Fluorophilic Surfactant for Emulsion Droplets

Peer-Reviewed Citation Analysis

A 2025 peer-reviewed study in Lab on a Chip used a Droplet Lab tensiometer to characterize PFH–water interfacial properties by the pendant-drop method. The study quantified how a fluorophilic boronic acid copolymer surfactant (FBA) and PVA affected the interface, then combined those measurements with interfacial rheology and emulsion experiments to investigate stabilization.

At-a-Glance Summary

What the Droplet Lab instrument did and did not do

The Droplet Lab tensiometer measured interfacial tension at the perfluorohexane–water interface across four additive conditions, producing Figure 2b–c, 2 of the paper's 13 figure panels. It did not measure the hexane–water or hexane–perfluorohexane interfaces, did not produce the interfacial rheology of the FBA–PVA film (TA Instruments HR 20, Figure 3a–d), and did not produce the emulsion morphology results (glass capillary microfluidics and confocal microscopy, Figure 4).

Primary surface measurement reported

Pendant-drop interfacial tension measurements of the perfluorohexane–water interface, reported as values and distributions across four additive conditions.

How the paper credits the instrument

Materials and methods, verbatim: "The surface tensions of the interfaces are characterized using pendant drop method on the droplet lab tensiometer and analyzed with the OpenDrop package available at https://github.com/jdber1/opendrop."

How the interfacial tension data were used in the study

The tension values compare PFH–water interfaces with and without FBA (in PFH) and PVA (in water). The FBA only, PVA only and combined conditions gave similar tension (around 20 and 17 mN m⁻¹, versus about 30 mN m⁻¹ without additives), including ones that did not give lasting stabilisation: the paper states that lasting stabilisation is "only obtained for the combined FBA–PVA system, not when only the individual components are used." Tension alone therefore did not distinguish the combined system from the single component ones.

Paper Details

Title

Fluorophilic boronic acid copolymer surfactant for stabilization of complex emulsion droplets with fluorinated oil

Authors

Zhang Wu; Brendan T. Deveney; Jörg G. Werner; Stefano Aime; David A. Weitz

Journal

Lab on a Chip

Year

2025

Volume

25

Pages / Article

2315–2319

DOI

10.1039/d5lc00309a

Article type

Communication (RSC short format), peer-reviewed. Received 30 March 2025, accepted 14 April 2025, published 15 April 2025.

Funding & interests

Funded by NSF through the Harvard MRSEC (DMR-2011754) and the Center for Nanoscale Systems (NNCI, NSF 1541959). Authors at Harvard SEAS and Physics, Boston University, and ESPCI Paris. The paper states "there are no conflicts to declare." Droplet Lab appears in no funding, acknowledgement, affiliation or conflict statement.

10.8

Scopus metrics (Elsevier / Scopus rating 2024)

CiteScore 2024

Scopus metrics (Elsevier / Scopus rating 2024)

CiteScore subject ranks (CiteScore 2024)

Q1 - Biochemistry, Genetics and Molecular Biology - Biochemistry (47/441)
Q1 - Chemistry - Chemistry (all) (51/404)

1.163

Scopus metrics (Elsevier / Scopus rating 2024)

SNIP 2024

1.201

Scopus metrics (Elsevier / Scopus rating 2024)

SJR 2024

5.4

Journal Impact Factor (Clarivate JCR)

Journal Impact Factor (JCR 2024)

What Was Measured

Primary surface / interfacial measurement

Interfacial tension at the perfluorohexane–water interface, measured by pendant drop and fitted with OpenDrop, across four conditions: PFH with deionised water; PFH with PVA-in-water; PFH containing FBA with deionised water; PFH containing FBA with PVA-in-water. This is the only interface for which tension values are reported. Reported as boxplots (median, IQR, min/max, individual points, outliers) in Fig. 2b–c; the paper states no replicate count, measurement temperature or phase densities.

Supporting measurements

Interfacial rheology was used to assess the rheological properties of the FBA–PVA interfacial film using oscillatory amplitude and frequency sweeps with a double wall ring configuration. Imaging (bright-field and fluorescent confocal micrographs) was used to characterize droplet and microcapsule morphologies at room temperature and approximately 0 °C.

Instruments Mentioned

Role of the Droplet Lab instrument

Using the pendant drop method on the "droplet lab tensiometer," the authors measured interfacial tension at the perfluorohexane–water interface, analysing droplet shapes with the OpenDrop package; third-party open-source software to obtain values in mN m⁻¹ across four additive conditions: PFH with deionised water, PFH with PVA-in-water, PFH containing FBA with deionised water, and PFH containing FBA with PVA-in-water.

