Newtonian Fluids – Cosmetic Uses in Fluid and Low-Viscosity Formulations

What Are Newtonian Fluids?

Newtonian fluids are fluids whose viscosity remains essentially constant regardless of the applied shear rate. Their flow behaviour can therefore be described relatively simply compared with non-Newtonian cosmetic systems.

In cosmetic formulations, the viscosity of a fluid can be modified by adding small amounts of particulate or polymeric materials. For non-interacting, buoyant particles, the resulting dispersion viscosity can be predicted using the Einstein relation.

Cosmetic Applications

Rheology-modifying materials can be selected when a formulation needs to maintain a relatively smooth or fluid-like consistency.

Examples of materials that may modify the viscosity of these systems include:

• Silica gels
• Fumed silica
• Carbon black
• Titanium dioxide
• Aluminium-magnesium stearates

These materials can be effective at relatively low concentrations when the particles do not strongly interact with one another.

Low-molecular-weight polymers may also be preferred when a smooth, fluid-like formulation is desired.

Newtonian Behaviour in Cosmetic Formulation

Understanding whether a formulation behaves as a Newtonian or non-Newtonian fluid is important when designing its texture, processing characteristics, and application properties. Newtonian systems provide relatively predictable flow behaviour, while many creams, gels, emulsions, and suspensions exhibit more complex rheological behaviour.

References

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