Emulsion stability is unguestionably a very important subject to cosmetic chemists and a quick and reliable determination of the stability without a prolonged testing period is very desirable from a practical view point. Toward such a goal, many workers have investigated and published various methods of stability measurement.
Emulsion is a very complex system and its stability is dependent on various factors such as the surfactant type and quantity, viscosity, droplet size and electric charge etc.
Since emulsion stability can not be determined by any individual factor alone, often two or three parameters of emulsion properties are measured and the stabiliy is inductively determined by comparing with the apparent change in the properties of emulsion which have been kept at an elevated tempmperature.
By utilizing the light scattering property of emulsions, a method has been developed to allow determination of emulsion stability byspectal absorption.
Up to a certain limit, the scattering of light from an emulsion increases with a decrease in the droplet size. moreover, the shorter the wave length of the light, the greater is the light scattering.
By combining the above two observations, and bydetermining the absorption at two different wave lengths, it was possible to determine an absorptionratio which was found to be related to emulsion stability. This ratio was defined as emulsion stability index and the relation ships between this index and surfactant composition and concentration were investigated inthis report.