complexfluid

A complex fluid is a material whose flow behavior cannot be adequately described by the classical laws of Newtonian fluid mechanics. These fluids often exhibit non-Newtonian characteristics, meaning their viscosity is not constant but depends on factors such as shear rate, time, and the presence of other substances. Examples of complex fluids include suspensions, emulsions, polymers in solution, gels, and foams. The intricate microstructure of these fluids, which may involve particles, droplets, or polymer chains, is responsible for their unique rheological properties.

The behavior of complex fluids is governed by phenomena such as shear thinning, shear thickening, viscoelasticity, thixotropy, and rheopexy. Shear thinning fluids become less viscous as they are stirred or mixed, while shear thickening fluids become more viscous under similar conditions. Viscoelastic fluids exhibit both viscous and elastic properties, meaning they can deform and flow like a liquid but also return to their original shape to some extent like a solid. Thixotropic fluids show a time-dependent decrease in viscosity under shear, recovering slowly when the shear is removed, while rheopectic fluids show a time-dependent increase.

Understanding and predicting the flow of complex fluids is crucial in various scientific and industrial applications. These include the processing of food products, paints, cosmetics, pharmaceuticals, and the development of advanced materials. The study of complex fluids, often referred to as rheology, employs specialized experimental techniques and theoretical models to characterize their behavior and engineer their properties for specific uses.