Case Study

A physics lab at Emory University needed oil and water interfacial tensions for its own emulsions. After one method fix, its Dropometer values went into two Soft Matter papers.

Last Updated

November 9, 2026

Industry

Soft matter physics research

Location

Atlanta, Georgia, USA

Customer since

November 2019

Published with the Dropometer

2 Soft Matter papers and 1 PhD thesis

Instrument

Manual Dropometer, surface tension (current model shown)

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Named in Soft Matter in 2021 and 2024 Drop shape method validated against a KRÜSS DSA100E in peer review Two peer reviewed validation papers

Prof. Eric Weeks's group studies emulsions, glasses and jamming, and scales its results by the tension between oil and water. The first oil it tried was lighter than water and climbed the needle. Droplet Lab's advice was to make the heavier liquid the drop. The lab then reported 3 mN/m for TPM oil in 2021 and about 10 mN/m for octane in 2024.

Dropometer contact angle and surface tension instrument with smartphone camera, sample stage and light source (current model)

Written by

Abhimanyu Bhandankar

Holds an MBA from Schulich School of Business and a BE in IT. He joined Droplet Lab in July 2019 and now leads sales and marketing.

CEO at Droplet Lab

Primary outcome: two measured interfacial tensions, each used in a peer reviewed paper

Oil and water interfacial tension, pendant drop on a Dropometer

Values as reported in the papers

TPM oil and water (Cao, Liao, Breedveld and Weeks, Soft Matter, 2021) 3 mN/m

Octane and water, 0.5% Tween 20 (Cheng et al., Soft Matter, 2024) About 10 mN/m

Both values come from the group's own papers (Cao, Liao, Breedveld and Weeks, Soft Matter, 2021; Cheng et al., Soft Matter, 2024). The 2021 paper notes that 3 mN/m "is consistent with previous work". Neither paper reports the number of drops, the temperature or a standard deviation.

2 + 1 papers + thesis

Two Soft Matter papers and one PhD thesis from the group used the instrument.

4 emulsions

Yield stress of four TPM emulsions, 1.03 to 2.03 µm droplets, scaled by the measured tension (Cao, Liao, Breedveld and Weeks, Soft Matter, 2021, Fig. 5b).

Executive Summary

Who

Prof. Eric Weeks's soft matter physics group at Emory University in Atlanta, which studies emulsions, colloidal glasses, jamming and the flow of deformable droplets.

Problem

The group needed the oil and water tension for its own oil to scale its data, because the earlier studies it compared with used other oils. The first oil it tried was lighter than water, the hard case for pendant drop measurement.

Solution

A manual Dropometer for pendant drop measurement, plus a method fix from Droplet Lab: make the heavier liquid the drop, backlight it as a silhouette and calibrate with the needle in use.

Time to Value

The first value was published in January 2021, about a year after first use and including a three month lab closure.

Results

The values went into two Soft Matter papers and a PhD thesis: 3 mN/m for TPM oil and water (2021) and about 10 mN/m for octane in water (2024).

Someone from my lab was able to get feedback from your company ... they got good help.

Emory University, at a glance

Research focus

Soft matter physics: glass and jamming transitions in emulsions, colloidal glasses, and the flow and clogging of deformable droplets.

Products / applications

Fundamental research on emulsions, glasses and the flow of deformable droplets.

Measurement stage

Characterising each oil and water system before rheology or flow experiments, so results can be scaled by the measured tension.

Users

PhD students and postdocs, led by Prof. Eric Weeks.

Materials and surfaces tested

TPM oil emulsions with Synperonic F108 and NaCl; octane in water with Tween 20.

Key constraints

The first oil tried and octane are both lighter than water; low tensions of 3 to 10 mN/m; a lab closure from March to June 2020.

The challenge: an oil that would not hang from the needle

An oil lighter than water, low tensions, and a lab closure.

Why the lab needed its own number

In the 2021 paper Rheology finds distinct glass and jamming transitions in emulsions, the group divides each yield stress data set by its own oil and water tension. The earlier studies it compared with used oils at 9.8 and 1.5 mN/m. This interfacial tension (IFT) is also one of the quantities behind emulsion stability and phase separation control.

