Grade: toilet read

What is foam and how is it formed?

  1. What is foam and how is it formed
  2. But does more foam = more cleanliness?

Foam occurs when pockets of gas are trapped in a solid or liquid. We see it all around us: from the foam in the waves on the beach to the foam in the beer we're about to drink, from the mattress we use for camping to the sponge we use to wash up.
The incorporation of gas occurs mainly by mechanical action, that is because we violently beat the liquid in the presence of gas. However, there are substances that, by lowering the surface tension of the liquid, can facilitate this mechanism: our beloved surfactants.

So, surfactants help form foam AND surfactants clean. No wonder that the cleaning power of a detergent has always been perceived as related to its foaming power!

In reality the connection is not so direct. I won't go into detail about the forces at play at the molecular level [1,2]. Let's just say that, while the ability to create foam has to do with how the surfactant molecules interact with the molecules on the surface of the liquid, the cleaning power is determined by how the surfactant molecules interact with the dirt molecules.

Cleaning power and foaming power are therefore not directly related and it is only our habit that makes us perceive them so.

It's a proof the fact that there is a whole class of surfactants developed because they clean very well and create very little foam: they are indicated in all those cases where having a lot of foam would be a problem, such as dishwashers.

The paradox is that, over time, consumer association has become so strong that now many brands choose the mix of surfactants so that some are there just to make foam. Crazy!

poolito says

We chose our surfactants for their cleaning power, disregarding their foaming abilities. Let's see if, now that you know how it works, you can overcome the force of habit. ☺

[1] "Surfactants and Interfacial Phenomena", Milton J. Rosen, Joy T. Kunjappu, John Wiley & Sons, Mar 6, 2012
[2] "Chemical water technology", Dmitry Yu. Murzin, Walter de Gruyter GmbH & Co KG, Apr 9, 2018