I've measured contact angle with a commercial instrument and also with the following method. Place your sample on a flat surface with a piece of white paper ~ 1 ft. behind it. Take a camera and place it so you are at eye level with the air/sample interface. After you have gotten where you will place a droplet of water in focus and the camera ready for a picture, place a drop of water (~ 0.1-1 mL) on your sample with a syringe. Then quickly take a few pictures. This should be easier to do if your sample is hydrophobic. Use an image analysis software to measure the angle between the sample/water interface and the edge of the water droplet/air interface (should be less than 90 deg.). I use ImageJ software, which is free from the U.S. NIH and available online.
I've measured contact angle with a commercial instrument and also with the following method. Place your sample on a flat surface with a piece of white paper ~ 1 ft. behind it. Take a camera and place it so you are at eye level with the air/sample interface. After you have gotten where you will place a droplet of water in focus and the camera ready for a picture, place a drop of water (~ 0.1-1 mL) on your sample with a syringe. Then quickly take a few pictures. This should be easier to do if your sample is hydrophobic. Use an image analysis software to measure the angle between the sample/water interface and the edge of the water droplet/air interface (should be less than 90 deg.). I use ImageJ software, which is free from the U.S. NIH and available online.
The answer above is right. Find an suitable instrument for contact angle measurement. Normally it has built-in camera and angle measurement software. The surface with contact angles greater than 90° are designated as hydrophobic.But if you use chemically deposited CdS then the angle might vary with grain size and post thermal treatment.
I have used a commercial contact angle measurement instrument (Krüss, EasyDropDSA15B) for the measurement of contact angle of water droplet. I have used 1 micrometer diameter tip with 4 microleter of deionized water drop onto the sample surface.
When the contact angle is less than 5 degree, the surface is called superhydrophilic. When the contact angle is less than 90 degree but greater than 5 degree, the surface is called hydrophilic. When the contact angle is greater than 90 degree but less than 150 degree, the surface is called hydrophobic. Lastly, when the contact angle is greater than 150 degree, the surface is called superhydrophobic. In order to be superhydrophobic, the sliding angle should be under 5 degree. You can measure the sliding angle by tilting the sample.
I've used a KSV Instruments CAM200 to do this, but Kirstin's idea sounds pretty cool. Certainly a lot cheaper than buying a new instrument!
In addition to Kirstin answer, usually, the water drop is of order microleter. For accurate and more precise measurements, you can measure contact angle at several different position by putting double deionized water drop of same quantitiy by microsyringe. You can also You can take avergae of them. There may be variation in the thickness of the films and grain size which can affect the measurement.
Once you have measured at one position, you cna again measure there by blowing nitrogen or by heating if you have any doubt there.
- Badges
- Science topic