How silicone foam stabilizers
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
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.
|Foam Without Silicone Surfactant||Foam 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.
Silicone benefits for foam stabilization
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
care products, such as shaving creams, shampoos, and foaming hand
other types of silicones work.