Many cosmetic products are neither purely liquids nor purely solids. They deform under stress but can also recover part of their original structure after the stress is removed.

This combined behavior is known as viscoelasticity.

Creams, gels, polymer solutions, structured emulsions and some hair styling products can exhibit significant viscoelastic behavior.

Cosmetic Importance

Viscoelastic properties influence texture, stringiness, firmness, spreadability, dispensing and the perception of product richness.

A highly elastic gel may recover its structure rapidly, while a more viscous system may flow more readily.

Measurement

Oscillatory rheology can be used to characterize elastic and viscous components. Common parameters include storage modulus (G') and loss modulus (G'').

These measurements can provide information about the internal structure of a formulation that cannot be obtained from a single viscosity measurement.

References

Barnes, H. A. A Handbook of Elementary Rheology.

ISO 3219-1. Rheology — Part 1: General principles and rheometry.

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