A colloidal dispersion, or simply colloid, is a mixture that has the particles of the disperse with a size between 1 and 1000 nm.
As colloidal dispersions are very present in our daily lives and there is great diversity, they are classified according to the physical state (solid, liquid and gaseous) of the dispersant and the scattered. Thus, there are nine types of colloids. However, for the moment we'll talk a little more about just one type of colloid: the foam.
Foam is a mixture made between a solid or liquid dispersant and a dispersed in a gaseous state.
For example, when a gas is bubbled into a liquid, we notice huge bubbles forming; some with colloidal dimensions. One such example is whipped cream, which is made by beating fresh cream. This means that air (dispersed gas) was mixed with a liquid (milk cream), forming a foam.
Soap scum, snow white and firefighting foam are also examples of liquid foams.
As for solids with pores of colloidal dimensions, we have solid foams. This is the case, for example, with pumice stones, styrofoam, charcoal, soft marie, styrofoam and polyurethane (foam often used in mattresses, shoes, car seats, etc.). In all the cases mentioned, the disperse that forms the pores is air.
By Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/espuma-um-tipo-dispersao-coloidal.htm