Introduction to Rheology: Deformation of Materials and Practical Applications

Rheology is the scientific discipline that studies the deformation of materials in response to applied forces. The term was coined by Eugene Bingham, who founded the Society of Rheology in the United States, and its roots lie in the Greek word for flow. Rheology encompasses the theoretical foundations and the practical aspects of material deformation.

Rheology is concerned with understanding how a material responds to an applied force, which can be quantified in terms of strain or strain rate. There are two types of strain: shear and normal. Shear strains are associated with changes in shape and are encountered in flows along tubes, such as arteries. Normal strains, on the other hand, are related to changes in size, like those created by extension. Both types of strains determine the rheology of a material, which is crucial for understanding its flow behavior.

Rheology is particularly relevant in the field of ophthalmology, where it is used to study the viscoelastic properties of materials within the eye, such as the vitreous humor, the liquid in the tear film, and the blood in capillaries. Understanding the rheology of these materials can help researchers and clinicians better understand various eye conditions and develop more effective treatments.

Rheological experiments can be performed using rotational or oscillatory methods. In rotational tests, a material is subjected to shear stress, and the resulting strain is measured to determine the viscosity. In oscillatory tests, the material is subjected to a combination of stress and strain, measuring the viscoelasticity of the material. These tests can provide insights into the time-dependent and nonlinear behavior of materials, which is important in fields like food processing and biomedical applications.

Rheology is a practical subject that requires careful consideration in both measurement and interpretation. It is essential to define the characteristic timescale, mode, and extent of deformation involved in the flow of interest, as these factors determine the type of device used for rheometry. The field of rheology has wide-ranging applications in various industries, including food science, materials science, and biomedical engineering.