A group of researchers from around the world has caught the interest of experts in the field with their computational findings on the behavior of ring polymers under shear forces. They demonstrated that for the simplest situation of connected ring pairs, the type of linkage — whether chemically bonded or mechanically linked — has significant effects on the dynamic properties under continuous shear. In these scenarios, new rheological patterns emerge.
enna and her team demonstrated that the type of connection between linked rings, whether it’s chemically bonded or mechanically linked, has a significant impact on their dynamic properties when subjected to continuous shear. This leads to the emergence of new rheological patterns. The study was recently published in Physical Review Letters and was also selected as an “Editors’ Suggestion” due to its unique findings.
Fluid shearing, which involves the movement of fluid layers against each other under shear forces, is a critical concept in both nature and rheology, the science that examines fluid flow.field of rheology involves the use of particle-laden fluids to study their shear behavior. This approach has gained increasing attention due to the potential applications in various industries, such as in the development of new materials and in the optimization of manufacturing processes. The study of shear behavior in particle-laden fluids can provide valuable insights into the interactions between the particles and the surrounding fluid, as well as the overall flow behavior of the material. By understanding these fundamental mechanisms, researchers can develop improved models and predictive tools to better control and optimize the performance of particle-laden fluids in practical applications. This article discusses the significance of studying the shear behavior of particle-laden fluids and highlights the potential impact of this research in various fields.The current research focuses on studying the spatial arrangement and structure of molecules, known as polymer topology, using ring polymers. Ring polymers are large molecules made up of repeating units that form closed loops with no free ends.
Connecting the Dots
Lead author Reyhaneh Farimani explains, “In our computer simulation experiments involving shear, we looked at two types of connected ring pairs: One with a chemical linkage, known as bonded rings (BRs), and one with a mechanical linkage via a Hopf link, known as polycatenanes (PCs).” The researchers placed particular emphasis on considering the behavior of these interconnected ring polymers.The study focused on accurately simulating hydrodynamic interactions to understand how emerging patterns are influenced by the interplay of fluctuating hydrodynamics and topology. The surprising results showed that the response of the two components, BRs and PCs, was very different from each other and from other polymer types like linear, star, or branched. Specifically, the dominant dynamic pattern under shear in other polymers (“vorticity tumbling”) is either suppressed in BRs or virtually absent in PCs due to their topological modifications.
Polymers have been found to exhibit unexpected types of tumbling, as discovered by Christos Likos, co-author of the study. These dynamic patterns, known as gradient-tumbling and slip-tumbling, were observed in both ring polymer types. The interplay between hydrodynamics and ring topology causes the BR molecules to tumble around the gradient direction, perpendicular to the vorticity and flow axes. BRs were observed to exhibit continuous gradient-tumbling motion under shear. Conversely, PCs become thin, orient themselves close to the flow axis, and maintain a fixed, stretched, and non-tumbling orientation.
The article discusses the behavior of polymer compounds under shear and highlights the unique dynamics exhibited by polymer compounds (PCs). The PCs show intermittent dynamics with occasional exchange of the two rings as they slip through each other, a pattern referred to as “slip-tumbling” by the authors. These unexpected modes of motion are influenced by the topologies of the polymer compounds, emphasizing the interplay between hydrodynamics and polymer architecture. The researchers found that when backflow effects are artificially eliminated, the differences between BRs and PCs disappear in their simulations.The movement of polymers, known as BRs, and particles, known as PCs, affects the mechanical properties of the solution. BRs release internal stresses by tumbling, while PCs permanently store stresses, which leads to a higher viscosity. This difference in movement and structure between PCs and BRs could potentially influence the shear viscosity of highly concentrated solutions or polymer melts. More research is needed to test this hypothesis. The study was conducted by a scientific team.The University of Vienna, the Sharif University of Technology in Iran, and the International School of Advanced Studies (SISSA) in Italy have collaborated on a scientific project. The study, “Effects of Linking Topology on the Shear Response of Connected Ring Polymers: Catenanes and Bonded Rings Flow Differently,” was published in Physical Review Letters in 2024. The authors of the study are Reyhaneh A. Farimani, Zahra Ahmadian Dehaghani, Christos N. Likos, and Mohammad Reza Ejtehadi. The journal reference for this study is Physical Review Letters, 132(14), DOI: 10.1103/PhysRevLett.132.148101.Here is the HTML code as requested:
10.1103/PhysRevLett.132.148101