With collaborators, chemical and biomolecular engineering researchers Johnny Ching-Wei Lee (left) and Simon Rogers (right) are challenging previous assumptions regarding polymer behavior using their newly developed laboratory techniques that measure polymer flow at the molecular level. Photo: L. Brian Stauffer.Before designing the next generation of soft materials, researchers must first understand how they behave during rapidly changing deformation. In a new study, researchers have challenged previous assumptions regarding polymer behavior using newly developed laboratory techniques that measure polymer flow at the molecular level.
This approach may lead to the design of new materials for biomedical, industrial and environmental applications – from polymers that aid in blood clotting to materials that more efficiently extract oil and gas from wells. The researchers report their findings in a paper in Physical Review Letters.
Understanding the mechanics of how materials molecularly react to changing flows is critical to developing high-quality materials, and defining a framework for interpreting and describing these properties has eluded scientists for decades.
"When polymeric materials – synthetic or biologic – are deformed, they react at both macroscopic and molecular scales," said Simon Rogers, a chemical and biomolecular engineering professor at the University of Illinois at Urbana-Champaign and lead author of the paper. "The relationship between the two scales of response is complex and has been, until now, difficult to describe."
Previous studies have attempted to characterize the relationship between the microscopic and macroscopic behaviors of polymer deformation mathematically, but have been unable to relate the physics to any well-defined microstructural observations.
"In our study, we wanted to measure both the structural and mechanical properties of polymers during deformation, directly shedding light on the origin of unique mechanical properties," said Johnny Ching-Wei Lee, a graduate student and co-author of the paper. "We thought perhaps it was best to try and use direct observations to explain the complex physics."
In the lab, the researchers simultaneously measured multiscale deformations by combining traditional tools for measuring stress and deformation at the macroscopic level with a technique called neutron scattering to observe the structure at the molecular scale. This revealed something unexpected.
"With simultaneous neutron scattering and flow measurements, we are able to directly correlate structure and mechanical properties with a time resolution on the order of milliseconds, " explained co-author Katie Weigandt, a researcher from the US National Institute of Standards and Technology Center for Neutron Science. "This approach has led to fundamental understanding in a wide range of nanostructured complex fluids, and in this work, validates new approaches to making polymer flow measurements."
"Previous research had assumed that the amount of applied deformation at the macroscale is what soft materials experience at the microscale," Lee said. "But the neutron-scattering data from our study clearly shows that it is the deformation that can be recovered that matters because it dictates the whole response, in terms of macroscopic flow – something that was previously unknown."
According to the researchers, this development will help to rectify several poorly understood phenomena in polymer research, such as why polymers expand during 3D printing processes.
"We have come up with what we call a structure-property-processing relationship," Rogers said. "This subtle, yet fundamentally different way of thinking about the polymer behavior summarizes what we see as a simple and beautiful relationship that we expect to be quite impactful."
The research brings key insights to the long-standing challenge in soft condensed matter, and the team said that the established structure-property-processing relationships could provide a new design criterion for soft materials.
This story is adapted from material from the University of Illinois at Urbana-Champaign, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.