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Ministerio de Economía y Competitividad DPI2016-78887-C3-R-1

The collapse of a bubble of radius Ro at the surface of a liquid generating a liquid jet and a subsequent first drop of radius R is universally scaled using the Ohnesorge number Oh 1⁄4 μ=ðρσRoÞ1=2 and a critical value Oh below which no droplet is ejected; ρ, σ, and μ are the liquid density, surface tension, and viscosity, respectively. First, a flow field analysis at ejection yields the scaling of R with the jet velocity V as R=lμ ∼ ðV=VμÞ−5=3, where lμ 1⁄4 μ2=ðρσÞ and Vμ 1⁄4 σ=μ. This resolves the scaling problem of curvature reversal, a prelude to jet formation. In addition, the energy necessary for the ejection of a jet with a volume and averaged velocity proportional to RoR2 and V, respectively, comes from the energy excess from the total available surface energy, proportional to σR2 o, minus the one dissipated by viscosity, proportional to μðσR3 o=ρÞ1=2. Using the scaling variable φ 1⁄4 ðOh − OhÞOh−2, it yields V=Vμ 1⁄4 kvφ−3=4 and R=lμ 1⁄4 kdφ5=4, which collapse published data since 1954 and resolve the scaling of R and V with kv 1⁄4 16, kd 1⁄4 0.6, and Oh 1⁄4 0.043 when gravity effects are negligible. Ministerio de Economía, Industria y Competitividad, Gobierno de España DPI2016-78887-C3-1-R

We examine both theoretically and experimentally the breakup of a pendant drop loaded with an insoluble surfactant. The experiments show that a significant amount of surfactant is trapped in the resulting satellite droplet. This result contradicts previous theoretical predictions, where the effects of surface tension variation were limited to solutocapillarity and Marangoni stresses.We solve numerically the hydrodynamic equations, including not only those effects but also those of surface shear and dilatational viscosities. We show that surface viscosities play a critical role to explain the accumulation of surfactant in the satellite droplet. Ministerio de Economía y Competitividad DPI2013-46485-C3-1-R, TRA2013- 45808-R Junta de Extremadura GR10047

Electro-flow focusing, a technique combining the features of electrospray (ES) and flow focusing (FF), provides a reliable tool to reach parametrical microjetting ranges not attainable by ES or FF alone under specific operational regimes (liquid properties and flow rate). In this Letter, we provide not only a closed theoretical model predicting the diameter of a high electrical conductivity electro-flow focused liquid microjet, but also its convective or absolute instability, linked to the jetting-to-dripping transition and the minimum liquid flow rate that can be ejected in steady jetting regime, in which the smallest droplets are issued. Good agreement is found with experimental values. Ministerio de Ciencia y Tecnología de España DPI2004-07197