Many physiological materials and fluids exhibit complicated rheology, like blood in the capillaries, liquid in the tear film, or vitreous humour. The question here is – what is rheology? How does a material respond to a force?
In simple words, rheology is the science of deformation of material.
While it is known that rheology is the branch of physics that deals with the deformation and flow of matter, a lesser-known fact is that - it is distinguished from fluid dynamics as it is concerned with all three states of matter rather than only with liquids and gases. Also, unlike polymer physics, it is concerned with macroscopic properties and behaviour, not molecular structure. Rheologic analysis provides a mathematical description of the viscoelastic behaviour of matter. Applications of rheology are essential in many industries involving metals, plastics, food, and many more.
What is rheology testing?
As mentioned earlier, rheology testing involves measuring the deformation of matter under the influence of an imposed stress by analysing the internal response of materials to forces. Material flow characteristics are critical in all conversion and production processes. The material is forced to flow, and the rheological characteristics determine the processability.
Since flow is an important characteristic in the processing of materials in manufacturing, understanding the fluid rheology is essential. Molding or processing of polymer materials is heavily reliant on maintaining the correct rheological properties to avoid quality issues..
In addition to the above, mechanical properties and behavior are also influenced by rheology. Rheological measurements can be considered for product characterization and quality control purposes. Such measurements are often used for examining and understanding the interaction of the different constituents of a multi-component materials.
The rheological properties of complex fluids, like polymer melts, depend upon the rate of deformation (shear rate), the molecular weight, the structure, the concentration of various additives and fillers, as well as the temperature. In addition, even at a constant rate of deformation, stresses may be time dependent
Rheological characterization of materials gives an overall idea about the viscoelastic flow behavior. Rheology is very important to every material because the rheological responses are closely related to final structures of the system or product.
In a nutshell, rheological measurements are performed tostudy and investigate the molecular structure, evaluate product performance, and help process materials.
Why is rheology testing important?
Rheology research and testing laboratories test materials for rheological properties. Rheological characterization is performed on various materials, including polymers, liquids, adhesives, and other samples, using a wide range of test conditions.
Rheology testing ensures that materials are appropriately processed with minimal product degradation. Rheological tests measure the viscosity of a polymer ranging from single-point tests to variable shear-rate tests.
Rheology is a vital part of the materials' characterization process, whether for optimizing the polymer flow or studying the flow of fluids like oils, lotions, or greases. Particularly for fluids, understanding and predicting the rheology of a sample can be highly complex.
To summarize, rheology testing can be used to:
• Measure the viscosity of fluids.
• Test soft solid materials.
• Evaluate the yield and flow properties of complex fluids.
Uses of rheological analysis
Rheological analysis is used to optimize specific processes like injection molding of plastics where the viscosity of the material must be low enough for it to flow freely into the molds. However, manufacturers are reluctant to use excessive heat to maintain material quality. This is where rheological analysis comes into play.
In other words, rheological analysis is used to measure the flowing properties of fluids that do not have constant viscosity independent of the stress applied to them. How these non-Newtonian materials flow in processes is paramount when designing industrial processes or equipment.
Applications of rheological measurements in the food and beverage industry
Food products include solids, simple liquids, emulsions, suspensions, foams, and mixtures. Rheological measurements are helpful when new products or alternative ingredients have to be developed, such as alternatives to meat or milk.
The study of the rheological properties of plant-based proteins helps research and development specialists improve product quality. However, meat analogs still differ in taste, feel, and flavor from real meat. Another vital piece of information about animal and plant-based food items is fat's behavior at various temperatures.
Also, an in-depth analysis of rheological characteristics can provide insight into the stability and appearance of starch-based products. So, the coatability and flow behavior are crucial for their visual and sensory appeal when it comes to food products like ketchup, sauces, and dressings. A material's cling (ability to hold onto food) results from three rheological factors: yield stress, zero-shear viscosity, and viscoelasticity.
Although there is a significant demand for milk alternatives, consumer acceptance is low due to differences in appearance, mouthfeel, and storage behavior. Similarly, zero-fat yogurts are also expected to have a creamy, silky texture.
Rheology is a powerful tool that can be used to develop new food items or improve or control existing products.
At AMETEK Brookfield, we offer rheological laboratory analysis for samples ranging from polymers, liquids, suspensions, and gels. Our Rheometers are innovative advanced, and have been specially designed to carry out viscoelastic measurements within minutes. Our RSX series of rheometers have been crafted to conduct sophisticated rheological analysis under controlled shear rate and controlled stress modes. They are preferred in research laboratories as they offer superior features including a rugged design for production floors, a large, user-friendly touch screen, and the ability to test very small sample sizes.
Why small sample volumes?
Small samples are preferred and recommended for viscosity measurements as they offer a tremendous advantage - highly sophisticated and accurate measurements can be made using tiny sample sizes with all the precautions in place. The measurement errors and biases can also be easily controlled and identified in a small sample.
Advantages of using small sample volumes
When determining the best instrument for your rheology measurements, it is important to have a firm understanding of the sample volume available for testing. It is crucial to match the sample volume available with the instrument requirements for testing.
Small sample volumes for viscosity measurements are a challenge, especially when measuring costly samples like proteins, specialty chemicals, oils, etc. Small sample volumes are a safer and preferred option in cases of new drug development, as the candidate drugs may only be available in small sizes.
AMETEK Brookfield Viscometers and Rheometers have been designed to carry out small sample volume testing. Measuring the viscosity of small sample volumes can provide advantages, like convenience, accuracy, reduced costs, safety, and simplified testing processes. Some materials can be very costly. Testing with small sample sizes may simplify the formulation and testing. The ability to identify viscosity changes from one batch to another helps to identify batch inconsistencies and quality issues.
Another critical point of utmost concern is the testing safety, especially when dangerous and hazardous materials are being tested. When samples from biopharmaceutical and chemical industries are evaluated, they can exhibit acidic or volatile behaviour. Reducing the amount of sample used is one way to mitigate the risk.
With the help of AMETEK Brookfield Viscometers and Rheometers, it is possible to get reliable and accurate testing results using small sample sizes and with great convenience, flexibility, and safety for end users.
If you want more information on how to save costs and, at the same time, improvise your viscosity and rheological testing needs, get in touch with us for a consultation or sample testing.