Goal: Develop low-cost, high-throughput, automatable measurements of surface tension, which can inform knowledge of a variety of physical chemistry processes (micelle formation, etc.)…

Drop tensiometry

Physical principle: Determine shape and size of droplet as a function of surface tension

Automation? Camera + computer vision to watch droplet size with a diffuse light background. OpenDrop software exists for this. Use a syringe with blunt needle to dispense the droplets (to be fancy, maybe you want some liquid nearby to saturate humidity)

Limitation: You want to use a wide blunt needle (on a luer lock syringe) of known diameter for dispensing the droplets. Maybe you want to use a washing station of some kind? Or maybe you just don’t overthink it too much—–the Huck paper SI looks like they just jam one of these blunt needles on an OT-2, don’t aspirate too much volume, and then just eject it.

Precedent: Widely used method. Precedent for automation is work by Huck & Robinson & co. npj Comput Mater 2025 (done on OT-2 for mixture prep and measurement although they don’t address washing issue)

Capillary rise

Physical principle: Measure the height of a column of liquid.

Automation? Use a camera + computer vision to look at the rise (need a side angle) Use disposable precision capillary tubes for each measurement. Avoids need for cleaning (just dispose of tube). Needs clear, level side view of solution.

Limitation: Requires knowledge of the solution density.

Precedent: Huck-Iriart et al. J Chem Educ 2016 — USB microscope camera with manual image analysis

Drop Weight

Physical principle: Surface tension keeps drops from falling until they get big. Determine mass of the drops.

Automation? Use a drop counter or camera + computer vision to count drops. Use an analytical balance to measure a collection of 20 drops in a batch. In principle this could be on the robot deck (e.g., Mettler Toledo WMS or WXS series) or some other type of rig (e.g., Kedar’s placement of a MT balance under an OT-2)

Limitation: Empirical correction factor to account for the full mass of a pendant drop not being detached from the dispenser. Need analytical balance (0.1 mg) on robot, and these are pricey (3-5k USD used?)

Precedent: Gascon et al J. Chem. Educ 2019 — used manual disposable plastic pipettes + 20 drops + analytical balance (0.1 mg)

Capillary waves

Physical principle: Energy to excite waves on a surface depends on the surface tension. Measure the waves

How? Immerse an exciter needle (virbating at acoustic frequencies) into the liquid (Eur. J. Phys 2012)[https://dx.doi.org/10.1088/0143-0807/33/6/1677] or use a smart phone vibrator motor to shake a paper cup

Automation? Exciter needle approach would require cleaning. CapCam is non-contact: Place iPhone on cup to perform excitation at 144.5 Hz, and use light + camera to look at trough patterns, with computer vision to determine wavelength.

Limitation: Requires large volume of liquid (typical wavelength is order of 3 mm, paper-cup sized volume)