Primary surface measurement reported
PFH-water interfacial tension was measured by pendant drop tensiometry for PFH interfaces containing FBA in the fluorinated oil phase, PVA in the aqueous phase, or both.
Client Citation Analysis
Engineering Functional Microcapsules for Controlled Cargo Delivery
This study develops fluorophilic boronic acid-stabilized hydrocarbon-fluorocarbon-water emulsions and uses pendant-drop PFH-water interfacial tension measurements to compare additive combinations that lead to stable, thermally reconfigurable droplets.
At-a-Glance Summary
Dropometer attribution in the paper
The study states that surface tensions were measured “using pendant drop method on the droplet lab tensiometer.”
How the surface-tension / contact-angle data were used in the study
These measurements were used to compare interface formulations and to show that durable stabilization against coalescence followed the combined FBA-PVA interfacial assembly rather than interfacial-tension reduction alone. They also framed the downstream interpretation of elastic-film formation, interfacial rheology, and thermally reconfigurable capsule behavior.
Paper Details
Title
Adaptive Stimuli-Triggered Response to Dynamic Environment: Thermally Reconfigurable Elastic Capsules
Authors
Zhang Wu
Journal
Harvard University Graduate School of Arts and Sciences
Year
2025
Pages / Article
54–65
License
Other Posted Material (LAA)
Journal context
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What Was Measured
Primary surface / interfacial measurement
The study reports PFH-water interfacial tension from pendant-drop measurements with no additive, with 5 wt % FBA in PFH, with 10 wt % PVA in deionized water, and with the combined FBA-PVA condition. Figure 3.2 presents the pendant-drop images and the corresponding surface-tension values.
Supporting measurements
The interface interpretation is supported by transient wrinkle formation during drop retraction, DWR interfacial rheology of HFE-7500/water interfaces with different surfactants, and bright-field and fluorescent confocal microscopy of reconfigurable hexane-perfluorohexane elastic capsules at room temperature and around 0 ºC. The study also uses a glass capillary microfluidic device to fabricate the double-emulsion templates for the capsules.
Role of the Dropometer
The study states that “the surface tensions of the interfaces are characterized using pendant drop method on the droplet lab tensiometer.” In practice, this was applied to PFH-water drop interfaces with and without FBA in the PFH phase and PVA in the aqueous phase, generating the interfacial-tension values reported in Figure 3.2.
Within the workflow, these Dropometer measurements were used to benchmark how each additive combination changed the PFH-water interface and to show that similar or reduced interfacial tensions did not by themselves account for lasting fluorocarbon-water emulsion stabilization.
Key Findings
Interfacial tension dropped with both individual additives
The PFH-water baseline in Figure 3.2b was 71.6 mN/m. Adding 5 wt % FBA to PFH lowered the measured value to 46.0 mN/m, and adding 10 wt % PVA to the aqueous phase lowered it to 37.1 mN/m.
The combined FBA-PVA interface behaved differently from tension reduction alone
The combined FBA-in-PFH/PVA-in-water condition showed a similarly low value of 38.5 mN/m. The study states that lasting stabilization against coalescence was obtained only in the combined FBA-PVA system, showing that lowered interfacial tension alone did not explain the stabilization outcome.
Elastic interfacial film formation was directly visualized
Transient wrinkle formation during retraction of an HFE-7500 drop containing 3 wt % FBA from a water bath containing 0.08 M HEPES and 2 wt % PVA indicated formation of a solid elastic interfacial film. The slow disappearance of the wrinkles and return of the drop to its original shape supported the dynamic nature of the boronic ester bonds.
Interfacial mechanics increased strongly with the FBA-PVA pair
Interfacial rheology showed that the FBA-PVA interface exhibited a complex shear modulus two orders of magnitude higher than interfaces with 008-FluoroSurfactant from RAN Biotechnologies, PVA alone, or no surfactants. The frequency sweep also showed marked shear-thinning behavior.
The stabilized system supported thermal morphology reconfiguration
After interfacial crosslinking, double emulsion droplets with a water core and a 1:1 hexane:PFH shell became elastic capsules. Because hexane and PFH exhibit temperature-dependent miscibility with an LCST around 23 ºC, cooling from room temperature to 0 ºC led to phase separation and lower-symmetry two-core triple emulsion drops.
Figures & Visuals
Figure 3.2 — Direct surface-tension comparison across interface formulations
What it shows
It shows pendant-drop images and surface-tension values for PFH-water interfaces with no additive, with FBA in PFH, with PVA in water, and with the combined FBA-PVA condition.
Figure 3.1 — Mechanistic evidence for elastic interfacial film formation
What it shows
It shows the boronic-acid coupling chemistry and the transient wrinkling observed when an FBA-containing fluorinated-oil drop retracts from PVA-containing water.
Figure 3.3 — Mechanical follow-up to the tension data
What it shows
It shows DWR interfacial rheology, including the higher modulus and shear-thinning response of the FBA-PVA interface.
Figure 3.4 — Downstream droplet reconfiguration after interfacial stabilization
What it shows
It shows microfluidic fabrication of the capsules and the morphology change between room temperature and around 0 ºC for the hexane-perfluorohexane system.
Why It Matters
In this study, Dropometer-derived interfacial tension measurements anchored the comparison between interface formulations for hydrocarbon-fluorocarbon-water emulsions. Because FBA alone, PVA alone, and the combined condition all lowered the PFH-water interfacial tension to different extents, the pendant-drop data gave the authors a direct way to separate simple tension reduction from the more specific stabilization behavior they were engineering.
That distinction carried through the rest of the workflow. Once the combined FBA-PVA interface was linked to lasting stabilization against coalescence, the study could connect that interface design to elastic-film formation, higher interfacial modulus, and temperature-driven reconfiguration of the resulting capsules into more complex morphologies.
Practical Takeaways
Use pendant-drop data comparatively
The surface-tension measurements were used to compare additive placement across the PFH and aqueous phases using the same interface readout.
Low tension was not the full design criterion
In this workflow, several conditions lowered the PFH-water interfacial tension, but durable stabilization tracked with the combined FBA-PVA assembly.
Pair tension with interfacial mechanics
The study combined Dropometer measurements with wrinkle observation and DWR rheology to distinguish elastic-film formation from simple adsorption effects.
Connect interface screening to downstream capsule behavior
The interfacial formulation that stabilized the PFH-water interface was then used in 1:1 hexane:PFH shell capsules that reconfigured on cooling.