Rheological Measurements

Abstract

This article is concerned with the experimental measurement of 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, ie, viscosity. This concept is defined and discussed in terms of both theoretical flow models and practical consequences. Temperature, thixotropic and other time dependence, 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 elastic solids are made up of a combination of permanent deformation and recoverable elastic deformation. Additionally, a number of liquids show elastic as well as flow behavior. Mechanical models for this viscoelastic behavior are discussed. Also described are additional techniques beyond those indicated for simple solids and liquids, which are needed for complete characterization of 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, ie, creep; and the measurement of the rate and degree of recovery after removal of stress, ie, creep recovery or recoil. Special topics such as the Weissenberg Effect, time–temperature superposition, and electrorheological behavior are also discussed.

Solvent composition and rheology of starch–DMSO–water solutions

“…We observed a completely different behavior in our study: at DMSO : water ratios higher than 70 : 30 (where we do have amylose predominantly in its helical form) the solutions had a discrete dilatant behavior; at DMSO : water ratios lower than 70 : 30 (amylose in its random coil conformation) we had a clearly pseudoplastic behavior. We thus reasoned that, perhaps, what was thought to be shear‐induced physical crosslinking, in our case was an effect in great part the result of solvent–solvent interactions, which would have influence in the type of flow experienced by the fluid: laminar or turbulent 18. In laminar flow we have the fluid represented by layers of infinitesimal thicknesses; viscosity is related to shear between different layers, without mass transfer between them.…”

Synthesizing the schemes of multifunctional measuring transduсers of the fluid parameters

“…Dynamic and kinematic viscosity, thermal conductivity and heat capacity, density, etc. are the main parameters for Newtonian fluids while rheological parameters are the main parameters for non-Newtonian fluids [1]. Pressure, velocity, flow, temperature, etc.…”

Dynamic or Oscillatory Testing of Complex Fluids

“…The instrument used for this analysis is a rotational rheometer, which is described in detail in UNITS here &here. References to rheometers that are commercially available can be found in Schoff and Kamarchi (). To measure viscosity, a steady shear stress or shear rate is applied, and the sample response is measured in terms of shear rate or shear stress, respectively.…”