Department of Applied Physics

Oscillating Droplet Tribometer. The most accurate characterization of your superhydrophobic surface.

We provide Oscillating Droplet Tribometry as a service to characterize also your surface. In addition, we offer comprehensive wetting characterization, including advancing contact angle, receding contact angle and sliding angle.

Interested? Please contact us at [email protected]
A ferrofluid droplet sitting on a measurement surface in the oscillating droplet tribometer measurement scheme. The magnet underneath the surface is also seen.
Oscillating droplet tribometry is a surface characterization method that uses a magnetic water droplet as a probe to measure superhydrophobicity. Aalto University / Jaakko V.I. Timonen & Mika Latikka

The problem

Superhydrophobic surfaces are challenging to characterize by contact angle goniometry [1]. When contact angles are larger than 150°, the error in contact angle measurement grows steeply to 10° or more. Still, there is a growing need for the accurate measurement of such surfaces. 

Our solution

Prof. Robin Ras and his team developed the Oscillating Droplet Tribometer to measure the friction force between droplet and superhydrophobic surface with accuracy as small as 10 nN. The measurement principle is based on the back-and-forth oscillation of a magnetic water droplet and was published in Nature Communications[2]. The magnetic water droplet has the same surface tension as pure water. Below is an example and a video of the measurement. 

[1] Liu K., Vuckovac M., Latikka M., Huhtamäki T., Ras R.H.A., Improving surface-wetting characterization, Science 363, 1147−1148 (2019). (link) (press release); [2] Timonen J.V.I., Latikka M., Ikkala O., Ras R.H.A., Free-Decay and Resonant Methods for Investigating the Fundamental Limit of Superhydrophobicity, Nature Communications 4, 2398 (2013). (link)

 

Example measurement

The figure shows plots of Oscillating Droplet Tribometer data captured on two commercial superhydrophobic coatings with both having contact angles in the order of 170 degrees. Data is in the shape of gradually decaying harmonic oscillation. Analysis reveals that the technique can clearly distinguish between the two surfaces by contact angle hysteresis force.
Measurement of two commercial superhydrophobic coatings with nearly equal contact angles close to 170°. The surfaces show clearly different droplet oscillations. Aalto University / Heikki Nurmi

The figure above shows Oscillating Droplet Tribometer measurements on two commercial superhydrophobic coatings that have water contact angles close to 170°. Analysis of the decaying oscillations shows large contrast in the contact angle hysteresis force (FCAH), demonstrating that the technique can clearly distinguish small variations of wettability on repellent surfaces.

Visit also the website of Prof. Robin Ras' research group.

Interested in Oscillating Droplet Tribometry for your surfaces?

Please contact us at [email protected]

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