In a partnership with Austria-based laboratory instrumentation manufacturer Anton Paar, the Helgeson Lab has developed new measurement methods for a specialized, state-of-the-art rheometer that not only allows researchers to characterize the mechanical behavior of non-Newtonian liquids and soft matter, but also to witness at the microscopic level how the fluid and structures flow and deform in response to stress. The knowledge generated by this type of instrumentation will have wide applications in academic and industrial research.
A typical rheometer usually consists of two moving surfaces, such as concentric cylinders, that rotate to cause the fluid to deform. By measuring the force required to rotate the cylinders, it is possible to determine the mechanical properties of the fluid. It is usually impossible to see the flow in these geometries, and so it is assumed that the amount of deformation in the fluid between the surfaces is the same everywhere, as is the case for a Newtonian liquid such as water. Not so with many non-Newtonian fluids, according to Helgeson. “It gets much more complicated,” he said. “Typically what happens is that you get a little region that yields so that it’s flowing, and everything else is just sitting there or moving very slowly.” More force does not always equal more flow, he added, until the yielded region grows to fill the fluid volume.
“This transition that goes from not flowing to flowing is important for a wide range of complex fluids,” said Helgeson. And the details of flow in this process, he explained, are often inaccessible to rheometers, which are typically only sensitive to the fluid flowing right at the surfaces. “One of the advances of this instrumentation we’ve developed with Anton Paar is the ability to directly visualize what’s going on in the flow,” Helgeson said. With the help of laser optics and light-scattering particles, researchers will be able to track the fluid deformation and use it to understand what is happening in the fluid’s microstructure. “If you want to engineer these fluids, you really need to be able to characterize what’s going on in the flow to cause the macroscopic response that you measure,” he said. As manufacturing methods and materials become more sophisticated, this knowledge will become essential.
According to Helgeson, the partnership with Anton Paar is unusual in that UCSB researchers are having a hand in the creation of new instrumentation and measurement methods before they become commercially available. “In that sense, the partnership is really a two-way street,” he said. “The new rheometer provides us with state-of-the-art measurement capabilities, and at the same time we’re providing new tools and analysis that others in the scientific and industrial community can use.”
Read more about the partnership and the Helgeson Lab's research in The Current