An Introduction to Modular Compact Rheometers

Interview conducted by Stuart MilneAug 2 2016

Oliver Sack, International Product Manager at Anton Paar, talks to AZoM about their new MCR rheometer models 72 and 92, both offering rotational and oscillatory modes.

Please could you provide our readers with a brief introduction to the two different MCR rheometer models you offer?

As a leading developer and manufacturer of high-performance rheometer systems, we decided to extend our successful Modular Compact Rheometer portfolio with the two new members the MCR 72 und MCR 92.

MCR 72 is equipped with a mechanical ball bearing motor, very robust in use, and therefore mainly recommended for rotational tests. MCR 92, on the other hand, works with a highly sensitive air-bearing motor and is recommended for rotational and oscillatory tests, especially of sensitive samples.

Both new models are particularly streamlined for the daily lab routine, easy to use in a Plug and Play fashion. In short, MCR 72 and MCR 92 are the ideal instruments to carry out rheological tests at a reasonable price.

Both rheometers enable measurements in both rotational and oscillatory mode. Why is this important and how does this compare to a typical viscometer?

First of all, a typical viscometer is not able to carry out oscillatory tests. Whereas rotational tests are mainly used to determine the flow and deformation behavior, with oscillatory tests, a material’s structure can be investigated. One of the major advantages of oscillatory tests is the extended sample variety: In this way, all kinds of viscoelastic samples, from very low viscous liquids to gels and even semi-solids can be measured. As a consequence, a typical viscometer is limited in its application. Moreover, depending on the model, it is often also limited in its ability to observe a samples viscosity during a longer time period under varying rotational speeds and also temperature in the course of only one measurement.

Why should a potential user consider the MCR 72 system over the MCR 92 if investigating the deformation and flow behavior of samples?

If a user is mainly interested in investigating the deformation and flow behavior of a sample, MCR 72 is the better choice, because the main focus of this model is on rotational test in controlled-rate (CR), controlled-stress (CS) or controlled-deformation (CD) mode. And this is mainly what you need in this case, nothing less, and nothing more. General benefits of a ball-bearing based rheometer are lower purchasing and operating costs (no compressed air required) and its robustness.

Why should a potential user consider the MCR 92 system over the MCR 72 if observing the structure of samples?

The MCR 92 with its more sensitive air bearing motor, compared to the mechanical ball bearing motor of the MCR 72, covers a much broader viscoelastic sample range, e.g. from water like samples up to semi-solid samples. Clearly a semi-solid sample like rubber, cannot be sheared but only oscillated to get practical results. As a matter of fact, rheometers with air-bearing motors are much better suited for performing oscillatory tests due to their sensitivity. Not only semi-solid, but also very sensitive samples of all kinds of consistency require a higher resolution and oscillatory measurements to gain useful results.

How does the air-bearing-supported synchronous EC motor technology allow users to gain accurate results across a wide viscosity range?

The main difference between both motor technologies is the internal friction of the motor bearing. The internal friction of an air bearing is radically reduced compared to a ball bearing and therefore the smallest torque in the nanoscale is possible. In fact, the torque load in the air-bearing of the MCR 92 can be compared to a human hair on an extended arm. In this way, the system can carry out smallest movements of the measuring system. I prefer to explain these movements with the example of the earth’s equator: Imagine, there is a movement every 32 cm and transfer this to a measuring plate of 25 mm diameter. This sensitivity enables highly accurate results across a wide viscosity range (e.g. to also detect deformation of very stiff materials). However, as far as instrument handling and sample handling are concerned, there is no difference.

How does this compare to a typical viscometer?

Typical viscometers are neither able to measure the viscoelastic sample behavior over a varying speed or shear rate range in one measurement, nor to measure the inner structure or the structural strength of a sample. Viscometers are mainly used to determine a viscosity value in dependence of a specific applied speed or shear rate.

What features do the two systems offer to ensure reproducible results and what advantages does this offer users compared to other systems available on the market?

Reproducible settings are essential for obtaining reliable and reproducible rheological results. MCR 72 and MCR 92 feature a fully automatic motor-driven elevation mechanism, Automatic Gap Control, Automatic Gap Setting and the SafeGap technology, which ensure that the setting of the measuring gap is always identical for every measurement and exactly reproducible every time. In contrast to manual gap-setting systems of other devices, this ensures 100% reproducibility. Furthermore, the slow and precise setting minimizes any influence on the sample’s structure.

Another feature is the user-friendly rheometer software that provides pre-set templates (that can also be customized), where every setting and movement are saved and in this way the process can be identically reproduced for every measurement.

How does TruRay help users gain more information about their samples?

TruRay, the unique light concept, provides a clear view of the sample and measurement surface. This is especially important when filling the measuring gap. In fact, a clear visibility during the gap setting and measurement procedure is essential for good results. In this way for example air bubbles within the measuring gap or overfilled cone-plate or plate-plate measuring systems, which lead to measurement deviations in rotational and also in oscillatory tests, can be avoided.

Do you have any case studies that you're particularly proud of?

Recently we had one case where a customer replaced their viscometer with an MCR 72 because they wanted to see more than the one point, their former instrument gave them. They wanted to do further investigations also on the temperature dependent change of the flow behavior of their sample over varying shear rates. This was especially important for their production process, where the material is exposed to these changes every day. They wanted to get rid of unwanted behavior at a certain point and with our device, they are now finally able to optimize their process because they know their material much better and can react (composition) to every change.

Where can readers learn more?

It is very important to us to accompany and support users on their way to becoming a rheology expert. Therefore, we provide a wealth of applicative, practical information on the www.world-of-rheology.com. There you can also gain access to eLearning courses as well as our extensive applications database, the “tips and tricks” article series and webinars. Last but not least there is a guidebook on applied rheology, “Applied Rheology – With Joe Flow on Rheology Road”.

About Oliver Sack

Oliver Sack has been working at Anton Paar Germany GmbH as an International Product Manager in the field of Rheology since 2005.

He is responsible for the SmartPave 102, MCR 52, MCR 72 and MCR 92.

Oliver studied Chemical Engineering at the University of Applied Science in Stuttgart.

He wrote his diploma thesis on the subject of rheological characterization of paints, varnishes and coatings and worked for years in this field where he gained extensive experience in the field of top coats for vehicles.