Reological

Reological is an adjective related to rheology, the scientific study of the deformation and flow of matter. It describes the properties, behaviors, and measurements that pertain to how materials deform when subjected to forces and how they move when subjected to shear or stress. Reological analyses consider both instantaneous and time-dependent responses, as many materials change their structure under stress.

Fundamental concepts include viscosity, the resistance to flow; viscoelasticity, the combination of viscous and elastic response; and yield stress, the stress required to initiate flow. Materials may be Newtonian, with constant viscosity, or non-Newtonian, exhibiting shear-thinning or shear-thickening, thixotropy (time-dependent decrease in viscosity) or rheopecty (time-dependent increase). Constitutive models such as Newtonian, Bingham plastic, Herschel–Bulkley, and power-law relations describe these behaviors.

Measurement is performed with rheometers in geometries such as cone-plate, parallel-plate, or coaxial-cylinder setups. Reological data inform processing and performance in a wide range of industries, including food, cosmetics, polymers, paints, lubricants, and asphalt. They guide formulation, processing temperatures, mixing, pumping, and end-use behavior, and are essential for quality control and research and development.