The measurements quantify how FBA in the fluorinated oil phase and PVA in the aqueous phase each change PFH–water interfacial tension. FBA alone, PVA alone and the combination gave similar tension, while only the combination produced lasting stabilisation. The authors conclude that "the synergistic and beneficial interfacial assembly of the FBA and PVA is necessary for stabilization", which they relate to the elastic interfacial film formed by the two components.

The emulsion system contains three interfaces: hexane–water, perfluorohexane–water, and hexane–perfluorohexane. The tension measurements cover the perfluorohexane–water interface. The paper describes the hexane–perfluorohexane interfacial tension as "low" and relates it, together with micro-confinement, to the reconfiguration into two-core triple emulsion drops. The interfacial rheology in Figure 3 used HFE-7500 and water interfaces, while the tension measurements used perfluorohexane.

Technique / Model

Pendant drop method (pendant drop tensiometry) on the “droplet lab tensiometer”

Methods location

“Characterization of the FBA–PVA interfacial properties” (Materials and methods)

Data output figures

Fig. 2b–c

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Method Snapshot

Method Snapshot Table

System / interface (as shown)	Fluorinated oil phase	Aqueous phase	Surface measurement output	Analysis approach	Data figure(s)	Conditions / notes
PFH/DIW	PFH	Deionized water (DIW)	Surface tension distribution (boxplot + individual points)	Pendant drop method on the “droplet lab tensiometer”; OpenDrop analysis	Fig. 2b–c	PFH–water drop interfaces presented as grayscale pendant-drop images and boxplots
PFH + FBA/DIW	PFH + FBA (in PFH phase)	DIW	Surface tension distribution (boxplot + individual points)	Pendant drop method on the “droplet lab tensiometer”; OpenDrop analysis	Fig. 2b–c	Condition explicitly compared against PFH/DIW
PFH/PVA–water	PFH	PVA in DIW phase (“PVA–water”)	Surface tension distribution (boxplot + individual points)	Pendant drop method on the “droplet lab tensiometer”; OpenDrop analysis	Fig. 2b–c	Condition explicitly compared against PFH/DIW
PFH + FBA/PVA–water	PFH + FBA (in PFH phase)	PVA in DIW phase (“PVA–water”)	Surface tension distribution (boxplot + individual points)	Pendant drop method on the “droplet lab tensiometer”; OpenDrop analysis	Fig. 2b–c	Surface tension compared against single-additive cases; presented as boxplots with outliers marked

Key Findings

FBA lowers PFH–water interfacial tension

Adding FBA to PFH reduces the interfacial tension of the PFH–water interface to around 20 mN m⁻¹, compared to approximately 30 mN m⁻¹ without additives.

PVA lowers PFH–water interfacial tension

Adding PVA to water reduces the interfacial tension of the PFH–water interface to around 17 mN m⁻¹.

Combined FBA + PVA yields similar surface tension

Paper, verbatim: "A similar surface tension is obtained when using the combination of FBA-in-PFH and PVA-in-water."

Similar interfacial tension for the single component and combined systems

FBA alone, PVA alone and the combination gave similar interfacial tension, yet only the combination gave lasting stabilisation. The paper states: "However, lasting stabilization against coalescence of fluorocarbon–water emulsions is only obtained for the combined FBA–PVA system, not when only the individual components are used. This indicates that the synergistic and beneficial interfacial assembly of the FBA and PVA is necessary for stabilization." The paper then characterises the FBA–PVA interfacial film by interfacial rheology (Fig. 3).

Interfacial rheology of the FBA–PVA film (TA Instruments HR 20)

The FBA–PVA interface showed a complex shear modulus two orders of magnitude higher than 008-FluoroSurfactant (RAN Biotechnologies), PVA alone, or no surfactant. Both amplitude and frequency sweeps show G′ > G″ ; a viscoelastic solid film with shear-thinning consistent with dynamic covalent bonding. The storage modulus for HFE-7500 with 10 wt% PVA was "beyond the detection limit of the interfacial rheometer."

Double emulsions reconfigured into two-core triple emulsions on cooling

Hexane and perfluorohexane have an upper critical solution temperature near 23 °C. Cooling microfluidically generated double emulsion drops to approximately 0 °C drove phase separation inside the droplet, producing lower-symmetry two-core triple emulsion drops. The paper presents this as an application of the FBA–PVA surfactant system.

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What it shows

Selected grayscale pendant-drop images for PFH–water interfaces with and without FBA in the PFH phase or PVA in the DIW phase.

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What it shows

Boxplots and individual data points show the distribution of surface tension values for PFH/DIW, PFH/PVA–water, PFH + FBA/DIW, and PFH + FBA/PVA–water interfaces.

3 wt% FBA copolymer; 0.08 M HEPES; 2 wt% PVA. Scale bar 500 µm.

