Foaming and Foam Stability
Several conditions are needed to produce foam: there must be mechanical work, surface active components (surfactants) that reduce the surface tension, and the formation of foam faster than its breakdown. To create foam, work (W) is needed to increase the surface area (ΔA):
where γ is the surface tension.
Stabilisation of foam is caused by van der Waals forces between the molecules in the foam, electrical double layers created by dipolar surfactants, and the Marangoni effect, which acts as a restoring force to the lamellas.
Several destabilising effects can break foam down. (i) Gravitation causes drainage of liquid to the foam base, (ii)osmotic pressure causes drainage from the lamellas to the Plateau borders due to internal concentration differences in the foam, while (iii)Laplace pressure causes diffusion of gas from small to large bubbles due to pressure difference. Films can break under disjoining pressure, These effects can lead to rearrangement of the foam structure at scales larger than the bubbles, which may be individual (T1 process) or collective (even of the "avalanche" type).
Read more about this topic: Froth
Famous quotes containing the words foaming, foam and/or stability:
“Thanks to the morning light,
Thanks to the foaming sea,
To the uplands of New Hampshire,
To the green-haired forest free.”
—Ralph Waldo Emerson (1803–1882)
“And his wish is intimacy,
Intimater intimacy,
And a stricter privacy;
The impossible shall yet be done,
And, being two, shall still be one.
As the wave breaks to foam on shelves,
Then runs into a wave again,
So lovers melt their sundered selves,
Yet melted would be twain.”
—Ralph Waldo Emerson (1803–1882)
“Every nation ... whose affairs betray a want of wisdom and stability may calculate on every loss which can be sustained from the more systematic policy of its wiser neighbors.”
—James Madison (1751–1836)