible to disturb the jet such that these satellite droplets are not formed, thereby generating a monodisperse spray. 1,15 From all the above mentioned atomization methods, electrohydrodynamic atomization (EHDA) is one of the few which is capable to generate monodisperse micrometer size droplets. Another unique feature of this method is the electric charge acquired by the droplets which provides self dispersion and prevents coalescence. 3,16 In view of these appealing characteristics, the production of monodisperse sprays using EHDA has attracted considerable attention in the literature. [2][3][4][5][6][7]10,12,17,18 Some examples are the works of Tang and Gomez (1994), who investigated monodisperse electrosprayed water droplets for targeted drug delivery 7 and monodisperse sprays of low conductivity liquids 3 as well as the works of Deng et al. (2009) and Arnanthigo et al. (2011) who have developed multiplex systems for the production of such spr...

When a high voltage is applied to a liquid pumped through a needle, charged microdroplets can be formed, which are carried along the electric field lines. This phenomenon is called electrohydrodynamic atomization (EHDA), or simply electrospray. In this work we show that in the case of water, droplets may reverse their paths flying back toward the liquid meniscus, sometimes making contact with it. Such reverse movement is caused by polarization of the water inside the strong electric field. To understand this phenomenon we developed a way to calculate the droplet charge using its trajectory obtained by high-speed imaging. The values found showed that these droplets are charged between 2.5% and 19% of their Rayleigh limit.