Non-Newtonian Fluids – Cosmetic Uses in Formulation and Application

What Are Non-Newtonian Fluids?

Unlike Newtonian fluids, non-Newtonian fluids have viscosities that depend on the applied shear rate. They may also exhibit elastic stresses when subjected to high shear rates.

This behaviour is particularly important in cosmetic formulations because products can experience very different shear conditions during storage, pouring, pumping, rubbing, and spraying.

Cosmetic Applications

At low shear rates, close to resting conditions, non-Newtonian fluids generally exhibit relatively high viscosity. This is known as zero-shear viscosity and is highly influenced by the molecular weight and concentration of rheological additives.

A sufficiently high zero-shear viscosity can help control forces associated with sedimentation and levelling, contributing to formulation stability.

At moderate shear rates, viscosity decreases. This makes products easier to pour and pump, which is particularly useful for creams, gels, emulsions, and other viscous cosmetic products.

Shear-Thinning Behaviour

At high shear rates, a second Newtonian plateau may be reached, characterised by the so-called infinite-shear viscosity. The shear conditions in this region can be similar to those experienced during rubbing and spraying.

The lower viscosity at high shear reduces resistance during application and can contribute to a smooth sensory feel when the product is spread over the skin.

Understanding non-Newtonian behaviour therefore helps formulators balance stability at rest with easy dispensing and pleasant application.

References

Handbook of Cosmetic Science and Technology – André O. Barel, Marc Paye, Howard I. Maibach.