Shear rate describes the rate at which a material is deformed during flow and is commonly expressed in reciprocal seconds (s⁻¹).

Cosmetic formulations experience different shear rates during manufacturing and use.

For example, mixing, homogenization, pumping through a filling line and spreading a cream on the skin can expose the formulation to very different shear conditions.

Formulation Importance

The viscosity of many cosmetic products changes with shear rate. A cream may be thick when standing in a container but become much easier to spread when subjected to shear.

Understanding this behavior helps formulators predict dispensing and application performance.

Processing

Shear rate is also relevant when transferring laboratory formulations to production scale. A process that produces the desired structure in a laboratory mixer may not generate the same shear conditions in a production vessel.

References

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

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