# How can I measure a droplets contact angle without a setup?

I have to use a phone camera to replicate the Sessile drop analyzer, but there doesn't seem to be a standard to different parameters, such as how far away should my camera be from the droplet or how much liquid should I use for my droplets? Is it possible to get accurate results this way, and how should I go about it?

• Quick search unveiled this video tutorial which, I guess, uses Bikerman method. The tricky part might be getting the lens attachment, you might need a donor device to harvest the lens from, e.g. a webcam or an old microscope. Probably a magnifying glass will do too. – andselisk Jul 4 '17 at 12:34

In 2010, Borguet et al. published in Journal of Chemical Education, DOI: 10.1021/ed100468u an intentionally simplified setup which may be useful as a reference. A Sony Cybershot camera was placed in front of a sample scrutinized under diffuse illumination:

The additional lens shown is focussed on the drop (both for water and $n$-hexadecane, the authors recommend a volume of $\pu{5 uL}$; focal length of the length used equals $\pu{50 mm}$):.

With photos recorded like this

the contact angle determination was performed with the contact angle plugin of imageJ. As Fiji, it is open source, free ware, and java based/OS portable. To quote from their publication:

For each easurement, the user must choose two points to manually define the baseline and three points along the drop profile (see the supporting information that features a set of instructions supplying all the details on the procedure used to make the measurement). The program then fits the profile of the drop and calculates the contact angle using the sphere approximation or the ellipse approximation. In our study, the ellipse approximation gave consistent results for contact angles $> 40^\circ{}$. For drops with contact angles $< 40^\circ{}$, the sphere approximation was used.

In comparison with reference data, the authors judge contact angles recorded as well as the subsequently calculated surface tensions as good enough for instruction / lab classes and research lab.