Influence of Fluorinated Surfactant Composition on the Stability of Emulsion Drops

Abstract

Aqueous drops of a well‐defined size are often used as small containers for conducting chemical and biochemical reactions, cell assays and as templates to produce microparticles. To prevent their coalescence, they must be stabilized, for example, using surfactants. The ability of different nonionic diblock and triblock copolymer surfactants to stabilize water drops that are dispersed in fluorinated oils is compared. In particular, the influence of the length of their hydrophilic poly(ethylene glycol) (PEG) block on the drop stability is studied. The stability of drops coated with triblock copolymers scales with the interfacial tension, whereas that of drops coated with diblock copolymers scales with their packing density. Surfactants whose ratio of the radii of gyration of PEG to the hydrophobic block (FSH) is between 0.54 and 0.67 impart the best stability to aqueous drops containing low salt concentrations. By contrast, surfactants whose ratio of the radii of gyration is between 0.34 and 0.37 impart the best stability to aqueous drops containing high salt concentrations. Hence, the choice of the best surfactant strongly depends on the composition of the fluids.

Selectively Permeable Double Emulsions

“…This observation is in stark contrast to double emulsions stabilized with catechol‐functionalized surfactants and indicates that catechols delay the surfactant‐driven transport of fluorescein across the oil phase. The interfacial tensions of these two systems are very similar: It is 9 mN m −1 between HFE 7100 containing 1 × 10 −3 m of FSH‐ED900‐HA and water, and 11 mN m −1 between HFE 7500 containing 1 × 10 −3 m FSH‐ED600‐FSH and water . Hence, the observed difference in release kinetics cannot be caused by differences in the interfacial tension.…”

“…These tests have always been performed on emulsions stabilized with uncharged, unfunctionalized block‐copolymer surfactants. To assess the influence of catechols on this process, we produce fluorescein‐loaded double emulsions and stabilize them with a nonfunctionalized triblock copolymer surfactant FSH‐ED600‐FSH . This triblock copolymer surfactant is chosen as it does not contain any unreacted primary amines such that it is uncharged and independent of pH.…”

“…The NHS‐HA was reacted with 1.2 mol equivalent of ED900 in 40 mL dry ethyl acetate overnight at room temperature under an argon atmosphere, to obtain ED900‐HA. Finally, the product ED900‐HA was reacted with FSH as previously reported to obtain a perfluorinated di‐block surfactant FSH‐ED900‐HA …”

“…Indeed, double emulsions are frequently employed to store and deliver reagents, as picoliter‐sized reaction vessels to conduct chemical and biochemical reactions, or as templates to produce microcapsules . Certain surfactant‐stabilized double emulsions are permeable toward hydrophilic encapsulants, even though their solubility in the oil phase is very low . These double emulsions allow passive exchange of reagents.…”

Microfluidic device for on-chip mixing and encapsulation of lysates

“…The stability of drops coated with perfluorinated triblock copolymers can be compromised by the presence of high concentrations of ions. 41 To test if we can increase the drop stability, we decrease the concentration of 3-PGA to 4 mM. However, also in this case, single emulsion drops tend to coalesce albeit to a smaller extent, as summarized in Figure 3a and shown in the fluorescence micrographs in Figures S2a and S2b.…”