Understanding Dilatant Fluids

A dilatant fluid is a specific type of non-Newtonian fluid. Non-Newtonian fluids are those whose viscosity changes under stress. Unlike Newtonian fluids (like water), where viscosity is constant regardless of shear rate, the viscosity of a non-Newtonian fluid can vary.

What is a Shear Thickening Fluid?

A dilatant fluid is also known as a shear thickening fluid. This means that its viscosity increases when it is subjected to shear stress or shear rate. Imagine stirring a mixture: the faster you stir (higher shear rate), the more resistant the fluid becomes (higher viscosity).

Examples of dilatant fluids include:

• Cornstarch and water mixture (often called oobleck)
• Wet sand
• Certain types of inks and paints

When low stress is applied, the particles in the fluid can slide past each other easily, resulting in lower viscosity. However, under high shear stress, the particles rearrange themselves and become jammed or closely packed, making the fluid resist flow and thus increasing its viscosity significantly.

Analyzing the Options

• Option 1: It is a fluid with suspended colour pigments. While fluids with suspended pigments might be non-Newtonian, this description doesn't define a dilatant fluid specifically. Many types of fluids contain pigments.
• Option 2: It is a shear thickening fluid. This is the defining characteristic of a dilatant fluid. Its viscosity increases under increasing shear stress.
• Option 3: It is a fluid that sustains shear stress without any deformation. This describes a solid, not a fluid. Fluids deform continuously under shear stress.
• Option 4: It is a shear thinning fluid. A shear thinning fluid (like ketchup or paint) is the opposite of a dilatant fluid. Its viscosity decreases under increasing shear stress.

Based on the properties of dilatant fluids, the most accurate description is that it is a shear thickening fluid.