Rheological

Rheological is an adjective relating to rheology, the science that studies the deformation and flow of matter. It encompasses liquids, suspensions, gels, pastes, foams, and soft solids, and seeks to relate applied stresses and strains to time, structure, and temperature. Rheology focuses on how internal microstructure determines macroscopic flow and deformation.

Key quantities include shear stress, shear rate, viscosity, and elastic moduli. Materials can be Newtonian, with constant viscosity, or non-Newtonian, where viscosity depends on shear rate or time. Many materials exhibit viscoelastic behavior, combining elastic storage with viscous dissipation. They may also show thixotropy or rheopecty, where viscosity changes with time under shear, and yield behavior, where flow begins only after surpassing a yield stress.

Constitutive models describe material response. Simple fluids use Newton's law of viscosity; more complex fluids may be described by Bingham plastic, power-law (Ostwald-de Waele), Herschel-Bulkley, or viscoelastic models like Maxwell, Kelvin-Voigt, or Standard Linear Solid.

Experimental rheology uses rheometers and viscometers to perform tests such as steady-shear, oscillatory (to measure G' and G''), creep and recovery, and stress relaxation.

Applications span polymer processing, food science, cosmetics and personal care, pharmaceuticals, geophysics and soils, and biological fluids. Rheological data inform material design, processing, stability, and performance across industries. The field is interdisciplinary, integrating concepts from physics, chemistry, materials science, and engineering.