Gardco PG-1 Manual do utilizador - Página 13

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e)
Push the spring-loaded dispenser downwards until the droplet gently contacts the
specimen surface. Try to obtain a contact angle as high as possible.
f)
Upon contact the droplet is usually "released" from the dispensing tip, in which case you
continue to take a reading. When the droplet is "trapped" and not releasing from the
dispensing tip, lift the manual dispenser to release the droplet (Section 2.4).
g)
Take a reading avoiding the parallax error (Section 2.6).

4.2 Dynamic Surface Hysteresis

This approach is valid for smooth, solid surfaces where the test liquid does not penetrate into
the substrate. For liquids with high viscosity (e.g. glycerine) the contact angle reading is taken
when the liquid droplet is not spreading any further (at "equilibrium" conditions).
PLEASE NOTE! The approach described below is commonly used in the industry.
Extreme care must be taken as contaminants on the specimen surface may change the
properties of the probing test liquid leading to erroneous test data.
4.2.1 Common procedure ("Reverse flow")
a)
Cut a specimen (Section 5) and install it on the specimen stage (Section 2.2).
The specimen surface should be viewed slightly from above.
b)
Fill the manual dispenser with the preferred test liquid (Section 2.3).
c)
Insert the manual dispenser into the dispensing bridge.
d)
Pump out a droplet big enough to make contact with the specimen surface. Increase the
droplet volume while the dispensing tip is still inside the droplet. The droplet should not
spread outside the field of view and the purpose is to capture a situation where the
contact angle is "the highest" as it advances across the specimen surface.
h)
Use the protractor disk to take a reading (Section 2.6.1) from the "advancing" contact
angle, which describes the wetting of a dry specimen surface.
i)
Turn the wheel for volume setting in a clock-wise direction (seen from above) to reverse
the flow of liquid while the dispensing tip is kept inside the droplet. As the droplet
recedes, a lower contact angle will appear. The purpose is now to capture a situation
where the contact angle is "the lowest".
j)
Use the protractor disk to take a reading (Section 2.6.1) from this "receding" contact
angle, which describes the de-wetting of a wet specimen surface.
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