Vienna, August 7, 2025 — Scientists from the University of Vienna and the University of Edinburgh have introduced a groundbreaking method to reversibly control the shape of ring-shaped polymers by manipulating their electric charge through pH changes. Published in Physical Review Letters, the research marks a significant step toward the development of programmable, shape-adaptive materials.
Using computer simulations and theoretical modeling, the team demonstrated how small pH-induced changes in the ionization of monomer units can shift the balance between twist (local rotation) and writhe (large-scale coiling) in supercoiled polymers. This balance determines the overall structure of the polymer, influencing mechanical and flow properties—such as elasticity, viscosity, and yield stress—without altering its chemical structure.
At low charge levels, polymers exhibit compact, writhe-dominated shapes. As charge increases, electrostatic repulsion causes them to extend and transition to twist-dominated forms. Notably, at higher levels of supercoiling, the model predicts a novel phenomenon: the coexistence of twist- and writhe-rich domains, a form of topological microphase separation never previously observed in such systems.
The researchers introduced a Landau-type mean-field model to predict how and when these transitions occur, providing a reliable theoretical framework for future experiments.
“By adjusting the local charge, we can shift the balance between twist and writhe – and that gives us a handle on the shape of the whole molecule,” said Roman Staňo, lead author from the University of Vienna’s Faculty of Physics, now based at Cambridge University. The work opens possibilities for synthetic DNA rings with pH-sensitive side chains that could act as dynamic scaffolds, reshaping in response to chemical signals.
According to Christos Likos, co-author and professor at the University of Vienna, the study shows how topology can be used as a tool for responsive material design, offering new ways to encode function not just in chemical composition, but in molecular architecture.
This research may pave the way for future applications in microfluidics, smart materials, and responsive soft matter systems.
Source: University of Vienna
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