Capillarity and Surface Forces (Liquids) - Surface and Colloid Chemistry: Principles and Applications - page 22

Detergent

FIGure 2.9 Reflection of light waves from the outer layer and the inner layer. Interference
is caused by the difference in the path of light traveling inside the thin film.

The transmitted light, I tr , is related to the incident light, I in , and the reflected
intensity, I re :

I tr = I in − I re (2.31)

The daylight consists of different wavelengths of colors:

Red 680 nm

Orange 590 nm

Yellow 580 nm

Green 530 nm

Blue 470 nm

Violet 405 nm

Slightly thicker soap films (ca. 150 nm) sometimes look golden. In the thinning pro-
cess, the different colors get cut off. Thus, if blue color gets cut off, the film appears
amber to magenta.
The following are some recipes for soap bubble solutions:
Soap bubble solutions : In general one may use a detergent solution (1-10 g/L
detergent concentration). However, to produce stable bubbles (which means slow
evaporation rates, stability to vibration effects, etc.), some additives have been used.
A common recipe is

Detergent (dishwashing) 1-10 g/L

Glycerin Less than 10%

Water The rest

Another recipe has the following composition (Lovett, 1994):

100 g glycerine + 1.4 g triethanolamine + 2 g oleic acid