Experiments - Hydrophobic properties of silicone fluids/Variant B

1. Experiment is contained in the WACKER's Experimental Kit.	Yes
2. Experimental procedure has been modified	Yes, additions
3. A separate experimental procedure has been devised	No
4. Video clip available	Yes ( as wmv or as mov)
5. Flash animation available	Yes
6. Other materials: Worksheet 2, Worksheet 9, Slide DH5

Hydrophobic Properties of Silicone Fluids/Variant B

1 Materials, Chemicals, Time Needed

Dropping pipet

Various clean surfaces (e.g. glass, ceramic, metal, paper, paper tissues, cotton fabric)
Silicone fluids from the WACKER schoools experiments kit or products from the experiments "Hydrolysis of chloromethylsilanes" and "Rate of hydrolysis of chloromethylsilanes"

Each sample takes less than 5 minutes.

2 Procedure and Observations

Uniformly coat part of the various surfaces with silicone fluid. Apply a drop of water to both the siliconized and the untreated surfaces.


	The water droplets on the siliconized surfaces are comparatively spherical and do not run off. When viewed on smooth surfaces from the side, they are much taller. They are slowly absorbed by paper tissues and cotton fabric.

In contrast, the water drops on the untreated surfaces run off more extensively and also adhere better to them. Cotton fabric and paper tissues absorb the water droplets immediately.

3 Discussion of Results

The experiment reveals a marked increase in contact angle for non-absorbent smooth surfaces. The contact angle, θ, is a measure of a substance’s water repellency and is illustrated in the adjacent diagram.

The molecules of the silicone fluid spontaneously align themselves on the surface such that the methyl groups stick out from the surface. They create the water-repellent effect. In the diagram below, the methyl groups are represented by R.

The diagram is taken from the WACKER WERK + WIRKEN magazine quoted in the References.

4 Tips and Comments

The silicone fluid can be baked into glass and then rubbed off with a paper towel so that the coating is almost invisible. Even then, the water-repellent effect can still be observed. Baking can be done by dry heating the silicone-treated glass at over 100 °C for 10 to 15 minutes.
For more information on water-repellent or hydrophobic properties, see also "Variant A" of this experiment and the experiment "Siliconized filter paper."
This experiment and the ones mentioned above are safe and may be performed without reservation by the pupils. They are suitable for demonstrating the relationship between particle structure and material properties. This CD and the references listed below contain substantial amounts of information that may be used in chemistry lessons.

5 Supplementary Information

See also 5 Supplementary Information on Variant A of this experiment.

6 References

M. Tausch, M. von Wachtendonk (editors), CHEMIE S II, STOFF-FORMEL-UMWELT, C.C. Buchner, Bamberg (1993), (1998)
M. Tausch, M. von Wachtendonk (editors), STOFF-CHEMIE S I, FORMEL-UMWELT, C.C. Buchner, Bamberg (1996), (1997)
M. Tausch, M. von Wachtendonk (editors), CHEMIE 2000+, C.C. Buchner, Bamberg (2001)
WACKER Werk+Wirken, Zeitschrift der Wacker Chemie AG, München, 48 (6), 22 (1997)