rheologi

Rheology is the science that studies the deformation and flow of matter, including liquids, soft solids, suspensions, emulsions, gels, and polymers. It investigates how materials respond to applied forces, such as shear or stress, and how this response depends on time, temperature, and deformation rate.

Key concepts include viscosity, which measures resistance to flow; viscoelasticity, where materials show both solid-like and liquid-like behavior; and the dependence of response on shear rate and history of deformation. Materials are classified as Newtonian or non-Newtonian based on their flow curves, and as elastic, viscous, or viscoelastic. Time-dependent effects, thixotropy (spontaneous structure breakdown under shear), and rheopexy (structure buildup under shear) are also important in many systems.

Measurement is carried out with rheometers and rheometry techniques. Rotational rheometers use cone-plate or parallel-plate geometries to measure steady or oscillatory shear, while capillary rheometers assess high-shear flow. Oscillatory rheometry characterizes the storage modulus G' and loss modulus G'' to describe elastic and viscous components, and to determine the complex modulus G* under varying frequencies and temperatures.

Constitutive models describe material behavior, ranging from simple Newtonian and power-law fluids to viscoelastic models such as Maxwell, Kelvin-Voigt, and Oldroyd-B. More complex materials may show thixotropy, rheopexy, yield stress, or time-dependent structure changes.

Rheology has wide applications in industries such as polymers, foods, cosmetics, pharmaceuticals, and construction, as well as in geophysics and biofluids. It informs formulation, processing, quality control, and material design. The field emerged from early viscosity studies and uses terminology derived from Greek roots meaning flow and study, integrating experiment, theory, and modeling to understand complex fluids and soft solids.