Viscoelasticity – Cosmetic Uses in Rheology and Product Formulation

What Is Viscoelasticity?

Viscoelasticity is the property of a material that exhibits both viscous and elastic behaviour when subjected to deformation.

A purely viscous material flows when a force is applied, while a purely elastic material deforms but tends to recover its original shape when the force is removed. Many cosmetic formulations fall between these two extremes and therefore behave as viscoelastic materials.

Cosmetic examples can include creams, gels, emulsions, shower gels and other structured formulations.

Viscoelasticity in Cosmetic Formulations

The balance between viscous and elastic behaviour influences how a cosmetic product behaves during manufacturing, dispensing and application.

A formulation with a significant elastic component may maintain its structure at rest and resist deformation. When sufficient stress is applied, it can begin to flow while still retaining some of its internal structure.

This behaviour is important for products that need to:

• Remain stable in the container
• Resist excessive flow or settling
• Be dispensed easily
• Spread smoothly on the skin
• Provide a specific texture or sensory experience

Viscoelasticity and Rheology

Viscoelasticity is part of the broader field of rheology, which examines the flow and deformation behaviour of materials.

The rheological behaviour of cosmetic formulations can be affected by factors such as:

• Molecular structure
• Polymer type and concentration
• Shear rate
• Temperature
• Phase composition
• Particle size and distribution
• Emulsifier system
• Rheological modifiers

Non-Newtonian cosmetic systems can exhibit shear-dependent viscosity as well as elastic stresses when subjected to higher shear rates.

Viscoelasticity and Product Performance

The viscoelastic properties of a formulation can influence its stability and sensory characteristics. For example, a structured emulsion may need sufficient elasticity to maintain its structure during storage, while also having enough viscous behaviour to allow it to spread easily during application.

Understanding this balance can help formulators optimise consistency, spreadability, smoothness, dispensing behaviour and physical stability.

Rheological measurements using rotational or oscillatory methods can be used to characterise these properties during formulation development and quality control.

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