Self-Similar Dynamics of Large Polymer Rings: A Neutron Spin Echo Study.

Abstract

This work clarifies the self-similar dynamics of large polymer rings using pulsed-field gradient nuclear magnetic resonance and neutron spin echo spectroscopy. We find center of mass diffusion taking place in three dynamic regimes starting (i)with a strongly subdiffusive domain ⟨r^{2}(t)⟩_{com}∼t^{α} (0.4≤α≤0.65); (ii)a second subdiffusive region ⟨r^{2}(t)⟩_{com}∼t^{0.75} that (iii)finally crosses over to Fickian diffusion. While the t^{0.75} range previously has been found in simulations and was predicted by theory, we attribute the first to the effect of cooperative dynamics resulting from the correlation hole potential. The internal dynamics at scales below the elementary loop size is well described by ring Rouse motion. At larger scales the dynamics is self-similar and follows very well the predictions of the scaling models with preference for the self-consistent fractal loopy globule model.