Many industries measure viscosity. “The use of viscometers runs the gamut,” says Robert McGregor, general manager of marketing and sales for high-end lab instruments at Brookfield Engineering (Middleboro, MA). “The biggest user is the quality control department using single-point measurement.” Research scientists also use viscometers to see how a material reacts to being sheared.
“A viscometer is more or less a single-purpose instrument,” says Ross Clark, distinguished research fellow at CP Kelco (San Diego, CA). “You measure viscosity under a defined set of conditions.”
The task at hand determines the kind of viscometer to use.
Range of change
Different viscometers measure different magnitudes of viscosity and different changes in it. For example, Steven Trainoff, PhD, chief scientist at Wyatt Technology (Santa Barbara, CA), says, “We make a detector for very small changes in viscosity, a differential viscometer that measures the change in the sample eluting from a chromatography column.” He adds, “Our goal is to measure viscosity differences as small as 10–6.”
The changes in viscometers involve more than the samples. “Traditionally,” says Trainoff, “polymer chemists used viscometers to look at the properties of materials, but there is an increasing use in the chromatography of proteins and carbohydrates.” Still, he adds, “the mainstay is for measuring polymers.”
As the applications expand, the technology improves. “From our point of view,” says Trainoff, “viscometers have evolved to be more sensitive and easier to use.” The technology is also becoming useful for a wider range of samples. For instance, Trainoff says, “we are improving the range of chemicals that you can expose the instrument to. Synthetic polymers are typically in organic solvents, so there’s no corrosion, but pharmaceuticals are often prepared in salty solutions, which require corrosion-resistant materials.”
Ideas for advances
Clark believes that almost any instrument could be improved in two ways: a better user interface and increased dynamic range. “We tend to be stuck in the way we defined instruments thirty to forty years ago,” Clark says. “These things need to get to the point where you’d have an app on your phone that would run a viscometer.”
McGregor mentions that other devices, like a computer, can control current viscometers. “Future generations will be run by a handheld device using wireless communication,” he says.
For dynamic range, Clark points out that an electronic, top-loading balance can cover four orders of magnitude or more. By comparison, he says, “most common viscometers have a dynamic range of about 20 to 1 from highest to lowest.” He adds, “You get around that by the size of the spindle you put in the liquid, but that’s like cutting up something to weigh it in ten uniform pieces.” So he believes that the dynamic range of viscometers needs improvement.
In buying a viscometer, Clark encourages users to consider robustness. “You might be better off with a more robust viscometer, even if you have to give up some sensitivity,” he says.
For the best results, a user needs to ask the right questions about a viscometer at the start.
For additional resources on viscometers, including useful articles and a list of manufacturers, visit www.labmanager.com/viscometers
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