Catastrophic Drop Breakup in Electric Field

Abstract

We report novel observations revealing the catastrophic breakup of water drops containing surfactant molecules, which are suspended in oil and subjected to an electric field of strength approximately 10(5) V/m. The observed breakup was distinctly different from the gradual end pinch-off or tip-streaming modes reported earlier in the literature. There was no observable characteristic deformation of the drop prior to breakup. The time scales involved in the breakup and the resultant droplet sizes were much smaller in the phenomenon observed by us. We hypothesize that this mode of drop breakup is obtained by the combined effect of an external electric field that imposes tensile stresses on the surface of the drop, and characteristic stress-strain behavior for tensile deformation exhibited by the liquid drop in the presence of a suitable surfactant, which not only lowers the interfacial tension (and hence the cohesive strength) of the drop but also simultaneously renders the interface nonductile or brittle at high enough concentration. We have identified the relevant thermodynamic parameter, viz., the sum of interfacial tension, sigma, and the Gibbs elasticity, epsilon, which plays a decisive role in determining the mode of drop breakup. The parameter (epsilon + sigma) represents the internal restoration stress of a liquid drop opposing rapid, short-time-scale perturbations or local deformations in the drop shape under the influence of external impulses or stresses. A thermodynamic "state" diagram of (epsilon + sigma) versus interfacial area per surfactant molecule adsorbed at the drop interface shows a "maximum" at a critical transition concentration (ctc). Below this concentration of the surfactant, the drop undergoes tip streaming or pinch off. Above this concentration, the drop may undergo catastrophic disintegration if the external stress is high enough to overcome the ultimate cohesive strength of the drop's interface.

The standard free energy of surfactant adsorption at air/water and oil/water interfaces: Theoretical vs. empirical approaches

“…(11) into the Gibbs adsorp tion equation, Eq. (6), and integrating, we obtain the surface equation of state, π s = π s (Γ), in the form: (12) where is an integration variable. Furthermore, to obtain a theoretical expression for , we substitute c and π s from Eqs.…”

“…In addition, our goal is to check whether the determined ΔG°, ΔH° and ΔS° are sensitive to the kind of the used theoretical model. Here, we compare the applicability of the adsorption models of Frumkin, van der Waals and Helfand-Frisch-Lebowitz, which have found numerous applications for the interpretation of sur face tension data [9][10][11][12][13][14][15]. Generalizations of these models to the cases of ionic surfactants and mixed sys tems are also available [16][17][18][19][20].…”

Coaxial Electrohydrodynamic Atomization for the Production of Drug-Loaded Micro/Nanoparticles

“…An external electric field is utilized to adjust the formation process of droplets. During the operation progress, the electric field induces surface charging of the liquid at the tip of the nozzle, and the liquid is transformed into a conical shape, called a Taylor cone [22]. In addition, a grounded electrode is included in this device.…”

Electric fields enable tunable surfactant transport to microscale fluid interfaces

“…Interface deformation, and mechanisms of instability for systems of pure fluids, i.e., without added surfactant, has been well characterized [12][13][14][15][16][17][18][19][20][21]. The limited existing work on the deformation of surfactant-laden interfaces under electric fields is restricted to experiments and computations to predict drop deformation and breakup [22][23][24][25][26][27]. An inherent assumption in the computations is that the surfactant is insoluble; therefore, the effect of electric field on surfactant transport from bulk to the interface is not accounted for.…”