Dilatant

Shear rate vs. Shear stress

Dilatant

A dilatant (also known as a shear thickening fluid) is a non-Newtonian fluid where the viscosity increases with the rate of shear strain. This behavior is in contrast to pseudoplastic fluids, which exhibit a decrease in viscosity with an increase in shear rate. Dilatant materials are characterized by their ability to become more viscous or even solid-like under stress.

Properties

Dilatant materials exhibit a unique property where their viscosity increases as the applied shear rate increases. This phenomenon is due to the rearrangement of particles within the fluid, which creates a more resistant structure to flow. The behavior of dilatant fluids can be described by the following equation:

\(\tau = k \dot{\gamma}^n\)

where:

• \(\tau\) is the shear stress,
• \(k\) is the consistency index,
• \(\dot{\gamma}\) is the shear rate,
• \(n\) is the flow behavior index (for dilatant fluids, \(n > 1\)).

Examples

Common examples of dilatant materials include:

• Cornstarch and water mixtures (often referred to as "oobleck")
• Certain types of suspensions and slurries
• Some polymer solutions

Applications

Dilatant materials have various applications due to their unique properties. Some of these applications include:

• Body armor: Dilatant materials are used in body armor to provide protection by becoming rigid upon impact.
• Vibration damping: These materials can be used in systems where vibration damping is required, as they become more viscous under stress.
• Industrial processes: Dilatant fluids are used in processes where control over viscosity is necessary, such as in pumping and mixing operations.

Related Concepts

• Non-Newtonian fluid
• Rheology
• Thixotropy
• Viscosity

See Also

• Shear thinning
• Newtonian fluid
• Viscoelasticity
• Rheometer