Effect of Soluble Surfactants on the Kinetics of Thinning of Liquid Bridges during Drops Formation and on Size of Satellite Droplets

Abstract

The results of an experimental study on thinning and breakage of liquid bridges during detachment of a drop from the tip of a capillary are presented for a series of surfactant solutions (including cationic, anionic, and nonionic surfactants) over a broad range of molecular masses, values of critical micelle concentration, and concentrations. The used experimental protocol revealed that the kinetics of the bridge thinning depends much more on the dynamics of adsorption at the surface of the drop before it destabilizes, rather than on the depletion of surfactant from the surface of the thinning bridge due to its stretching as the instability develops. The kinetics of the bridge thinning and the size of satellite droplets formed after the bridge breakage depend considerably on the surfactant concentration and the value of critical micelle concentration. It is proposed that the dynamic surface tension on the time scale of the drop formation can be used as an effective surface tension for the description of the bridge kinetics over the broad range of experimental conditions used.

Dynamics of retracting surfactant-laden ligaments at intermediate Ohnesorge number

“…Craster et al [9] have studied the breakup of a viscous thread in the presence of soluble surfactant at concentrations that are potentially above the critical micelle concentration and have shown that Marangoni stresses cause the formation of large satellites. This prediction was observed experimentally by Kovalchuk et al [22,23] where the satellite drop size increased by up to three times when soluble surfactant was added; the diffusion from the bulk to the interface has also been studied experimentally by Roche et al [42]. Craster et al [9] have also shown that the scalings for the minimum neck radius and axial velocity as the breakup singularity is approached are the same as the ones derived by Eggers [11] as surfactant is swept away from the thinning region.…”

Effect of moderate DC electric field on formation of surfactant-laden drops

“…The addition of glycerol practically does not influence the interfacial tension of surfactant solutions at concentrations above CMC (Kovalchuk et al, 2016(Kovalchuk et al, , 2018. This was confirmed also by our measurements giving interfacial tension of 30 mM solutions of SDS and C12TAB in 60% glycerol/40% water mixture with mineral oil around 9 mN/m, close to interfacial tension of solutions in water.…”

“…The concentration is normalised by the corresponding values of CMC: 8.2 mM for SDS and 15 mM for C 12 TAB. Addition of salt results in a decrease of CMC value, therefore for composition SDS + NaBr the CMC values, c CMC have been calculated using the equation reported previously (Kovalchuk et al, 2016;Anon, 2001):…”

“…Normally, surfactants are used in emulsification processes to stabilize drops against coalescence. The presence of surfactants can affect considerably the kinetics of drop formation and the size of forming drops not only by reducing interfacial tension, but also due to dynamic effects of surfactant adsorption (Liao et al, 2004;de Saint Vincent et al, 2012;Kovalchuk et al, 2016Kovalchuk et al, , 2017. Moreover, the interaction of surfactant molecules, especially in the case of ionic surfactant with an electric field can have an additional effect.…”

Effects of surfactant adsorption on the formation of compound droplets in microfluidic devices

“…20,21 Roché et al showed that the dynamic interfacial tension controlled by the surfactant led to the changes of the neck thinning rate. 22 Kovalchuk et al pointed out that the dynamic interfacial tension during the formation process depended on the adsorption kinetics of the surfactant at the surface of the droplet [23][24][25][26] and the effect of the surfactant on the transition between ow regimes correlated with the dynamic surface tension. Kamat et al demonstrated by the simulation and experiment that Marangoni stresses resulting from the nonuniformity of surfactant concentration on the interface led to reduced thread thinning rate and formation of multiple satellites.…”