Rheology
Start with the big picture
Shear stress describes force applied per unit area, while shear rate describes how quickly adjacent fluid layers move relative to one another. For Newtonian fluids, viscosity is the ratio of shear stress to shear rate and remains constant as shear changes; non-Newtonian systems respond differently. Plastic, pseudoplastic, and dilatant flow describe distinct responses to applied shear. Thixotropy and rheopexy capture viscosity changes over time, while viscoelasticity combines viscous and elastic behavior. Rheology also considers how temperature and formulation factors—such as polymer properties, particle size, pH, and electrolyte strength—affect viscosity. These concepts help relate measured flow behavior to pharmaceutical formulation, processing, stability, and performance.
What you'll learn
- Define shear stress, shear rate, and viscosity in the context of rheology.
- Distinguish Newtonian flow from plastic, pseudoplastic, and dilatant behavior.
- Explain how thixotropy, rheopexy, and viscoelasticity describe material response.
- Identify formulation and temperature factors that can alter viscosity.
- Recognize the role of capillary and rotational viscometers in rheological measurement.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