Figure 2a (paper) — instrument not stated in the source

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3 wt% FBA copolymer; 0.08 M HEPES; 2 wt% PVA. Scale bar 500 µm.

Transient wrinkle formation during retraction of an HFE-7500 drop containing FBA from a water bath containing HEPES and PVA is shown as a visual indicator of interfacial film behavior in the combined-component system.

Why It Matters

The pendant-drop measurements enable direct comparison of PFH–water interfacial tension across four additive conditions, presented in Fig. 2b–c. They are one of four measurement modes in the paper: interfacial shear rheology (Fig. 3a–d), glass capillary microfluidic drop generation (Fig. 4a–b) and confocal microscopy (Fig. 4c) carry the paper's conclusions.

The paper reports similar tension values across additive conditions that behave very differently, with stabilisation "only obtained for the combined FBA–PVA system, not when only the individual components are used." The authors attribute it to "the synergistic and beneficial interfacial assembly of the FBA and PVA," and the interfacial rheology shows a complex shear modulus two orders of magnitude above the controls. For a formulator, the practical reading is that tension screens candidates and interfacial rheology discriminates them.

Practical Takeaways

Condition-to-condition interfacial comparison

Pendant-drop tensiometry compares PFH–water interfaces across baseline, FBA-only, PVA-only, and combined FBA–PVA conditions in a single figure set (Fig. 2b–c).

Distribution-first reporting

Interfacial tension is presented as boxplots with individual data points and outliers marked, showing spread rather than a single mean. The paper does not state the replicate count, measurement temperature or phase densities for these measurements.

Tie surface tension to formulation outcomes

The study uses the measured PFH–water tensions to contextualise coalescence behaviour. Because tension values were similar across the single additive and combined conditions, tension alone did not predict the outcome. The paper states stabilisation was "only obtained for the combined FBA–PVA system, not when only the individual components are used."

Pair tensiometry with interfacial mechanics when relevant

Interfacial rheology on a TA Instruments HR 20 with a double wall ring characterised the FBA–PVA film, showing a complex shear modulus two orders of magnitude higher than 008-FluoroSurfactant (RAN Biotechnologies), PVA alone, or no surfactant, with G′ > G″ in both amplitude and frequency sweeps. Pair tensiometry with interfacial rheology when tension values alone do not separate your formulations.

FAQ

Frequently Asked Questions

Does the paper name a Droplet Lab Dropometer?

It names the maker but not a product. Its instrument statement reads: "The surface tensions of the interfaces are characterized using pendant drop method on the droplet lab tensiometer and analyzed with the OpenDrop package available at https://github.com/jdber1/opendrop." No product or model name is given. The drop shape analysis was performed with OpenDrop, third-party open-source software.

Which interfaces were measured?

The tension measurements cover the perfluorohexane–water interface, across four conditions: PFH with deionised water, PFH with PVA-in-water, PFH containing FBA with deionised water, and PFH containing FBA with PVA-in-water (Figure 2b–c). The paper describes the hexane–perfluorohexane interface qualitatively, as "the low hexane–PFH interfacial tension." The interfacial rheology used HFE-7500 and water interfaces (Figure 3).

What tension values were reported?

Perfluorohexane against water without additives, approximately 30 mN/m. With FBA in the fluorinated phase, around 20 mN/m. With PVA in the water phase, around 17 mN/m. With both, the paper states "a similar surface tension is obtained." All values are stated as approximations.

Did lower interfacial tension explain the emulsion stability?

Not on its own, according to the paper. FBA alone, PVA alone and the combination all give similar interfacial tension, yet "lasting stabilization against coalescence of fluorocarbon–water emulsions is only obtained for the combined FBA–PVA system, not when only the individual components are used." The authors attribute stabilisation to "the synergistic and beneficial interfacial assembly of the FBA and PVA." The supporting evidence is interfacial shear rheology, where the FBA–PVA interface showed a complex shear modulus two orders of magnitude higher than the controls (a commercial fluorosurfactant, PVA alone, or no surfactant).

Formal Reference

Wu, Z.; Deveney, B. T.; Werner, J. G.; Aime, S.; Weitz, D. A. (2025). Fluorophilic boronic acid copolymer surfactant for stabilization of complex emulsion droplets with fluorinated oil. Lab on a Chip, 25, 2315–2319.

Short Cite + DOI

https://doi.org/10.1039/d5lc00309a

Fluorophilic boronic acid copolymer surfactant for stabilization of complex emulsion droplets with fluorinated oil

At-a-Glance Summary

Paper Details

What Was Measured

Role of the Droplet Lab instrument

Bring This Measurement Into Your Lab

Method Snapshot

Key Findings

Figures & Visuals

Why It Matters

Practical Takeaways

Frequently Asked Questions

References

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