Surface tension effects on submerged electrosprays

Abstract

Electrosprays are a powerful technique to generate charged micro/nanodroplets. In the last century, the technique has been extensively studied, developed, and recognized with a shared Nobel price in Chemistry in 2002 for its wide spread application in mass spectrometry. However, nowadays techniques based on microfluidic devices are competing to be the next generation in atomization techniques. Therefore, an interesting development would be to integrate the electrospray technique into a microfluidic liquid-liquid device. Several works in the literature have attempted to build a microfluidic electrospray with disputable results. The main problem for its integration is the lack of knowledge of the working parameters of the liquid-liquid electrospray. The "submerged electrosprays" share similar properties as their counterparts in air. However, in the microfluidic generation of micro/nanodroplets, the liquid-liquid interfaces are normally stabilized with surface active agents, which might have critical effects on the electrospray behavior. In this work, we review the main properties of the submerged electrosprays in liquid baths with no surfactant, and we methodically study the behavior of the system for increasing surfactant concentrations. The different regimes found are then analyzed and compared with both classical and more recent experimental, theoretical and numerical studies. A very rich phenomenology is found when the surface tension is allowed to vary in the system. More concretely, the lower states of electrification achieved with the reduced surface tension regimes might be of interest in biological or biomedical applications in which excessive electrification can be hazardous for the encapsulated entities.

The nature of chemical reaction-driven tip-streaming

“…The properties of the fluid used in that study, 68 which are of interest here, correspond to (a) the greater than one viscosity ratio of the dispersed to that of the external fluid, l i =l o > 1, which is opposite to our case, (b) lower than our conductivity, j < Oð0:1 S=mÞ, and (c) higher than our interfacial tensions. According to this work, 68 the addition of surfactant below the CMC for the high conductivity case (closest to our study) does not appear to modify ES properties appreciably. However, above the CMC, no typical conejet mode is found, but instead one observes thicker unstable jets (compare to our larger emitted droplets), reduced dependence of current on flow rate, higher currents than expected from standard ES theory (versus our lower currents), and droplet diameter increase with decreasing interfacial tension.…”

“…The other report of using surfactant is by Hayati et al, 67 who added an ionic surfactant "AOT" to hexadecane to adjust the conductivity of the sprayed liquid (hexadecane), but there is no mention of its effect on surface tension variation. Only recently, 68 an attempt to systematically investigate the effect of surfactants on the cone-jet mode in liquid-liquid electrosprays was made. The properties of the fluid used in that study, 68 which are of interest here, correspond to (a) the greater than one viscosity ratio of the dispersed to that of the external fluid, l i =l o > 1, which is opposite to our case, (b) lower than our conductivity, j < Oð0:1 S=mÞ, and (c) higher than our interfacial tensions.…”

“…Only recently, 68 an attempt to systematically investigate the effect of surfactants on the cone-jet mode in liquid-liquid electrosprays was made. The properties of the fluid used in that study, 68 which are of interest here, correspond to (a) the greater than one viscosity ratio of the dispersed to that of the external fluid, l i =l o > 1, which is opposite to our case, (b) lower than our conductivity, j < Oð0:1 S=mÞ, and (c) higher than our interfacial tensions. According to this work, 68 the addition of surfactant below the CMC for the high conductivity case (closest to our study) does not appear to modify ES properties appreciably.…”

“…14. Fluid properties of CRDTS versus that of liquid-liquid 52,68,69 (L-L ES) and liquid-gas 55,57,70 electrosprays (L-G ES).…”

Design criteria for developing low-resource magnetic bead assays using surface tension valves

“…Some of the many aspects of the phenomena that control microdroplet formation were recently presented in a special collection of papers. [18][19][20][21] Interestingly, some of the physical properties that influence fluid stability within our self-contained format, such as surface and interfacial tension and solution density difference at the fluid-fluid interface, are similar to those that govern microdroplet formation in multiphase microfluidics. In our system, additional variables and constraints associated with magnetic particles are discussed in the context of the multiphase fluidic system.…”