Non-Newtonian fluid

A non-Newtonian fluid is a fluid whose viscosity is variable based on applied stress or force. Unlike a Newtonian fluid, where the viscosity remains constant regardless of the stresses applied, the viscosity of a non-Newtonian fluid can change when under force, making it either more liquid or more solid. This behavior is a key characteristic that distinguishes non-Newtonian fluids from Newtonian fluids, which have a constant flow regardless of the stress applied.

The study of non-Newtonian fluids falls within the realm of rheology, the science of the flow and deformation of matter. Non-Newtonian fluids can be classified into several types based on their behavior under stress: shear-thinning, shear-thickening, thixotropic, and rheopectic among others.

Shear-thinning fluids, also known as pseudoplastic fluids, decrease in viscosity when shear stress is applied. An example of a shear-thinning fluid is paint, which becomes less viscous when stirred or brushed.
Shear-thickening fluids, or dilatant fluids, increase in viscosity when subjected to shear stress. An example is a mixture of cornstarch and water, which can act solid when a sudden force is applied.
Thixotropic fluids decrease in viscosity over time under constant shear stress, while rheopectic fluids increase in viscosity over time under constant shear stress.

The behavior of non-Newtonian fluids has practical applications in various industries. For example, in the food industry, the consistency of sauces and gravies can be controlled using non-Newtonian principles. In the automotive industry, non-Newtonian fluids are used in shock absorbers and dampers to improve performance under varying conditions.

Understanding the properties of non-Newtonian fluids is also crucial in the field of biomedical engineering, where the behavior of bodily fluids such as blood (which is a non-Newtonian fluid) is essential for the design of medical devices and in the analysis of physiological processes.