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: Frothy
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)
““To dine!” she shrieked in dragon-wrath.
“To swallow wines all foam and froth!
To simper at a table-cloth!”
Say, can thy noble spirit stoop
To join the gormandising troop
Who find solace in the soup?”
—Lewis Carroll [Charles Lutwidge Dodgson] (1832–1898)
“The message you give your children when you discipline with love is “I care too much about you to let you misbehave. I care enough about you that I’m willing to spend time and effort to help you learn what is appropriate.” All children need the security and stability of food, shelter, love, and protection, but unless they also receive effective and appropriate discipline, they won’t feel secure.”
—Stephanie Marston (20th century)