Co-surfactant
- Also known as
- cosurfactant
A co-surfactant is a secondary surface-active ingredient used alongside a primary surfactant to improve how the formulation performs, for example by lowering interfacial tension further, stabilizing a microemulsion, boosting wetting or foam, or making the system milder.
What is a co-surfactant?
Most formulated products contain more than one surfactant. The primary surfactant does most of the work; a co-surfactant is added in a smaller amount to improve the result. The co-surfactant may itself be a surfactant, or, in some systems such as microemulsions, a short- or medium-chain alcohol that has weak surface activity on its own.
What co-surfactants do
- Synergy at interfaces. Mixtures of different surfactants often pack more efficiently at an interface than either does alone, lowering surface tension or interfacial tension further and reducing the critical micelle concentration of the mixture.
- Microemulsion formation. In microemulsions, a co-surfactant makes the surfactant film more flexible, which helps the system form spontaneously and remain stable.
- Performance tuning. Co-surfactants are used to improve wetting, boost or control foaming, improve tolerance to hard water or salt, adjust viscosity, or reduce the irritation caused by harsher primary surfactants.
- Lower total load. Because of synergy, a co-surfactant can let a formulator use less total surfactant for the same performance.
A familiar example is the combination of an anionic surfactant with an amphoteric betaine in many cleaners, where the betaine improves foam and mildness.
Choosing a co-surfactant
Formulators select co-surfactants by compatibility with the primary surfactant and the rest of the formula, by charge (ionic combinations can be strongly synergistic or can precipitate), by their effect on hydrophilic-lipophilic balance, and by regulatory and environmental requirements. Testing in the actual formulation is essential, because synergy depends on ratios and conditions.
Co-surfactants at Locus
Locus positions its Amphi glycolipid biosurfactants as co-surfactants that formulators add to existing surfactant systems, describing them as improving wetting, dispersion and stability at lower total surfactant loadings.
Frequently asked questions
The difference is role, not chemistry. The primary surfactant provides most of the surface activity; a co-surfactant is used in smaller amounts to enhance or adjust its performance.
Short- and medium-chain alcohols insert into the surfactant film between oil and water, making it more flexible and helping the microemulsion form and stay stable over a wider range of conditions.
Sources
- Surfactants and Interfacial Phenomena, 4th edition, M. J. Rosen and J. T. Kunjappu, Wiley, 2012
- microemulsion, IUPAC Compendium of Chemical Terminology (Gold Book)