DGMFG Optical Contact Angle Meter Goniometer

This tool allow you to measure the surface energy or wetting/adhesion of solids. 

Bill of Materials

• 40-1000x USB Microscope (Required)
• Rechargeable LED Light Panel (Required)
• .5-10μl Micro Pipette (Required)
• 10μl Micro Pipette Tips (Required)
• Lab Grade Deionized Water (Optional)
• Gorilla Glue Superglue (Optional)
• Zip Ties (Required)

This assumes you are using drops ranging up to 10 micro-liters. Otherwise you'll have to adjust the pipette setup.

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Printing Notes

The design is fairly simple to print with PLA+ or similar. You may need supports for a few items depending on choice of orientation. You don't need a ton of infill unless supporting heavy items. You will need to print some of the models multiple times. If using small samples you can use the small sample plate instead of the large puzzle piece looking one. You won't need as long of a track then.

Assembly Notes

Assembly is very straight forward. Everything either screws together with jam nuts or comes together in a friction fit. The microscope should be held in place with zip ties so you have a lot of friction to align it. I do recommend superglue on the friction fit components if you don't intend to disassemble. 

Using The Goniometer

This device was meant to be easy to use. If you've used an optical contact meter before it should be fairly simple. You can also take a look at my video where I use it:

General instructions are as follows:

1. Setup the instrument on a level surface.
2. Place sample substrate on sample plate (small or large).
3. Plugin microscope into laptop, android phone, or workstation.
4. Turn on background light.
5. Insert micro pipette into its holder and align over sample closer to the edge.
6. Adjust microscope to desired alignment with substrate so you have a good profile view. Note that microscopes are focused by moving them backwards/forwards not by adjusting the zoom level. Many people on amazon are leaving negative reviews because they're using it wrong.
7. Adjust the micro pipette holder height until its tip comes into view of the microscope from the top.
8. Drip calibration drop on the substrate with the micro pipette. I found 3 micro-liter and larger droplets fall reliably.
9. Adjust microscope focus, pipette height and ambient light as needed to have an optimal view. I recommend very low settings for the light, as low as 1% depending on ambient lighting. Somewhat dim ambient lighting helps, but it doesn't have to be pitch dark in the room.
10. Move substrate on the plate slightly so you have a fresh test spot.
11. Ensure you can still see the pipette tip and drip a new drop on the fresh test spot.
12. Quickly adjust focus and take a snapshot before any of the water evaporates.
13. Repeat steps 10 through 12 to get more sample shots so you can average results.

Calculating Drop Angles

You can use ImageJ software, specifically version 1.46, (i.e. ij146-jdk6-64bit-setup.exe) and the Drop Analysis Plugin to calculate angles. You should read the guide included with the plugin. I recommend running the software in Windows XP SP2 compatibility mode for the best UI and plugin performance.

1. Start ImageJ and open your image.
2. Convert the image to 8-bit black and white.
3. Launch the Drop Analysis Plugin. There are two different calculation models DropSnake and LBADSA.
4. I prefer DropSnake. I find it's best to mark the first points yourself and then refine them with drop snake buttons in the UI rather than letting the software figure out the first points.
5. The UI is a bit oldschool so give yourself some time to work it how the plugin works.
6. The LBADSA method is easier to understand, but it takes longer to process each sample, DropSnake is faster once you figure it out.