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 data were used in the study
These measurements were used to compare interface formulations. The thesis reports that the individual additives and the combined condition all lowered the interfacial tension, while lasting stabilization against coalescence was obtained only with the combined FBA-PVA system.
Paper Details
Title
Engineering Functional Microcapsules for Controlled Cargo Delivery (Chapter 3: Adaptive Stimuli-Triggered Response to Dynamic Environment: Thermally Reconfigurable Elastic Capsules)
Authors
Zhang Wu
Institution
Doctoral dissertation, Harvard University Graduate School of Arts and Sciences
Year
2025
Pages / Article
54–65
License
Other Posted Material (LAA)
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.
Instruments Mentioned
Interfacial tension
droplet lab tensiometer
Interfacial rheology
HR 20 discovery hybrid rheometer by TA instruments
Interfacial rheology geometry
Double Wall Ring (DWR) setup
Droplet generation
glass capillary microfluidic device
Capsule morphology imaging
confocal microscopy
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, together with the author's coalescence observations, to indicate that similar or reduced interfacial tensions did not by themselves account for lasting fluorocarbon-water emulsion stabilization.
Bring This Measurement Into Your Lab
If you need to compare how additives change interfacial tension between oil and water, we can show you the pendant drop workflow on your liquids.
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, which the author attributes to the synergistic interfacial assembly of FBA and PVA.
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
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.
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.
What it shows
It shows DWR interfacial rheology, including the higher modulus and shear-thinning response of the FBA-PVA interface.
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 interfacial tension measurements were used to compare interface formulations for hydrocarbon-fluorocarbon-water emulsions. FBA alone, PVA alone, and the combined condition all lowered the PFH-water interfacial tension to different extents, while the thesis reports lasting stabilization against coalescence only for the combined condition.
The rest of the chapter characterizes the combined FBA-PVA interface further, linking it 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.
Frequently Asked Questions
What did the Droplet Lab tensiometer measure in this chapter?
The dissertation states that interfacial tensions were characterized by the pendant drop method on the Droplet Lab tensiometer. The measured interfaces were between perfluorohexane (PFH) and water, with and without the fluorophilic boronic acid (FBA) copolymer in the PFH phase and poly(vinyl alcohol) (PVA) in the water phase (Figure 3.2).
What interfacial tension values were reported?
Without additives the PFH and water interface measured about 72 mN/m. FBA in the PFH phase lowered it to 46 mN/m and PVA in the water phase lowered it to 37 mN/m, while combining both gave a similar value.
What do these results mean for emulsion stability?
The author reports that lasting stabilization against coalescence was obtained only with the combined FBA and PVA system, even though each additive alone also lowered the interfacial tension. The chapter attributes stabilization to a synergistic interfacial assembly, supported by wrinkle observations and double wall ring interfacial rheology rather than by tension values alone. Pendant drop values for the hexane and PFH interface used in the capsule shells are not reported.