Droplet formation in microfluidic T-junction generators operating in the transitional regime. III. Dynamic surfactant effects

Abstract

This study extends our previous work on droplet generation in microfluidic T-junction generators to include dynamic interfacial tension effects created by the presence of surfactants. In Paper I [T. Glawdel, C. Elbuken, and C. L. Ren, Phys. Rev. E 85, 016322 (2012)], we presented experimental findings regarding the formation process in the squeezing-to-transition regime, and in Paper II [T. Glawdel, C. Elbuken, and C. L. Ren, Phys. Rev. E 85, 016323 (2012)] we developed a theoretical model that describes the performance of T-junction generators without surfactants. Here we study dynamic interfacial tension effects for two surfactants, one with a small molecular weight that adsorbs quickly, and the other with a large molecular weight that adsorbs slowly. Using the force balance developed in Paper II we extract the dynamic interfacial tension from high speed videos obtained during experiments. We then develop a theoretical model to predict the dynamic interfacial tension in microfluidic T-junction generators as a function of the surfactant properties, flow conditions, and generator design. This model is then incorporated into the overall model for generator performance to effectively predict the size of droplets produced when surfactants are present.

The dynamic adsorption of different surfactants on droplet formation in coaxial microfluidic devices

“…Secondly, compared with SDS and CTAB, Tween 20 and TX 100 both have larger molecular weights and smaller diffusion coefficients in water, shown in Table 1. According to the previous work, Tween 20 and SDS were used to represent two typical surfactants as macromolecule and micromolecule surfactants (Glawdel and Ren, 2012;Wang et al, 2009). The viscosities of the N-hexane and aqueous phase were measured using an Ubbelohde viscometer, and the equilibrium interfacial tensions of the N-hexane/surfactant solution systems were measured with a tensiometer using the pendent drop technique (OCAH200, DataPhysics Instruments GmbH, Germany).…”

Generation of Oil Droplets in a Non-Newtonian Liquid Using a Microfluidic T-Junction

“…Actually, we found that Triton X-100 was not soluble in glycerol/water solutions above 60%. Furthermore, for xanthan solutions, the concentration of the surfactant was comparable to that of the polymer and it is well known that the presence of the surfactant can affect the droplet formation [28].…”

“…Actually, we found that Triton X-100 was not soluble in glycerol/water solutions above 60%. Furthermore, for xanthan solutions, the concentration of the surfactant was comparable to that of the polymer and it is well known that the presence of the surfactant can affect the droplet formation [28]. To overcome such limitations, we switched to microchannels in PDMS whose walls were made hydrophilic after a surface treatment with polyvinylpyrrolidone, PVP (molecular weight, M w~4 0,000 g/mol, Sigma Aldrich, St. Louis, MI, USA).…”

Droplet confinement and leakage: Causes, underlying effects, and amelioration strategies

“…5 In most droplet-based microfluidic systems, surfactants are used to adjust interfacial tensions to allow stable and monodisperse droplet formation. 7 Surfactants in such environments are normally long-chain molecules that contain hydrophilic and oleophilic regions and hence assemble at the water/oil interface, with the potential to stabilise droplets against aggregation and wetting. 8 The most common surfactant used in microfluidic research (with fluorous continuous phases) is a polyethylene glycol-perfluoropolyether (PEG-PFPE) block copolymer 9 known as "EA surfactant" or "RainDance."…”