What is it about?

The group of Dr. Eyal Zussman from The Technion-Israel Institute of Technology and Dr. Alexander Yarin from the University of Illinois at Chicago experimentally discovered and provided a comprehensive theory of new phenomena in thin threads of aqueous solutions of rod-like polyelectrolyte macromolecules with adjacent neutral polymer. These threads are suspended between two disk-like electrodes, providing an axial electric field.

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Why is it important?

Typically, threads of Newtonian viscous liquids, flexible or rigid-rod polymers thin under surface tension, with their cross-sectional diameters over time serving as a measure of rheological parameters. These measurements are derived from standard rheological constitutive equations for Newtonian or viscoelastic fluids. However, the polyelectrolyte solutions in this study exhibited anomalous behavior. At low electric field strengths, the thinning process deviated from expected patterns, while at high field strengths, thread thinning was arrested and alternated with swelling. The theoretical model developed in this work considers polyelectrolyte macromolecules as electric dipoles, predicting their axial orientation in an electric field and the resulting axial elastic stress. This stress influences the thread's evolution under capillary pressure. The observed thread oscillations were identified as a peculiar case of Hadamard instability, a characteristic of ill-posed mathematical problems, with the present one, characterized by strong elastic stresses, being one of them.

Perspectives

The novel phenomena in the elongational rheometry based on the capillary thread thinning of polyelectrolyte-CNC solutions discovered and explained in this work can also open a novel avenue of forming polymer fibers with permanently embedded electric charges (permanent electrets). Filters comprised of such fibers can significantly facilitate filtration of fine particulate matter employing electric forces.

Alexandrer Yarin

This work advances our understanding of how polyelectrolytes and charged rodlike macromolecules influence elongational viscosity under an applied electric field, paving the way to tailor systems for improved processability in electrically and capillarily dominated processes such as electrospinning.

Patrick Martin
Technion Israel Institute of Technology

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This page is a summary of: Capillary self-thinning of threads of polyelectrolyte solutions with axial electric fields, Proceedings of the National Academy of Sciences, October 2025, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2422879122.
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