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Reptation and Beyond: Neutron Spin Echo Experiments Verify the Fundamental Predictions of the Cooperative-Dynamics Generalized Langevin Equation Theory

Margarita Kruteva1, Jürgen Allgaier1, Marina Guenza2, Rustem Valiullin3, Ingo Hoffmann4, and Dieter Richter1

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Phys. Rev. Lett. 137, 038101 – Published 13 July, 2026

DOI: https://doi.org/10.1103/9n96-whkp

Abstract

We have investigated the dynamics of nonentangled and weakly entangled polyisoprene (PI) melts using neutron spin echo spectroscopy and pulsed field gradient NMR and compared the spectra with those from a highly entangled PI melt. Except for Brownian diffusion, which was observed in the long-time regime using NMR, the spectra from nonentangled and weakly entangled PI chains were identical. Dividing out Brownian diffusion, these reduced spectra also quantitatively agree with those from the highly entangled PI melt. Reevaluating the results for poly(butylene oxide) leads to an identical observation, indicating universality. These experiments provide quantitative proof of key predictions of theory: (i) the correlation hole potential governs both the subdiffusivity of nonentangled systems and the cooperative dynamics within the entanglement volume, and (ii) as the spectra from a weakly entangled PI melt also coincide with those from the shorter and highly entangled PI, the entanglement potential, which creates topological constraints, acts in the same way for weakly and strongly entangled melts.

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Corrections

17 July, 2026

Correction: The author names in Ref. [24] were presented incorrectly and have been fixed.

Article Text

Supplemental Material

References (27)

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  27. The difference between Ne values derived from macroscopic rheology experiments and microscopic NSE measurements is a general finding. For all investigated polymers by NSE Ne is found to be about 40% larger than the rheological result (see, e.g., Ref. [26]). We might add the chain confinement in NSE is directly observed as the Fourier transformed of the reptation tube. Apparently, the microscopic confinement observed by NSE is weaker than that derived from rheo-theories.

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Phys. Rev. Lett. 137, 038101– Published 13 July, 2026
  • Received 28 January 2026
  • Accepted 29 May 2026
  • Corrected 17 July 2026
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