Why an oil lighter than water is hard

Pendant drop works when the drop is the heavier liquid. The group first injected oil into the aqueous solution and, in Prof. Weeks's words, "the droplet density was lighter than water so the droplet was climbing up the needle." The fitted contour then missed the drop edge. See also why water forms droplets in oil but oil spreads in water and our oil and water interfacial tension experiment. EN 14210 uses a ring or stirrup instead, so report each value with its method.

What was at stake

The 2020 PhD dissertation Glassy and Jammed Systems: Structures and Dynamics and the 2021 paper both depended on the value, and Emory closed its labs from March to June 2020. The 2024 study with Yale, Flow and clogging of capillary droplets, later needed the value for octane.

What success would require

A drop that hangs, calibration for the needle in use and a clean silhouette, repeatable by a student after a three month gap. The same basics apply to reproducible contact angle measurement.

The fix: make the heavier liquid the drop

What Was Deployed

Delivered configuration: a manual Dropometer with the surface tension module for pendant drop analysis, an LG G6 smartphone and manual drop dispensing. The method from Droplet Lab's support in 2020: let the heavier liquid form the drop, backlight it as a silhouette, calibrate in the app with the needle in use, and check the fitted contour against the drop edge before keeping a value. Pendant drop is covered in our surface tension measurement guide. Labs choosing an instrument can see our guide to the best tensiometer for surfactant and CMC research and our Chemicals guide.

What Made it a Fit

Pendant drop interfacial tension on the same bench as the emulsion work, with the drop shape fit done on the phone.

The fitted contour is drawn over the drop image, so users can check the fit before keeping a value.

Direct access to drop shape experts by email and video call.

Drop shape method validated against a KRÜSS DSA100E in Review of Scientific Instruments and Colloids and Surfaces A.

The Origin

From first measurements to a question about oil drops

The lab began using its Dropometer in early 2020. On 21 March 2020, PhD student Cong Cao wrote to Droplet Lab: the oil was being injected into the aqueous solution, and the fitted contour did not match the drop. The reply named the cause. The oil was lighter than water, so the drop climbed the needle, and the heavier liquid has to form the drop. As Prof. Weeks put it in April 2020, "the problem was obvious in hindsight". When the lab reopened in June 2020, Droplet Lab helped with lighting and calibration, and arranged a video call for 2 July 2020 with Dr Alidad Amirfazli, Co-founder and Scientific Advisor of Droplet Lab. In August 2020 the student agreed to speak with another university that was considering the instrument.

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Before vs After

Metric	Before	After
Interfacial tension for the lab's own oil	Comparison studies used other oils, at 9.8 and 1.5 mN/m	3 mN/m for TPM oil and water (2021)
Pendant drop with an oil lighter than water	Oil injected into water; the drop climbed the needle (March 2020)	Heavier liquid used as the drop, so it hangs from the needle
Calibration	Default value used with the lab's own needle after the supplied syringe broke	Calibrate in the app with the needle in use
Lighting	Dark outline with a bright centre (June 2020)	Backlit silhouette, as in the surface tension guide
Publications with Dropometer values	0	2 Soft Matter papers and 1 PhD thesis

Rollout timeline

Timeline (high level)

November 2019 to early 2020: Purchase and first use

Purchase order 6 November 2019 for a manual Dropometer with surface tension
Invoiced 15 January 2020; lab begins measuring

March 2020: The oil drop problem

First support question on 21 March: the fit misses the drop
Cause found: the oil is lighter than water and climbs the needle

March to June 2020: Lab closure

Emory labs closed for COVID-19
Method picked up again when the lab reopened in June

June to August 2020: Method fixed

Lighting and calibration advice and the surface tension guide
Video call with Dr Alidad Amirfazli arranged for 2 July

2020 to 2021: First values published

PhD dissertation (2020) reports 3 mN/m measured with the Dropometer
3 mN/m published in Soft Matter on 21 January 2021

2023 to 2024: Update and second paper

Free software update with the new interface in March 2023
About 10 mN/m for octane reported in Soft Matter with Yale, September 2024

Training & SOP updates

No formal training session. The method came from Droplet Lab's surface tension guide, email replies in 2020 and a video call arranged with Dr Amirfazli.

