Basic Principles and Good Practices of Rheology for Polymers for Teachers and Beginners

Introduction

Rheology Defined: Study of materials' response (deformation or flow) to applied forces. Heraclitus of Ephesus stated, "everything flows."
Applications: Covers materials science, engineering, pharmaceutical, cosmetics, foods, etc.
Importance: Key tool for quality control in various industries, providing insights into material consistency, stability, and texture.
Objective: Provide an accessible introduction to polymer rheology for educational purposes.

Rheological Behavior: Materials can be purely viscous, elastic, or viscoelastic.
Viscoelastic Materials: Exhibit both viscous and elastic properties. Not accurately described by linear models due to complexity.
Testing Methods: Includes rotation, shear, torque, extension, and compression tests.

Newtonian vs Non-Newtonian Fluids: Newtonian fluids have constant viscosity; non-Newtonian fluids’ viscosity varies with shear rate.
Shear Thinning: Common non-Newtonian behavior where viscosity decreases with increase in shear rate, seen in coatings, gels, paints.
Shear Thickening/Dilatancy: Opposite of shear thinning; viscosity increases with shear rate.

Moduli Explained:
- Storage Modulus (G'): Represents stored energy, showing elastic behavior.
- Loss Modulus (G''): Represents energy dissipated as heat, showing viscous behavior.

Combination Models:
- Maxwell Model: Describes stress relaxation.
- Voigt-Kelvin Model: Describes creep behavior.
Creep Test: Measures material's response to constant stress over time.
Oscillatory Shear Measurement: Common technique to analyze viscoelastic behavior.

Influence of Temperature: Affects viscoelastic properties, causing transitions between solid-like and liquid-like states.
Thermal Transitions: Include glass transition, sub-glass transitions, and melting points.

Purpose: Extends relaxation spectra using temperature and time, predicting behavior over different conditions.
Limitations: Not all materials fit this model due to phase transitions or complex compositions.

Summary: Overview of basic principles, experimental methods, and good practices for understanding and teaching polymer rheology.
Educational Value: Provides foundational knowledge for educators and students in polymer science, emphasizing practical applications and measurement techniques.

Guidelines and Exercises: Step-by-step guides for estimating rheological properties using different approaches.

Contributions and Funding: Contributions and funding acknowledgments for the research.

For further detailed reading and exercises, refer to the supplementary materials provided in the article.