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8.7
Manual testing in static and dynamic mode
In some special situations, it might be necessary to make a manual
determination of the droplet.
One example is when the captured droplet image is too bright and therefore
does not have a solid contour resulting in a “zero result”.
Another example is when the droplet base is hidden against a too dark
surface and the base line is then incorrectly set. In these situations the
captured image sequence can still be used for a semi-automatic or manual
approach described later in this section.
Double-click on a data point in the diagram or a line in the Results Window
to bring up the corresponding image as shown in Figure 9.9.
8.7.1 Adjust the image contrast
Double-click the image to select binary mode and slide the handle Gain
offset up or down to make the binary image brighter or darker. Try to find
a position where the contour is continuous and the base of the droplet
separated from the background. This will activate the button Save, with its
light indicator. Right-click on this button to assign a new mode (Fig 9.8). If the
button already has the appropriate selection (e.g. “All images”), simply click
the button to change the contrast settings for selected images. These images
will then be recalculated using the new gain setting. Use the slider below the
image to step between images and check the results.
If a suitable contrast setting cannot be found using the Gain offset control, it
will be necessary to use the Enhance function.. (see section 8.9.1
8.7.2 Adjust the position of an incorrect baseline
When the automatic base line is set incorrectly, pick up the base line handle
(BL) in Figure 9.9 with the mouse and slide it to the correct position. This
will activate the button Save data with its light indicator. Right-click on the
button to assign a new mode. If the button already has the appropriate
mode (e.g. “All images”), simply click the button to move the base line for
selected images. These images will then be recalculated with the new base
line setting.
8.7.3 Exclude fragments above droplet
When the automatic analysis picks up fragments of the dispensing tip,
slide the top line handle (TL) below the fragments that could disturb the
measurement. This will activate the button Save data and the changed
setting will update all images in the measurement. The new top line setting
will also update the region setting of the corresponding test button on the
Image Control Panel.
8.7.4 Make a manual measurement
Select the greyscale view and click the button Manual to open the zoom
window (Figure 9.10).
Click with the cursor at the contact point between the droplet base and the
test surface.
Click again at the contact point on the opposite side and once at the top of
the droplet.
The manual results will now appear in the top left-hand corner of the
image together with the original data. To save the manual results instead of
the original results, click on “Save data”, which will also store the manually
selected points superimposed in the image. To select three new points along
the contour, click on “Reset”. To close the Zoom window, click on “Close”.
Save Image stores a copy of the image with the manual results
superimposed.
Use the slider below the image to shift to another image.
8.8
Surface ‘free’ energy (SFE)
As this surface property cannot be measured directly; it is calculated from
contact angle measurements using different, properly characterized liquids.
Depending on the substrate, one or more liquids are used. Please note SFE
calculations are subject to the following constraints:
•
No penetration of test liquid into surface (check that volume
remains constant over time)
•
No chemical reaction between test liquid and surface (check con-
tact angle is constant over time)
•
Surface must by sufficiently smooth
Here the operator starts by selecting a Calculation Model from the following
options:
•
ASTM D5946
•
Polar/Dispersive
•
Acid/Base
The first option, ASTM D5946 is the “Standard Test Method for Corona-Treated
Polymer Films using Water Contact Angle Measurements” (copyright ASTM
International) where the water contact angle is converted into a dyne value.
For this option only the topmost liquid field (Water) is activated and used for
the SFE calculations.
The second option ‘Polar/Dispersive’ uses contact angle readings from two
selected test liquids to determine the SFE of a substrate. Here the two first
liquid fields (Water and DIM) are activated.
For these calculations, the Harmonic approach (Wu) is used as the first option
as this is considered ‘more accurate’. This approach can, however, end up in
negative roots, so there is not always a solution to these equations. In this
situation the program changes to the Geometric approach (Owens-Wendt),
which always gives a solution. The SFE report indicates which method was
eventually used (Harmonic or Geometric) for the calculation. It is possible to
force the Geometric method if the parameter SFEMETHOD is changed from
H to G (see section 11).
The third option ‘Acid/Base’ (Lewis) uses three liquids to calculate the surface
energy from an equation system. Here all three liquid fields are activated
(Water, DIM and Formamide).
Please note the calculated results depend on the liquid combination used.
To select an input data file, use the associated Browse button.
For Water, the browse button will present files with a wgs extension only as
these should contain results from water contact angles. In a similar way the
other two browse buttons (if active) can be used to select other result files
measured with DIM or Formamide. As soon as the result file for Water has
been selected, the first part of the file name is used for the field ‘Sample ID’
(e.g. 45901).
The program will automatically search for associated result fields. The
condition is, however, that all files must use the same ID as a file name (e.g.
45901.wgs and 45901.dgs). The operator can still overwrite information
displayed in the contact angle fields, in which case the Sample ID window
will be erased. As soon as the input fields (one, two or three) have been
completed, the program will automatically calculate the SFE results. When
manual data is typed into the input fields, it is necessary to click on ‘Calculate’
to determine the SFE values. The SFE results are displayed in the Results
Window at the bottom of the screen.
The Save button will store a copy of the report in the default directory (e.g.
\fibro\pg) with the extension sfe (e.g. 45901.sfe). When the file has been
stored the ‘Save’ button becomes inactive until a new result is calculated.
