Polyelectrolyte Entanglement in Solution

• Applicant: Carlos Gonzalez Lopez, Ph.D.
• Subject Area: Experimental and Theoretical Physics of Polymers
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 440957830

The motion of polymer chains in semidilute and concentrated solutions is heavily influenced by topological constraints created by neighbouring chains known as entanglements. Despite their importance to the viscoelastic properties of polymeric materials, relevant to industrial applications and biophysics, our understanding of what exactly constitutes an entanglement is relatively thin. Polyelectrolytes are interesting systems to study polymer entanglement in solution because they can adopt a range of conformations that are inaccessible with neutral polymers.Despite the broad importance of polyelectrolyte dynamics for both fundamental science and industrial applications, polyelectrolyte entanglement is poorly understood. Several reviews over the last decade identify entanglement formation in polyelectrolyte solutions as one of the major open questions in polyelectrolyte science. Recently published results and unpublished data included in this proposal show that key concepts used to explain entanglement formation in neutral polymers do not hold for polyelectrolytes in solution. We argue that this is not the result of polyelectrolyte specific features but rather due to flaws in existing models of entanglement formation, which only become apparent when studying systems with conformational parameters that lay outside what is typically achievable with non-ionic polymers. Based on these observations, we propose an experimental plan to study the dynamics of polyelectrolyte solutions. We plan to employ rotational rheometry, making use of time-temperature superposition (TTS) with super-cooled solvents to access an unprecedented range of relaxation phenomena in polyelectrolyte systems. Small angle neutron scattering is employed to study the conformation and thermodynamics of polyelectrolytes, in order to correlate polymer structure with their entanglement properties.The knowledge gained in this project will contribute to develop new concepts of entanglement formation in polymer solutions, and enhance our understanding of polymer dynamics in general. The results obtained in this project will provide the most extensive experimental test up to now for current and future models of entangled polymer dynamics.

• DFG Programme: Research Grants