Difference between revisions of "Stability of Thin Films: Foams"

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(Summary)
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This paper examines the structures of foams, a dispersion of gas within a smaller volume of liquid. Thin films form the interfaces between the gas and liquid faces and are stabilized by surfactants.  
 
This paper examines the structures of foams, a dispersion of gas within a smaller volume of liquid. Thin films form the interfaces between the gas and liquid faces and are stabilized by surfactants.  
 +
 +
Neighboring bubble surfaces in a foam interact
 +
through a variety of forces that depend on the composition and thickness of liquid
 +
between them, and on the physical chemistry of their liquid–vapor interfaces.
 +
For a foam to be relatively stable, the net interaction must be sufficiently repulsive
 +
at short distances to maintain a significant layer of liquid in between neighboring
 +
bubbles. Otherwise two bubbles could approach so closely as to expel all
 +
the liquid and fuse into one larger bubble. Repulsive interactions typically
 +
become important only for bubble separations smaller than a few hundredths
 +
of a micrometer, a length small in comparison with typical bubble sizes. Thus
 +
attention can be restricted to the vapor–liquid–vapor film structure formed
 +
between neighboring bubbles, and this structure can be considered essentially
 +
flat.
 +
  
 
=== Disjoining Forces ===
 
=== Disjoining Forces ===

Revision as of 18:05, 12 November 2012

Entry by Grant Gonzalez, 9 Nov 2012

Foams

Keywords: Thin Films, Disjoining Forces, Foams, Surfactants

Authors: Arnaud Saint-James, Douglas J. Durian, David A. Weitz

Summary

This paper examines the structures of foams, a dispersion of gas within a smaller volume of liquid. Thin films form the interfaces between the gas and liquid faces and are stabilized by surfactants.

Neighboring bubble surfaces in a foam interact through a variety of forces that depend on the composition and thickness of liquid between them, and on the physical chemistry of their liquid–vapor interfaces. For a foam to be relatively stable, the net interaction must be sufficiently repulsive at short distances to maintain a significant layer of liquid in between neighboring bubbles. Otherwise two bubbles could approach so closely as to expel all the liquid and fuse into one larger bubble. Repulsive interactions typically become important only for bubble separations smaller than a few hundredths of a micrometer, a length small in comparison with typical bubble sizes. Thus attention can be restricted to the vapor–liquid–vapor film structure formed between neighboring bubbles, and this structure can be considered essentially flat.


Disjoining Forces

Film Thickness vs Disjoining Pressure.jpg

Possible Applications

  1. Firefighting
  2. Food
  3. Separations
  4. Oil Recovery
  5. Detergents
  6. Textiles
  7. Cosmetics

Discussion

Reference

Saint-James, A., Durian, D. J., Weitz, D. A. and Updated by Staff 2012. Foams. Kirk-Othmer Encyclopedia of Chemical Technology. 1–24.