- Pour a bit of milk on the bowl;
- Add 2 drops of blue food coloring;
- Now, away from the blue, add another 2 drops of red food coloring;
- Let your restless play with the toothpicks and the milk on the bowl, let them "draw" at will, What happens?
- Now, add a drop of detergent;
The colors blend immediately, almost instantly, after we add the detergent
When we add the food coloring, it just stay there, exactly where we placed it.
Then, when we introduce the detergent to the equation, the colors blend in a sec. That’s because the detergent will make the surface tension to drop, and the "milk skin", that allows the color "to sit there", will disappear.
As we saw here, this skin works as a coat that maintains other molecules at surface, and therefore preventing its dissolution n the milk. When his surface tension is disturbed, the food coloring (and other milk molecules) find less resistance and therefore they can move all around in the bowl.
But there is another phenomena happening in the bowl: Some milk protein denaturate by the action of detergent.
Both things contribute for the surface tension changes.
See the video:
A ocean of colors!