Dilatant

A dilatant material, also known as a shear thickening fluid (STF), is a non-Newtonian fluid whose viscosity increases under stress. This means that when subjected to increased shear stress, the material's resistance to flow increases. In simpler terms, the harder you try to push or deform a dilatant material, the more solid-like it becomes. This behavior is the opposite of thixotropic fluids, which become less viscous under stress.

The increase in viscosity is typically temporary and reversible. When the stress is removed, the dilatant material returns to its original, more fluid state.

The mechanism behind dilatancy is related to the particle arrangement within the fluid. At rest or under low stress, the particles are usually dispersed and lubricated by the liquid phase, allowing them to move relatively freely past each other. Under high stress, however, the particles are forced closer together, overcoming the lubricating forces and causing them to jam or interlock. This interlocking creates internal friction, which increases the resistance to flow and results in the observed increase in viscosity. The particles are then forced to move over one another, requiring more energy and manifesting as increased resistance.

Dilatant behavior depends on factors such as particle size, shape, concentration, and the nature of the suspending fluid. Typically, dilatant materials consist of a high concentration of solid particles suspended in a liquid. The particles are usually small and uniform in size.

Applications of dilatant materials are being explored in a variety of fields, including body armor, vibration damping, and enhanced traction devices.