Data capture

The phone records the drop image and fits the drop profile, with the fitted contour drawn over the image so it can be checked against the edge.

Calibration

Calibrate in the app with the needle actually in use; the default value holds only for the supplied needle.

Support Model

Email support with access to drop shape experts, a video call when email stalls, and free software updates.

Proof and validation: what the papers report, and what they leave out

Test method

Pendant drop interfacial tension on a Dropometer. 2021: TPM oil (3-(trimethoxysilyl)propyl methacrylate) and an aqueous phase; the emulsions were stabilised with 0.5 wt% Synperonic F108 and 5 mM NaCl. 2024: octane (0.703 g/mL) and water (0.997 g/mL) with 0.5% Tween 20.

Sample size and operators

Not reported in either paper. The first measurements in 2020 were made by a PhD student.

Repeatability / reproducibility

Not reported. The 2021 paper states that 3 mN/m is consistent with previous work. The 2024 paper gives the value to one significant figure.

Notes / assumptions

Each paper reports one interfacial tension value, and the 2020 thesis gives the same 3 mN/m; rheology, microscopy and simulation make up the rest of each study. In the 2024 paper the measured value places the experiments on a dimensionless surface tension scale; the simulations were fitted separately. Drop volume, temperature, number of drops and standard deviation are not reported. Droplet Lab gave method support only and took no part in the measurements.

Our contact angle and pendant-drop surface tension methods have been benchmarked against KRÜSS DSA100E reference measurements.

See scientific validation

Our instruments are referenced in peer-reviewed journals, theses, and conference publications.

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Outcomes to date

Measured Outcomes

3 mN/m

TPM oil and water

Set the scale of droplet deformation energy, which the authors compared with thermal energy to tell glass from jamming behaviour (Cao, Liao, Breedveld and Weeks, Soft Matter, 2021).

About 10 mN/m

Octane and water, 0.5% Tween 20

Placed droplet flow experiments on a dimensionless surface tension scale for comparison with simulations (Cheng et al., Soft Matter, 2024).

4

Emulsions on common axes

Yield stress of four TPM emulsions divided by the measured tension and compared with two earlier studies that used other oils (Cao, Liao, Breedveld and Weeks, Soft Matter, 2021, Fig. 5b).

Operational Outcomes

Method that survived a lab closure

Measurements resumed after the three month closure, and the first value was published in January 2021.

A user willing to be a reference

In August 2020 the PhD student who ran the first measurements agreed to speak with another university considering the instrument.

Published output

Two Soft Matter papers and one PhD thesis credit Droplet Lab's instrument by name.

What the lab said

The image quality is great and all experiments went smoothly.

PhD researcher - Physics

PhD researcher, Department of Physics, Emory University

What's next

Delivered

Interfacial tension in Soft Matter (2021) and Soft Matter with Yale (2024)

PhD dissertation, Glassy and Jammed Systems: Structures and Dynamics (2020)

Free software update with the new interface (March 2023)

In Pilot

Raw drop images behind both papers invited into Droplet Lab's open interfacial tension dataset (October 2026)

How do you measure interfacial tension when the oil is lighter than water?

Make the heavier liquid the drop so it hangs from the needle. When the lab injected a lighter oil into water, the drop climbed the needle and the fitted contour missed the edge. Backlight the drop as a silhouette and calibrate with the needle in use.

What interfacial tensions did the lab publish?

The group reported 3 mN/m for TPM oil and water in Soft Matter in 2021, and about 10 mN/m for octane in water in a 2024 Soft Matter paper with Yale. The 2020 PhD thesis reports the same 3 mN/m value.

Which configuration did the lab use?

A manual Dropometer with the surface tension module for pendant drop analysis.

Next Step

Is your oil lighter than water?

Oils lighter than water are the hard case for pendant drop measurement. Droplet Lab's advice to the Weeks lab was to make the heavier liquid the drop, light a clean silhouette and calibrate with the needle in use. The Dropometer's drop shape method is validated against a KRÜSS DSA100E in peer review, and setup takes about 2 minutes. Book a 15-minute consult about your liquids and their densities.

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