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.
Then you may have some amazing phenomenon that you have never found as shown below.
1, Measuring contact angle of hydrophilic surface of powder with high speed camera with speed 420FPS:
The sample of power has a large initial contact angle of larger than 120° due to the enlarged nanostructure and its effect. According to the Wenzel-Cassie model, the contact angle of this sample will tent to has a hydrophobic surface. So, the drop of water bounced from the surface of powder and then be adsorbed into the sample due to the surface tension, gravity. You can also have a new and different conclusion that sample with contact angle smaller than 120°can also bounce from the sample surface is the structure of sample is good enough for bouncing drop. The spring structure of the enlarged nanostructure of powder bounced the water drop due to the contact force.
2, Measuring contact angle of hydrophilic surface of powder with high speed camera with speed 420FPS
The drop of water adsorbed into the powder very fast and didn’t bounce from the powder surface due to the lower initial contact angle. The force of spring structure is smaller than the net force of surface tension, gravity.
3, Measuring contact angle of powder with super-hydrophobic surface with high speed camera.
The contact angle of powder surface is larger than 140° and it has a super-hydrophobic surface. In contrast with the drop bouncing from the lotus leaf with super-hydrophobic surface, the drop of water bounced more times (7 times) than the bouncing of the lotus leaf (5 times). The main factor is the effect of the spring structure of the enlarged nanostructure between the interval of powders. So, the effect factors of the drop bouncing are not just hydrophobic or hydrophilic surface, it also includes the effect of the nanostructure such as lotus leaf and enlarged structure such as powder and fiber.
4, Measuring contact angle of powder with density lower than water.
Sample of powder with lower density is really a big challenge for measurement of contact angle. And the same thing will also be happened for the Washburn method. Water will not be adsorbed into the powder by the Washburn method. But if you measure contact angle with the same method as shown before, you also cannot get the acceptable result.
We have tried the MicroDrop method from KINO to measure the contact angle for this sample of powder, but we were also failure to get the acceptable result.
So, the most acceptable method is:
1), Compressing the sample into tablet with the tablet machine,
2), Measuring contact angle of tablet by immersing the sample into the water in a cuvette made of quartz glass, forming a bubble of air at the upper side of tablet and then measuring contact angle of powder tablet by the MicroDrop Method from KINO.
USA KINO is the leader at the surface chemistry instruments. We have more than 15 years at the measurement of powder and fiber and we know how to get more acceptable result of contact angle. We are the only one who have 3D contact angle meter which is more effective and has higher accuracy than others. 3D contact angle meter is special for 98% objective surfaces of solid which have asymmetric drop shape of contact angle.
Contacting us when you have questions at the measurement of contact angle, surface tension or interfacial tension.
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