Non-Newtonian fluids are liquids or suspensions that do not follow Newton's law of viscosity, which states that the rate of shear strain of a fluid is directly proportional to the applied shear stress. This means that their viscosity, or resistance to flow, changes depending on the amount of stress applied to them.
The response of non-Newtonian fluids to stress is due to their microstructure. These fluids have particles or molecules that are able to move and rearrange when a force is applied to them, causing their viscosity to change. This behavior is also known as shear thinning or shear thickening.
The response of non-Newtonian fluids to stress varies depending on the type of fluid. Some fluids, such as cornstarch and water mixtures, become more viscous and resist flow when stress is applied, while others, such as ketchup, become less viscous and flow more easily. Some fluids, like the ones used in industrial processes, can exhibit a combination of both behaviors.
Non-Newtonian fluids have many practical applications, ranging from household products such as toothpaste and shampoo to industrial processes like oil drilling and paint manufacturing. They are also used in medical procedures, such as making casts and molds, and in food products, like sauces and dressings.
Scientists use various methods to study and measure the response of non-Newtonian fluids to stress. These include rheometers, which measure the viscosity and other flow properties of fluids, and viscometers, which measure the resistance to flow under different conditions. Other techniques, such as microscopy and spectroscopy, are also used to study the microstructure and behavior of these fluids.