The effect of alkane tail length of C E8 surfactants on transport to the silicone oil–water interface

Electric fields enable tunable surfactant transport to microscale fluid interfaces

“…Here, we have the oil-soluble surfactant in the cell, and water in the capillary; and quantify surfactant transport from the oil phase to the oil-water interface. The interfacial tension of pure Isopar-water was measured to be 52.5 ± 0.3, which is typical of alkane-water interfaces [43], and that of silicone oil-water was 40.3 ± 0.4 mN/m, in agreement with reported values [45]. Under an applied electric field, the interfacial tension was not observed to change beyond the error of the instrument (1 mN/m), for field strengths used in this study.…”

“…For diffusion to spherical interfaces, the length scale for diffusion, h s , depends on the radius of curvature of the interface, bulk concentration and isotherm [34]. We do not measure the equilibrium isotherm of OLOA at the Isopar-water interface, however, using typical parameter values of equilibrium surfactant coverage for surfactants at oil-water interfaces [45], and the radii and bulk concentrations used in this study, h s ≈ 0.35 − 3.5 mm. The time scale for the surfactant complex to migrate this distance under an electric field is τ E = h s /U E ≈ 7 − 700 s. The diffusion time scale is given by τ d = h 2 s /D, where D is the diffusion coefficient.…”

Competition Between Viscoelasticity and Surfactant Dynamics in Flow Focusing Microfluidics

“…However, it is interesting to note that other nonionic surfactant-oil-water systems exhibit tipstreaming when the adsorption timescale is of the order of a few milliseconds and is therefore comparable to the convection timescale, or the droplet breakup timescale. [4,5,50] The polymer relaxation times relevant to the present study are also of order a few milliseconds, indicating that in the right conditions, elasticity at the interface (i.e., Marangoni stresses) and elasticity in the bulk (i.e., polymer stretching) can both act to stabilize interfaces, leading to substantially longer threads.…”

The importance of experimental design on measurement of dynamic interfacial tension and interfacial rheology in diffusion-limited surfactant systems

“…as it describes the behavior of surfactant used in this work. [1,[17][18][19] The parameters that are specific to the surfactant are D (the molecular diffusion coefficient) and the four isotherm parameters, K, which represents a surface van der Waals interaction term, n, a fitting parameter that adjusts the isotherm between the Frumkin (n=1) and Langmuir (n=0) equations, a, the ratio of the desorption to adsorption kinetic rate constants and, Γ ∞ , the surface coverage at its maximum value. [20] Note that none of these parameters should depend on the bulk concentration or the geometry of the interface.…”