attension Theta, User Manual

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Figure 3.21. Recording the images of the meniscus experiment.
3.4 Useful tips
Cleanliness: as in all surface chemistry applications cleanliness is essential for reproducible results. All
liquids should be pure and uncontaminated. Any plastic or glassware that comes into contact with liquids
should be scrupulously rinsed to remove any traces of surfactants used in cleaning. In order for the
results to be reproducible the solids that are tested must have a consistent history of events or
exposures which might affect the surface.
Lighting: The lighting system for Theta provides ideal illumination for sharp image capture. The
brightness of the image may be adjusted with the Adjust camera parameters. Note that the image need
not be a bright one to get good results, indeed in most bright lighting situations the highlights present on
the drop may detract from the ability to model the curve profile accurately.
Magnification: The quality of the image profile and curve fitting is enhanced if the image of the drop fills a
larger part of the screen. Whenever possible set the magnification so that the image of the drop is as
large as possible.
Size of drops: Ideal drop size varies with different applications. Line tension effects may cause small
drops to exhibit higher contact angles, whereas the gravity has larger influence on larger drops. Drops of
1 - 10

l are reasonable; the most important factor is the consistent use of the same volume.
Dynamic angles: Tilting cradle is utilized to measure receding and advancing contact angles (see
Chapter 4). Alternately, droplet volume may be changed dynamically to advance or recede a drop and
capture images of the drop in motion.
To measure advancing angles lower the syringe tip near the solid so that the tip remains attached to the
drop after contact with the solid. Create the advanced angle by expanding the drop with the embedded
syringe tip. Use the smallest, cleanest tip available and move the execution area (area enclosed by the
blue rectangle) to neglect the section of the drop distorted by contact with the tip.
To produce receded angles use the embedded syringe tip method described above but remove fluid
from the drop as opposed to adding fluid to it.