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11.1
Instrument storage
The liquid system (dispenser, tubing and liquid container) should never be
left with a liquid for a long time as this may clog the system. The procedures
below are recommended when your PGX+ is to be stored for some time or
shipped to another location.
When using the PGX+ with liquids other than water (e.g. solvents, inks) it is
necessary to clean the liquid system after the test has been finished. If the
instrument will be stored for some time it is also recommended to empty the
liquid system in the following way:
a)
Release the pump lid screw to access the pump tubing
b)
Lift out the liquid container, remove the plug and the empty
container
c)
Blow liquid container dry with air
d)
Connect syringe with the RED tip to the dispensing tip and pump
air through the tubing until dry
e)
Push the plug back into liquid container top and re-install the
container
f )
Put the pump tubing in position
g)
Re-install the pump lid and secure the pump lid screw gently
NOTE:
DO NOT tighten the pump lid screw completely when stored!
11.2
Transportation
Before shipping, the instrument should be prepared as described in above
section.
Please note it is important to empty even a water-based system completely if
shipping might include airfreight at high altitude as this might cause freezing
damages.
Always ship the instrument in a complete case with all instrument
accessories.
Make sure the case is shipped in sufficient padding to avoid damaging the
instrument case and its contents.
11 MISCELLANEOUS
11.3
Droplets
11.3.1 Recommended droplet sizes
The default droplet size is 4,0 µl, which has been used as the recommended
size in contact angle testing for historical reasons. In general the contact
angle is not affected by the droplet size as long as the droplet is not affected
by the gravity. For water (having a high surface tension) the contact angle
will be stable as long as the full droplet remains in view.
The droplet size may still have an input on the reading, as a bigger droplet
will cover a larger test area and might easier pick up contaminants on an
inhomogeneous test surface.
For absorbent surfaces it might be easier to track the penetration of liquid
into the substrate if a slightly bigger droplet is used for the test. On the other
hand, a bigger droplet may spread outside the field of view or cause the test
surface to warp leading to erroneous test results.
If the specimen warps when the liquid droplet is applied, it might be
necessary to attach the specimen strip to a flat surface with a suitable
adhesive.
11.3.2 Detection of the droplet in Dynamic Mode
The distance between the pendant droplet and the specimen surface is
necessary for the droplet to form and release from the dispensing tip before
the droplet touches the surface.
The impact on the contact angle from a falling droplet of 4.0 µl is very small.
This can be verified if a solid, non-absorbent surface is tested for the static
contact angle with 6-8 droplets. When the same specimen is tested with the
dynamic approach the contact angles should match the average result from
the static test.
Smaller droplets will require a bigger falling distance to release from the
dispensing tip.
A droplet of 2.0 µl falling from a two-mm distance will still give the same
contact angle reading.
Bigger droplets will give lower contact angles for bigger falling distances.
This principle can be used to determine the “receding “ contact angle
describing the de-wetting properties of a surface.
