Rheology (Rheology)

Rheology

Rheology deals with time-dependent material deformation and flow under stress. Rheological testing investigates the elastic, viscous and viscoelastic behaviour and properties of materials, under various shear and temperature conditions. Rheology tests can be done for a range of materials including liquids, semi-solids, gels, emulsions, suspensions, dispersion, slurries, polymer melts and solids. Rheological properties are used in numerous industrial applications including fluid transportation systems, polymer extrusion and molding, formulation and processing of pharmaceutical and cosmetic products, paints and coatings, rubber, food-processing, liquids and gel packaging, adhesives production and packaging, chemical or bio-reactor design and operation.

Rheometers are used to perform shear tests and torsional tests on materials They can operate by continuous rotation or rotational oscillation modes, to measure viscosities or viscoelastic properties respectively at controlled temperatures. The measured torque, deflection angle and speed of the measuring bob in both modes are correlated with rheological properties such as viscosity, storage modulus G’, loss modulus G’’ and damping factor Tan δ.

Solid specimens are subjected to torsional tests including oscillatory tests to investigate their dynamic-mechanical behaviour.

Common Uses of Rheology Tests

• Viscosity and gelling characteristics determination at various shear stresses and shear rates for Hydraulic design of non-Newtonian fluid transport
• Viscoelastic classification of materials
• Characterization of Dispersions, Suspensions, emulsions for process and product design
• Paints and coatings characterization for product application and final finish quality
• Polymer processing system design
• Packaging of gels and materials displaying non-Newtonian flow behaviour

Advantages of Rheology Tests

• Understanding Rheology is key to effective design and operation of many industrial important systems.
• Rheology concepts are valid across the spectrum from solids to liquids, providing a common theoretical framework.

Limitations of Rheology Tests

• Difficult to test small quantities of sample in Rheometers
• Thorough cleaning of instrument is needed especially when dealing with adhesives
• Special materials of construction needed for aggressive materials

Industrial Applications of Rheology Tests

• Hydraulic design
• Polymer processing
• Pharmaceutical production
• Cosmetics production
• Paints and coatings
• Food processing
• Adhesives production
• Biotechnology
• Chemical reactor design
• Crude oil processing
• Oil well drilling muds