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Fascinating Silicone™ Chemistry Corner – Foam Stabilizers

How silicone foam stabilizers work

Sometimes foam is a good thing. Polyurethane foams, for example, are formed by allowing a liquid mixture containing a large amount of a polyol to react, while a blowing agent generates the foam cells.

Stabilizing the foam requires the use of a surface active agent, which orients itself on the cell walls in a precise manner and causes them to thin. Many organic surfactants have a surface tension that is higher than 32 mN/m, the surface tension of the polyol in the foam mixture. Consequently, they are not able to stabilize polyurethane foam.

Silicone polyethers have such low surface tension, they can potentially lower the surface tension of the foam another 10 mN/m! This makes them ideal surfactants for use not only in polyurethane foam but also in other applications where the creation of stable foams is desired.

Silicone surfactants help stabilize foams two ways: by thinning the cell walls and by promoting the creation of large numbers of small vs. large bubbles.

The Marangioni effect on cell stabilization

  • Fluid flows from low surface tension to high.
  • Liquid flow pushes the fluid back to stabilize the thinned wall.

Polyurethane foam made without silicone surfactant has a coarse, irregular appearance.Polyurethane foam made with silicone surfactant is finer, and more consistent.
  
Foam Without Silicone SurfactantFoam With Silicone Surfactant

Anatomy of a Silicone Polyether Surfactant

The silicone polyether surfactant acts at the interfaces of the formulation components. Its backbone aligns with hydrophobic/nonpolar materials, while its pendant polyether groups can be designed to be soluble in different polar components of the system.

A silicone polyether has a siloxane backbone to which pendant polyether groups are attached.

Silicone benefits for foam stabilization

Silicone surfactants:

  • Improve the compatibility of formulation ingredients
  • Help disperse inlet gas
  • Prevent bubbles from coalescing
  • Stabilize the bubbles

Typical foam stabilization applications

  • Flexible foams for furniture cushions, subway train seats, auto dashboards, and packaging
  • Rigid foams for insulation and construction applications
  • Personal care products, such as shaving creams, shampoos, and foaming hand cleansers
  • Fire-fighting foams
  • Carpet cleaners

Learn how other types of silicones work.

Did you know ... silicones not only stabilize foam. They can also destroy it! Learn how silicone defoamers work.

Expand your understanding

Learn about:
Silicones for Manufacturing

Easy reading:
Safer subway seats ... all aboard!

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