It is important to understand that, while the term "rheology" may not sound familiar to you, we actually encounter "rheological events" in our daily life. These include pouring tomato sauce from the bottle, pumping and dispensing liquid, spray drying of milk, scooping yoghurt from the cup, mixing/stirring, spreading peanut butter on the toast, etc.
What is 'Rheology'What is this strange term called rheology? Actually the term rheology comes from Greek rheos, meaning ‘to flow’. The Greek philosopher Heraclitus described rheology as panta rei—everything flows. Translated into rheological term, this means everything will flow, even the mountain, if you just wait long enough.
Rheology is the study of the manner in which materials respond to applied strain and stress. All materials have rheological properties and the subject is relevant in many fields of studies: formulation of paint, plastic processing, pharmaceutical technology, geology and mining, bioengineering, etc. The focus of this course is, of course, food, where understanding of rheology is critical in optimizing product development, food processing/production, and final product quality. Rheology of food products is a significant component of the food processing industry. Good understanding rheology of ingredients is important for successful process control and systems engineering.
- We normally take for granted a lot of things in life and these include some of the “rheological events”. Actually we encounter rheology in our daily life. When we get up in the morning, we usually use toothpaste. This has been formulated to give and easily handled paste that can be squeezed out from the tube but that does not roll off or sink through the bristles of the toothbrush. We eat breakfast, perhaps using a range of spreads for toast, or perhaps we eat yoghurt with pieces of fruit suspended in it.
This video summarizes the essence of topic on food rheology (the first part).
- The presentation below gives an overview of rheology and its definition.
- Here are some interesting resources to help you learn more about rheology (general principles):
Malvern Instruments(manufacturer of rheometer, particle size analyzer) provides recorded version of live webcast on various topics, including the subject of rheology. First, you have to register before you can download the tutorial. Downlod a webcast entitled "A basic introduction to rheology".
- On Demand Training
Interesting topics on rheology are also available as part of the On Demand Training on Malvern Instruments website. Check under the topic of "Rheology". Download and listen to the presentation. Believe me, you will learn a lot! Need to register first.
- Application Library@TA Instrument
TA Instrumnents is another manufacturer of rheometers and thermal analysis instruments. They have an extensive literature on rheology and thermal analysis studies in the Application Library. Login, peruse and download to your heart content.
- What is Rheology Anyway?
Read this article entitled "What is Rheology Anyway?", written by F.A. Morrison. He explained rheology from "phenomenogical" perspective, i.e., things that we observed or experienced everyday. You may download the pdf version of the article. Enjoy!
- This video was created about half a century ago to explain fluid mechanics. Though very old video but the explanation about fluid behavior is very clear.
UNDERSTANDING THE CONCEPT OF STRESS & STRAIN
- To understand rheology, you need to grasp the concept of two important terms, STRESS and STRAIN. In the context of rheology, stress is related to force whereas strain is related to deformation (change of shape or dimension as a result of the applied force).
Let's think of one extreme example: hold one egg (just hold it still) about 1 meter from the floor. Did you see anything drastic happen to the egg? Now, let it go...prrraaap...what have you done?? It's broken...well, rheologically speaking, the egg has deformed...permanently. The egg fell to the ground (floor) due to gravity force and resulted in permanent change of shape (deformation) of the egg. It's not possible to calculate the strain in this case. Why? (Well, I will answer my own question this time...because...the egg has broken up into small pieces!!). This example is rather extreme, but perhaps you can imagine another example, for instance, pressing a soft tomato fruit with your finger. I hope the illustration helped you to understand and visualize the concept.