Reologi

Reologi, or rheology, is the science that studies how materials deform and flow in response to applied forces. It covers liquids, suspensions, gels, pastes, emulsions, foams, and other complex fluids. The aim is to describe and predict material behavior through constitutive relationships that connect stress, strain, time, and temperature.

Key concepts include viscosity (resistance to flow), shear rate, shear stress, and viscoelasticity (the combined elastic and viscous response). Materials are classified as Newtonian, whose viscosity remains constant, or non-Newtonian, whose viscosity depends on shear rate, time, or both. Non-Newtonian behaviors include shear thinning or thickening, thixotropy and rheopexy, and yield stress (as in Bingham or Herschel-Bulkley models).

Rheological measurements use devices such as rotational rheometers, capillary rheometers, and oscillatory rheometers. Rotational rheometry characterizes flow under steady or controlled rates; capillary rheometry measures high-shear behavior; oscillatory rheometry probes viscoelastic moduli by applying sinusoidal strains.

Models used to describe behavior include Newtonian, power-law (Ostwald-de Waele), Carreau, Herschel-Bulkley, and Bingham, plus viscoelastic models such as Maxwell and Kelvin-Voigt. These models help relate experimental data to material structure and processing conditions.

Applications span polymer processing, coatings, food and cosmetic formulation, pharmaceuticals, soil and rock mechanics, geophysics, and biomechanics. Understanding rheology supports material design, processing optimization, quality control, and product performance. Common units include pascal-second for viscosity and pascals for stress.