Rheology and Rheological Measurements

Abstract

AbstractThis article presents the experimental measurement of the rheological properties of both liquids and solids and the principles on which these measurements are based. The flow properties of a liquid are defined by its resistance to flow, that is, viscosity. This concept is defined and discussed in terms of both theoretical flow models and practical consequences. Temperature, thixotropic and other time‐dependent, and concentration effects are covered for dilute polymer solutions, melts, and dispersed systems. Techniques and viscometers for capillary, rotational, and moving‐body measurements are described. The rheological properties of viscoelastic solids are made up of a combination of permanent deformation and recoverable elastic deformation. Additionally, a number of liquids show elastic and flow behaviors, which are commonly termed as the viscoelastic materials. Some additional techniques have been included beyond those indicated for simple solids and liquids, which are needed for a complete characterization of the mechanical behavior of materials in terms of elasticity and viscoelasticity. Examples of such methods are the dynamic measurement of response to sinusoidal oscillatory motion; the measurement of flow with time after application of stress, that is, creep; and the measurement of the rate and degree of recovery after removal of stress, that is, creep recovery or recoil. A few special topics, including the Weissenberg effect, time–temperature superposition principles (TTSP), and electrorheological measurements, are also discussed. Nonlinear dynamic measurements of the complex fluids in terms of the large amplitude oscillatory shear (LAOS) measurements, including the Fourier transform rheology and Lissajous curves, are discussed.