Measuring contact angle of powder with hydrophilic surface by optical contact angle meter
Contact angle meter for measurement of contact angle of powder and its bouncing drop.
Measuring contact angle of powder or a bunch of fibers is always a difficult mission for the experimenter. Some experimenters suggested to use Washburn method or modified Washburn method to measure the adsorbing time of water adsorbed into the powder or a bunch of fibers using the analytical balance. But as you may know that the updated speed of balance usually is 10 data/s for Sartorius’s or 46-92 data/s for METTLER TOLEDO’s. And if you want to get the value of contact angle, you must have a probe liquid which has zero contact angle with the powder or fiber. So usually, the result you get from the weigh or force method is just the adsorbing time of different sample, not the real value of contact angle. And more important thing is the result from the Washburn method rarely has the comparability with optical contact angle method.
The main challenge of measurement of contact angle of powder and a bunch of fibers is:
1), capillary phenomenon and its effect to the result of contact angle,
2), chemical diversity of the powder or fiber itself,
3), nanostructure of the powder or fiber.
4), capillary phenomenon and interval between the powders or fibers, the enlarged nanostructure and its effect.
Some experimenters use tablet machine for infrared spectrometer to compress the powders or fibers into a tablet and then measuring contact angle of powder tablet or fiber tablet. But these efforts will lead to the possibility of Invalid nanostructure effect for super-hydrophobic surface or ball structure of powder which is very useful for the application.
The most workable solution from the suggestion of KINO is
1), Measuring the contact angle powder or a bunch of fiber without compressing them,
2), Flatting the sample of powder or keeping the surface of fibers flat by a holder,
3), Measuring contact angle of powder or fiber with high speed camera faster than 400FPS. Please be noted that this speed is much faster than the analytical balance. And camera has no time delay.
In this article, we measured four different samples of powder by the optical contact angle meter with high speed camera.
Initial contact Angle
1, sample 2
Drop is adsorbed into the power very fast.
Drop bounced at the surface and it has a high initial contact angle (136 degree)
Drop cannot bounce at the surface due to its lower initial contact angle (101 degree)
Drop is adsorbed into the power fast due to the lower initial contact angle (47.1 degree)