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Engineers and scientists measure the flow of materials to determine many other properties
Scientists and engineers are putting viscometry to traditional uses and creating new ones. Ken Kreiman, the in-house viscometry expert at Cole-Palmer (Vernon Hills, Ill.), explains, “In terms of applications, we are continuing to see the more traditional uses for viscometry—mostly quality assurance for products such as creams, oils, paints, etcetera.” As for new uses, David Nieto Simavilla, an applications engineer at RheoSense (San Ramon, Calif.), says, “There is a shift towards using viscosity as a parameter to determine many other properties—including stability, structure, molecular size, efficacy and injectability—for new materials and formulations, rather than just as a bulk material property.”
Viscometry keeps jet fuel flowing as designed, even in challenging environments. (Image courtesy of the U.S. Air Force/Maj. Eugenia Ramirez-Griffin.)The new applications of viscometry are also spurring changes in what qualifies as a useful sample and in the expectations of results. Nieto Simavilla says, “Trends indicate an increasing interest in the reduction of sample volume.” That kind of miniaturization opens up new possibilities in viscometry that can impact research and manufacturing.
Turning up the tech
Some experts point out that the technology for standard applications is the same as it was in past decades. The development of more complex fluids, however, is driving engineers to create novel methods and devices with new capabilities. According to Nieto Simavilla, the available shear rate now extends from 0.01 to 1,600,000 per second. He adds that there’s been “a general effort towards automated, high-throughput systems.”
In some cases, researchers use methods based on specific shear rates. A team of scientists from the University of Kentucky in Louisville used a 450/second shear rate to study the influence of neutrophils—white blood cells—on peripheral resistance in the circulatory system. Reporting the results in a 2015 issue of the Journal of Biomechanical Engineering, the researchers wrote, “Collectively, our findings provide supportive evidence that activated neutrophils passing through the microcirculation may alter hemodynamic resistance due to their altered rheology in the noncapillary microvasculature.” The ability to fine-tune the features of viscometry affects the accuracy of such findings in life science research simply by letting researchers control the parameters so precisely.
Whether for research or manufacturing, a broader range of controllable parameters, like shear rate, provides more opportunities to use viscosity measurements. Improving the throughput of measurements will increase the odds of using viscometry in real time in manufacturing.
Handling smaller samples
Breadth of control and speed do not resolve every application concern. Nieto Simavilla says, “Viscometry technologies are developing to offer more for less. This means higher accuracy and repeatability, the ability to measure a range of viscosities over a wider range of shear rates and a wider and better-controlled temperature range.” These advances can also be achieved with much smaller sample sizes.
“A recent advancement in technology is the use of MEMS—microelectromechanical systems—and microfluidics,” says Kreiman. Using these technologies, viscosity can be calculated by measuring the pressure drop as a fluid flows through a microfluidic channel. Nieto Simavilla explains, “Our technological advantages come from our microfluidic-based Viscometer/Rheometer-On-a-Chip, or VROC”—which maximizes the use of small samples. According to Kreiman, “The advantages of this technology are smaller sample sizes, down to 100 microliters, which can be important for more expensive samples; quick measurements; and small instrument size due to the microfluidic technology.” Cole-Palmer carries viscometry devices from RheoSense that provide these features.
RheoSense is also improving automation of the process. Nieto Simavilla says, “We will be launching the first fully automated viscometer that utilizes VROC technology, the VROC initium, into the viscosity market.” He adds, “It will allow for full characterization of up to 96 samples in 8 hours or less, with automated cleaning, loading, testing and temperature control.”
More accurate jet petrol testing
Standards also affect technology, and a recent change provides new possibilities for one approach to measuring viscosity. ASTM International (West Conshohocken, Penn.), which has developed more than 12,000 global standards covering a wide range of industries, delivered ASTM D7042: “Standard Test Method for Dynamic Viscosity and Density of Liquids by Stabinger Viscometer (and the Calculation of Kinematic Viscosity).” According to Eric Swertfeger, director of sales and marketing for viscosity-related products at Anton Paar USA (Ashland, Vir.), “Over the past year, there have been a number of developments in viscosity testing, and one of the most important was the acceptance of the ASTM D7042.” He says, “This marks the first time since 1965 when a viscometer other than the ASTM D445 capillary-style kinematic viscometer can be used by the petroleum industry to certify petroleum fuels.”
Viscometers provide increasingly accurate controls and higher levels of throughput. (Image courtesy of Anton Paar.)This new standard will improve measurements in jet fuel. Swertfeger says, “With these developments, the jet fuel industry is beginning to move towards actual viscosity measurements at –40 degrees Celsius versus using viscosity-extrapolation measurements.” According to viscopedia.com, the Stabinger viscometer is “an entirely new design, combining the accuracy of kinematic viscosity determination with a wide measuring range.” The description continues, “The jet fuel industry has started to adopt the Stabinger viscometer to take an actual measurement simply because extrapolating a viscosity measurement is less accurate than an actual measurement. A number of government agencies and military customers are adopting the Stabinger viscometer with the same rationale.”
Even more viscometry applications
Since viscosity affects so many things, the expanse of applications covers disparate areas. A team of researchers from Taiwan used measurements of viscosity to characterize tapioca starch granules turning into a gel. As they reported in 2014 in the open-access journal IUCrJ, “Correlated structure and viscosity changes suggest closely associated amylose and amylopectin chains in the semicrystalline layers, and the release of amylose chains for enhanced solution viscosity occurs largely after melting of the semicrystalline structure.” The researchers studied this process by measuring changes in viscosity. Some of those details are even on the nanoscale. The authors stated that “increased solution viscosity coincides with the development of nanocluster aggregation....”
The application of viscosity stretches from soft materials like starch to steel. Researchers from Tarbiat Modares University in Iran developed a new technique for studying oxidation in liquid metal. Their findings are reported in a 2014 issue of Review of Scientific Instruments. They summarize, “A novel method was introduced to investigate oxidation behavior of melts in different conditions such as flux, alloying element, atmosphere, etc.... This approach was based on rheology properties of melts, in which by tracing viscosity variations during oxidation, the behavior of melt can be explored.” The researchers showed how a modified form of a falling-ball viscometer can be used to explore the process of oxidation in aluminum and aluminum alloys.
How materials flow, especially under a wide variety of environmental conditions, impacts everything from foods to airplane flights. This technology can be used in basic and applied research as well as in manufacturing and is becoming easier and faster to use with today’s technology.
Mike May is a freelance writer and editor living in Ohio. He can be reached at [email protected].